Abstracts

Rationale: Temporal lobe epilepsy (TLE), the most common form of acquired epilepsies, is characterized by chronic unprovoked seizures arising from an inciting insult such as status epilepticus (SE) with a variable seizure-free latent period . These features can be replicated by systemic administration of a chemoconvulsant to induce SE. The mechanisms by which an inciting injury induces chronic epilepsy, known as epileptogenesis, involves multiple molecular and physiological changes resulting in altered hyperexcitable circuitry. Our laboratory has previously demonstrated altered mitochondrial function(s) and redox state during epileptogenesis. The sirtuins are a family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases implicated in the maintenance of cellular homeostasis. NAD+ is a co-factor in many metabolic and redox reactions, thereby linking sirtuin activity to the energetic state of the cell. SIRT1, a nuclear and cytosolic isoform, exerts control of these processes through deacetylation of numerous transcription factors. SIRT3 is known to regulate energy metabolism and antioxidant activities in the mitochondria as the major deacetylase in this cellular compartment. We hypothesized that SIRT1 and SIRT3 expression and/or activity would be reduced in the hippocampus of male Sprague-Dawley rats with chemoconvulsant-induced epileptogenesis, and this would be associated with impaired bioenergetics, reflected by decreases in NAD+ and the ratio of adenosine triphosphate (ATP) to adenosine diphosphate (ADP).Methods: Western blot was used to measure SIRT1/SIRT3 protein expression and SIRT1 activity, as assessed by the acetylation state of the SIRT1 substrate p53. NAD+ and ATP/ADP levels were determined via HPLC.Results: In the acute period following SE, NAD+ levels were reduced by 25% (p<0.01) vs control rats and this was accompanied by a decrease in SIRT1 activity (p<0.05). There was no change in SIRT3 protein expression, however the ratio of ATP/ADP was decreased by 38% (p<0.01). In the latent seizure-free period, SIRT1 activity returned to control levels and SIRT3 expression was modestly elevated (p<0.05), however analysis of ATP/ADP levels indicated a 45% reduction vs control rats (p<0.01). In chronically epileptic animals, SIRT1 activity and SIRT3 expression were reduced (p<0.05) and the ATP/ADP ratio was decreased 37% (p<0.01) vs control rats.Conclusions: These results indicate that chemoconvulsant-induced SE and epileptogenesis result in a deficit in SIRT1 activity and SIRT3 levels and this is associated with a reduction in NAD+ concentrations and the ATP/ADP ratio in the hippocampus. This suggests that these changes may contribute to the metabolic and redox dysfunction associated with epilepsy, and warrant further mechanistic insight into the specific sirtuin substrates with altered activities in this process. Further, these novel findings indicate that activation of SIRT1 and SIRT3 may be therapeutic targets for the treatment of TLE. Acknowledgements: RO1NS039587, CURE (MP)