The ability of the human immunodeficiency virus, type 1 (HIV-1) protein Nef to induce cytoskeleton changes in infected host cells is a key event in viral replication. In renal podocytes, we found that Nef induced loss of stress fibers and increased lamellipodia, pathological changes leading to proteinuria in HIV-associated nephropathy. These morphological changes were mediated by Nef-induced Rac1 activation and RhoA inhibition. We identified a new interaction between Nef and diaphanous interacting protein (DIP), a recently described regulator of Rho and Rac signaling. We found that the Src homology 3 binding domain of DIP and the Nef PXXP motif were required for this interaction.

Recent studies suggest that Stat3, a transcription factor that mediates cytokine signaling, plays a critical role in the pathogenesis of diabetic nephropathy. Complete Stat3 gene knockout is embryonic lethal; therefore, we crossed Stat3+/– mice with Stat3 mutant mice (SA/SA) that lack full Stat3 activity. This strategy generated Stat3SA/– mice (25% activity) and Stat3SA/+ mice (75% activity), which were made diabetic using streptozotocin in order to define the role of Stat3 in diabetic kidney disease. While the glomerular number was not different between these two groups of mice, the diabetic SA/– mice had significantly less proteinuria, mesangial expansion, glomerular cell proliferation, and macrophage infiltration than the diabetic SA/+ mice. The reduction in Stat3 activity did not affect glomerular hyperfiltration seen after the induction of diabetes, as it was increased to the same degree in both groups of mice. Phosphorylation of Stat3 was markedly increased in the glomeruli of diabetic SA/+ mice compared to diabetic SA/– mice. The expression of inflammatory markers, IL-6, MCP-1, and activated NF-κB; type IV collagen, TGF-β, and ICAM-1 mRNA; or type IV collagen and TGF-β protein, were all found to be significantly less in glomeruli isolated from diabetic SA/– mice, as compared with diabetic SA/+ mice. Our study shows that Stat3 plays a critical role in the regulation of inflammation and abnormal matrix synthesis at an early stage of DN.

All-trans retinoic acid protects against the development of HIV-associated nephropathy (HIVAN) in HIV-1 transgenic mice (Tg26). In vitro, all-trans retinoic acid inhibits HIV-induced podocyte proliferation and restores podocyte differentiation markers by activating its receptor-α (RARα). Here, we report that Am580, a water-soluble RARα-specific agonist, attenuated proteinuria, glomerosclerosis, and podocyte proliferation, and restored podocyte differentiation markers in kidneys of Tg26 mice. Furthermore, RARα−/− Tg26 mice developed more severe kidney and podocyte injury than did RARα+/− Tg26 mice. Am580 failed to ameliorate kidney injury in RARα−/− Tg26 mice, confirming our hypothesis that Am580 acts through RARα. Although the expression of RARα-target genes was suppressed in the kidneys of Tg26 mice and of patients with HIVAN, the expression of RARα in the kidney was not different between patients with HIVAN and minimal change disease. However, the tissue levels of retinoic acid were reduced in the kidney cortex and isolated glomeruli of Tg26 mice. Consistent with this, the expression of two key enzymes in the retinoic acid synthetic pathway, retinol dehydrogenase type 1 and 9, and the overall enzymatic activity for retinoic acid synthesis were significantly reduced in the glomeruli of Tg26 mice. Thus, a defect in the endogenous synthesis of retinoic acid contributes to loss of the protection by retinoic acid in HIVAN. Hence, RARα agonists may be potential agents for the treatment of HIVAN.

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