NBCe1 mediates the regulation of the NADH/NAD(+) redox state in cortical astrocytes by neuronal signals

Astrocytes are a glial cell type, which is indispensable for brain energy metabolism. Within cells, the NADH/NAD(+) redox state is a crucial node in metabolism connecting catabolic pathways to oxidative phosphorylation and ATP production in mitochondria. To characterize the dynamics of the intracellular NADH/NAD(+) redox state in cortical astrocytes Peredox, a genetically encoded sensor for the NADH/NAD(+) redox state, was expressed in cultured cortical astrocytes as well as in cortical astrocytes in acutely isolated brain slices. Calibration of the sensor in cultured astrocytes revealed a mean basal cytosolic NADH/NAD(+) redox ratio of about 0.01; however, with a broad distribution and heterogeneity in the cell population, which was mirrored by a heterogeneous basal cellular concentration of lactate. Inhibition of glucose uptake decreased the NADH/NAD(+) redox state while inhibition of lactate dehydrogenase or of lactate release resulted in an increase in the NADH/NAD(+) redox ratio. Furthermore, the NADH/NAD(+) redox state was regulated by the extracellular concentration of K+, and application of the neurotransmitters ATP or glutamate increased the NADH/NAD(+) redox state dependent on purinergic receptors and glutamate uptake, respectively. This regulation by K+, ATP, and glutamate involved NBCe1 mediated sodium-bicarbonate transport. These results demonstrate that the NADH/NAD(+) redox state in astrocytes is a metabolic node regulated by neuronal signals reflecting physiological activity, most likely contributing to adjust astrocytic metabolism to energy demand of the brain.