Effect of Hyperglycemia on Circadian Rhythm of Human Retinal Vascular Endothelial Cells

Abstract

Purpose : Circadian rhythms are an important regulator of many key biological processes including cellular metabolism, cardiovascular function and energy homeostasis in the liver and other peripheral tissues. The central mammalian circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, composed of self-contained circadian oscillators governed by finely tuned transcriptional-translational feedback loops. The transcriptional output time of the molecular clock in the SCN is set to 24-h by retinal light input, to synchronize this central clock proteins with the environment. One of such clock protein Per2 (period) involved in retinal vascular regulation consists of glucocorticoid responsive element that plays a critical role in glucose homeostasis. In addition, recent evidence suggests that NAD-dependent histone deacetylases (HDAC) regulate the circadian clock. In this study, we evaluated how hyperglycemia can affect circadian protein Per2 in human retinal vascular endothelial cells.

Methods : Human retinal endothelial cells (HREC) were maintained at 37°C in presence of 95% air and 5% CO₂. These cells were exposed to hyperglycemia by adding 25 mM glucose to retinal endothelial cells for 72 hrs. Cells exposed to 5 mM glucose were used as controls. Cell viability was evaluated using WST-1 assay. Association of circadian protein with hyperglycemia was analyzed by presence of Per2 protein using immunoblot. Regulation of circadian protein Per2 by HDAC proteins sirt1 and sirt6 in hyperglycemic condition was noted. In addition, hypoxia inducible factor (HIF)-1a, 2a expression was also evaluated.

Results : HREC cells exposed to hyperglycemia (25 mM glucose) for 72 hrs showed 31.3± 6.2% viability compared to control cell viability. Circadian protein Per2 was observed only in control cells whereas Per2 protein expression was not observed in cells exposed to hyperglycemia. In addition, sirt1 protein was down regulated in hyperglycemic cells as compared to control cells. Both HIF-1a and HIF-2a were noted in control and hyperglycemic cells but the HIF-2a expression was upregulated in hyperglycemic cells only (p<0.05).

Conclusions : Our data suggest that there is an association of circadian protein Per2 in human retinal vascular endothelial cells in response to hyperglycemia.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.