Shan Liying, Liao Xiaoxia, Yang Xiaoli, Zhu Endong, Yuan Hairui, Zhou Jie, Li Xiaoxia, Wang Baoli
NHC Key Lab of Hormones and Development and Tianjin Key Lab of Metabolic Diseases, Tianjin Medical University Chu Hsien-I Memorial Hospital & Institute of Endocrinology, Tianjin 300134, China.
College of Basic Medical Sciences, Tianjin Medical University, Tianjin 300070, China.
Genes Dis. 2024 Jan 12;12(1):101209. doi: 10.1016/j.gendis.2024.101209. eCollection 2025 Jan.
Naked cuticle homolog 2 (NKD2) has been recognized as an antagonist of Wnt/β-catenin signaling and a tumor suppressor. The role of NKD2 in osteoblast and osteoclast differentiation and the mechanism are not fully understood. In this study, we identified the up-regulation of NKD2 during osteoblast and adipocyte differentiation. Functional experiments revealed that NKD2 stimulated osteoblast differentiation and suppressed adipocyte formation. Furthermore, NKD2 down-regulated the expression of receptor activator of nuclear factor-κB ligand in bone marrow mesenchymal stem cells and inhibited osteoclast formation from osteoclast precursor cells. Mechanistic investigations revealed that the regulation of osteoblast and adipocyte differentiation by NKD2 involved Wnt/β-catenin and tuberous sclerosis complex subunit 1 (TSC1)/mechanistic target of rapamycin complex 1 (mTORC1) signaling pathways. Unlike in undifferentiated mesenchymal cells where NKD2 promoted Dishevelled-1 degradation, in the cells differentiating toward osteoblasts or adipocytes NKD2 down-regulated secreted frizzled related protein 1/4 expression and failed to destabilize Dishevelled-1, thereby activating Wnt/β-catenin signaling. Moreover, NKD2 bound to TSC1 and inhibited mTORC1 signaling. Further investigation uncovered an interplay between TSC1/mTORC1 and Wnt/β-catenin signaling pathways. Finally, transplantation of NKD2-overexpressing bone marrow mesenchymal stem cells into the marrow of mice increased osteoblasts, reduced osteoclasts and marrow fat, and partially prevented bone loss in ovariectomized mice. This study provides evidence that NKD2 in mesenchymal stem/progenitor cells reciprocally regulates the differentiation of osteoblasts and adipocytes by modulating Wnt/β-catenin and mTORC1 pathways and inhibits osteoclast formation by down-regulating receptor activator of nuclear factor-κB ligand. It suggests that NKD2 up-regulation may ameliorate postmenopausal bone loss.
裸角质同源物2（NKD2）已被公认为是Wnt/β-连环蛋白信号通路的拮抗剂和肿瘤抑制因子。NKD2在成骨细胞和破骨细胞分化中的作用及其机制尚未完全明确。在本研究中，我们发现NKD2在成骨细胞和脂肪细胞分化过程中表达上调。功能实验表明，NKD2可促进成骨细胞分化并抑制脂肪细胞形成。此外，NKD2可下调骨髓间充质干细胞中核因子κB受体活化因子配体的表达，并抑制破骨细胞前体细胞向破骨细胞的分化。机制研究表明，NKD2对成骨细胞和脂肪细胞分化的调节涉及Wnt/β-连环蛋白和结节性硬化复合物亚基1（TSC1）/雷帕霉素靶蛋白复合物1（mTORC1）信号通路。与在未分化的间充质细胞中NKD2促进Dishevelled-1降解不同，在向成骨细胞或脂肪细胞分化的细胞中，NKD2下调分泌型卷曲相关蛋白1/4的表达，且未能使Dishevelled-1不稳定，从而激活Wnt/β-连环蛋白信号通路。此外，NKD2与TSC1结合并抑制mTORC1信号通路。进一步研究发现TSC1/mTORC1与Wnt/β-连环蛋白信号通路之间存在相互作用。最后，将过表达NKD2的骨髓间充质干细胞移植到小鼠骨髓中，可增加成骨细胞数量，减少破骨细胞和骨髓脂肪，并部分预防去卵巢小鼠的骨质流失。本研究提供的证据表明，间充质干/祖细胞中的NKD2通过调节Wnt/β-连环蛋白和mTORC1通路，相互调节成骨细胞和脂肪细胞的分化，并通过下调核因子κB受体活化因子配体抑制破骨细胞形成。这表明NKD2表达上调可能改善绝经后骨质流失。
