Low-Glucose Culture Conditions Bias Neuronal Energetics Towards Oxidative Phosphorylation

Neurons are almost exclusively cultured in media containing glucose at much higher concentrations than found in the brain. To test whether these "standard" hyperglycemic culture conditions affect neuronal respiration relative to near-euglycemic conditions, we compared neuronal cultures grown with minimal glial contamination from the hippocampus and cortex of neonatal C57BL/6NCrl mice in standard commercially available media (25 mM Glucose) and in identical media with 5 mM glucose. Neuronal growth in both glucose concentrations proceeded until at least 14 days in vitro, with similar morphology and synaptogenesis. Neurons grown in high glucose were highly dependent on glycolysis as their primary source of ATP, measured using ATP luminescence and cellular respirometry assays. In contrast, neurons grown in 5 mM glucose showed a more balanced dependence on glycolysis and mitochondrial oxidative phosphorylation (OXPHOS), greater reserve mitochondrial respiration capacity, and increased mitochondrial population relative to standard media. Our results show that neurons cultured in artificially high glucose-containing media preferentially use glycolysis, opposite to what is known for neurons in vivo as the primary pathway for ATP maintenance. Changes in gene and protein expression levels corroborate these changes in function and additionally suggest that high glucose culture media increases neuronal inflammation. We suggest using neuronal culture systems in 5 mM glucose to better represent physiologically relevant neuronal respiration.