Brockhaus Katrin, Hemsen Isabel, Jauch-Speer Saskia-Larissa, Niland Stephan, Vogl Thomas, Eble Johannes A
Institute of Physiological Chemistry and Pathobiochemistry, University of Münster, Münster, Germany.
Institute of Immunology, University of Münster, Münster, Germany.
Front Cell Dev Biol. 2024 Aug 15;12:1448725. doi: 10.3389/fcell.2024.1448725. eCollection 2024.
Osteoclasts determine bone tissue turnover. Their increased activity causes osteoporosis, their dysfunction osteopetrosis.
Murine monocytic ER-Hoxb8 cells differentiate into OCs upon treatment with M-CSF and RANKL and upregulate the collagen-binding integrin α2β1 distinctly earlier than other OC markers, such as the OC-associated receptor, OSCAR. Integrin α2β1 promotes OC differentiation at multiple levels by stimulating differentiation-relevant genes, by regulating cell matrix adhesion and the formation of adhesion-promoting protrusions, and by the upregulation of proteins involved in precursor cell fusion. The two key factors in osteoclastogenesis, RANK and NFATc1, were essentially unaffected after knocking out the ITGA2 gene encoding integrin α2 subunit. However, compared to integrin α2β1 expressing ER-Hoxb8 cells, ITGA2-deficient cells adhered differently with more branched filopodia and significantly longer tunneling nanotubes. Despite the higher number of fusion-relevant TNTs, they form fewer syncytia. They also resorb less hydroxyapatite, because integrin α2β1 regulates expression of lacuna proteins necessary for bone matrix resorption. The impaired syncytia formation of ITGA2-deficient OC precursor cells also correlated with reduced gene activation of fusion-supporting DC-STAMP and with an almost abolished transcription of tetraspanin CD9. CD9 only partially colocalized with integrin α2β1 in TNTs and filopodia of integrin α2β1-expressing OC precursors.
Our findings define integrin α2β1 as an early marker of OC differentiation.
破骨细胞决定骨组织的更新。其活性增加会导致骨质疏松，功能障碍则会导致骨质石化。
小鼠单核细胞系ER-Hoxb8细胞在接受M-CSF和RANKL处理后分化为破骨细胞，并比其他破骨细胞标志物（如破骨细胞相关受体OSCAR）更早地显著上调胶原结合整合素α2β1。整合素α2β1通过刺激与分化相关的基因、调节细胞与基质的黏附以及促进黏附的突起的形成，以及上调参与前体细胞融合的蛋白质，在多个水平上促进破骨细胞分化。在敲除编码整合素α2亚基的ITGA2基因后，破骨细胞生成的两个关键因子RANK和NFATc1基本未受影响。然而，与表达整合素α2β1的ER-Hoxb8细胞相比，缺乏ITGA2的细胞黏附方式不同，丝状伪足更多分支，隧道纳米管明显更长。尽管与融合相关的隧道纳米管数量更多，但它们形成的多核巨细胞更少。它们对羟基磷灰石的吸收也更少，因为整合素α2β1调节骨基质吸收所需的腔隙蛋白的表达。缺乏ITGA2的破骨细胞前体细胞多核巨细胞形成受损还与融合支持蛋白DC-STAMP的基因激活减少以及四跨膜蛋白CD9的转录几乎完全消失有关。在表达整合素α2β1的破骨细胞前体细胞的隧道纳米管和丝状伪足中，CD9仅部分与整合素α2β1共定位。
我们的研究结果将整合素α2β1定义为破骨细胞分化的早期标志物。
