Abstract 15889: High Glucose Leads to Increased Inflammatory Gene Expression via Epigenetic Histone H3 Lysine 9 Methylation in Cardiomyocyte
Diabetic patients continue to develop inflammation and cardiovascular complications even after achieving glycemic control. The poorly understood “metabolic memory” phenomenon poses major challenges in treating diabetes. Also, the mechanism by which high levels of glucose (HG) causes inflammation and diabetic cardiomyopathy are not known. Recent studies demonstrate a link between epigenetic changes such as chromatin histone methylation and gene expression. Thus, we tested whether histone 3 lysine-9 tri-methylation (H3K9me3), a key epigenetic chromatin marker, was involved in HG-induced inflammation and metabolic memory. Incubating H9C2 rat ventricular cells in high glucose (25 mM) resulted in increased inflammatory cytokine IL-6 mRNA levels (3.3 ± 0.4 fold at 72 h, p<0.02), and MCP-1 mRNA levels (2.8 ± 0.6 fold at 72 h, p<0.05, assessed by real-time PCR) when compared with myocytes incubated in normal glucose (NG) (5 mM), whereas mannitol (25 mM, osmotic control) has no effect. Chromatin immunoprecipitation (ChIP) assays showed that H3K9me3 levels were significantly decreased at the promoters of these two key inflammatory genes. Immunoblotting demonstrated that protein levels of the H3K9me3 methyltransferase Suv39h1 were also reduced after HG treatment compare to NG. If we changed HG to NG before 48 h of HG treatment, the effects of HG on the expression of inflammatory cytokines and the levels of H3K9me3 was irreversible, however, HG-induced apoptosis (O.D. value = 0.39 ± 0.06 in HG group vs. 0.13 ± 0.04 in NG, as assessed by Death ELISA, p<0.05), and mitochondrial dysfunction (assessed by Rh-123) were reversible. These results suggest that HG-induced sustained inflammatory phenotype and epigenetic histone dysfunction, but not that HG-induced mitochondrial dysfunction and apoptosis, may be a major mechanism for “metabolic memory”. In conclusion, our data demonstrate that HG increases expression of inflammatory cytokine and decreases the levels of histone-3 methylation at the cytokine promoter, and suggest that modulating histone 3 methylation and inflammatory cytokine expression may be a useful strategy to prevent metabolic memory and cardiomyopathy in diabetic patients.
- © 2010 by American Heart Association, Inc.