Search

Studies have found that blood flow to the renal medulla is an important determinant of pressure-natriuresis and the long-term regulation of arterial pressure. First, a brief review of methods developed enabling the study of the medullary circulation is presented. Second, studies performed in rats are presented showing medullary blood flow plays a vital role in the pressure-natriuresis relationship and thereby in hypertension. Third, it is shown that chronic reduction of medullary blood flow results in hypertension and that enhancement of medullary blood flow reduces hypertension hereditary models of both salt-sensitive rats and salt-resistant forms of hypertension. The key role that medullary nitric oxide production plays in protecting this region from ischemic injury associated with circulating vasoconstrictor agents and reactive oxygen species is presented. The studies cited are largely the work of my students, research fellows, and colleagues with whom I have performed these studies dating from the late 1980s to more recent years., Competing Interests: None,

Background: We have previously shown that high salt stimulates the expression of miR-429 in the renal medulla, which induces mRNA decay of HIF prolyl-hydroxylase 2 (PHD2), an enzyme to promote the degradation of hypoxia-inducible factor (HIF)-1α, and increases the HIF-1α-mediated activation of antihypertensive genes in the renal medulla, consequently promoting extra sodium excretion. Our preliminary results showed that high salt-induced increase of miR-429 was not observed in Dahl S rats. This present study determined whether correction of this impairment in miR-429 would reduce PHD2 levels, increase antihypertensive gene expression in the renal medulla and attenuate salt-sensitive hypertension in Dahl S rats., Methods: Lentiviruses encoding rat miR-429 were transfected into the renal medulla in uninephrectomized Dahl S rats. Sodium excretion and blood pressure were then measured., Results: Transduction of lentiviruses expressing miR-429 into the renal medulla increased miR-429 levels, decreased PHD2 levels, and upregulated HIF-1α target gene NOS-2, which restored the adaptive mechanism to increase the antihypertensive gene after high-salt intake in Dahl S rats. Functionally, overexpression of miR-429 transgene in the renal medulla significantly improved pressure natriuretic response, enhanced urinary sodium excretion, and reduced sodium retention upon extra sodium loading, and consequently, attenuated the salt-sensitive hypertension in Dahl S rats., Conclusions: Our results suggest that the impaired miR-429-mediated PHD2 inhibition in response to high salt in the renal medulla may represent a novel mechanism for salt-sensitive hypertension in Dahl S rats and that correction of this impairment in miR-429 pathway could be a therapeutic approach for salt-sensitive hypertension., (© American Journal of Hypertension, Ltd 2021. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Chronic allograft injury (CAI) is a significant reason for which many grafts were lost. The study was conducted to assess the usefulness of diffusional kurtosis imaging (DKI) technology in the non-invasive assessment of CAI., Methods: Between February 2019 and October 2019, 110 renal allograft recipients were included to analyze relevant DKI parameters. According to estimated glomerular filtration rate (eGFR) (mL/min/ 1.73 m 2 ) level, they were divided to 3 groups: group 1, eGFR ≥ 60 (n = 10); group 2, eGFR 30-60 (n = 69); group 3, eGFR < 30 (n = 31). We performed DKI on a clinical 3T magnetic resonance imaging system. We measured the area of interest to determine the mean kurtosis (MK), mean diffusivity (MD), and apparent diffusion coefficient (ADC) of the renal cortex and medulla. We performed a Pearson correlation analysis to determine the relationship between eGFR and the DKI parameters. We used the receiver operating characteristic curve to estimate the predicted values of DKI parameters in the CAI evaluation. We randomly selected five patients from group 2 for biopsy to confirm CAI., Results: With the increase of creatinine, ADC, and MD of the cortex and medulla decrease, MK of the cortex and medulla gradually increase. Among the three different eGFR groups, significant differences were found in cortical and medullary MK (P = 0.039, P < 0.001, P < 0.001, respectively). Cortical and medullary ADC and MD are negatively correlated with eGFR (r = - 0.49, - 0.44, - 0.57, - 0.57, respectively; P < 0.001), while cortical and medullary MK are positively correlated with eGFR (r = 0.42, 0.38; P < 0.001). When 0.491 was set as the cutoff value, MK's CAI assessment showed 87% sensitivity and 100% specificity. All five patients randomly selected for biopsy from the second group confirmed glomerulosclerosis and tubular atrophy/interstitial fibrosis., Conclusion: The DKI technique is related to eGFR as allograft injury progresses and is expected to become a potential non-invasive method for evaluating CAI.

Earlier evidence from studies of rat hypertension models undermines the widespread view that the rate of renal medullary blood flow (MBF) is critical in control of arterial pressure (MAP). Here, we examined the role of MBF in rats that were normotensive, with modest short-lasting pressure elevation, or with overt established hypertension. The groups studied were anaesthetised Sprague-Dawley rats: (1) normotensive, (2) with acute i.v. norepinephrine-induced MAP elevation, and (3) with hypertension induced by unilateral nephrectomy followed by administration of deoxycorticosterone-acetate (DOCA) and 1% NaCl drinking fluid for 3 weeks. MBF was measured (laser-Doppler probe) and selectively increased using 4-h renal medullary infusion of bradykinin. MAP, renal excretion parameters and post-experiment medullary tissue osmolality and sodium concentration were determined. In the three experimental groups, baseline MAP was 117, 151 and 171 mmHg, respectively. Intramedullary bradykinin increased MBF by 45%, 65% and 70%, respectively, but this was not associated with a change in MAP. In normotensive rats a significant decrease in medullary tissue sodium was seen. The intramedullary bradykinin specifically increased renal excretion of water, sodium and total solutes in norepinephrine-treated rats but not in the two other groups. As previously shown in models of rat hypertension, in the normotensive rats and those with acute mild pressure elevation (resembling labile borderline human hypertension), 4-h renal medullary hyperperfusion failed to decrease MAP. Nor did it decrease in DOCA-salt model mimicking low-renin human hypertension. Evidently, within the 4-h observation, medullary perfusion was not a critical determinant of MAP in normotensive and hypertensive rats.

Histone deacetylase (HDAC) enzymes regulate transcription through epigenetic modification of chromatin structure, but their specific functions in the kidney remain elusive. We discovered that the human kidney expresses class I HDACs. Kidney medulla-specific inhibition of class I HDACs in the rat during high-salt feeding results in hypertension, polyuria, hypokalemia, and nitric oxide deficiency. Three new inducible murine models were used to determine that HDAC1 and HDAC2 in the kidney epithelium are necessary for maintaining epithelial integrity and maintaining fluid-electrolyte balance during increased dietary sodium intake. Moreover, single-nucleus RNA-sequencing determined that epithelial HDAC1 and HDAC2 are necessary for expression of many sodium or water transporters and channels. In performing a systematic review and meta-analysis of serious adverse events associated with clinical HDAC inhibitor use, we found that HDAC inhibitors increased the odds ratio of experiencing fluid-electrolyte disorders, such as hypokalemia. This study provides insight on the mechanisms of potential serious adverse events with HDAC inhibitors, which may be fatal to critically ill patients. In conclusion, kidney tubular HDACs provide a link between the environment, such as consumption of high-salt diets, and regulation of homeostatic mechanisms to remain in fluid-electrolyte balance.

The process of kidney stone formation is complex and still not completely understood. Supersaturation and crystallization are the main drivers for the etiopathogenesis of uric acid, xanthine and cystine stones but this physicochemical concept fails to adequately explain the formation of calcium-based nephrolithiasis, which represents the majority of kidney stones. Contemporary concepts of the pathogenesis of calcium-based nephrolithiasis focus on a nidus-associated stone formation of calcium-based nephrolithiasis on Randall's plaques or on plugs of Bellini's duct. Randall's plaques originate from the interaction of interstitial calcium supersaturation in the renal papilla, vascular and interstitial inflammatory processes and mineral deposits of calcifying nanoparticles on the basal membrane of the thin ascending branch of the loop of Henle; however, plugs of Bellini's duct are assumed to be caused by mineral deposits on the wall of the collecting ducts. Aggregation and overgrowth are influenced by the interaction of matrix proteins with calcium supersaturated urine, by an imbalance between promoters and inhibitors of stone formation in the calyceal urine. Current research has elucidated many factors contributing to stone formation by revealing novel insights into the physiology of nephron and papilla, by analyzing vascular, inflammatory and calcifying processes in the renal medulla, by examining the proteome, the microbiome, promoters and inhibitors of stone formation in the urine and by conducting the first genome-wide association studies; however, more future research is mandatory to fill the gap of knowledge and hopefully, to obtain novel prophylactic, therapeutic and metaphylactic tools beyond the current state of knowledge.

