Focal segmental glomerulosclerosis (FSGS) is a clinical-pathologic syndrome characterized by the accumulation of fibrotic proteins in glomeruli, initially involving only some glomeruli (focal) and involving portions (segments) of the affected glomeruli. FSGS can be classified as follows: idiopathic FSGS, HIV-associated FSGS, hyperfiltration FSGS (due to reduced renal mass, renal toxins, or obesity), and genetic causes. In order to define the molecular mechanisms responsible for HIV-associated FSGS, we have established a line of mice in which transgene expression can be regulated in the glomerular podocyte using an tetracycline-regulated system. We have shown that expression is tightly regulated and is restricted to the podocyte. We have used this system to express the HIV-1 accessory protein Vpr in the podocyte. These mice develop proteinuria beginning 4 weeks after treatment with tetracycline and with 95% of mice developing proteinuria by 20 weeks. FSGS appears at 8 weeks, progressing to global glomerulosclerosis and end-stage kidney disease. Podocyte phenotype is abnormal, with reduced expression of the differentiation marker synaptopodin and de novo expression of the injury marker desmin. Increased cell proliferation is present in the glomerular tuft, parietal epithelum, and tubular epithelium. These results demonstrate that Vpr is sufficient to induce HIV-associated FSGS in transgenic mice. We have recently generated mutant Vpr mice, bearing the R80A mutation that abrogates the cell cycle arrest functio, and we find that kidney disease is abrogated. Using these transgenic mice, we have established triple transgenic podocyte cell lines, which bear the podocin/rtTA, tetop/Vpr and TS SV40 Tag transgenes. These cells were found to express characteristic podocyte markers, including podocin, nephrin, and WT1. Following induction with tetracycline, these cells express Vpr RNA and undergo widespread cell death at 24 hr. We are currently analyzing the nature of cell death. We will use these cell lines to define the molecular mechanisms of Vpr induced podocyte injury. Many patients with podocyte diseases, including minimal change disease and FSGS are refractory to all conventional remittive therapy. We have embarked on studies with retinoids (all-trans-retinoic acid, a synthetic pan-RAR inhibitor, and a synthetic pan-RXR inhitibor), using both alb/TGFbeta mice and cultured cells (human mesangial cells, human podocytes). Our goal is to define the pathways by which retinoids prevent or reverse cellular dedifferentiation and antagonized pro-fibrotic pathways. Furthermore, we have initiated an randomized, open label study of two retinoids (all-trans retinoic acid, isotretinoin) in patients with podocyte diseases.
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