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-β (TGF-β) 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/β-catenin pathway in response to TGF-β signalling. Inactivation of extracellular Wnt with secreted Frizzled-related protein 2 (sFRP2) or inhibition of Wnt secretion with Wnt-C59 prevented TGF-β-mediated transformation of inflammatory precursors and cardiac fibroblasts into pathogenic myofibroblasts. Inhibition of T-cell factor (TCF)/β-catenin-mediated transcription with ICG-001 or genetic loss of β-catenin also prevented TGF-β-induced myofibroblasts formation. Furthermore, blocking of Smad-independent TGF-β-activated kinase 1 (TAK1) pathway completely abrogated TGF-β-induced Wnt secretion. Activation of Wnt pathway in the absence of TGF-β, 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/β-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-β-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.