Alterations in Brain Inflammation, Synaptic Proteins, and Adult Hippocampal Neurogenesis during Epileptogenesis in Mice Lacking Synapsin2

Abstract

Synapsins are pre-synaptic vesicle-associated proteins linked to the pathogenesis of epilepsy through genetic association studies in humans. Deletion of synapsins causes an excitatory/inhibitory imbalance, exemplified by the epileptic phenotype of synapsin knockout mice. These mice develop handling-induced tonic-clonic seizures starting at the age of about 3 months. Hence, they provide an opportunity to study epileptogenic alterations in a temporally controlled manner. Here, we evaluated brain inflammation, synaptic protein expression, and adult hippocampal neurogenesis in the epileptogenic (1 and 2 months of age) and tonic-clonic (3.5-4 months) phase of synapsin 2 knockout mice using immunohistochemical and biochemical assays. In the epileptogenic phase, region-specific microglial activation was evident, accompanied by an increase in the chemokine receptor CX3CR1, interleukin-6, and tumor necrosis factor-α, and a decrease in chemokine keratinocyte chemoattractant/ growth-related oncogene. Both post-synaptic density-95 and gephyrin, scaffolding proteins at excitatory and inhibitory synapses, respectively, showed a significant up-regulation primarily in the cortex. Furthermore, we observed an increase in the inhibitory adhesion molecules neuroligin-2 and neurofascin and potassium chloride co-transporter KCC2. Decreased expression of γ-aminobutyric acid receptor-δ subunit and cholecystokinin was also evident. Surprisingly, hippocampal neurogenesis was reduced in the epileptogenic phase. Taken together, we report molecular alterations in brain inflammation and excitatory/inhibitory balance that could serve as potential targets for therapeutics and diagnostic biomarkers. In addition, the regional differences in brain inflammation and synaptic protein expression indicate an epileptogenic zone from where the generalized seizures in synapsin 2 knockout mice may be initiated or spread.

Nonconvulsive status epilepticus in rats leads to brain pathology

“…In the ipsilateral HPC, both NL‐2 and synapsin II were reduced (Table ). Again, protein levels did not change in the cortex and subcortex, except for a small decrease in N‐cadherin levels in the subcortex (Table ). At 4 weeks post‐NCSE, no changes in synaptic protein levels were detected in the contralateral or ipsilateral HPC compared to Ctrl.…”

“…At 1week post‐NCSE, when rats had exhibited acute symptomatic seizures, levels of PSD‐95 and NL‐1 were decreased in the contralateral HPC, whereas the excitatory synapse‐associated adhesion molecule N‐cadherin was unaltered. At the inhibitory synapses, the postsynaptic scaffolding protein gephyrin was reduced, but not accompanied by a change in the adhesion molecule NL‐2 or NF . Synapsin II was reduced, whereas synapsin I levels remained unaltered (Figure ).…”

“…Irrespectively, the synaptic reaction may be involved in the development of epilepsy. We have previously documented alterations in the same synaptic proteins prior to the occurrence of provoked generalized seizures in genetically modified mice depleted of synapsin II, and gephyrin levels are reduced after pilocarpine‐induced convulsive SE . Several of these synaptic proteins can also be disrupted in patients with epilepsy .…”

“…For biochemical analyses, rats were decapitated and brains were immediately removed, divided into ipsilateral and contralateral hemispheres related to electrode implantation, further dissected into HPC, cortex, and subcortex, frozen on dry ice, and stored at −80°C. Homogenization and determination of protein concentration were performed as previously described …”

Upholding WAG/Rij rats as a model of absence epileptogenesis: Hidden mechanisms and a new theory on seizure development

“…To this aim, animal models have been the major source of our current understanding and have led to the identification of potential targets for epilepsy development prevention and/or progression; however, none of the currently available models has been clinically validated (Kobow et al, 2012;Pitkanen and Lukasiuk, 2011;Pitkanen et al, 2013). New insights are now coming from so-called genetic animal models which are being reconsidered as potential models to study the pathophysiology of the epileptogenic process (differently from acquired/post-insult models) and the potential antiepileptogenic efficacy of drug treatments (Blumenfeld et al, 2008;Chugh et al, 2015;Liautard et al, 2013;Marguet et al, 2015). Our current knowledge suggests that some processes (e.g.…”