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Thrombotic microangiopathy, hemolysis and acute kidney injury are typical clinical characteristics of hemolytic-uremic syndrome (HUS), which is predominantly caused by Shiga-toxin-producing Escherichia coli. Free heme aggravates organ damage in life-threatening infections, even with a low degree of systemic hemolysis. Therefore, we hypothesized that the presence of the hemoglobin- and the heme-scavenging proteins, haptoglobin and hemopexin, respectively impacts outcome and kidney pathology in HUS. Here, we investigated the effect of haptoglobin and hemopexin deficiency (haptoglobin

Over the past 2 decades, scoring systems for multiple glomerular diseases have emerged, as have consortia of pathologists and nephrologists for the study of glomerular diseases, including correlation of pathologic findings with clinical features and outcomes. However, one important limitation faced by members of these consortia and other renal pathologists and nephrologists in both investigative work and routine practice remains a lack of uniformity and precision in clearly defining the morphologic lesions on which the scoring systems are based. In response to this issue, the Renal Pathology Society organized a working group to identify the most frequently identified glomerular lesions observed by light microscopy and electron microscopy, review the literature to capture the published definitions most often used for each, and determine consensus terms and definitions for each lesion in a series of online and in-person meetings. The defined lesions or abnormal findings are not specific for any individual disease or subset of diseases, but rather can be applied across the full spectrum of glomerular diseases and within the context of the different scoring systems used for evaluating and reporting these diseases. In addition to facilitating glomerular disease research, standardized terms and definitions should help harmonize reporting of medical kidney diseases worldwide and lead to more-precise diagnoses and improved patient care.

There has been much debate as to whether the distinction between lupus nephritis class IV-S and class IV-G is clinically relevant and whether antineutrophil cytoplasmic antibodies are pathomechanistically involved because they have been associated with the more necrotic and pauci-inflammatory phenotype of lupus nephritis that is more often seen in class IV-S. Recent data show that antineutrophil cytoplasmic antibody positivity indeed influences the histological pattern of lupus nephritis and is associated with worse baseline renal function and more active lupus serology.

The incidence and prevalence of heart failure (HF) and chronic kidney disease (CKD) are increasing, and as such a better understanding of the interface between both conditions is imperative for developing optimal strategies for their detection, prevention, diagnosis, and management. To this end, Kidney Disease: Improving Global Outcomes (KDIGO) convened an international, multidisciplinary Controversies Conference titled Heart Failure in CKD. Breakout group discussions included (i) HF with preserved ejection fraction (HFpEF) and nondialysis CKD, (ii) HF with reduced ejection fraction (HFrEF) and nondialysis CKD, (iii) HFpEF and dialysis-dependent CKD, (iv) HFrEF and dialysis-dependent CKD, and (v) HF in kidney transplant patients. The questions that formed the basis of discussions are available on the KDIGO website http://kdigo.org/conferences/heart-failure-in-ckd/, and the deliberations from the conference are summarized here.

Calcitriol, a powerful regulator of phosphate metabolism and immune response, is generated by 25-hydroxyvitamin D 1α-hydroxylase in the kidney and macrophages. Renal 1α-hydroxylase expression is suppressed by Klotho and FGF23, the expression of which is stimulated by calcitriol. Interferon γ (INFγ) regulates 1α-hydroxylase expression in macrophages through transcription factor interferon regulatory factor-1. INFγ-signaling includes Janus kinase 3 (JAK3) but a role of JAK3 in the regulation of 1α-hydroxylase expression and mineral metabolism has not been shown. Thus, the impact of JAK3 deficiency on calcitriol formation and phosphate metabolism was measured. Renal interferon regulatory factor-1 and 1α-hydroxylase transcript levels, serum calcitriol and FGF23 levels, intestinal phosphate absorption as well as absolute and fractional renal phosphate excretion were significantly higher in jak3 knockout than in wild-type mice. Coexpression of JAK3 increased the phosphate-induced current in renal sodium–phosphate cotransporter–expressing Xenopus oocytes. Thus, JAK3 is a powerful regulator of 1α-hydroxylase expression and phosphate transport. Its deficiency leads to marked derangement of phosphate metabolism.

