Brain calcification‐associated JAM2 pathogenic mutations impair JAM2 – JAM3 tight junction structure and the blood–brain barrier integrity

Abstract

Abstract Primary brain calcification (PBC) is a neurodegenerative disorder characterized by bilateral brain calcification. JAM2 is a PBC causative gene, encoding the tight junction protein JAM2 and critical for blood–brain barrier (BBB) integrity, with an uncertain pathogenic mechanism. We analyzed two JAM2 missense mutations identified in PBC patients using plasmid constructs, immunoprecipitation, flow cytometry, and structural modeling. A Jam2 knockout (KO) mouse model was generated to assess behavioral deficits, brain calcification, and BBB integrity via histology, Evans blue assay, and in situ hybridization. JAM2‐ W108C mutants showed abnormal localization, while JAM2 ‐R108H specifically disrupted JAM2–JAM3 interaction, mirroring the pathogenic JAM3‐E116K mutation. Jam2 KO mice exhibited midbrain calcification (von Kossa staining) and motor impairments (rotarod/beam‐walking tests) at 6–12 months. JAM2 and JAM3 co‐localized in brain endothelial cells, and KO mice demonstrated BBB leakage (Evans blue extravasation). The main pathogenic mechanism of JAM2 ‐PBC should be associated with the impaired JAM2–JAM3 heterodimer formation, compromising tight junctions and BBB integrity. Our study indicates JAM2–JAM3 interaction as a potential therapeutic target for PBC and related brain calcification disorders.