Elevated cytokines in osteoporotic blood correlate with immune microenvironment shifts and dysregulated circRNA profiles.

BACKGROUND: Osteoporosis (OP) pathogenesis is inextricably linked to immune microenvironment dysregulation. However, the sex-specific immunoregulatory disparities between senile osteoporosis (SOP) and postmenopausal osteoporosis (PMOP) remain incompletely elucidated. METHODS: In this study, we integrated multi-cohort bulk transcriptomics, single-cell RNA sequencing (scRNA-seq), and independent clinical validations to systematically decipher the distinct immune landscapes and circular RNA (circRNA) regulatory axes underlying SOP and PMOP. RESULTS: Bulk transcriptomic analysis revealed pervasive cytokine activation in OP, and such activation may be linked to divergent gene signatures between cohorts. Notably, LAG3 and TBX21 emerged as core cytokine-related hub genes across datasets. Immune deconvolution demonstrated sexually dimorphic microenvironment remodeling: male SOP patients exhibited a significant decrease in CD4+ T cells alongside expanded NK and CD8+ T cells, whereas female PMOP patients were primarily characterized by an increased proportion of monocytes. Furthermore, we constructed an immune-targeted competitive endogenous RNA (ceRNA) regulatory network and identified three core circRNAs (hsa-KMT5B_0001, hsa-TMEM55A_0001, and hsa-TNFRSF21_0001) as potential upstream regulators of these immune shifts. Subsequent scRNA-seq analysis of bone marrow mononuclear cells validated the peripheral immune imbalances and overexpressed the heightened expression of key cytokine genes predominantly to dendritic cells and monocytes. Finally, quantitative RT-PCR and flow cytometry in an independent clinical cohort further validated the upregulation of the target transcripts and the specific expansion of NK cells in SOP. CONCLUSION: This study unveils the sex-divergent immune-associated mechanisms underlying OP and delineates three novel circRNA-cytokine networks. These findings provide a theoretical basis and candidate molecular targets for the development of stratified, sex-specific clinical interventions for OP.