Volume retention in nephrotic syndrome has been linked to activation of the epithelial sodium channel (ENaC) by proteolysis of its γ-subunit following urinary excretion of serine proteases such as plasmin. Here we tested whether pharmacological inhibition of urinary serine protease activity might protect from ENaC activation and volume retention in nephrotic syndrome. Urine from both nephrotic mice (induced by doxorubicin injection) and nephrotic patients exhibited high aprotinin-sensitive serine protease activity. Treatment of nephrotic mice with the serine protease inhibitor aprotinin by means of subcutaneous sustained-release pellets normalized urinary serine protease activity and prevented sodium retention, as did treatment with the ENaC inhibitor amiloride. In the kidney cortex from nephrotic mice, immunofluorescence revealed increased apical γ-ENaC staining, normalized by aprotinin treatment. In Xenopus laevis oocytes heterologously expressing murine ENaC, aprotinin had no direct inhibitory effect on channel activity but prevented proteolytic channel activation. Thus, our study shows that volume retention in experimental nephrotic syndrome is related to proteolytic ENaC activation by proteasuria and can be prevented by treatment with aprotinin. Hence, inhibition of urinary serine protease activity might become a therapeutic approach to treat patients with nephrotic-range proteinuria.

The activation of the receptor for advanced glycation end products (RAGE) is involved in the development of diabetic nephropathy. Analysis of protein phosphatase-1 indicated that advanced glycation end products did not affect its expression, but increased its phosphatase activity. Using differential display analysis we previously demonstrated that stimulation of RAGE in podocytes modulates the expression of numerous genes, among others nuclear inhibitor of protein phosphatase-1 (NIPP1). Here we found that silencing of NIPP1 induced podocyte hypertrophy, cell cycle arrest, and significantly increased protein phosphatase-1 activity. NIPP1 downregulation was associated with increased p27 Kip1 protein expression. Reporter assays revealed a transcriptional activation of nuclear factor-κB in podocytes after suppression of NIPP1. The protein level of NIPP1 was also significantly reduced in podocytes of diabetic mice. Blocking the RAGE in vivo by a soluble analog elevated the NIPP1 protein in podocytes of diabetic mice. Thus, activation of the RAGE by advanced glycation end products or other ligands suppresses NIPP1 expression in diabetic nephropathy, contributes to podocyte hypertrophy, and glomerular inflammation.

The glycoprotein CD44 is barely detected in normal mouse and human glomeruli, but is increased in glomerular parietal epithelial cells following podocyte injury in focal segmental glomerulosclerosis (FSGS). To determine the biological role and regulation of CD44 in these cells, we employed an in vivo and in vitro approach. Experimental FSGS was induced in CD44 knockout and wild-type mice with a cytotoxic podocyte antibody. Albuminuria, focal and global glomerulosclerosis (periodic acid–Schiff stain), and collagen IV staining were lower in CD44 knockout compared with wild-type mice with FSGS. Parietal epithelial cells had lower migration from Bowman's capsule to the glomerular tuft in CD44 knockout mice with disease compared with wild type mice. In cultured murine parietal epithelial cells, overexpressing CD44 with a retroviral vector encoding CD44 was accompanied by significantly increased collagen IV expression and parietal epithelial cell migration. Because our results showed de novo co-staining for activated ERK1/2 (pERK) in parietal epithelial cells in experimental FSGS, and also in biopsies from patients with FSGS, two in vitro strategies were employed to prove that pERK regulated CD44 levels. First, mouse parietal epithelial cells were infected with a retroviral vector for the upstream kinase MEK-DD to increase pERK, which was accompanied by increased CD44 levels. Second, in CD44-overexpressing parietal epithelial cells, decreasing pERK with U0126 was accompanied by reduced CD44. Finally, parietal epithelial cell migration was higher in cells with increased and reduced in cells with decreased pERK. Thus, pERK is a regulator of CD44 expression, and increased CD44 expression leads to a pro-sclerotic and migratory parietal epithelial cell phenotype.

