Abstracts

Rationale: Temporal lobe epilepsy (TLE) is a major cause of therapy-resistant epilepsy. A better understanding of the mechanisms involved in seizure generation and therapy resistance may lead to improved diagnostic and therapeutic strategies. While animal models point towards a causal role for mitochondrial dysfunction and oxidative stress in epileptogenesis, little is known about their relationship to epileptogenesis in humans. Impaired mitochondria function can result in increased reactive oxygen species production, oxidative damage and decreased ATP production. In turn, energetic and oxidative stress may trigger neuroprotective defense mechanisms, including induction of AMP-activated protein kinase (AMPK) pathway, upregulation of antioxidant enzymes and the formation of cytosolic protein/RNA condensates known as stress granules. In this study, we hypothesized that cortical tissue resected from patients with TLE would exhibit alterations in markers of mitochondrial function and antioxidant stress response.

Methods: The TLE samples, prospectively collected following brain surgeries performed at the Hospital of the University of Pennsylvania (n=16 for cortex, n=15 for hippocampus), were compared with matched control autopsy samples (n=8) obtained from the NIH NeuroBioBank. The expression of mitochondrial oxidative phosphorylation complexes (OXPHOS I, II, III, and V), energetic and oxidative stress response markers AMPK and phospho-AMPK Thr172 (pAMPK), glutathion peroxidase 4 (GPX4), stress granule marker Ras-GTPase-activating protein binding protein 1 (G3BP1), and Fragile X mental retardation protein (FMRP) were quantified by western blotting.

Results: TLE patient samples demonstrated a selective deficiency of OXPHOS V in cortex (72% of control, p< 0.01) and a selective elevation of both OXPHOS II and OXPHOS V in hippocampus (178% of control, p< 0.05, and 127% of control, p< 0.05, respectively). This perturbation in mitochondrial function was accompanied by a significant increase in the ratio of pAMPK/AMPK in cortex and hippocampus (661% of control, p< 0.01, and 411% of control, p< 0.0001, respectively), consistent with diminished mitochondrial ATP production. We also found an adaptive oxidative stress response via increased GPX4 in cortex (139% of control, p< 0.001). In addition, we found evidence of a stress granule response with increased G3BP1 in cortex and hippocampus (334% of control, p< 0.0001, and 215% of control, p< 0.001, respectively), as well as increased FMRP in cortex and hippocampus (222% of control, p< 0.05, and 264% of control, p< 0.01, respectively).