Cardiac Circular RNAs CDR1as, Circ-RCAN2, Circ-C12orf29 Show Cell-Specific Hypoxia-Induced Dysregulation and Distinct In Vitro Effects

Circular RNAs (circRNAs) are looped RNA molecules with regulatory roles in myocardial infarction and post-infarction cascades. We aimed to (i) confirm the circularity of novel circRNAs (CDR1as, circ-RCAN2, circ-C12orf29) implicated in myocardial infarction, (ii) examine cell-specific regulation patterns under hypoxia, and (iii) assess their effects on cell viability and downstream miRNA targets. Experiments were conducted on porcine cardiac progenitor cells (pCPCs), bone marrow mesenchymal stem cells (pMSCs) and cardiac fibroblasts (pCFs). Circularity was assessed by RNase R treatment, subsequent qPCR, gel electrophoresis and Sanger sequencing. Hypoxia experiments with/without serum deprivation mimicked ischemia. Effects on viability with/without hypoxia (MTT assay) and downstream miRNA targets were assessed via short interfering RNA (siRNA)-mediated knockdown of circ-RCAN2 and circ-C12orf29. Following RNase R treatment, qPCR product electrophoresis demonstrated amplification of singular products for all circRNAs, with backsplice junction amplification confirmed via Sanger sequencing. Serum deprivation and hypoxia resulted in cell-specific circRNA expression patterns, with an upregulation of all candidates in pCPCs across all intervals of hypoxia, an upregulation of circ-RCAN2 and circ-C12orf29 in pMSCs with prolonged hypoxia, and no detectable dysregulation in pCFs. siRNA knockdown of circ-RCAN2 reduced pCF- and increased pMSC-viability. circ-C12orf29 knockdown increased pCPC- and reduced pMSC-viability. circ-C12orf29 knockdown also upregulated ssc-miR-21-5p and ssc-miR-181c in pCPCs, with no detectable targets for circ-RCAN2. In conclusion, CDR1as, circ-RCAN2 and circ-C12orf29 are circular and dysregulated in a time- and cell-type-specific manner following hypoxia. circ-RCAN2 and circ-C12orf29 exhibit cell-type specific effects on viability, with circ-C12orf29 also targeting downstream miRNAs.