Werner Sherry L, Sharma Ramaswamy, Woodruff Kathleen, Horn Diane, Harris Stephen E, Gorin Yves, Lee Doug-Yoon, Hua Rui, Gu Sumin, Fajardo Roberto J, Habib Samy L, Jiang Jean X
Department of Pathology University of Texas Health Science Center at San Antonio TX USA.
Department of Cell Systems and Anatomy University of Texas Health Science Center at San Antonio TX USA.
JBMR Plus. 2019 Jun 13;4(7):e10080. doi: 10.1002/jbm4.10080. eCollection 2020 Jul.
CSF-1 is a key factor in regulating bone remodeling; osteocytes express CSF-1 and its receptor. Viable osteocytes are essential for bone remodeling through cell-cell contact and secretion of factors that regulate osteoblasts and osteoclasts. Increased oxidative stress contributes to osteocyte death and correlates with bone loss during aging. The NADPH oxidase Nox4 is a major source of ROS in bone. CSF-1 decreases Nox4, suggesting that CSF-1 protects against oxidative stress. Here, we show that osteocyte apoptosis previously reported in our global CSF-1KO mice is associated with increased Nox4, as well as 4-HNE expression in osteocytes. Osteocytes isolated from CSF-1KO mice were less viable and showed increased intracellular ROS, elevated NADPH oxidase activity/Nox4 protein, activation of mTOR/S6K, and downstream apoptosis signals compared with WT osteocytes. Nox4 expression was also increased in CSF-1KO osteocytes and colocalized with MitoTracker Red in mitochondria. Notably, CSF-1 inhibited Nox4 expression and apoptosis cascade signals. In additional studies, shNox4 decreased these signals in CSF-1KO osteocytes, whereas overexpression of Nox4 in WT osteocytes activated the apoptosis pathway. To determine the role of CSF-1 in osteocytes, DMP1Cre-CSF-1cKO (CSF-1cKO) mice that lack CSF-1 in osteocytes/late osteoblasts were developed. Osteocyte defects in CSF-1cKO mice overlapped with those in CSF-1KO mice, including increased apoptosis, Nox4, and 4-HNE-expressing osteocytes. CSF-1cKO mice showed unbalanced cancellous bone remodeling with decreased bone formation and resorption. Continued exposure to high Nox4/ROS levels may further compromise bone formation and predispose to bone loss and skeletal fragility. Taken together, our findings suggest a novel link between CSF-1, Nox4-derived ROS, and osteocyte survival/function that is crucial for osteocyte-mediated bone remodeling. Results reveal new mechanisms by which CSF-1/oxidative stress regulate osteocyte homeostasis, which may lead to therapeutic strategies to improve skeletal health in aging. © 2018 American Society for Bone and Mineral Research.
集落刺激因子-1（CSF-1）是调节骨重塑的关键因子；骨细胞表达CSF-1及其受体。存活的骨细胞对于通过细胞间接触以及分泌调节成骨细胞和破骨细胞的因子来进行骨重塑至关重要。氧化应激增加会导致骨细胞死亡，并与衰老过程中的骨质流失相关。NADPH氧化酶Nox4是骨骼中活性氧（ROS）的主要来源。CSF-1可降低Nox4水平，这表明CSF-1可抵御氧化应激。在此，我们发现，先前在我们的全身性CSF-1基因敲除（KO）小鼠中报道的骨细胞凋亡与Nox4增加以及骨细胞中4-羟基壬烯醛（4-HNE）表达增加有关。与野生型（WT）骨细胞相比，从CSF-1 KO小鼠分离出的骨细胞活力较低，且细胞内ROS增加、NADPH氧化酶活性/Nox4蛋白升高、雷帕霉素靶蛋白（mTOR）/核糖体蛋白S6激酶（S6K）激活以及下游凋亡信号增强。CSF-1 KO骨细胞中Nox4表达也增加，并与线粒体中的MitoTracker Red共定位。值得注意的是，CSF-1可抑制Nox4表达和凋亡级联信号。在进一步的研究中，短发夹RNA干扰Nox4（shNox4）可降低CSF-1 KO骨细胞中的这些信号，而在WT骨细胞中过表达Nox4则激活凋亡途径。为了确定CSF-1在骨细胞中的作用，我们构建了在骨细胞/晚期成骨细胞中缺乏CSF-1的DMP1 Cre-CSF-1条件性基因敲除（CSF-1 cKO）小鼠。CSF-1 cKO小鼠的骨细胞缺陷与CSF-1 KO小鼠的缺陷重叠，包括凋亡增加、Nox4增加以及表达4-HNE的骨细胞增加。CSF-1 cKO小鼠显示松质骨重塑失衡，骨形成和骨吸收减少。持续暴露于高水平的Nox4/ROS可能会进一步损害骨形成，并易导致骨质流失和骨骼脆弱。综上所述，我们的研究结果表明CSF-1、Nox4衍生的ROS与骨细胞存活/功能之间存在新的联系，这对于骨细胞介导的骨重塑至关重要。研究结果揭示了CSF-1/氧化应激调节骨细胞稳态的新机制，这可能会带来改善衰老过程中骨骼健康的治疗策略。©2018美国骨与矿物质研究学会。
