tretinoin and AIDS-Associated-Nephropathy

Podocyte injury resulting from a loss of differentiation is the hallmark of many glomerular diseases. We previously showed that retinoic acid (RA) induces podocyte differentiation via stimulation of the cAMP pathway. However, many podocyte maturity markers lack binding sites for RA-response element or cAMP-response element (CREB) in their promoter regions. We hypothesized that transcription factors induced by RA and downstream of CREB mediate podocyte differentiation. We performed microarray gene expression studies in human podocytes treated with and without RA to identify differentially regulated genes. In comparison with known CREB target genes, we identified Krüppel-like factor 15 (KLF15), a kidney-enriched nuclear transcription factor, that has been previously shown to mediate cell differentiation. We confirmed that RA increased KLF15 expression in both murine and human podocytes. Overexpression of KLF15 stimulated expression of differentiation markers in both wild-type and HIV-1-infected podocytes. Also, KLF15 binding to the promoter regions of nephrin and podocin was increased in RA-treated podocytes. Although KLF15(-/-) mice at base line had minimal phenotype, lipopolysaccharide- or adriamycin-treated KLF15(-/-) mice had a significant increase in proteinuria and podocyte foot process effacement with a reduction in the expression of podocyte differentiation markers as compared with the wild-type treated mice. Finally, KLF15 expression was reduced in glomeruli isolated from HIV transgenic mice as well as in kidney biopsies from patients with HIV-associated nephropathy and idiopathic focal segmental glomerulosclerosis. These results indicate a critical role of KLF15 in mediating podocyte differentiation and in protecting podocytes against injury.

Topics: AIDS-Associated Nephropathy; Animals; Cell Differentiation; Cell Line, Transformed; DNA-Binding Proteins; Gene Expression Regulation; HIV-1; Humans; Kruppel-Like Transcription Factors; Mice; Mice, Knockout; Nuclear Proteins; Podocytes; Response Elements; Transcription Factors; Tretinoin

HIV-associated nephropathy is characterized by renal podocyte proliferation and dedifferentiation. This study found that all-trans retinoic acid (atRA) reverses the effects of HIV-1 infection in podocytes. Treatment with atRA reduced cell proliferation rate by causing G1 arrest and restored the expression of the differentiation markers (synaptopodin, nephrin, podocin, and WT-1) in HIV-1-infected podocytes. It is interesting that both atRA and 9-cis RA increased intracellular cAMP levels in podocytes. Podocytes expressed most isoforms of retinoic acid receptors (RAR) and retinoid X receptors (RXR) with the exception of RXRgamma. RARalpha antagonists blocked atRA-induced cAMP production and its antiproliferative and prodifferentiation effects on podocytes, suggesting that RARalpha is required. For determination of the effect of increased intracellular cAMP on HIV-infected podocytes, cells were stimulated with either forskolin or 8-bromo-cAMP. Both compounds inhibited cell proliferation significantly and restored synaptopodin expression in HIV-infected podocytes. The effects of atRA were abolished by Rp-cAMP, an inhibitor of the cAMP/protein kinase A pathway and were enhanced by rolipram, an inhibitor of phosphodiesterase 4, suggesting that the antiproliferative and prodifferentiation effects of atRA on HIV-infected podocytes are cAMP dependent. Furthermore, both atRA and forskolin suppressed HIV-induced mitogen-activated protein kinase 1 and 2 and Stat3 phosphorylation. In vivo, atRA reduced proteinuria, cell proliferation, and glomerulosclerosis in HIV-1-transgenic mice. These findings suggest that atRA reverses the abnormal phenotype in HIV-1-infected podocytes by stimulating RARalpha-mediated intracellular cAMP production. These results demonstrate the mechanism by which atRA reverses the proliferation of podocytes that is induced by HIV-1.

Topics: AIDS-Associated Nephropathy; Animals; Cell Differentiation; Cell Proliferation; Cells, Cultured; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Extracellular Signal-Regulated MAP Kinases; HIV Infections; HIV-1; Humans; Mice; Mice, Transgenic; Phenotype; Phosphorylation; Podocytes; Receptors, Retinoic Acid; Retinoic Acid Receptor alpha; STAT3 Transcription Factor; Tretinoin