Loss of function of XBP1 splicing activity of IRE1a favors B cell tolerance breakdown

Tolerance breakdown leads to the development of autoimmune diseases in an increasing manner. B cells strongly contribute to the pathogenesis of these diseases, notably via the production of autoantibodies leading to cell depletion, receptor modulation and organ damages. However, the molecular mechanisms of B cell tolerance breakdown are badly known. Autoimmune diseases are frequently aggregated in families in two or more generations. The study of these familial forms could therefore help to better describe common biological mechanisms leading to B cell tolerance breakdown. By Whole-Exome Sequencing, we describe here in a multiplex family with several members presenting autoantibody-mediated autoimmunity a new heterozygous mutation (p.R594C) in ERN1 gene, coding for IRE1α. Using human cell lines and a knock-in (KI) transgenic mouse model, we showed that this mutation leads to a profound defect of IRE1α ribonuclease activity on XBP1 splicing. The KI mice developed a broad panel of autoantibodies, however in a subclinical manner. These results suggest that a decrease of XBP1s production could contribute to B cell tolerance breakdown and give new insights into the function of IRE1α which are important to consider for the development or IRE1α targeting strategies. We performed CITEseq to asses in an unbiased manner whether the R594C mutation in IRE1 affects the immune cell compartment.

免疫耐受崩溃（tolerance breakdown）可导致自身免疫性疾病的进行性发生。B细胞（B cell）在这类疾病的发病机制中发挥关键作用，尤其通过产生自身抗体（autoantibody）介导细胞耗竭、受体调控及器官损伤。然而，B细胞免疫耐受崩溃的分子机制尚不甚明确。自身免疫性疾病常于家族中连续两代或多代聚集出现，因此对这类家族性病例的研究有助于更好地阐明驱动B细胞免疫耐受崩溃的共同生物学机制。本研究通过全外显子组测序（Whole-Exome Sequencing），在一个存在多名自身抗体介导自身免疫病患者的多发家系（multiplex family）中，发现了编码IRE1α的ERN1基因的一种新型杂合突变（heterozygous mutation，p.R594C）。通过使用人细胞系及敲入（KI）转基因小鼠模型，我们证实该突变会显著破坏IRE1α针对XBP1剪接（XBP1 splicing）的核糖核酸酶（ribonuclease）活性。该敲入小鼠可产生多种自身抗体，但呈现亚临床表型。上述结果提示，XBP1s的产生减少可能参与B细胞免疫耐受崩溃的过程，同时为IRE1α的功能研究提供了新视角，这对于开发IRE1α靶向治疗策略（IRE1α targeting strategies）具有重要参考价值。我们还开展了CITE-seq实验，以无偏方式（unbiased manner）评估IRE1上的R594C突变是否会影响免疫细胞区室（immune cell compartment）。