Authors: Alexander Ksendzovsky, MD; Stuart Walbridge, BS; Muzna Bachani, BS; Marcelle Altshuler, BS; Sara Inati, MD; Joseph Steiner, PhD; John Williamson, BS; John Heiss, MD; Jaideep Kapur, MD, PhD; Kareem Zaghloul, MD, PhD (Bethesda, MD)
Introduction: Anaerobic respiration, marked by lactate dehydrogenase alpha (LDHA), has recently been found to play an important role in epileptogenesis. However, the metabolic state of excited neurons is unknown. In this study, we demonstrate a switch from aerobic to anaerobic respiration in chronically activated neurons in human and murine models of epilepsy. Using an in vitro epilepsy model, we establish the AMP-activated protein kinase/hypoxia-inducible factor-1a (AMPK/HIF1a) hypoxia pathway as a key regulator leading to increased LDHA expression and anaerobic respiration. Methods: First, we analyzed human tissue for LDHA expression based on electrographic characteristics of overlying subdural electrodes, as determined during intracranial monitoring (epileptic vs normal cortex). Second, two epilepsy mouse models (pentylenetetrazole (PTZ) and electrical stimulation) were probed for LDHA after seizure development. Finally, a low Mg 2+ in vitro epilepsy model was developed to elucidate AMPK/HIF1a’s role in regulating the metabolic switch from aerobic to anaerobic metabolism. Results: In human and mouse studies, LDHA expression was significantly upregulated in epileptic neurons. PTZ and electrical stimulation confirmed a positive correlation between seizure frequency and LDHA expression. Treatment of cultured neurons with low Mg 2+ caused an increase in bursting activity, or in vitro seizures. Neuronal bursting caused depletion of intracellular ATP and subsequent activation of the AMPK/HIF1a pathway through phosphorylation of AMPK. Furthermore, chronic activation of AMPK led to HIF1a and LDHA upregulation and a subsequent switch from an aerobic to a glycolytic cellular phenotype in neurons. Conclusion: These data suggest that seizures cause a metabolic switch from aerobic to anaerobic respiration in neurons, which occurs through activation of the canonical AMPK/HIF1a hypoxia pathway. To our knowledge this is the first study to demonstrate the metabolic consequences of neuronal over-activation and the key regulatory pathway responsible. We believe our data opens up significant potential for future investigation into mechanisms of epilepsy and new therapeutic targets.