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.

中文翻译：

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RUNX2在通过AKT / NFATc1 / CTSK轴调节破骨细胞分化中的新功能。

颅骨发育不良是由RUNX2突变引起的常染色体显性骨骼疾病。尚未报道RUNX2突变对破骨细胞生成和骨吸收的影响。为了研究RUNX2在破骨细胞中的作用，检测了RUNX2在巨噬细胞（RAW 264.7细胞）中的表达。建立了表达野生型RUNX2或突变的RUNX2的稳定RAW 264.7细胞系（c.514delT，p.172 fs），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-肌动蛋白环的形成和骨吸收，而突变体RUNX2减弱其正向分化作用。野生型RUNX2增加了mTORC2的表达和活性。随后，mTORC2特异性促进了丝氨酸473残基上AKT的磷酸化。活化的AKT改善了NFATc1的核转运，并增加了下游基因（包括CTSK）的表达。AKT磷酸化的抑制作用废除了野生型巨噬细胞的破骨细胞形成，而组成型活化的AKT拯救了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轴促进破骨细胞生成和骨吸收。RUNX2突变体失去了调节破骨细胞分化和骨重塑的功能，导致了颅骨发育不良中牙齿萌发途径的缺陷形成和恒牙的撞击。这项研究首次验证了RUNX2对破骨细胞分化和骨吸收的作用，并为解释颅骨发育不良提供了新的见识。