Nogo-B Receptor Directs Mitochondria-Associated Membranes to Regulate Vascular Smooth Muscle Cell Proliferation

Mitochondria-associated membranes (MAM) are a well-recognized contact link between the mitochondria and endoplasmic reticulum that affects mitochondrial biology and vascular smooth muscle cells (VSMCs) proliferation via the regulation of mitochondrial Ca2+(Ca-m(2+)) influx. Nogo-B receptor (NgBR) plays a vital role in proliferation, epithelial-mesenchymal transition, and chemoresistance of some tumors. Recent studies have revealed that downregulation of NgBR, which stimulates the proliferation of VSMCs, but the underlying mechanism remains unclear. Here, we investigated the role of NgBR in MAM and VSMC proliferation. We analyzed the expression of NgBR in pulmonary arteries using a rat model of hypoxic pulmonary hypertension (HPH), in which rats were subjected to normoxic recovery after hypoxia. VSMCs exposed to hypoxia and renormoxia were used to assess the alterations in NgBR expression in vitro. The effect of NgBR downregulation and overexpression on VSMC proliferation was explored. The results revealed that NgBR expression was negatively related with VSMCs proliferation. Then, MAM formation and the phosphorylation of inositol 1,4,5-trisphosphate receptor type 3 (IP(3)R3) was detected. We found that knockdown of NgBR resulted in MAM disruption and augmented the phosphorylation of IP(3)R3 through pAkt, accompanied by mitochondrial dysfunction including decreased Ca-m,(2+) respiration and mitochondrial superoxide, increased mitochondrial membrane potential and HIF-1 nuclear localization, which were determined by confocal microscopy and Seahorse XF-96 analyzer. By contrast, NgBR overexpression attenuated IP(3)R3 phosphorylation and HIF-1 nuclear localization under hypoxia. These results reveal that dysregulation of NgBR promotes VSMC proliferation via MAM disruption and increased IP(3)R3 phosphorylation, which contribute to the decrease of Ca-m(2+) and mitochondrial impairment.