Sortilin对肝细胞apoAV分泌的调控在肥胖相关高甘油三酯血症中作用机制的研究

Apoliprotein A-V(apoAV), secreted from hepatocyte, is well known to reduce plasma TG through LPL. Whereas apoAV also be retained in hepatocytes and intracellular apoAV has been demonstrated to promote intracellular TG accumulation. Therefore, secretion from hepatocyte is cardinal for the apoAV to reduce plasma TG. However, the regulatory mechanism underlying this process is undetermined. Sortilin has been reported to mediate hepatic lipoprotein secretion. It has been previously reported that sortilin could bind with apoAV. Increased hepatic sortilin expression in mice reduced plasma TG levels. Our preliminary study found insufficient hepatic apoAV secretion in obese patients. Besides, reduced hepatic sortilin expression was observed in obese mice, while siRNA-mediated knockdown of sortilin in HepG2 cell exhibited reduced secretion of apoAV. Based on these evidence, we hypothezise that sortilin may bind with apoAV through Vps10p domain and facilitate its secrestion from hepatocyte. In obese status, increased plasma TG may be due to insufficient hepatic sortilin expression which result in impaired hepatic apoAV secretion. This study is going to confirm the binding of sortilin with apoAV as well as their subcellular location. Besides, this study is going to further study the regulatory effect of sortilin on hepatic apoAV secretion and plasma TG in obese status, with the aim to delineate the mechanism by which sortilin regulate hepatic apoAV secretion and its implication in hypertriglycemia observed in obesity.

载脂蛋白AV（apoAV）除分泌至细胞外降低血浆TG，还可滞留在肝细胞内，促进细胞内TG聚集。因此，促进肝细胞apoAV分泌是其降低血浆TG的关键，但调控其分泌的机制不明。已知sortilin参与脂蛋白转运，体外可结合apoAV，且其水平与血浆TG有关。前期研究发现肥胖患者肝脏apoAV分泌不足，肥胖小鼠肝脏sortilin表达下调，而沉默sortilin可致肝细胞内apoAV滞留。据此推测：sortilin可通过Vps10p结构域与肝细胞apoAV结合并促进其分泌；肥胖时，肝脏sortilin表达下调及其介导apoAV分泌不足，血浆TG升高。本项目拟先验证sortilin结合apoAV及亚细胞定位，接着观察其对肝细胞apoAV分泌的调节及机制，再探讨其对肥胖小鼠肝脏apoAV分泌及血浆TG的影响，从而明确sortiin对肝细胞apoAV分泌的调节机制及其在肥胖相关高甘油三酯血症中的作用。

APOA5的基因多态性与高甘油三酯血症、心肌梗死的发生密切相关。本项目观察了冠心病患者血清sortilin与PCSK9的水平及相关性。研究发现未接受他汀类药物治疗的冠心病患者血清中sortilin浓度较高，提示他汀类药物可能影响循环sortilin和sortilin介导的PCSK9分泌。然而，它们之间相互作用的潜在机制还需要进一步探索。此外，本项目还发现NAFLD患者血清sortilin水平显著升高，与ApoA-V呈正相关。血清sortilin水平与NAFLD相关，可作为NAFLD的生物标志物。另外，为了明确sortilin对肝细胞apoAV表达的调节机制及其在脂肪肝相关高甘油三酯血症中的作用。申请人以体外培养的 HepG2 细胞为对象，发现sortilin 在肝细胞内可与 apoAV 相互结合，sortilin 可能作为分子伴侣，促进apoAV 在肝细胞内的滞留；同时探讨了sortilin对高脂饮食诱导的脂肪肝小鼠肝脏 apoAV 表达及血浆 TG 的影响，从而明确 sortilin 对肝细胞 apoAV 表达的调节机制及其与脂肪肝的相关性。