Response of rat retinal capillary pericytes and endothelial cells to glucose

The purpose of this study was to investigate the effects of hyperglycemia, its fluctuations, and glucose starvation on the expression of glucose-regulated protein 78/binding immunoglobulin protein (GRP78/BiP), one of the most commonly used markers of endoplasmic reticulum stress, in rat capillary pericytes and endothelial cells cultured separately and together.

Conditionally immortalized rat retinal pericyte and endothelial cell lines were cultured in dishes coated with collagen type I in Dulbecco's modified Eagle's medium containing 5.5  mM glucose. For cocultures, pericytes and endothelial cells were seeded together on rat tail collagen type I-coated cell culture plates. After 24  h of initial culture, the medium was replaced with serum-free medium containing 0-100  mM glucose for periods of up to 72  h. GRP78/BiP, caspase-3, and nuclear factor-κB expression were investigated using western blots.

No significant increase in GRP78/BiP expression was observed when pericytes, endothelial cells, or cocultures were exposed to either 25, 50, or 100  mM glucose for 48  h compared with the control level of 5.5  mM glucose. Similarly, no change in expression of GRP78/BiP was observed when media glucose levels were reduced from either 5.5 or 25 to 1  mM. GRP78/BiP expression significantly increased when cells were cultured for 24  h in glucose-deprived medium. This was accompanied by a time-dependent increase in the expression of caspase-3 and nuclear factor-κB.

In diabetic retinopathy, hyperglycemia has been reported to induce apoptosis in retinal capillary vascular cells, but these studies suggest that the apoptosis is not linked to the expression of GRP78/BiP, one of the most commonly used markers of endoplasmic reticulum stress. However, GRP78/BiP-linked apoptosis may play a role in vascular changes associated with retinal ischemia/reperfusion.