The insulin‐like growth factor binding protein–microfibrillar associated protein–sterol regulatory element binding protein axis regulates fibroblast–myofibroblast transition and cardiac fibrosis.

Background and Purpose: Excessive fibrogenesis is associated with adverse cardiac remodelling and heart failure. The myofibroblast, primarily derived from resident fibroblast, is the effector cell type in cardiac fibrosis. Megakaryocytic leukaemia 1 (MKL1) is considered the master regulator of fibroblast–myofibroblast transition (FMyT). The underlying transcriptional mechanism is not completely understood. Our goal was to identify novel transcriptional targets of MKL1 that might regulate FMyT and contribute to cardiac fibrosis. Experimental Approach: RNA sequencing (RNA‐seq) performed in primary cardiac fibroblasts identified insulin‐like growth factor binding protein 5 (IGFBP5) as one of the genes most significantly up‐regulated by constitutively active (CA) MKL1 over‐expression. IGFBP5 expression was detected in heart failure tissues using RT‐qPCR and western blots. Key Results: Once activated, IGFBP5 translocated to the nucleus to elicit a pro‐FMyT transcriptional programme. Consistently, IGFBP5 knockdown blocked FMyT in vitro and dampened cardiac fibrosis in mice. Of interest, IGFBP5 interacted with nuclear factor of activated T‐cell 4 (NFAT4) to stimulate the transcription of microfibril‐associated protein 5 (MFAP5). MFAP5 contributed to FMyT and cardiac fibrosis by enabling sterol response element binding protein 2 (SREBP2)‐dependent cholesterol synthesis. Conclusions and Implications: Our data unveil a previously unrecognized transcriptional cascade, initiated by IGFBP5, that promotes FMyT and cardiac fibrosis. Screening for small‐molecule compounds that target this axis could yield potential therapeutics against adverse cardiac remodelling. [ABSTRACT FROM AUTHOR]