The Role And Underlying Mechanism Of FGF18 And Osteocalcin In The Progression Of Parkinson’s Disease

Objective The aim of this study is to investigate the role of bone metabolism-related proteinsfibroblast growth factor 18(FGF18)and osteocalcin in the pathogenesis of Parkinson’s disease(PD)and its corresponding protective mechanism.Methods In the experiments where 6-OHDA was injected into the right striatum at one-point,FGF18 and osteocalcin were administered into the rigt striatum of SD rats 4 hours before injection of 6-OHDA.In the experiments where 6-OHDA was injected into the right medial forebrain bundle at two-point,osteocalcin was administrated through enterocoelia 2 days before the injection of 6-OHDA into SD rats,and lastfor one week.An open field test was performed one week prior to PD modeling to confirm that there was no significant difference in motor behavior among all the experimentalgroups at the baseline level.After intervention,the rats were subjected to open field test,cylinder test and elevated body swing test to investigate the movement state of the rats.The brain tissue was extracted and immunohistochemical staining on the tyrosine hydroxylase was performed.In the in vitro experiments,PC12 cells were used as cell model of PD to observe the protective effect of FGF18 or osteocalcin on PC12 cytotoxicity induced by 6-OHDA through applying the CCK8,flow cytometry and apoptotic protein detection test.To verify whether the AKT/GSK3β signaling pathway was served as a specific mechanism mediating FGF18 and osteocalcin neuroprotective effect by using the AKT/GSK3β corresponding inhibitor.Results The results from open filed test showed that there was no significant difference in motor behavior in SD rats among all the groups before injection of 6-OHDA,indicating aconsistent baseline.In the experiment where FGF18 and osteocalcin was injected into striatum,both FGF18 and osteocalcin were able to significantly alleviate 6-OHDA-induced motor impairment and improve the frequency of use of left and right forelimbs in 6-OHDA PD rats,but the difference was not statistical significantly.The immunohistochemical staining of tyrosine hydroxylase demonstrated that FGF18 and osteocalcin significantly alleviated the loss of dopaminergic neurons and fibers in the right substantia nigra and striatum system caused by 6-OHDA.In the experiment where osteocalcin intervention intraperitoneally,osteocalcin was able to significantly relieve the motor defective caused by 6-OHDA and was improve thefrequency of use of the left and right forelimbs of 6-OHDA rats in the cylinder experiment.The results of immunohistochemical staining illustrated that osteocalcin could reduce the loss of dopaminergic neurons in the right substantia nigra induced by 6-OHDA.The results from in vitro experiments showed that both FGF18 and osteocalcin played a protective effect on the neurotoxicity of PC12 cells induced by 6-OHDA via activating AKT/GSK3β signaling pathway.Conclusions Both FGF18 and steocalcin,two protein involved in bone metabolism,could ameliorate the pathogenesis of Parkinson’s disease through the activatin the AKT/GSK3β signaling pathway.Both peripheral administration of osteocalcin,and intra-striatumadministration of osteocalcin or FGF18 can significantly improve the motor function of Parkinson’s disease rats and inhibit the loss of dopaminergic neurons in the substantia nigra striatum system induced by 6-OHDA.The results from in vitro experiments showed that osteocalcin and FGF18 were involved in the protection of PC12 cells by activating AKT/GSK3β pathway.