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An increase of glomerular filtration rate (GFR) is a common observation in early diabetes and is considered a key risk factor for subsequent kidney injury. However, the mechanisms underlying diabetic hyperfiltration have not been fully clarified. Here, we tested the hypothesis that macula densa neuronal nitric oxide synthase (NOS1) is upregulated via sodium glucose cotransporter type 1 (SGLT1) in diabetes, which then inhibits tubuloglomerular feedback (TGF) promoting glomerular hyperfiltration. Therefore, we examined changes in cortical NOS1 expression and phosphorylation, nitric oxide production in the macula densa, TGF response, and GFR during the early stage of insulin-deficient (Akita) diabetes in wild-type and macula densa-specific NOS1 knockout mice. A set of sophisticated techniques including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of kidney tubules in vivo, and clearance kinetics of plasma fluorescent-sinistrin were employed. Complementary studies tested the role of SGLT1 in SGLT1 knockout mice and explored NOS1 expression and phosphorylation in kidney biopsies of cadaveric donors. Diabetic mice had upregulated macula densa NOS1, inhibited TGF and elevated GFR. Macula densa-selective NOS1 knockout attenuated the diabetes-induced TGF inhibition and GFR elevation. Additionally, deletion of SGLT1 prevented the upregulation of macula densa NOS1 and attenuated inhibition of TGF in diabetic mice. Furthermore, the expression and phosphorylation levels of NOS1 were increased in cadaveric kidneys of diabetics and positively correlated with blood glucose as well as estimated GFR in the donors. Thus, our findings demonstrate that the macula densa SGLT1-NOS1-TGF pathway plays a crucial role in the control of GFR in diabetes.

Hypertension is a common comorbid condition in patients with diabetes. The pathogenesis of hypertension in diabetes has not been fully clarified. Primary tubular hyperreabsorption may contribute, which may be counteracted by glomerular hyperfiltration in the early diabetic kidney. In this study, we hypothesize that in early diabetes, the macula densa neuronal nitric oxide synthase (NOS1)-derived nitric oxide (NO) production is enhanced, which blunts tubuloglomerular feedback (TGF) response, promotes glomerular hyperfiltration, and maintains normal blood pressure; conversely, insufficient NO generation by the macula densa induces hypertension by lowering glomerular filtration rate and thus inhibiting natriuresis. To test this hypothesis, we examined the changes of macula densa NOS1 expression and phosphorylation as well as NO production, TGF response, glomerular filtration rate, sodium excretion, and blood pressure in a murine model of leptin receptor-deficient (db/db) diabetes with or without macula densa-specific NOS1 deletion. We found that db/db mice presented reduced fractional renal sodium excretion and only a small increase in blood pressure, associated with upregulated expression and activity of macula densa NOS1, inhibited TGF response, and glomerular hyperfiltration. Genetic knockout of macula densa NOS1 restored the TGF response and attenuated glomerular hyperfiltration in db/db mice but also further reduced fractional renal sodium excretion and substantially increased blood pressure. In conclusion, the present study demonstrates that in the early stage of leptin receptor-deficient diabetes, the upregulation of macula densa NOS1 inhibits TGF and increases glomerular filtration rate, which counteracts renal sodium retention and limits the rise in blood pressure.

Sodium-glucose co-transporter 2 inhibitors (SGLT2-Is) have emerged as a promising class of antidiabetic drugs with cardioprotective and renoprotective effects in patients with type 2 diabetes (T2D). The sodium-glucose co-transporters 1 and 2 (SGLT 1 and SGLT2) located in the renal proximal tubules are responsible for glucose reabsorption from the glomerular filtrate back into the systemic circulation. Inhibition of SGLT2, which accounts for about 90% of the glucose reabsorption, leads to a significant reduction in blood glucose levels and a concomitant increase in the urinary excretion of glucose (glycosuria). Multiple mechanisms contribute to the nephroprotective effects of SGLT2-Is in T2D patients. These include: (1) Restoration of the tubuloglomerular feedback by increasing sodium delivery at macula densa, leading to afferent arteriolar constriction and reduced glomerular hyperfiltration, (2) Decreased activation of the intra-renal renin-angiotensin-aldosterone system, which also contributes to reducing glomerular hyperfiltration, (3) Increased production of ketone bodies, which serves as an alternate fuel for adenosine triphosphate production in mitochondria, which helps in attenuating inflammation, and (4) Protection against hypoxia, oxidative stress, and fibrosis. This review elaborates on the key mechanisms that underlie the nephroprotective effects and the adverse effects of SGLT2-Is in T2D patients with progressive diabetic kidney disease.

