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.

[A potentially fatal intoxication with colchicine]

BACKGROUND

Approximately ten times a year the Dutch National Poisons Information Centre (NVIC) is consulted regarding a colchicine intoxication or overdose.

CASE DESCRIPTION

An 18-year old woman was admitted to the intensive care unit after a suicide attempt with a potentially lethal dosage of colchicine tablets (0.5 mg/kg body weight). After a few hours the patient developed abdominal pain and vomited. Over subsequent days she developed anaemia, thrombocytopenia and a paralytic ileus. Treatment mainly comprised intensive supportive care, including sedation, ventilation and repeated administration of activated charcoal. After a week she gradually began to recover and was able to leave IC 10 days after ingestion.

CONCLUSION

Early recognition and treatment of colchicine intoxication is crucial to preventing a fatal outcome. Complete recovery is possible if extensive supportive treatment is given.

Management of prolonged QT interval and torsades de pointes in the intoxicated patient

Many drugs can significantly influence cardiac repolarisation causing an increased duration of this repolarisation phase, challenging the repolarisation reserve. This may set the stage for life-threatening ventricular arrhythmias such as torsades de pointes (TdP). TdP generally occurs in conjunction with a prolonged QT interval (QT) on the electrocardiogram. The Dutch Poisons Information Centre (NVIC) often receives information requests about drugs that can influence the QT already at therapeutic dosages. Drug-induced QT prolongation is dose dependent and hence can be particularly pronounced in overdose situations. Also, additional risk factors for the development of life-threatening arrhythmias are often present in intoxicated patients. This review focuses on identification and management of drug-intoxicated patients who are at risk for a reduction in their repolarisation reserve, measured by their QT interval. The QT interval is strongly dependent on heart rate, which has led to the introduction of different methods to adjust the QT interval, i.e. the QTc. Bazett's formula, which has been used for decades, lacks accuracy concerning QTc calculation at higher and lower heart rates, situations often relevant when dealing with intoxicated patients. Additionally, we highlight drugs with QT-prolonging potential that are commonly associated with an overdose setting in the Netherlands. Finally, standard treatment options specifically pointed toward the intoxicated patient at risk of QT prolongation and TdP will be discussed.

Identification of Srp9 as a febrile seizure susceptibility gene

OBJECTIVE

Febrile seizures (FS) are the most common seizure type in young children. Complex FS are a risk factor for mesial temporal lobe epilepsy (mTLE). To identify new FS susceptibility genes we used a forward genetic strategy in mice and subsequently analyzed candidate genes in humans.

METHODS

We mapped a quantitative trait locus (QTL1) for hyperthermia-induced FS on mouse chromosome 1, containing the signal recognition particle 9 (Srp9) gene. Effects of differential Srp9 expression were assessed in vivo and in vitro. Hippocampal SRP9 expression and genetic association were analyzed in FS and mTLE patients.

RESULTS

Srp9 was differentially expressed between parental strains C57BL/6J and A/J. Chromosome substitution strain 1 (CSS1) mice exhibited lower FS susceptibility and Srp9 expression than C57BL/6J mice. In vivo knockdown of brain Srp9 reduced FS susceptibility. Mice with reduced Srp9 expression and FS susceptibility, exhibited reduced hippocampal AMPA and NMDA currents. Downregulation of neuronal Srp9 reduced surface expression of AMPA receptor subunit GluA1. mTLE patients with antecedent FS had higher SRP9 expression than patients without. SRP9 promoter SNP rs12403575(G/A) was genetically associated with FS and mTLE.

INTERPRETATION

Our findings identify SRP9 as a novel FS susceptibility gene and indicate that SRP9 conveys its effects through endoplasmic reticulum (ER)-dependent synthesis and trafficking of membrane proteins, such as glutamate receptors. Discovery of this new FS gene and mechanism may provide new leads for early diagnosis and treatment of children with complex FS at risk for mTLE.

Protein expression profiling of inflammatory mediators in human temporal lobe epilepsy reveals co-activation of multiple chemokines and cytokines

Mesial temporal lobe epilepsy (mTLE) is a chronic and often treatment-refractory brain disorder characterized by recurrent seizures originating from the hippocampus. The pathogenic mechanisms underlying mTLE remain largely unknown. Recent clinical and experimental evidence supports a role of various inflammatory mediators in mTLE. Here, we performed protein expression profiling of 40 inflammatory mediators in surgical resection material from mTLE patients with and without hippocampal sclerosis, and autopsy controls using a multiplex bead-based immunoassay. In mTLE patients we identified 21 upregulated inflammatory mediators, including 10 cytokines and 7 chemokines. Many of these upregulated mediators have not previously been implicated in mTLE (for example, CCL22, IL-7 and IL-25). Comparing the three patient groups, two main hippocampal expression patterns could be distinguished, pattern I (for example, IL-10 and IL-25) showing increased expression in mTLE + HS patients compared to mTLE-HS and controls, and pattern II (for example, CCL4 and IL-7) showing increased expression in both mTLE groups compared to controls. Upregulation of a subset of inflammatory mediators (for example, IL-25 and IL-7) could not only be detected in the hippocampus of mTLE patients, but also in the neocortex. Principle component analysis was used to cluster the inflammatory mediators into several components. Follow-up analyses of the identified components revealed that the three patient groups could be discriminated based on their unique expression profiles. Immunocytochemistry showed that IL-25 IR (pattern I) and CCL4 IR (pattern II) were localized in astrocytes and microglia, whereas IL-25 IR was also detected in neurons. Our data shows co-activation of multiple inflammatory mediators in hippocampus and neocortex of mTLE patients, indicating activation of multiple pro- and anti-epileptogenic immune pathways in this disease.

Genome-wide microRNA profiling of human temporal lobe epilepsy identifies modulators of the immune response

Mesial temporal lobe epilepsy (mTLE) is a chronic neurological disorder characterized by recurrent seizures. The pathogenic mechanisms underlying mTLE may involve defects in the post-transcriptional regulation of gene expression. MicroRNAs (miRNAs) are non-coding RNAs that control the expression of genes at the post-transcriptional level. Here, we performed a genome-wide miRNA profiling study to examine whether miRNA-mediated mechanisms are affected in human mTLE. miRNA profiles of the hippocampus of autopsy control patients and two mTLE patient groups were compared. This revealed segregated miRNA signatures for the three different patient groups and 165 miRNAs with up- or down-regulated expression in mTLE. miRNA in situ hybridization detected cell type-specific changes in miRNA expression and an abnormal nuclear localization of select miRNAs in neurons and glial cells of mTLE patients. Of several cellular processes implicated in mTLE, the immune response was most prominently targeted by deregulated miRNAs. Enhanced expression of inflammatory mediators was paralleled by a reduction in miRNAs that were found to target the 3'-untranslated regions of these genes in reporter assays. miR-221 and miR-222 were shown to regulate endogenous ICAM1 expression and were selectively co-expressed with ICAM1 in astrocytes in mTLE patients. Our findings suggest that miRNA changes in mTLE affect the expression of immunomodulatory proteins thereby further facilitating the immune response. This mechanism may have broad implications given the central role of astrocytes and the immune system in human neurological disease. Overall, this work extends the current concepts of human mTLE pathogenesis to the level of miRNA-mediated gene regulation.