The vasopressin type 2 receptor antagonist tolvaptan may have renoprotective effects in patients with heart failure (HF). This study aimed to reveal the renoprotective effect of tolvaptan from the viewpoint of hemodynamic combined with catheter and ultrasound examinations in a hypertensive HF model. Dahl salt-sensitive rats (n = 24) were fed an 8% high-salt diet after the age of 6 weeks and were treated with tolvaptan (n = 16) or vehicle (control group; n = 8). The tolvaptan-treated rats were divided into two groups: a low-dose group (0.01% tolvaptan diet; Low-Tol) and a high-dose group (0.05% tolvaptan diet; High-Tol). At 24 weeks, catheterizations to measure central venous pressure (CVP) and renal medullary pressure (RMP) were performed, followed by intrarenal Doppler (IRD) studies and contrast-enhanced ultrasonography (CEUS) to evaluate renal medullary perfusion. The tolvaptan diet reduced CVP (7.7 ± 1.5, 9.0 ± 1.1, and 12.2 ± 0.8 mmHg in the High-Tol, Low-Tol, and control groups, respectively; p < 0.001) and RMP (7.7 ± 0.8, 9.4 ± 1.3, and 13.7 ± 1.2 mmHg in the High-Tol, Low-Tol, and control groups, respectively; p < 0.001). Tolvaptan also reduced the venous impedance index (VII) in the IRD analysis (0.18 ± 0.03, 0.26 ± 0.04, and 0.40 ± 0.08 in the High-Tol, Low-Tol, and control groups, respectively; p < 0.001), and the time to peak intensity in CEUS (6.0 ± 0.5, 7.3 ± 1.3, 9.8 ± 1.8 s in the High-Tol, Low-Tol, and control groups, respectively; p < 0.001). Creatinine clearance (Ccr) was preserved in both the High-Tol and Low-Tol groups compared to the control group (4.80 ± 1.9, 4.24 ± 0.8, and 1.35 ± 0.3 mg/min, respectively; p = 0.001). Ccr was negatively correlated with RMP (R = -0.76, P < 0.001), the venous impedance index (R = -0.70, p < 0.001), time to peak intensity (R = -0.75, P < 0.001), and renal fibrosis (R = -0.70, p < 0.001). In contrast, Ccr had modest correlations with systolic blood pressure (R = -0.50, P = 0.02) and left ventricular ejection fraction (R = 0.48, P = 0.03). This study revealed that the renoprotective effects of tolvaptan in a hypertensive HF model depended on renal decongestion.

Background: Adenosine-5'-diphosphate (ADP) can influence intrarenal vascular tone and tubular transport, partly through activation of purine P2Y12 receptors (P2Y12-R), but their actual in vivo role in regulation of renal circulation and excretion remains unclear., Methods: The effects of intravenous ADP infusions of 2-8mg/kg/hour were examined in anesthetized Wistar rats that were untreated or chronically pretreated with clopidogrel, 20mg/kg/24hours, a selective P2Y12-R antagonist. Renal blood flow (transonic probe) and perfusion of the superficial cortex and medulla (laser-Doppler fluxes) were measured, together with urine osmolality (U osm ), diuresis (V), total solute (U osm V), sodium (U Na V) and potassium (U K V) excretion., Results: ADP induced a gradual, dose-dependent 15% decrease of mean arterial pressure, a sustained increase of renal blood flow and a 25% decrease in renal vascular resistance. Clopidogrel pretreatment attenuated the mean arterial pressure decrease, and did not significantly alter renal blood flow or renal vascular resistance. Renal medullary perfusion was not affected by ADP whereas U osm decreased from 1,080 ± 125 to 685 ± 75 mosmol/kg H 2 0. There were also substantial significant decreases in U osm V, U Na V and U K V; all these changes were attenuated or abolished by clopidogrel pretreatment. Two-weeks' clopidogrel treatment decreased V while U osm U osm V and U Na V increased, most distinctly after 7 days. Acute clopidogrel infusion modestly decreased mean arterial pressure and significantly increased outer- and decreased inner-medullary perfusion., Conclusions: Our functional studies show that ADP can cause systemic and renal vasodilation and a decrease in mean arterial pressure, an action at least partly mediated by P2Y12 receptors. We confirmed that these receptors exert tonic action to reduce tubular water reabsorption and urine concentration., (Copyright © 2018 Southern Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.)

High salt induced renal disease is a condition resulting from the interactions of genetic and dietary factors causing multiple complications. To understand the metabolic alterations associated with renal disease, we comprehensively analyzed the metabonomic changes induced by high salt intake in Dahl salt-sensitive (SS) rats using GC-MS technology and biochemical analyses. Physiological features, serum chemistry, and histopathological data were obtained as complementary information. Our results showed that high salt (HS) intake for 16 weeks caused significant metabolic alterations in both the renal medulla and cortex involving a variety pathways involved in the metabolism of organic acids, amino acids, fatty acids, and purines. In addition, HS enhanced glycolysis (hexokinase, phosphofructokinase and pyruvate kinase) and amino acid metabolism and suppressed the TCA (citrate synthase and aconitase) cycle. Finally, HS intake caused up-regulation of the pentose phosphate pathway (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase), the ratio of NADPH/NADP + , NADPH oxidase activity and ROS production, suggesting that increased oxidative stress was associated with an altered PPP pathway. The metabolic pathways identified may serve as potential targets for the treatment of renal damage. Our findings provide comprehensive biochemical details about the metabolic responses to a high salt diet, which may contribute to the understanding of renal disease and salt-induced hypertension in SS rats., (Copyright © 2018. Published by Elsevier Inc.)

Studies exploring the development of hypertension have traditionally been unable to distinguish which of the observed changes are underlying causes from those that are a consequence of elevated blood pressure. In this study, a custom-designed servo-control system was utilized to precisely control renal perfusion pressure to the left kidney continuously during the development of hypertension in Dahl salt-sensitive rats. In this way, we maintained the left kidney at control blood pressure while the right kidney was exposed to hypertensive pressures. As each kidney was exposed to the same circulating factors, differences between them represent changes induced by pressure alone. RNA sequencing analysis identified 1,613 differently expressed genes affected by renal perfusion pressure. Three pathway analysis methods were applied, one a novel approach incorporating arterial pressure as an input variable allowing a more direct connection between the expression of genes and pressure. The statistical analysis proposed several novel pathways by which pressure affects renal physiology. We confirmed the effects of pressure on p-Jnk regulation, in which the hypertensive medullas show increased p-Jnk/Jnk ratios relative to the left (0.79 ± 0.11 vs. 0.53 ± 0.10, P < 0.01, n = 8). We also confirmed pathway predictions of mitochondrial function, in which the respiratory control ratio of hypertensive vs. control mitochondria are significantly reduced (7.9 ± 1.2 vs. 10.4 ± 1.8, P < 0.01, n = 6) and metabolomic profile, in which 14 metabolites differed significantly between hypertensive and control medullas ( P < 0.05, n = 5). These findings demonstrate that subtle differences in the transcriptome can be used to predict functional changes of the kidney as a consequence of pressure elevation.

Experimental or spontaneous genomic mutations of the renin-angiotensin system or its pharmacological inhibition in early life leads to renal abnormalities, including poorly developed renal medulla, papillary atrophy, hydronephrosis, inability to concentrate the urine, polyuria, polydipsia, renal failure, and anemia. At the core of such complex phenotype is the presence of unique vascular abnormalities: the renal arterioles do not branch or elongate properly and they have disorganized, concentric hypertrophy. This lesion has been puzzling because it is often found in hypertensive individuals whereas mutant or pharmacologically inhibited animals are hypotensive. Remarkably, when renin cells are ablated with diphtheria toxin, the vascular hypertrophy does not occur, suggesting that renin cells per se may contribute to the vascular disease. To test this hypothesis, on a Ren1 c -/- background, we generated mutant mice with reporter expression ( Ren1 c -/- ;Ren1 c -Cre;R26R.mTmG and Ren1 c -/- ;Ren1 c -Cre;R26R.LacZ ) to trace the fate of renin null cells. To assess whether renin null cells maintain their renin promoter active, we used Ren1 c -/- ;Ren1 c -YFP mice that transcribe YFP (yellow fluorescent protein) directed by the renin promoter. We also followed the expression of Akr1b7 and miR-330-5p, markers of cells programmed for the renin phenotype. Contrary to what we expected, renin null cells did not die or disappear. Instead, they survived, increased in number along the renal arterial tree, and maintained an active molecular memory of the myoepitheliod renin phenotype. Furthermore, null cells of the renin lineage occupied the walls of the arteries and arterioles in a chaotic, directionless pattern directly contributing to the concentric arterial hypertrophy., (© 2017 American Heart Association, Inc.)

Vasoconstriction within the renal medulla contributes to the development of hypertension. This study investigated the role of reactive oxygen species (ROS) in regulating renal medullary and cortical blood perfusion (MBP and CBP respectively) in both stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar rats. CBP and MBP were measured using a laser-Doppler flow meter before and after intra-renal infusion of tempol, the superoxide dismutase (SOD) mimetic or tempol plus catalase, the hydrogen peroxide-degrading enzyme. Tempol infusion significantly elevated blood perfusion within the renal medulla (MBP) in both SHRSP (by 43 ± 7%, P < 0.001) and Wistar rats (by 17 ± 2%, P < 0.05) but the magnitude of the increase was significantly greater in the SHRSP (P < 0.01). When the enzyme catalase and tempol were co-infused, MBP was again significantly increased in SHRSP (by 57 ± 6%, P < 0.001) and Wistar rats (by 33 ± 6%, P < 0.001), with a significantly greater increase in perfusion being induced in the SHRSP relative to the Wistar rats (P < 0.01). Notably, this increase was significantly greater than in those animals infused with tempol alone (P < 0.01). These results suggest that ROS plays a proportionally greater role in reducing renal vascular compliance, particularly within the renal medulla, in normotensive and hypertensive animals, with effects being greater in the hypertensive animals. This supports the hypothesis that SHRSP renal vasculature might be subjected to elevated level of oxidative stress relative to normotensive animals.