Renin and neuronal nitric oxide synthase in the kidney control the renin-angiotensin and tubuloglomerular feedback systems. The present study investigated the expression of renin and neuronal nitric oxide synthase in the dysplastic kidneys of three young dogs. Renin-immunoreactivity, which occurs in the juxtaglomerular and tubular cells of dysplastic kidneys, did not differ from that in the normal kidneys of young dogs. Macula densa cells in the normal kidneys showed neuronal nitric oxide synthase -immunoreactivity, but those in the dysplastic kidneys showed no apparent signals. This observation may be correlated with the pathological mechanisms of renal failure in young dogs.

BACKGROUND: Proximal tubule cells dominate the kidney parenchyma numerically, although less abundant cell types of the distal nephron have disproportionate roles in water and electrolyte balance. METHODS: Coupling of a FACS-based enrichment protocol with single-cell RNA-seq profiled the transcriptomes of 9099 cells from the thick ascending limb (CTAL)/distal convoluted tubule (DCT) region of the mouse nephron. RESULTS: Unsupervised clustering revealed Slc12a3(+)/Pvalb(+) and Slc12a3(+)/Pvalb(−) cells, identified as DCT1 and DCT2 cells, respectively. DCT1 cells appear to be heterogeneous, with orthogonally variable expression of Slc8a1, Calb1, and Ckb. An additional DCT1 subcluster showed marked enrichment of cell cycle–/cell proliferation–associated mRNAs (e.g., Mki67, Stmn1, and Top2a), which fit with the known plasticity of DCT cells. No DCT2-specific transcripts were found. DCT2 cells contrast with DCT1 cells by expression of epithelial sodium channel β- and γ-subunits and much stronger expression of transcripts associated with calcium transport (Trpv5, Calb1, S100g, and Slc8a1). Additionally, scRNA-seq identified three distinct CTAL (Slc12a1(+)) cell subtypes. One of these expressed Nos1 and Avpr1a, consistent with macula densa cells. The other two CTAL clusters were distinguished by Cldn10 and Ptger3 in one and Cldn16 and Foxq1 in the other. These two CTAL cell types were also distinguished by expression of alternative Iroquois homeobox transcription factors, with Irx1 and Irx2 in the Cldn10(+) CTAL cells and Irx3 in the Cldn16(+) CTAL cells. CONCLUSIONS: Single-cell transcriptomics revealed unexpected diversity among the cells of the distal nephron in mouse. Web-based data resources are provided for the single-cell data.

Antacids are usually alkaline substances that are used to neutralise excess acid in the stomach. Antacids were developed based on the hydroxides and carbonates of the group II and III metals, as well as the bicarbonates of the alkali metals. Antacids can be classified into two main classes being non-absorbable or absorbable antacids. Non-absorbable antacids have fewer side effects and further advantageous properties. Each antacid has a specific active ingredient which has a different effect on the gastric acid. Antacids act similar to when an acid reacts with a hydroxide; a salt and water are produced. Antacids are more effective in the form of suspension. The average therapeutic dose of an antacid is 10–15 ml of liquid or one to two tablets three to four times a day. These drugs have small volumes of distribution, undergo minimal hepatic metabolism and are excreted in faeces. Antacids that contain calcium, magnesium and aluminium ions are chelators. To avoid undesirable interactions, antacids are usually used two hours before or after taking any medication. Stress ulcerations are common in intensive care unit (ICU) patients. The pathophysiology of the ulceration probably results from an imbalance between mucosal protection and gastric acid hypersecretion. Whilst prophylaxis was provided to every patient previously, it is wise to individualise the decision and to only provide it to high risk patients. For critically ill patients who are able to receive enteral medications and in whom prophylaxis is indicated, an oral proton pump inhibitor (PPI) is preferred rather than an alternative prophylactic agent. For critically ill patients who cannot receive enteral medications, an intravenous (IV) histamine 2 (H2) receptor blocker or IV PPI can be administered. Where PPIs or H2 blockers cannot be administered, sucralfate is a suitable oral alternative.

Glomerular filtration rate is controlled by the contractile effect of angiotensin II on afferent and efferent arterioles. The renin positivity of the afferent arterioles depends on tubuloglomerular feedback via the macula densa (MD) and short loop feedback via the afferent arteriolar endothelia. The renin-producing cells are trans-differentiated from smooth muscle cells (SMCs) of mainly the afferent arterioles, the MD cells are trans-differentiated from the neighboring tubular cells, and the high-permeability endothelial cells are trans-differentiated from normal permeability endothelial cells facing the renin-negative part of the afferent arterioles. All of the trans-differentiations depend on the activity of the renin-angiotensin system (RAS). The distribution of AT1 receptors for angiotensin II expresses the contractile effects of angiotensin II on renin-negative SMCs and the negative effect on trans-differentiation of renin-positive SMCs and MD cells. The purpose of this review is to summarize the stereological data of molecules like angiotensin II AT1 receptors, L-type calcium channels, and renin receptors in the juxtaglomerular apparatus of normal and STZ-induced diabetic rat kidneys, thus showing their functional relevancies on trans-differentiation among the juxtaglomerular apparatus' elements.

