TMEM232 associates with the IP3R3-GRP75-VDAC1 complex to enhance ER-Mitochondrial calcium transfer and impair tight junctions in atopic dermatitis

Atopic dermatitis (AD) is a chronic skin disease characterized by genetically mediated inflammation and skin barrier dysfunction. Transmembrane protein 232 ( TMEM232 ) is a susceptibility gene for AD. This study aimed to explore TMEM232’s role and mechanism in AD barrier dysfunction. AD skin samples, primary keratinocytes, and human adult low-calcium cutaneous keratinocytes were used to investigate the role of TMEM232 in tight junction (TJ) regulation. Protein associations were analyzed by co-immunoprecipitation, proximity ligation assay and immunofluorescence colocalization. Endoplasmic reticulum (ER) and mitochondrial calcium ion (Ca 2+ ) dynamics were monitored with Mag-Fluo-4 and Rhod-2. TJ function was assessed by transepithelial electrical resistance and permeability assays. Tmem232 knockout mice and locally used si- Tmem232 were employed to investigate TMEM232’s role in vivo. TMEM232 expression was significantly upregulated in AD lesions and positively correlated with TJ dysfunction. Mechanistically, TMEM232 was predominantly localized to the perinuclear region and enriched at mitochondria-associated endoplasmic reticulum membranes (MAMs), which serve as hubs for Ca 2+ transfer. TMEM232 overexpression decreased ER Ca 2+ levels and increased mitochondrial Ca 2+ accumulation by associating with the inositol 1,4,5-trisphosphate receptor 3 (IP3R3)-glucose-regulated protein 75 (GRP75)-voltage-dependent anion channel 1 (VDAC1) complex and promoting its assembly. This Ca 2+ dysregulation subsequently triggered ER stress and increased both mitochondrial superoxide and total intracellular reactive oxygen species levels. Disruption of the IP3R3-GRP75-VDAC1 complex or alleviation of ER stress effectively rescued TMEM232 induced TJ impairment. In vivo, Tmem232 knockout and topical small interfering RNA-mediated knockdown both ameliorated AD-like dermatitis in a 2,4-dinitrobenzene-induced mouse model. Our findings demonstrate that TMEM232 impairs epidermal TJ integrity in AD by promoting IP3R3-GRP75-VDAC1 complex assembly, which enhances ER-mitochondrial Ca 2+ transfer and leads to ER stress and elevated mitochondrial oxidative stress. Targeting TMEM232 represents a potential therapeutic strategy for AD.