Proteomic analysis of mitochondria-ER contacts reveals key proteins involved in metabolic regulation in hepatocytes.

The hepatocytes orchestrate anabolic and catabolic pathways by dynamically modulating mitochondria–endoplasmic reticulum contacts (MERCs) in response to dietary fluctuations. While MERCs exhibit pronounced dietary sensitivity, the underlying regulatory mechanisms remain poorly elucidated. Here, a bimolecular fluorescence complementation-based proximity labeling strategy was utilized to identify the MERCs proteomes in hepatocytes under various nutritional conditions. As a result, many previously uncharacterized MERCs proteins were identified to be sensitive to nutritional state, suggesting that these proteins might play important roles in regulating hepatic metabolism. We further demonstrated that FADS3 accumulates at MERCs under starvation. FADS3 was proved to play important role for the maintenance of MERCs in both cell lines and mice liver. Deficiency of FADS3 in mice liver induces altered sphingolipid metabolism under starvation. Our study provided comprehensive insights into the composition and dynamics of mitochondria-ER contacts in hepatocytes under various metabolic conditions, and also revealed key regulatory proteins linking mitochondria-ER contacts and metabolic adaptation.