Kidney size and glomerular filtration rate (GFR) often increase with the onset of diabetes, and elevated GFR is a risk factor for the development of diabetic kidney disease. Hyperfiltration mainly occurs in response to signals passed from the tubule to the glomerulus: high levels of glucose in the glomerular filtrate drive increased reabsorption of glucose and sodium by the sodium–glucose cotransporters SGLT2 and SGLT1 in the proximal tubule. Passive reabsorption of chloride and water also increases. The overall capacity for proximal reabsorption is augmented by growth of the proximal tubule, which (alongside sodium–glucose cotransport) further limits urinary glucose loss. Hyperreabsorption of sodium and chloride induces tubuloglomerular feedback from the macula densa to increase GFR. In addition, sodium–glucose cotransport by SGLT1 on macula densa cells triggers the production of nitric oxide, which also contributes to glomerular hyperfiltration. Although hyperfiltration restores sodium and chloride excretion it imposes added physical stress on the filtration barrier and increases the oxygen demand to drive reabsorption. Tubular growth is associated with the development of a senescence-like molecular signature that sets the stage for inflammation and fibrosis. SGLT2 inhibitors attenuate the proximal reabsorption of sodium and glucose, normalize tubuloglomerular feedback signals and mitigate hyperfiltration. This tubule-centred model of diabetic kidney physiology predicts the salutary effect of SGLT2 inhibitors on hard renal outcomes, as shown in large-scale clinical trials.

The kidneys filter large amounts of glucose. To prevent the loss of this valuable fuel, the tubular system of the kidney, particularly the proximal tubule, has been programmed to reabsorb all filtered glucose. The machinery involves the sodium-glucose cotransporters SGLT2 and SGLT1 on the apical membrane and the facilitative glucose transporter GLUT2 on the basolateral membrane. The proximal tubule also generates new glucose, particularly in the post-absorptive phase but also to enhance bicarbonate formation and maintain acid-base balance. The glucose reabsorbed or formed by the proximal tubule is primarily taken up into peritubular capillaries and returned to the systemic circulation or provided as an energy source to further distal tubular segments that take up glucose by basolateral GLUT1. Recent studies provided insights on the coordination of renal glucose reabsorption, formation, and usage. Moreover, a better understanding of renal glucose transport in disease states is emerging. This includes the kidney in diabetes mellitus, when renal glucose retention becomes maladaptive and contributes to hyperglycemia. Furthermore, enhanced glucose reabsorption is coupled to sodium retention through the sodium-glucose cotransporter SGLT2, which induces secondary deleterious effects. As a consequence, SGLT2 inhibitors are new anti-hyperglycemic drugs that can protect the kidneys and heart from failing. Recent studies discovered unique roles for SGLT1 with implications in acute kidney injury and glucose sensing at the macula densa. This review discusses established and emerging concepts of renal glucose transport, and outlines the need for a better understanding of renal glucose handling in health and disease.

The kidney plays an essential role in homeostasis, accomplished through the regulation of pH, electrolytes and fluids, by the building blocks of the kidney, the nephrons. One of the important markers of the proper functioning of a kidney is the glomerular filtration rate. Diabetes is characterised by an enlargement of the glomerular and tubular size of the kidney, affecting the afferent and efferent arteriole resistance and hemodynamics, ultimately leading to chronic kidney disease. We postulate that the diabetes-induced changes in kidney may exhibit significant sex differences as the distribution of renal transporters along the nephron may be markedly different between women and men, as recently shown in rodents. The goals of this study are to (i) analyze how kidney function is altered in male and female patients with diabetes, and (ii) assess the renal effects, in women and men, of an anti-hyperglycemic therapy that inhibits the sodium-glucose cotransporter 2 (SGLT2) in the proximal convoluted tubules. To accomplish these goals, we have developed computational models of kidney function, separate for male and female patients with diabetes. The simulation results indicate that diabetes enhances Na+ transport, especially along the proximal tubules and thick ascending limbs, to similar extents in male and female patients, which can be explained by the diabetes-induced increase in glomerular filtration rate. Additionally, we conducted simulations to study the effects of diabetes and SGLT2 inhibition on solute and water transport along the nephrons. Model simulations also suggest that SGLT2 inhibition, which constricts the afferent arteriole to attenuate glomerular hyperfiltration, can then limit Na+-glucose transport, consequently raising luminal [Cl-] at the macula densa and finally restoring the tubuloglomerular feedback signal. By inducing osmotic diuresis in the proximal tubules, SGLT2 inhibition reduces paracellular transport, eventually leading to diuresis and natriuresis. Those effects on urinary excretion are blunted in women, in part due to their higher distal transport capacity.

