Desmoplakin Mutations in Cardiac Fibroblasts Cause TGFβ1-Mediated Pathological Fibrogenesis in Desmoplakin Cardiomyopathy Via Beclin-1 Regulation.

Abstract

Pathological fibrosis is a major finding in cardiovascular diseases and can result in arrhythmia and heart failure. Desmosome gene mutations can lead to arrhythmogenic cardiomyopathy. Among arrhythmogenic cardiomyopathies, pathogenic DSP (desmoplakin) variants cause a distinctive cardiomyopathy with excessive cardiac fibrosis that could precede ventricular dysfunction. <i>DSP</i> variants are also linked to other fibrotic diseases. Whether DSP plays any role in pathological fibrosis remains unknown. Mesenchymal stromal cells (MSCs) are resident fibroblast-like cells that are responsible for fibrogenesis in most organs, including the heart. We first used RNA-seq genome-wide analyses to generate cardiac fibroblast-like, induced pluripotent stem cell-derived MSCs from normal donors and patients with arrhythmogenic cardiomyopathy with <i>DSP</i> mutations. We then studied the fibrogenic responses of cardiac MSCs to TGFβ1 (transforming growth factor β1) using Western/Co-IP, autophagy assays, gene knockdowns/over-expressions, genomic analyses, mouse DSP knockdown models, immunostaining, and qPCR. TGFβ1 induced excessive accumulation of VIM (vimentin)/fibrillar collagens and over-activated fibrotic genes in <i>DSP</i>-mutant MSCs when compared with normal MSCs. In normal MSCs, VIMs bind to wild-type DSP during normal fibrogenesis after TGFβ1. <i>DSP</i>-mutant MSCs exhibited a haplo-insufficient phenotype with increased DSP-unbound VIMs that sequestered BECN1 (beclin-1) from activating autophagy and CAV1 (caveolin-1)-mediated endocytosis. Decreased autophagy caused collagen accumulation, and diminished CAV1 endocytosis resulted in abnormal CAV1 plaque formation that over-activated fibrotic genes (<i>COL1A1</i>, <i>COL3A1</i>, and fibronectin [<i>FN</i>]) via heightened p38 activity after TGFβ1. Genome-wide analysis and DSP knockdown in mouse fibroblasts confirmed this novel role of <i>DSP</i> mutations in pathological fibrosis. Overexpression of VIM-binding domains of DSP could suppress pathological fibrosis by increasing collagen autophagic degradation and decreasing fibrotic gene expression. Our data reveal that DSP deficiency in MSCs/fibroblasts leads to exaggerated fibrogenesis in DSP-cardiomyopathy by decreasing BECN1 availability for autophagy and CAV1-endocytosis. Overexpression of VIM binding domains of DSP could be a new strategy to treat pathological fibrosis.