Defining the Role of Dynamic X Chromosome Inactivation in Age-Associated B Cells for Female-Biased Systemic Lupus Erythematosus

项目总结/摘要 90%被诊断患有系统性红斑狼疮（SLE）的个体是女性，但潜在的 自身免疫性疾病中性别偏见的机制尚不清楚。SLE易感性增加 与个体携带的X染色体数量有关，X连锁基因的表达增加， 在女性SLE患者中发现。这些发现表明来自两条X染色体的基因表达可能 有助于女性偏向的SLE发病机制。哺乳动物中X连锁基因表达的剂量 一个以上的X染色体通过X染色体的表观遗传沉默来平衡 失活（XCI）。XCI在体细胞中通过抑制性表观遗传学特征与 失活X染色体（Xi），包括用长非编码RNA Xist包被Xi。尽管有这些 抑制特征，一些基因已被证明逃脱沉默从Xi。我们的实验室发现B 细胞是SLE发病机制中的关键细胞类型，具有XCI的“动态”维持，其中幼稚B细胞缺乏可见的 Xist RNA信号还显示激活后Xist RNA重新定位于Xi。动态XCI维护 在SLE B细胞中，X连锁免疫基因被破坏， 抑制性表观遗传标记在Xi上的定位可引起免疫基因从Xi的异常逃逸， 增强B细胞活性。“乳腺癌相关B细胞”（ABC）正在成为女性偏见的关键细胞类型。 自身免疫性，并通过TLR 7途径对信号传导作出强烈反应。几个TLR 7通路成员 是X连锁的，并已被确定为SLE的风险变异。确定贡献的重要性， 在女性偏向性SLE中的X染色体，我将定义ABC中Xi的表观遗传学特征，并阐明 B细胞区室中XCI维持紊乱对SLE发病机制的影响在目标1中，我假设 ABCs具有动态XCI维持，X连锁免疫调节基因在ABCs中逃避沉默， ABC。我将分离小鼠脾B细胞，并观察抑制性表观遗传特征与小鼠脾淋巴细胞增殖的关系。 Xi在ABC的分化和活化过程中，并进行等位基因特异性RNA测序，以确定基因 能逃过ABC的沉默在目标2中，我将以我的初步数据为基础，证明雌性小鼠 具有B细胞特异性Xist缺失产生干扰的XCI（“Xist cKO”）的人更容易自发性地和/或自发性地感染， 化学诱导的SLE样疾病。我假设在雌性Xist cKO小鼠中受损的XCI维持 导致免疫调节X连锁基因的上调，产生B细胞，更容易分化为 效应子群体并在刺激时产生更多抗体。我将分析转录和功能 稳态时和自发性肿瘤发生过程中雌性Xist cKO小鼠B细胞的特征 和化学诱导的SLE研究ABC中XCI维持的表观遗传机制将揭示 来自Xi的遗传贡献对ABC功能是如何至关重要的，这将首次阐明X染色体 基于染色体的机制，是女性偏好自身免疫的基础。

Project Summary / Abstract 90% of individuals diagnosed with systemic lupus erythematosus (SLE) are women, but the underlying mechanisms that govern sex bias in autoimmune disease are not understood. Susceptibility to SLE increases with the number of X chromosomes carried by an individual, and increased expression of X-linked genes has been found in women with SLE. These findings suggest that gene expression from two X chromosomes likely contributes to female-biased SLE pathogenesis. The dosage of X-linked gene expression in mammals with more than one X chromosome is balanced by epigenetically silencing one X chromosome through X-chromosome inactivation (XCI). XCI is maintained in somatic cells by association of repressive epigenetic features with the inactive X chromosome (Xi), including coating of the Xi with the long non-coding RNA Xist. Despite these repressive features, some genes have been shown to escape silencing from the Xi. Our lab discovered that B cells, a key cell type in SLE pathogenesis, have “dynamic” maintenance of XCI, where naïve B cells lack visible Xist RNA signal yet demonstrate re-localization of Xist RNA to the Xi upon activation. Dynamic XCI maintenance is disrupted and X-linked immune genes are aberrantly expressed in SLE B cells, suggesting that impaired localization of repressive epigenetic marks on the Xi may cause aberrant escape of immune genes from the Xi, enhancing B cell activity. “Age-associated B cells” (ABCs) are emerging as a critical cell type in female-biased autoimmunity and respond robustly to signaling through the TLR7 pathway. Several TLR7 pathway members are X-linked and have been identified as risk variants in SLE. To determine the importance of contributions from the X chromosome in female-biased SLE, I will define epigenetic features of the Xi in ABCs and elucidate the impact of perturbed XCI maintenance in the B cell compartment on SLE pathogenesis. In Aim 1, I hypothesize that ABCs have dynamic XCI maintenance, and that X-linked immune-regulatory genes escape silencing in ABCs. I will isolate murine splenic B cells and visualize the association of repressive epigenetic features with the Xi during differentiation and activation of ABCs and perform allele-specific RNA sequencing to determine genes that escape silencing in ABCs. In Aim 2, I will build on my preliminary data that demonstrates that female mice with a B cell-specific Xist deletion yielding perturbed XCI (“Xist cKO”) are more susceptible to spontaneous and chemically-induced SLE-like disease. I hypothesize that impaired XCI maintenance in female Xist cKO mice leads to upregulation of immune-regulatory X-linked genes, yielding B cells that differentiate more readily into effector populations and produce more antibodies upon stimulation. I will assay transcriptional and functional characteristics of B cells from female Xist cKO mice at steady state and during the development of spontaneous and chemically induced SLE. Investigating the epigenetic mechanisms of XCI maintenance in ABCs will reveal how genetic contributions from the Xi are critical for ABC function, and for the first time will illuminate an X chromosome-based mechanism that underlies female-biased autoimmunity.