Ferritin is the main intracellular storage of iron. Animal studies show that female liver and kidney express more ferritin and accumulate more iron than male. However, no study so far has investigated sex and age differences in light (FtL) and heavy (FtH) ferritin chain expression. To address this, we relied on specific antibodies and immunochemical methods to analyse the expression of both ferritin chains in the liver and kidney of 3-month and 2-year-old male and female Wistar rats. To see how sex hormones may affect expression we also studied adult animals gonadectomised at the age of 10 weeks. FtL and FtH were more expressed in both organs of female rats, while gonadectomy increased the expression in males and decreased it in females, which suggests that it is stimulated by female and inhibited by male steroid hormones. Normal kidney ferritin distribution and change with aging warrant more attention in studies of (patho) physiological and toxicological processes., Feritin je glavni skladišni protein unutarstaničnoga željeza. U korelaciji s ekspresijom feritina, istraživanja na životinjama pokazuju da jetra i bubrezi u ženki nakupljaju više željeza nego u mužjaka. Međutim, dosad se nijedno istraživanje nije bavilo spolnim i dobnim razlikama u ekspresiji lakog (FtL) i teškog (FtH) lanca koji čine feritinski nanokavez. Kako bismo to riješili, oslonili smo se na specifična protutijela i imunokemijske metode za analizu ekspresije obaju feritinskih lanaca u jetri i bubrezima odraslih i starih mužjaka i ženki štakora soja Wistar. Da bismo vidjeli kako spolni hormoni mogu utjecati na ekspresiju feritina, proučavali smo i gonadektomirane odrasle životinje. FtL i FtH bili su izraženiji u odraslih i starih životinja u obama organima u ženki štakora; gonadektomija je povećala ekspresiju u mužjaka, a smanjila je u ženki, što upućuje na to da feritine stimuliraju ženski, a inhibiraju muški steroidni hormoni. Normalna raspodjela feritina u bubrezima i promjena sa starenjem zahtijevaju više pažnje u proučavanju (pato)fizioloških i toksikoloških procesa.

The kidneys play an important role in blood pressure regulation under normal and pathological conditions. We examined the histological changes and expression patterns of cyclooxygenase-2, renin, and (pro)renin receptor (PRR) in the renal cortex of prehypertensive spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKYs). Moreover, blood pressure and plasma urea, creatinine, angiotensin II, and angiotensin (1–7) levels were measured. The results showed that both strains had similar blood pressure and plasma urea and creatinine levels. The glomerular area, basement membrane thickness, collagen fiber content, and arterial wall thickness were greater in SHRs than in WKYs. By immunohistochemistry, cyclooxygenase-2 was localized in the macula densa and renal tubules of both strains. In SHRs, cyclooxygenase-2 was detected in a larger number of tubules, and the cortical expression of cyclooxygenase-2 was also increased. In both strains, PRR and renin were localized in the tubular epithelium and juxtaglomerular cells, respectively. In SHRs, PRR immunolocalization was increased in the glomerulus. The cortical expression of immature renin was markedly increased in SHRs compared to that in WKYs, while renin was significantly decreased. These changes were associated with higher plasma angiotensin II levels and lower plasma angiotensin (1–7) levels in SHRs. The results indicate that the kidneys of SHRs showed morphological changes and variations in cortical expression patterns of PRR, cyclooxygenase-2, and renin before the development of hypertension.

Macula densa (MD) cells, a chief sensory cell type in the nephron, are endowed with unique microanatomic features including a high density of protein synthetic organelles and secretory vesicles in basal cell processes (“maculapodia”) that suggest a so far unknown high rate of MD protein synthesis. This study aimed to explore the rate and regulation of MD protein synthesis and their effects on glomerular function using novel transgenic mouse models, newly established fluorescence cell biology techniques, and intravital microscopy. Sox2-tdTomato kidney tissue sections and an O-propargyl puromycin incorporation-based fluorescence imaging assay showed that MD cells have the highest level of protein synthesis within the kidney cortex followed by intercalated cells and podocytes. Genetic gain of function of mammalian target of rapamycin (mTOR) signaling specifically in MD cells (in MD-mTOR(gof) mice) or their physiological activation by low-salt diet resulted in further significant increases in the synthesis of MD proteins. Specifically, these included both classic and recently identified MD-specific proteins such as cyclooxygenase 2, microsomal prostaglandin E(2) synthase 1, and pappalysin 2. Intravital imaging of the kidney using multiphoton microscopy showed significant increases in afferent and efferent arteriole and glomerular capillary diameters and blood flow in MD-mTOR(gof) mice coupled with an elevated glomerular filtration rate. The presently identified high rate of MD protein synthesis that is regulated by mTOR signaling is a novel component of the physiological activation and glomerular hemodynamic regulatory functions of MD cells that remains to be fully characterized. NEW & NOTEWORTHY This study discovered the high rate of protein synthesis in macula densa (MD) cells by applying direct imaging techniques with single cell resolution. Physiological activation and mammalian target of rapamycin signaling played important regulatory roles in this process. This new feature is a novel component of the tubuloglomerular cross talk and glomerular hemodynamic regulatory functions of MD cells. Future work is needed to elucidate the nature and (patho)physiological role of the specific proteins synthesized by MD cells.

