Upregulations of CRH and CRHR1 in the Epileptogenic Tissues of Patients with Intractable Infantile Spasms

Hypothalamic-Pituitary-Adrenal Axis and Epilepsy

Epilepsy is a recurrent, transient seizure disorder of the nervous system that affects the intellectual development, life and work, and psychological health of patients. People with epilepsy worldwide experience great suffering. Stressful stimuli such as infection, mental stress, and sleep deprivation are important triggers of epilepsy, and chronic stressful stimuli can lead to frequent seizures and comorbidities. The hypothalamic-pituitary-adrenal (HPA) axis is the most important system involved in the body's stress response, and dysfunction thereof is thought to be associated with core epilepsy symptoms and related psychopathology. This article explores the intrinsic relationships of corticotropin-releasing hormone, adrenocorticotropic hormone, and glucocorticoids with epilepsy in order to reveal the role of the HPA axis in the pathogenesis of epilepsy. We hope that this information will yield future possible directions and ideas for fully understanding the pathogenesis of epilepsy and developing antiepileptic drugs.

Animal Models in Epileptic Spasms and the Development of Novel Treatment Options

SUMMARY

The infantile spasms (IS) syndrome is a catastrophic developmental epileptic encephalopathy syndrome characterized by an age-specific expression of epileptic spasms that are associated with extremely abnormal, oftentimes described as chaotic, interictal EEG pattern known as hypsarrhythmia. Patients with IS generally have poor neurodevelopmental outcomes, in large part because of the frequent epileptic spasms and interictal EEG abnormalities. Current first-line treatments such as adrenocorticotropic hormone or vigabatrin are often ineffective and are associated with major toxic side effects. There is therefore a need for better and safer treatments for patients with IS, especially for the intractable population. Hope is on the horizon as, over the past 10 years, there has been robust progress in the development of etiology-specific animal models of IS. These models have been used to identify potential new treatments for IS and are beginning to provide some important insights into the pathophysiological substrates for this disease. In this review, we will highlight strengths and weaknesses of the currently available animal models of IS in addition to new insights into the pathophysiology and treatment options derived from these models.

Corticotropin Releasing Factor Mediates KCa3.1 Inhibition, Hyperexcitability, and Seizures in Acquired Epilepsy

Temporal lobe epilepsy (TLE), the most common focal seizure disorder in adults, can be instigated in experimental animals by convulsant-induced status epilepticus (SE). Principal hippocampal neurons from SE-experienced epileptic male rats (post-SE neurons) display markedly augmented spike output compared with neurons from nonepileptic animals (non-SE neurons). This enhanced firing results from a cAMP-dependent protein kinase A-mediated inhibition of KCa3.1, a subclass of Ca2+-gated K+ channels generating the slow afterhyperpolarizing Ca2+-gated K+ current (IsAHP). The inhibition of KCa3.1 in post-SE neurons leads to a marked reduction in amplitude of the IsAHP that evolves during repetitive firing, as well as in amplitude of the associated Ca2+-dependent component of the slow afterhyperpolarization potential (KCa-sAHP). Here we show that KCa3.1 inhibition in post-SE neurons is induced by corticotropin releasing factor (CRF) through its Type 1 receptor (CRF1R). Acute application of CRF1R antagonists restores KCa3.1 activity in post-SE neurons, normalizing KCa-sAHP/IsAHP amplitudes and neuronal spike output, without affecting these variables in non-SE neurons. Moreover, pharmacological antagonism of CRF1Rs in vivo reduces the frequency of spontaneous recurrent seizures in post-SE chronically epileptic rats. These findings may provide a new vista for treating TLE.SIGNIFICANCE STATEMENT Epilepsy, a common neurologic disorder, often develops following a brain insult. Identifying key cellular mechanisms underlying acquired epilepsy is critical for developing effective antiepileptic therapies. In an experimental model of acquired epilepsy, principal hippocampal neurons manifest hyperexcitability because of downregulation of KCa3.1, a subtype of Ca2+-gated K+ ion channels. We show that KCa3.1 downregulation is mediated by corticotropin releasing factor (CRF) acting through its Type 1 receptor (CRF1R). Congruently, acute application of selective CRF1R antagonists restores KCa3.1 channel activity, leading to normalization of neuronal excitability. In the same model, injection of a CRF1R antagonist to epileptic animals markedly decreases the frequency of electrographic seizures. Therefore, targeting CRF1Rs may provide a new strategy in the treatment of acquired epilepsy.