Fractal analysis and Gray level co-occurrence matrix method represent two novel mathematical algorithms commonly used in medical sciences as potential parts of computer-aided diagnostic systems. In this study, we tested the ability of these methods to discriminate the kidney medullar tissue suffering from reperfusion injury, from normal tissue. A total of 320 digital micrographs of Periodic acid-Schiff (PAS) - stained kidney medulla from 16 Wistar albino mice (20 per animal), were analyzed using National Institutes of Health ImageJ software (NIH, Bethesda, MD) and its plugins. 160 micrographs were obtained from the experimental group with induced reperfusion injury, and another 160 were obtained from the controls. For each micrograph we calculated the values of fractal dimension, lacunarity, as well as five GLCM features: angular second moment, entropy, inverse difference moment, GLCM contrast, and GLCM correlation. Discriminatory value of the parameters was tested using receiver operating characteristic (ROC) analysis, by measuring the area below ROC curve. The results indicate that certain features of GLCM algorithm have excellent discriminatory ability in evaluation of damaged kidney tissue. Fractal dimension and lacunarity as parameters of fractal analysis also had a relatively good discriminatory value in differentiation of injured from the normal tissue. Both methods have potentially promising application in future design of novel techniques applicable in cell physiology, histology and pathology., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Aims: Arterial spin labelling (ASL) MRI measures perfusion without administration of contrast agent. While ASL has been validated in animals and healthy volunteers (HVs), application to chronic kidney disease (CKD) has been limited. We investigated the utility of ASL MRI in patients with CKD., Methods: We studied renal perfusion in 24 HVs and 17 patients with CKD (age 22-77 years, 40% male) using ASL MRI at 3.0T. Kidney function was determined using estimated glomerular filtration rate (eGFR). T1 relaxation time was measured using modified look-locker inversion and xFB02;ow-sensitive alternating inversion recovery true-fast imaging and steady precession was performed to measure cortical and whole kidney perfusion., Results: T1 was higher in CKD within cortex and whole kidney, and there was association between T1 time and eGFR. No association was seen between kidney size and volume and either T1, or ASL perfusion. Perfusion was lower in CKD in cortex (136 ± 37 vs. 279 ± 69 ml/min/100 g; p < 0.001) and whole kidney (146 ± 24 vs. 221 ± 38 ml/min/100 g; p < 0.001). There was significant, negative, association between T1 longitudinal relaxation time and ASL perfusion in both the cortex (r = -0.75, p < 0.001) and whole kidney (r = -0.50, p < 0.001). There was correlation between eGFR and both cortical (r = 0.73, p < 0.01) and whole kidney (r = 0.69, p < 0.01) perfusion., Conclusions: Significant differences in renal structure and function were demonstrated using ASL MRI. T1 may be representative of structural changes associated with CKD; however, further investigation is required into the pathological correlates of reduced ASL perfusion and increased T1 time in CKD., (© 2016 S. Karger AG, Basel.)

The goal of this study was to investigate the reciprocal interactions among oxygen (O2), nitric oxide (NO), and superoxide (O2 (-)) and their effects on medullary oxygenation and urinary output. To accomplish that goal, we developed a detailed mathematical model of solute transport in the renal medulla of the rat kidney. The model represents the radial organization of the renal tubules and vessels, which centers around the vascular bundles in the outer medulla and around clusters of collecting ducts in the inner medulla. Model simulations yield significant radial gradients in interstitial fluid oxygen tension (Po2) and NO and O2 (-) concentration in the OM and upper IM. In the deep inner medulla, interstitial fluid concentrations become much more homogeneous, as the radial organization of tubules and vessels is not distinguishable. The model further predicts that due to the nonlinear interactions among O2, NO, and O2 (-), the effects of NO and O2 (-) on sodium transport, osmolality, and medullary oxygenation cannot be gleaned by considering each solute's effect in isolation. An additional simulation suggests that a sufficiently large reduction in tubular transport efficiency may be the key contributing factor, more so than oxidative stress alone, to hypertension-induced medullary hypoxia. Moreover, model predictions suggest that urine Po2 could serve as a biomarker for medullary hypoxia and a predictor of the risk for hospital-acquired acute kidney injury., (Copyright © 2015 the American Physiological Society.)

Background: In response to high salt intake, transcription factor hypoxia-inducible factor (HIF) 1α activates many antihypertensive genes, such as heme oxygenase 1 (HO-1) 1 and cyclooxygenase 2 (COX-2) in the renal medulla, which is an important molecular adaptation to promote extra sodium excretion. We recently showed that high salt inhibited the expression of HIF prolyl-hydroxylase 2 (PHD2), an enzyme that promotes the degradation of HIF-1α, thereby upregulating HIF-1α, and that high salt-induced inhibition in PHD2 and subsequent activation of HIF-1α in the renal medulla was blunted in Dahl salt-sensitive hypertensive rats. This study tested the hypothesis that silencing the PHD2 gene to increase HIF-1α levels in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats., Methods: PHD2 short hairpin RNA (shRNA) plasmids were transfected into the renal medulla in uninephrectomized Dahl S rats. Renal function and blood pressure were then measured., Results: PHD2 shRNA reduced PHD2 levels by >60% and significantly increased HIF-1α protein levels and the expression of HIF-1α target genes HO-1 and COX-2 by >3-fold in the renal medulla. Functionally, pressure natriuresis was remarkably enhanced, urinary sodium excretion was doubled after acute intravenous sodium loading, and chronic high salt-induced sodium retention was remarkably decreased, and as a result, salt-sensitive hypertension was significantly attenuated in PHD2 shRNA rats compared with control rats., Conclusions: Impaired PHD2 response to high salt intake in the renal medulla may represent a novel mechanism for hypertension in Dahl S rats, and inhibition of PHD2 in the renal medulla could be a therapeutic approach for salt-sensitive hypertension.

Objectives: To quantitatively assess the correlation between the corticomedullary strain ratio and cortical fibrosis in renal transplants., Methods: Using quasistatic ultrasound elasticity imaging, we prospectively assessed the corticomedullary strain ratio in renal allografts of 33 patients who underwent renal transplant sonography and biopsy. Based on Banff score criteria for renal cortical fibrosis, 33 allografts were divided into 2 groups: group 1 (n = 19), with mild (<25%) fibrosis; and group 2 (n = 14), with moderate (>26%) fibrosis. We used 2-dimensional speckle-tracking software to perform offline analysis of cortical and medullary strain induced by external compression by the ultrasound transducer. We then calculated the corticomedullary strain ratio (cortical normalized strain/medullary normalized strain; normalized strain = developed strain/applied strain [deformation from the abdominal wall to the pelvic muscles]). An unpaired 2-tailed t test was used to determine differences in normalized strain and the strain ratio between the groups. Receiver operating characteristic curve analysis was performed to determine the best strain ratio cutoff value for identifying moderate fibrosis., Results: Normalized strain differed between the cortex and medulla (mean ± SD: group 1, 4.58 ± 2.02 versus 2.58 ± 1.38; P = .002; group 2, 1.71 ± 0.42 versus 2.60 ± 0.87; P = .0011). The strain ratio in group 1 was higher than in group 2 (2.06 ± 1.33 versus 0.70 ± 0.20; P = .0007). The area under the receiver operating characteristic curve was 0.964. The sensitivity and specificity of a strain ratio cutoff value of 0.975 for determining moderate fibrosis were 92.9% and 94.7%, respectively., Conclusions: Strain values vary in different compartments of the kidney. The corticomedullary strain ratio on ultrasound elasticity imaging decreases with increasing renal cortical fibrosis, which makes it potentially useful as a noninvasive quantitative marker for monitoring the progression of fibrosis in renal transplants.

Injury to the adult kidney induces a number of developmental genes thought to regulate repair, including Wnt4. During kidney development, early nephron precursors and medullary stroma both express Wnt4, where it regulates epithelialization and controls smooth muscle fate, respectively. Expression patterns and roles for Wnt4 in the adult kidney, however, remain unclear. In this study, we used reporters, lineage analysis, and conditional knockout or activation of the Wnt/β-catenin pathway to investigate Wnt4 in the adult kidney. Proliferating, medullary, interstitial myofibroblasts strongly expressed Wnt4 during renal fibrosis, whereas tubule epithelia, except for the collecting duct, did not. Exogenous Wnt4 drove myofibroblast differentiation of a pericyte-like cell line, suggesting that Wnt4 might regulate pericyte-to-myofibroblast transition through autocrine signaling. However, conditional deletion of Wnt4 in interstitial cells did not reduce myofibroblast proliferation, cell number, or myofibroblast gene expression during fibrosis. Because the injured kidney expresses multiple Wnt ligands that might compensate for the absence of Wnt4, we generated a mouse model with constitutive activation of canonical Wnt/β-catenin signaling in interstitial pericytes and fibroblasts. Kidneys from these mice exhibited spontaneous myofibroblast differentiation in the absence of injury. Taken together, Wnt4 expression in renal fibrosis defines a population of proliferating medullary myofibroblasts. Although Wnt4 may be dispensable for myofibroblast transformation, canonical Wnt signaling through β-catenin stabilization is sufficient to drive spontaneous myofibroblast differentiation in interstitial pericytes and fibroblasts, emphasizing the importance of this pathway in renal fibrosis.

