Department of Pediatrics, Far Eastern Memorial Hospital, New Taipei City, Taiwan; Oriental Institute of Technology, New Taipei City, Taiwan.
Department of Pediatrics, Far Eastern Memorial Hospital, New Taipei City, Taiwan.
J Hepatol. 2016 Dec;65(6):1209-1216. doi: 10.1016/j.jhep.2016.06.029. Epub 2016 Jul 12.
BACKGROUND & AIMS: Autophagy has been shown to be crucial in the regulation of the intracellular lipid stores in hepatocytes. We hypothesize that immunity-related GTPase family M (IRGM) gene (an autophagy-related gene) variants confer the susceptibility to non-alcoholic fatty liver disease (NAFLD) development.
832 obese children and adolescents aged 6-18years were recruited. NAFLD was determined by liver ultrasonography. We genotyped PNPLA3 rs738409, GCKR rs780094, TM6SF2 rs58542926, six IRGM single nucleotide polymorphisms (rs13361189, rs9637876, rs72553867, rs10065172, rs1000113, and rs11747270). To understand the molecular mechanism, we examined the effects of IRGM knockdown and overexpression on autophagic flux and lipid droplet metabolism in human hepatoma cells.
22.8% of recruited obese children and adolescents had NAFLD. Multiple logistic regression analysis revealed that after controlling for the effects of age- and gender-adjusted body mass index, gender, PNPLA3, GCKR, and TM6SF2 polymorphisms, variant IRGM rs10065172 TT genotype independently increased the odds ratio of NAFLD by 2.04 (95% confidence interval 1.22-3.42; p=0.007), as compared to the CC genotype. The predictive model was validated by means of 10-fold cross validation. Functional assay revealed that IRGM knockdown inhibited autophagic flux and increased lipid droplet content in HepG2 and PLC/PRF/5 cells, which were reversed by the autophagy inducer rapamycin administration. Similarly, wortmannin (an autophagy inhibitor) increased intracellular lipid droplet content. In contrast, overexpression of IRGM caused decreased lipid droplet content in HepG2 cells.
Our findings suggest that IRGM may contribute to the development of human NAFLD by altering hepatic lipid metabolism through the autophagy pathway.
Autophagy is involved in the process of lipid metabolism in hepatocytes. The mechanism of autophagy regulation by IRGM has just been unveiled. This study demonstrates that genetic variants in IRGM confer risk of human non-alcoholic fatty liver disease. The functional studies reveal how IRGM regulates hepatic lipid droplet content.
自噬在调节肝细胞内脂质储存中起着至关重要的作用。我们假设免疫相关鸟苷三磷酸酶家族 M（IRGM）基因（一种自噬相关基因）的变异与非酒精性脂肪性肝病（NAFLD）的易感性有关。
招募了 832 名年龄在 6 至 18 岁的肥胖儿童和青少年。通过肝脏超声检查确定 NAFLD。我们对 PNPLA3 rs738409、GCKR rs780094、TM6SF2 rs58542926 进行基因分型，以及六个 IRGM 单核苷酸多态性（rs13361189、rs9637876、rs72553867、rs10065172、rs1000113 和 rs11747270）。为了了解分子机制，我们检测了 IRGM 敲低和过表达对人肝癌细胞自噬流和脂滴代谢的影响。
22.8%的肥胖儿童和青少年患有 NAFLD。多因素逻辑回归分析显示，在控制年龄和性别调整的体重指数、性别、PNPLA3、GCKR 和 TM6SF2 多态性的影响后，IRGM 变体 rs10065172 TT 基因型与 NAFLD 的比值比独立增加了 2.04（95%置信区间 1.22-3.42；p=0.007），与 CC 基因型相比。该预测模型通过 10 倍交叉验证进行了验证。功能分析显示，IRGM 敲低抑制了 HepG2 和 PLC/PRF/5 细胞中的自噬流并增加了脂滴含量，而自噬诱导剂雷帕霉素的给药可逆转这一结果。同样，wortmannin（一种自噬抑制剂）增加了细胞内脂滴含量。相比之下，IRGM 的过表达导致 HepG2 细胞中的脂滴含量减少。
我们的研究结果表明，IRGM 通过自噬途径改变肝内脂质代谢，可能导致人类 NAFLD 的发生。
自噬参与肝细胞内脂质代谢的过程。IRGM 通过调节自噬的机制刚刚被揭示。这项研究表明，IRGM 中的遗传变异赋予了人类非酒精性脂肪性肝病的风险。功能研究揭示了 IRGM 如何调节肝内脂滴含量。
