Expression Profiling after Prolonged Experimental Febrile Seizures in Mice Suggests Structural Remodeling in the Hippocampus

Febrile seizures are the most prevalent type of seizures among children up to 5 years of age (2-4% of Western-European children). Complex febrile seizures are associated with an increased risk to develop temporal lobe epilepsy. To investigate short- and long-term effects of experimental febrile seizures (eFS), we induced eFS in highly febrile convulsion-susceptible C57BL/6J mice at post-natal day 10 by exposure to hyperthermia (HT) and compared them to normotherm-exposed (NT) mice. We detected structural re-organization in the hippocampus 14 days after eFS. To identify molecular candidates, which entrain this structural re-organization, we investigated temporal changes in mRNA expression profiles eFS 1 hour to 56 days after eFS. We identified 931 regulated genes and profiled several candidates using in situ hybridization and histology at 3 and 14 days after eFS. This is the first study to report genome-wide transcriptome analysis after eFS in mice. We identify temporal regulation of multiple processes, such as stress-, immune- and inflammatory responses, glia activation, glutamate-glutamine cycle and myelination. Identification of the short- and long-term changes after eFS is important to elucidate the mechanisms contributing to epileptogenesis

Timed regulation of biological processes after eFS.

<p>Bar blackness indicates the peak effect of the process. P10: postnatal day 10, 1H: 1 hour post-eFS, 3D: 3 days post-eFS, 14D: 14 days post-eFS, 56D: 56 days post-eFS, Glu/Gln cycle: glutamate/glutamine cycle.</p

Hierarchical clustering analysis of mRNA expression after eFS.

<p>Hierarchical clustering analysis of differentially expressed genes (930) in all experimental littermate couples (1 hour, 3 and 14 days post-eFS). Rows depict differential expression levels per HT/NT littermate couple, per time-point after eFS. Clustering was performed based on gene and sample clustering using Pearson correlation on average linkage. Tree cluster, right from heat-map, shows hierarchical distance between samples from the different time points. Differential gene expression (log2(Fc) between HT/NT littermate couples is shown in the heatmap as upregulated (red), downregulated (green), or no change (white) according to colored-scale bar.</p

Validation of microarray results by qPCR analysis.

<p>Gene expression levels as determined by qPCR (Rn) in normothermic (NT) and hyperthermic (HT) animals compared to fold-change in expression of 5 genes as detected by microarray analysis (Rm). <i>P</i> < 0.05 was considered significant (one-tailed Student’s t-test). Indicated are mean ± standard error of the mean.</p

Expression of candidate genes mRNA related to structural reorganization.

<p>(A, C, E, G) Representative images of <i>Nrxn1</i>, <i>Dpysl3</i>, <i>Ptprd</i>, and <i>Slit2</i> gene expression in the hippocampus of NT (left panel) and HT (right panel) animals three days after eFS. (B, D, F, H) Comparison of <i>Nrxn1</i>, <i>Dpysl3</i>, <i>Ptprd</i>, and <i>Slit2</i> gene expression levels in subfields of the hippocampus in HT (<i>n</i> = 9, red bars) animals compared to NT (<i>n</i> = 9, blue bars) littermates. <i>Ptprd</i> is upregulated in the CA2 subfield of the hippocampus of HT animals, * indicates a significant difference of <i>P</i> = 0.0097, littermate-paired Student’s t-test. Bars represents mean ± standard error of the mean. Scalebars in panel A, C, E, and G: 500μm.</p

Hyperthermia induces upregulation of neurofilament protein-expression.

<p>(A) Neurofilament (NF) immunostaining in the hippocampus of a normothermic (NT) control animal, 14 days post-hyperthermia exposure. Square marks subfield enlargement; panel B. (B) Immunostaining for NF in the stratum lucidum of NT control animal (left panel) and in hyperthermia-exposed (HT) littermate (right panel). (C) Comparison of NF-based DAB staining in the stratum lucidum between NT and HT littermates. All HT (<i>n</i> = 10) animals showed increased DAB-staining in the stratum lucidum. Pair-wise comparison of DAB-staining intensities showed increased NF expression in HT animals compared to NT littermates (<i>n</i> = 10), Wilcoxon signed-rank test, * indicates a significance of <i>P</i> = 0.0049. Tukey-style box plots. Scalebars: 100 μm.</p