Renal medullary hypoxia-inducible factor (HIF)-1α and its target genes, such as haem oxygenase and nitric oxide synthase, have been indicated to play an important role in the regulation of sodium excretion and blood pressure. HIF prolyl hydroxylase domain-containing proteins (PHDs) are major enzymes to promote the degradation of HIF-1α. We recently reported that high salt intake suppressed the renal medullary PHD2 expression and thereby activated HIF-1α-mediated gene regulation in the renal medulla in response to high salt. To further define the functional role of renal medullary PHD2 in the regulation of renal adaptation to high salt intake and the longer term control of blood pressure, we transfected PHD2 expression plasmids into the renal medulla in uninephrectomized rats and determined its effects on pressure natriuresis, sodium excretion after salt overloading and the long-term control of arterial pressure after high salt challenge. It was shown that overexpression of PHD2 transgene increased PHD2 levels and decreased HIF-1α levels in the renal medulla, which blunted pressure natriuresis, attenuated sodium excretion, promoted sodium retention and produced salt sensitive hypertension after high salt challenge compared with rats treated with control plasmids. There was no blood pressure change in PHD2-treated rats that were maintained in low salt diet. These results suggested that renal medullary PHD2 is an important regulator in renal adaptation to high salt intake and a deficiency in PHD2-mediated molecular adaptation in response to high salt intake in the renal medulla may represent a pathogenic mechanism producing salt sensitive hypertension., (© 2012 The Authors Journal of Cellular and Molecular Medicine © 2012 Foundation for Cellular and Molecular Medicine/Blackwell Publishing Ltd.)

The aim of this study was to gage the magnitude of changes of the apparent renal medullary transverse relaxation time (ΔT(2)) induced by inhalation of pure oxygen (O(2) ) or carbogen (95% O(2) , 5% CO(2) ) versus baseline breathing of room air. Eight healthy volunteers underwent 2D multi-gradient echo MR imaging at 1.5 T and 3.0 T. Parametrical T(2) relaxation time maps were computed and average T(2) was measured in regions of interest placed in the renal medulla and cortex. The largest T(2) changes were measured in the renal medulla, with a relative ∆T(2) of 33.8 ± 22.0% (right medulla) and 34.7 ± 17.6% (left medulla) as compared to room air for oxygen breathing (p > 0.01), and 53.8 ± 23.9% and 53.5 ± 33.9% (p < 0.01) for carbogen breathing, respectively at 3 T. At 1.5 T, the corresponding values were 13.7 ± 18.5% and 24.1 ± 17.1% (p < 0.01) for oxygen breathing and 23.9 ± 17.2% and 38.9 ± 37.6% (p < 0.01) for carbogen breathing. As a result, we showed that renal medullary T(2) times responded strongly to inhalation of hyperoxic gases, which may be attributed to the hypoxic condition of the medulla and subsequent reduction in deoxyhemoglobin., (Copyright © 2012 John Wiley & Sons, Ltd.)

Crim1 hypomorphic (Crim1(KST264/KST264)) mice display progressive renal disease characterized by glomerular defects, leaky peritubular vasculature, and progressive interstitial fibrosis. Here we show that 27% of these mice also present with hydronephrosis, suggesting obstructive nephropathy. Dynamic magnetic resonance imaging using Magnevist showed fast development of hypo-intense signal in the kidneys of Crim1(KST264/KST264) mice, suggesting pooling of filtrate within the renal parenchyma. Rhodamine dextran (10 kDa) clearance was also delayed in Crim1(KST264/KST264) mice. Pyeloureteric peristalsis, while present, was less co-ordinated in Crim1(KST264/KST264) mice. However, isolated renal pelvis preparations suggest normal pelvic smooth muscle contractile responses. An analysis of maturation during the immediate postnatal period [postnatal day (P) 0-15] revealed defects in papillary extension in Crim1({KST264/KST264) mice. While Crim1 expression is weak in pelvic smooth muscle, strong expression is seen in the interstitium and loops of Henle of the extending papilla, commencing at the tip of the P1 papilla and disseminating throughout the papilla by P15. These results, as well as implicating Crim1 in papillary extension and pelvic smooth muscle contractility, highlight the previously unrecognized association between defects in papillary development and progression to chronic kidney disease later in life., (Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Contrast media induce various factors that may increase vasoconstriction and decrease vasodilatation in the renal medulla, leading to hypoxia and acute tubular necrosis known as contrast-induced nephropathy (CIN) that tends to occur in diabetics and patients with preexisting renal insufficiency. Contrast media inhibit mitochondrial enzyme activities and subsequently increase adenosine through hydrolysis of ATP. Both catabolism of adenosine and medullary hypoxia generate reactive oxygen species (ROS) that scavenge nitric oxide (NO). Released along with endothelin and prostaglandin from endothelial cells exposed to contrast media, adenosine activates the A1 receptor that mainly constricts afferent arteriole at the glomerulus but not the medullary vasculature. Adenosine also activates the A2 receptor that increases NO production, leading to medullary vasodilatation which is induced by activation of endothelin-B receptor and G-protein coupled E-prostanoid receptor 2, and 4 of prostaglandin PGE2 respectively as well. Conversely medullary vasoconstriction is mediated by activating endothelin-A receptor and G-protein coupled E-prostanoid receptor 1, and 3 of prostaglandin PGE2 respectively. The osmotic load of contrast media increases interstitial pressure and sodium transport and thus oxygen consumption. Risking hypoxia, increased medullary oxygen consumption may also result from stimulating Na(+)-K(+)-ATPase activity by endothelin-A receptor. N-acetylcysteine (NAC) scavenges ROS and therefore preserves NO that not only dilates medullary vasculature but also reduces sodium reabsorption and oxygen consumption, tipping the balance against medullary vasoconstriction, hypoxia, and thus CIN. While prostacyclin and its analog, iloprost, prevent CIN by inducing medullary vasodilatation, atrial natriuretic peptide (ANP) may do so by inhibiting renin secretion., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

The adult kidney contains a population of low-cycling cells that resides in the papilla. These cells retain for long periods S-phase markers given as a short pulse early in life; i.e., they are label-retaining cells (LRC). In previous studies in adult rat and mice, we found that shortly after acute kidney injury many of the quiescent papillary LRC started proliferating (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009; Oliver JA, Maarouf O, Cheema FH, Martens TP, Al-Awqati Q. J Clin Invest 114: 795-804, 2004) and, with cell-tracking experiments, we found upward migration of some papillary cells including LRC (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009). To identify molecular cues involved in the activation (i.e., proliferation and/or migration) of the papillary LRC that follows injury, we isolated these cells from the H2B-GFP mice and found that they migrated and proliferated in response to the cytokine stromal cell-derived factor-1 (SDF-1). Moreover, in a papillary organ culture assay, the cell growth out of the upper papilla was dependent on the interaction of SDF-1 with its receptor Cxcr4. Interestingly, location of these two proteins in the kidney revealed a complementary location, with SDF-1 being preferentially expressed in the medulla and Cxcr4 more abundant in the papilla. Blockade of Cxcr4 in vivo prevented mobilization of papillary LRC after transient kidney ischemic injury and worsened its functional consequences. The data indicate that the SDF-1/Cxcr4 axis is a critical regulator of papillary LRC activation following transient kidney injury and during organ repair.

Renal blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) is a noninvasive fast technique to characterize renal function. Here we evaluated the impact of renal function on the relaxation rate (R2(*)) in the cortex and medulla to provide baseline data for further use of renal BOLD-MRI. This parameter was evaluated in 400 patients scheduled for abdominal imaging who underwent transversal blood oxygen level-dependent measurements with a multi-echo gradient-echo sequence with 12 echo times. The loss of phase coherence (T2(*)) maps were generated in which kidney regions of interest were selected to differentiate the medulla and cortex, and R2(*) was equated to 1/T2(*). Individual R2(*) values were, in turn, correlated to the eGFR (MDRD formula of 280 patients with available serum creatinine measurements), age, and gender each for 1.5 and 3.0 T field-strength scans of 342 patients. At both the field strengths, no significant differences in R2(*) of the cortex and medulla were found between patient gender, age, eGFR, or between different stages of chronic kidney disease determined using the KDOQI system. Thus, BOLD-MRI of a non-specific patient population failed to discriminate between the patients with various stages of chronic kidney disease.

1. Salt-sensitive hypertension is commonly associated with diabetes, obesity and chronic kidney disease. The present review focuses on renal mechanisms involved in the development of this type of hypertension. 2. The renal medullary circulation plays an important role in the development of salt-sensitive hypertension. In vivo animal studies have demonstrated that the balance between nitric oxide (NO) and reactive oxygen species (ROS) in the renal medulla is an important element of salt-sensitive hypertension. The medullary thick ascending limb (mTAL) in the outer medulla is an important source of NO and ROS production and we have explored the mechanisms that stimulate their production, as well as the effects of NO superoxide and hydrogen peroxide on mTAL tubular sodium reabsorption and the regulation of medullary blood flow. 3. Angiotensin II-stimulated NO produced in the mTAL is able to diffuse from the renal mTAL to the surrounding vasa recta capillaries, providing a mechanism by which to increase medullary blood flow and counteract the direct vasoconstrictor effects of angiotensin II. Enhanced oxidative stress attenuates NO diffusion in this region. 4. Carbonyl stress, like oxidative stress, can also play an important role in the pathogenesis of chronic kidney disease, such as insulin resistance, salt-sensitive hypertension and renal vascular complications. 5. Despite the large number of studies undertaken in this area, there is as yet no drug available that directly targets renal ROS. Oxidative and/or carbonyl stress may be the next target of drug discovery to protect against salt-sensitive hypertension and associated end-organ damage., (© 2011 The Authors. Clinical and Experimental Pharmacology and Physiology © 2011 Blackwell Publishing Asia Pty Ltd.)

