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Modulation of VEGF production by pH and glucose in retinal Müller cells
S E Brooks1, X Gu, P M Kaufmann
1Department of Ophthalmology, Medical College of Georgia, Augusta 30912, USA. sbrooks@mail.mcg.edu
Purpose:
To investigate the influence of pH and glucose concentration, both of which represent significant biochemical variables in tissue ischemia, on the production of VEGF protein by retinal Müller cells and C6 glioma cells, under normoxic and hypoxic conditions.
Methods:
Rat retinal Müller cells and C6 glioma cells grown in tissue culture monolayers were studied. The effect of pH (range 7.0-8.0) and glucose concentration (0.6-25 mmol/L) on VEGF protein production, under both normoxic and hypoxic conditions, were evaluated by ELISA analysis of the conditioned media. Establishment of significant cell hypoxia was verified by measurement of lactate release into the conditioned media.
Results:
Hypoxia caused a 7.9-fold increase in VEGF production in C6 cells at 24 h, and a 3.4-fold increase in Müller cells after 48 h. Under hypoxic conditions, VEGF protein production was increased further by increasing pH and increasing glucose, and decreased by low pH and low glucose. Varying the glucose concentration or pH of the medium did not result in significant induction of VEGF protein production by either cell type under normoxic conditions.
Conclusions:
Both glucose and pH significantly affected VEGF production induced by low oxygen. However, neither exerted a measurable stimulatory effect on VEGF production in normoxic conditions. Coexisting hypoxia and acidosis or hypoglycemia, as might occur in severe tissue ischemia, may render glial cells incapable of effectively upregulating VEGF synthesis, while alkalosis or hyperglycemia may augment hypoxia-induced VEGF production.
Insights
Hypoxia significantly increases vascular endothelial growth factor (VEGF) production in glial cells. However, factors like pH and glucose levels modulate this response, impacting potential therapeutic strategies for ischemic conditions.
Area of Science:
- Biochemistry
- Cell Biology
- Ophthalmology
Background:
- Tissue ischemia involves significant biochemical changes, including altered pH and glucose levels.
- Vascular Endothelial Growth Factor (VEGF) plays a crucial role in angiogenesis and is implicated in various ischemic conditions.
- Retinal Müller cells and C6 glioma cells are relevant models for studying glial cell responses.
Purpose of the Study:
- To determine how pH and glucose concentration influence VEGF protein production in retinal Müller cells and C6 glioma cells.
- To investigate these effects under both normoxic and hypoxic conditions, mimicking physiological states relevant to tissue ischemia.
Main Methods:
- Cultured rat retinal Müller cells and C6 glioma cells were used.
- VEGF protein production was measured using ELISA analysis of conditioned media.
- Effects of varying pH (7.0-8.0) and glucose (0.6-25 mmol/L) were assessed under normoxic and hypoxic conditions.
- Cell hypoxia was confirmed by measuring lactate release.
Main Results:
- Hypoxia significantly increased VEGF production in both cell types, with greater fold-increase in C6 cells (7.9x at 24h) compared to Müller cells (3.4x at 48h).
- Under hypoxia, elevated pH and glucose levels further increased VEGF production, while low pH and glucose decreased it.
- Neither pH nor glucose concentration significantly affected VEGF production under normoxic conditions.
Conclusions:
- Hypoxia-inducible VEGF production by glial cells is significantly modulated by both pH and glucose concentration.
- Acidosis or hypoglycemia, occurring with severe ischemia, may impair glial cells' ability to upregulate VEGF synthesis.
- Alkalosis or hyperglycemia, in conjunction with hypoxia, may enhance VEGF production, suggesting complex regulatory mechanisms in ischemic environments.