African-Americans have an increased risk of developing chronic and end-stage kidney disease, with much of it attributed to two common genetic variants in the APOL1 gene, termed G1 and G2. Direct evidence demonstrating that these APOL1 risk alleles are pathogenic is still lacking as the APOL1 gene is only present in some primates and humans; thus experimental proof of causality of these risk alleles for renal disease has been challenging. Here, we generated mice with podocyte-specific inducible expression of the APOL1 reference allele (termed G0) or each of the risk alleles (G1 or G2). We show that mice with podocyte-specific expression of either APOL1 risk allele, but not the G0 allele, develop functional (albuminuria, azotemia), structural (foot process effacement and glomerulosclerosis) and molecular (gene expression) changes that closely resemble the human kidney disease. Disease development was cell-type specific, and likely reversible, and the severity correlated with the level of expression of the risk allele. We further found that expression of the APOL1 risk alleles interferes with endosomal trafficking and blocks autophagic flux, leading ultimately to inflammatory-mediated podocyte death and glomerular scarring. In summary, this is the first in vivo demonstration that expression of APOL1 risk alleles are causal for altered podocyte function and glomerular disease.

Podocytes are specialized actin-rich epithelial cells that line the kidney glomerular filtration barrier. The interface between the podocyte and the glomerular basement membrane requires integrins, and defects in either α 3 or β 1 integrin, or the α 3 β 1 ligand laminin result in nephrotic syndrome in murine models. The large cytoskeletal protein talin1 is not only pivotal for integrin activation, but also directly links integrins to the actin cytoskeleton. Here, we found that mice lacking talin1 specifically in podocytes display severe proteinuria, foot process effacement, and kidney failure. Loss of talin1 in podocytes caused only a modest reduction in β 1 integrin activation, podocyte cell adhesion, and cell spreading; however, the actin cytoskeleton of podocytes was profoundly altered by the loss of talin1. Evaluation of murine models of glomerular injury and patients with nephrotic syndrome revealed that calpain-induced talin1 cleavage in podocytes might promote pathogenesis of nephrotic syndrome. Furthermore, pharmacologic inhibition of calpain activity following glomerular injury substantially reduced talin1 cleavage, albuminuria, and foot process effacement. Collectively, these findings indicate that podocyte talin1 is critical for maintaining the integrity of the glomerular filtration barrier and provide insight into the pathogenesis of nephrotic syndrome.

SummaryBackground and objectives Hyperphosphatemia, vitamin D deficiency, hyperparathyroidism, and high serum fibroblast growth factor 23 (FGF23) levels, when studied separately, were found to predict the progression of CKD. However, studies with simultaneous measurement of mineral bone disorder (MBD)-related factors were scarce. This study aimed to identify factors predicting renal outcome independent of other factors.Design, setting, participants, & measurements This was a prospective cohort study of 738 Japanese predialysis outpatients in the nephrology departments of two hospitals. The outcome was defined as a doubling of serum creatinine or initiation of dialysis.Results Mean estimated GFR (eGFR) was 35 ml/min per 1.73 m 2 . At enrollment, the increase in intact FGF23 with decreasing eGFR was the earliest among changes in MBD-related factors, followed by 1,25-dihydroxyvitamin D decrease, parathyroid hormone increase, and phosphate increase. Conclusions Combined use of two markers is useful for the risk stratification of renal outcome.

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Our results provide evidence for the renoprotective action of febuxostat against the formation of interstitial fibrosis. A decrease in macrophage infiltration and interstitial fibrosis, along with a decrease of the oxidative stress marker, strongly suggests the existence of a causal relationship between them. Febuxostat may have therapeutic value in slowing or preventing interstitial fibrosis in patients with CKD.

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We demonstrated the breakdown of the vitamin D activation system in podocyte injury, and established a preventative role for vitamin D in podocyte injury.

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