Choi Hyewon, Srikanth Sonal, Atti Elisa, Pirih Flavia Q, Nervina Jeanne M, Gwack Yousang, Tetradis Sotirios
Division of Oral Biology and Medicine, School of Dentistry, University of California at Los Angeles, 10833 Le Conte Ave., Los Angeles, CA 90095-1668, United States.
Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095-1751, United States.
Bone Rep. 2018 Apr 5;8:147-155. doi: 10.1016/j.bonr.2018.03.007. eCollection 2018 Jun.
Osteoblast lineage cells, a group of cells including mesenchymal progenitors, osteoblasts, and osteocytes, are tightly controlled for differentiation, proliferation and stage-specific functions in processes of skeletal development, growth and maintenance. Recently, the plasma membrane calcium channel Orai1 was highlighted for its role in skeletal development and osteoblast differentiation. Yet the roles of Orai1 in osteoblast lineage cells at various stages of maturation have not been investigated. Herein we report the severe bone loss that occurred in Orai1-/- mice, aggravated by aging, as shown by the microcomputed tomography (mCT) and bone histomorphometry analysis of 8-week and 12-week old Orai1-/- mice and sex-matched WT littermates. We also report that Orai1 deficiency affected the differentiation, proliferation, and type I collagen secretion of primary calvarial osteoblasts, mesenchymal progenitors, and osteocytes in Orai1-/- mice; specifically, our study revealed a significant decrease in the expression of osteocytic genes Fgf23, DMP1 and Phex in the cortical long bone of Orai1-/- mice; a defective cellular and nuclear morphology of Orai1-/- osteocytes; and defective osteogenic differentiation of Orai1-/- primary calvarial osteoblasts (pOBs), including a decrease in extracellular-secretion of type I collagen. An increase in the mesenchymal progenitor population of Orai1-/- bone marrow cells was indicated by a colony forming unit-fibroblasts (CFU-F) assay, and the increased proliferation of Orai1-/- pOBs was indicated by an MTT assay. Notably, Orai1 deficiency reduced the nuclear localization and transcription activity of the Nuclear Factor of Activated T-cell c1 (NFATc1), a calcium-regulated transcription factor, in pOBs. Altogether, our study demonstrated the crucial role of Orai1 in bone development and maintenance, its diverse effects on osteoblast lineage cells from mesenchymal progenitors to osteocytes.
成骨细胞谱系细胞，包括间充质祖细胞、成骨细胞和骨细胞，在骨骼发育、生长和维持过程中，其分化、增殖和阶段特异性功能受到严格调控。最近，质膜钙通道Orai1因其在骨骼发育和成骨细胞分化中的作用而受到关注。然而，Orai1在成骨细胞谱系细胞不同成熟阶段的作用尚未得到研究。在此，我们报告了Orai1基因敲除小鼠出现严重的骨质流失，且随着年龄增长而加剧，这通过对8周龄和12周龄的Orai1基因敲除小鼠及其性别匹配的野生型同窝小鼠进行微型计算机断层扫描（mCT）和骨组织形态计量学分析得以证实。我们还报告称，Orai1基因缺失影响了Orai1基因敲除小鼠原代颅骨成骨细胞、间充质祖细胞和骨细胞的分化、增殖及I型胶原蛋白分泌；具体而言，我们的研究显示，Orai1基因敲除小鼠皮质长骨中骨细胞基因Fgf23、DMP1和Phex的表达显著降低；Orai1基因敲除骨细胞的细胞和细胞核形态存在缺陷；Orai1基因敲除原代颅骨成骨细胞（pOBs）的成骨分化存在缺陷，包括I型胶原蛋白细胞外分泌减少。集落形成单位-成纤维细胞（CFU-F）试验表明Orai1基因敲除骨髓细胞中间充质祖细胞群体增加，MTT试验表明Orai1基因敲除pOBs增殖增加。值得注意的是，Orai1基因缺失降低了pOBs中钙调节转录因子活化T细胞核因子c1（NFATc1）的核定位和转录活性。总之，我们的研究证明了Orai1在骨骼发育和维持中的关键作用，以及它对从间充质祖细胞到骨细胞的成骨细胞谱系细胞的多种影响。
