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

PLoS One. 2015 Jul 15;10(7):e0132366. doi: 10.1371/journal.pone.0132366. eCollection 2015.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carrier Proteins / metabolism
  • Cell Adhesion Molecules, Neuronal / metabolism
  • Cerebral Cortex / metabolism
  • Chemokines / metabolism
  • Cytokines / metabolism
  • Disease Models, Animal
  • Disks Large Homolog 4 Protein
  • Encephalitis / metabolism
  • Encephalitis / pathology*
  • Guanylate Kinases / metabolism
  • Hippocampus / metabolism*
  • Hippocampus / pathology
  • Membrane Proteins / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Microglia / metabolism
  • Microglia / pathology
  • Nerve Tissue Proteins / metabolism
  • Neurogenesis
  • Seizures / metabolism
  • Seizures / pathology*
  • Synapses / metabolism*
  • Synapsins / deficiency
  • Synapsins / genetics*
  • Up-Regulation
  • gamma-Aminobutyric Acid / metabolism

Substances

  • Carrier Proteins
  • Cell Adhesion Molecules, Neuronal
  • Chemokines
  • Cytokines
  • Disks Large Homolog 4 Protein
  • Dlg4 protein, mouse
  • Membrane Proteins
  • Nerve Tissue Proteins
  • Synapsins
  • gephyrin
  • neuroligin 1
  • neuroligin 2
  • gamma-Aminobutyric Acid
  • Guanylate Kinases

Grants and funding

This work was supported by the Swedish Research Council, ALF Grant for funding for medical training and research, Zoega´s Foundation, O. E. and Edla Johanssons Scientific Foundation, Tore Nilson´s Foundation, and Åhlens´s Foundation. The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n°602102 (EPITARGET). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.