The clinical use of HIV-1 protease inhibitors (PIs) in highly active anti-retroviral therapy (HART) has led to significant improvements in the prognosis and quality of life in HIV-1 infected patients. However, long-term use of PIs has resulted in side effects such as peripheral lipodystrophy, hyperlipidemia, insulin resistance, and disruption of the adipogenic process. Our preliminary studies have shown that PIs suppress adipogenic differentiation in 3T3-L1 cells and the addition of TNFalpha further suppressed the rate of adipogenesis. In contrast, the insulin sensitizing agent, troglitazone, blocked this suppression even in TNFalpha sensitized cells. The primary goal of the proposed research is to investigate the molecular mechanisms involved in the PI-induced modulation of adipogenesis and to test the hypothesis that preadipocytes are sensitized by HIV-1 induced inflammatory cytokine TNFalpha and/or HIV-1 Tat protein, to PI-induced disruption of adipogenesis. This will be achieved by the following specific aims: 1.) To determine the in vitro effects of PIs on adipogenic differentiation in human bone marrow stromal progenitor cells. Transcripts of early, middle and late genetic markers i.e., pref-1, lipoprotein lipase (LPL) and GAPDH, respectively will be determined. Levels of nuclear transcription factors, PPAR-gamma and C/EBP-alpha will be determined by transient transfection assays and gel mobility shift assays. 2.) to determine the sensitizing effect of the HIV-1 induced inflammatory cytokine, TNFalpha and/or HIV-1 Tat protein on PI-induced inhibition of adipogenic differentiation in human bone marrow stromal progenitor cells. 3.) To determine the in vitro effects of PIs on the activity of ECM degrading proteases in human stromal adipogenic progenitor cells. Fibrinolytic activity in undifferentiated and differentiated cells will be monitored by using a chromogenic plasmin substrate. The ECM production at different stages of differentiation will be determined by SDS-PAGE electrophoresis and the activation of ECM degrading proteolytic enzymes (MMPs) will be monitored by gelatin zymography. Real time RT-PCR studies will monitor gene expression of tPA, PAI-1/2 and MMPs/TIMPs which are involved in the fibrinolytic cascade. 4.) To investigate the ameliorative effects of insulin sensitizers on PI-induced lipodystrophy. We will investigate the efficacy of thiazolidinediones (rosiglitazone and pioglitazone) and biguanides (metformin) in suppressing the effects of PI-induced inhibition of adipogenic differentiation. These studies will delineate the molecular mechanisms that may be responsible for the adipogenic side effects induced by the PIs in the presence of HIV infection.