鹅补体系统C3基因在脂肪肝形成中的表达及作用机制研究

Goose liver can deposit a lot of fat without obvious pathological symptoms in the process of overfeeding, suggesting there exists a tolerance mechanism in goose liver. Complement, a set of proteins with enzyme activity, exists in the blood, interstitial fluid and cell surface. These proteins are mainly synthesized and released by the liver. In addition to participating in body's defense against microbial pathogens, immune modulation, and response to immune pathological injury, complement is also involved in inflammation and metabolic diseases (such as fatty liver disease). Our previous high-throughput sequencing data showed that unlike in the mammals, a large number of components of the complement system were suppressed in goose fatty liver, which supports the existence of a tolerance mechanism in goose liver. Unfortunately, this mechanism is unclear. In this project, we will determine the expression of C3, the core components of the complement system, at mRNA and protein levels in the livers of normally-fed and overfed geese and in cultured primary goose hepatocytes treated with factors associated with fatty liver. Moreover, we will identify downstream targets, signaling pathways and biological function of C3 through molecular biology approaches (i.e., overexpression and knockdown of C3 gene). Thus, this project will reveal the relationship between the complement system and the development of goose fatty liver and the relevant mechanism.

鹅在填饲过程中肝脏可以沉积大量脂肪而不发生明显的病理症状，表明鹅在肝脂肪变性过程中存在耐受机制。补体是一组存在于血液、组织液和细胞表面，主要由肝脏合成分泌的酶活性蛋白质，除参与机体的微生物防御、免疫调节和介导免疫病理的损伤性反应外，还与炎症反应、相关代谢疾病（如脂肪肝）有关。本课题组前期的高通量测序结果表明，与哺乳动物的情形不同，补体系统的大量组分在鹅肥肝形成过程中受到抑制，推测这与鹅肝脏存在耐受机制有关。目前，这种补体系统受到抑制的机制并不清楚。本项目将从补体系统核心组分C3基因入手，在组织水平检测C3基因在鹅肥肝形成过程中的mRNA和蛋白表达水平；在细胞水平检测C3基因在脂肪肝形成相关因子刺激下的mRNA和蛋白表达水平；并干预C3基因的表达（过表达和敲低）以探索其下游信号通路及生物学效应，最终通过对补体系统核心组分C3的一系列研究来探索鹅补体系统与脂肪肝形成的关系及相关调控机制

脂肪肝是人类日常生活中的普遍现象，其直接原因是机体肝脏脂肪代谢失去平衡，根据发展程度可以分为单纯性脂肪肝、脂肪肝炎、肝硬化甚至肝癌。鹅肥肝是由高能饲粮所诱导，在填饲过程中其肝脏可以沉积大量脂肪而不发生明显的病理症状，表明鹅肝中存在某种特殊的保护机制阻止或减缓其由单纯性脂肪肝发展为脂肪肝炎。补体系统作为介导“炎症反应”的核心系统，在鹅肥肝形成中扮演了重要角色。本项目一方面通过组织试验证实了补体系统核心组分C3在鹅肝中mRNA和蛋白水平均处于抑制状态，一方面通过在不同细胞中进行营养因子处理试验发现油酸可以显著抑制鹅原代肝细胞中C3的表达，而促进人肝癌细胞和鼠原代肝细胞中C3的表达。表明这一在鹅肥肝形成中大量产生的不饱和脂肪酸极有可能是导致鹅肝中补体系统抑制的重要诱导因素，而探索油酸与补体系统的相互作用机制以及朗德鹅中相关基因的特殊性将成为解开鹅肥肝保护机制之谜的钥匙，并为其他动物的脂肪肝研究和治疗打开新的思路。