Disruption of Branched-Chain Amino Acids Homeostasis Exacerbates MCD-induced Steatohepatitis by Amplifying a Pro-Inflammatory Positive Feedback Loop Between Hepatocytes and Macrophages.

Accumulating evidence links branched-chain amino acids (BCAAs, including leucine, isoleucine, and valine) to obesity, diabetes, and related metabolic disorders; however, their role in metabolic dysfunction-associated steatohepatitis (MASH) remains unclear. Interrogation of human and mouse transcriptomic datasets (GSE147304, GSE263770) revealed suppressed hepatic BCAAs catabolic gene expression in MASH. In a murine model of MASH induced by a methionine- and choline-deficient (MCD) diet, BCAAs catabolic gene expression was suppressed in the liver, accompanied with the accumulation of branched-chain keto acids (BCKAs), the products of BCAAs. Furthermore, MASH was exacerbated in the PP2Cm knockout mice in which BCAAs catabolism was impaired and BCAAs and BCKAs accumulated. Dietary supplementation with BCAAs also exacerbated MCD-induced steatohepatitis with elevated BCAAs and BCKAs abundance in the liver. Mechanistically, BCKAs promoted cell-autonomous inflammatory responses in hepatocytes and macrophages, respectively, and amplified the pro-inflammatory positive feedback loop between these two types of cells. Finally, pharmacological enhancement of BCAAs catabolism with the small molecule BT2 reduced BCKAs abundances and ameliorated liver injury and fibrosis in MASH. Together, this study reveals that the disruption of BCAAs homeostasis exacerbated inflammation and fibrosis in MCD-induced steatohepatitis, at least partially through mutually reinforcing inflammatory responses in hepatocytes and macrophages. The vicious cycle amplified by the dysregulated BCAAs homeostasis provides potential pharmacological and nutritional therapeutic strategies for MASH.