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

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.

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).

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.

These findings demonstrate that a super enhancer-associated circular RNA-circKrt4 modulates PAEC injury to promote pulmonary hypertension by targeting Pura and Glpk.