The Role Of Autophagy In The Pathogenesis Of Glucocorticoid-induced Osteoporosis

Objective: To investigate the influence of glucocorticoid in osteoblast andto explore the role of autophagy in the pathogenesis of glucocorticoid-inducedosteoporosis. Methods: One hundred and twenty female3-month-old SD ratswere randomly divided into four groups, control group (CONT, saline)，low dosedexamethasone(Dex) group (LDG,1mg/kg), medium dose Dex group (MDG,2.5mg/kg) and high dose Dex group (HDG,5mg/kg). The rats were injectedintramuscularly twice a week, weighted once a week. Each group was inventedfor4weeks,9weeks and12weeks respectively. The BMD was measured at thebeginning and after the intervention by DXA densitometer. After the rats weresacrificed, the expression of LC3, Beclin1, Atg5, osteocalcin(OCN) and alkalinephosphatase （ALP） mRNA in osteoblast was measured by means of in situhybridization and the protein expression was measured by means ofimmunocytochemistry. The auphagy of osteoblast was observed by thetransmission electron microscope. Results：1.The body weight of rats in Contwas increased with time, the body weight of HDG group was decreased withtime. For four weeks, nine weeks or twelve weeks intervention, compared withCont,the body weight of Dex intervention groups was decreased （p＜0.05）,and the body weight of HDG was lower than the LDG and HDG.2.For4weeks intervention, compared with Cont, the BMD of Dexintervention groups had no significant difference（P＞0.05）, the there was no significant difference between Dex intervention groups（P＞0.05）. For9weeks intervention, compared with Cont, the BMD of Dex intervention groupswas decreased（P＜0.05）, there was no significant difference between Dexintervention groups（P＞0.05）. For12weeks intervention, compared withCont, the BMD of Dex intervention groups was decreased（P＜0.05）, and theBMD of HDG was lower than LDG and MDG.3. For4weeks intervention, compared with Cont, the expression of OCNmRNA, OCN protein, ALP mRNA, ALP protein in Dex intervention groupshad no significant difference （P＞0.05）, the expression of OCN mRNA, OCNprotein, ALP in mRNA, ALP protein in Dex intervention groups had nosignificant difference （P＞0.05）. For9weeks intervention, the expression ofOCN mRNA、OCN protein in HDG was lower than Cont（P＜0.01），theexpression of ALP mRNA, ALP protein in Dex intervention groups was lowerthan Cont（P＜0.01）,there was no significant difference betweent Dexintervention groups（P＞0.05）. For12weeks intervention, the expression ofOCN mRNA、ALP mRNA was lower than Cont（P＜0.01）, there was nosignificant difference betweent Dex intervention groups（P＞0.05）. Theexpression of OCN protein, ALP protein in intervention groups was lowerlower than Cont（P＜0.05）, and the expression of OCN protein, ALP proteinin HDG was lower than LDG and MDG（P＜0.05）. The expression of OCNmRNA in Cont for9weeks and12weeks intervention was lower than4weeksintervention. For4weeks,9weeks and12weeks intervention, the expression ofOCN mRNA, OCN protein, ALP mRNA, ALP protein in Dex interventiongroups had significant difference（P＜0.05）, The expression of OCN mRNA,OCN protein, ALP mRNA, ALP protein was decreased with time. 4. For4weeks intervention, compared with Cont, the expression of LC3mRNA, Beclin1mRNA, Atg5mRNA in Dex intervention groups had nosignificant difference （P＞0.05）, there was no significant differencebetweent intervention group（sP＞0.05）. The expression of LC3protein, Beclin1protein, Atg5protein was hihger than the Cont, there was no significantdifference betweent intervention groups（P＞0.05）. For9weeks intervention,compared with the Cont, the expression of LC3mRNA、Beclin1mRNA inintervention groups was decreased （P＜0.05）, there was no significantdifference betweent Dex intervention groups（P＞0.05）. The expression ofAtg5mRNA in HDG was lower than MDG and LDG（P＜0.05）.The expressionof LC3protein、Beclin1protein in HDG was lower than the LDG（P＜0.05）, theexpression of Atg5protein in Dex intervention groups had no significantdifference（P＞0.05）. For12weeks intervention, compared with the Cont, theexpression of LC3mRNA、LC3protein in Dex intervention groups wasdecreased（P＜0.05）. The expression of LC3mRNA in HDG was lower thanLDG（P＜0.05）. Compared with Cont, the expression of Beclin1mRNA,Beclin1protein in intervention groups was decreased（P＜0.05）, the expressionof Beclin1mRNA in Dex ntervention groups had no significant difference（P＞0.05）. Compared with Cont, the expression of Atg5mRNA, Atg5protein inintervention groups was decreased （P＜0.05）, there was no significantdifference betweent Dex intervention groups（P＞0.05）. The expression of LC3protein、Beclin1mRNA、Beclin1protein、Atg5mRNA、Atg5protein for4weeks,9weeks,12weeks intervention in different doses Dex interventiongroups had significant difference （P＜0.05）, the expression of LC3mRNA，LC3protein，Beclin1protein，Atg5mRNA，Atg5protein decreased with time.For9weeks an12weeks intervention, the expression of Beclin1mRNAin Dex intervention groups was lower than4weeks intervention. For12weeksintervention, the expression of Beclin1mRNA in LDG was lower than9weeks intervention.5. By transmission electron microscope test, for4weeks intervention, thenumber of autophagosome in osteoblast cytoplasm in invervention groups wasincreased, for9weeks or12weeks intervention, the number of autophagosomein osteoblast cytoplasm in invervention groups was decreased,the cell showsobvious vacuolation.Conclusion1. Rats treated with glucocorticoid, bone formation and BMDmay decrease in a time and dose dependent manner.2.When the rats are treated with glucocorticoid in short time, the autophagyin osteoblast is induced, when treated with long time, the autophagy inosteoblast is inhibited.3.The change of osteoblast autophagic activity may be involved in thepathogenesis of GIOP.