HMGB1调节CD4+T细胞STAT3基因去甲基化分子机制及其在aGVHD发病中的作用

Accumulated studies have demonstrated that the elevated level of STAT3 in T lymphocyte could mediate Th17/Treg imbalance and then accelerate the progression of aGVHD (acute graft versus host disease), but the mechanism of STAT3 overexpression is still unknown. Our previous study has proved that pathologic DNA hypomethylation of STAT3 promoter region closely related to its overexpression in aGVHD CD4+ T cells, but the cause of STAT3 hypomethylation is unclear.In recent years, studies have confirmed that GADD45a could recruit TDG and AID then collaborate with TET family proteins, which mediate DNA demethylation in mammalian. HMGB1 and GADD45a could compose a complex, then participate in DNA demethylation of CD70 and CD11a.Our preliminary results showed that the expression of HMGB1 was significantly increased in aGVHD CD4+ T cells, and its expression remarkably negative correlation with methylation of STAT3 promoter region. So we propose the novel hypothesis：the overexpression of HMGB1 could cause DNA demethylation of STAT3 promoter region by recruiting GADD45a, TDG, AID and TET, result in upregulation of STAT3, then promote Th17/Treg imbalance, which ultimately lead to the onset of aGVHD. In this study, this hypothsis will be comfirmed through investigating molecular mechanisms of HMGB1 regulating STAT3 DNA demethylation in CD4+ T cell and effect of Th17/Treg in aGVHD.

研究表明，T细胞中异常升高的STAT3介导的Th17/Treg比例失衡是aGVHD的重要发病机制之一。我们前期研究发现，aGVHD患者CD4+ T细胞中STAT3基因启动子区显著低甲基化与其异常表达密切相关。研究证实，GADD45a能募集TDG和AID，协同TET家族蛋白介导哺乳类的DNA去甲基化。核蛋白HMGB1参与GADD45a介导的甲基化敏感基因CD70和CD11a去甲基化。我们预实验结果显示aGVHD患者CD4+ T细胞HMGB1表达显著增高，与STAT3启动子甲基化水平明显负相关。因此我们提出CD4+ T细胞中升高的HMGB1招募GADD45a等去甲基化相关蛋白介导STAT3启动子DNA去甲基化，上调STAT3表达导致Th17/Treg比例失衡，诱发aGVHD这一全新假说。本项目将通过研究aGVHD CD4+ T细胞中HMGB1介导的STAT3低甲基化分子机制证实这一假说。

T细胞中异常升高的STAT3介导的Th17/Treg比例失衡是aGVHD的重要发病机制之一。我们前期研究发现，aGVHD患者CD4+T细胞中STAT3基因启动子区显著低甲基化与其异常表达密切相关。目前，aGVHD患者CD4+T细胞中STAT3基因启动子区低甲基化的分子机制尚不明确。我们通过检测CD4+T细胞中过表达及干扰HMGB1后STAT3的表达水平，证实了HMGB1能上调STAT3的表达。此外，我们通过Co-IP及ChIP-PCR实验证实HMGB1能募集GADD45a，TDG，AID和TET2介导STAT3启动子DNA去甲基化，进而上调STAT3表达。我们的研究首次探明了aGVHD患者CD4+T细胞中STAT3基因启动子区的DNA低甲基化状态，并通过证实HMGB1招募GADD45a，AID，TDG和TET2，靶向调节STAT3基因DNA去甲基化，对aGVHD患者CD4+T细胞中STAT3启动子DNA低甲基化进行了解释。