Background: Regulation of renal hemodynamics and blood pressure (BP) via tubuloglomerular feedback (TGF) may be an important adaptive mechanism during pregnancy. Because the β-splice variant of nitric oxide synthase 1 (NOS1β) in the macula densa is a primary modulator of TGF, we evaluated its role in normal pregnancy and gestational hypertension in a mouse model. We hypothesized that pregnancy upregulates NOS1β in the macula densa, thus blunting TGF, allowing glomerular filtration rate (GFR) to increase and BP to decrease. Methods: We employed sophisticated techniques, including microperfusion of juxtaglomerular apparatus in vitro, micropuncture of renal tubules in vivo, clearance kinetics of plasma FITC-sinistrin, and radio-telemetry BP monitoring, to determine the effects of normal pregnancy or reduced uterine perfusion pressure (RUPP) on macula densa NOS1β/NO levels, TGF responsiveness, GFR, and BP in wild-type and macula densa-specific NOS1 knockout (MD-NOS1KO) mice. Results: Macula densa NOS1β was upregulated during pregnancy, resulting in blunted TGF, increased GFR, and decreased BP. These pregnancy-induced changes in TGF and GFR were largely diminished, with a significant rise in BP, in MD-NOS1KO mice. In addition, RUPP resulted in a downregulation in macula densa NOS1β, enhanced TGF, decreased GFR, and hypertension. The superimposition of RUPP into MD-NOS1KO mice only caused a modest further alteration in TGF and its associated changes in GFR and BP. Finally, in African green monkeys, renal cortical NOS1β expression increased in normotensive pregnancies but decreased in spontaneous gestational hypertensive pregnancies. Conclusions: Macula densa NOS1β plays a critical role in control of renal hemodynamics and BP during pregnancy.

A patient with renal glucosuria due to a congenital knock-out of the sodium-glucose cotransporter 2 (SGLT-2) protein because of a compound heterozygous mutation in the SLC5A2 gene may provide a natural model mimicking the effects of long-term SGLT-2 inhibitor therapy, which has been shown to exert kidney-protective effects beyond its antidiabetic properties. One possible mechanism for the protective effects of SGLT-2 inhibitor therapy might be the activation of tubuloglomerular feedback by increased outflow of sodium, chloride, and glucose to distal parts of the nephron, including the macula densa. Subsequently, afferent arteriolar vasoconstriction is induced and blood flow, intraglomerular filtration pressure, and glomerular filtration rate (GFR) all decline. However, prolonged tubuloglomerular feedback activation could change the sensitivity of tubuloglomerular feedback and hence decrease the beneficial effects of SGLT-2 inhibition on kidney function. Tubuloglomerular feedback is mediated by the Na+/K+/2Cl− cotransporter. Hence furosemide, which blocks this cotransporter, is a medical option to test tubuloglomerular feedback because GFR should increase after administration of this loop diuretic. In our patient with long-term activated tubuloglomerular feedback due to SGLT-2 mutations, we show that the sensitivity of tubuloglomerular feedback is maintained, demonstrated by an increase in GFR measured using iohexol clearance following furosemide administration. This observation supports the idea that long-term SGLT-2 inhibitor therapy is kidney protective through a functional tubuloglomerular feedback. Index Words: SGLT-2 Inhibitor, glomerular filtration rate, tubuloglomerular feedback, kidney protection, iohexol clearance

