Expression of connexin 43 and connexin 32 gap-junction proteins in epilepsy-associated brain tumors and in the perilesional epileptic cortex

Epilepsy and demyelination: Towards a bidirectional relationship

Demyelination stands out as a prominent feature in individuals with specific types of epilepsy. Concurrently, individuals with demyelinating diseases, such as multiple sclerosis (MS) are at a greater risk of developing epilepsy compared to non-MS individuals. These bidirectional connections raise the question of whether both pathological conditions share common pathogenic mechanisms. This review focuses on the reciprocal relationship between epilepsy and demyelination diseases. We commence with an overview of the neurological basis of epilepsy and demyelination diseases, followed by an exploration of how our comprehension of these two disorders has evolved in tandem. Additionally, we discuss the potential pathogenic mechanisms contributing to the interactive relationship between these two diseases. A more nuanced understanding of the interplay between epilepsy and demyelination diseases has the potential to unveiling the molecular intricacies of their pathological relationships, paving the way for innovative directions in future clinical management and treatment strategies for these diseases.

Fluoxetine enhances the antitumor effect of olfactory ensheathing cell-thymidine kinase/ganciclovir gene therapy in human glioblastoma multiforme cells through upregulation of Connexin43 levels

Glioblastoma multiforme (GBM) is the most invasive form of primary brain astrocytoma, resulting in poor clinical outcomes. Herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy is considered a promising strategy for GBM treatment. Since Connexin43 (Cx43) expression is reduced in GBM cells, increasing Cx43 levels could enhance the effectiveness of gene therapy. The present study aims to examine the impact of fluoxetine on HSV-TK/GCV gene therapy in human GBM cells using human olfactory ensheathing cells (OECs) as vectors. The effect of fluoxetine on Cx43 levels was assessed using the western blot technique. GBM-derived astrocytes and OECs-TK were Cocultured, and the effect of fluoxetine on the Antitumor effect of OEC-TK/GCV gene therapy was evaluated using MTT assay and flow cytometry. Our results showed that fluoxetine increased Cx43 levels in OECs and GBM cells and augmented the killing effect of OECs-TK on GBM cells. Western blot data revealed that fluoxetine enhanced the Bax/Bcl2 ratio and the levels of cleaved caspase-3 in the coculture of OECs-TK and GBM cells. Moreover, flow cytometry data indicated that fluoxetine increased the percentage of apoptotic cells in the coculture system. This study suggests that fluoxetine, by upregulating Cx43 levels, could strengthen the Antitumor effect of OEC-TK/GCV gene therapy on GBM cells.

Fluid Biomarkers of Neuro-Glial Injury in Human Status Epilepticus: A Systematic Review

As per the latest ILAE definition, status epilepticus (SE) may lead to long-term irreversible consequences, such as neuronal death, neuronal injury, and alterations in neuronal networks. Consequently, there is growing interest in identifying biomarkers that can demonstrate and quantify the extent of neuronal and glial injury. Despite numerous studies conducted on animal models of status epilepticus, which clearly indicate seizure-induced neuronal and glial injury, as well as signs of atrophy and gliosis, evidence in humans remains limited to case reports and small case series. The implications of identifying such biomarkers in clinical practice are significant, including improved prognostic stratification of patients and the early identification of those at high risk of developing irreversible complications. Moreover, the clinical validation of these biomarkers could be crucial in promoting neuroprotective strategies in addition to antiseizure medications. In this study, we present a systematic review of research on biomarkers of neuro-glial injury in patients with status epilepticus.

Role of Impaired Astrocyte Gap Junction Coupling in Epileptogenesis

The gap-junction-coupled astroglial network plays a central role in the regulation of neuronal activity and synchronisation, but its involvement in the pathogenesis of neuronal diseases is not yet understood. Here, we present the current state of knowledge about the impact of impaired glial coupling in the development and progression of epilepsy and discuss whether astrocytes represent alternative therapeutic targets. We focus mainly on temporal lobe epilepsy (TLE), which is the most common form of epilepsy in adults and is characterised by high therapy resistance. Functional data from TLE patients and corresponding experimental models point to a complete loss of astrocytic coupling, but preservation of the gap junction forming proteins connexin43 and connexin30 in hippocampal sclerosis. Several studies further indicate that astrocyte uncoupling is a causal event in the initiation of TLE, as it occurs very early in epileptogenesis, clearly preceding dysfunctional changes in neurons. However, more research is needed to fully understand the role of gap junction channels in epilepsy and to develop safe and effective therapeutic strategies targeting astrocytes.

Astrocyte-neuron circuits in epilepsy

The epilepsies are a diverse spectrum of disease states characterized by spontaneous seizures and associated comorbidities. Neuron-focused perspectives have yielded an array of widely used anti-seizure medications and are able to explain some, but not all, of the imbalance of excitation and inhibition which manifests itself as spontaneous seizures. Furthermore, the rate of pharmacoresistant epilepsy remains high despite the regular approval of novel anti-seizure medications. Gaining a more complete understanding of the processes that turn a healthy brain into an epileptic brain (epileptogenesis) as well as the processes which generate individual seizures (ictogenesis) may necessitate broadening our focus to other cell types. As will be detailed in this review, astrocytes augment neuronal activity at the level of individual neurons in the form of gliotransmission and the tripartite synapse. Under normal conditions, astrocytes are essential to the maintenance of blood-brain barrier integrity and remediation of inflammation and oxidative stress, but in epilepsy these functions are impaired. Epilepsy results in disruptions in the way astrocytes relate to each other by gap junctions which has important implications for ion and water homeostasis. In their activated state, astrocytes contribute to imbalances in neuronal excitability due to their decreased capacity to take up and metabolize glutamate and an increased capacity to metabolize adenosine. Furthermore, due to their increased adenosine metabolism, activated astrocytes may contribute to DNA hypermethylation and other epigenetic changes that underly epileptogenesis. Lastly, we will explore the potential explanatory power of these changes in astrocyte function in detail in the specific context of the comorbid occurrence of epilepsy and Alzheimer's disease and the disruption in sleep-wake regulation associated with both conditions.

Antitumor Potential of Antiepileptic Drugs in Human Glioblastoma: Pharmacological Targets and Clinical Benefits

Glioblastoma (GBM) is characterized by fast-growing cells, genetic and phenotypic heterogeneity, and radio-chemo-therapy resistance, contributing to its dismal prognosis. Various medical comorbidities are associated with the natural history of GBM. The most disabling and greatly affecting patients' quality of life are neurodegeneration, cognitive impairment, and GBM-related epilepsy (GRE). Hallmarks of GBM include molecular intrinsic mediators and pathways, but emerging evidence supports the key role of non-malignant cells within the tumor microenvironment in GBM aggressive behavior. In this context, hyper-excitability of neurons, mediated by glutamatergic and GABAergic imbalance, contributing to GBM growth strengthens the cancer-nervous system crosstalk. Pathogenic mechanisms, clinical features, and pharmacological management of GRE with antiepileptic drugs (AEDs) and their interactions are poorly explored, yet it is a potentially promising field of research in cancer neuroscience. The present review summarizes emerging cooperative mechanisms in oncogenesis and epileptogenesis, focusing on the neuron-to-glioma interface. The main effects and efficacy of selected AEDs used in the management of GRE are discussed in this paper, as well as their potential beneficial activity as antitumor treatment. Overall, although still many unclear processes overlapping in GBM growth and seizure onset need to be elucidated, this review focuses on the intriguing targeting of GBM-neuron mutual interactions to improve the outcome of the so challenging to treat GBM.

