Myofibroblast-Specific TGFβ Receptor II Signaling in the Fibrotic Response to Cardiac Myosin Binding Protein C-Induced Cardiomyopathy

Abstract

Rationale: Hypertrophic cardiomyopathy occurs with a frequency of about 1 in 500 people. Approximately 30% of those affected carry mutations within the gene encoding cardiac myosin-binding protein C (cMyBP-C). Cardiac stress, as well as cMyBP-C mutations, can trigger production of a 40kDa truncated fragment derived from the amino terminus of cMyBP-C (Mybpc340kDa). Expression of the 40kDa fragment in mouse cardiomyocytes leads to hypertrophy, fibrosis and heart failure. Here we use genetic approaches to establish a causal role for excessive myofibroblast activation in a slow, progressive genetic cardiomyopathy - one that is driven by a cardiomyocyte-intrinsic genetic perturbation that models an important human disease. Objective: Transforming growth factor-β (TGFβ) signaling is implicated in a variety of fibrotic processes and the goal of this study was to define the role of myofibroblast TGFβ signaling during chronic Mybpc340kDa expression. Methods and Results: To specifically block TGFβ signaling only in the activated myofibroblasts in Mybpc340kDa transgenic (Tg) mice, quadruple compound mutant mice were generated, in which the TGFβ receptor II (TβRII) alleles (Tgfbr2) were ablated using the Postn (periostin) allele, myofibroblast-specific, tamoxifen-inducible Cre (Postnmcm) gene-targeted line. Tgfbr2 was ablated either early or late during pathological fibrosis. Early myofibroblast specific Tgfbr2 ablation during the fibrotic response reduced cardiac fibrosis, alleviated cardiac hypertrophy, preserved cardiac function, and increased lifespan of the Mybpc340kDa Tg mice. Tgfbr2 ablation late in the pathological process reduced cardiac fibrosis, preserved cardiac function, and prolonged Mybpc340kDa mouse survival but failed to reverse cardiac hypertrophy. Conclusions: Fibrosis and cardiac dysfunction induced by cardiomyocyte-specific expression of Mybpc340kDa were significantly decreased by Tgfbr2 ablation in the myofibroblast. Surprisingly, pre-existing fibrosis was partially reversed if the gene was ablated subsequent to fibrotic deposition, suggesting that continued TGFβ signaling through the myofibroblasts was needed to maintain the heart’s fibrotic response to a chronic, disease-causing cardiomyocyte-only stimulus.

The Extracellular Matrix in Ischemic and Nonischemic Heart Failure

“…However, recent evidence from mouse models of genetic cardiomyopathies has challenged the notion that ECM remodeling is an innocent companion. In transgenic mouse models of HCM, myofibroblast-specific disruption or pharmacologic inhibition of TGF-β signaling reduced myocardial fibrosis, prolonged survival, and preserved cardiac function 246 , 247 . These observations may suggest that activation of a fibrogenic program may exacerbate dysfunction and worsen outcome in subjects with sarcomeric mutations.…”

Cardiac Fibrosis and Cardiac Fibroblast Lineage-Tracing: Recent Advances

“…Interestingly, even though both cardiac fibroblast-specific deletion of Tgfbr1/2 and Smad2/3 significantly reduced cardiac fibrosis induced by transverse aortic constriction (TAC), only the deletion of Tgfbr1/2 in cardiac fibroblasts ameliorated cardiac hypertrophy and resulted in a functional improvement at 4 and 12 weeks after TAC (Khalil et al, 2017). Similarly, myofibroblast-specific Tgfbr2 deletion led to improved cardiac function in mouse models of proteotoxic cardiac disease and cardiac myosin binding protein C-induced cardiomyopathy (Bhandary et al, 2018;Meng et al, 2018). Studies conducted by another group using Postn-Cre-mediated myofibroblast-specific deletion of Smad3 and Smad2 found that while deletion of Smad2 temporarily improved cardiac function around 7 days after myocardial infarct (MI) in mice, deletion of Smad3 caused a reduction in cardiac function 28 days after MI (Kong et al, 2018;Huang et al, 2019).…”

Protective transcriptional mechanisms in cardiomyocytes and cardiac fibroblasts

“…This complex stimulates ubiquitination and degradation of P53, thereby promoting cell cycle progression and proliferation of CFs [140]. While TGFβ signaling is essential to initiate CF activation, a recent study demonstrated that ablation of TGFβR2 in activated Postn+ CFs reduced fibrosis, indicating that sustained TGFβ signaling is required to maintain CF activation [154].…”