Background/aims: Owing to the precarious blood supply to the renal medulla and the high metabolic requirement of the medullary thick ascending limb of Henle's loop, this nephron segment should be especially vulnerable when its supply of O(2) declines., Methods: Rats were exposed to 8 or 21% O(2) at different time points up to 5 h, and samples were collected for urine flow rate, urine (U(osm)) and renal papillary (RP(osm)) osmolality, urinary excretion of Na(+), Cl(-), K(+) and Mg(2+), blood gases, erythropoietin and vasopressinase activity in plasma. Other groups of rats were pretreated with desmopressin acetate (dDAVP) or underwent bilateral nephrectomy (BNX) 1 h prior to the exposure., Results: Hypoxic rats had water diuresis (WD) within 2.5 h, as evidenced by lower U(osm) (333 ± 42 mosm/l) and RP(osm) (869 ± 57 mosm/l), thus suggesting that hypoxia led to a failure to achieve osmotic equilibrium within the renal papilla. Circulating vasopressinase activity increased, which was partially renal in origin because it was lower after BNX. The renal concentrating ability during hypoxia was maintained with dDAVP pretreatment, suggesting that dDAVP may have improved O(2) delivery and the active reabsorption of Na(+) in the renal medullary region., Conclusions: WD or high vasopressinase activity may be valuable diagnostic tools to assess renal medullary hypoxia. Pretreatment with dDAVP may prevent these changes during hypoxia., (Copyright © 2012 S. Karger AG, Basel.)

1. Endothelin (ET)-1, which was originally found to be secreted by the vascular endothelium, is highly expressed in the kidney, particularly in the renal medulla. 2. Recent studies using genetic models have provided significant breakthroughs in the role of ET-1 in the kidney. For example, ET-1 in the medullary collecting duct physiologically regulates water and salt reabsorption, thereby controlling blood pressure. Surprisingly, to explain the blood pressure regulation both ET(A) and ET(B) receptors are necessary in collecting duct. In fact, we recently revealed that ET(A) receptor stimulation in the renal medulla was natriuretic and diuretic. 3. The expression and secretion of ET-1 in the renal medulla are regulated by multiple mechanisms, such as changes in osmolality, exaggerated renin-angiotensin system activity and hypoxia. The changes in the renal medullary ET system are likely to work as compensatory 'protective' natriuretic factors in response to high sodium exposure in the kidney. 4. In the present review, we focus on recent publications that describe our current knowledge of the functional role of renal medullary ET-1, including the recently characterized actions of ET(A) receptors, the second messenger systems, mechanisms of stimulating ET-1 production and how the ET system is involved in the development of hypertension., (© 2011 The Authors. Clinical and Experimental Pharmacology and Physiology © 2011 Blackwell Publishing Asia Pty Ltd.)

Cells residing in the hypertonic, hypoxic renal medulla depend on dynamic adaptation mechanisms to respond to changes in energy supply and demand. The serine/threonine kinase 5'-AMP protein kinase (AMPK) is a sensor of cellular energy status, but whether it contributes to the survival of cells in the renal medulla is unknown. Here, hypertonic conditions induced a decrease in AMPK phosphorylation within 12 hours in renal medullary interstitial cells (RMIC), followed by a gradual return to baseline levels. Activation of AMPK markedly increased hypertonicity-induced apoptosis of RMICs and suppressed both hypertonicity-induced NFκB nuclear translocation and cyclooxygenase-2 (COX-2) activation; overexpression of COX-2 significantly attenuated these effects. AMPK activation also markedly reduced generation of reactive oxygen species and nuclear expression of tonicity-responsive enhancer-binding protein, which prevented upregulation of osmoprotective genes. In vivo, pharmacologic activation of AMPK led to massive apoptosis of RMICs and renal dysfunction in the setting of water deprivation in mice. Taken together, these results identify a critical role for AMPK in the maintenance of RMIC viability and suggest that AMPK modulates the NFκB-COX-2 survival pathway in the renal medulla. Furthermore, this study raises safety concerns for the development of AMPK activators as anti-diabetic drugs, especially for patients prone to dehydration.

We hypothesized that angiotensin (Ang) II hypertensive rats have impaired natriuresis after renal medullary endothelin (ET) B receptor stimulation that would be more evident in male versus female rats. Acute intramedullary infusion of the ET(B) agonist sarafotoxin 6c in normotensive male rats increased sodium excretion from 0.51±0.11 μmol/min during baseline to 1.64±0.19 μmol/min (P<0.05) after S6c. After 2 weeks of Ang II infusion (260 ng/kg per minute SC), male rats had an attenuated natriuretic response to S6c of 0.62±0.16 μmol/min during baseline versus 0.95±0.07 μmol/min after S6c. In contrast, ET(B)-dependent natriuresis was similar in female hypertensive rats (0.48±0.07 versus 1.5±0.18 μmol/min; P<0.05) compared with normotensive controls (1.05±0.07 versus 2.14±0.24 μmol/min; P<0.05). Because ET(A) receptors also mediate natriuresis in normotensive female rats, we examined ET(A) receptor function in female Ang II hypertensive rats. Intramedullary infusion of ET-1 increased sodium excretion in both hypertensive and normotensive female rats, which was partially blocked by the ET(A) antagonist BQ-123. Maximum ET(B) receptor binding in inner medullary membrane preparations was comparable between vehicle and Ang II hypertensive females; however, maximum ET(B) binding was significantly lower in male hypertensive rats (1952±251 versus 985±176 fmol/mg; P<0.05). These results indicate that renal ET(B) function is impaired in male Ang II hypertension attributed, at least in part, to a reduced number of ET(B) binding sites. Furthermore, renal ET receptor function is preserved in female rats during chronic Ang II infusion, suggesting that renal ET receptor function could serve to limit hypertension in females compared with males.

The renal medulla plays an important role in cardiovascular regulation, through interactions with the autonomic nervous system. Hydronephrosis is characterized by substantial loss of renal medullary tissue. However, whether alterations in autonomic control of the heart are observed in this condition is unknown. Thus we assessed resting hemodynamics and baroreflex sensitivity (BRS) for control of heart rate in urethane/chloralose-anesthetized Sprague-Dawley rats with normal or hydronephrotic kidneys. While resting arterial pressure was similar, heart rate was higher in rats with hydronephrosis (290 ± 12 normal vs. 344 ± 11 mild/moderate vs. 355 ± 13 beats/min severe; P < 0.05). The evoked BRS to increases, but not decreases, in pressure was lower in hydronephrotic rats (1.06 ± 0.06 normal vs. 0.72 ± 0.10 mild/moderate vs. 0.63 ± 0.07 ms/mmHg severe; P < 0.05). Spectral analysis methods confirmed reduced parasympathetic function in hydronephrosis, with no differences in measures of indirect sympathetic activity among conditions. As a secondary aim, we investigated whether autonomic dysfunction in hydronephrosis is associated with activation of the renin-angiotensin system (RAS). There were no differences in circulating angiotensin peptides among conditions, suggesting that the impaired autonomic function in hydronephrosis is independent of peripheral RAS activation. A possible site for angiotensin II-mediated BRS impairment is the solitary tract nucleus (NTS). In normal and mild/moderate hydronephrotic rats, NTS administration of the angiotensin II type 1 receptor antagonist candesartan significantly improved the BRS, suggesting that angiotensin II provides tonic suppression to the baroreflex. In contrast, angiotensin II blockade produced no significant effect in severe hydronephrosis, indicating that at least within the NTS baroreflex suppression in these animals is independent of angiotensin II.

To determine whether in the transgenic rat model [TGR(Cyp1a1Ren2)] with inducible ANG II-dependent malignant hypertension changes in the activation of intrarenal renin-angiotensin system may contribute to the pathogenesis of hypertension, we examined the gene expression of angiotensinogen (AGT) in renal cortical tissues and renin and prorenin receptor [(P)RR] in the collecting duct (CD) of the kidneys from Cyp1a1Ren2 rats (n = 6) fed a normal diet containing 0.3% indole-3-carbinol (I3C) for 10 days and noninduced rats maintained on a normal diet (0.6% NaCl diet; n = 6). Rats induced with I3C developed malignant hypertension and exhibited alterations in the expression of renin and (P)RR expressed by the CD cells. In the renal medullary tissues of the Cyp1a1Ren2 transgenic rats with malignant hypertension, renin protein levels in CD cells were associated with maintained renin content and lack of suppression of the endogenous Ren1c gene expression. Furthermore, these tissues exhibited increased levels of (P)RR transcript, as well as of the protein levels of the soluble form of this receptor, the s(P)RR. Intriguingly, although previous findings demonstrated that urinary AGT excretion is augmented in Cyp1a1Ren2 transgenic rats with malignant hypertension, in the present study we did not find changes in the gene expression of AGT in renal cortical tissues of these rats. The data suggest that upregulation of renin and the s(P)RR in the CD, especially in the renal medullary tissues of Cyp1a1Ren2 transgenic rats with malignant hypertension, along with the previously demonstrated increased availability of AGT in the urine of these rats, may constitute a leading mechanism to explain elevated formation of kidney ANG II levels in this model of ANG II-dependent hypertension.

