Osteogenesis Imperfecta (OI) is a heritable collagen-related bone dysplasia characterized by bone fractures, growth deficiency and skeletal deformity. Type XIV OI is a recessive OI form caused by null mutations in TMEM38B, which encodes the ER membrane intracellular cation channel TRIC-B. Previously, we showed that absence of TMEM38B alters calcium flux in the ER of OI patient osteoblasts and fibroblasts, which further disrupts collagen synthesis and secretion. How the absence of TMEM38B affects osteoblast function is still poorly understood. Here we further investigated the role of TMEM38B in human osteoblast differentiation and mineralization. TMEM38B-null osteoblasts showed altered expression of osteoblast marker genes and decreased mineralization. RNA-Seq analysis revealed that cell-cell adhesion was one of the most downregulated pathways in TMEM38B-null osteoblasts, with further validation by real-time PCR and Western blot. Gap and tight junction proteins were also decreased by TRIC-B absence, both in patient osteoblasts and in calvarial osteoblasts of Tmem38b-null mice. Disrupted cell adhesion decreased mutant cell proliferation and cell cycle progression. An important novel finding was that TMEM38B-null osteoblasts had elongated mitochondria with altered fusion and fission markers, MFN2 and DRP1. In addition, TMEM38B-null osteoblasts exhibited a significant increase in superoxide production in mitochondria, further supporting mitochondrial dysfunction. Together these results emphasize the novel role of TMEM38B/TRIC-B in osteoblast differentiation, affecting cell-cell adhesion processes, gap and tight junction, proliferation, cell cycle, and mitochondrial function.

成骨不全症（OI）是一种遗传性胶原相关骨发育不良，其特征是骨折、生长缺陷和骨骼畸形。XIV 型 OI 是由 TMEM38B 无效突变引起的隐性 OI 形式，TMEM38B编码 ER 膜细胞内阳离子通道 TRIC-B。此前，我们发现TMEM38B的缺失会改变成骨不全患者成骨细胞和成纤维细胞内质网中的钙通量，从而进一步破坏胶原蛋白的合成和分泌。TMEM38B的缺失如何影响成骨细胞功能仍知之甚少。在这里，我们进一步研究了TMEM38B在人成骨细胞分化和矿化中的作用。TMEM38B缺失的成骨细胞表现出成骨细胞标记基因的表达改变和矿化减少。RNA-Seq 分析表明，细胞间粘附是TMEM38B缺失的成骨细胞中下调幅度最大的途径之一，并通过实时 PCR 和蛋白质印迹进一步验证。在患者成骨细胞和Tmem38b缺失小鼠的颅骨成骨细胞中，间隙和紧密连接蛋白也因 TRIC-B 缺失而减少。细胞粘附破坏降低了突变细胞增殖和细胞周期进程。一项重要的新发现是，TMEM38B缺失的成骨细胞具有延长的线粒体，并且融合和裂变标记物 MFN2 和 DRP1 发生了改变。此外，TMEM38B缺失的成骨细胞表现出线粒体中超氧化物产量的显着增加，进一步支持线粒体功能障碍。这些结果共同强调了TMEM38B /TRIC-B 在成骨细胞分化中的新作用，影响细胞间粘附过程、间隙和紧密连接、增殖、细胞周期和线粒体功能。