Novel Roles for IRE1 in Regulating Cardiac Fibrosis - Project Summary: Cardiovascular disease has consistently been the leading cause of death in the US for the last century with resultant heart failure (HF) accounting for nearly 800,000 deaths per year. Despite substantial advancements in clinically available interventions, the incidence of HF continues to rise with a staggering estimated economic burden of >$900 billion per year by 2030. Virtually all etiologies of cardiovascular disease leading to both heart failure with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF) involve pathological remodeling of the left ventricle characterized by excessive deposition of extracellular matrix (ECM) proteins that impair ventricular compliance and perpetuate HF pathogenesis. The primary cell type responsible for synthesizing and secreting ECM proteins are resident cardiac fibroblasts (CFBs) that become activated by diverse stimuli during HF. As a testament to the secretory potential of CFBs, a single fibroblast can produce >500,000 procollagen chains per hour which necessitates the presence of a robust network of protein folding machinery in the endoplasmic reticulum to maintain cellular proteostasis and allow for the proper processing of nascent ECM proteins. Such protein folding demands trigger activation of the unfolded protein response (UPR), an adaptive component of the proteostasis network to facilitate proper protein quality control. Our long-term goal is to determine the mechanistic contributions of the UPR in regulating chronic CFB activation and reactive cardiac fibrosis in response to HFrEF and HFpEF. Our preliminary data support the notion that the IRE1 arm of the UPR plays a pivotal role in protecting against fibrotic remodeling in the heart via targeted mRNA degradation of transcripts encoding proteins required for CFB activation, namely Tmem100. We’ve also characterized a novel small molecule activator of IRE1 with potential to ameliorate functional decline in a preclinical model of HFrEF. In this proposal, we will focus on IRE1 and whether tactile control of the endonuclease activity of IRE1 could alter CFB activation and ECM deposition with the hypothesis that IRE1 protects against pathological cardiac fibrosis in HF via regulating the selective degradation of Tmem100 and a pro-fibrotic transcriptome. We will address this hypothesis using fibroblast-specific gene targeting in complimentary mouse models of HF, as well as mechanistic studies in primary CFBs, in the following Specific Aims which are to: (Aim 1) determine the cardiac fibroblast transcriptomic profile regulated by IRE1 using a mouse model of HFrEF, (Aim 2) determine the functional significance of IRE1-mediated degradation of Tmem100 mRNA in fibrotic remodeling using a mouse model of HFrEF, and (Aim 3) evaluate the therapeutic efficacy of novel small molecule activator of IRE1 in mitigating fibrotic remodeling using mouse models of HFrEF or HFpEF. These studies are significant as they present the opportunity to identify novel mechanisms contributing to CFB activation and ECM deposition as well as to test new therapeutic strategies with potential to ameliorate fibrotic remodeling associated with both HFrEF and HFpEF.
