Cardiac fibroblast-derived IGFBP6 orchestrates cardiac remodeling by coupling the EGR1-MFAP4 axis

Rationale: The transition of fibroblasts into activated myofibroblasts is a pivotal driver of collagen deposition and adverse cardiac remodeling. Insulin-like growth factor-binding protein 6 (IGFBP6), a critical modulator of cellular growth and metabolism via its regulation of IGF-II activity, has been implicated in immune and fibrotic responses. However, its specific role in fibroblast-mediated cardiac remodeling, particularly in the regulation of myofibroblast transition, remains incompletely understood. Methods: We analyzed IGFBP6 expression in ischemic cardiomyopathy-associated cardiac fibrosis using Gene Expression Omnibus (GEO) dataset. Serum IGFBP6 levels in patients with chronic myocardial infarction (MI) were quantified via ELISA. Cardiac fibroblast and myofibroblast-specific IGFBP6 knockout mice were generated by crossing IGFBP6 floxed (IGFBP6^f/f) mice with tamoxifen-inducible Col1a2-Cre and Postn-MerCreMer mice. Cardiac function, tissues morphology, and molecular alterations were analyzed following MI or isoproterenol (ISO) challenge. The mechanisms underlying the regulation of fibroblast-to-myofibroblast transition (FMT) by IGFBP6 were elucidated using LC-MS/MS and RNA sequencing. Results: IGFBP6 expression was significantly upregulated in cardiac fibroblasts isolated from murine fibrotic hearts and was responsive to TGF-β1 stimulation. The elevated serum IGFBP6 levels were correlated with the incidence of chronic MI. Conditional knockout of IGFBP6 in cardiac fibroblasts and myofibroblasts markedly attenuated post-MI fibrotic remodeling, ventricular dysfunction, and ISO-induced cardiac hypertrophy and fibrosis. IGFBP6 silencing abolished TGF-β1-triggered FMT. Mechanistically, TGF-β1 stimulation facilitated the translocation of IGFBP6 in cardiac fibroblasts, where its N-terminal domain directly interacted with early growth regulator 1 (EGR1). This interaction enhanced EGR1 binding to the promoter of microfibril-associated protein 4 (MFAP4), a pro-fibrotic mediator. Overexpression of MFAP4 significantly reversed the protective effects by IGFBP6 knockout in cardiac fibroblast transition and adverse remodeling post-MI. Conclusion: Our study identifies fibroblast-derived IGFBP6 as a novel regulator of cardiac fibrosis through the EGR1-MFAP4 signaling axis, driving myofibroblasts differentiation and adverse remodeling. Targeting this pathway may offer therapeutic potential for cardiac remodeling disorders.