miRNA-21 Targets Left Ventricular Peroxisome Proliferator-activated Receptor Alpha in a Rat Model of Type 4 Cardiorenal Syndrome

Type 4 cardiorenal syndrome (CRS4) is a condition in which chronic kidney disease (CKD) contributes to cardiovascular pathology including cardiac dysfunction, left ventricular (LV) hypertrophy, atherosclerosis, and heart failure. We have used a rat model of CKD, the 5/6 nephrectomy (5/6 NX), to study molecular mechanisms that mediate the development of cardiac pathology in CRS4. We previously reported that the upregulation of microRNA miR-21-5p (miR-21) in the left ventricle (LV) was accompanied by pathological remodeling and a drop in fractional shortening in adult male Sprague Dawley rats 7 weeks after 5/6 NX. Systemic knockdown of miR-21 in 5/6 NX rats with LNA-modified anti-miR-21 improved cardiac function, however it did not reduce the modest fibrosis observed with our 5/6 NX model or upregulate miR-21 targets identified in other models of cardiac pathology, suggesting a novel cardiac target for miR-21 in this model. Through next-generation mRNA sequencing of LV tissues from anti-miR-21 treated rats, and subsequent Ingenuity Pathway Analysis, we have found cardioprotective alterations in genes related to cardiac hypertrophy, metabolism, immune and inflammatory signaling, and atherosclerosis. Suppression or reduction of miR-21 target peroxisome proliferator-activated receptor alpha (PPARa), a master regulator of fatty acid oxidation, has been reported to be involved in all of these processes. Translational suppression of PPARa through miR-21 has been confirmed in other tissues, but not in the myocardium. The average LV PPARa protein expression level was significantly reduced (-37.7 ± 5.4%) in the 5/6 NX model and restored by miR-21 knockdown (Western blot; n=5-6/group; mean ± SEM). Immunohistochemistry revealed that the pronounced alterations in PPARa expression occurred within cardiomyocytes (CMs) in these samples. Transfection of neonatal CMs with pre-miR-21, significantly reduced PPARa protein expression within 48 hours (-23.0 ± 0.9%; n=3/group). These data indicate that PPARa suppression by miR-21 occurs within LV in 5/6 NX model of CKD and that miR-21 can regulate PPARa in CMs. This regulation may be relevant in other models of chronic cardiac disease where increased miR-21 and suppression of PPARa have been independently reported.