ROLE OF CIRCULAR PVT1 IN ISCHEMIC HEART FAILURE

Circular RNAs (circRNAs) are involved in the pathogenesis of several cardiovascular diseases (CVDs), including heart failure (HF). circRNAs can bind microRNAs (miRNAs), acting as competing endogenous RNAs (ceRNA), thus regulating the expression levels of miRNA target mRNAs. However, these interactions and their respective functions in ischemic HF (IHF) remain largely unknown. This study aimed to identify circRNA-based ceRNA networks in non-end-stage IHF. Transcriptome analysis of left ventricles of IHF patients identified significant differentially expressed circRNAs, miRNAs and mRNAs. Potential miRNAs interacting with validated circRNAs as well as mRNA targets of sponged miRNAs were determined using bioinformatics tools. Predicted miRNAs and mRNAs were filtered for their dysregulation in IHF, resulting in 662 circRNA-miRNA-mRNA interactions. KEGG terms of the identified interacting mRNAs indicated CVD-related signaling pathways. circPVT1 emerged as one of the main hubs of circRNA-miRNA-mRNA network in IHF. RNA-Seq analysis following circPVT1 knockdown in immortalized human cardiomyocytes identified differentially expressed genes mainly involved in fibrosis and in cellular senescence. Interestingly, circPVT1 expression significantly increased in cardiac fibroblasts after TGF-β1 treatment. circPVT1 silencing attenuated the levels of pro-fibrotic markers induced by TGF-β1, highlighting a pro-fibrotic role of circPVT1. RNA pull-down assays confirmed the interaction between circPVT1 and three fibrosis-related miRNAs, miR-30a-5p, miR-125b-5p and miR-369-5p. The levels of these miRNAs were not altered upon circPVT1 knockdown. However, the expression of their mRNA targets was deregulated upon circPVT1 silencing, suggesting that circPVT1 modulate miRNA cellular bioavailability. Inhibition of either miR-30a-5p or miR-125b-5p, but not miR-369-5p, significantly reversed the reduced expression of TGF-β1-induced pro-fibrotic markers following circPVT1 silencing, indicating that both miR-30a-5p and miR-125b-5p act as downstream effectors of circPVT1 in cardiac fibroblast activation. Our findings suggest that circPVT1 has a pro-fibrotic function and regulate cardiac fibroblast activation via miR-30a-5p and miR-125b-5p sponging.