Sirt6, Deubiquitinated and Stabilised by USP9X, Takes Essential Actions on the Pathogenesis of Experimental Autoimmune Myasthenia Gravis by Regulating CD4+ T Cells

Myasthenia gravis (MG) presents with symptoms that significantly affect patients' daily lives. Long-term MG therapies may lead to substantial side effects, predominantly due to prolonged immune suppression. Sirt6, which plays a vital role in maintaining cellular homeostasis and is recognised for its involvement in cytokine production in immune cells, has not yet been explored in relation to MG. PBMCs and CD4(+) T cells were isolated from blood samples. RT-qPCR, western blot and ELISA were used to assess the expression of target genes and proteins. Flow cytometry was used to identify the subsets of T helper cells. Co-IP was conducted to investigate the interaction between USP9X and Sirt6. Finally, the experimental autoimmune myasthenia gravis (EAMG) model was established. In MG patients, Sirt6 levels were downregulated compared to healthy controls. Sirt6 overexpression led to a reduction in Th1 and Th17 cell populations while augmenting Treg cells in PBMCs. USP9X interacted with Sirt6, leading to its deubiquitination and stabilisation. Elevated Sirt6 levels subsequently mitigated symptoms in the EAMG model. The stabilisation of Sirt6, mediated by USP9X, has been found to relieve symptoms of EAMG by influencing the subtypes of T helper cells. This highlights the promising potential of Sirt6 as a viable therapeutic target in the treatment of MG.