Mettl3-Mediated m6A Methylation of Pdgfrb Regulates the Angiogenesis-Dependent Bone Formation.

CD31hiEMCNhi (type H) vessels orchestrate the bone metabolic microenvironment, yet the epigenetic control of their endothelial identity remains unclear. N6-methyladenosine (m6A), catalyzed by Mettl3, is essential for mRNA fate and emerging as a regulator of skeletal homeostasis. After isolating and validating type H bone microvascular endothelial cells (H-BMECs) from mouse femora, we used lentiviral shRNA and endothelial-specific Cdh5-Cre;Mettl3fl/fl mice to silence Mettl3 in vitro and in vivo. m6A-seq and RNA-seq pinpointed downstream targets; qPCR, Western blot, MeRIP-qPCR, RNA stability, migration, and tube formation assays dissected mechanisms. Local platelet-derived growth factor-BB (PDGF-BB) administration was employed to rescue Mettl3-null phenotypes. Mettl3 expression and global m6A levels were reduced in ovariectomy-induced osteoporosis. Knock-down or genetic deletion of Mettl3 decreased m6A methylation within the 3'UTR of Pdgfrb, accelerated Pdgfrb mRNA decay, blunted PI3K/AKt signaling and impaired H-BMEC proliferation, migration and tube formation. Consequently, type H vessels and trabecular bone mass were markedly diminished. PDGF-BB ligand delivery restored Pdgfrb abundance, reactivated PI3K/AKt, and fully reversed vascular and skeletal defects in Mettl3-null mice. Mettl3-mediated m6A methylation preserves Pdgfrb mRNA stability in bone endothelial cells and is associated with the maintenance of type H vessels, thereby coupling angiogenesis to bone formation. Targeting the Mettl3-m6A-Pdgfrb/PI3K-AKt axis may represent a potential therapeutic strategy for estrogen-deficiency-induced bone loss.