circMFN2 Regulates the IGF2BP3-PDK4 to Ameliorate Pulmonary Hypertension

BACKGROUND: Circular RNAs have emerged as key regulators of vascular remodeling and promising therapeutic targets, yet their specific contributions to pulmonary hypertension (PH) remain largely unknown. METHODS: We identified a PH-related circular RNA, circMFN2, generated from the MFN2 (mitofusin-2) locus, which was significantly downregulated in the peripheral blood of patients with PH and in pulmonary arteries of Sugen/hypoxia-induced PH mice. Functional studies were performed in human pulmonary artery smooth muscle cells under hypoxic conditions and in Sugen/hypoxia mice treated intranasally with R8-circMFN2 (R8-peptide-modified liposomal circMFN2). Transcriptomic profiling, RNA-protein interaction assays, and mitochondrial function analyses were used to define the downstream mechanisms. RESULTS: circMFN2 overexpression significantly attenuated hypoxia-induced human pulmonary artery smooth muscle cell proliferation, migration, and mitochondrial dysfunction. RNA sequencing after circMFN2 knockdown revealed activation of gene networks associated with respiratory system diseases. Mechanistically, circMFN2 directly bound the RNA-binding protein IGF2BP3 (insulin-like growth factor 2 mRNA-binding protein 3), thereby blocking its stabilization of PDK4 (pyruvate dehydrogenase kinase 4) mRNA. This circMFN2-IGF2BP3-PDK4 regulatory axis limited PDK4-mediated metabolic reprogramming, restored mitochondrial fusion, reduced reactive oxygen species, and normalized oxidative phosphorylation. In Sugen/hypoxia mice, therapeutic intranasal delivery of R8-circMFN2 significantly improved pulmonary hemodynamics, reduced vascular remodeling, and downregulated PDK4 expression. CONCLUSIONS: circMFN2 functions as a hypoxia-responsive regulator that preserves mitochondrial homeostasis by restraining the IGF2BP3-PDK4 axis. Intranasal delivery of R8-circMFN2 establishes a translational potential for noninvasive circular RNA-based therapy to reverse pulmonary vascular remodeling and hemodynamic impairment in PH.