Glucocorticoids promote steroid-induced osteonecrosis of the femoral head by down-regulating serum alpha-2-macroglobulin to induce oxidative stress and facilitate SIRT2-mediated BMP2 deacetylation

Our study investigated the possible molecular mechanism of glucocorticoid in steroid-induced osteonecrosis of the femoral head (SINFH) through regulating serum alpha-2-macroglobulin and SIRT2-mediated BMP2 deacetylation. Essential genes involved in glucocorticoid-induced SINFH were screened by transcriptome sequencing and analyzed by bioinformatics, followed by identifying downstream regulatory targets. Rat bone marrow mesenchymal stem cells were isolated and treated with methylprednisolone (MP) for in vitro cell experiments. Besides, a glucocorticoid-induced rat ONFH was established using the treatment of MP and LPS. ChIP-PCR detected the enrichment of SIRT2 in the promoter region of BMP2, and the deacetylation modification of SIRT2 on BMP2 was determined. Bioinformatics analysis revealed that glucocorticoids may induce ONFH through the SIRT2/BMP2 axis. In vitro cell experiments showed that glucocorticoids up-regulated SIRT2 expression in BMSCs by inducing oxidative stress, thereby promoting cell apoptosis. The up-regulation of SIRT2 expression may be due to the decreased ability of α2 macroglobulin to inhibit oxidative stress, and the addition of NOX protein inhibitor DPI could significantly inhibit SIRT2 expression. SIRT2 could promote histone deacetylation of the BMP2 promoter and inhibit its expression. In vitro cell experiments further indicated that knocking down SIRT2 could protect BMSC from oxidative stress and cell apoptosis induced by glucocorticoids by promoting BMP2 expression. In addition, animal experiments conducted also demonstrated that the knockdown of SIRT2 could improve glucocorticoid-induced ONFH through up-regulating BMP2 expression. Glucocorticoids could induce oxidative stress by down-regulating serum α2M to promote SIRT2-mediated BMP2 deacetylation, leading to ONFH.