Na+-glucose cotransporter (SGLT)1 mediates glucose reabsorption in late proximal tubules. SGLT1 also mediates macula densa (MD) sensing of an increase in luminal glucose, which increases nitric oxide (NO) synthase 1 (MD-NOS1)-mediated NO formation and potentially glomerular filtratrion rate (GFR). Here, the contribution of SGLT1 was tested by gene knockout (−/−) in type 1 diabetic Akita mice. A low-glucose diet was used to prevent intestinal malabsorption in Sglt1−/−mice and minimize the contribution of intestinal SGLT1. Hyperglycemia was modestly reduced in Sglt1−/−versus littermate wild-type Akita mice (480 vs. 550 mg/dl), associated with reduced diabetes-induced increases in GFR, kidney weight, glomerular size, and albuminuria. Blunted hyperfiltration was confirmed in streptozotocin-induced diabetic Sglt1−/−mice, associated with similar hyperglycemia versus wild-type mice (350 vs. 385 mg/dl). Absence of SGLT1 attenuated upregulation of MD-NOS1 protein expression in diabetic Akita mice and in response to SGLT2 inhibition in nondiabetic mice. During SGLT2 inhibition in Akita mice, Sglt1−/−mice had likewise reduced blood glucose (200 vs. 300 mg/dl), associated with lesser MD-NOS1 expression, GFR, kidney weight, glomerular size, and albuminuria. Absence of Sglt1 in Akita mice increased systolic blood pressure, associated with suppressed renal renin mRNA expression. This may reflect fluid retention due to blunted hyperfiltration. SGLT2 inhibition prevented the blood pressure increase in Sglt1−/−Akita mice, possibly due to additive glucosuric/diuretic effects. The data indicate that SGLT1 contributes to diabetic hyperfiltration and limits diabetic hypertension. Potential mechanisms include its role in glucose-driven upregulation of MD-NOS1 expression. This pathway may increase GFR to maintain volume balance when enhanced MD glucose delivery indicates upstream saturation of SGLTs and thus hyperreabsorption.

Background Glomerular hyperfiltration is common in early diabetes and is considered a risk factor for later diabetic nephropathy. We propose that sodium-glucose cotransporter 1 (SGLT1) senses increases in luminal glucose at the macula densa, enhancing generation of neuronal nitric oxide synthase 1 (NOS1)–dependent nitric oxide (NO) in the macula densa and blunting the tubuloglomerular feedback (TGF) response, thereby promoting the rise in GFR. Methods We used microperfusion, micropuncture, and renal clearance of FITC–inulin to examine the effects of tubular glucose on NO generation at the macula densa, TGF, and GFR in wild-type and macula densa–specific NOS1 knockout mice. Results Acute intravenous injection of glucose induced hyperglycemia and glucosuria with increased GFR in mice. We found that tubular glucose blunts the TGF response in vivo and in vitro and stimulates NO generation at the macula densa. We also showed that SGLT1 is expressed at the macula densa; in the presence of tubular glucose, SGLT1 inhibits TGF and NO generation, but this action is blocked when the SGLT1 inhibitor KGA-2727 is present. In addition, we demonstrated that glucose increases NOS1 expression and NOS1 phosphorylation at Ser1417 in mouse renal cortex and cultured human kidney tissue. In macula densa–specific NOS1 knockout mice, glucose had no effect on NO generation, TGF, and GFR. Conclusions We identified a novel mechanism of acute hyperglycemia–induced hyperfiltration wherein increases in luminal glucose at the macula densa upregulate the expression and activity of NOS1 via SGLT1, blunting the TGF response and promoting glomerular hyperfiltration.

At the onset of diabetes, the kidney grows large and the glomerular filtration rate becomes abnormally high. These structural and hemodynamics changes affect kidney function and may contribute to the development of chronic kidney disease. The goal of this study is to analyze how kidney function is altered in patients with diabetes and the renal effects of an anti-hyperglyceamic therapy that inhibits the sodium-glucose cotransporter 2 (SGLT2) in the proximal convoluted tubules. To accomplish that goal, we have developed a computational model of kidney function in a patient with diabetes and conducted simulations to study the effects of diabetes and SGLT2 inhibition on solute and water transport along the nephrons. Simulation results indicate that diabetes-induced hyperfiltration and tubular hypertrophy enhances Na+ transport, especially along the proximal tubules and thick ascending limbs. These simulations suggest that SGLT2 inhibition may attenuate glomerular hyperfiltration by limiting Na+-glucose transport, raising luminal [Cl−] at the macula densa, restoring the tubuloglomerular feedback signal, thereby reducing single-nephron glomerular filtration rate.

Although macula densa (MD) cells are chief regulatory cells in the nephron with unique microanatomical features, they have been difficult to study in full detail due to their inaccessibility and limitations in earlier microscopy techniques. The present study used a new mouse model with a comprehensive imaging approach to visualize so far unexplored microanatomical features of MD cells, their regulation, and functional relevance. MD-GFP mice with conditional and partial induction of green fluorescent protein (GFP) expression, which specifically and intensely illuminated only single MD cells, were used with fluorescence microscopy of fixed tissue and live MD cells in vitro and in vivo with complementary electron microscopy of the rat, rabbit, and human kidney. An elaborate network of major and minor cell processes, here named maculapodia, were found at the cell base, projecting toward other MD cells and the glomerular vascular pole. The extent of maculapodia showed upregulation by low dietary salt intake and the female sex. Time-lapse imaging of maculapodia revealed highly dynamic features including rapid outgrowth and an extensive vesicular transport system. Electron microscopy of rat, rabbit, and human kidneys and three-dimensional volume reconstruction in optically cleared whole-mount MD-GFP mouse kidneys further confirmed the presence and projections of maculapodia into the extraglomerular mesangium and afferent and efferent arterioles. The newly identified dynamic and secretory features of MD cells suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD cells and between MD and other target cells. NEW & NOTEWORTHY This study illuminated a physiologically regulated dense network of basal cell major and minor processes (maculapodia) in macula densa (MD) cells. The newly identified dynamic and secretory features of these microanatomical structures suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD and other target cells. Detailed characterization of the function and molecular details of MD cell intercellular communications and their role in physiology and disease warrant further studies.

