miRNA Mediated Cross-Talk in CRS4: The Role of the miR-21-5p/PPAR-Alpha Pathway

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PROJECT SUMMARY/ABSTRACT: Chronic kidney disease (CKD) puts patients at a greatly increased risk of cardiovascular disease, in a condition termed Type 4 Cardiorenal Syndrome (CRS4). While a large amount of clinical data on CKD patients has identified some risk factors, very little is known about the mechanisms by which this condition develops. We have utilized the 5/6 nephrectomy (5/6 NX) model in Sprague Dawley rats to study the development of cardiac dysfunction resulting from declining kidney function in a controlled animal model. The goal of our work is to identifying molecular mechanisms that are mediating dysfunction and target them therapeutically. Small RNA sequencing of left ventricle tissue identified miR-21-5p as a microRNA that is upregulated in response to 5/6 NX. MicroRNAs are a class of several hundred endogenously produced small RNAs that are involved with post-transcriptional regulation of gene expression in the heart and elsewhere. Systemic knockdown of miR-21 prevented cardiac hypertrophy and enhanced cardiac function without improving renal function or reducing blood pressure. This data suggests that suppression of miR-21-5p prevented pathology through pressure independent mechanisms. Subsequent mRNA sequencing identified gene expression changes in pathways relating to fatty acid oxidation, glycolysis, hypertrophic signaling, inflammation, immune function and atherosclerosis in response to miR-21 knockdown, suggesting that miR-21-5p may be targeting peroxisome proliferator-activated receptor alpha (PPAR. PPAR is miR-21 target in humans and is involved with regulation of all of the above mentioned pathways. PPAR is well known to be suppressed with cardiac pathology, however miR-21 targeting of PPARa has not yet been reported in a model of cardiac disease. We hypothesize that miR-21-5p produced by the 5/6Nx remnant kidney supplies the LV with a pathological amount of miR-21-5p, contributing to cardiac remodeling and dysfunction, at least in part, through targeting PPAR. This proposal will focus understanding the functional and pathological implications of that regulation. We will also locate LV cell types and tissue regions in which miR-21 targeting of PPAR is occurs and study the gene expression changes that result. A role for the miR-21-5p/PPAR pathway has not been reported in CRS4, or any other cardiac pathology. The studies outlined in this proposal are designed to characterize the upstream and downstream mechanisms of this pathway in the 5/6Nx model. The discovery of a direct role for circulating miR-21-5p in disease development would be an innovative breakthrough in the field of microRNA research, expanding our understanding of circulating miRNAs from markers of disease to mediators of disease. Further, findings from the proposed study could help elucidate mechanisms that regulate cardiac dysfunction in CRS4 and identify new therapeutic approaches for preventing or improving cardiac dysfunction in CKD patients.