Endoplasmic reticulum activation of the caspase-12/9/3 cascade via ATG5 leads to sterogenic femoral head necrosis 

Abstract

Programmed osteocyte death might be a pathogenesis of steroid-related avascular necrosis of the femoral head (SANFH). Autophagy-related gene 5 (ATG5) can activate the unfolded protein response pathway under endoplasmic reticulum stress (ERS) to participate in cell regulation, but the regulatory mechanism remains unclear. We examined the role of ERS in SANFH pathogenesis by studying the ATG5 participation mechanism in osteoblast apoptosis regulation to provide a theoretical basis for developing new SANFH therapeutic targets. Rat bone marrow mesenchymal stem cells cultured in vitro underwent osteogenic induction and alizarin red staining. The resultant osteoblasts were divided into Control, SANFH (methylprednisolone-treated), SANFH+ATG5 small interfering RNA (siRNA) (methylprednisolone-treated ATG5 siRNA transfection) groups. Beclin 1, MAP1LC3, ATG5, PERK, and caspase-3, -9, and -12 mRNA and protein expression levels were detected, the osteoblast survival rate was measured, and apoptosis was detected. The relationship between Beclin 1, MAP1LC3, ATG5, PERK, and caspase-3, -9, and -12 mRNA and protein expression levels and osteoblast apoptosis was analyzed. The SANFH group had enhanced expression of the autophagy-related genes Beclin 1 and MAP1LC3 and numerous autophagosomes were formed. Osteoblast injury stimulated ERS. ATG5 siRNA inhibited the glucocorticoid-induced osteoblast autophagy and ERS. The ER stimulated the caspase-12/9/3 cascade through ATG5 to enhance apoptosis and improve persistent ERS. The continuous action of methylprednisolone increased Beclin 1 and MAP1LC3 gene expression, resulting in bone cell injury and stimulating ERS. The ER activated the caspase-12/9/3 cascade via ATG5 under persistent and unchangeable ERS, leading to apoptosis and SANFH.