Modification of glial cell VEGF production by extracellular glucose and PH

Purpose. To investigate the effects of extracellular glucose concentration and pH on VEGF production by retinal Müller cells and C6 glioma cells, under normoxic and hypoxic conditions Methods- Rat retinal Müller cells and C6 glioma cells were grown separately in tissue culture monolayers, in normoxia (95% room air, 5% CO₂) or hypoxia (95% N2, 5% C02), for 24-48 hrs, at 37°C, in serum free DMEM. In one experiment the starting glucose concentration was either 10, 100, or 450 mg/dl, with initial pH 7.4-7.5. In a second experiment, initial pH was either 6.5, 7.5, or 8.5 (in 20mM HEPES), with initial glucose of 100 mg/dl. Following incubation, the conditioned media was assayed for lactate, lactate dehydrogenase, glucose, and pH. VEGF was assayed by Western blot or ELISA. Results. Hypoxia caused increased lactate, decreased glucose and pH, and upregulation of VEGF in both Müller and C6 cells. The degree of hypoxia-induced upregulation was increased in high glucose and high pH and decreased in low glucose and low pH. Glucose and extracellular pH changes alone did not lead to VEGF upregulation in normoxia. Conclusion. Hypoxic upregulation of VEGF may be caused by a shift to anaerobic metabolism ana subsequent decrease in intracellular pH. Increased glucose levels might facilitate intracellular acidification while increased extracellular pH may provide a steeper pH gradient during hypoxia. Although glucose deprivation may occur in ischemia, it does not appear to upregulate glial VEGF in the absence of hypoxia, and actually diminishes the upregulation induced by hypoxia. Supported by an unrestricted departmental award from Research to Prevent Blindness, Inc., and NIH grant EY04186. None.