Project Summary/Abstract Obesity and increased adiposity contribute to cardiovascular disease and mortality, but high-altitude populations have lower rates of chronic metabolic disease and cardiovascular mortality. In mice, oxygen deprivation recapitulates these effects, lowering body weight, adiposity, and blood glucose levels. Elucidating the mechanisms underlying this metabolic reprogramming can inspire effective therapies for obesity. Untargeted metabolic profiling of adipose tissue from hypoxic mice revealed the enrichment of branched-chain hydroxyacids (BCHAs), which are understudied derivatives of branched-chain amino acids (BCAAs). Notably, impaired BCAA clearance has consistently been associated with obesity and insulin resistance. Understanding the regulation of BCAA metabolism in hypoxia can uncover causal mechanisms linking BCAA metabolism to metabolic health. Hypoxia may promote BCHA production by driving a shift in adipocytes from canonical BCAA metabolism to this alternative pathway. Little is known about the regulatory mechanisms that control the metabolic pathway producing BCHAs. The enzyme that catalyzes BCHA production has not been identified, but human genetics data suggests that lactate dehydrogenase A (LDHA) expression is associated with BCHA levels. Moreover, prior work suggests that the biochemical effects of hypoxia disrupt complexes of canonical BCAA metabolism enzymes, facilitating BCHA production through the alternative pathway. In vitro models of adipose tissue hypoxia will be used to determine whether these mechanisms drive hypoxia-induced BCHA production (Aim 1). Beyond these regulatory mechanisms, the impact of BCHA production is not known, but observational data from mice and humans shows that increased BCHA production is associated with diminished adiposity. Therefore, BCHA production may contribute to the decreased fat mass in hypoxia. This hypothesis will be tested using Bckdk-knockout mice, which exhibit impaired BCHA production (Aim 2). Measuring adiposity and glucose clearance of these mice in hypoxia will reveal the metabolic role of BCHA production in hypoxia. These experiments will elucidate the mechanisms underlying the reprogramming of adipose BCAA metabolism in hypoxia. These experiments will be conducted with the guidance of Dr. Isha Jain and Dr. Andrei Goga, both experts in the regulation of cellular metabolism and metabolic physiology. Investigating the causal relationship between BCAA metabolism and metabolic health will inspire new therapeutic approaches for obesity.