Aortic carboxypeptidase-like protein potentiates β1 integrin signaling in mesenchymal progenitors

Fibrosis is a pathological process characterized by persistent fibroblast activation and excessive ECM accumulation. Aortic carboxypeptidase-like protein (ACLP), a secreted ECM protein that binds fibrillar collagen, is up-regulated in fibrotic tissues and promotes fibroblast differentiation through canonical TGFβ receptor signaling. We hypothesized that when presented within the collagen matrix, ACLP would engage integrin-dependent mechanical signaling pathways that contribute to fibrogenic activation. Using 10T1/2 mouse mesenchymal progenitor cells, we identify a previously unrecognized mechanism through which collagen-bound ACLP induces fibrogenic activation via β1 integrin–mediated signaling. Collagen-bound ACLP induced rapid cell spreading, increased β1 integrin activation, and promoted focal adhesion maturation. These adhesion events triggered activation of the GTPases RhoA and Rac1, accompanied by enhanced F-actin assembly and nuclear accumulation of myocardin-related transcription factor A, a key regulator of fibrogenic gene expression. Transcriptomic profiling revealed enrichment of focal adhesion, ECM–receptor interaction, and actin cytoskeletal pathways downstream of collagen-bound ACLP, which was conserved in primary adipose-derived stromal cells. Together, these findings establish collagen-bound ACLP as a matrix-derived cue that links ECM composition to integrin-dependent fibrogenic activation.