Role of RBP in programming and reprogramming of cardiac fibroblasts

Cardiac fibroblasts (CFs) are the major cardiac cell type responsible for producing extracellular matrix (ECM) proteins, forming a structural scaffold crucial for supporting cardiac tissue during development and homeostasis. CFs are also known for their high plasticity, enabling them to swiftly respond to injuries and pathological conditions. Under such circumstances, CFs are rapidly activated and become transdifferentiated into myofibroblasts that produce and secrete an excessive amount of ECM components, ultimately leading to fibrotic scarring that disrupts tissue compliance and accelerates the progression toward heart failure. The transformation of CFs into myofibroblasts requires wholesale programming of the CF transcriptome. Yet, in addition to transcriptional regulation, post-transcriptional regulation by RNA-binding proteins (RBPs) has emerged as a critical regulatory layer for controlling gene expression. RBPs actively regulate every step of mRNA life cycle, including splicing, stability, and translation. In our preliminary studies, we found that one of RBPs, Ybx1, was significantly upregulated during CF to myofibroblast conversion and further discovered a potentially important role of this RBP in myofibroblast formation. Specifically, we found that Tcf21:MerCreMer mediated ablation of Ybx1 inhibits the transformation of CFs into myofibroblasts and reduces cardiac fibrosis. While the conversion CFs to myofibroblasts is inherently pathological, the extensive pool and plasticity of resident CFs has been recently harnessed for cardiac regeneration whereby CFs are reprogrammed into induced cardiomyocytes (iCMs) by local delivery of three cardiac transcription factors (TFs) - Gata4, Mef2c, Tbx5 (abbreviated as GMT). Building upon our intriguing finding that depletion of Ybx1 attenuates CF to myofibroblast conversion and reduces cardiac fibrosis, we posed the question whether Ybx1 ablation enhances GMT-mediated iCM reprogramming. Indeed, our preliminary study indicates that, compared to MGT-mediated iCM reprogramming, delivery of GMT with Ybx1 depletion enhances iCM induction, further attenuating cardiac fibrosis and improves heart function following MI. Combining these two lines of investigation and the corresponding preliminary data, in this proposal we will leverage our series of unique tools, reagents, and animal models to address our hypothesis that Ybx1 activity exerts a significant influence on the fate switch involving CFs, specifically the transformation of CFs into myofibroblasts and the reprogramming of CFs into iCMs, which can be leveraged for reducing fibrotic scarring and regenerating lost myocardium after MI.