Background: Succinate is a well-known intermediate in the tricarboxylic acid (Krebs) cycle, where it is converted to form fumarate by succinate dehydrogenase from succinyl-CoA. Surprisingly, besides as a general metabolic intermediate, succinate can selectively activate orphan G receptor GPR91, which is highly expressed in the kidney, including glomerular vasculature, the macula densa (MD), proximal tubules, distal tubules, the cortical thick ascending limb of (cTAL) Henle’s loop, and the cortical as well as medullary collecting duct (CD). The level of succinate in patients with type 2 diabetes and obesity was much higher than healthy controls. However, the causative role of succinate in renal function is still unknown. Considering the excess succinate concentration, abundant expression of GPR91, and the importance of the kidney, we speculated that succinate could affect renal function. Methods: Male C57 BL/6 mice provided sterile drinking water containing 4% succinate ad libitum for 8 weeks and 12 weeks were used to investigate the effect of succinate on important renal functions. Results: Succinate administration markedly promoted water reabsorption via upregulating AQP2 protein and gene expression. Furthermore, Na + retention was significantly enhanced by succinate via increasing ENaC protein and gene expression. Moreover, succinate caused severe damage to the kidney, including glomerulus and proximal tubule, and tubulointerstitial fibrosis. These pathological changes were consistent with characteristics reported in diabetic kidney disease both in clinical patients and animal models. Conclusions: Other than a common metabolic intermediate in the Krebs cycle, elevated succinate in the circulation causes renal dysfunction and damage and recapitulates a diabetes-like phenotype of kidney disease, indicating that eliminating succinate from blood may improve clinic intervention in diabetic kidney disease. Funding Information: This study was supported by the National Natural Science Foundation of China (Grants 82070888, 82070882, 81770808, 81872165, 81701414, 81871211, and 81702879); National Key RD Guangdong Provincial Key RD Key Project of Nature Science Foundation of Guangdong Province, China (Grant 2019B1515120077); Guangdong Natural Science Fund (Grant 2019A1515011810, 2021A1515010434); Guangdong Science Technology Project (Grant 2017A020215075); Key Sci-Tech Research Project of Guangzhou Municipality, China (Grants 201803010017, 201807010069, and 202002020022); 2017 and 2019 Milstein Medical Asian American Partnership Foundation Research Project Award in Translational Medicine. Declaration of Interests: None. Ethics Approval Statement: All animal procedures were approved by the Animal Care and Use Committee of Sun Yat-Sen University (Ethics Committee of ZSSOM on Laboratory Animal Care No. 2020001017; Guangzhou, China).

