Knockdown Of Ggpsl In Chondrocyte Expedites Fracture Healing By Accelerating The Progression Of Endochondral Ossification In Mice

Objective:Statins,a class of 3-hydroxy-3-methylglutaryl(HMG)-CoA reductase inhibitors,have been widely used for the treatment of cardiovascular disease for decades.Researchers have reported that statins have strong effects on bone synthesis through the induction of Bmp2.Inhibition of Racl,which is regulated by geranylgeranyl diphosphate synthase 1(Ggps1),expression in chondrocyte culture reduces the mRNA levels of Sox 9,and influences the expression of chondrogenic matrix genes and glycosaminoglycan(GAG)accumulation.Accordingly,we would like to investigate the role of Ggpsl in bone fracture via endochondral ossification in mice.Methods:We used the Cre-loxP system,tamoxifen-inducible Collagen 2-CreERT2 Ggps1F1/F1,to specifically eliminate the Ggpsl activity in chondrocytes of 8-10 weeks old mice.Eight-to ten-week-old male Ggpsl-/-and strain-matched control mice were used as the bone fracture model.The embryonic skeletal were stained with Alcian blue and Alizarin red.Bone fracture tissues were analysed by histological,histomorphometric,western blot analysis,quantitative real-time polymerase chain reaction,micro-computed tomography imaging and radiography.To quantify mechanical strength,we harvested the femurs at 28 DPF.Numerical values for each measurement are shown as mean ± SE.P<0.05 was considered to represent statistical significance between mean values.Results:The histological analysis showed that the Cre-recombination efficiency was obvious in the callus tissue and Cre-recombination does not alter 10 and the expression of Ggpsl in other organs.Serial X-ray images analysis of fractured femurs in both groups revealed differences during the period of the fracture callus,which are consistent with micro-computed tomography imaging analysis.Endochondral bone formation and vasculogenesis were accelerated in the fractures of Ggpsl-/-mice.Meanwhile,Ggpsl mutant mice exhibited enhanced biomechanical properties in the newly formed bone.Bmp2 is an endogenous mediator regulatory protein molecule necessary for fracture repair.Conclusion:This study confirms that the specific deletion of Ggps1,using Collagen 2-CreERT2 mice,will accelerate the fracture healing process by activating the Bmp2/Smad-dependent Runx2 pathway.In addition,we were able to improve the fracture healing process by inhibiting the Ggpsl activity and its related products by statin drugs.