The Role of Xist in T Cell Activation and Female-Biased Autoimmunity

PROJECT SUMMARY Approximately 80% of individuals affected by autoimmune disease are female. While divergent sex hormones and chromosomes are known to contribute to sex bias, the roles of additional sex-specific factors are poorly understood. Xist, for instance, is a long non-coding RNA (lncRNA) expressed exclusively in females. Notably, Xist is more highly expressed in PBMCs from females with autoimmunity compared to healthy controls, suggesting a possible role for Xist in predisposing females to autoimmunity. Xist is a key regulator of X-linked gene expression, facilitating X chromosome inactivation (XCI) during early embryonic development. Recent work has identified Xist-mediated regulation of autosomal genes, a previously unappreciated Xist function, in cell types with atypical, dispersed Xist distribution. We and others have noted atypical, dispersed Xist in activated CD4+ T cells, an immune cell type critical in autoimmune pathogenesis. To study Xist in T cells and autoimmune pathogenesis, we engineered mice with T cell-specific Xist knockout. Preliminary studies reveal Xist-deficient CD4+ T cells are defective in proliferation and proinflammatory cytokine production, suggesting a critical role for Xist in T cell activation. However, the (1) mechanism by which Xist alters T cell effector function and (2) significance of Xist-driven phenotypic changes for autoimmune pathogenesis are not known. This proposal will test the hypothesis that Xist drives X-linked and autosomal chromatin accessibility and gene expression changes that support a proinflammatory T cell phenotype and contribute to female bias in autoimmunity. In Aim 1, we will perform ATAC-, RNA-, and RAP-sequencing in unstimulated and anti-CD3 stimulated Xist- deficient and WT CD4+ T cells to explore the mechanisms by which Xist regulates T cell effector function. In Aim 2, we will evaluate the role of T cell-intrinsic Xist in autoimmune pathogenesis using a mouse model of the female-biased, T cell-driven autoimmune disease, Sjogren’s Syndrome (SS). These studies will elucidate Xist function in T cells and explore T cell-intrinsic Xist as a potential determinant of female bias in autoimmunity. This work is guided by experts in T cell biology (Maureen Su, MD - sponsor; Gay Crooks, MD - thesis committee), lncRNA biology (Kathrin Plath, PhD - cosponsor), bioinformatics (Willy Hugo, PhD - collaborator), and sex differences in biology (Karen Reue, PhD – thesis committee) at the University of California Los Angeles. The trainee, Nicole Wilkinson, is richly supported for the work in this proposal and in reaching her career goal of running a translational immunology lab.