Whole transcriptome analysis of the hippocampus: toward a molecular portrait of epileptogenesis.

BACKGROUND: Uncovering the molecular mechanisms involved in epileptogenesis is critical to better understand the physiopathology of epilepsies and to help develop new therapeutic strategies for this prevalent and severe neurological condition that affects millions of people worldwide. RESULTS: Changes in the transcriptome of hippocampal cells from rats subjected to the pilocarpine model of epilepsy were evaluated by microarrays covering 34,000 transcripts representing all annotated rat genes to date. Using such genome-wide approach, differential expression of nearly 1,400 genes was detected during the course of epileptogenesis, from the early events post status epilepticus (SE) to the onset of recurrent spontaneous seizures. Most of these genes are novel and displayed an up-regulation after SE. Noteworthy, a group of 128 genes was found consistently hyper-expressed throughout epileptogenesis, indicating stable modulation of the p38MAPK, Jak-STAT, PI3K, and mTOR signaling pathways. In particular, up-regulation of genes from the TGF-beta and IGF-1 signaling pathways, with opposite effects on neurogenesis, correlate with the physiopathological changes reported in humans. CONCLUSIONS: A consistent regulation of genes functioning in intracellular signal transduction regulating neurogenesis have been identified during epileptogenesis, some of which with parallel expression patterns reported in patients with epilepsy, strengthening the link between these processes and development of epilepsy. These findings reveal dynamic molecular changes occurring in the hippocampus that may serve as a starting point for designing alternative therapeutic strategies to prevent the development of epilepsy after acquired brain insults.

Omega-transaminases as efficient biocatalysts to obtain novel chiral selenium-amine ligands for Pd-catalysis.

Omega-transaminases have been evaluated as biocatalysts in the reductive amination of organoselenium acetophenones to the corresponding amines, and in the kinetic resolution of racemic organoselenium amines. Kinetic resolution proved to be more efficient than the asymmetric reductive amination. By using these methodologies we were able to obtain both amine enantiomers in high enantiomeric excess (up to 99%). Derivatives of the obtained optically pure o-selenium 1-phenylethyl amine were evaluated as ligands in the palladium-catalyzed asymmetric alkylation, giving the alkylated product in up to 99% ee.

Granular cell dispersion and bilamination: two distinct histopathological patterns in epileptic hippocampi?

Cytoarchitectural modifications of the dentate gyrus are among the most obvious abnormalities observed in the hippocampal sclerosis associated with refractory epilepsy. Here, we examined the morphological changes of granular cells (dispersion, bilamination and cell loss) in sclerotic hippocampi from nine TLE patients, comparing abnormal and preserved areas. A total of 2,577 granular cells were analyzed with respect to four different histopathological patterns: areas with bilamination (n = 936), areas with dispersion (n = 905), areas with neuronal loss (n = 279), and preserved areas (n = 457). Quantitative parameters included somatic perimeter (P), area (A) and form factor (ff). Although different patterns were often observed in the same patient, highly significant differences were observed (p < 0.0001) when patterns were compared to one another. Since granular cell dispersion and bilamination have different morphological aspects in sclerotic hippocampi from TLE patients, we suggest that these patterns should be considered separately. Future studies are needed to determine the frequency with which these patterns occur in the general population and whether each one can interfere with seizure susceptibility.

Complex network analysis of CA3 transcriptome reveals pathogenic and compensatory pathways in refractory temporal lobe epilepsy.

We previously described - studying transcriptional signatures of hippocampal CA3 explants - that febrile (FS) and afebrile (NFS) forms of refractory mesial temporal lobe epilepsy constitute two distinct genomic phenotypes. That network analysis was based on a limited number (hundreds) of differentially expressed genes (DE networks) among a large set of valid transcripts (close to two tens of thousands). Here we developed a methodology for complex network visualization (3D) and analysis that allows the categorization of network nodes according to distinct hierarchical levels of gene-gene connections (node degree) and of interconnection between node neighbors (concentric node degree). Hubs are highly connected nodes, VIPs have low node degree but connect only with hubs, and high-hubs have VIP status and high overall number of connections. Studying the whole set of CA3 valid transcripts we: i) obtained complete transcriptional networks (CO) for FS and NFS phenotypic groups; ii) examined how CO and DE networks are related; iii) characterized genomic and molecular mechanisms underlying FS and NFS phenotypes, identifying potential novel targets for therapeutic interventions. We found that: i) DE hubs and VIPs are evenly distributed inside the CO networks; ii) most DE hubs and VIPs are related to synaptic transmission and neuronal excitability whereas most CO hubs, VIPs and high hubs are related to neuronal differentiation, homeostasis and neuroprotection, indicating compensatory mechanisms. Complex network visualization and analysis is a useful tool for systems biology approaches to multifactorial diseases. Network centrality observed for hubs, VIPs and high hubs of CO networks, is consistent with the network disease model, where a group of nodes whose perturbation leads to a disease phenotype occupies a central position in the network. Conceivably, the chance for exerting therapeutic effects through the modulation of particular genes will be higher if these genes are highly interconnected in transcriptional networks.

