Macrophage Epigenetic Reprogramming and Metabolic Memory in Response to Altering Glucose Exposure

Abstract

Objective Inflammatory-related diabetic complications persist long-term, despite achievements in glycemic control, a phenomenon termed “metabolic memory”. Current evidence suggests that this is, in part, mediated by hyperglycemia-induced epigenomic reprogramming that produces long-term pro-inflammatory phenotypic and functional outcomes in macrophages. However, the early temporal dynamics of macrophage epigenomic remodeling in response to metabolic fluctuations are not well understood. In this study we aimed to 1) characterize how the macrophage epigenomic landscape was remodeled early in response to fluctuations in the cellular metabolic environment 2) identify timepoints where these changes were most notable, and 3) investigate hyperglycemia-induced changes in the epigenome that persist over time, suggesting a metabolic memory effect. Methods Using an in vitro macrophage model, RAW264.7 cells were cultured in high (22.5 mM) or low (5.0 mM) glucose media for one week before switching the glucose concentration of the media and measuring changes in genome-wide chromatin accessibility over several timepoints by the “Assay for Transposase Accessible Chromatin using Sequencing” (ATAC-Seq). Results Changes in glucose concentration were not found to be the major influencer on chromatin accessibility, but rather, the addition of fresh media induced prominent changes in the epigenomic landscape. Nonetheless, with careful experimental design and sophisticated analysis tools we were able to observe persistent hyperglycemia-induced epigenomic remodeling and identified sites in the macrophage genome that change in accessibility consistent with metabolic memory. Conclusion Macrophages exhibit significant chromatin reorganization in response to changes in their metabolic environment with detectable metabolic memory in their epigenome in response to hyperglycemia. Furthermore, consideration should be given to the effect of fresh media on epigenomic remodeling in previously published and subsequent studies.