The in vivo assessment of renal damage after ischemia-reperfusion injury, such as in sepsis, hypovolemic shock or after transplantation, is a major challenge. This injury often results in temporary or permanent nonfunction. In order to improve the clinical outcome of the kidneys, novel therapies are currently being developed that limit renal ischemia-reperfusion injury. However, to fully address their therapeutic potential, noninvasive imaging methods are required which allow the in vivo visualization of different renal compartments and the evaluation of kidney function. In this study, MRI was applied to study kidney oxygenation and function in a murine model of renal ischemia-reperfusion injury at 7 T. During ischemia, there was a strongly decreased oxygenation, as measured using blood oxygen level-dependent MRI, compared with the contralateral control, which persisted after reperfusion. Moreover, it was possible to visualize differences in oxygenation between the different functional regions of the injured kidney. Dynamic contrast-enhanced MRI revealed a significantly reduced renal function, comprising perfusion and filtration, at 24 h after reperfusion. In conclusion, MRI is suitable for the noninvasive evaluation of renal oxygenation and function. Blood oxygen level-dependent or dynamic contrast-enhanced MRI may allow the early detection of renal pathology in patients with ischemia-reperfusion injury, such as in sepsis, hypovolemic shock or after transplantation, and consequently may lead to an earlier intervention or change of therapy to minimize kidney damage., (Copyright © 2010 John Wiley & Sons, Ltd.)

Stanniocalcin-1 (STC-1) is made by kidney collecting duct cells for autocrine and paracrine targeting of nephron cell mitochondria. Here, the ligand stimulates respiratory uncoupling and calcium uniport activity. However, the underlying purpose of these actions and how the renal gene is regulated are poorly understood. In a previous study, we described the time-dependent, stimulatory effects of water deprivation on renal STC-1 mRNA levels in both rats and mice. In cortical kidney, STC-1 mRNA levels were increased 8-fold by 72h of water deprivation, whereas the gene response in outer and inner medulla was less pronounced (2-4 fold). Gene induction occurred equally in males and females and was accompanied by increased mitochondrial STC-1 protein levels. As water deprivation increases extracellular fluid (ECF) tonicity and at the same time reduces ECF volume, the present study examined the individual effects of hypertonicity and hypovolemia on renal gene activity in rats. Hypertonicity, whether induced by mannitol, glucose or NaCl, uniquely stimulated the cortical gene, to the extent that transcript levels were positively correlated with serum osmolality. This was in contrast to high dietary sodium, which had no bearing on cortical or medullary transcript levels. The situation was reversed in the case of hypovolemia. Inner medullary gene expression was uniquely induced by hypovolemia (low sodium diet or polyethylene glycol) such that transcript levels were positively correlated with hematocrit, while cortical gene activity was unaffected or reduced. Hence, the cortical and medullary genes proved to be differentially regulated by changing ECF tonicity and volume, respectively. The findings are therefore indicative of cortical and medullary STC-1 having separate roles in the renal control of ECF balance., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Background: The renal medullary endothelin (ET-1) system plays an important role in the control of sodium excretion and arterial pressure (AP) through the activation of renal medullary ET-B receptors. We have previously shown that blockade of endothelin type B receptors (ET-B) leads to salt-sensitive hypertension through mechanisms that are not fully understood. One possible mechanism is through a reduction in renal medullary production of 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE, a metabolite of arachidonic acid, has natriuretic properties similar to ET-B activation. While these findings suggest a possible interaction between ET-B receptor activation and 20-HETE production, it is unknown whether blockade of medullary ET-B receptors in rats maintained on a high sodium intake leads to reductions in 20-HETE production., Methodology/principal Findings: The effect of increasing sodium intake from low (NS = .8%) to high (HS = 8%) on renal medullary production of 20-HETE in the presence and absence of renal medullary ET-B receptor antagonism was examined. Renal medullary blockade of ET-B receptors resulted in salt sensitive hypertension. In control rats, blood pressure rose from 112.8±2.4 mmHg (NS) to 120.7±9.3 mmHg (HS). In contrast, when treated with an ET-B receptor blocker, blood pressure was significantly elevated from 123.7±3.2 (NS) to 164.2±7.1 (HS). Furthermore, increasing sodium intake was associated with elevated medullary 20-HETE (5.6±.8 in NS vs. 14.3±3.7 pg/mg in HS), an effect that was completely abolished by renal medullary ET-B receptor blockade (4.9±.8 for NS and 4.5±.6 pg/mg for HS). Finally, the hypertensive response to intramedullary ET-B receptor blockade was blunted in rats pretreated with a specific 20-HETE synthesis inhibitor., Conclusion: These data suggest that increases in renal medullary production of 20-HETE associated with elevating salt intake may be, in part, due to ET-B receptor activation within the renal medulla.

It has been suggested that alterations in Na(+),K(+)-ATPase mediate the development of several aging-related pathologies, such as hypertension and diabetes. Thus, we evaluated Na(+),K(+)-ATPase function and H(2)O(2) production in the renal cortex and medulla of Wistar Kyoto (WKY) rats at 13, 52 and 91 weeks of age. Creatinine clearance, proteinuria, urinary excretion of Na(+) and K(+) and fractional excretion of Na(+) were also determined. The results show that at 91 weeks old WKY rats had increased creatinine clearance and did not have proteinuria. Despite aging having had no effect on urinary Na(+) excretion, urinary K(+) excretion was increased and fractional Na(+) excretion was decreased with age. In renal proximal tubules and isolated renal cortical cells, 91 week old rats had decreased Na(+),K(+)-ATPase activity when compared to 13 and 52 week old rats. In renal medulla, 91 week old rats had increased Na(+),K(+)-ATPase activity, paralleled by an increase in protein expression of α(1)-subunit of Na(+),K(+)-ATPase. In addition, renal H(2)O(2) production increased with age and at 91 weeks of age renal medulla H(2)O(2) production was significantly higher than renal cortex production. The present work demonstrates that although at 91 weeks of age WKY rats were able to maintain Na(+) homeostasis, aging was accompanied by alterations in renal Na(+),K(+)-ATPase function. The observed increase in oxidative stress may account, in part, for the observed changes. Possibly, altered Na(+),K(+)-ATPase renal function may precede the development of age-related pathologies and loss of renal function., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Females suffer a less severe ischemic acute renal failure than males, apparently because of higher nitric oxide (NO) bioavailability and/or lower levels of oxidative stress. Because the renal ischemic injury is associated with outer medullary (OM) endothelial dysfunction, the present study evaluated sex differences in OM changes of NO and peroxynitrite levels (by differential pulse voltammetry and amperometry, respectively) during 45 min of ischemia and 60 min of reperfusion in anesthetized Sprague-Dawley rats. Endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) protein expression and their phosphorylated forms [peNOS(Ser1177) and pnNOS(Ser1417)], 3-nitrotyrosine, reduced sulfhydryl groups (-SH), and glomerular filtration rate (GFR) were also determined. No sex differences were observed in monomeric eNOS and nNOS expression, NO, or 3-nitrotyrosine levels in nonischemic kidneys, but renal -SH content was higher in females. Ischemia increased dimeric/monomeric eNOS and nNOS ratio more in females, but the dimeric phosphorylated peNOS(Ser1177) and pnNOS(Ser1417) forms rose similarly in both sexes, indicating no sex differences in nitric oxide synthase activation. However, NO levels increased more in females than in males (6,406.0 ± 742.5 and 4,058.2 ± 272.35 nmol/l respectively, P < 0.05), together with a lower increase in peroxynitrite current (5.5 ± 0.7 vs. 12.7 ± 1.5 nA, P < 0.05) and 3-nitrotyrosine concentration, (28.7 ± 3.7 vs. 48.7 ± 3.7 nmol/mg protein, P < 0.05) in females than in males and a better preserved GFR after ischemia in females than in males (689.7 ± 135.0 and 221.4 ± 52.5 μl·min(-1)·g kidney wt(-1), P < 0.01). Pretreatment with the antioxidants N-acetyl-L-cysteine or ebselen abolished sex differences in peroxynitrite, nitrotyrosine, and GFR, suggesting that a greater oxidative and nitrosative stress worsens renal damage in males.

Activation of V2 receptors (V2R) during antidiuresis increases the permeability of the inner medullary collecting duct to urea and water. Extracellular osmolality is elevated as the concentrating capacity of the kidney increases. Osmolality is known to contribute to the regulation of collecting duct water (aquaporin-2; AQP2) and urea transporter (UT-A1, UT-A3) regulation. AQP1KO mice are a concentrating mechanism knockout, a defect attributed to the loss of high interstitial osmolality. A V2R-specific agonist, deamino-8-D-arginine vasopressin (dDAVP), was infused into wild-type and AQP1KO mice for 7 days. UT-A1 mRNA and protein abundance were significantly increased in the medullas of wild-type and AQP1KO mice following dDAVP infusion. The mRNA and protein abundance of UT-A3, the basolateral urea transporter, was significantly increased by dDAVP in both wild-type and AQP1KO mice. Semiquantitative immunoblots revealed that dDAVP infusion induced a significant increase in the medullary expression of the endoplasmic reticulum (ER) chaperone GRP78. Immunofluorescence studies demonstrated that GRP78 expression colocalized with AQP2 in principal cells of the papillary tip of the renal medulla. Using immunohistochemistry and immunogold electron microscopy, we demonstrate that vasopressin induced a marked apical targeting of GRP78 in medullary principal cells. Urea-sensitive genes, GADD153 and ATF4 (components of the ER stress pathway), were significantly increased in AQP1KO mice by dDAVP infusion. These findings strongly support an important role of vasopressin in the activation of an ER stress response in renal collecting duct cells, in addition to its role in activating an increase in UT-A1 and UT-A3 abundance.

