Adipocytes reprogram carbon and nitrogen metabolism to maintain lipogenic flux in the absence of Bckdha

Abstract

Dysregulated branched chain amino acid (BCAA) metabolism has emerged as a key metabolic feature associated with the obese insulin resistant state, and adipose BCAA catabolism is decreased in this context. BCAA catabolism is upregulated early in adipogenesis, but the impact of suppressing this pathway on the broader metabolic functions of the resultant adipocyte remain unclear. Here, we use CRISPR/Cas9 to target Bckdha and Acad8 in pre-adipocytes and induce a deficiency in BCAA or valine catabolism through differentiation. We characterise the transcriptional and metabolic phenotype of these cells using RNAseq and 13C metabolic flux analysis within a network spanning glycolysis, tricarboxylic (TCA) acid metabolism, BCAA catabolism, and fatty acid synthesis. While lipid droplet accumulation is maintained in Bckdha-deficient adipocytes, they display a more fibroblast-like transcriptional signature. In contrast, Acad8 deficiency minimally impacts gene expression. Decreased glycolytic flux emerges as the most distinct metabolic feature of Bckdha-deficient cells, accompanied by a [~]40% decrease in lactate secretion, yet pyruvate oxidation and utilization for de novo lipogenesis are increased to compensate for loss of BCAA carbon. Glutamine anaplerosis was also increased, though we observed a general decrease in levels of most non-essential amino acids consistent with an impact on nitrogen homeostasis. Overall, our data suggest that both metabolic and regulatory cross-talk exists between BCAA catabolism, glycolysis, and nitrogen metabolism in differentiated adipocytes. Suppression of BCAA catabolism associated with metabolic syndrome may result in a metabolically compromised adipocyte.