胆汁淤积下IL-32高表达促进肝脏炎症放大反应及肝纤维化的机制研究

Multiple pathologies i.e gallstone obstruction of the bile duct, biliary atresia, pancreas tumors and drug toxicity can cause persisting cholestasis which can lead to liver failure, fibrosis, cirrhosis and death. The persisting inflammatory plays a critical role on the progress of cholestasis. In our preliminary experiments, we first described that elevated hepatic IL-32 was observed in human obstructive cholestasis. Interleukin 32 (IL-32) was a new proinflammatory cytokine reported by the Kim et.al in 2005. Interestingly, IL-32 gene was identified in most mammals except rodents, which restrains in vivo studies. The mature IL-32 are intracellularly expressed and released by stimulations of various activators (e.g. TNFα). Recent studies demonstrated that IL-32 promotes the process of rheumatoid arthritis RA and chronic obstructive pulmonary diseases COPD. Our preliminary data indicated that hepatic IL-32 mRNA in obstructive cholestatic patients positively correlated with proinflammatory cytokines mRNA levels, such as IL-8 and MCP1, and fibrotic genes mRNA levels, such as Cola1 and Cola2, implying that IL-32 may promotes liver inflammation amplification and fibrosis process. We also found that IL-32 induces the IL-6 and IL-8 mRNA expression in hepatoma cells Huh7 and stimulates α-SMA expression in human hepatic stellate cells LX2. Recent studies reported that P38/MAPK pathway is activated by IL-32 in PBMCs. And phosphorylated P38 protein was significantly increased but not total P38 protein in human obstructive cholestatic livers.. All of these results trigger us to formulate a hypothesis: elevated hepatic IL-32 expression activates P38/MAPK signaling pathway promotes liver inflammation amplification and liver fibrosis process in obstructive cholestatic patients. In order to prove this hypothesis, we use different molecular biological techniques, such as human IL-32 liver-specific transgenic mice, TaqMan qPCR, western-blot, and human primary hepatocytes and stellate cells culture to study the functional role of IL-32 and clarify its molecular mechanism in human obstructive cholestasis, which will be promising for a clue of the clinical therapy and understanding the cholestasis.

胆汁淤积肝病发病率高，易致肝纤维化、肝衰竭。目前认为促炎因子对胆汁淤积肝病进展起关键作用。我们首次发现人阻塞性胆汁淤积下肝脏IL-32高表达，但其功能和调控机制不清楚。IL-32为新近发现的促炎因子，在啮齿类动物不表达，其表达定位于细胞浆。近期报道，IL-32对类风湿性关节炎等起促进作用。而我们预实验表明，胆汁淤积肝脏IL-32 mRNA与炎症因子IL-8等或肝纤维化指标α-SMA mRNA等呈正相关。而P38信号通路为IL-32极重要的下游通路，且在胆汁淤积肝脏被激活。细胞因子IL-32可诱导肝癌细胞株Huh7 表达IL-6等及人肝星状细胞株LX2活化。因此，我们提出假设：胆汁淤积下肝脏IL-32高表达可激活P38通路促进肝脏炎症放大反应及纤维化。本课题拟运用人源IL-32肝脏特异性转基因小鼠、人原代肝细胞和肝星状细胞培养等技术，明确上述假设。这将为胆汁淤积临床治疗提供新思路和理论依据。

胆汁淤积是多种因素所致肝损伤的常见临床综合症，不同病因导致的胆汁淤积肝病，其共同特点是肝脏内过度蓄积胆汁酸。持续的胆汁淤积易致肝纤维化、肝衰竭，炎症反应在胆汁淤积肝病进展中起关键作用。我们发现细胞因子白细胞介素 32(IL-32)在胆汁淤积患者肝脏内表达显著升高，但它在胆汁淤积肝病进程中的作用和分子调控机制尚不清楚。因此，我们开展了相关研究工作，取得如下重要结果：(1)利用胆汁淤积患者肝组织样本，明确了胆汁淤积下IL-32表达升高，并且与血清肝损伤标志物呈负相关。(2)构建人源IL-32肝脏特异性转基因小鼠并造胆汁淤积小鼠模型，确认IL-32高表达可通过抑制肝脏内胆汁酸蓄积和炎症反应发挥抗胆汁淤积肝损伤的效应。(3)在细胞和动物水平上，阐明IL-32可通过抑制β-Catenin与Fxr结合，促进Fxr转录活性，下调胆汁酸合成酶Cyp7a1表达，上调胆汁酸转运蛋白Ostα/β表达，减少肝脏内胆汁酸蓄积的机制。(4)体内外实验证实胆汁淤积下IL-32能够通过抑制JNK/MAPK信号通路激活，下调趋化因子Ccl2、Cxcl5、Cxcl10表达，减少肝脏内中性粒细胞和CD8+ T细胞浸润，减轻肝脏炎症反应的机制。(5)IL-32基因治疗能够明显减轻Abcb4基因敲除小鼠胆汁淤积肝损伤和肝纤维化，进一步明确IL-32高表达通过抑制肝脏内胆汁酸蓄积和炎症反应，减轻胆汁淤积肝损伤的效应。通过本项目的研究不仅能够使我们对胆汁淤积肝病发病机制理解更深入，同时也为临床治疗胆汁淤积提供了新靶点和理论依据。