Abstract 5751: High Glucose Induces Apoptosis in Endolthelial Cells via Epigenetic Regulation of Insulin-Like Growth Factor Receptor Expression

Abstract

High glucose-induced endothelial cell dysfunction is considered to be the main cause of the development of vascular complications in patients with diabetes. In this study, we examined the effect of high glucose (HG) on apoptosis of human umbilical vein endothelial cells (HUVEC) and investigated the molecular mechanisms involved. HUVEC was exposed to HG and apoptosis was assessed by Death ELISA. Our data showed that HG induced significant apoptosis in HUVEC cells after exposing to HG for 5 days (O.D. value = 0.36±0.07 in HG group vs. 0.13±0.05 in control, p<0.05). HG induced apoptosis in HUVEC is associated with decreased of insulin-like growth factor receptor (IGF-1R) mRNA (4.1±0.6 fold at 72 h, p<0.05) as assessed by real-time PCR and IGF-1R protein (3. 1±0.5 fold at 96 h, p<0.05) as assessed by western blot, which were dose- and time-dependent effects (25 mM of glucose rather than 5 mM at 72 h and 96 h). The effects of HG on reduced expression of IGF-1R and apoptosis were blocked by silencing histone deacetylase 1 (HDAC1) with small interference RNA (siRNA-HDAC1) compared to non-targeting scrambled siRNA. Moreover, HG negatively regulated IGF-1R promoter activity as determined by ChIP (chromatin immunoprecipitation) analysis, which was dependent on HDAC1 since siRNA-HDAC1 attenuated the effects of HG on IGF-1R promoter activity. HG also increased the association of IGF-1R promoter with HDAC1, and decreased the association of IGF-1R promoter with acetylated histone-4. Furthermore, trichostatin A, a specific HDAC inhibitor, relieved the repression of IGF-1R and prevented apoptosis of HUVEC following HG state. These results suggest that HG-induced repression of IGF-1R is mediated by the association of HDAC1 with the IGF-1R promoter, and by the subsequent reduced recruitment of chromatin-modifying proteins, such as histone 4 to the IGF-1R promoter. In conclusion, our data demonstrate that high glucose exposure decreases expression of IGF-1R and decreases the association of acetylated histone-4 with the IGF-1R promoter, and suggest that enhancing acetylation of histone 4 and IGF-1R expression may be a useful strategy to prevent diabetic-induced apoptosis of endothelial cells. This research has received full or partial funding support from the American Heart Association, South Central Affiliate (Arkansas, New Mexico, Oklahoma & Texas).