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Background Hypoxia mediated pulmonary hypertension (HPH) is a lethal disease and lacks effective therapy. CircRNAs play significant roles in physiological process. Recently, circRNAs are found to be m6A-modified. The abundance of circRNAs was influenced by m6A. Furthermore, the significance of m6A circRNAs has not been elucidated in HPH yet. Here we aim to investigate the transcriptome-wide map of m6A circRNAs in HPH. Results Differentially expressed m6A abundance was detected in lungs of HPH rats. M6A abundance in circRNAs was significantly reduced in hypoxia in vitro. M6A circRNAs were mainly from protein-coding genes spanned single exons in control and HPH groups. Moreover, m6A influenced the circRNA–miRNA–mRNA co-expression network in hypoxia. M6A circXpo6 and m6A circTmtc3 were firstly identified to be downregulated in HPH. Conclusion Our study firstly identified the transcriptome-wide map of m6A circRNAs in HPH. M6A can influence circRNA–miRNA–mRNA network. Furthermore, we firstly identified two HPH-associated m6A circRNAs: circXpo6 and circTmtc3. However, the clinical significance of m6A circRNAs for HPH should be further validated.

Angiotensin-converting enzyme 2 (ACE2) protects against hypoxic pulmonary hypertension (HPH) by inhibiting the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs). Under hypoxia, the hypoxia-inducible factor 1α (HIF-1α) inhibits ACE2 indirectly; however, the underlying mechanism is unclear. In the present study, we found that exposure to chronic hypoxia stimulated microRNA (miRNA) let-7b expression in rat lung via a HIF-1α-dependent pathway. Let-7b downregulated ACE2 expression by directly targeting the coding sequence of ACE2. Our in vitro and in vivo results revealed that let-7b contributed to the pathogenesis of HPH by inducing PASMCs proliferation and migration. Let-7b knockout mitigated right ventricle hypertrophy and pulmonary vessel remodeling in HPH by restoring ACE2 expression. Overall, we demonstrated that HIF-1α inhibited ACE2 expression via the HIF-1α-let-7b-ACE2 axis, which contributed to the pathogenesis of HPH by stimulating PASMCs proliferation and migration. Since let-7b knockout alleviated the development of HPH, let-7b may serve as a potential clinical target for the treatment of HPH.