Motif-driven microRNA regulation of B cell tolerance uncovers ERalpha as a female-specific checkpoint

Breakdown of B cell tolerance is a central feature of autoimmune diseases, yet the molecular mechanisms underlying the female predominance of these diseases remain unclear. Here, we identified miR-130b as an essential component of a miRNA network, defined by the GUGCA seed motif, that regulates central B cell tolerance. Elevated miR-130b levels impaired tolerance by promoting the survival of immature B cells upon B cell antigen receptor engagement. This network converged on the estrogen receptor pathway through downregulation of Esr1 and Pten. Genetic ablation of Esr1 in immature B cells was sufficient to compromise central B cell tolerance in females, but not in males, revealing an unrecognized role for ER in this process. In males, Esr1 deficiency reduced bone marrow B cell numbers, whereas in females, B cell numbers were preserved, with a greater proportion of cells displaying lower surface CD19 levels. Transcriptomic analysis revealed sex-specific genetic programs characterized by defective B cell development and skewed immunoglobulin gene usage in males, and increased PI3K-AKT signaling in females. In females, this molecular rewiring compensated for developmental defects, but also attenuated central tolerance mechanisms, allowing the escape of autoreactive B cells to the periphery. In patients with multiple sclerosis, elevated levels of miR-130b in circulating vesicles correlated with more severe disease, including increased formation of new demyelinating lesions, cognitive decline, and neurodegeneration. Together, our findings identify a sex-specific ER-dependent checkpoint in B cell tolerance controlled by a seed-driven miRNA network, providing a mechanistic framework for female predisposition to autoimmunity.