Functional and mechanistic delineation of HuR-Wisp1 signaling on myofibroblast activity

PROJECT SUMMARY: Cardiac fibrosis is regulated by the activation and phenotypic switching of quiescent cardiac fibroblasts (CFs) to active myofibroblasts (MFs) which have extracellular matrix (ECM) remodeling and contractile functions which play a central role in cardiac remodeling in response to injury. As such, there is consensus effort in the field to manipulate fibroblast activity for therapeutic gain. However, a more complete understanding of the signaling pathways and mechanisms that regulate MF activity in cardiac remodeling remains an unmet need. We previously demonstrated that the RNA binding protein Human antigen R (HuR) directly mediates hypertrophic signaling in cardiac myocytes (CMs), and that CM-specific genetic deletion or pharmacological inhibition of HuR reduces pathological remodeling and preserves cardiac function following transverse aortic constriction (TAC)-induced pressure overload in part through a reduction in pro-fibrotic gene expression. New preliminary data suggests that HuR activity in cardiac fibroblasts may play an equally important role in cardiac remodeling. Our new data demonstrates a necessary role for HuR in MF activation and the ECM-remodeling capacity of cardiac fibroblasts. Furthermore, we have identified Wisp1 (Ccn4) as a downstream HuR- dependent mediator of MF activation, and show that exogenous addition of recombinant Wisp1 partially restores MF activity upon HuR inhibition. The primary goal of this proposal is to determine the functional role that HuR-Wisp1 signaling plays on MF activity and whether functional inhibition of these pathways in fibroblasts will provide therapeutic benefit during pathological cardiac remodeling. Our central hypothesis is that HuR-Wisp1 signaling in cardiac fibroblasts is necessary for myofibroblast activity and promotes pathological cardiac remodeling. The specific Aims of this proposal are to: (1) Determine the functional role of HuR in CFs in vivo and define its pleiotropic role across cell types during pathological cardiac remodeling. (2) Identify the functional and mechanistic role of HuR-dependent control of Wisp1 expression on MF activity and pathological cardiac remodeling. The expected results of this proposal will provide a deeper understanding of the functional impact of the HuR-Wisp1 signaling axis across cardiac cell types during pathological cardiac remodeling that is necessary for potential therapeutic manipulation of HuR or HuR-dependent gene expression in cardiac remodeling as suggested by our previous work.