Human and mouse cortical astrocytes: a comparative view from development to morphological and functional characterization

The vision of astroglia as a bare scaffold to neuronal circuitry has been largely overturned. Astrocytes exert a neurotrophic function, but also take active part in supporting synaptic transmission and in calibrating blood circulation. Many aspects of their functioning have been unveiled from studies conducted in murine models, however evidence is showing many differences between mouse and human astrocytes starting from their development and encompassing morphological, transcriptomic and physiological variations when they achieve complete maturation. The evolutionary race toward superior cognitive abilities unique to humans has drastically impacted neocortex structure and, together with neuronal circuitry, astrocytes have also been affected with the acquisition of species-specific properties. In this review, we summarize diversities between murine and human astroglia, with a specific focus on neocortex, in a panoramic view that starts with their developmental origin to include all structural and molecular differences that mark the uniqueness of human astrocytes.

Early and extensive alterations of glial connexins, distal oligodendrogliopathy type demyelination, and nodal/paranodal pathology are characteristic of multiple system atrophy

The pathological hallmark of multiple system atrophy (MSA) is aberrant accumulation of phosphorylated α-synuclein in oligodendrocytes, forming glial cytoplasmic inclusions (GCIs). Extensive demyelination occurs particularly in the olivopontocerebellar and striatonigral pathways, but its precise mechanism remains elusive. Glial connexins (Cxs), which form gap junction channels between astrocytes and oligodendrocytes, play critical roles in myelin maintenance, and have not been studied in MSA. Therefore, we immunohistochemically investigated glial Cx changes in the cerebellar afferent fibers in 15 autopsied patients with MSA. We classified demyelinating lesions into three stages based on Klüver-Barrera staining: early (Stage I), intermediate (Stage II), and late (Stage III) stages showing subtle, moderate, and severe myelin reduction, respectively. Myelin-associated glycoprotein, but not myelin oligodendrocyte glycoprotein, was preferentially decreased in Stage I, suggesting distal oligodendrogliopathy type demyelination. Accumulation of phosphorylated α-synuclein in oligodendrocytes was frequently seen in Stage I but less frequently observed in Stages II and III. Tubulin polymerization-promoting protein (TPPP/p25α)-positive oligodendrocytes were preserved in Stage I but successively decreased in Stages II and III. Even at Stage I, Cx32 was nearly absent from myelin, despite the relative preservation of other nodal proteins, such as neurofascin, claudin-11/oligodendrocyte-specific protein, and contactin-associated protein 1, which successively decreased in the later stages. Cx32 was re-distributed in the oligodendrocyte cytoplasm and co-localized with GCIs. Cx47 gradually decreased at the oligodendrocyte surface in a stage-dependent manner but was not co-localized with GCIs. Astrocytic Cx43 was down-regulated in Stage I but up-regulated in Stages II and III, reflecting astrogliosis. Cx43/Cx47 gap junctions significantly decreased from Stage I to III. Activated microglia/macrophages and T cells infiltrated in Stage I rather than Stages II and III. Therefore, early and extensive alterations of glial Cxs, particularly Cx32 loss, occur in MSA and may accelerate distal oligodendrogliopathy type demyelination and nodal/paranodal dysfunction through disruption of inter-glial communication.

[Structural heterogeneity of epileptic foci in local drug-resistant epilepsy]

BACKGROUND

To study etiopathogenesis is one of the most important tasks of modern neurology. Various types of structural changes occur in drug-resistant epilepsy (DRE); however, they are described as distinct phenomena.

OBJECTIVE

To provide a comprehensive characterization of structural changes in the cortex and adjacent white matter in the electrophysiological activity zone (in the epileptic focus) in patients undergoing surgery for DRE.

MATERIAL AND METHODS

Biopsy material of fragments of the temporal lobe and hippocampus from 16 patients aged 21 to 54 years (mean age, 25 years) with DRE were intraoperatively obtained at the Prof. A.L. Polenov Russian Research Institute of Neurosurgery. The investigators studied histological sections stained with H&E, toluidine blue according to the Nissl method and the Spielmeyer method, as well as the results of immunohistochemical reactions with glial fibrillary acidic protein (GFAP), vimentin, and neurofilaments (NF) (Dako antibodies, Denmark).

RESULTS

Histological examination revealed a set of heterogeneous changes, reflecting the complex pathogenetic interactions that developed during the formation of an epileptic focus. Structural brain damage involved both gray and white matter. Focal cortical dysplasia was diagnosed in 14 (87.5%) cases; white matter neuronal heterotopia in 100%; neuronal reactive and destructive changes in 100%; epileptic leukoencephalopathy (vascular demyelination, microcysts, sclerosis and dystonia, gliosis) in 100%, cortical atrophy in 12.5%, and hippocampal sclerosis in 20% (in 2 out of the 10 examinees).

CONCLUSION

The morphopathological heterogeneity in the structure of epileptic foci reflects the complexity of etiopathogenetic interactions, the polymorphism of epileptic manifestations, and the individual nature of formation of the epileptic system, which requires an integral approach to understanding the pathogenesis and morphogenesis of formation of the epileptic system and provides a direction for a personalized approach to epilepsy treatment.

Astrocytic Connexin43 Channels as Candidate Targets in Epilepsy Treatment

In epilepsy research, emphasis is put on exploring non-neuronal targets such as astrocytic proteins, since many patients remain pharmacoresistant to current treatments, which almost all target neuronal mechanisms. This paper reviews available data on astrocytic connexin43 (Cx43) signaling in seizures and epilepsy. Cx43 is a widely expressed transmembrane protein and the constituent of gap junctions (GJs) and hemichannels (HCs), allowing intercellular and extracellular communication, respectively. A plethora of research papers show altered Cx43 mRNA levels, protein expression, phosphorylation state, distribution and/or functional coupling in human epileptic tissue and experimental models. Human Cx43 mutations are linked to seizures as well, as 30% of patients with oculodentodigital dysplasia (ODDD), a rare genetic condition caused by mutations in the GJA1 gene coding for Cx43 protein, exhibit neurological symptoms including seizures. Cx30/Cx43 double knock-out mice show increased susceptibility to evoked epileptiform events in brain slices due to impaired GJ-mediated redistribution of K⁺ and glutamate and display a higher frequency of spontaneous generalized chronic seizures in an epilepsy model. Contradictory, Cx30/Cx43 GJs can traffic nutrients to high-energy demanding neurons and initiate astrocytic Ca²⁺ waves and hyper synchronization, thereby supporting proconvulsant effects. The general connexin channel blocker carbenoxolone and blockers from the fenamate family diminish epileptiform activity in vitro and improve seizure outcome in vivo. In addition, interventions with more selective peptide inhibitors of HCs display anticonvulsant actions. To conclude, further studies aiming to disentangle distinct roles of HCs and GJs are necessary and tools specifically targeting Cx43 HCs may facilitate the search for novel epilepsy treatments.