Mammalian urine contains a range of macromolecule proteins that play critical roles in renal stone formation, among which Tamm-Horsfall protein (THP) is by far the most abundant. While THP is a potent inhibitor of crystal aggregation in vitro and its ablation in vivo predisposes one of the two existing mouse models to spontaneous intrarenal calcium crystallization, key controversies remain regarding the role of THP in nephrolithiasis. By carrying out a long-range follow-up of more than 250 THP-null mice and their wild-type controls, we demonstrate here that renal calcification is a highly consistent phenotype of the THP-null mice that is age and partially gene dosage dependent, but is gender and genetic background independent. Renal calcification in THP-null mice is progressive, and by 15 mo over 85% of all the THP-null mice develop spontaneous intrarenal crystals. The crystals consist primarily of calcium phosphate in the form of hydroxyapatite, are located more frequently in the interstitial space of the renal papillae than intratubularly, particularly in older animals, and lack accompanying inflammatory cell infiltration. The interstitial deposits of hydroxyapatite observed in THP-null mice bear strong resemblances to the renal crystals found in human kidneys bearing idiopathic calcium oxalate stones. Compared with 24-h urine from the wild-type mice, that of THP-null mice is supersaturated with brushite (calcium phosphate), a stone precursor, and has reduced urinary excretion of citrate, a stone inhibitor. While less frequent than renal calcinosis, renal pelvic and ureteral stones and hydronephrosis occur in the aged THP-null mice. These results provide direct in vivo evidence indicating that normal THP plays an important role in defending the urinary system against calcification and suggest that reduced expression and/or decreased function of THP could contribute to nephrolithiasis.

Recessive inheritance of mutations in ceroid neuronal lipofuscinosis type 3 (CLN3) results in juvenile neuronal ceroid lipofuscinosis (JNCL), a childhood neurodegenerative disease with symptoms including loss of vision, seizures, and motor and mental decline. CLN3p is a transmembrane protein with undefined function. Using a Cln3 reporter mouse harboring a nuclear-localized bacterial beta-galactosidase (beta-Gal) gene driven by the native Cln3 promoter, we detected beta-Gal most prominently in epithelial cells of skin, colon, lung, and kidney. In the kidney, beta-Gal-positive nuclei were predominant in medullary collecting duct principal cells, with increased expression along the medullary osmotic gradient. Quantification of Cln3 transcript levels from kidneys of wild-type (Cln3(+/+)) mice corroborated this expression gradient. Reporter mouse-derived renal epithelial cultures demonstrated a tonicity-dependent increase in beta-Gal expression. RT-quantitative PCR determination of Cln3 transcript levels further supported osmoregulation at the Cln3 locus. In vivo, osmoresponsiveness of Cln3 was demonstrated by reduction of medullary Cln3 transcript abundance after furosemide administration. Primary cultures of epithelial cells of the inner medulla from Cln3(lacZ/lacZ) (CLN3p-null) mice showed no defect in osmolyte accumulation or taurine flux, arguing against a requirement for CLN3p in osmolyte import or synthesis. CLN3p-deficient mice with free access to water showed a mild urine-concentrating defect but, upon water deprivation, were able to concentrate their urine normally. Unexpectedly, we found that CLN3p-deficient mice were hyperkalemic and had a low fractional excretion of K(+). Together, these findings suggest an osmoregulated role for CLN3p in renal control of water and K(+) balance.

Many renal diseases as well as several pharmacons cause a change in renal blood flow and/or renal oxygenation. The blood oxygenation level dependent (BOLD) imaging takes advantage of local field inhomogeneities and is based on a T2*-weighted sequence. BOLD is a non-invasive method allowing an estimation of the renal, particularly the medullary oxygenation, and an indirect measurement of blood flow without administration of contrast agents. Thus, effects of different drugs on the kidney and various renal diseases can be controlled and observed. This work will provide an overview of the studies carried out so far and identify ways how BOLD can be used in clinical studies., (2010. Published by Elsevier GmbH.)

While the fractional excretion of solutes have long been considered excellent research tools to investigate tubular physiology, their clinical use has become common over the last 40 years in the diagnoses of many disorders; however, none have reached the clinical utility of the fractional excretion of sodium in the ability to distinguish pre-renal azotemia from acute tubular necrosis. Nevertheless, there are many drugs and medical conditions that interfere with that utility and recently other solutes, including urea, uric acid and lithium, have been recently investigated to improve the diagnostic ability in clinical situations where the fractional excretion of sodium is known to be unreliable. We review the tubular physiology of these solutes and show how the differences in tubular physiology might be exploited to develop a strategy for their optimal clinical use.

The present studies evaluated intrarenal hemodynamics, pressure natriuresis, and arterial blood pressure in rats following recovery from renal ischemia-reperfusion (I/R) injury. Acute I/R injury, induced by 40 min of bilateral renal arterial occlusion, resulted in an increase in plasma creatinine that resolved within a week. Following 5 wk of recovery on a 0.4% NaCl diet, the pressure-natriuresis response was assessed in anesthetized rats in which the kidney was denervated and extrarenal hormones were administered intravenously. Increasing renal perfusion pressure (RPP) from 107 to 141 mmHg resulted in a fourfold increase in urine flow and sodium excretion in sham control rats. In comparison, pressure diuresis and natriuresis were significantly attenuated in post-I/R rats. In sham rats, glomerular filtration rate (GFR) averaged 1.6 +/- 0.2 mlxmin(-1)xg kidney weight(-1) and renal blood flow (RBF) averaged 7.8 +/- 0.7 mlxmin(-1)xg kidney weight(-1) at RPP of 129 mmHg. Renal cortical blood flow, measured by laser-Doppler flowmetry, was well autoregulated whereas medullary blood flow and renal interstitial hydrostatic pressure increased directly with elevated RPP in sham rats. In contrast, GFR and RBF were significantly reduced whereas medullary perfusion and interstitial pressure demonstrated an attenuated response to RPP in post-I/R rats. Further experiments demonstrated that conscious I/R rats develop hypertension when sodium intake is increased. The present data indicate that the pressure-natriuretic-diuretic response in I/R rats is blunted because of a decrease in GFR and RBF and the depressed pressure-dependent increase in medullary blood flow and interstitial pressure.

Oxygen consumption beyond the proximal tubule is mainly determined by active solute reabsorption, especially in the thick ascending limb of the Loop of Henle. Furosemide-induced suppression of oxygen consumption (FSOC) involves inhibition of sodium transport in this segment, which is normally accompanied by a marked decrease in the intrarenal deoxyhemoglobin detectable by blood oxygen level-dependent (BOLD)-magnetic resonance imaging (MRI). This study tested the hypothesis that the magnitude of BOLD-MRI signal change after furosemide is related to impaired renal function in renovascular hypertension. In 16 pigs with unilateral renal artery stenosis, renal hemodynamics, function, and tubular function (FSOC and fluid concentration capacity) were evaluated in both kidneys using MR and multidetector computerized tomography (MDCT) imaging. Animals with adequate FSOC (23.6 +/- 2.2%, P > 0.05 vs. baseline) exhibited a mean arterial pressure (MAP) of 113 +/- 7 mmHg, and relatively preserved glomerular filtration rate (GFR) of 60 +/- 4.5 ml/min, comparable to their contralateral kidney (66 +/- 4 ml/min, P > 0.05). In contrast, animals with low FSOC (3.1 +/- 2.1%, P = NS vs. baseline) had MAP of 124 +/- 9 mmHg and GFR (22 +/- 6 ml/min) significantly lower than the contralateral kidneys (66 +/- 4 ml/min, P < 0.05). The group with preserved GFR and FSOC showed an increase in intratubular fluid concentration as assessed by MDCT that was greater than that observed in the low GFR group, suggesting better preservation of tubular function in the former group. These results suggest that changes in BOLD-MRI after furosemide can differentiate between underperfused kidneys with preserved tubular function and those with tubular dysfunction. This approach may allow more detailed physiologic evaluation of poststenotic kidneys in renovascular hypertension than previously possible.

