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Focal segmental glomerulosclerosis (FSGS) is a leading cause of end-stage renal disease in children and adults. Genetic factors significantly contribute to early-onset FSGS, but the etiologies of most adult cases remain unknown. Genetic studies of monogenic syndromic FSGS exhibiting extra-renal manifestations have uncovered an unexpected biological role for genes in the development of both podocytes and other cellular lineages. To help define these roles, we studied two unrelated families with FSGS associated with Duane Retraction Syndrome, characterized by impaired horizontal eye movement due to cranial nerve malformation. All four affected individuals developed FSGS and Duane Retraction Syndrome in their first to second decade of life, manifested as restricted abduction together with globe retraction and narrowed palpebral fissure on attempted adduction. Hypoplasia of the abducens nerves and hearing impairment occurred in severely affected individuals. Genetic analyses revealed that affected individuals harbor a rare heterozygous substitution (p.Leu239Pro) in MAFB, a leucine zipper transcription factor. Luciferase assays with cultured monocytes indicated that the substitution significantly reduced transactivation of the F4/80 promoter, the known MAFB recognition element. Additionally, immunohistochemistry indicated reduced MAFB expression in the podocytes of patients. Structural modeling suggested that the p.Leu239Pro substitution in the DNA-binding domain possibly interferes with the stability of the adjacent zinc finger. Lastly, podocytes in neonatal mice with p.Leu239Pro displayed impaired differentiation. Thus, MAFB mutations impair development and/or maintenance of podocytes, abducens neurons and the inner ear. The interactions between MAFB and regulatory elements in these developing organs are likely highly specific based on spatiotemporal requirements.

The effect of acute renal failure (ARF) induced by ischemia/reperfusion (I/R) of rat kidney on the expression of organic anion transporters (OATs) was examined. The level of serum indoxyl sulfate (IS), a uremic toxin and substrate of OATs in renal tubules, shows a marked increase with the progression of ARF. However, this increase was significantly attenuated by ingestion of cobalt. The level of mRNA and protein of both rOAT1 and rOAT3 were markedly depressed in the ischemic kidney. The uptake of p-aminohippuric acid (PAH) and estrone sulfate (ES) by renal slices of ischemic rats was significantly reduced compared to control rats. Renal slices taken from ischemic rats treated with cobalt displayed significantly elevated levels of ES uptake. Cobalt intake did not affect PAH uptake, indicating the functional restoration of rOAT3 but not rOAT1. The expression of Na(+)/K(+)-ATPase was markedly depressed in the ischemic kidney, suggesting that the inward Na(+) gradient in renal tubular cells had collapsed, thereby reducing the outward gradient of alpha-ketoglutarate, a driving force of both rOATs. The decreased expression of Na(+)/K(+)-ATPase was significantly restored by cobalt treatment. Our results suggest that the downregulation of renal rOAT1 and rOAT3 could be responsible for the increase in serum IS level of ischemic rats. Cobalt treatment has a significant protective effect on ischemia-induced ARF, being accompanied by the restoration of rOAT3 and/or Na(+)/K(+)-ATPase function.

The function of intrinsic glomerular cells in active glomerular inflammation may be similar to that of monocytes/macrophages. Mesangial cells have phagocytic properties and release numerous mediators. In this study we examined whether human mesangial cells (hMCs) express a monocyte/macrophage phenotype in active glomerular inflammation. We report that the proto-oncogene c-fms, the macrophage colony-stimulating factor (M-CSF) receptor, which is a characteristic gene of monocytes/macrophages, is expressed in hMCs. Normal unmanipulated hMCs express weak c-fms mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR), and its expression increases after stimulation with platelet-derived growth factor-BB (PDGF-BB) and epidermal growth factor (EGF). The expression of c-fms was also demonstrated by flow cytometry with a specific polyclonal antibody. By immunohistochemistry, c-fms was prominently detected in acute glomerulonephritis, IgA nephritis, and lupus nephritis. These results indicate that hMCs express c-fms in active glomerular inflammation and are consistent with mesangial cells acquiring some macrophage-like characteristics in diseased states.

Endothelin-1 and endothelin B type receptor are induced in mesangial proliferative nephritis in the rat. We studied whether endothelin-1 (ET-1) and its receptor subtypes (ETaR, endothelin A type receptor; and ETbR, B type receptor) were up-regulated in the glomerulus of a rat model of mesangial proliferative glomerulonephritis induced by anti-thymocyte serum (anti-Thy-1 GN). A marked increase in preproET-1 mRNA could be demonstrated in glomerular RNA 3 and six days after disease induction (4.1- and 4.9-fold vs. day 0, respectively), corresponding to the time of mesangial cell proliferation, to the time of macrophage infiltration into glomeruli, and also to the time of increase in glomerular PDGF B-chain mRNA expression. The localization of ET-1 protein in the mesangial area and along the inner aspect of the glomerular capillary wall was also demonstrated by immunohistochemistry from day 3 and maximal at day 6. The major source of the cells expressing ET-1 in glomeruli appeared to be mesangial cells, glomerular endothelial cells and monocyte/macrophages. Furthermore, both gene and protein expression of ET-1 were associated with increased urinary excretion of ET-1. There was no increase in the plasma ET-1 immunoreactivity. Glomerular expression of ETbR mRNA increased in anti-Thy-1 GN (1.5-fold vs. day 0 at day 3 after disease induction, 3.6-fold at day 6 and 2.7-fold at day 10), but there was minimal change in ETaR mRNA expression. These results suggest that preproET-1 mRNA, which is induced in anti-Thy-1 GN, is linked primarily with ETbR mRNA expression. Up-regulated expressions of both preproET-1 mRNA and ET-1 protein, and increased urinary ET-1 excretion in the proliferative phase of anti-Thy-1 GN were dramatically suppressed by complement depletion with cobra venom factor treatment, and these ruled out the possibility that the change of ET-1 might be from the direct effect by anti-Thy-1 antibody itself. In conclusion, there is an induction of glomerular ET-1 and ETbR gene transcription and ET-1 protein synthesis in rat mesangial proliferative glomerulonephritis. PreproET-1 mRNA expression was closely associated with PDGF B-chain mRNA expression and the up-regulation of ET-1 expression may stimulate PDGF-dependent mesangial cell proliferation in anti-Thy-1 nephritis. ET-1 production in glomeruli may allow an amplification of mesangial cell proliferation and subsequent matrix expansion in this model.