IL-37缓解痛风急性炎症的作用机制---以Mertk为靶点的研究

Acute gout is a self-limited inflammatory response to MSU crystals in the joints and periarticular tissue. Recognition of MSU by resident macrophages triggers activation of the NALP3 inflammasome, release of active interleukin (IL)-1β and chemokines that drive the rapid recruitment of neutrophils and circulating monocytes to the inflamed site. The shutdown of this inflammatory response is linked to a number of regulatory events ranging from crystal coating and apoptotic cell clearance through to pro-inflammatory cytokine regulation and transforming growth factor β1 (TGFβ1) production. However, current research into the pathways involved in the resolution of inflammation is still limited. IL-37 is a member of the IL-1 family. IL-37 has emerged as a fundamental inhibitor of the innate immune response by shifting the cytokine equilibrium away from excessive inflammation. IL-37 now emerges as a dual-function cytokine with intra- and extracellular properties for suppressing innate inflammation. IL-37 interacted intracellularly with Smad3. Whereas, IL-1R8–IL-18Rα complex acts as the cell surface receptor for IL-37 and IL-37 uses IL-1R8 to trigger multiple intracellular switches to block inflammation, including not only the anticipated inhibition of MAPKs and NF-κB but also the unexpected pseudo-starvational effects on the mTOR pathway, inhibition of TAK1 and Fyn, activation of STAT3, Mertk and PTEN, and induction of p62(dok). In our previous studies, IL-37 plays a potent immune suppressive role in the pathogenesis of both experimental gouty models in vitro and in vivo by downregulating proinflammatory cytokines and chemokines, markedly reduced neutrophil and monocyte/macrophage recruitment, and mitigated pathological digitoplantar inflammation. Thus, in this study we will focus on the mechanisms of IL-37 and its dual-function properties, and furthor study whether IL-37 limit runaway inflammation initiated by MSU crystal induced immune responses, partly in a Mertk dependent way. This study may provide insight on the prevention and treatment of gouty arthritis.

尿酸钠晶体作为“危险信号”被单核/巨噬细胞识别并激活炎症小体Nalp3，产生大量IL-1β并招募炎症细胞是痛风最主要的炎症机制。另外，痛风具有自限性是其最大特点，虽然研究发现巨噬细胞非炎症性摄取MSU和清除凋亡中性粒细胞，释放TGFβ1是痛风缓解的重要因素，但其中的具体机制仍不十分明确。IL-37是新近发现的参与固有免疫应答的重要炎症抑制因子。IL-37属于IL-1家族，成熟的IL-37在细胞内外均具有显著抑制炎症作用：在细胞内通过smad3，在细胞外与抑制性受体IL1R8结合发挥炎症抑制作用。我们前期研究证实IL-37参与并缓解痛风急性炎症，且具有显著的预防和治疗作用。本项目拟在上述研究的基础上，进一步进行IL-37缓解痛风的机制研究：明确IL-37是否通过细胞内外双途径发挥作用，并对其可能靶点Mertk进行干预，证实Mertk介导IL-37促进巨噬细胞对MSU的非炎性吞噬和清除。

单钠尿酸钠（MSU）晶体作为“危险信号”被单核/巨噬细胞识别并激活炎症小体Nalp3，产生大量IL-1β并招募炎症细胞是痛风最主要的炎症机制。另外，痛风具有自限性是其最大特点，虽然研究发现巨噬细胞非炎症性摄取MSU和清除凋亡中性粒细胞，释放TGFβ1是痛风缓解的重要因素， 但其中的具体机制仍不十分明确。IL-37是新近发现的参与固有免疫应答的重要炎症抑制因子。IL-37属于IL-1家族，成熟的IL-37在细胞内外均具有显著抑制炎症作用：在细胞内通过smad 3，在细胞外与抑制性受体IL-1R8结合发挥炎症抑制作用。. 本研究通过体内外研究明确：①IL-37是否通过胞内Smad3和胞外IL-1R8途径缓解MSU诱导的急性炎症；②Mertk是否作为IL-37的靶点影响其抑炎作用。.体外研究发现，MSU分别刺激人THP-1和人滑膜细胞，IL-37处理组较未处理组，IL-1β、IL-8、CCL2表达明显降低，而TGF-β无明显变化。体内研究结果：小鼠痛风腹腔模型，IL-37干预组较对照组，趋化因子表达水平下降，而TGF-β水平无变化；腹腔液中性粒细胞及单核巨噬细胞比例明显下降。小鼠急性痛风关节炎模型，IL-37干预组较对照组足掌肿胀度和关节病理炎症程度明显减轻。小鼠急性痛风关节炎模型，IL-37干预组较IL-37未干预组足掌组织Mertk, pro-IL-1β，Smad3，IL-1R8，Socs3的mRNA表达明显上调，iNOS、Nalp3表达下调。足掌组织Western blot结果证实IL-1R8，Smad3，Socs3表达增高，而Nalp3表达下降。结果表明，在胞内外，IL-37分别通过Smad3和IL-1R8抑制Nalp3，上调Scos3，缓解MSU诱导的急性炎症。采用Mertk抑制剂干预，体外研究结果表明Mertk抑制剂组THP-1经MSU+IL37处理后IL-1β水平、IL-8和CCL2水平和吞噬MSU水平较无Mertk抑制剂组增高。体内研究：小鼠急性痛风炎症模型，IL-37（Mertk抑制剂±）干预，Mertk抑制剂组较无Mertk抑制剂组小鼠足掌肿胀度和组织病理炎症程度明显加重；Nalp3 mRNA水平和蛋白表达增高；Scos3 mRNA水平和蛋白表达下降。