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Abstract Our previous research revealed a close association between the acetylation of peroxisome proliferator-activated receptor γ (PPARγ) histone H3K27 and the adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). We preliminarily explored the epigenetic mechanism of steroid-induced avascular necrosis of the femoral head (SANFH) development, but the specific histone deacetylase (HDAC) involved in this regulatory process remains unknown. In this study, we combined cell, animal, and clinical specimen experiments to screen for specific HDAC genes that could regulate BMSC adipogenic differentiation and to explore their roles. The results showed that dexamethasone (DEX) significantly exacerbated the imbalance between the adipogenic and osteogenic differentiation of BMSCs, and there were differences in HDAC expression in the adipogenic differentiation cell models, with histone deacetylase 10 (HDAC10) showing the most significant decrease in expression. Subsequent use of a chromatin immunoprecipitation assay kit and quantitative polymerase chain reaction (ChIP‒qPCR) revealed a decrease in HDAC10 expression at predicted potential sites within the PPARγ promoter, indicating a significant decrease in HDAC10 enrichment in the PPARγ promoter region of BMSCs, thereby promoting sustained PPARγ expression. Additionally, immunohistochemistry of samples collected from mice and humans with SANFH and normal femoral heads revealed an imbalance between adipogenic and osteogenic differentiation in the necrotic area of femoral heads, with a significant decrease in the relative expression of HDAC10 in the necrotic area of femoral heads with SANFH. In summary, we speculate that HDAC10 affects the progression of SANFH by regulating BMSC adipogenic differentiation, a process possibly related to PPARγ histone acetylation. These findings provide a promising direction for the treatment of SANFH. Graphical abstract

Abstract Background By interacting with bone marrow mesenchymal stem cells (BMSCs) and regulating their function through exosomes, bone macrophages play crucial roles in various bone-related diseases. Research has highlighted a notable increase in the number of M1 macrophages in glucocorticoid-associated osteonecrosis of the femoral head (GA-ONFH). Nevertheless, the intricate crosstalk between M1 macrophages and BMSCs in the glucocorticoid-stimulated environment has not been fully elucidated, and the underlying regulatory mechanisms involved in the occurrence of GA-ONFH remain unclear. Methods We employed in vivo mouse models and clinical samples from GA-ONFH patients to investigate the interactions between M1 macrophages and BMSCs. Immunofluorescence staining was used to assess the colocalization of M1 macrophages and BMSCs. Flow cytometry and transcriptomic analysis were performed to evaluate the impact of exosomes derived from normal (n-M1) and glucocorticoid-stimulated M1 macrophages (GC-M1) on BMSC differentiation. Additionally, miR-1a-3p expression was altered in vitro and in vivo to assess its role in regulating adipogenic differentiation. Results In vivo, the colocalization of M1 macrophages and BMSCs was observed, and an increase in M1 macrophage numbers and a decrease in bone repair capabilities were further confirmed in both GA-ONFH patients and mouse models. Both n-M1 and GC-M1 were identified as contributors to the inhibition of osteogenic differentiation in BMSCs to a certain extent via exosome secretion. More importantly, exosomes derived from GC-M1 macrophages exhibited a heightened capacity to regulate the adipogenic differentiation of BMSCs, which was mediated by miR-1a-3p. In vivo and in vitro, miR-1a-3p promoted the adipogenic differentiation of BMSCs by targeting Cebpz and played an important role in the onset and progression of GA-ONFH. Conclusion We demonstrated that exosomes derived from GC-M1 macrophages disrupt the balance between osteogenic and adipogenic differentiation in BMSCs, contributing to the pathogenesis of GA-ONFH. Inhibiting miR-1a-3p expression, both in vitro and in vivo, significantly mitigates the preferential adipogenic differentiation of BMSCs, thus slowing the progression of GA-ONFH. These findings provide new insights into the regulatory mechanisms underlying GA-ONFH and highlight potential therapeutic targets for intervention. Graphical Abstract