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

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PROJECT SUMMARY: Cardiac fibrosis is regulated by the activation and phenotypic switching of quiescent cardiac fibroblasts (CFs) to active myofibroblasts (MFs). These MFs have extracellular matrix (ECM) remodeling and contractile functions which play a central role in cardiac remodeling in response to injury. As such, a consensus effort in the field is to manipulate fibroblast activity for therapeutic gain. However, a more complete understanding of the signaling pathways that regulate MF activity in cardiac remodeling remains an unmet need. We have 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.1,2 In this proposal, we now present new preliminary data showing that HuR (1) expression in cardiac fibroblasts strongly correlates with established markers (periostin, 𝛼SMA, CTGF, etc) of MFs, (2) is necessary for TGFߚ- dependent MF activation and ECM-remodeling in vitro, and (3) CF-specific deletion of HuR preserves cardiac function following TAC. Critically, we have identified Wisp1 (Ccn4) as a downstream HuR-dependent mediator of MF activation, and show that expression of Wisp1 is sufficient to induce MF activity downstream/independent of HuR. The primary goals of this proposal are to determine the functional benefit of targeting HuR deletion in cardiac fibroblasts during pathological cardiac remodeling and the mechanistic impact of HuR deletion in CFs across other cell types in the myocardium (Aim 1), as well as the mechanisms by which HuR mediates Wisp1 expression in MFs, the functional benefit of fibroblast-specific Wisp1 deletion on cardiac remodeling, and the translational impact of these pathways on cardiac remodeling in human heart failure (Aim 2). 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 mechanistic understanding of how HuR-Wisp1 signaling in cardiac fibroblasts modulates the functional response during pathological cardiac remodeling. Additionally, we will integrate previous translational work using a HuR small molecule inhibitor to better define the transcriptomic and functional changes across cardiac cell types in response to global and CF-specific abrogation of HuR signaling. In all, we expect this work to fill knowledge gaps in the signaling pathways that mediate cardiac fibroblast activation and ECM remodeling in the failing heart and provide a translational foundation for the targeting of HuR-Wisp1 signaling and/or HuR-dependent gene expression for therapeutic gain.