TET催化耐受性树突状细胞的5hmC修饰在变应性鼻炎免疫失衡中的作用

Allergic rhinitis (AR) is an allergic airway inflammation caused by Th1/Th2 immune imbalance. It has been confirmed that epigenetic regulation is involved in the differentiation of immune effector cells in AR, but the mechanism is not clear. Our group has confirmed the differentiation of tolerogenic dendritic cells (TolDCs) is impaired in AR. Our preliminary studies showed an increased 5-hydroxymethylcytosine level in genomic DNA in the impaired TolDCs in AR patients compared with healthy controls, accompanied by the up-regulated expression of the Ten-eleven translocation TET2 and TET3, which can enzymatically convert 5-methylcytosine (5-mC) to 5-hmC, suggesting that TET mediated epigenetic modification plays a role in causing TolDC differentiation defects. Therefore, we hypothesized that TET mediated the increase of 5-hmC modification in the genome of the impaired TolDC in AR patients, then caused the immune imbalance of Th1/Th2 in AR. In this research, we aimed to clarify the role of TET and 5-hmC modification in the impaired development of TolDC in AR patients. To investigate the genome-wide difference of 5-mC/5-hmC modification in TolDC between AR and healthy volunteers and explore the downstream signaling pathway in the impaired TolDC in AR patients. And to further explore the epigenetic regulation of TolDC developmental defects in vitro and in vivo. This study will help clarify the epigenetic mechanism of AR immune imbalance and provide a new strategy for the treatment of AR.

变应性鼻炎（AR）是由Th1/Th2免疫失衡引起的气道变应性炎症。最新研究显示表观遗传学参与AR免疫细胞分化的调控，但机制不清。课题组前期发现甲基胞嘧啶双加氧酶2、3（TET2、TET3）及其催化的5-羟甲基胞嘧啶（5hmC）在AR患者分化缺陷的耐受性树突状细胞（TolDC）中上调，提示TET催化的DNA 5hmC修饰可能介导了TolDC分化缺陷。据此我们提出假设：TET催化DNA 5hmC修饰而导致TolDC发育缺陷，从而引起Th1/Th2免疫失衡。本课题拟明确TET及其介导的5hmC在AR及健康对照TolDC中的差异，探讨AR与健康对照TolDC中5mC/5hmC的基因谱差异，探讨其下游细胞信号通路；以环境因素（如PM2.5）为干预因素，探讨其对TET介导的TolDC表观遗传学调控对AR的影响。本研究将有助于阐明AR免疫失衡的表观遗传学机制，为AR治疗提供新策略。

【背景】近数十年来，包括变应性鼻炎（AR）和哮喘在内的呼吸道变应性炎症患病率逐渐升高。交通相关空气污染（TRAP）与呼吸道变应性炎症患病率的上升、症状的加重有明显相关性。多研究表明，甲基胞嘧啶双加氧酶（TET）可介导环境因素参与调控免疫细胞分化进而影响疾病进程。.【主要研究内容】本项目探究了TET酶是否参与过敏原与TRAP等环境暴露对人体呼吸道变应性炎症的调控，包括其对呼吸道上皮及对人体外周免疫细胞（包括树突状细胞DC）的调控。.【重要结果及关键数据】本项目发现了AR患者外周血单个核细胞（PBMCs）中TET表达、整体5mC和5hmC水平均高于HC，且AR外周血中mDCs和pDCs中TET1水平也明显高于HC组。体外数据揭示了过敏原和PM2.5分别抑制moDCs中TET1的表达，对TET2、TET3无明显影响。敲减TET1的moDCs，其表型趋于成熟，且明显抑制活化型调节性T细胞（aTregs）的细胞比例。并进一步在在随机、双盲人体体内暴露试验中揭示了呼吸道变应性炎症患者呼吸道上皮的DNA甲基化水平及其主要调控酶（pTET 、pDNMT）在过敏原激发中有易感性，呼吸道上皮中TET的水平与呼吸道变应性炎症中炎症因子的分泌、肺功能相关；通过第二项随机、双盲人体体内暴露试验揭示了急性DE暴露（50 μg/m3及以上）显著降低了PBMCs中B细胞、Th17细胞和活化T细胞的比例。在DE暴露4h后， PBMCs中的TET酶水平明显上调，尤其是在 Th1、Th2和 Th17细胞中的TETs明显上调，且TET水平与血浆中促炎细胞因子的分泌明显相关。.【科学意义】综上所述，本研究首次在人体体内外试验中表明TET酶参与过敏原、PM2.5的暴露效应调控呼吸道变应性炎症，且TET酶具有调控DCs诱导免疫耐受的功能，有望成为辅助呼吸道变应性炎症诊断、治疗和预后评估的生物学标记物；本研究揭示了即使是短时间、轻度的空气污染，也可通过表观遗传修饰调控人体循环免疫，该研究为环境空气质量标准的制定提供了重要的客观依据。