University of Ulsan College of Medicine, Asan Medical Center, and Yonsei University College of Medicine, Seoul, Republic of Korea.
University of Ulsan College of Medicine and Asan Medical Center, Seoul, Republic of Korea.
Arthritis Rheumatol. 2020 May;72(5):750-760. doi: 10.1002/art.41180. Epub 2020 Mar 30.
Increased protein phosphatase magnesium-dependent 1A (PPM1A) levels in patients with ankylosing spondylitis regulate osteoblast differentiation in bony ankylosis; however, the potential mechanisms that regulate osteoclast differentiation in relation to abnormal bone formation remain unclear. This study was undertaken to investigate the relationship of PPM1A to osteoclast differentiation by generating conditional gene-knockout (PPM1A ;LysM-Cre) mice and evaluating their bone phenotype.
The bone phenotypes of LysM-Cre mice (n = 6) and PPM1A ;LysM-Cre mice (n = 6) were assessed by micro-computed tomography. Osteoclast differentiation was induced by culturing bone marrow-derived macrophages in the presence of RANKL and macrophage colony-stimulating factor (M-CSF), and was evaluated by counting tartrate-resistant acid phosphatase-positive multinucleated cells. Levels of messenger RNA for PPM1A, RANK, and osteoclast-specific genes were examined by real-time quantitative polymerase chain reaction, and protein levels were determined by Western blotting. Surface RANK expression was analyzed by fluorescence flow cytometry.
The PPM1A ;LysM-Cre mice displayed reduced bone mass (P < 0.001) and increased osteoclast differentiation (P < 0.001) and osteoclast-specific gene expression (P < 0.05) compared with their LysM-Cre littermates. Mechanistically, reduced PPM1A function in osteoclast precursors in PPM1A ;LysM-Cre mice induced osteoclast lineage commitment by up-regulating RANK expression (P < 0.01) via p38 MAPK activation in response to M-CSF. PPM1A expression in macrophages was decreased by Toll-like receptor 4 activation (P < 0.05). The Ankylosing Spondylitis Disease Activity Score was negatively correlated with the expression of PPM1A in peripheral blood mononuclear cells from patients with axial spondyloarthritis (SpA) (γ = -0.7072, P < 0.0001).
The loss of PPM1A function in osteoclast precursors driven by inflammatory signals contributes to osteoclast lineage commitment and differentiation by elevating RANK expression, reflecting a potential role of PPM1A in dynamic bone metabolism in axial SpA.
强直性脊柱炎患者中蛋白磷酸酶镁依赖性 1A（PPM1A）水平升高可调节骨强直中的成骨细胞分化；然而，与异常骨形成相关的调节破骨细胞分化的潜在机制尚不清楚。本研究旨在通过生成条件性基因敲除（PPM1A；LysM-Cre）小鼠并评估其骨表型来研究 PPM1A 与破骨细胞分化的关系。
通过微计算机断层扫描评估 LysM-Cre 小鼠（n=6）和 PPM1A；LysM-Cre 小鼠（n=6）的骨表型。通过在核因子-κB 受体活化因子配体（RANKL）和巨噬细胞集落刺激因子（M-CSF）存在的情况下培养骨髓来源的巨噬细胞来诱导破骨细胞分化，并通过计数抗酒石酸酸性磷酸酶阳性多核细胞来评估。通过实时定量聚合酶链反应检测 PPM1A、RANK 和破骨细胞特异性基因的信使 RNA 水平，并通过 Western 印迹法测定蛋白水平。通过荧光流式细胞术分析表面 RANK 表达。
与 LysM-Cre 同窝仔相比，PPM1A；LysM-Cre 小鼠表现出骨量减少（P<0.001）、破骨细胞分化增加（P<0.001）和破骨细胞特异性基因表达增加（P<0.05）。机制上，PPM1A；LysM-Cre 小鼠中破骨细胞前体中 PPM1A 功能降低，通过激活 p38 MAPK 上调 RANK 表达（P<0.01），从而诱导破骨细胞谱系的定向分化，对 M-CSF 作出反应。Toll 样受体 4 激活（P<0.05）可降低巨噬细胞中的 PPM1A 表达。来自轴性脊柱关节炎（SpA）患者的外周血单个核细胞中 PPM1A 的表达与 Ankylosing Spondylitis Disease Activity Score 呈负相关（γ=-0.7072，P<0.0001）。
炎症信号驱动的破骨细胞前体中 PPM1A 功能丧失通过升高 RANK 表达促进破骨细胞谱系的定向分化和分化，反映了 PPM1A 在轴性 SpA 中动态骨代谢中的潜在作用。
