Primary cilia are essential cellular organelles that are anchored at the cell surface membrane to sense and transduce signaling. Intraflagellar transport (IFT) proteins are indispensable for cilia formation and function. Although major advances in understanding the roles of these proteins in bone development have been made, the mechanisms by which IFT proteins regulate bone repair have not been identified. We investigated the role of the IFT80 protein in chondrocytes during fracture healing by creating femoral fractures in mice with conditional deletion of IFT80 in chondrocytes utilizing tamoxifen inducible Col2α1-CreER mice. Col2α1cre IFT80f/f mice had smaller fracture calluses than IFT80f/f (control) mice. The max-width and max-callus area were 31% and 48% smaller than those of the control mice, respectively. Col2α1cre IFT80f/f mice formed low-density/porous woven bony tissue with significantly lower ratio of bone volume, Trabecular (Tb) number and Tb thickness, and greater Tb spacing compared to control mice. IFT80 deletion significantly downregulated the expression of angiogenesis markers-VEGF, PDGF and angiopoietin and inhibited fracture callus vascularization. Mechanistically, loss of IFT80 in chondrocytes resulted in a decrease in cilia formation and chondrocyte proliferation rate in fracture callus compared to the control mice. Meanwhile, IFT80 deletion downregulated the TGF-β signaling pathway by inhibiting the expression of TGF-βI, TGF-βR, and phosphorylation of Smad2/3 in the fracture callus. In primary chondrocyte cultures in vitro, IFT80 deletion dramatically reduced chondrocyte proliferation, cilia assembly, and chondrogenic gene expression and differentiation. Collectively, our findings demonstrate that IFT80 and primary cilia play an essential role in fracture healing, likely through controlling chondrocyte proliferation and differentiation, and the TGF-β signaling pathway. © 2019 American Society for Bone and Mineral Research.

中文翻译：

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IFT80 通过控制软骨细胞分化和功能中 TGF-β 信号传导的调节来实现骨折愈合。


初级纤毛是重要的细胞器，锚定在细胞表面膜上以感知和转导信号传导。鞭毛内转运 (IFT) 蛋白对于纤毛的形成和功能是不可或缺的。尽管在理解这些蛋白质在骨发育中的作用方面已经取得了重大进展，但 IFT 蛋白质调节骨修复的机制尚未确定。我们通过使用他莫昔芬诱导的 Col2α1-CreER 小鼠条件性删除软骨细胞中的 IFT80，在小鼠中制造股骨骨折，研究了 IFT80 蛋白在骨折愈合过程中软骨细胞中的作用。 Col2α1cre IFT80f/f 小鼠的骨折愈伤组织比 IFT80f/f（对照）小鼠更小。最大宽度和最大愈伤组织面积分别比对照小鼠小 31% 和 48%。 Col2α1cre IFT80f/f 小鼠形成低密度/多孔编织骨组织，与对照小鼠相比，骨体积比、小梁 (Tb) 数量和 Tb 厚度显着降低，Tb 间距更大。 IFT80缺失显着下调血管生成标志物VEGF、PDGF和血管生成素的表达，并抑制骨折愈伤组织血管化。从机制上讲，与对照小鼠相比，软骨细胞中 IFT80 的缺失导致骨折愈伤组织中纤毛形成和软骨细胞增殖率降低。同时，IFT80缺失通过抑制骨折愈伤组织中TGF-βI、TGF-βR的表达和Smad2/3的磷酸化来下调TGF-β信号通路。在体外原代软骨细胞培养中，IFT80 缺失显着降低了软骨细胞增殖、纤毛组装以及软骨形成基因表达和分化。 总的来说，我们的研究结果表明，IFT80 和初级纤毛在骨折愈合中发挥着重要作用，可能是通过控制软骨细胞增殖和分化以及 TGF-β 信号通路来实现的。 © 2019 美国骨与矿物质研究学会。