Modulation of insulin degrading enzyme activity and liver cell proliferation

Diabetes mellitus type 2 (T2DM), insulin therapy, and hyperinsulinemia are independent risk factors of liver cancer. Recently, the use of a novel inhibitor of insulin degrading enzyme (IDE) was proposed as a new therapeutic strategy in T2DM. However, IDE inhibition might stimulate liver cell proliferation via increased intracellular insulin concentration. The aim of this study was to characterize effects of inhibition of IDE activity in HepG2 hepatoma cells and to analyze liver specific expression of <i>IDE</i> in subjects with T2DM. HepG2 cells were treated with 10 nM insulin for 24 h with or without inhibition of IDE activity using <i>IDE</i> RNAi, and cell transcriptome and proliferation rate were analyzed. Human liver samples (n = 22) were used for the gene expression profiling by microarrays. In HepG2 cells, <i>IDE</i> knockdown changed expression of genes involved in cell cycle and apoptosis pathways. Proliferation rate was lower in <i>IDE</i> knockdown cells than in controls. Microarray analysis revealed the decrease of hepatic <i>IDE</i> expression in subjects with T2DM accompanied by the downregulation of the p53-dependent genes <i>FAS</i> and <i>CCNG2</i>, but not by the upregulation of proliferation markers <i>MKI67, MCM2</i> and <i>PCNA</i>. Similar results were found in the liver microarray dataset from GEO Profiles database. In conclusion, <i>IDE</i> expression is decreased in liver of subjects with T2DM which is accompanied by the dysregulation of p53 pathway. Prolonged use of IDE inhibitors for T2DM treatment should be carefully tested in animal studies regarding its potential effect on hepatic tumorigenesis.

2型糖尿病（Diabetes mellitus type 2, T2DM）、胰岛素治疗与高胰岛素血症均为肝癌的独立危险因素。近期，一款新型胰岛素降解酶（Insulin Degrading Enzyme, IDE）抑制剂被提出可作为2型糖尿病的新型治疗策略。然而，胰岛素降解酶抑制可能通过升高细胞内胰岛素浓度，促进肝细胞增殖。本研究旨在阐明胰岛素降解酶活性抑制在HepG2肝癌细胞中的作用，并分析2型糖尿病患者肝脏中<i>IDE</i>的特异性表达情况。将HepG2细胞用10 nM胰岛素处理24小时，设置使用<i>IDE</i> RNAi（RNA干扰，RNA interference, RNAi）抑制胰岛素降解酶活性与不抑制的两组，随后对细胞转录组及增殖速率进行分析。本研究纳入22份人类肝脏样本，通过微阵列技术开展基因表达谱分析。在HepG2细胞中，<i>IDE</i>基因敲低会改变细胞周期与凋亡通路相关基因的表达；<i>IDE</i>敲低组细胞的增殖速率低于对照组。微阵列分析结果显示，2型糖尿病患者的肝脏<i>IDE</i>表达水平降低，同时伴随p53依赖型基因<i>FAS</i>与<i>CCNG2</i>的表达下调，但增殖标志物<i>MKI67</i>、<i>MCM2</i>及<i>PCNA</i>的表达并未出现上调。来自GEO Profiles数据库的肝脏微阵列数据集也验证了上述实验结果。综上，2型糖尿病患者肝脏中的<i>IDE</i>表达水平降低，同时伴随p53通路的调控异常。针对2型糖尿病的胰岛素降解酶抑制剂长期使用，应在动物实验中对其潜在的肝脏肿瘤发生风险进行严谨评估。