The role and mechanism of macrophage-to-myofibroblast transition in fibrotic diseases.

Fibrosis is a pathological process primarily characterized by excessive deposition of extracellular matrix (ECM), which leads to disruption of tissue architecture and progressive loss of organ function, serving as a key pathological basis for various chronic diseases. Recent studies have revealed that, in addition to conventional sources, macrophages can directly differentiate into ECM-producing myofibroblasts through a process termed macrophage-to-myofibroblast transition (MMT), thereby actively participating in fibrogenesis. The concept of MMT was initially proposed in the context of renal fibrosis and has since been validated in multiple organs, including the kidney, heart, lung, liver, and retina. This review aims to summarize the role of MMT in fibrotic diseases and to elucidate the mechanism underlying MMT and fibrosis progression. Unlike prior reviews that predominantly focus on MMT within individual organs or separately delineate their molecular pathways, this review adopts a cross-organ perspective to systematically identify conserved mechanisms, tissue-specific regulatory networks, and translational challenges of MMT across fibrotic diseases.