Desmoplakin Mutations in Cardiac Fibroblasts Cause TGFβ1-Mediated Pathological Fibrogenesis in Desmoplakin Cardiomyopathy Via Beclin-1 Regulation.
BACKGROUND: 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. DSP variants are also linked to other fibrotic diseases. Whether DSP plays any role in pathological fibrosis remains unknown. METHODS: 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 and DSP 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. RESULTS: TGFβ1 induced excessive accumulation of VIM (vimentin)/fibrillar collagens and over-activated fibrotic genes in DSP-mutant MSCs when compared with normal MSCs. In normal MSCs, VIMs bind to wild-type DSP during normal fibrogenesis after TGFβ1. DSP-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 (COL1A1, COL3A1, and fibronectin [FN]) via heightened p38 activity after TGFβ1. Genome-wide analysis and DSP knockdown in mouse fibroblasts confirmed this novel role of DSP 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. CONCLUSIONS: 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.