Astrocytes in the regulation of cerebrovascular functions

Astrocytes are the most numerous type of neuroglia in the brain and have a predominant influence on the cerebrovascular system; they control perivascular homeostasis, the integrity of the blood-brain barrier, the dialogue with the peripheral immune system, the transfer of metabolites from the blood, and blood vessel contractility in response to neuronal activity. These regulatory processes occur in a specialized interface composed of perivascular astrocyte extensions that almost completely cover the cerebral blood vessels. Scientists have only recently started to study how this interface is formed and how it influences cerebrovascular functions. Here, we review the literature on the astrocytes' role in the regulation of the cerebrovascular system. We cover the anatomy and development of the gliovascular interface, the known gliovascular functions, and molecular factors, the latter's implication in certain pathophysiological situations, and recent cutting-edge experimental tools developed to examine the astrocytes' role at the vascular interface. Finally, we highlight some open questions in this field of research.

Altered Expression of Glial Gap Junction Proteins Cx43, Cx30, and Cx47 in the 5XFAD Model of Alzheimer's Disease

Glial gap junction proteins, called connexins (Cxs), form gap junctions in the central nervous system (CNS) to allow the bidirectional cytosolic exchange of molecules between adjacent cells. Their involvement in inheritable diseases and the use of experimental animal models that closely mimic such diseases revealed the critical role of glial GJs in myelination and homeostasis. Cxs are also implicated in acquired demyelinating disorders, such as Multiple Sclerosis (MS) and Alzheimer's disease (AD). Animal and human studies have revealed a role of the astrocytic Cx43 in the progression of AD but the role of Cx47, which is the main partner of Cx43 in the astrocyte-oligodendrocyte GJs is still unknown. The aim of this study was to investigate the astrocytic connexins, Cx43 and Cx30 in relation to oligodendrocytic Cx47 in the cortex and thalamus of the 5XFAD mouse model of AD. The model was characterized by increased Aβ deposition, gliosis, neuronal loss, and memory impairment. Compared to wild-type mice, Cx43 and Cx30 showed increased immunoreactivity in older 5XFAD mice, reflecting astrogliosis, while Cx47 immunoreactivity was reduced. Moreover, Cx47 GJ plaques showed reduced colocalization with Cx43 plaques. Oligodendrocyte precursor cells (OPCs) and mature oligodendrocyte populations were also depleted, and myelin deficits were observed. Our findings indicate reduced astrocyte-oligodendrocyte gap junction connectivity and possibly a shift in Cx43 expression toward astrocyte-astrocyte gap junctions and/or hemichannels, that could impair oligodendrocyte homeostasis and myelination. However, other factors, such as Aβ toxicity, could directly affect oligodendrocyte survival in AD. Our study provides evidence that Cxs might have implications in the progression of AD, although the role of oligodendrocyte Cxs in AD requires further investigation.

Factors associated with seizure and cognitive outcomes after epilepsy surgery for low-grade epilepsy-associated neuroepithelial tumors in children

Low-grade epilepsy-associated neuroepithelial tumors (LEATs) are responsible for drug-resistant chronic focal epilepsy, and are the second-most common reason for epilepsy surgery in children. LEATs are extremely responsive to surgical treatment, and therefore epilepsy surgery should be considered as a treatment option for LEATs. However, the optimal time for surgery remains controversial, and surgeries are often delayed. In this review, we reviewed published article on the factors associated with seizure and cognitive outcomes after epilepsy surgery for LEATs in children to help clinicians in their decision whether to pursue epilepsy surgery for LEATs. The achievement of gross total resection may be the most important prognostic factor for seizure freedom. A shorter duration of epilepsy, a younger age at surgery, and extended resection of temporal lobe tumors have also been suggested as favorable prognostic factors in terms of seizure control. Poor cognitive function in children with LEATs is associated with a longer duration of epilepsy and a younger age at seizure onset.

Epileptogenesis and oncogenesis: An antineoplastic role for antiepileptic drugs in brain tumours?

The first description of epileptic seizures due to brain tumours occurred in 19th century. Nevertheless, after over one hundred years, scientific literature is still lacking on how epilepsy and its treatment can affect tumour burden, progression and clinical outcomes. In patients with brain tumours, epilepsy dramatically impacts their quality of life (QoL). Even antiepileptic therapy seems to affect tumor lesion development. Numerous studies suggest that certain actors involved in epileptogenesis (inflammatory changes, glutamate and its ionotropic and metabotropic receptors, GABA-A and its GABA-AR receptor, as well as certain ligand- and voltage-gated ion channel) may also contribute to tumorigenesis. Although some antiepileptic drugs (AEDs) are known operating on such mechanisms underlying epilepsy and tumor development, few preclinical and clinical studies have tried to investigate them as targets of pharmacological tools acting to control both phenomena. The primary aim of this review is to summarize known determinants and pathophysiological mechanisms of seizures, as well as of cell growth and spread, in patients with brain tumors. Therefore, a special focus will be provided on the anticancer effects of commonly prescribed AEDs (including levetiracetam, valproic acid, oxcarbazepine and others), with an overview of both preclinical and clinical data. Potential clinical applications of this finding are discussed.

The Roles of miRNA in Glioblastoma Tumor Cell Communication: Diplomatic and Aggressive Negotiations

Glioblastoma (GBM) consists of a heterogeneous collection of competing cellular clones which communicate with each other and with the tumor microenvironment (TME). MicroRNAs (miRNAs) present various exchange mechanisms: free miRNA, extracellular vesicles (EVs), or gap junctions (GJs). GBM cells transfer miR-4519 and miR-5096 to astrocytes through GJs. Oligodendrocytes located in the invasion front present high levels of miR-219-5p, miR-219-2-3p, and miR-338-3p, all related to their differentiation. There is a reciprocal exchange between GBM cells and endothelial cells (ECs) as miR-5096 promotes angiogenesis after being transferred into ECs, whereas miR-145-5p acts as a tumor suppressor. In glioma stem cells (GSCs), miR-1587 and miR-3620-5p increase the proliferation and miR-1587 inhibits the hormone receptor co-repressor-1 (NCOR1) after EVs transfers. GBM-derived EVs carry miR-21 and miR-451 that are up-taken by microglia and monocytes/macrophages, promoting their proliferation. Macrophages release EVs enriched in miR-21 that are transferred to glioma cells. This bidirectional miR-21 exchange increases STAT3 activity in GBM cells and macrophages, promoting invasion, proliferation, angiogenesis, and resistance to treatment. miR-1238 is upregulated in resistant GBM clones and their EVs, conferring resistance to adjacent cells via the CAV1/EGFR signaling pathway. Decrypting these mechanisms could lead to a better patient stratification and the development of novel target therapies.