Chronic kidney disease (CKD) is associated with increased risk and worse prognosis of cardiovascular disease, including peripheral artery disease. An impaired angiogenic response to ischemia may contribute to poor outcomes of peripheral artery disease in patients with CKD. Hypoxia inducible factors (HIF) are master regulators of angiogenesis and therefore represent a promising target for therapeutic intervention. To test this we induced hind-limb ischemia in rats with CKD caused by 5/6 nephrectomy and administered two different treatments known to stabilize HIF protein in vivo : carbon monoxide and a pharmacological inhibitor of prolyl hydroxylation 2-(1-chloro-4- hydroxyisoquinoline-3-carboxamido) acetate (ICA). Expression levels of pro-angiogenic HIF target genes ( Vegf, Vegf-r1, Vegf-r2, Ho-1 ) were measured by qRT-PCR. Capillary density was measured by CD31 immunofluorescence staining and HIF expression was evaluated by immunohistochemistry. Capillary density in ischemic skeletal muscle was significantly lower in CKD animals compared to sham controls. Rats with CKD showed significantly lower expression of HIF and all measured pro-angiogenic HIF target genes, including VEGF. Both HIF stabilizing treatments rescued HIF target gene expression in animals with CKD and led to significantly higher ischemia-induced capillary sprouting compared to untreated controls. ICA was effective regardless of whether it was administered before or after induction of ischemia and led to a HIF expression in skeletal muscle. Thus, impaired ischemia-induced angiogenesis in rats with CKD can be improved by HIF stabilization, even if started after onset of ischemia.

Intrauterine growth retardation (IUGR) aggravates the course of acute mesangioproliferative glomerulonephritis (GN) in the rat. Observational studies in children suggest that IUGR may be associated with a severe course of kidney diseases such as IgA nephropathy. We tested the hypothesis that IUGR leads to aggravation of acute mesangioproliferative GN in former IUGR rats. IUGR was induced in Wistar rats by isocaloric protein restriction in pregnant dams. Litter size was reduced to six male neonates in low protein animals (LP) and normal protein animals (NP). At 8 weeks GN was induced by injection of an anti-Thy-1.1 antibody. Rats were killed on days 4 and 14 after induction of GN and kidneys were investigated for inflammation and sclerosis using real-time polymerase chain reaction and histological methods. On day 4 after induction of GN, LP animals showed more glomerulosclerosis and tubulointerstitial lesions. On day 14, inflammatory markers (expression of monocyte chemoattractant protein 1, osteopontin, tumor necrosis factor and interleukin-6), extracellular matrix accumulation and markers of sclerosis (plasminogen activator inhibitor-1 expression, transforming growth factor-beta1 expression, score for glomerulosclerosis, glomerular deposition of collagen I and collagen IV) were more severe in LP animals. Some degree of induction of inflammatory and profibrotic markers was also present in non-nephritic LP animals. However, these rats did not display marked glomerulosclerosis or interstitial fibrosis. We conclude that after IUGR inflammatory damage is aggravated and the reparation of the kidney is impaired during the course of acute mesangioproliferative GN, leading to more sclerotic lesions.

