MACF1结合CDK12参与模拟失重抑制骨形成的作用及机制

The gravity plays critical role in maintaining normal structure and function of bone. Weightlessness condition suppresses bone formation, resulting in weightlessness-induced bone loss. However, the mechanism of weightlessness inhibiting bone formation is still unclear. As a cytoskeletal crosslinking factor, MACF1 participates in simulated weightlessness inhibiting osteoblast differentiation and bone formation by regulating β-catenin - Runx2 signaling. Our recent advances showed that CDK12 was an interacting protein of MACF1 and silence of CDK12 promoted osteoblast differentiation. Besides, simulated weightlessness upregulated the expression of CDK12. Therefore, we propose that MACF1 regulates osteoblast differentiation by interacting with CDK12, thus participating in the inhibitory effect of simulated weightlessness on bone formation. Based on the previous research, this project will further investigate the following content at molecular, cellular and animal levels. (1) The effects of simulated weightlessness on bone formation, and the expression of MACF1 and CDK12; (2) The effects of simulated weightlessness on the interaction between MACF1 and CDK12, the interaction between CDK12 and Runx2, and the phosphorylation level of Runx2; (3) The rescue effects and mechanism of high expression of MACF1 on the decreased bone formation induced by simulated weightlessness. The objective of this project is to provide some new experimental evidence for deeply understanding the mechanism of weightlessness inhibiting bone formation, which results in weightlessness-induced bone loss and also to provide new vision for the prevention and therapy of osteoporosis related bone diseases.

重力对于维持骨骼的正常结构功能起重要作用。失重环境抑制骨形成，导致失重性骨质流失，但是其具体机制尚不明确。MACF1作为一种细胞骨架交联分子，通过调节β-catenin - Runx2信号转导，参与模拟失重抑制成骨细胞分化与骨形成。我们新近研究发现：CDK12是MACF1的互作蛋白，CDK12低表达促进成骨细胞分化，且模拟失重上调CDK12表达。因此提出：MACF1可能通过结合CDK12调节成骨分化参与模拟失重抑制骨形成过程。本项目拟从分子、细胞及整体动物水平，研究：(1)模拟失重对骨形成，MACF1、CDK12表达的影响；(2)模拟失重对MACF1与CDK12，CDK12与Runx2相互作用，以及对Runx2磷酸化的影响；(3)MACF1高表达对模拟失重抑制骨形成的挽救作用及其机制。为深入理解失重抑制骨形成导致骨质流失的作用机制提供新的实验依据，并为骨质疏松症等疾病的防治研究提供新思路。

本项目围绕“失重抑制骨形成的作用机制”这一航天医学与空间生物学研究领域的重要科学问题，以 “微管微丝交联因子1(microtubule actin crosslinking factor 1，MACF1)”为切入点，从分子、细胞、整体动物水平，深入研究MACF1及其互作分子CDK12在模拟失重抑制骨形成中的作用及机制。本项目主要研究内容包括：(1)模拟失重对骨形成、MACF1、CDK12表达的影响；(2)模拟失重对MACF1与CDK12，CDK12与Runx2相互作用，以及对Runx2磷酸化的影响；(3)MACF1高表达对模拟失重抑制骨形成的挽救作用及其机制。获得主要研究结果如下：(1)模拟失重条件抑制成骨细胞增殖、成骨细胞分化与小鼠骨形成，并下调骨组织中MACF1表达，而上调骨组织中CDK12表达，有趣的是，模拟失重条件抑制增殖期成骨细胞中CDK12的表达，而促进成骨分化期成骨细胞中CDK12的表达；(2)MACF1在成骨细胞响应模拟失重条件中起重要作用，MACF1低表达成骨细胞对模拟失重条件不敏感；(3)CDK12低表达抑制成骨细胞增殖，而促进成骨细胞分化，CDK12高表达促进成骨细胞增殖；(4) MACF1高表达起到挽救模拟失重条件抑制骨形成的作用，而CDK12高表达起到挽救模拟失重条件抑制成骨细胞增殖的作用，抑制CDK12起到挽救模拟失重条件抑制成骨细胞分化的作用。本项目研究揭示了模拟失重抑制骨形成的新机制，对深入理解失重性骨质流失发生的分子机制具有重要的科学意义，并且为骨质疏松等骨疾病的防治研究提供了新靶点，具有防治航天员骨质流质与地面人群骨质疏松的潜在应用价值。