Cell-specific ablation of Hsp47 defines the collagen-producing cells in the injured heart

Hadi Khalil,Katja K Kilian,Kunito Kawasaki,Vikram Prasad,Tobias Schips,Ronald J Vagnozzi,Jeffery D Molkentin,Robert N Correll,Matthew J Brody,Anne Katrine Johansen,Kazuhiro Nagata,Bryan D Maliken,Onur Kanisicak,Justin G Boyer

doi:10.1172/jci.insight.128722

Abstract

Collagen production in the adult heart is thought to be regulated by the fibroblast, although cardiomyocytes and endothelial cells also express multiple collagen mRNAs. Molecular chaperones are required for procollagen biosynthesis, including heat shock protein 47 (Hsp47). To determine the cell types critically involved in cardiac injury–induced fibrosis the Hsp47 gene was deleted in cardiomyocytes, endothelial cells, or myofibroblasts. Deletion of Hsp47 from cardiomyocytes during embryonic development or adult stages, or deletion from adult endothelial cells, did not affect cardiac fibrosis after pressure overload injury. However, myofibroblast-specific ablation of Hsp47 blocked fibrosis and deposition of collagens type I, III, and V following pressure overload as well as significantly reduced cardiac hypertrophy. Fibroblast-specific Hsp47-deleted mice showed lethality after myocardial infarction injury, with ineffective scar formation and ventricular wall rupture. Similarly, only myofibroblast-specific deletion of Hsp47 reduced fibrosis and disease in skeletal muscle in a mouse model of muscular dystrophy. Mechanistically, deletion of Hsp47 from myofibroblasts reduced mRNA expression of fibrillar collagens and attenuated their proliferation in the heart without affecting paracrine secretory activity of these cells. The results show that myofibroblasts are the primary mediators of tissue fibrosis and scar formation in the injured adult heart, which unexpectedly affects cardiomyocyte hypertrophy.

Highlights

The extracellular matrix (ECM) in the heart is comprised of diverse structural proteins that provide a rigid but dynamic framework that mechanically supports contracting cardiomyocytes
Loss of heat shock protein 47 (Hsp47) enhanced the secretion of 11 factors/cytokines, including matrix metalloproteinase 3 (MMP3), osteoprotegerin, and pentraxin 2 (Supplemental Figure 2, D–F), while only the secretion of IL-17 was significantly reduced (Supplemental Figure 2G). These results suggest that Hsp47 regulates the secretion of ECM-associated collagens in cultured cardiac fibroblasts and its deletion does not otherwise compromise the secretory function of these fibroblasts
The results presented here are the first to our knowledge to directly demonstrate in vivo that it is the myofibroblast that serves as the primary source of collagen production in the acutely stressed or chronically diseased heart

Summary

Introduction

The extracellular matrix (ECM) in the heart is comprised of diverse structural proteins that provide a rigid but dynamic framework that mechanically supports contracting cardiomyocytes. The ECM in the adult heart is composed predominantly of collagen type I, other fibrillar and nonfibrillar collagens are present [1]. The fibrillar collagens typically serve as the primary support network in the adult heart, and they likely contribute to mechanosensation as part of cardiomyocyte and fibroblast reactive signaling [4]. While initially an adaptive response, excessive myocardial collagen deposition after pressure overload–induced hypertrophy or from a previous ischemic injury event predisposes to heart failure with diminished ventricular compliance, reduced diffusion efficiency within the tissue, and maladaptive structural remodeling [8,9,10,11,12]

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Results

Conclusion