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IFT80 is required for fracture healing through controlling the regulation of TGFβ signaling in chondrocyte differentiation and function

Authors
  • LIU, MIN1
  • ALHARBI, MOHAMMED2
  • GRAVES, DANA3
  • YANG, SHUYING1
  • 1 Dept. of Anatomy and Cell Biology, University of Pennsylvania, Philadelphia, PA
  • 2 Dept. of Endodontics, Faculty of Dentistry, King Abdulaziz University, Saudi Arabia
  • 3 Dept. of Periodontics, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA
Type
Published Article
Journal
Journal of Bone and Mineral Research
Publisher
Wiley (John Wiley & Sons)
Publication Date
Nov 22, 2019
Volume
35
Issue
3
Pages
571–582
Identifiers
DOI: 10.1002/jbmr.3902
PMID: 31643106
PMCID: PMC7525768
Source
PubMed Central
Keywords
License
Unknown

Abstract

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. Col2α1creIFT80f/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. Col2α1creIFT80f/f mice formed low-density/porous woven bony tissue with significantly lower ratio of bone volume, Trabecular (Tb) number, Tb thickness and greater Tb spacing compared to control mice. IFT80 deletion significantly down-regulated 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 down-regulated 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 the fracture healing, likely through controlling chondrocyte proliferation, differentiation and TGF-β signaling pathway.

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