HuR inhibition reduces post-ischemic cardiac remodeling by dampening inflammatory gene expression and the innate immune response

In this study, we applied a novel small molecule inhibitor of HuR to define the functional role of HuR in the acute response to I/R injury and gain a better understanding of the HuR-dependent mechanisms during post-ischemic myocardial remodeling. Our results show an early post-ischemic increase in HuR activity that is necessary for inflammatory gene expression in cardiomyocytes. Despite the early reductions inflammatory gene expression, HuR inhibition has no effect on initial infarct size at 24-hours post-I/R. However, in agreement with previously published work by our group using a pressure overload model, we do see a protection with regard to pathological remodeling and cardiac function at two weeks post-I/R upon HuR inhibition. RNA-sequencing analysis of neonatal rat ventricular myocytes (NRVMs) post-LPS treatment to model damage associated molecular pattern (DAMP)-mediated activation of toll like receptors (TLRs) demonstrates a broad HuR-dependent regulation of pro-inflammatory chemokine and cytokine gene expression in cardiomyocytes. Importantly, we show that conditioned media from NRVMs pre-treated with HuR inhibitor loses the ability to induce inflammatory gene expression in bone marrow derived macrophages (BMDMs) compared to NRVMs treated with LPS alone. Functionally, HuR inhibition in NRVMs also reduces their ability to induce endocrine migration of peripheral blood monocytes in vitro and reduces post-ischemic macrophage infiltration to the heart in vivo. In summary, these results suggest a HuR-dependent expression of pro-inflammatory gene expression by cardiomyocytes that leads to subsequent monocyte recruitment and macrophage activation in the post-ischemic myocardium. Neonatal rat ventricular myocytes (NRVMs) treated with LPS to mimic toll-like receptor (TLR) receptor signaling via damage associated molecular patterns (DAMPs) that often occurs during in vivo I/R injury. NRVMs were treated with LPS with or without HuR inhibition (KH-3) and RNA-sequencing was performed at two hours post-treatment.