Super Enhancer-Associated Circular RNA-CircKrt4 Regulates Hypoxic Pulmonary Artery Endothelial Cell Dysfunction in Mice

Abstract

Background: Circular RNAs (circRNAs) have been implicated in pulmonary hypertension progression through largely unknown mechanisms. Pulmonary artery endothelial cell (PAEC) dysfunction is a hallmark in the pathogenesis of pulmonary hypertension. However, the specific role of circular RNAs in PAEC injury caused by hypoxia remains unclear. Methods: In this study, using the Western blotting, RNA pull down, Dual-luciferase reporter assay, immunohistochemistry, and immunofluorescence, we identified a novel circular RNA derived from alternative splicing of the keratin 4 gene (circKrt4). Results: CircKrt4 was upregulated in lung tissues and plasma and specifically in PAECs under hypoxic conditions. In the nucleus, circKrt4 induces endothelial-to-mesenchymal transition by interacting with the Pura (transcriptional activator protein Pur-alpha) to promote N-cadherin gene activation. In the cytoplasm, increased circKrt4 leads to mitochondrial dysfunction by inhibiting cytoplasmic-mitochondrial shuttling of mitochondrial-bound Glpk (glycerol kinase). Intriguingly, circKrt4 was identified as a super enhancer-associated circular RNA that is transcriptionally activated by a transcription factor, CEBPA (CCAAT enhancer binding protein alpha). Furthermore, RBM25 (RNA-binding-motif protein 25) was found to regulate circKrt4 cyclization by increase the back-splicing of Krt4 gene. Conclusions: These findings demonstrate that a super enhancer-associated circular RNA-circKrt4 modulates PAEC injury to promote pulmonary hypertension by targeting Pura and Glpk.