Branched-chain amino acid metabolism is a crucial modulator of cellular senescence
Cellular senescence is a complex stress response that results in the permanent arrest of cell proliferation. The accumulation of senescent cells occurs during aging in living organisms, and contributes to tissue dysfunction. Although there are growing lines of evidence that various metabolic changes occur in senescent cells, the link between cellular metabolism and senescence is not yet fully understood. In this study, we demonstrate that alterations in the metabolism of branched-chain amino acids (BCAAs) play a crucial role in establishing cellular senescence. Furthermore, we identified mitochondrial BCAA transamination as a crucial step in this process. Our findings show that various types of cellular stress lead to a reduction in the expression of BCAA aminotransferase 2 (BCAT2), one of the BCAA catabolic enzymes, resulting in decreased catabolism of BCAAs and reduced synthesis of glutamate. The reduction of BCAA catabolites, together with the consequent limitation in glutathione production from glutamate, triggers cellular senescence. Furthermore, we demonstrate that a reduction in BCAT2 levels alone is sufficient to induce cellular senescence, both in cultured cells and in mice. Additionally, our results demonstrate that aging alters BCAA metabolism in both mice and humans. Our findings provide new insights into the metabolic mechanisms underlying cellular senescence, with a particular focus on the role of BCAAs.