Glucocorticoid receptors participate in epilepsy in FCDII patients and MP model rats: A potential therapeutic target for epilepsy in patients with focal cortical dysplasia II (FCDII)

BACKGROUND

Glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) are involved in neuronal excitability, neurogenesis, and neuroinflammation. However, the roles of GRs and MRs in epilepsy in focal cortical dysplasia II (FCDII) have not been reported.

RESEARCH DESIGN AND METHODS

We evaluated GRs and MRs expression and distribution in FCDII patients and methylazoxymethanol-pilocarpine-induced epilepsy model rats (MP rats), and the effects of a GR agonist on neurons in human FCDII and investigated the electrophysiological properties of cultured neurons and neurons of MP rats after lentivirus-mediated GR knockdown or overexpression and GR agonist or antagonist administration.

RESULTS

GR expression (not MR) was decreased in specimens from FCDII patients and model rats. GR agonist dexamethasone reduced neuronal excitatory transmission and increased neuronal inhibitory transmission in FCDII. GR knockdown increased the excitability of cultured neurons, and GR overexpression rescued the hyperexcitability of MP-treated neurons. Moreover, dexamethasone decreased neuronal excitability and excitatory transmission in MP rats, while GR antagonist exerted the opposite effects. Dexamethasone reduced the seizure number and duration by approximately 85% and 60% in MP rats within one to two hours.

CONCLUSIONS

These results suggested that GRs play an important role in epilepsy in FCDII and GR activation may have protective and antiepileptic effects in FCDII.

Investigation of the association between imbalance of the intestinal flora and infantile spasms: a pilot case-control study

BACKGROUND

The intestinal flora (IF) regulates brain function via the neuroendocrine and neuroimmune systems and influences the development of several neuropsychiatric diseases, including epilepsy. Here, we investigated the specific relationship between the IF and infantile spasms (IS), a specific form of epilepsy.

METHODS

Twenty-three children suffering from IS were recruited from the Chinese PLA General Hospital. According to patient response to adrenocorticotropic hormone (ACTH) treatment, the cohort was subdivided into 2 groups: an ACTH-response group and an ACTH-no response (NR) group. A total of 21 healthy children were recruited as a control group (healthy controls: HCs) during the same time period. Fecal samples were collected from infants in the IS and HC groups, and the population of fecal microorganisms was analyzed by 16s ribosomal DNA sequencing. The α and β diversity of the fecal microflora was determined, and the relative abundance of each species was classified. Tax4Fun2 was used to analyze the metabolic pathways utilized by the microflora, and the Kyoto Encyclopedia of Genes and Genomes database was used to analyze differentially expressed genes and pathways.

RESULTS

No significant differences existed in α or β diversity when compared between the IS and HC groups, nor between the ACTH-response and ACTH-NR groups which were separated before and after ACTH treatment. Although there was no significant difference between the ACTH-response and ACTH-NR groups with respect to α diversity, there was a significant difference in β diversity. Compared with that of the HCs, the IF of the IS group featured lower proportions of Lactobacillus, Roseburia, and Lachnospira, and a higher proportion of Clostridium. In the IS group, the proportion of Staphylococcus in the IF was higher before treatment than after treatment. Compared with the ACTH-NR group, the ACTH-response group had reduced populations of Odoribacter, Phascolarctobacterium, Anaerotruncus, Mitsuakella, and Robinsoniella. However, an increase was observed in the population of Bifidobacterium. A significant difference was also identified between the IS and HC groups with regard to the expression levels of genes associated with lipoic acid synthesis.

CONCLUSIONS

Our analysis demonstrated that imbalance of the IF may be involved in the pathogenesis of IS and is related to response to ACTH. Regulating the composition of the IF may pave the way to developing a potential adjuvant therapy for patients with IS.

Downregulated GPR30 expression in the epileptogenic foci of female patients with focal cortical dysplasia type IIb and tuberous sclerosis complex is correlated with 18 F-FDG PET-CT values