p27 Kip1 knockout mice are protected from diabetic nephropathy: Evidence for p27 Kip1 haplotype insufficiency. Background High glucose up-regulates the mesangial cell expression of p27 Kip1 , an inhibitor of cyclin-dependent kinases/cyclin complexes. Previous in vitro studies using cultured mesangial cells from p27 Kip1−/− mice demonstrated that these cells do not undergo high glucose-mediated cellular hypertrophy. Since glomerular hypertrophy is an early feature of diabetic nephropathy and may precede the development of glomerulosclerosis, interference with p27 Kip1 expression may attenuate diabetic nephropathy. However, it is unclear whether deletion of p27 Kip1 protects the kidneys of diabetic nephropathy in vivo. Methods Type 1 diabetes mellitus was induced in p27 Kip1+/+ , p27 Kip1+/− , and p27 Kip1−/− mice by injection of streptozotocin (STZ). Mice were studied for 6 weeks. Animals injected with citrate buffer only served as controls. At the end of the experiments, urine was collected, albuminuria was determined with an enzyme-linked immunosorbent assay (ELISA), and blood glucose concentrations were measured. Kidneys were perfusion-fixed for quantitative morphologic analysis with glutaraldehyde and for immunohistochemical studies with formaldehyde. Glomerular cell number and volume were analyzed. Glomerulosclerosis, tubulointerstitial, and vascular damage indices were semiquantitatively assessed according to standard methodology. Quantitative glomerular parameters (cell numbers and volumes of endothelial, mesangial, and epithelial cells) were measured on semithin sections. Expression of transforming growth factor-β1 (TGF-β1), laminin, and collagen type IV were determined by immunohistochemical staining. Results In contrast to animals only injected with citrate buffer, mice that received STZ developed hyperglycemia. There was no significant difference in the degree of hyperglycemia among p27 Kip1+/+ , p27 Kip1+/− , and p27 Kip1−/− mice. Diabetic p27 Kip1+/+ , but not control p27 Kip1+/+ animals, developed albuminuria. Albuminuria was significantly reduced in diabetic p27 Kip1+/− and more profoundly in p27 Kip1−/− animals. Diabetic p27 Kip1+/+ mice revealed a significant increase in mean glomerular volume at 6 weeks. The volumes of mesangial and endothelial cells and podocytes all increased, whereas cell numbers were reduced, consistent with cell hypertrophy. Glomerular, endothelial, mesangial and podocyte hypertrophy were reduced in diabetic p27 Kip1+/− and p27 Kip1−/− animals. Diabetic p27 Kip1 +/+ animals had significantly increased glomerulosclerosis, tubulointerstium, and vascular damage indices compared to nondiabetic p27 Kip1+/+ controls. Diabetic p27 Kip1−/− mice exhibited significantly less structural damage than diabetic wild-type animals. Diabetic p27 Kip1+/− animals revealed intermediate glomerulosclerosis, tubulointerstium, and vascular damage values. Immunohistological stainings demonstrated increases in TGF-β1, collagen type IV, and laminin expression in kidneys of diabetic p27 Kip1+/+ animals compared to nondiabetic p27 Kip1+/+ controls. Staining intensity for type IV collagen and laminin, but not for TGF-β1, was significantly lower in diabetic p27 Kip1−/− mice. Conclusion Deletion of p27 Kip1 attenuates the functional and morphologic features of diabetic nephropathy. Although deletion of p27 Kip1 abolished some parameters of diabetic glomerular hypertrophy, the significant reduction of TGF-β1 expression in the tubulointerstitium indicates that other protective mechanisms could be operative. The p27 Kip1 gene is haplo-insufficient because diabetic p27 Kip1 +/- mice exhibited an intermediate degree of functional and structural renal injury. Our data shows that p27 Kip1 plays an important role in diabetic nephropathy.

Racial differences in renal arteriolar structure in children with minimal change nephropathy. Background African Americans are at increased risk for hypertension and chronic renal disease. Some data suggest this results from renal microvascular disease. The aim of this study was to determine if renal vascular changes were more pronounced in African Americans, were independent of blood pressure, and occurred in early childhood Methods We performed morphometric analysis on small cortical arteries and arterioles from 44 renal biopsies done in African American and white children (mean age 8.4 ± SD 5.0 years) with minimal change nephropathy. Outer and inner vessel diameters were measured and wall:lumen and wall:outer diameter ratios (WT/OD) calculated. Clinical data on blood pressure, steroid use, serum creatinine, gender, age, and proteinuria were abstracted by chart review. A z score for systolic and diastolic blood pressure was calculated. Follow-up clinical data were available for 11 children. Data were compared using analysis of covariance (ANCOVA) and t test for paired data. Results Lumen diameters of African Americans were 3.1 μm (23%) smaller that those of white children ( P = 0.024). Similarly, their WT/OD was greater than in the whites, 0.31±0.03 vs. 0.28 ± 0.02 ( P = 0.048). These changes were independent of age, steroid use, systolic blood pressure and diastolic blood pressure z scores. Follow-up data showed a rise in serum creatinine (>50%) in five patients, +1.42 ± 0.79 mg/dL ( P = 0.016), of whom four were African American. There was no change in blood pressure. Conclusion The renal arterioles of African American children with minimal change nephropathy exhibit significantly smaller lumens and thicker walls than white children. The changes occur very early in life and are independent of age, blood pressure, and steroid use. Such changes may contribute to the African American predisposition to chronic renal disease and hypertension.