白介素-37蛋白变体的功能比较及其差异机制研究

In contrast with other IL-1 protein family members, interleukin-37 (IL-37) has been reported to be a fundamental suppressor of innate immunity and involved in the pathogenesis of many inflammatory diseases. Recently, we discovered two more IL-37 variants other than the NCBI reference protein sequence through in silico analysis. Evolutionary genetic analysis strongly suggests that human IL-37 variants originate from a common ancestor very earlier during hominid evolution and are shaped by selection and deviate from neutrality. Therefore, we hypothesize that human IL-37 variants have evolved for different biological functions. Importantly, our preliminary experimental data support this hypothesis. In this proposal, we will further characterize and compare the functions of the IL-37 variants both in vitro and in vivo, including: 1) biochemical analysis of their recombinant proteins; 2) comparing their anti-inflammatory functions in cultured cell lines; 3) investigating the mechanism(s) underlying functional differences among these variants; 4) assessment of their protection role in animal disease model. These studies should help us to further understand the biological functions of IL-37 as well as how it exerts such functions. In addition, the relevant results will also provide rationale for investigating the influence of genetic polymorphism of IL-37 on certain immune diseases susceptibility.

白介素-37(IL-37)具有免疫抑制作用，或与多种炎性疾病相关。我们最近发现了两种主要的IL-37蛋白变体（Var1和Var2），其中Var2与参考序列 (Ref)相比有5个氨基酸残基改变，均位于蛋白功能区；进化遗传学分析强烈提示，IL-37变体的演化来自选择压力，而非中性改变。因此我们猜测：三种IL-37蛋白变体的生物学功能或存在差别。我们的前期结果支持这一猜想，此外，我们还发现IL-37变体的胞内稳定性有差别。在此基础上，本项目拟开展以下研究：1)鉴定IL-37蛋白变体的生物化学性质；2) 比较IL-37蛋白变体的免疫调节功能；3) 探索导致IL-37蛋白变体免疫功能差异的背后机制；4) 验证IL-37蛋白变体是否在体内发挥不同作用。该研究将能揭示IL37基因遗传变异的功能意义，加深对IL-37免疫功能和调控机制的理解，以期为今后发现和理解IL-37变体如何影响疾病表型提供理论依据。

IL-37是免疫调节系统的一个重要成员，是人体中一个重要的炎症抑制分子。在进化压力下，人群中现有三种主要的IL-37蛋白变体共存，IL37-Var2存在由非同义单核苷酸多态性(SNP)导致的5个氨基酸替换，且均位于蛋白的功能区。因此，我们猜测：IL-37的三种蛋白变体(IL37-Ref, -Var1、-Var2)具有不尽相同的生物学功能。围绕这一猜测，我们利用稳定表达IL37-Ref、-Var1或者-Var2的细胞系，鉴定和比较了三种IL-37蛋白变体在免疫细胞天然免疫应答中发挥的功能。证实在细胞水平上，IL37-Ref, IL37-Var1和IL37-Var2调节固有免疫应答的能力具有显著差异。不论是稳态还是刺激条件下，细胞内IL37-Var2的蛋白表达水平都显著低于IL37-Ref和IL37-Var1。在炎症或固有免疫刺激信号作用下，IL37-Var2表现出一过性的蛋白表达水平增加。进一步研究发现，IL37-Var2蛋白在细胞内易被泛素化降解。与胞内表达不同，三种IL37变体重组蛋白在胞外抑制炎性因子的表达的能力没有显著区别。探索其在HIV免疫病理及治疗预后中的作用，我们发现，血浆中IL-37含量与HIV初治患者血清病毒载量及CD4+T细胞计数无显著相关性，但与初治患者的免疫激活状态存在密切联系。综上所述，IL-37 Var2在细胞内易于被泛素化降解，表现为蛋白稳定性较差而弱化了其免疫调节能力。该发现与我们先前的遗传进化分析推测一致，并表明IL-37基因多态性可能与人类免疫疾病的发生发展相关。