Evolving Mechanistic Concepts of Epileptiform Synchronization and their Relevance in Curing Focal Epileptic Disorders

The synchronized activity of neuronal networks under physiological conditions is mirrored by specific oscillatory patterns of the EEG that are associated with different behavioral states and cognitive functions. Excessive synchronization can, however, lead to focal epileptiform activity characterized by interictal and ictal discharges in epileptic patients and animal models. This review focusses on studies that have addressed epileptiform synchronization in temporal lobe regions by employing in vitro and in vivo recording techniques. First, we consider the role of ionotropic and metabotropic excitatory glutamatergic transmission in seizure generation as well as the paradoxical role of GABAA signaling in initiating and perhaps maintaining focal seizure activity. Second, we address non-synaptic mechanisms (which include voltage-gated ionic currents and gap junctions) in the generation of epileptiform synchronization. For each mechanism, we discuss the actions of antiepileptic drugs that are presumably modulating excitatory or inhibitory signaling and voltage-gated currents to prevent seizures in epileptic patients. These findings provide insights into the mechanisms of seizure initiation and maintenance, thus leading to the development of specific pharmacological treatments for focal epileptic disorders.

Canine Primary Intracranial Cancer: A Clinicopathologic and Comparative Review of Glioma, Meningioma, and Choroid Plexus Tumors

In the dog, primary intracranial neoplasia represents ~2-5% of all cancers and is especially common in certain breeds including English and French bulldogs and Boxers. The most common types of primary intracranial cancer in the dog are meningioma, glioma, and choroid plexus tumors, generally occurring in middle aged to older dogs. Much work has recently been done to understand the characteristic imaging and clinicopathologic features of these tumors. The gross and histologic landscape of these tumors in the dog compare favorably to their human counterparts with many similarities noted in histologic patterns, subtype, and grades. Data informing the underlying molecular abnormalities in the canine tumors have only begun to be unraveled, but reveal similar pathways are mutated between canine and human primary intracranial neoplasia. This review will provide an overview of the clinicopathologic features of the three most common forms of primary intracranial cancer in the dog, delve into the comparative aspects between the dog and human neoplasms, and provide an introduction to current standard of care while also highlighting novel, experimental treatments that may help bridge the gap between canine and human cancer therapies.

Targeting different domains of gap junction protein to control malignant glioma

A rational treatment strategy for glioma, the most common primary central nervous system tumor, should focus on early invasive growth and resistance to current therapeutics. Connexin 43 (Cx43), a gap junction protein, plays important roles not only in the development of the central nervous system and but also in the progression of glioma. The different structural domains of Cx43, including extracellular loops, transmembrane domains, and an intracellular carboxyl terminal, have distinct functions in the invasion and proliferation of gliomas. Targeting these domains of Cx43, which is expressed in distinct patterns in the heterogeneous glioma cell population, can inhibit tumor cell invasion and new tumor formation. Thus, this review summarizes the structural characteristics of Cx43, the effects of regulating different Cx43 domains on the biological characteristics of glioma cells, intervention strategies targeting different domains of Cx43, and future research directions.

A Microfluidic Human Model of Blood-Brain Barrier Employing Primary Human Astrocytes

The neurovascular unit (NVU) is the most important biological barrier between vascular districts and central nervous system (CNS) parenchyma, which maintains brain homeostasis, protects the CNS from pathogens penetration, and mediates neuroimmune communication. T lymphocytes migration across the blood-brain barrier is heavily affected in different brain diseases, representing a major target for novel drug development. In vitro models of NVU could represent a primary tool to investigate the molecular events occurring at this interface. To move toward the establishment of personalized therapies, a patient-related NVU-model is set, incorporating human primary astrocytes integrated into a microfluidic platform. The model is morphologically and functionally characterized, proving to be an advantageous tool to investigate human T lymphocytes transmigration and thus the efficacy of potential novel drugs affecting this process.

Targeting gap junction in epilepsy: Perspectives and challenges

Gap junctions (GJs) are multiple cellular intercellular connections that allow ions to pass directly into the cytoplasm of neighboring cells. Electrical coupling mediated by GJs plays a role in the generation of highly synchronous electrical activity. Accumulative investigations show that GJs in the brain are involved in the generation, synchronization and maintenance of seizure events. At the same time, GJ blockers exert potent curative potential on epilepsy in vivo or in vitro. This review aims to shed light on the role of GJs in epileptogenesis. Targeting GJs is likely to be served as a novel therapeutic approach on epileptic patients.

Conflicting Roles of Connexin43 in Tumor Invasion and Growth in the Central Nervous System

The tumor microenvironment is known to have increased levels of cytokines and metabolites, such as glutamate, due to their release from the surrounding cells. A normal cell around the tumor that responds to the inflammatory environment is likely to be subsequently altered. We discuss how these abnormalities will support tumor survival via the actions of gap junctions (GJs) and hemichannels (HCs) which are composed of hexamer of connexin43 (Cx43) protein. In particular, we discuss how GJ intercellular communication (GJIC) in glioma cells, the primary brain tumor, is a regulatory factor and its attenuation leads to tumor invasion. In contrast, the astrocytes, which are normal cells around the glioma, are “hijacked” by tumor cells, either by receiving the transmission of malignant substances from the cancer cells via GJIC, or perhaps via astrocytic HC activity through the paracrine signaling which enable the delivery of these substances to the distal astrocytes. This astrocytic signaling would promote tumor expansion in the brain. In addition, brain metastasis from peripheral tissues has also been known to be facilitated by GJs formed between cerebral vascular endothelial cells and cancer cells. Astrocytes and microglia are generally thought to eliminate cancer cells at the blood–brain barrier. In contrast, some reports suggest they facilitate tumor progression as tumor cells take advantage of the normal functions of astrocytes that support the survival of the neurons by exchanging nutrients and metabolites. In summary, GJIC is essential for the normal physiological function of growth and allowing the diffusion of physiological substances. Therefore, whether GJIC is cancer promoting or suppressing may be dependent on what permeates through GJs, when it is active, and to which cells. The nature of GJs, which has been ambiguous in brain tumor progression, needs to be revisited and understood together with new findings on Cx proteins and HC activities.

Combating malignant astrocytes: Strategies mitigating tumor invasion

Malignant gliomas are glial-derived, primary brain tumors that carry poor prognosis. Existing therapeutics are largely ineffective and dramatically affect quality of life. The standard of care details a taxing combination of surgical resection, radiation of the resection cavity, and temozolomide (TMZ) chemotherapy, with treatment extending life by only an average of months (Maher et al., 2001; Stupp et al., 2005). Despite scientific and technological advancement, surgery remains the most important treatment modality. Therapeutic obstacles include xenobiotic protection conveyed by the blood-brain barrier (Zhang et al., 2015), invasiveness and therapeutic resistance of tumor cell populations (Bao et al., 2006), and distinctive attributes of secondary glioma occurrence (Ohgaki and Kleihues, 2013). While these brain malignancies can be classified by grade or grouped by molecular subclass, each tumor presents itself as its own complication. Based on all of these obstacles, new therapeutic approaches are urgently needed. These will likely emerge from numerous exciting studies of glioma biology that are ongoing and reviewed here. These show unexpected roles for ion channels, amino-acid transporters, and connexin gap junctions in supporting the invasive growth of gliomas. These studies have identified a number of proteins that may be targeted for therapy in the future.

