Smooth muscle-specific HuR knockout induces defective autophagy and atherosclerosis

Human antigen R (HuR) is a widespread RNA-binding protein involved in homeostatic regulation and pathological processes in many diseases. Atherosclerosis is the leading cause of cardiovascular disease and acute cardiovascular events. However, the role of HuR in atherosclerosis remains unknown. In this study, mice with smooth muscle-specific HuR knockout (HuRSMKO) were generated to investigate the role of HuR in atherosclerosis. HuR expression was reduced in atherosclerotic plaques. As compared with controls, HuRSMKO mice showed increased plaque burden in the atherosclerotic model. Mechanically, HuR could bind to the mRNAs of adenosine 5′-monophosphate-activated protein kinase (AMPK) α1 and AMPKα2, thus increasing their stability and translation. HuR deficiency reduced p-AMPK and LC3II levels and increased p62 level, thereby resulting in defective autophagy. Finally, pharmacological AMPK activation induced autophagy and suppressed atherosclerosis in HuRSMKO mice. Our findings suggest that smooth muscle HuR has a protective effect against atherosclerosis by increasing AMPK-mediated autophagy.

Abstract 536: Human Antigen R (HuR) in the Myofibroblasts is a Critical Regulator of Pressure-Overload Induced Cardiac Remodeling

Cardiac fibrosis is characterized by the excessive deposition of extracellular matrix (ECM) and is an important target because excess ECM leads to a stiffened myocardium and worsens the prognosis of heart failure. Human Antigen R (HuR) is an RNA binding protein known to stabilize mRNA through binding to AU rich regions in the 3’UTR, and we have previously shown HuR to play a central role in the development of cardiac hypertrophy. To interrogate the role of HuR in cardiac fibrosis, we used both a small molecule inhibitor of HuR as well as an inducible genetic deletion of HuR in the activated cardiac myofibroblasts (iMF-HuR -/- ). Results using an in vitro scratch assay showed that primary adult cardiac fibroblasts treated with a small molecule inhibitor of HuR display a delayed wound healing response concomitant with a reduced expression of ECM remodeling genes. In vivo , we used an 8-week TAC (transverse aortic constriction) model of pressure overload to induce pathological cardiac remodeling. We hypothesized that deleting HuR in the activated fibroblasts would dampen myofibroblast-mediated ECM remodeling leading to a less stiff myocardium with reduced fibrotic burden and improved cardiac function in iMF-HuR -/- mice following pressure overload (TAC). However, echocardiography results show that cardiac function declined more rapidly in iMF-HuR -/- following TAC. The iMF-HuR -/- mice also had significantly enlarged hearts compared to the controls indicated by the heart weight/tibia length ratio. This suggests a critical role for HuR and myofibroblast activity in the early response to pressure overload. Future studies will focus on determining how the fibroblasts and the ECM composition/stiffness affect myocyte function in the early cardiac remodeling phase post-TAC and how HuR is involved in this relationship.