Changes Of Bone, Glucose And Lipid Homeostasis In OPG-deficiency Mice

Part one Zoledronate reverses mandibular bone loss in OPG-deficient miceObject:The study aimed to characterize both the changes in the mandible in osteoprotegerin-deficient mice(OPG^-/-) and the possibly preventable effect on mandibular bone loss by Zoledronate.Methods:Twenty eight six-week female mice including OPG^-/- (n=21) and wild-type(WT)(n=7) were assigned to four groups:wild mice with vehicle(WT);OPG^-/- mice with vehicle(OPG^-/-);OPG^-/- mice, and subcutaneously injected 50 or 150μg/kg Zoledronate(Zol-50μg, Zol-150μg).They were sacrificed after 4 weeks of treatments.Serum was harvested for biochemical analysis.The right mandible and tibia were prepared for micro-CT analysis.Student's t-test was performed for the comparisons of bone parameters between different sites in WT group. Analysis of variance(ANOVA) was used to compare the biomarkers and bone parameters.Results:The serum B-ALP and TRAP-5b were significantly decreased in WT mice as compared to OPG^-/- mice(P＜0.05).High serum B-ALP activity in OPG^-/- mice treated with Zoledreonate was inhibited. There were greater variations in BMD and microstructure between mandibular and proximal tibia trabeculae.Mandibular bone loss was less affected by OPG gene deprivation in comparison with proximal tibia. Mice treated with low and high dosage of Zoledreonate had both a greater trabecular BV/TV,Tb.Th,Tb.N as well as Conn.D,and a significant decrease in BS/BV,Tb.Sp and SMI as compared to OPG^-/- mice(P＜0.05). However,higher apparent BMD and more compacted plate-like trabeculae treated by Zoledronate were observed in mandible as comparison to proximal tibia.No significant differences were found in all the parameters between both Zol groups.Conclusions:The present study showed that Zoledronate could reverse mandible bone loss induced by OPG-gene deficiency.This preventable effect was accompanied with a severe inhibition of bone turnover rate,indicating that the risk of jaw osteonecrosis may develop when it was long-term used. Part two Changes of glucose and lipid homeostasis in OPG-deficiency miceObject:To study the effect of OPG deletion on TG,TC,HDL,LDL, FFA,blood glucose and insulin secretion.Methods:10-week-old(n=8) and 20-week-old(n=8) male OPG-deficient mice(OPG^-/-),as well as 8 age-matched male wild type (WT) littermates were involved in the study.Adipose index,TG,TC, HDL,LDL,FFA,blood glucose and insulin level were determined. Intraperitoneal glucose tolerance test(IPGTT),insulin tolerance test (ITT),and acute insulin release test(AIRT) were used to evaluate the glucose disposal and insulin sensitivity.The ultrastructural property of the pancreatic isletβ-cells was investigated.In addition,the effect of RANKL on differentiation of primary brown adipocyte was explored in vitro.Results:OPG^-/- mice had a lower concentration of non-fasting and fasting blood glucose,blood triglyceride and FFA with a higher adipose index compared with WT mice(P＜0.05).At 15 and 30 min of IPGTT, 10-week-old OPG^-/- mice showed a significantly lower blood glucose concentration than 20-week-old OPG^-/- mice(P＜0.05).Both 10-week-old OPG^-/- and 20-week-old OPG^-/- mice presented significantly lower blood glucose concentrations than age-matched WT mice at all time points from 15 min to 120 min of IPGTT(P＜0.05).At 2 and 5 min in AIRT,OPG^-/- mice showed higher insulin levels than WT mice(P＜0.05).20-week-old OPG^-/- mice had a higher glucose concentration compared with WT mice to ITT response(P＜0.05),suggesting that insulin resistance was developed in OPG^-/- mice.Electron-density of dense core in the secretory granule decreased in OPG^-/- mice isletβ-cells,which may involved in an increase in non-fasting insulin level in OPG^-/- mice.Higher RNAKL level was observed in OPG^-/- mice than WT mice,and RANKL increased the PPAR_γexpression and intracellular fat accumulation during differentiation of primary brown adipocyte in vitro.Conclusions:OPG^-/- mice showed a disturbant profile of lipid and glucose metabolism,and abnormal isletβ-cell degranulation.It is suggested that OPG may contribute to the glucose-lipid homeostasis by promotion of adipose tissue lipolysis and regulation of isletβ-cell function. Part three High fat/carbohydrate diet induced hyperglycaemia and insulin resistance in OPG-deficient miceObject:To explore the effect of high fat/carbohydrate diet on TG, TC,HDL,LDL,FFA and blood glucose metabolism in OPG-deficient mice.Method:10-week-old OPG-deficient(OPG^-/-) and age-matched wild-type(WT) male mice were involved in the study.OPG^-/- and WT mice were randomly divided into groups of control(n=8,n=8; respectively) and high fat/carbohydrate diet(HD)(n=9,n=9; respectively).After 16 weeks of treatment with control diet or HD,body weight,adipose index,TG,TC,HDL,LDL,FFA,blood glucose and insulin level in OPG^-/- mice were compared with WT mice. Intraperitoneal glucose tolerance test(IPGTT),insulin tolerance test (ITT),and acute insulin release test(AIRT) were used to evaluate the changes of glucose disposal and insulin sensitivity.Results:Body weight gain was similar in the OPG^-/- and WT mice fed with HD.Serum TG and FFA levels showed no changes in OPG^-/- mice after fed with HD and were lower than that in HD-fed WT mice. However,adipose index was significantly increased in HD-fed OPG^-/- mice than HD-fed WT littlemates.After fed with HD,OPG^-/- mice showed a higher glucose concentration than HD-fed WT mice during IPGTT and ITT,and displayed severely impaired insulin release compared to WT mice with HD.Conclusions:High fat/carbohydrate diet can induce hyperglycemia and insulin resistance in OPG-deficient mice.OPG may favorite the insulin sensitivity and acute insulin release,and a high serum OPG level may be the consequence of physiological compensation to high blood glucose.