Transforming growth factor-β-dependent Wnt secretion controls myofibroblast formation and myocardial fibrosis progression in experimental autoimmune myocarditis

Aims Myocardial fibrosis critically contributes to cardiac dysfunction in inflammatory dilated cardiomyopathy (iDCM). Activation of transforming growth factor-beta (TGF-beta) signalling is a key-step in promoting tissue remodelling and fibrosis in iDCM. Downstream mechanisms controlling these processes, remain elusive. Methods and results Experimental autoimmune myocarditis (EAM) was induced in BALB/c mice with heart-specific antigen and adjuvant. Using heart-inflammatory precursors, as well as mouse and human cardiac fibroblasts, we demonstrated rapid secretion of Wnt proteins and activation of Wnt/b-catenin pathway in response to TGF-beta signalling. Inactivation of extracellular Wnt with secreted Frizzled-related protein 2 (sFRP2) or inhibition of Wnt secretion with Wnt-C59 prevented TGF-beta-mediated transformation of inflammatory precursors and cardiac fibroblasts into pathogenic myofibroblasts. Inhibition of T-cell factor (TCF)/beta-catenin-mediated transcription with ICG-001 or genetic loss of beta-catenin also prevented TGF-beta-induced myofibroblasts formation. Furthermore, blocking of Smad-independent TGF-beta-activated kinase 1 (TAK1) pathway completely abrogated TGF-beta-induced Wnt secretion. Activation of Wnt pathway in the absence of TGF-beta, however, failed to transform precursors into myofibroblasts. The critical role of Wnt axis for cardiac fibrosis in iDCM is also supported by elevated Wnt-1/Wnt-5a levels in human samples from hearts with myocarditis. Accordingly, and as an in vivo proof of principle, inhibition of Wnt secretion or TCF/beta-catenin-mediated transcription abrogated the development of post-inflammatory fibrosis in EAM. Conclusion We identified TAK1-mediated rapid Wnt protein secretion as a novel downstream key mechanism of TGF-beta-mediated myofibroblast differentiation and myocardial fibrosis progression in human and mouse myocarditis. Thus, pharmacological targeting of Wnts might represent a promising therapeutic approach against iDCM in the future.