Interleukin-1beta Causes Energy Depletion and Death of Glucose-deprived R28 and RGC-5 Retinal Neuronal Cells

Abstract

Purpose:: To examine the effects of the pro-apoptotic cytokine interleukin-1beta (IL-1ß) on the metabolism and viability of R28 and RGC-5 cells, two rat cell lines that are routinely used to study apoptosis in retinal neuronal-like cell systems.

Methods:: Cellular reductive capacity was measured using WST-1 tetrazolium salt. Cellular ATP levels were measured with a luciferase assay. Caspase-3/7 activation was measured with a DEVDase fluorescent assay. Cell death and lysis was evaluated by measuring release of lactate dehydrogenase (LDH). Glucose utilization and lactate production was assessed by measuring glucose disappearance and lactate appearance in cell culture media.

Results:: IL-1ß (1-10 ng/ml) caused a pronounce (50-60%) decrease in the ability of these cells to reduce WST-1 tetrazolium salt, a decline of intracellular ATP levels, caspase-3/7 activation and LDH release. The effects of IL-1ß were dependent on cell density, coinciding with depletion of media glucose. IL-1ß treatment increased rates of glucose utilization and lactate release, suggesting increased reliance on glycolysis for energy production. Addition of high glucose (20 mM) to cell cultures blocked the detrimental effects of IL-1ß on energy metabolism and cell viability. The glycolytic substrate mannose also blocked the effects of IL-1ß, whereas other, non-glycolytic metabolic substrates did not.

Conclusions:: There is growing evidence that inflammatory cytokines and other inflammatory markers are increased in the vitreous humor and retina during diabetic retinopathy, which may contribute to diabetic retinal neurodegeneration. The present results suggest that IL-1ß alters energy metabolism of retinal neuronal cells so that they are highly dependent upon glycolysis for maintenance of cell viability. This may have implications for neurodegeneration in ischemic regions of diabetic retinas or during periods of diabetic hypoglycemia.

Keywords: neuroprotection • inflammation • metabolism