烟酰胺抑制Th17细胞与滤泡辅助性T细胞分化的分子机制及其对红斑狼疮的治疗作用

Nicotinamide and tetracycline have been used for the treatment of lupus erythematosus in dogs as an alternative to steroids and immunosuppressants, showing good therapeutic effect. However, the therapeutic mechanisms remain unclear. Our previous studies have shown that nicotinamide treatment can reduce the percentage of Th17 cells and follicular helper T (Tfh) cells in human CD4+ T cells. In addition, our results have found that continuous in vivo intervention with nicotinamide in MRL/lpr lupus-like mice decreases the percentage of Th17 cells in mice splenocytes, ameliorates the lupus skin lesions, reduces urine protein level, and decreases the serum level of anti-dsDNA autoantibodies. Recent evidence indicated that RORγt and Bcl-6, the key transcription factors in Th17 and Tfh differentiation, respectively, might have interaction with Sirt1, a histone deacetylase that was abnormally overexpressed in CD4+ T cells from lupus patients and also in CD4+ T cells from MRL/lpr mice. Hence, we hypothesize that nicotinamide may hinder Th17 and Tfh differentiation by inhibiting Sirt1, and therefore protect the lupus mice from inflammatory injury and autoantibody production. In the current project, we will try to validate our hypothesis by investigating the modulation of nicotinamide on the key transcription factors in Th17 and Tfh differentiation and its therapeutic effects on lupus mice, and by evaluating the effect of Sirt1 overexpression/inhibition on Th17/Tfh differentiation and lupus phenotypes. This project would help further elucidate the therapeutic mechanisms and molecular targets of nicotinamide in the treatment for lupus erythematosus, and provide novel perspectives in potential new treatments for this disease.

作为类固醇和免疫抑制剂的替代，烟酰胺联合四环素应用于狗的红斑狼疮取得较好疗效，但机制不明。我们的前期预实验发现烟酰胺可降低正常人T细胞中的Th17、Tfh细胞比例；烟酰胺持续干预MRL/lpr狼疮小鼠可显著抑制Th17细胞，并改善皮损、减少尿蛋白、降低血清抗dsDNA抗体水平。最新研究提示，Th17、Tfh分化的关键转录因子RORγt、Bcl-6可能与组蛋白去乙酰化酶Sirt1存在相互作用，而Sirt1在狼疮患者和MRL/lpr小鼠T细胞中表达升高。因此，我们提出烟酰胺通过抑制Sirt1阻遏Th17、Tfh分化从而抑制红斑狼疮炎症及自身抗体产生的全新假说。本项目拟通过烟酰胺对Th17、Tfh分化关键转录因子的调控及其对红斑狼疮小鼠的治疗效果，干预Sirt1对Th17、Tfh分化及红斑狼疮表型的影响来证实该假说。本研究将有助于阐明烟酰胺治疗红斑狼疮的机理及靶点，为治疗红斑狼疮提供新的思路。

T 淋巴细胞异常分化与活化是 SLE 的重要免疫学特征之一，其中，具有辅助 B 细胞产生自身抗体能力的滤泡辅助性T细胞（Tfh），在 SLE的发生发展过程中起着至关重要的作用。大量研究证实SLE 患者外周血中循环 Tfh 细胞比例升高，并且与疾病严重程度成正相关。 然而，SLE中Tfh细胞异常增殖和分化的内在机制仍尚未清晰。我们实验室前期研究表明，SIRT1作为NAD+依赖的组蛋白去乙酰化酶， 在SLE患者及狼疮小鼠的CD4+T细胞中表达升高，并与疾病活动性呈正相关。 通过尾静脉注射miRNA选择性抑制SIRT1可降低MRL/lpr狼疮小鼠血清中抗dsDNA抗体水平和肾脏IgG沉积，并一定程度缓解肾脏病理损害。我们推测，SIRT1)可能在SLE发生发展过程中参与正向调控Tfh细胞的分化，而抑制SIRT1可能带来治疗新策略。本课题通过体外实验初步探讨了SLE患者中异常高表达的SIRT1参与SLE发病的机制，从多方面验证了SIRT1是Tfh细胞分化的一个正向调控因子。进而通过体内外研究证实了烟酰胺作为一种天然的SIRT1抑制剂对于Tfh、Th17细胞分化的负向调控作用及其对于狼疮模型小鼠皮损、关节炎、尿蛋白及血清抗dsDNA抗体水平等临床表型的改善作用。本项目研究为阐明SIRT1高表达参与SLE发生发展的机制提供了初步的理论和实验依据，而烟酰胺作为SIRT1抑制剂有望为SLE临床治疗提供一种低毒副作用、安全廉价的药物新选择。