Department of Preventive Dentistry, Peking University School and Hospital of Stomatology & National Clinical Research Center for Oral Diseases & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, People's Republic of China.
Central Laboratory, Department of Oral and Maxillofacial Surgery, Peking University School and Hospital of Stomatology & National Clinical Research Center for Oral Diseases & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, People's Republic of China.
Calcif Tissue Int. 2020 May;106(5):553-566. doi: 10.1007/s00223-020-00666-7. Epub 2020 Feb 1.
Cleidocranial dysplasia is an autosomal dominant skeletal disorder resulting from RUNX2 mutations. The influence of RUNX2 mutations on osteoclastogenesis and bone resorption have not been reported. To investigate the role of RUNX2 in osteoclast, RUNX2 expression in macrophages (RAW 264.7 cells) was detected. Stable RAW 264.7 cell lines expressing wild-type RUNX2 or mutated RUNX2 (c.514delT, p.172 fs) were established, and their functions in osteoclasts were investigated. Wild-type RUNX2 promoted osteoclast differentiation, formation of F-actin ring, and bone resorption, while mutant RUNX2 attenuated the positive differentiation effect. Wild-type RUNX2 increased the expression and activity of mTORC2. Subsequently, mTORC2 specifically promoted phosphorylation of AKT at the serine 473 residue. Activated AKT improved the nuclear translocation of NFATc1 and increased the expression of downstream genes, including CTSK. Inhibition of AKT phosphorylation abrogated the osteoclast formation of wild-type macrophages, whereas constitutively activated AKT rescued the osteoclast formation of mutant macrophages. The present study suggested that RUNX2 promotes osteoclastogenesis and bone resorption through the AKT/NFATc1/CTSK axis. Mutant RUNX2 lost the function of regulating osteoclast differentiation and bone remodeling, resulting in the defective formation of the tooth eruption pathway and impaction of permanent teeth in cleidocranial dysplasia. This study, for the first time, verifies the effect of RUNX2 on osteoclast differentiation and bone resorption and provides new insight for the explanation of cleidocranial dysplasia.
颅锁骨发育不全是一种常染色体显性骨骼疾病，由 RUNX2 突变引起。RUNX2 突变对破骨细胞形成和骨吸收的影响尚未报道。为了研究 RUNX2 在破骨细胞中的作用，检测了巨噬细胞（RAW 264.7 细胞）中 RUNX2 的表达。建立了稳定表达野生型 RUNX2 或突变型 RUNX2（c.514delT，p.172fs）的 RAW 264.7 细胞系，并研究了它们在破骨细胞中的功能。野生型 RUNX2 促进破骨细胞分化、F-肌动蛋白环形成和骨吸收，而突变型 RUNX2 减弱了阳性分化作用。野生型 RUNX2 增加了 mTORC2 的表达和活性。随后，mTORC2 特异性促进 AKT 丝氨酸 473 残基的磷酸化。激活的 AKT 改善 NFATc1 的核易位，并增加下游基因包括 CTSK 的表达。抑制 AKT 磷酸化可消除野生型巨噬细胞的破骨细胞形成，而组成型激活 AKT 可挽救突变型巨噬细胞的破骨细胞形成。本研究表明，RUNX2 通过 AKT/NFATc1/CTSK 轴促进破骨细胞形成和骨吸收。突变型 RUNX2 丧失了调节破骨细胞分化和骨重塑的功能，导致牙萌出途径缺陷和颅锁骨发育不全中恒牙阻生。本研究首次验证了 RUNX2 对破骨细胞分化和骨吸收的影响，为解释颅锁骨发育不全提供了新的见解。