The ischemia/reperfusion (I/R) model in rats allows pharmacological investigation of protective renal effects of certain agents to thereby diminish the incidence of delayed graft function (DGF). The aim of this study was to determine the effects of preconditioning with triiodothyronine (T(3)) on renal function and oxidative status in renal I/R injury. Forty male Wistar rats were preconditioned with T(3) (100 microg/kg) or control (normal saline) at 24 hours prior to 45 minutes of renal ischemia, followed by a 4-hour (groups C-4h and T(3)-4h) or 24-hour (groups C-24h and T(3)-24h) reperfusion period. We determined renal function parameters (urea, creatinine, and proteinuria), oxidative stress biomarkers in plasma (malondialdehyde [MDA], glutathione [GSH], and superoxide dismutase [SOD]), urine (hydrogen peroxide [H(2)O(2)]), and renal tissue (GSH and MDA), and poly(ADP-ribose) polymerase (PARP-1) expression. Proteinuria was significantly lower in the T(3)-treated group (4.63 +/- 1.9 vs 9.27 +/- 0.72 mg/mL/100 g body weight). Pretreated rats showed lower levels of plasma and tissue MDA and urine H(2)O(2) (50.57 +/- 1.17 vs 71.16 +/- 1.14 micromol/100 g body weight). The T(3) treatment was associated with lower postischemia GSH concentrations (3.82 +/- 1.16 vs 4.89 +/- 0.68 nmol/mg protein) and higher SOD levels at 24 hours (11.27 +/- 0.86 vs 9.92 +/- 1.77 nmol/mg protein). Preconditioning with the hormone also reduced PARP-1 tissue expression by 18% (P

Background: The natriuretic peptide (NP) system plays a central role in the renal adaptations to acute volume expansion. However, the modulation of the NP system in chronic renal insufficiency (CRI) remains to be elucidated. In the present study, we evaluated cardiac haemodynamics, plasma type-B natriuretic peptide (BNP) levels and the expression of natriuretic peptide receptor A (NPR-A) and NPR-C in the renal cortex (RC) and medulla (RM) of Sham and (3/4) nephrectomized ((3/4)nx) rats, up to 26 weeks after surgery., Methods: Male Wistar-Han rats (190-220 g; n = 49) were randomly assigned to (3/4)nx or Sham surgery. Two, 10 and 26 weeks after surgery, non-invasive blood pressure (BP) and left ventricular (LV) haemodynamics were performed, and urine and blood were collected for metabolic studies and plasma BNP determination. In addition, tissue samples from RC and RM were obtained for NPR-A and NPR-C quantification (RT-PCR and western blotting) as well as NPR-A immunodetection., Results: In (3/4)nx rats, the progressive interstitial fibrosis and tubular atrophy were accompanied by a time-dependent increase of BP and impaired natriuretic response to volume expansion (VE). This was accompanied in (3/4)nx rats by an early and time-dependent elevation of BNP circulating levels that was not associated with cardiac dysfunction or increased myocardial BNP gene expression. In (3/4)nx rats, NPR-A expression in the remnant RM was consistently reduced at 2, 10 and 26 weeks, and this was accompanied by an increase in NPR-C expression in the remnant RC from (3/4)nx rats., Conclusions: BP elevation and compromised natriuretic response to VE in (3/4)nx rats is associated with increased circulating BNP levels in the absence of cardiac dysfunction. This is accompanied in (3/4)nx rats by both impaired NPR-A expression in the RM and upregulation of NPR-C in the RC suggesting a novel mechanism for NP resistance in CRI.

Stimulation of the bone morphogenetic protein (BMP) pathway protects the kidney from acute and chronic injury. Numerous regulators in the kidney control BMP signaling, offering many targets for therapeutic manipulation. Here, we screened for modulators of BMP signaling in the ischemia-sensitive S3 segment and found that Chordin-like 1 is expressed in this segment of both the mouse and human nephron. Chordin-like 1 specifically antagonizes BMP7, which is expressed in the neighboring distal nephron, and this depends on the presence of the protein Twisted gastrulation. Upon ischemia-induced degeneration of the S3 segment, we observed a reduction in Chordin-like 1 expression coincident with intense BMP signaling in tubules of the recovering kidney. Restored expression accompanied proximal tubule epithelia redifferentiation, again coincident with decreased BMP signaling. We propose that Chordin-like 1 reduces BMP7 signaling in healthy proximal tubules, and the loss of this activity upon sloughing of injured epithelia promotes BMP7 signaling in repopulating, dedifferentiated epithelia. As regenerating epithelia differentiate, Chordin-like 1 is again expressed, antagonizing BMP7. These data suggest a mechanism for dynamic regulation of renoprotective BMP7 signaling in the S3 segment of the proximal tubule.

The complications of partial nephrectomy include hemorrhage, urinary leak, infection, formation of urinary fistula, and the development of renal insufficiency. We report a unique case of a patient who was found to have necrotic-appearing, bleeding, renal papillae after undergoing laparoscopic partial nephrectomy. A 66-year-old man was diagnosed with a left-sided, solid, enhancing, 2.5-cm, exophytic renal mass. Laparoscopic partial nephrectomy was performed, and the warm ischemia time was 31 minutes. He recovered uneventfully from surgery, but he started having episodes of gross hematuria approximately 5 months later. Computed tomography scan showed changes consistent with previous partial nephrectomy but no other abnormality. Ureterorenoscopy allowed us to identify several necrotic-appearing papillae in the same kidney that had undergone laparoscopic partial nephrectomy. A papilla in the lower pole was actively bleeding, and it was successfully obliterated using neodymium:yttrium-aluminum-garnet laser technology. Papillary necrosis can be a rare complication of laparoscopic or open partial nephrectomy. Additional study and close follow-up of patients who undergo partial nephrectomy is warranted.

Ischemia-reperfusion injury (IRI) is a common cause of acute kidney injury (AKI) and is characterized by widespread tubular and microvascular damage. The tumor suppressor p53 is upregulated after IRI and contributes to renal injury in part by promoting apoptosis. Acute, short-term inhibition of p53 with pifithrin-alpha conveys significant protection after IRI. The hypoxia-inducible factor-1 (HIF-1) pathway is also activated after IRI and has opposing effects to those promoted by p53. The balance between the HIF-1 and p53 responses can determine the outcome of IRI. In this manuscript, we investigate whether p53 regulates the HIF-1 pathway in a rodent model of IRI. HIF-1alpha is principally expressed in the collecting tubules (CT) and thick ascending limbs (TAL) under physiological conditions. However, inhibition of p53 with pifithrin-alpha increases the faint expression of HIF-1alpha in proximal tubules (PT) under physiological conditions. Twenty-four hours after IRI, HIF-1alpha expression is decreased in both CT and TAL. HIF-1alpha expression in the PT is not significantly altered after IRI. Acute inhibition of p53 significantly increases HIF-1alpha expression in the PT after IRI. Additionally, pifithrin-alpha prevents the IRI-induced decrease in HIF-1alpha in the CT and TAL. Parallel changes are observed in the HIF-1alpha transcriptive target, carbonic anhydrase-9. Finally, inhibition of p53 prevents the dramatic changes in Von Hippel-Lindau protein morphology and expression after IRI. We conclude that activation of p53 after IRI mitigates the concomitant activation of the protective HIF-1 pathway. Modulating the interactions between the p53 and HIF-1 pathway can provide novel options in the treatment of AKI.

We previously reported that, both in cell culture and in the renal inner medulla in vivo, elevating NaCl increased the number of DNA breaks, which persisted as long as NaCl remained high but were rapidly repaired when NaCl was lowered. Furthermore, those breaks did not induce the DNA repair protein gammaH2AX or cause activation of the MRN (Mre11, Rad50, Nbs1) complex. In contrast, others recently reported that high NaCl does induce gammaH2AX and MRN complex formation and concluded that these activities are associated with repair of the DNA (Sheen MR, Kim SW, Jung JY, Ahn JY, Rhee JG, Kwon HM, Woo SK. Am J Physiol Renal Physiol 291: F1014-F1020, 2006). The purpose of the present studies was to resolve the disparity. The important difference is that HeLa cells, which were the main subject of the later report, are much less tolerant of high NaCl than are the mIMCD3 cells, which were our main subject. mIMCD3 cells survive levels of NaCl that kill HeLa cells by apoptosis. Here we demonstrate that in both cell types raising NaCl to a level that the cells survive (higher for mIMCD3 than HeLa) increases DNA breaks without inducing gammaH2AX or activating the MRN complex and that the DNA breaks persist as long as NaCl remains elevated, but are rapidly repaired when it is lowered. Importantly, in both cell types, raising NaCl further to cause apoptosis activates these DNA damage response proteins and greatly fragments DNA, associated with cell death. We conclude that gammaH2AX induction and MRN activation in response to high NaCl are associated with apoptosis, not DNA repair.

Heat shock protein (HSP) HSP27, HSP60, HSP70, and HSP90 are induced by cellular stresses and play a key role in cytoprotection. Both hyperglycemia and glomerular hypertension are crucial determinants in the pathogenesis of diabetic nephropathy and impose cellular stresses on renal target cells. We studied both the expression and the phosphorylation state of HSP27, HSP60, HSP70, and HSP90 in vivo in rats made diabetic with streptozotocin and in vitro in mesangial cells and podocytes exposed to either high glucose or mechanical stretch. Diabetic and control animals were studied 4, 12, and 24 wk after the onset of diabetes. Immunohistochemical analysis revealed an overexpression of HSP25, HSP60, and HSP72 in the diabetic outer medulla, whereas no differences were seen in the glomeruli. Similarly, exposure neither to high glucose nor to stretch altered HSP expression in mesangial cells and podocytes. By contrast, the phosphorylated form of HSP27 was enhanced in the glomerular podocytes of diabetic animals, and in vitro exposure of podocytes to stretch induced HSP27 phosphorylation via a P38-dependent mechanism. In conclusion, diabetes and diabetes-related insults differentially modulate HSP27, HSP60, and HSP70 expression/phosphorylation in the glomeruli and in the medulla, and this may affect the ability of renal cells to mount an effective cytoprotective response.