Reserch On The Mechanism Of Endoplasmic Reticulum Stress-mediated Osteoblast Apoptosis In SANFH

Objective:How steroid-induced avascular necrosis of the femoral head（SANFH）occurs has not yet been fully explained.Many previous experiments have proved that several factors that are strongly correlated with SANFH include endoplasmic reticulum stress（ERS）and programmed cell death.During the formation of autophagosomes,autophagy-related protein 5 can participate in regulation,and then activate ERS-related sensors to initiate a unique apoptosis program;on the other hand,when ERS persists,calpain is activated,and autophagy-related protein ATG5 is cleaved into ATG5-t N,and ATG5-t N has a pro-apoptotic effect.In this study,we explored the mechanism of ATG5,ERS,autophagy,and apoptosis in SANFH by establishing a SANFH model,and evaluated whether ATG5-si RNA could provide new ideas and inspiration for the prevention and treatment of SANFH.Methods:We took SD rats as the research object and then randomly divided them into three groups.Group A was used as a control,group B was injected with methylprednisolone intramuscularly,and group C was injected with methylprednisolone intramuscularly and transfected with ATG5-si RNA.We observed autophagosomes and apoptosis in each group,and detected the m RNA and protein expressions of ATG5,PERK,Caspase3,9,and 12 in each group to explore the mechanism of apoptosis and ERS in the pathogenesis of SANFH.Whether ATG5-si RNA can reversely regulate ERS-mediated osteocyte apoptosis.Results:（1）Methylprednisolone made the trabecular arrangement of rat femoral head tissue disordered or even broken and formed empty bone lacuna;（2）Methylprednisolone increased apoptotic cells in rat femoral head tissue,and enhanced the m RNA and protein expressions of Caspase3,9,and 12;（3）Methylprednisolone induces an increase in autophagosomes in rat femoral head osteocytes;（4）Methylprednisolone enhanced the expression of PERK protein and m RNA in rat femoral head osteocytes;（5）After ATG5-si RNA transfection,the protein and m RNA expression of ATG5 was inhibited,the number of autophagosomes was also decreased,and the expression of PERK was also decreased;（6）After ATG5-si RNA transfection,the m RNA and protein expressions of PERK,Caspase3,9,12 were decreased;（7）After ATG5-si RNA transfection,the histopathological changes of the femoral head of the rats were relieved compared with the hormone group.Conclusion:（1）Osteocyte apoptosis can be mediated by ERS and promote the pathological changes of femoral head structure,which is closely related to the occurrence and development of SANFH.（2）ATG5 blockers can inhibit the unfolded protein response,thereby reducing the degree of endoplasmic reticulum stress,inhibiting the expression of osteocyte apoptosis proteins related to the PERK signaling pathway,and delaying or blocking the pathogenesis of SANFH.Under the action of methylprednisolone,the expression of autophagy-related protein ATG5 is enhanced,which on the one hand causes the increase of autophagosome synthesis,induces ERS,unfolded protein response（UPR）,and its related PERK signaling The expression of the pathway then increases,causing apoptosis;On the other hand,endoplasmic reticulum stress persists,and Ca²⁺balance disorder activates calpain,cleaves ATG5,and its cleavage product can also initiate apoptosis.The above reasons finally led to the emergence of SANFH.As a blocker of ATG5,ATG5-si RNA can alleviate the above process and become a new target in the treatment of SANFH,and these provide new perspectives,research directions and focus on how to treat and prevent SANFH.