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.
Keywords: Diabetic nephropathy; Epigenetics; Metabolic memory; Type 2 diabetes.
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