Hippocampal CA3 transcriptome signature correlates with initial precipitating injury in refractory mesial temporal lobe epilepsy.

BACKGROUND: Prolonged febrile seizures constitute an initial precipitating injury (IPI) commonly associated with refractory mesial temporal lobe epilepsy (RMTLE). In order to investigate IPI influence on the transcriptional phenotype underlying RMTLE we comparatively analyzed the transcriptomic signatures of CA3 explants surgically obtained from RMTLE patients with (FS) or without (NFS) febrile seizure history. Texture analyses on MRI images of dentate gyrus were conducted in a subset of surgically removed sclerotic hippocampi for identifying IPI-associated histo-radiological alterations. METHODOLOGY/PRINCIPAL FINDINGS: DNA microarray analysis revealed that CA3 global gene expression differed significantly between FS and NFS subgroups. An integrative functional genomics methodology was used for characterizing the relations between GO biological processes themes and constructing transcriptional interaction networks defining the FS and NFS transcriptomic signatures and its major gene-gene links (hubs). Co-expression network analysis showed that: i) CA3 transcriptomic profiles differ according to the IPI; ii) FS distinctive hubs are mostly linked to glutamatergic signalization while NFS hubs predominantly involve GABAergic pathways and neurotransmission modulation. Both networks have relevant hubs related to nervous system development, what is consistent with cell genesis activity in the hippocampus of RMTLE patients. Moreover, two candidate genes for therapeutic targeting came out from this analysis: SSTR1, a relevant common hub in febrile and afebrile transcriptomes, and CHRM3, due to its putative role in epilepsy susceptibility development. MRI texture analysis allowed an overall accuracy of 90% for pixels correctly classified as belonging to FS or NFS groups. Histological examination revealed that granule cell loss was significantly higher in FS hippocampi. CONCLUSIONS/SIGNIFICANCE: CA3 transcriptional signatures and dentate gyrus morphology fairly correlate with IPI in RMTLE, indicating that FS-RMTLE represents a distinct phenotype. These findings may shed light on the molecular mechanisms underlying refractory epilepsy phenotypes and contribute to the discovery of novel specific drug targets for therapeutic interventions.

Damage, reorganization, and abnormal neocortical hyperexcitability in the pilocarpine model of temporal lobe epilepsy.

PURPOSE: Clinical, neuropathological, and electrophysiological data have shown that limbic structures are involved in the pathogenesis of temporal lobe epilepsy (TLE). In most cases, limbic-originated seizures frequently spread to extrahippocampal areas. It is unclear whether such distant circuitries, especially the neocortex, exhibit abnormal electrophysiology as consequences of a chronic epileptogenic process. The present research studied neuropathological abnormalities and in vitro electrophysiological properties of sensorimotor neocortex in pilocarpine-treated epileptic rats. METHODS: Adult epileptic animals showing six to seven seizures/week and saline-injected rats were selected for neurohistology. Coronal sections were sampled throughout the anteroposterior extent of the diencephalon and stained with cresyl violet (Nissl). Immunocytochemistry (ICC) was performed using anti-neurofilament (SMI-311) antibody. Extracellular (layer II/III) and intracellular (layer V) recordings were performed in coronal sensorimotor neocortical slices. Several electrophysiological aspects were examined such as evoked responses, intrinsic properties, and firing patterns of layer V pyramidal cells. RESULTS: Nissl staining showed a significant decrease of cortical thickness in epileptic rats when compared with controls, particularly in superficial layers (II-IV). Such abnormalities were also revealed by SMI-311 staining. SMI-311-labeled dendrite arborizations were more complex in layers I-II of epileptic rats. Epileptic rats manifested several abnormalities in extracellular field responses including hyperresponsiveness and presence of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-mediated polysynaptic activity. Although no significant changes were observed concerning passive intrinsic properties, it was possible to detect a higher proportion of bursting neurons distributed in layer V (60%) of epileptic rats compared with 22% in control slices. CONCLUSIONS: Taken together, our findings indicate damage, reorganization, and chronic hyperexcitability of sensorimotor neocortex in experimental TLE.