Kumar Sandeep, Pamulapati Himani, Tikoo Kulbhushan
Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research, S.A.S. Nagar, Mohali, Punjab, 160062, India.
Mol Cell Endocrinol. 2016 Feb 15;422:233-242. doi: 10.1016/j.mce.2015.12.019. Epub 2015 Dec 30.
Accumulating evidence suggest that diabetic complications persist even after the maintenance of normal glucose levels. However, the molecular mechanisms involved are still unclear. In the present study, we have investigated the molecular mechanism behind the presence of insulin resistance (IR) condition even after normalization of circulating lipids levels both in vivo and in vitro. Persistent inhibition of insulin signalling in absence of elevated circulating lipids level confirms the presence of metabolic memory in our model of IR. IR in human urine derived podocyte-like epithelial cells (HUPECs) was developed by incubating cells with palmitate (750 μM) for 24 h and in SD rats by feeding high fat diet for 16 weeks. Inhibition of insulin induced FOXO1 (regulator of gluconeogenic genes) degradation persisted even after 48 h of palmitate removal from the culture media. Metabolic memory by palmitate was found to be associated with increased FOXO1 activity as evident from increased expression of FOXO1 target genes such as PDK4, p21, G6Pc and IGFBP1. To understand the reason for prolonged activation of FOXO1 and its target genes, chromatin immuno-precipitation (ChIP) was performed with histone H3K36me2 and H3K27me3 antibodies. ChIP assay shows persistent increase in abundance of histone H3K36me2 on promoter region of FOXO1. We also show decreased abundance of histone H3K27me3 on promoter region of FOXO1, in the kidneys of HFD fed rats, which persisted even after 8 weeks of diet reversal. Taken together, we provide first evidence that circulating lipids generate metabolic memory possibly by altering the abundance of histone H3K36me2 and H3K27me3 on FOXO1 promoter.
越来越多的证据表明，即使血糖水平维持正常，糖尿病并发症仍会持续存在。然而，其中涉及的分子机制仍不清楚。在本研究中，我们在体内和体外研究了即使循环脂质水平恢复正常后胰岛素抵抗（IR）状态仍然存在的分子机制。在循环脂质水平未升高的情况下对胰岛素信号传导的持续抑制证实了我们的IR模型中存在代谢记忆。通过将人尿液来源的足细胞样上皮细胞（HUPECs）与棕榈酸（750 μM）孵育24小时来诱导IR，在SD大鼠中则通过喂食高脂饮食16周来诱导IR。即使从培养基中去除棕榈酸48小时后，胰岛素诱导的FOXO1（糖异生基因调节因子）降解的抑制仍持续存在。从FOXO1靶基因如PDK4、p21、G6Pc和IGFBP1的表达增加可以明显看出，棕榈酸引起的代谢记忆与FOXO1活性增加有关。为了理解FOXO1及其靶基因长期激活的原因，我们用组蛋白H3K36me2和H3K27me3抗体进行了染色质免疫沉淀（ChIP）实验。ChIP分析显示FOXO1启动子区域组蛋白H3K36me2的丰度持续增加。我们还发现，在喂食高脂饮食的大鼠肾脏中，FOXO1启动子区域组蛋白H3K27me3的丰度降低，即使在饮食恢复正常8周后这种情况仍持续存在。综上所述，我们首次提供证据表明，循环脂质可能通过改变FOXO1启动子上组蛋白H3K36me2和H3K27me3的丰度来产生代谢记忆。
