The influence of glucose concentration and hypoxia on VEGF secretion by cultured retinal cells

To study the relationship of oxygen level and glucose concentration on the secretion of vascular endothelial growth factor (VEGF) mRNA and protein in several types of cultured retinal cells.

Several types of human and bovine retinal cells were cultured in medium without glucose, or containing 5 mM or 25 mM D-glucose or 5 mM D-glucose and 20 mM D-galactose. Cells were cultured in 20% O(2) ("normoxia") or in 1% O(2) ("hypoxia"). After being cultured for 8-96 hr, we measured VEGF protein in the medium and VEGF mRNA in the cell layer, as well as the concentrations of glucose, lactate, and pyruvate in the medium.

Hypoxia increased VEGF mRNA and protein in these cells. In normoxia, culture in high glucose medium had no significant effect on basal VEGF production in normal glucose. However, culture in hypoxia and high glucose significantly blunted hypoxic VEGF up-regulation. Culture in normoxia, with no glucose in the medium, significantly increased VEGF. Culture in high galactose medium did not significantly affect VEGF production. Despite considerable lactate production, especially in the presence of 25 mM glucose, addition of strong buffers to the medium had little effect on VEGF production.

Cultured retinal cells up-regulate their VEGF production when their energy supply, including glucose and/or O(2), is inadequate. Supplying glucose to the cells in the presence of low O(2) reduces their VEGF production. We suggest that "early worsening" of retinopathy results when diabetic patients with minimal to moderate retinopathy, whose retinal circulation and, hence, retinal oxygen supply is compromised, are placed on a "tight" glucose control regimen and their major remaining retinal energy source is reduced, with VEGF up-regulation as a compensatory mechanism.