Quantitative high-content screening methods reveal a regulation of cell-to-cell variability of the energy metabolism of brain cells

Astrocytes are non-neuronal cells tiling the entire central nervous systems. They are vital for neural circuit function but have traditionally been viewed as simple, homogenous cells that serve the same essential supportive roles everywhere. However, astrocytes are subject to intrinsic noise, signaling pathways and control mechanisms leading to a cell-to-cell variability, whose functional relevance poorly remains poorly understood. Recent evidence indicated that single astrocytes release variable concentrations of lactate in response to stimulation, raising the possibility that they have different energy metabolisms.
To investigate this hypothesis, we used high-content screening methods to monitor at the single cell level the variability in cellular ATP level in cultured astrocytes. An automated image analysis pipeline enabled the time-resolved quantification of both, the single-cell ATP level and the coefficient of variation in a cellular population. At resting state, astrocytes exhibited a significant variability in cellular ATP levels. As previously reported, glutamate induced a decrease in cellular ATP levels that recovered after stimulation. During the glutamatergic stimulation, the heterogeneity in the cellular ATP level decreased, suggesting that the decrease in cellular energy status is potentially regulated to avoid decreasing below a biological threshold. Interestingly, the cytosolic ATP level increased during recovery to a similar level among cells, independently from their basal cellular ATP which further decreased the heterogeneity in cellular ATP levels after stimulation.
Therefore, our results suggest that glutamatergic stimulation decreases the heterogeneity in energy metabolism in astrocytes. We speculate that the change in metabolic heterogeneity aims to prime the population to answer more rapidly a next stimulation challenge.