Abstracts

Rationale: Astrogliosis has long been observed in both human and animal models of epilepsy, and neuro-inflammation has been implicated as a key causative mechanism. Further, dysregulation of mTOR (mammalian target of rapamycin) signalling has increasingly been shown to contribute to epileptogenesis and mTOR kinase activity was recently shown to be increased following kainic acid (KA)-induced status epilepticus in rats (PMID: 23724051). In this context, recent studies have shown that the high-fat ketogenic diet (KD) an efficacious treatment for medically refractory epilepsy down-regulates pathological increases in mTOR signalling (PMID: 21371020) and suppresses the release of pro-inflammatory mediators originating from astrocytes in a rodent model of multiple sclerosis (PMID: 22567104). Here, we asked whether the anti-seizure and neuroprotective effects of the KD might be linked to alterations in astrogliosis seen following KA-induced seizures.Methods: Normal C3HeB/FeJ or GFAP-Luc transgenic mice generated in the FVB/N background (N=10 in each group) were fed either the Bio-Serv F3666 diet or standard rodent diet (SD) for 2-3 weeks beginning at P42. Seizure activity was assessed with the Stellate-DSI-Harmonie video monitoring system for 24 hours immediately following a single IP injection of KA (20 or 30 mg/kg) or saline as a control. We non-invasively monitored changes in brain content of glial fibrillary acidic protein (GFAP; a marker for astrocytes) after KA injection using a luciferase-tagged GFAP mouse model (GFAP-luc) and the Xenogen in vivo imaging system (IVIS) that quanitifies biophotonic signals upon luciferin administration. Hippocampal lysates were collected for western blots from four groups of mice: SD-fed and KD-fed mice exposed either to KA or sham injection.Results: The KD markedly suppressed seizure activity over a 4-hr duration in SD-fed GFAP-luc mice exposed to KA (p<0.05; using a modified Racine seizure severity scale). Similar results were obtained in KD-fed C3HeB/FeJ mice treated with KA. In SD-fed GFAP-luc mice, KA resulted in a gradual increase in bioluminescence detected with the Xenogen IVIS system. In contrast, at 24 hrs post KA injection, KD-fed GFAP-Luc mice exhibited a significant decrease in bioluminescent intensity compared to controls (p<0.01). Consistent with our earlier findings in epileptic Kcna1-null mice [AES 1.262, 2012], KD treatment led to a reduction in phospho-S6, a downstream effector of mTOR, in both kainate-treated C3HeB/FeJ and GFAP-Luc animals.Conclusions: The KD not only reduces the severity of KA-induced seizures in two different mouse strains, but also attenuates GFAP expression (a marker of gliosis) in vivo. Further, as mTOR activation has recently been observed following KA-induced status epilepticus, our finding that phospho-S6 is reduced by KD treatment suggests a mechanistic link between mTOR inhibition and decreases in astrogliosis, both mechanisms that could contribute to the anti-seizure and neuroprotective effects of the KD.