CircALMS1 Alleviates Pulmonary Microvascular Endothelial Cell Dysfunction in Pulmonary Hypertension.

Background: Circular RNAs can serve as regulators influencing the development of pulmonary hypertension (PH). However, their function in pulmonary vascular intimal injury remains undefined. Thus, we aimed to identify specifically expressed circular RNAs in pulmonary microvascular endothelial cells (PMECs) under hypoxia and PH.

Methods And Results: Deep RNA sequencing and quantitative real-time polymerase chain reaction revealed that circALMS1 (circular RNA Alstrom syndrome protein 1) was reduced in human PMECs under hypoxia (<0.0001). Molecular biology and histopathology experiments were used to elucidate the roles of circALMS1 in regulating PMEC dysfunction among patients with PH. The circALMS1 expression was decreased in the plasma of patients with PH (=0.0315). Patients with lower circALMS1 levels had higher risk of death (=0.0006). Moreover, the circALMS1 overexpression of adeno-associated viruses improved right ventricular function and reduced pulmonary vascular remodeling in monocrotaline-PH and sugen/hypoxia-PH rats (<0.05). Furthermore, circALMS1 overexpression promoted apoptosis and inhibited PMEC proliferation and migration under hypoxia by directly downregulating miR-17-3p (<0.05). Dual luciferase assay confirmed the direct binding of circALMS1 to miR-17-3p and miR-17-3p binding to its target gene YT521-B homology domain-containing family protein 2 (YTHDF2) (<0.05). The YTHDF2 levels were also downregulated in hypoxic PMECs (<0.01). The small interfering RNA YTHDF2 reversed the effects of miR-17-3p inhibitors on PMEC proliferation, migration, and apoptosis. Finally, the results indicated that, although YTHDF2, as an N(6)-methyladenosine reader protein, contributes to the degradation of many circular RNAs, it could not regulate the circALMS1 levels in PMECs (=0.9721).

Conclusions: Our study sheds new light on circALMS1-regulated dysfunction of PMECs by the miR-17-3p/YTHDF2 pathway under hypoxia and provides insights into the underlying pathogenesis of PH.