Complex role of connexin 43 in astrocytic tumors and possible promotion of glioma‑associated epileptic discharge (Review)

Connexin (Cx)43 is a multifunction protein which forms gap junction channels and hemi‑channels. It also contains abundant binding domains which possess the ability to interact with certain Cx43‑associated proteins and therefore serve a fundamental role in various physiological and pathological functions. However, the understanding of the association between cancer and Cx43 along with Cx43‑gap junctions (GJ) remains unclear. All available data illustrate that Cx43 and its associated GJ serve important functions in cancers. The expression levels of Cx43 demonstrate a downward trend and an increase in the levels of malignancy, particularly in astrocytomas. The GJ intercellular communication activity in glioma cells can be adjusted via Cx43 phosphorylation and through the combination of Cx43 and its associated protein. Available evidence reveals Cx43 as a tumor‑inhibiting factor that suppresses glioma growth and proliferation. However, its mechanism is also regarded as complicated and ambiguous. Furthermore, it is apparent that Cx43‑GJ and the carboxyl tail may contribute to glioma growth and proliferation too. However, this valuable role could be weakened by its effects on migration and invasiveness. The detailed mechanism remains unclear and full of controversies. Cx43 can enhance the motor ability and invasiveness of astrocytic glioma cells. It is also able to influence glioma cells to detach from the tumor core to the peritumoral neocortex. This peritumoral region has recently been regarded as the basic focus of glioma‑associated seizure. Thus, Cx43 may take part in the onset and development of glioma‑associated epileptic discharge. In addition, change and increase of Cx43 expression in GJs has been observed in seizure perilesional tissue, which is associated with brain tumors. Cx43 or GJ/hemi‑channels exert enduring effects in the promotion of glioma‑associated epileptic release through direct mass effects and change of the tumor microenvironment. However, there are still a number of issues concerning this aspect that require further exploration. Cx43, as a potential treatment target against this incurable disease and its common symptom of epilepsy, requires further investigation.

Do Evolutionary Changes in Astrocytes Contribute to the Computational Power of the Hominid Brain?

It is now well accepted that astrocytes are essential in all major nervous system functions of the rodent brain, including neurotransmission, energy metabolism, modulation of blood flow, ion and water homeostasis, and, indeed, higher cognitive functions, although the contribution of astrocytes in cognition is still in early stages of study. Here we review the most current research findings on human astrocytes, including their structure, molecular characterization, and functional properties. We also highlight novel tools that have been established for translational approaches to the comparative study of astrocytes from humans and experimental animals. Understanding the differences in astrocytes is essential to elucidate the contribution of astrocytes to normal physiology, cognitive processing and diverse pathologies of the central nervous system.

Disorders of Astrocytes: Alexander Disease as a Model

Astrocytes undergo important phenotypic changes in many neurological disorders, including strokes, trauma, inflammatory diseases, infectious diseases, and neurodegenerative diseases. We have been studying the astrocytes of Alexander disease (AxD), which is caused by heterozygous mutations in the GFAP gene, which is the gene that encodes the major astrocyte intermediate filament protein. AxD is a primary astrocyte disease because GFAP expression is specific to astrocytes in the central nervous system (CNS). The accumulation of extremely large amounts of GFAP causes many molecular changes in astrocytes, including proteasome inhibition, stress kinase activation, mechanistic target of rapamycin (mTOR) activation, loss of glutamate and potassium buffering capacity, loss of astrocyte coupling, and changes in cell morphology. Many of these changes appear to be common to astrocyte reactions in other neurological disorders. Using AxD to illuminate common mechanisms, we discuss the molecular pathology of AxD astrocytes and compare that to astrocyte pathology in other disorders.

Human astrocytes: structure and functions in the healthy brain

Data collected on astrocytes’ physiology in the rodent have placed them as key regulators of synaptic, neuronal, network, and cognitive functions. While these findings proved highly valuable for our awareness and appreciation of non-neuronal cell significance in brain physiology, early structural and phylogenic investigations of human astrocytes hinted at potentially different astrocytic properties. This idea sparked interest to replicate rodent-based studies on human samples, which have revealed an analogous but enhanced involvement of astrocytes in neuronal function of the human brain. Such evidence pointed to a central role of human astrocytes in sustaining more complex information processing. Here, we review the current state of our knowledge of human astrocytes regarding their structure, gene profile, and functions, highlighting the differences with rodent astrocytes. This recent insight is essential for assessment of the relevance of findings using animal models and for comprehending the functional significance of species-specific properties of astrocytes. Moreover, since dysfunctional astrocytes have been described in many brain disorders, a more thorough understanding of human-specific astrocytic properties is crucial for better-adapted translational applications.

Human astrocytes in the diseased brain

Astrocytes are key active elements of the brain that contribute to information processing. They not only provide neurons with metabolic and structural support, but also regulate neurogenesis and brain wiring. Furthermore, astrocytes modulate synaptic activity and plasticity in part by controlling the extracellular space volume, as well as ion and neurotransmitter homeostasis. These findings, together with the discovery that human astrocytes display contrasting characteristics with their rodent counterparts, point to a role for astrocytes in higher cognitive functions. Dysfunction of astrocytes can thereby induce major alterations in neuronal functions, contributing to the pathogenesis of several brain disorders. In this review we summarize the current knowledge on the structural and functional alterations occurring in astrocytes from the human brain in pathological conditions such as epilepsy, primary tumours, Alzheimer's disease, major depressive disorder and Down syndrome. Compelling evidence thus shows that dysregulations of astrocyte functions and interplay with neurons contribute to the development and progression of various neurological diseases. Targeting astrocytes is thus a promising alternative approach that could contribute to the development of novel and effective therapies to treat brain disorders.

Predictors and mechanisms of epilepsy occurrence in cerebral gliomas: What to look for in clinicopathology

Gliomas, especially low-grade gliomas, are highly epileptogenic brain tumors. Histopathological information is valuable in evaluating the diagnosis and/or biologic behavior of various gliomas. Here we explored the clinical data and histopathological predictors of the occurrence of epilepsy in patients with gliomas. A retrospective study examined 310 consecutive patients who had undergone surgical treatment for gliomas in our institution from January 2013 to January 2015. Clinical data and pathological examination results were analyzed. Literatures regarding the predictors and etiology of glioma associated epileptic seizures in the period of 1995-2015 were also reviewed. A total of 234 (75.5%) astrocytic tumors and 76 (24.5%) oligodendrial tumors were included. At diagnosis, 33.6% of patients had epileptic seizures. Multivariate analysis revealed cortex involvement (OR=7.991, 95%CI=1.599-39.926), lower World Health Organization grade (OR=3.584, 95%CI=1.032-12.346) and topoisomerase II (TopoII) positivity (OR=0.943, 95%CI=0.903-0.982) were strong predictors for preoperative epileptic seizures. Gender, disease course, tumor classification, location or volume did not significantly affect epileptic seizure occurrence. Forty-three publications involved glioma-associated epilepsy were found in PubMed online database and key data were extracted and summarized. The present studies on glioma-related epilepsy are relatively limited and inconsistent. Low-grade gliomas, cortex involvement and TopoII positivity were independent predictors of a history of epileptic seizures at diagnosis. Further studies to examine the underlying mechanism of topoisomerase II as well as other molecules in epilepsy occurrence in brain gliomas are needed in the future.

