RADX突变体通过基因组损伤激活NF-kappaB信号导致单基因炎症性肠病的机制研究

单基因炎症性肠病（IBD）发病早，致病基因及分子机制不清是其诊治困难的原因。通过家系全外显子测序，预实验发现2位IBD患儿分别携带RADX错义突变（I777T, G829S）。RADX是基因组维稳基因，但其突变是否介导单基因IBD尚不明确。进一步研究表明：突变患儿结肠粘膜中RADX蛋白水平显著下降，而自噬降解是其主要降解途径；敲低RADX显著增加DNA损伤并激活NF-κB信号，且Radx敲除小鼠结肠组织呈现自发炎症表型。据此假设：RADX突变蛋白通过增强其自噬途径信号加速降解，造成基因组损伤、NF-κB异常激活和炎症性肠病的发生。我们拟通过蛋白质谱和免疫共沉淀等技术研究RADX的降解机制、阐明RADX表达缺陷调控的NF-κB信号途径，并利用基因敲除鼠验证RADX对肠道炎症的保护作用及突变体的致病性。本研究首次揭示RADX突变造成单基因IBD的发病机制，将为疾病提供新的诊断标志和药物靶点。

Monogenic inflammatory bowel disease (IBD) poses a significant burden to many infants and children. A general lack of knowledge on disease causal genes and their mechanisms of function significantly hampered clinical diagnosis and patient’s prognosis. We performed whole exome sequencing of a cohort of children with IBD and found that RADX missense variants (I777T/G829S) were present in two children. RADX is known to play a critical role in maintaining genomic stability, but whether it mediates monogenic IBD is currently unknown. We uncovered that patients with I777T/G829S variants showed decreased mucosal RADX expression by immunofluorescence examination. Autophagic degradation was the main degradation mechanism of RADX. Furthermore, RADX deficiency in a human macrophage cell line can induce heightened DNA damage, which in turn activated NF-κB mediated inflammatory responses. Moreover, Radx knock out mice spontaneously activate inflammatory response in colonic tissue. Accordingly, we hypothesized that missense variants destabilized RADX protein expression by autophagic degradation, which in turn promoted DNA damage responses and NF-κB activation. To further validate this hypothesis, we will identify the protein degradation mechanism of RADX and NF-κB signaling mediated by RADX with mass spectrometry and co-immunoprecipitation assays，and confirm the pathogenicity of RADX variants using colitis model in Radx-/- or RadxI777T/G829S mutated mice. This is the first report that RADX is a candidate monogenic IBD causal gene. It will aid the diagnosis and treatment of children carrying similar variants.