Diabetes impairs fracture healing through disruption of cilia formation in osteoblasts

Diabetes-associated fracture risk and impaired fracture healing represents a serious health threat. It is well known that type 1 diabetes mellitus (T1DM) impairs fracture healing due to its effect on osteoblasts and their progenitor cells. Previous studies have showed that primary cilia and intraflagellar transport protein 80 (IFT80) are critical for bone formation. However, whether TIDM impairs fracture healing due to influencing ciliary gene expression and cilia formation is unknown. Here, we investigated the effect of T1DM on primary cilia in a streptozotocin induced diabetes mouse model and examined the impact of cilia on fracture healing in osteoblasts by deletion of IFT80 in osteoblast linage using osterix (OSX)-cre (OSX^cretTAIFT80^f/f). The results showed that diabetes inhibited ciliary gene expression and primary cilia formation to an extent that was similar to normoglycemic mice with IFT80 deletion. Moreover, diabetic mice and normoglycemic mice with cilia loss in osteoblasts (OSX^cretTAIFT80^f/f) both exhibited delayed fracture healing with significantly reduced bone density and mechanical strength as well as with reduced expression of osteoblast markers, decreased angiogenesis and proliferation of bone lining cells at the fracture sites. In vitro studies showed that advanced glycation end products (AGEs) downregulated IFT80 expression in osteoblast progenitors. Moreover, AGEs and IFT80 deletion significantly reduced cilia number and length which inhibited differentiation of primary osteoblast precursors. Thus, this study for the first time report that primary cilia are essential for bone regeneration during fracture healing and loss of cilia caused by diabetes in osteoblasts resulted in defective diabetic fracture healing.