Methylglyoxal Increases Mitochondrial Superoxide Production in Rat Colony-Forming Endothelial Progenitor Cells (cf-EPCs)

Abstract

Endothelial progenitor cells (EPC) play an important role in replenishing the vasculature and its inability will lead to endothelial dysfunction. It is known that endothelium becomes dysfunctional during diabetes and that production of reactive carbonyl species (RCS) increases. What remains undefined is the impact RCS have on the function of EPC. This study was designed to determine effects of the potent RCS methylglyoxal (MGO) on EPC function and viability. Colony-forming EPCs (cf-EPC) were isolated from whole blood of male Sprague-Dawley rats using Ficoll density gradient centrifugation and RT-PCR was used to confirm the presence of cf-EPC markers. After 7 days in culture, cf-EPC (10,000 cells per well) from controls were incubated with MGO for 24 hr at 37°C. Thereafter mitochondrial dehydrogenase activities were determined using the MTT assay. Cf-EPC were isolated from rats overexpressing glyoxalase 1 (AAV2/9-Glo1), the enzyme that degrades MGO. Changes in cytoplasmic Ca2+ and mitochondrial superoxide were determined using Fluo-3 and MitoSOX with confocal microscopy. Approximately 2-2.5 million cells were isolated per mL of rat blood. MGO induced a dose-dependent decrease in mitochondrial dehydrogenase activities in control cf-EPC. In cf-EPC from rats overexpressing glyoxalase 1, low concentrations of MGO (5-20 μM) enhanced mitochondrial dehydrogenase activities. Higher concentrations (30-500 μM) inhibited this activity. Acute exposure of control cf-EPC to 100 μM MGO increased basal cytoplasmic Ca2+ and this was followed by an increased production of mitochondrial superoxide. These new data suggest that MGO whose production is increased shortly after the onset of hyperglycemia is inducing cf-EPC demise by mechanisms that involve perturbations in intracellular calcium homeostasis and increased production of mitochondrial superoxide. Overexpression of glyoxalase 1 minimizes the effects of MGO. This work was funded in part by NIH HL085061 and the Nebraska Redox Biology Center.