Hypoxia drives cardiac miRNAs and inflammation in the right and left ventricle

Alveolar and myocardial hypoxia may be causes or sequelae of pulmonary hypertension (PH) and heart failure. We hypothesized that hypoxia initiates specific epigenetic and transcriptional, pro-inflammatory programs in the right ventricle (RV) and left ventricle (LV). We performed an expression screen of 750 miRNAs by qPCR arrays in the murine RV and LV in normoxia (Nx) and hypoxia (Hx; 10% O₂ for 18 h, 48 h, and 5d). Additional validation included single qPCR analysis of miRNA and pro-inflammatory transcripts in murine and human RV/LV, and neonatal rat cardiomyocytes (NRCMs). Differential qPCR-analysis (Hx vs. Nx in RV, Hx vs. Nx in LV, and RV vs. LV in Hx) identified nine hypoxia-regulated miRNAs: let-7e-5p, miR-29c-3p, miR-127-3p, miR-130a-3p, miR-146b-5p, miR-197-3p, miR-214-3p, miR-223-3p, and miR-451. Hypoxia downregulated miR-146b in the RV (p < 0.01) and, less so, in the LV (trend; p = 0.28). In silico alignment showed significant binding affinity of miR-146b-5p sequence with the 3'UTR of TRAF6 known to be upstream of pro-inflammatory NF-kB. Consistently, hypoxia induced TRAF6, IL-6, CCL2(MCP-1) in the mouse RV and LV. Incubating neonatal rat cardiomyocytes with pre-miR-146b led to a downregulation of TRAF6, IL-6, and CCL2(MCP-1). TRAF6 mRNA expression was also increased by 3-fold in the RV and LV of end-stage idiopathic pulmonary arterial hypertension (PAH) patients vs. non-PAH controls. We identified hypoxia-regulated, ventricle-specific miRNA expression profiles in the adult mouse heart in vivo. Hypoxia suppresses miR-146b, thus de-repressing TRAF6, and inducing pro-inflammatory IL-6 and CCL2(MCP-1). This novel hypoxia-induced miR-146b-TRAF6-IL-6/CCL2(MCP-1) axis likely drives cardiac fibrosis and dysfunction, and may lead to heart failure. KEY MESSAGES: Chouvarine P, Legchenko E, Geldner J, Riehle C, Hansmann G. Hypoxia drives cardiac miRNAs and inflammation in the right and left ventricle. • Hypoxia drives ventricle-specific miRNA profiles, regulating cardiac inflammation. • miR-146b-5p downregulates TRAF6, known to act upstream of pro-inflammatory NF-κB. • Hypoxia downregulates miR-146b and induces TRAF6, IL-6, CCL2 (MCP-1) in the murine RV and LV. • The inhibitory regulatory effects of miR-146b are confirmed in primary rat cardiomyocytes (pre-miR, anti-miR) and human explant heart tissue (endstage pulmonary arterial hypertension). • A novel miR-146b-TRAF6-IL-6/CCL2(MCP-1) axis likely drives cardiac inflammation, fibrosis and ventricular dysfunction.