Expression of a gap junction protein, connexin43, in a large panel of human gliomas: new insights

Precise diagnosis of low and high grades of brain tumors permits determining therapeutical strategies. So far, diagnosis and prognosis of gliomas were based on histological and genetic criteria which need being completed by a panel of molecular markers. Highly distributed in brain, gap junction proteins, connexins, could be considered as markers of glioma progression as previous studies indicated that expression of a connexin type, connexin43 (Cx43), is inversely correlated to tumor grading. However, this assumption was weakened by the low number of glioma samples used. Taking advantage of tissue microarray technique, we pursued this analysis by studying in situ expression of Cx43 on 85 samples (37 grade IV, 18 grade III, 24 grade II, and 6 grades II to III). Our analysis confirmed the global diminution of Cx43 expression in glioblastomas that was observed in previous studies. However, this analysis brought new insights such as the following ones. First, the high number of samples permitted to show that more than 60% of glioblastomas still express Cx43. Second, no gradual decrease in Cx43 expression was observed between grades II and III, but Cx43 appeared to be a marker distinguishing oligodendrocytic and astrocytic grade III tumors. Third, independently from tumor grade, a Cx43 nuclear staining was detected in areas where leukocytes are present. In conclusion, our study emphasizes the importance of in situ immunohistochemical approaches by giving more precise insights in the subcellular localization of Cx43. It also emphasizes the necessity to carry out such analysis on a wide range of samples to circumvent the high glioma heterogeneity.

Differential Expression of Adenosine P1 Receptor ADORA1 and ADORA2A Associated with Glioma Development and Tumor-Associated Epilepsy

Level of adenosine, an endogenous astrocyte-based neuromodulator, is primarily regulated by adenosine P1 receptors. This study assessed expression of adenosine P1 receptors, ADORA1 (adenosine A1 receptor) and ADORA2A (adenosine A2a receptor) and their association with glioma development and epilepsy in glioma patients. Expression of ADORA1/ADORA2A was assessed immunohistochemically in 65 surgically removed glioma tissue and 21 peri-tumor tissues and 8 cases of normal brain tissues obtained from hematoma patients with cerebral trauma. Immunofluorescence, Western blot, and qRT-PCR were also used to verify immunohistochemical data. Adenosine P1 receptor ADORA1 and ADORA2A proteins were localized in the cell membrane and cytoplasm and ADORA1/ADORA2A immunoreactivity was significantly stronger in glioma and peri-tumor tissues that contained infiltrating tumor cells than in normal brain tissues (p < 0.05). The World Health Organization (WHO) grade III gliomas expressed even higher level of ADORA1 and ADORA2A. Western blot and qRT-PCR confirmed immunohistochemical data. Moreover, higher levels of ADORA1 and ADORA2A expression occurred in high-grade gliomas, in which incidence of epilepsy were lower (p < 0.05). In contrast, a lower level of ADORA1/ADORA2A expression was found in peri-tumor tissues with tumor cell presence from patients with epilepsy compared to patients without epilepsy (p < 0.05). The data from the current study indicates that dysregulation in ADORA1/ADORA2A expression was associated with glioma development, whereas low level of ADORA1/ADORA2A expression could increase susceptibility of tumor-associated epilepsy.

Common mechanisms linking connexin43 to neural progenitor cell migration and glioma invasion

Cell migration is critical for cell differentiation, tissue formation and organ development. Several mechanisms come to play in the process of cell migration, orchestrating changes in cell polarity, adhesion, process extension and motility. Recent findings have shown that gap junctions, and specifically connexin43 (Cx43), can play a significant role in these processes, impacting adhesion and cytoskeletal rearrangements. Thus Cx43 within a cell regulates its motility and migration via intracellular signaling. Furthermore, Cx43 in the host cells can impact the degree of cellular migration through that tissue. Similarities in these connexin-based processes account for both neural progenitor migration in the developing brain, and for glioma cell invasion in the mature brain. In both cases, Cx43 in the tissue ("soil") in which cells ("seeds") exist facilitates their migration and, for glioma cells, tissue invasion. Cx43 mediates these effects through channel- and non-channel-dependent mechanisms which have similarities in both paradigms of cell migration. This provides insight into developmental processes and pathological situations, as well as possible therapeutic approaches regarding specific functional domains of gap junction proteins.

Epilepsy in glioma patients: mechanisms, management, and impact of anticonvulsant therapy

Seizures are a well-recognized symptom of primary brain tumors, and anticonvulsant use is common. This paper provides an overview of epilepsy and the use of anticonvulsants in glioma patients. Overall incidence and mechanisms of epileptogenesis are reviewed. Factors to consider with the use of antiepileptic drugs (AEDs) including incidence during the disease trajectory and prophylaxis along with considerations in the selection of anticonvulsant use (ie, potential side effects, drug interactions, adverse effects, and impact on survival) are also reviewed. Finally, areas for future research and exploring the pathophysiology and use of AEDs in this population are also discussed.

Adenosine deaminase and adenosine kinase expression in human glioma and their correlation with glioma‑associated epilepsy

The aim of the present study was to investigate adenosine deaminase (ADA) and adenosine kinase (ADK) expression in human glioma and to explore its correlation with glioma-associated epilepsy. Tumor tissues (n=45) and peritumoral tissues (n=14) were obtained from glioma patients undergoing surgery. Normal control tissues (n=8) were obtained from brain trauma patients. The disease grade was determined by histological evaluation and the degree of tumor invasion was evaluated using immunofluorescence analyses. mRNA and protein expression of ADA and ADK were evaluated using reverse transcription quantitative polymerase chain reaction or western blot analysis, respectively. Based on histological evaluations, four cases were classified as Grade I gliomas, 18 cases as Grade II, 17 cases as Grade III and six cases were considered Grade IV. Increased ADA and ADK expression was observed in tumor tissues. ADA was predominantly distributed in the cytoplasm of tumor cells, whereas ADK was detected in the cytoplasm as well as in the nuclei. ADA and ADK levels were upregulated in patients with Grade II and Grade III gliomas compared to those in control subjects (p<0.05). In addition, tumor invasion was detected in peritumoral tissues. The number of ADA-positive or ADK-positive cells in tumor tissues was similar between glioma patients with and without epilepsy (p>0.05). However, ADA and ADK expression was upregulated in peritumoral tissues derived from patients with epilepsy compared to that in glioma patients without epilepsy. The results of the present study suggested that ADA and ADK are involved in glioma progression, and that increased ADA and ADK levels in peritumoral tissues may be associated with epilepsy in glioma patients.

Tissue-specific transcriptome assemblies of the marine medaka Oryzias melastigma and comparative analysis with the freshwater medaka Oryzias latipes

Background

The marine medaka Oryzias melastigma has been demonstrated as a novel model for marine ecotoxicological studies. However, the lack of genome and transcriptome reference has largely restricted the use of O. melastigma in the assessment of in vivo molecular responses to environmental stresses and the analysis of biological toxicity in the marine environment. Although O. melastigma is believed to be phylogenetically closely related to Oryzias latipes, the divergence between these two species is still largely unknown. Using Illumina high-throughput RNA sequencing followed by de novo assembly and comprehensive gene annotation, we provided transcriptomic resources for the brain, liver, ovary and testis of O. melastigma. We also investigated the possible extent of divergence between O. melastigma and O. latipes at the transcriptome level.

