Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA.
Department of Biochemistry and Cambridge Systems Biology Centre, University of Cambridge, Cambridge, United Kingdom.
Hepatology. 2021 Sep;74(3):1203-1219. doi: 10.1002/hep.31771. Epub 2021 May 22.
Human transmembrane 6 superfamily 2 (TM6SF2) variant rs58542926 is associated with NAFLD and HCC. However, conflicting reports in germline Tm6sf2 knockout mice suggest no change or decreased very low density lipoprotein (VLDL) secretion and either unchanged or increased hepatic steatosis, with no increased fibrosis. We generated liver-specific Tm6Sf2 knockout mice (Tm6 LKO) to study VLDL secretion and the impact on development and progression of NAFLD.
Two independent lines of Tm6 LKO mice exhibited spontaneous hepatic steatosis. Targeted lipidomic analyses showed increased triglyceride species whose distribution and abundance phenocopied findings in mice with liver-specific deletion of microsomal triglyceride transfer protein. The VLDL triglyceride secretion was reduced with small, underlipidated particles and unchanged or increased apolipoprotein B. Liver-specific adeno-associated viral, serotype 8 (AAV8) rescue using either wild-type or mutant E167K-Tm6 reduced hepatic steatosis and improved VLDL secretion. The Tm6 LKO mice fed a high milk-fat diet for 3 weeks exhibited increased steatosis and fibrosis, and those phenotypes were further exacerbated when mice were fed fibrogenic, high fat/fructose diets for 20 weeks. In two models of HCC, either neonatal mice injected with streptozotocin (NASH/STAM) and high-fat fed or with diethylnitrosamine injection plus fibrogenic diet feeding, Tm6 LKO mice exhibited increased steatosis, greater tumor burden, and increased tumor area versus Tm6 flox controls. Additionally, diethylnitrosamine-injected and fibrogenic diet-fed Tm6 LKO mice administered wild-type Tm6 or E167K-mutant Tm6 AAV8 revealed significant tumor attenuation, with tumor burden inversely correlated with Tm6 protein levels.
Liver-specific Tm6sf2 deletion impairs VLDL secretion, promoting hepatic steatosis, fibrosis, and accelerated development of HCC, which was mitigated with AAV8- mediated rescue.
人类跨膜 6 超家族 2（TM6SF2）变体 rs58542926 与非酒精性脂肪性肝病（NAFLD）和肝细胞癌（HCC）相关。然而，种系 Tm6sf2 敲除小鼠的相互矛盾的报告表明，极低密度脂蛋白（VLDL）分泌没有变化或减少，肝脂肪变性不变或增加，纤维化没有增加。我们生成了肝脏特异性 Tm6Sf2 敲除小鼠（Tm6 LKO），以研究 VLDL 分泌及其对 NAFLD 发展和进展的影响。
两条独立的 Tm6 LKO 小鼠线表现出自发性肝脂肪变性。靶向脂质组学分析显示，甘油三酯的分布和丰度发生变化，其表型类似于肝脏特异性微粒体甘油三酯转移蛋白缺失的小鼠。VLDL 甘油三酯的分泌减少，形成小的、低脂质化的颗粒，载脂蛋白 B 不变或增加。使用野生型或突变型 E167K-Tm6 的肝脏特异性腺相关病毒（AAV8）挽救，可减少肝脂肪变性并改善 VLDL 分泌。高脂奶喂养 3 周的 Tm6 LKO 小鼠表现出更严重的脂肪变性和纤维化，而当这些小鼠接受致纤维化、高脂/果糖饮食喂养 20 周时，这些表型进一步加重。在两种 HCC 模型中，即链脲佐菌素（NASH/STAM）注射的新生小鼠和高脂喂养，或二乙基亚硝胺（DEN）注射加致纤维化饮食喂养，与 Tm6flox 对照相比，Tm6 LKO 小鼠表现出更严重的脂肪变性、更大的肿瘤负担和更大的肿瘤面积。此外，在 DEN 注射和致纤维化饮食喂养的 Tm6 LKO 小鼠中，给予野生型 Tm6 或 E167K 突变型 Tm6 AAV8，发现肿瘤明显减轻，肿瘤负担与 Tm6 蛋白水平呈负相关。
肝脏特异性 Tm6sf2 缺失会损害 VLDL 分泌，促进肝脂肪变性、纤维化和 HCC 的加速发展，而 AAV8 介导的挽救可减轻这些影响。
