N6-methyladenosine-driven miR-143/145-KLF4 circuit orchestrates the phenotypic switch of pulmonary artery smooth muscle cells.

Pulmonary hypertension (PH) is characterized by vascular remodeling predominantly driven by a phenotypic switching in pulmonary artery smooth muscle cells (PASMCs). However, the underlying mechanisms for this phenotypic alteration remain incompletely understood. Here, we identified that RNA methyltransferase METTL3 is significantly elevated in the lungs of hypoxic PH (HPH) mice and rats, as well as in the pulmonary arteries (PAs) of HPH rats. Targeted deletion of Mettl3 in smooth muscle cells exacerbated hemodynamic consequences of hypoxia-induced PH and accelerated pulmonary vascular remodeling in vivo. Additionally, the absence of METTL3 markedly induced phenotypic switching in PASMCs in vitro. Mechanistically, METTL3 depletion attenuated m6A modification and hindered the processing of pri-miR-143/145, leading to a downregulation of miR-143-3p and miR-145-5p. Inhibition of hnRNPA2B1, an m6A mediator involved in miRNA maturation, similarly resulted in a significant reduction of miR-143-3p and miR-145-5p. We demonstrated that miR-145-5p targets Krüppel-like factor 4 (KLF4) and miR-143-3p targets fascin actin-bundling protein 1 (FSCN1) in PASMCs. The decrease of miR-145-5p subsequently induced an upregulation of KLF4, which in turn suppressed miR-143/145 transcription, establishing a positive feedback circuit between KLF4 and miR-143/145. This regulatory circuit facilitates the persistent suppression of contractile marker genes, thereby sustaining PASMC phenotypic switch. Collectively, hypoxia-induced upregulation of METTL3, along with m6A mediated regulation of miR-143/145, might serve as a protective mechanism against phenotypic switch of PASMCs. Our results highlight a potential therapeutic strategy targeting m6A modified miR-143/145-KLF4 loop in the treatment of PH.

Exploring the Spectrum of Long Non-Coding RNA CARMN in Physiological and Pathological Contexts.

Cardiac mesoderm enhancer-associated non-coding RNA (CARMN), an evolutionarily conserved long non-coding RNA (lncRNA), serves as the host gene for the miR143/145 cluster. It plays a crucial role in cardiovascular cell differentiation and the maintenance of vascular smooth muscle cell (VSMC) homeostasis, which are vital for normal physiological processes. Specifically, CARMN is associated with the pathological progression of cardiovascular diseases such as atherosclerosis, abdominal aortic aneurysm, and chronic heart failure. Moreover, it acts as a tumor suppressor in various cancers, including hepatocellular carcinoma, bladder cancer, and breast cancer, highlighting its potential as a beneficial biomarker and therapeutic target. This review provides a detailed examination of the roles of CARMN, its evolutionary conservation, expression patterns, and regulatory mechanisms. It also outlines its significant implications in the diagnosis, prognosis, and treatment of these diseases, underscoring the need for further translational research to exploit its clinical potential.