Spreading depolarizations exhaust neuronal ATP in a model of cerebral ischemia

Abstract

Spreading depolarizations (SDs) have been identified in various brain pathologies. SDs increase the cerebral energy demand and, concomitantly, oxygen consumption, which indicates enhanced synthesis of adenosine triphosphate (ATP) by oxidative phosphorylation. Therefore, SDs are considered particularly detrimental during reduced supply of oxygen and glucose. However, measurements of intracellular neuronal ATP ([ATP]i), ultimately reporting the balance of ATP synthesis and consumption during SDs, have not yet been conducted. In this study, we investigated neuronal ATP homeostasis during SDs using 2-photon imaging in acute brain slices from adult mice, expressing the ATP sensor ATeam1.03YEMK in neurons. SDs were induced by application of potassium chloride or by oxygen and glucose deprivation (OGD) and were detected by recording the local field potential, extracellular potassium, as well as the intrinsic optical signal. We found that, in the presence of oxygen and glucose, SDs were accompanied by a substantial but transient drop in neuronal [ATP]i. OGD, which prior to SD was accompanied by a slight reduction in [ATP]i only, led to an even larger, terminal drop in [ATP]i during SDs. Subsequently, we investigated whether neurons could still regenerate ATP if oxygen and glucose were promptly resupplied following SD detection. The data show that ATP depletion was essentially reversible in most cells. Our findings indicate that SDs are accompanied by a substantial increase in ATP consumption beyond production. This, under conditions that mimic reduced blood supply, leads to a breakdown of [ATP]i. Therefore, our findings support therapeutic strategies targeting SDs after cerebral ischemia. Significance statementSpreading depolarizations occur in many brain pathologies, and are suggested to contribute to brain damage through a mismatch in energy supply and demand. However, measurements directly demonstrating an imbalance between ATP production and consumption, particularly in individual neurons, have not been reported. Here we show that spreading depolarizations lead to a transient decrease in intracellular neuronal ATP even in presence of ample glucose and oxygen. When the supply of oxygen and glucose was interrupted, ATP declined gradually until spreading depolarization led to the exhaustion of neuronal ATP. This process would be terminal without the renewed supply of oxygen and glucose. Therefore, therapies targeting spreading depolarizations could preserve neuronal ATP or delay its loss in brain pathologies.