Results

More than 14,000 transcripts across brain, liver, ovary and testis in marine medaka were annotated, of which 5880 transcripts were orthologous between O. melastigma and O. latipes. Tissue-enriched genes were identified in O. melastigma, and Gene Ontology analysis demonstrated the functional specificity of the annotated genes in respective tissue. Lastly, the identification of marine medaka-enriched transcripts suggested the necessity of generating transcriptome dataset of O. melastigma.

Conclusions

Orthologous transcripts between O. melastigma and O. latipes, tissue-enriched genes and O. melastigma-enriched transcripts were identified. Genome-wide expression studies of marine medaka require an assembled transcriptome, and this sequencing effort has generated a valuable resource of coding DNA for a non-model species. This transcriptome resource will aid future studies assessing in vivo molecular responses to environmental stresses and those analyzing biological toxicity in the marine environment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1325-7) contains supplementary material, which is available to authorized users.

Podoplanin: a marker for reactive gliosis in gliomas and brain injury

Reactive astrogliosis is associated with many pathologic processes in the central nervous system, including gliomas. The glycoprotein podoplanin (PDPN) is upregulated in malignant gliomas. Using a syngeneic intracranial glioma mouse model, we show that PDPN is highly expressed in a subset of glial fibrillary acidic protein-positive astrocytes within and adjacent to gliomas. The expression of PDPN in tumor-associated reactive astrocytes was confirmed by its colocalization with the astrocytic marker S100β and with connexin43, a major astrocytic gap junction protein. To determine whether the increase in PDPN is a general feature of gliosis, we used 2 mouse models in which astrogliosis was induced either by a needle injury or ischemia and observed similar upregulation of PDPN in reactive astrocytes in both models. Astrocytic PDPN was also found to be coexpressed with nestin, an intermediate filament marker for neural stem/progenitor cells. Our findings confirm that expression of PDPN is part of the normal host response to brain injury and gliomas, and suggest that it may be a novel cell surface marker for a specific population of reactive astrocytes in the vicinity of gliomas and nonneoplastic brain lesions. The findings also highlight the heterogeneity of glial fibrillary acidic protein-positive astrocytes in reactive gliosis.

Novel astrocyte targets: new avenues for the therapeutic treatment of epilepsy

During the last 20 years, it has been well established that a finely tuned, continuous crosstalk between neurons and astrocytes not only critically modulates physiological brain functions but also underlies many neurological diseases. In particular, this novel way of interpreting brain activity is markedly influencing our current knowledge of epilepsy, prompting a re-evaluation of old findings and guiding novel experimentation. Here, we review recent studies that have unraveled novel and unique contributions of astrocytes to the generation and spread of convulsive and nonconvulsive seizures and epileptiform activity. The emerging scenario advocates an overall framework in which a dynamic and reciprocal interplay among astrocytic and neuronal ensembles is fundamental for a fuller understanding of epilepsy. In turn, this offers novel astrocytic targets for the development of those really novel chemical entities for the control of convulsive and nonconvulsive seizures that have been acknowledged as a key priority in the management of epilepsy.

Reciprocal regulation of epileptiform neuronal oscillations and electrical synapses in the rat hippocampus

Gap junction (GJ) channels have been recognized as an important mechanism for synchronizing neuronal networks. Herein, we investigated the participation of GJ channels in the pilocarpine-induced status epilepticus (SE) by analyzing electrophysiological activity following the blockade of connexins (Cx)-mediated communication. In addition, we examined the regulation of gene expression, protein levels, phosphorylation profile and distribution of neuronal Cx36, Cx45 and glial Cx43 in the rat hippocampus during the acute and latent periods. Electrophysiological recordings revealed that the GJ blockade anticipates the occurrence of low voltage oscillations and promotes a marked reduction of power in all analyzed frequencies.Cx36 gene expression and protein levels remained stable in acute and latent periods, whereas upregulation of Cx45 gene expression and protein redistribution were detected in the latent period. We also observed upregulation of Cx43 mRNA levels followed by changes in the phosphorylation profile and protein accumulation. Taken together, our results indisputably revealed that GJ communication participates in the epileptiform activity induced by pilocarpine. Moreover, considering that specific Cxs undergo alterations through acute and latent periods, this study indicates that the control of GJ communication may represent a focus in reliable anti-epileptogenic strategies.

Peritumoral epilepsy: relating form and function for surgical success

Seizures are a prominent symptom in patients with both primary and secondary brain tumors. Medical management of seizure control in this patient group is problematic as the mechanisms linking tumorigenesis and epileptogenesis are poorly understood. It is possible that several mechanisms contribute to tumor-associated epileptic zone formation. In this review, we discuss key candidates that may be implicated in peritumoral epileptogenesis and, in so doing, hope to highlight areas for future research. Furthermore, we summarize the current role of antiepileptic medications in this type of epilepsy and examine the changes in surgical practice which may lead to improved seizure rates after tumor surgery. Lastly, we speculate on possible future preoperative and intraoperative considerations for improving seizure control after tumor resection.

Time to focus on brain tumor-related epilepsy trials

Brain tumor-related epilepsy (BTRE) is a common complication of cerebral glioma. It has a serious impact on the patient's confidence and quality of life and can be life threatening. There are significant differences in the management of BTRE and nontumoral epilepsy in adults. Surgery is performed early in management, and resection can be curative. Radiotherapy can also improve seizure frequency. Antiepileptic drugs (AEDs) are started after first seizure but are only effective at stopping attacks in 50% of cases. There are no satisfactory randomized controlled clinical trials, or even good prospective series, to support using one AED over another with respect to efficacy. Guidelines are therefore based on poor levels of evidence. In general, the choice of AED may depend on risk of early side effect (rash, biochemical, or hematological effects) and whether drug interactions with chemotherapy are likely. In patients with suspected low-grade glioma, where use of chemotherapy early in the management is not standard practice and survival in measured in many years, the drug interactions are less relevant, and rational seizure management should focus on drugs with the fewest long-term effects on neurocognition, personality, mood, and fatigue. While intriguing and potentially very important, there is no good evidence that any specific AED has a clinical antitumor effect or improves survival. Development of special interest groups in BTRE within countries, or between countries, may be a model for promoting better BTRE trials in the future.

Epistemology of the origin of cancer: a new paradigm

Background

Carcinogenesis is widely thought to originate from somatic mutations and an inhibition of growth suppressors, followed by cell proliferation, tissue invasion, and risk of metastasis. Fewer than 10% of all cancers are hereditary; the ratio in gastric (1%), colorectal (3-5%) and breast (8%) cancers is even less. Cancers caused by infection are thought to constitute some 15% of the non-hereditary cancers. Those remaining, 70 to 80%, are called “sporadic,” because they are essentially of unknown etiology. We propose a new paradigm for the origin of the majority of cancers.