Immunosuppression based on calcineurin inhibitors (CNI) such as cyclosporine A (CsA) is the current standard for patients undergoing organ transplantation. Nephrotoxic side effects of CsA include reduction of renal cortical cyclooxygenase 2 (COX-2) expression along with pathophysiological alterations of glomerular filtration rate and sodium balance. The underlying molecular mechanisms are poorly understood. Since CsA stimulates the renin-angiotensin system (RAS), we hypothesized that suppression of COX-2 relates to enhanced RAS activity. Inhibition of calcineurin in cultured macula densa (MD) cells using CsA or siRNA technology increased COX-2 expression and activity via stimulation of p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-kB). Concomitant application of angiotensin II abolished these effects suggesting a dominant role for RAS. In rats, short (3 days) as well as chronic CsA treatment (3 weeks) led to increased renin biosynthesis, decreased COX-2 expression in the kidney cortex, reduced creatinine clearance, and sodium retention due to activation of major distal salt transporters, Na+-K+-2Cl- cotransporter (NKCC2) and Na+-Cl- cotransporter (NCC). Simultaneous administration of a RAS inhibitor candesartan during short term CsA partially restored COX-2 expression and creatinine clearance, diminished sodium retention and prevented NKCC2 and NCC activation. These parameters were completely normalized in the chronic experiment after three weeks of concomitant candesartan treatment. Single administration of the selective COX-2 inhibitor, celecoxib, during three days largely recapitulated the effects of CsA and significantly reduced the beneficial effects of candesartan by concomitant drug application. These results suggest that suppression of COX-2 is a major signal that contributes to CsA nephrotoxicity. In summary, the present study has established calcineurin as an endogenous inhibitor of tubular COX-2, acting via suppression of p38 MAPK and NF-kB activity. CsA-induced RAS activation critically reduces cortical COX-2 activity, thus overriding local stimulatory effects of calcineurin inhibition. Our data support the use of RAS inhibitors for alleviation of CsA nephrotoxicity., Calcineurin Inhibitoren (CNI) bilden aktuell die Basis für immunsuppressive Strategien nach Organtransplantation. Allerdings führt die Anwendung von CNI zur Hemmung der Cyclooxygenase-2 (COX-2) in der Nierenrinde mit assoziierten pathophysiologischen Veränderungen der glomerulären Filtrationsrate (GFR) und des Salzhaushalts. Die dafür verantwortlichen pathogenetischen Mechanismen sind nicht ausreichend charakterisiert. Es ist bekannt, dass CNI das Renin-Angiotensin-System (RAS) stimulieren. In der vorliegenden Arbeit wird die Hypothese verfolgt, dass die gesteigerte RAS-Aktivität als Ursache für die COX-2 Suppression bei CNI Gabe fungiert. Um diese Hypothese zu testen, wurden zunächst Effekte des CNI Cyclosporin A (CsA) in kultivierten Macula densa (MD) Zellen und in Rattennieren charakterisiert. Im Gegensatz zur COX-2 Suppression in der intakten Niere zeigten kultivierte MD Zellen eine Steigerung der COX-2 Expression nach CsA-Behandlung bzw. nach Calcineurin-Suppression mittels siRNA. Weitere Experimente in MD Zellen zeigten, dass die CsA-abhängige Steigerung der COX-2 Expression sich hier durch Enthemmung der p38 mitogen-activated protein kinase (p38 MAPK) und Aktivierung des nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-kB) erklärt. Diese lokalen Effekte der Calcineurin-Inhibition konnten durch gleichzeitige Applikation von Angiotensin II (Ang II) vollständig aufgehoben werden. Im Gegenzug konnte die CsA-abhängige COX-2 Suppression in der intakten Rattenniere durch gleichzeitige akute (3 Tage) oder chronische (3 Wochen) Verabreichung eines Ang II-Rezeptor Typ 1 (AT1R) Antagonisten teilweise bzw. komplett aufgehoben werden. Die bei CsA-Gabe auftretende GFR-Reduktion und renale Natriumretention wurden durch den AT1R Antagonisten gleichfalls teilweise oder komplett verhindert. Diese Wirkungen des AT1R Antagonisten wurden durch die gleichzeitige Applikation des selektiven COX-2 Inhibitors Celecoxib deutlich abgeschwächt. Insgesamt zeigen diese Daten, dass die Suppression der renalen COX-2 bei CNI durch die gesteigerte RAS Aktivität bedingt ist, welche über die lokalen, COX-2-stimulierenden Effekte der Calcineurin-Inhibition in MD-Zellen dominiert. AT1R Blockade normalisiert die COX-2 Aktivität und verbessert damit die Nierenfunktion. Diese Studie liefert neue Einblicke in die Pathogenese der CNI Nephrotoxizität und unterstreicht die protektive Wirkung von RAS Inhibitoren.

Molecular characterization of the individual cell types in human kidney as well as model organisms are critical in defining organ function and understanding translational aspects of biomedical research. Previous studies have uncovered gene expression profiles of several kidney glomerular cell types, however, important cells, including mesangial (MCs) and glomerular parietal epithelial cells (PECs), are missing or incompletely described, and a systematic comparison between mouse and human kidney is lacking. To this end, we use Smart-seq2 to profile 4332 individual glomerulus-associated cells isolated from human living donor renal biopsies and mouse kidney. The analysis reveals genetic programs for all four glomerular cell types (podocytes, glomerular endothelial cells, MCs and PECs) as well as rare glomerulus-associated macula densa cells. Importantly, we detect heterogeneity in glomerulus-associated Pdgfrb-expressing cells, including bona fide intraglomerular MCs with the functionally active phagocytic molecular machinery, as well as a unique mural cell type located in the central stalk region of the glomerulus tuft. Furthermore, we observe remarkable species differences in the individual gene expression profiles of defined glomerular cell types that highlight translational challenges in the field and provide a guide to design translational studies., The molecular identity of renal glomerular cells is poorly characterized and rodent glomerulopathy models translate poorly to humans. Here, the authors show molecular signatures of glomerulus-associated cells using single cell RNA sequencing and highlight differences between mouse and human cells.