The unified objective of the 2 R01 projects in this RFA is to specify a key molecular mechanisms underlying HIV-associated lipodystrophy syndrome (HLS), and the consequent metabolic derangements that lead to its clinical manifestations. These manifestations suggest increased glucocorticoid sensitivity in fat, muscle and liver. Recent work shows that an HIV-1 viral protein, Vpr, potentiates ligand-mediated activation of the glucocorticoid receptor (GR), and antagonized PPAR-gamma mediated gene transcription. Preliminary studies also show that HLS patients have lipid and glucose kinetics consistent with these molecular effects of Vpr. The hypotheses for the Basic Science R01 project are that a) over expression of Vpr in mice leads to metabolic changes characteristic of GR activation; b) Vpr affects adipogenesis and lipogenesis differentially in central vs. peripheral adipocytes; c) Vpr exerts these effects by direct interactionwith the transcriptional complexes of the GR and PPAR-gamma, leading to activation of GR-regulated genes and inhibition of PPAR-gamma regulated genes. The Specific Aims are: a) measurements of body composition and lipid, protein and glucose metabolism, using stable isotopes/mass spectrometry, in transgenic mice over expressing Vpr, following dietary manipulations and protease inhibitor administration; b) functional assays of adipogenesis and lipogenesis in central vs. peripheral adipocytes removed from these mice; c) molecular dissection of the mechanism and effects of Vpr-mediated regulation of the GR and PPAR-gamma in preadipocyte cell lines and primary cultures of human preadipocytes derived from abdominal and peripheral fat depots. The hypotheses for the clinical Science R01 are that a) patients who develop HLS progressively manifest the metabolic effects of persistent GR activation fat, muscle, and liver, namely, increased whole body lipolysis, increased hepatic lipogenesis, enhanced triglyceride storage in abdominal fat, increased protein turnover, and elevated endogenous glucose production while fasting and feeding; b) these changes are secondary to increased sensitivity to glucocorticoids due to the actions of Vpr. The Specific Aims involve longitudinal, intensive GCRC studies on newly diagnosed HIV-infected patients and matched normal subjects, to measure; a) whole body lipid kinetics (lipolysis, lipogenesis, reesterification, VLDL synthesis, triglyceride utilization), regional lipolysis, protein turnover, and endogenous glucose production, while feeding and fasting, using stable isotopes/mass spectrometry b) glucocorticoid sensitivity towards proteolysis and lipolysis; c) Vpr concentrations in plasma, abdominal fat- and thigh fat-extracellular fluid; d) detailed body composition and biochemical parameters of HLS. These projects will be performed by a coordinated team experienced in metabolic protocols and stable isotope techniques, HIV clinical specialists, and experts in the molecular biology of the GR and Vpr. They will detail a molecular pathway to this novel lipodystrophic syndrome, which likely predates the use of effective anti-retroviral therapy but comes clinically obvious during therapy as a result of increased nutrient intake, and translate to clinical science the Vpr-mediated mechanism of metabolic dysregulation.