Abnormal DNA Methylation Induced by Hyperglycemia Reduces CXCR4 Gene Expression in CD34⁺ Stem Cells

Background: CD34⁺ stem/progenitor cells are involved in vascular homeostasis and in neovascularization of ischemic tissues. The number of circulating CD34⁺ stem cells is a predictive biomarker of adverse cardiovascular outcomes in diabetic patients. Here, we provide evidence that hyperglycemia can be “memorized” by the stem cells through epigenetic changes that contribute to onset and maintenance of their dysfunction in diabetes mellitus. Methods and Results: Cord-blood–derived CD34⁺ stem cells exposed to high glucose displayed increased reactive oxygen species production, overexpression of p66^shc gene, and downregulation of antioxidant genes catalase and manganese superoxide dismutase when compared with normoglycemic cells. This altered oxidative state was associated with impaired migration ability toward stromal-cell–derived factor 1 alpha and reduced protein and mRNA expression of the C-X-C chemokine receptor type 4 (CXCR4) receptor. The methylation analysis by bisulfite Sanger sequencing of the CXCR4 promoter revealed a significant increase in DNA methylation density in high-glucose CD34⁺ stem cells that negatively correlated with mRNA expression (Pearson r=−0.76; P=0.004). Consistently, we found, by chromatin immunoprecipitation assay, a more transcriptionally inactive chromatin conformation and reduced RNA polymerase II engagement on the CXCR4 promoter. Notably, alteration of CXCR4 DNA methylation, as well as transcriptional and functional defects, persisted in high-glucose CD34⁺ stem cells despite recovery in normoglycemic conditions. Importantly, such an epigenetic modification was thoroughly confirmed in bone marrow CD34⁺ stem cells isolated from sternal biopsies of diabetic patients undergoing coronary bypass surgery. Conclusions: CD34⁺ stem cells “memorize” the hyperglycemic environment in the form of epigenetic modifications that collude to alter CXCR4 receptor expression and migration.