霉酚酸活化NLRP3炎性小体促进白介素-1β分泌的机制和意义

Mycophenolate mofetil(MMF), widely used in autoimmune diseases, exerts pharmacological effects through its active metabolite Mycophenolic acid(MPA) in vivo. Previous studies on lupus nephritis(LN) showed that patients treated with MMF have better clinical outcomes but lower infection incidence than patients treated with cyclophosphamide(CYC). For the first time, our study found that MPA, in association with LPS, was able to promote the secretion of IL-1β in monocytes via NLRP3 inflammasome, which contradicts the traditional conception that immunosuppressants inhibit the secretion of pro-inflammatory cytokines and may be to explain that MMF treated LN patients have better clinical outcomes but lower infection incidence. In order to investigate the mechanism that MPA and LPS promotes the secretion of IL-1β on SLE patients, we expore the effect of MPA, in association with LPS, on NF-κB and NLRP3 inflammasome pathway in vitro. Aslo we investigate the effect of MMF on SLE patients and SLE-prone mice with sepsis infection in vivo by analyse NLRP3 inflammasome activation, cytokine profiles and T cell subsets. This study conduct the experiments in vitro and in vivo to clarify the mechanisms of MPA synergizes with LPS to increase IL-1β secretion, but also provide theoretical evidence for more effective and realiable immunosuppressive protocol.

霉酚酸酯(MMF)通过在体内转换为霉酚酸(MPA)发挥免疫抑制作用,在自身免疫病中应用广泛。大量有关狼疮肾炎的研究发现:MMF与环磷酰胺（CYC）相比疗效更好、感染率更低。我们首次发现：MPA通过NLRP3炎性小体协同脂多糖(LPS)促进单核细胞分泌IL-1β,该结果挑战了免疫抑制剂抑制炎性因子分泌的传统理论。本研究拟探讨MPA及LPS对NF-κB通路及NLRP3炎性小体通路的影响，明确其促进IL-1β分泌的机制。给予狼疮小鼠模型MMF、CYC或生理盐水处理后，造感染模型；检测各组NLRP3炎症小体活化情况、疗效、感染率、死亡率及全血细胞因子分泌差异及细胞亚群变化。收集用MMF及CYC治疗的红斑狼疮患者外周血，检测细胞亚群及IL-1β等细胞因子变化。本研究通过体外实验、动物实验及临床试验，阐明MPA协同LPS促进IL-1β分泌的机制及临床意义,为临床更合理有效地应用免疫抑制剂提供理论基础。

免疫抑制剂霉酚酸酯（MMF）通过在体内转换为霉酚酸（MPA）发挥治疗作用,在自身免疫病中应用广泛。既往RCT试验（Randomized Controlled Trial）报道：MMF较CYC（环磷酰胺）更安全、更有效、机会感染率更低。但具体机制尚不明确。在国家自然科学基金青年基金资助下，课题组通过3年研究，探讨了MPA对NF-κB通路及NLRP3炎性小体/caspase-1通路的影响，明确MPA协同LPS促进IL-1β分泌的机制；构建了狼疮小鼠的脓毒症感染模型，检测了MMF、CYC或生理盐水处理组NLRP3炎症小体活化情况、疗效、感染率、死亡率及全血细胞因子分泌的差异。目前，课题组基本完成了预定研究任务，并有重要发现。研究发现：（1）不同免疫抑制剂对IL-1β分泌的作用不同，单用MPA不影响IL-1β分泌，但MPA可浓度依赖性地协同LPS促进IL-1β分泌；（2）MPA协同LPS促进IL-1β分泌的机制是通过激活NLRP3炎性小体/caspase-1信号通路；（3）在LPS诱导的狼疮小鼠脓毒症模型中，MMF能降低脓毒血症小鼠死亡率，对小鼠具有保护作用，其可能与其促进NLRP3炎性小体活化，促进血浆IL-1β升高有关。本研究阐述了MPA新的作用靶点，并为课题组后续“NLRP3炎性小体与自身免疫病”相关研究提供了基础。借鉴了“NLRP3炎性小体活化介导细胞焦亡”等新近研究，课题组继续深入研究，探讨了NLRP3炎性小体活化，加重MRL/lpr狼疮小鼠、胶原诱导的关节炎小鼠、TDI诱导的哮喘小鼠病情的机制。发现，选择性抑制NLRP3炎性小体活化，能阻止小鼠体内细胞焦亡发生，降低血浆中IL-1β等炎症因子分泌，对多种免疫性疾病模型小鼠发挥一定的治疗作用。上述研究为治疗免疫性疾病提供了新的思路与方法。