Presentation of hypothesis

Our paradigm postulates that cancer originates following a sequence of events that include (1) a pathogenic stimulus (biological or chemical) followed by (2) chronic inflammation, from which develops (3) fibrosis with associated changes in the cellular microenvironment. From these changes a (4) pre-cancerous niche develops, which triggers the deployment of (5) a chronic stress escape strategy, and when this fails to resolve, (6) a transition of a normal cell to a cancer cell occurs. If we are correct, this paradigm would suggest that the majority of the findings in cancer genetics so far reported are either late events or are epiphenomena that occur after the appearance of the pre-cancerous niche.

Testing the hypothesis

If, based on experimental and clinical findings presented here, this hypothesis is plausible, then the majority of findings in the genetics of cancer so far reported in the literature are late events or epiphenomena that could have occurred after the development of a PCN. Our model would make clear the need to establish preventive measures long before a cancer becomes clinically apparent. Future research should focus on the intermediate steps of our proposed sequence of events, which will enhance our understanding of the nature of carcinogenesis. Findings on inflammation and fibrosis would be given their warranted importance, with research in anticancer therapies focusing on suppressing the PCN state with very early intervention to detect and quantify any subclinical inflammatory change and to treat all levels of chronic inflammation and prevent fibrotic changes, and so avoid the transition from a normal cell to a cancer cell.

Implication of the hypothesis

The paradigm proposed here, if proven, spells out a sequence of steps, one or more of which could be interdicted or modulated early in carcinogenesis to prevent or, at a minimum, slow down the progression of many cancers.

Roles of gap junctions, connexins, and pannexins in epilepsy

Enhanced gap junctional communication (GJC) between neurons is considered a major factor underlying the neuronal synchrony driving seizure activity. In addition, the hippocampal sharp wave ripple complexes, associated with learning and seizures, are diminished by GJC blocking agents. Although gap junctional blocking drugs inhibit experimental seizures, they all have other non-specific actions. Besides interneuronal GJC between dendrites, inter-axonal and inter-glial GJC is also considered important for seizure generation. Interestingly, in most studies of cerebral tissue from animal seizure models and from human patients with epilepsy, there is up-regulation of glial, but not neuronal gap junctional mRNA and protein. Significant changes in the expression and post-translational modification of the astrocytic connexin Cx43, and Panx1 were observed in an in vitro Co⁺⁺ seizure model, further supporting a role for glia in seizure-genesis, although the reasons for this remain unclear. Further suggesting an involvement of astrocytic GJC in epilepsy, is the fact that the expression of astrocytic Cx mRNAs (Cxs 30 and 43) is several fold higher than that of neuronal Cx mRNAs (Cxs 36 and 45), and the number of glial cells outnumber neuronal cells in mammalian hippocampal and cortical tissue. Pannexin expression is also increased in both animal and human epileptic tissues. Specific Cx43 mimetic peptides, Gap 27 and SLS, inhibit the docking of astrocytic connexin Cx43 proteins from forming intercellular gap junctions (GJs), diminishing spontaneous seizures. Besides GJs, Cx membrane hemichannels in glia and Panx membrane channels in neurons and glia are also inhibited by traditional gap junctional pharmacological blockers. Although there is no doubt that connexin-based GJs and hemichannels, and pannexin-based membrane channels are related to epilepsy, the specific details of how they are involved and how we can modulate their function for therapeutic purposes remain to be elucidated.

Epilepsy related to developmental tumors and malformations of cortical development

Structural abnormalities of the brain are increasingly recognized in patients with neurodevelopmental delay and intractable focal epilepsies. The access to clinically well-characterized neurosurgical material has provided a unique opportunity to better define the neuropathological, neurochemical, and molecular features of epilepsy-associated focal developmental lesions. These studies help to further understand the epileptogenic mechanisms of these lesions. Neuropathological evaluation of surgical specimens from patients with epilepsy-associated developmental lesions reveals two major pathologies: focal cortical dysplasia and low-grade developmental tumors (glioneuronal tumors). In the last few years there have been major advances in the recognition of a wide spectrum of developmental lesions associated with a intractable epilepsy, including cortical tubers in patients with tuberous sclerosis complex and hemimegalencephaly. As an increasing number of entities are identified, the development of a unified and comprehensive classification represents a great challenge and requires continuous updates. The present article reviews current knowledge of molecular pathogenesis and the pathophysiological mechanisms of epileptogenesis in this group of developmental disorders. Both emerging neuropathological and basic science evidence will be analyzed, highlighting the involvement of different, but often converging, pathogenetic and epileptogenic mechanisms, which may create the basis for new therapeutic strategies in these disorders.

Extensive dysregulations of oligodendrocytic and astrocytic connexins are associated with disease progression in an amyotrophic lateral sclerosis mouse model

Background

Non-cell-autonomous motor neuronal death is suggested in a mutant Cu/Zn superoxide dismutase 1 (mSOD1)-mediated amyotrophic lateral sclerosis (ALS) model, in which glial cells play significant roles in disease progression. Connexins (Cxs) form homotypic or heterotypic gap junctions (GJs) and allow direct intercellular communications among nervous tissue cells. The role of Cxs in motor neuron disease has never been investigated; therefore, we aimed to evaluate alterations of Cxs in mSOD1-transgenic (mSOD1-Tg) mice in comparison with their non-transgenic (non-Tg) littermates at the same ages.

Methods

We pathologically evaluated temporal changes to astrocytic Cx43/Cx30 and oligodendrocytic Cx47/Cx32 immunoreactivities at presymptomatic, disease-progressive, and end stages, relative to aquaporin-4 (AQP4), glial fibrillary acidic protein (GFAP), excitatory amino acid transporter-2 (EAAT2), myelin-oligodendrocyte glycoprotein (MOG), and Nogo-A immunoreactivities, and observed neuronal loss by NeuN and neurofilament immunostaining, and microglial response by Iba-1 immunostaining. We also performed quantitative immunoblotting and real-time PCR analyses for Cxs.

Results

The mSOD1-Tg mice showed neuronal and axonal loss in the anterior horns of the lumbar spinal cord accompanied by increased activation of microglia compared with non-Tg mice at the disease-progressive and end stages. Expression patterns of Cxs were not different between mSOD1-Tg and non-Tg mice at the presymptomatic stage, but immunoreactivities for GFAP, Cx43, Cx30 and AQP4 were increased in the anterior horns of mSOD1-Tg mice at the disease-progressive and end stages. By contrast, Cx47 and Cx32 immunoreactivities were markedly diminished in Nogo-A-positive oligodendrocytes in the anterior horns of mSOD1-Tg mice at the disease-progressive and end stages, especially in oligodendrocytes showing SOD1 accumulation. EAAT2 immunoreactivity was also diminished in the anterior horns of mSOD1-Tg mice at the disease-progressive and end stages. Quantitative immunoblotting revealed a significant reduction in Cx47 and Cx32 protein levels in mSOD1-Tg mice at the disease-progressive and end stages. The levels of Cx47 and Cx32 mRNAs were also decreased at these stages.

Conclusions

Our findings indicate that oligodendrocytic and astrocytic GJ proteins in the anterior horns of spinal cord in mSOD1-Tg mice are profoundly affected at the disease-progressive and end stages, where disruption of GJs among glial cells may exacerbate motor neuronal death.