Matricellular Protein Cilp1 Promotes Myocardial Fibrosis in Response to Myocardial Infarction

Abstract

Rationale: Cilp1 (cartilage intermediate layer protein 1) is a secreted extracellular matrix protein normally associated with bone and cartilage development. Its function and mechanism of action in adult heart disease remain elusive. Objective: To establish the function and mechanism of action of Cilp1 in postmyocardial infarction (MI) cardiac remodeling. Methods and Results: We investigated the expression of Cilp1 in mouse models of pathological cardiac remodeling and human heart failure patients. Cilp1 was expressed predominantly in cardiac fibroblasts and upregulated in response to cardiac injury and in the heart and blood of patients with heart failure. We generated Cilp1 knock out (KO) and transgenic (Tg) mice with NCilp1 (N-terminal half of the protein) overexpressed in myofibroblasts. Cilp1 KO mice had better cardiac function, reduced number of immune cells and myofibroblasts, and enhanced microvascular survival after MI compared with wild-type littermates. Conversely, NCilp1-transgenic mice had augmented loss of cardiac function, increased number of myofibroblasts and infarct size after the MI injury. RNA-seq and gene ontology analysis indicated that cell proliferation and mTORC1 (mammalian Target of Rapamycin Complex 1) signaling were downregulated in KO hearts compared with wild-type hearts. In vivo BrdU labeling and immunofluorescence staining showed that myofibroblast proliferation in the Cilp1 KO heart was downregulated. Biaxial mechanical testing and extracellular matrix gene expression analysis indicated that while MI caused significant stiffness in wild-type hearts it had little effect on KO hearts. Upregulation of collagen expression after MI injury was attenuated in KO hearts. Recombinant CILP1 protein or NCilp1-conditioned medium promoted proliferation of neonatal rat ventricular cardiac fibroblasts via the mTORC1 signaling pathway. Conclusions: Our studies established a pathological role of Cilp1 in promoting post-MI remodeling, identified a novel function of Cilp1 in promoting myofibroblast proliferation, and suggested that Cilp1 may serve as a potential biomarker for pathological cardiac remodeling and target for fibrotic heart disease.