Abstract
Myofibroblasts are the cells responsible for collagen production, leading to tissue fibrosis. Because 20.5% of the total amino acids in collagen are proline, myofibroblasts must acquire a well-developed proline-producing mechanism during their differentiation. However, the detailed mechanism for myofibroblasts to acquire and keep the developed proline biosynthesis machinery remains obscure. Here, we show branched-chain amino acid transaminase 1 (Bcat1) is up-regulated in a substantial subset of Postn-expressing proto-myofibroblast-like fibroblasts, transitional cells en route to fully differentiated myofibroblasts, as well as in myofibroblasts in the fibrotic heart and liver of mice and humans and promotes the proline production. The branched-chain amino acid (BCAA) production by BCAT1 promotes SMAD3 phosphorylation via HDAC5 phosphorylation at Ser488, thereby enhancing SMAD3-dependent transcription of proline biosynthesis-related genes, Aldh18a1, Pycr1, and Eprs, in proto-myofibroblast-like fibroblasts and myofibroblasts. In BCAT1-deficient mice, expression of proline biosynthesis-related genes is significantly attenuated in their hearts after myocardial infarction, resulting in decreased cardiac fibrosis. Moreover, BCAT1 inhibitor treatment of mice with myocardial infarction reduces cardiac fibrosis. Our results identified a BCAT1-mediated pathway that promotes collagen production via proline biosynthesis regulation in proto-myofibroblast-like fibroblasts and myofibroblasts, which may provide a therapeutic target for cardiac fibrosis.
Authors
Noburo Takizawa, Takanori Hironaka, Hayato Watanabe, Haruna Suetsugu, Keisuke Yoshioka, Yuma Horii, Yuri Nagata, Hiroaki Matoba, Hidetaka Kosako, Kenji Hamase, Go Hirai, Michio Nakaya
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Copyright © 2026 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)