Focal cortical dysplasia type IIb (FCDIIb) and tuberous sclerosis complex (TSC) are typical causes of developmental delay and refractory epilepsy. G‐protein‐coupled receptor 30 (GPR30) is a specific estrogen receptor that is critical in neurodevelopment, neuroinflammation, and neuronal excitability, suggesting that it plays a potential role in the epilepsy of patients with FCDIIb and TSC. Therefore, we investigated the role of GPR30 in patients with FCDIIb and TSC. We found that the expression of GPR30 and its downstream protein kinase A (PKA) pathway were decreased and negatively correlated with seizure frequency in female patients with FCDIIb and TSC, but not in male patients. GPR30 was widely distributed in neurons, astrocytes, and microglia, and its downregulation was especially notable in microglia. The GPR30 agonist G‐1 increased the expression of PKA and p‐PKA in cultured cortical neurons, and the GPR30 antagonist G‐15 exhibited the opposite effects of G‐1. The NF‐κB signaling pathway was also activated in the specimens of female patients with FCDIIb and TSC, and was regulated by G‐1 and G‐15 in cultured cortical neurons. We also found that GPR30 regulated cortical neuronal excitability by altering the frequency of spontaneous excitatory postsynaptic currents and the expression of NR2A/B. Further, the relationship between GPR30 and glycometabolism was evaluated by analyzing the correlations between GPR30 and ¹⁸F‐FDG PET‐CT values (standardized uptake values, SUVs). Positive correlations between GPR30 and SUVs were found in female patients, but not in male patients. Intriguingly, GPR30 expression and SUVs were significantly decreased in the epileptogenic tubers of female TSC patients, and ROC curves indicated that SUVs could predict the localization of epileptogenic tubers. Taken together, our results suggest a potential protective effect of GPR30 in the epileptogenesis of female patients with FCDIIb and TSC.

Modeling epileptic spasms during infancy: Are we heading for the treatment yet?

Infantile spasms (IS or epileptic spasms during infancy) were first described by Dr. William James West (aka West syndrome) in his own son in 1841. While rare by definition (occurring in 1 per 3200-3400 live births), IS represent a major social and treatment burden. The etiology of IS varies - there are many (>200) different known pathologies resulting in IS and still in about one third of cases there is no obvious reason. With the advancement of genetic analysis, role of certain genes (such as ARX or CDKL5 and others) in IS appears to be important. Current treatment strategies with incomplete efficacy and serious potential adverse effects include adrenocorticotropin (ACTH), corticosteroids (prednisone, prednisolone) and vigabatrin, more recently also a combination of hormones and vigabatrin. Second line treatments include pyridoxine (vitamin B6) and ketogenic diet. Additional treatment approaches use rapamycin, cannabidiol, valproic acid and other anti-seizure medications. Efficacy of these second line medications is variable but usually inferior to hormonal treatments and vigabatrin. Thus, new and effective models of this devastating condition are required for the search of additional treatment options as well as for better understanding the mechanisms of IS. Currently, eight models of IS are reviewed along with the ideas and mechanisms behind these models, drugs tested using the models and their efficacy and usefulness. Etiological variety of IS is somewhat reflected in the variety of the models. However, it seems that for finding precise personalized approaches, this variety is necessary as there is no "one-size-fits-all" approach possible for both IS in particular and epilepsy in general.

Corticotropin-releasing hormone-binding protein is up-regulated by brain-derived neurotrophic factor and is secreted in an activity-dependent manner in rat cerebral cortical neurons

A recent study revealed that corticotropin-releasing hormone (CRH) in the cerebral cortex (CTX) plays a regulatory role in emotional behaviors in rodents. Given the functional interaction between brain-derived neurotrophic factor (BDNF) and the CRH-signaling pathway in the hypothalamic-pituitary-adrenal axis, we hypothesized that BDNF may regulate gene expression of CRH and its related molecules in the CTX. Findings of real-time quantitative PCR (RT-qPCR) indicated that stimulation of cultured rat cortical neurons with BDNF led to marked elevations in the mRNA levels of CRH and CRH-binding protein (CRH-BP). The BDNF-induced up-regulation of CRH-BP mRNA was attenuated by inhibitors of tropomyosin related kinase (Trk) and MEK, but not by an inhibitor for PI3K and Phospholipase C gamma (PLCγ). The up-regulation was partially blocked by an inhibitor of lysine-specific demethylase (KDM) 6B. Fluorescent imaging identified the vesicular pattern of pH-sensitive green fluorescent protein-fused CRH-BP (CRH-BP-pHluorin), which co-localized with mCherry-tagged BDNF in cortical neurons. In addition, live-cell imaging detected drastic increases of pHluorin fluorescence in neurites upon membrane depolarization. Finally, we confirmed that tetrodotoxin partially attenuated the BDNF-induced up-regulation of CRH-BP mRNA, but not that of the protein. These observations indicate the following: In cortical neurons, BDNF led to gene expression of CRH-BP and CRH. TrkB, MEK, presumably ERK, and KDM6B are involved in the BDNF-induced gene expression of CRH-BP, and BDNF is able to induce the up-regulation in a neuronal activity-independent manner. It is suggested that CRH-BP is stored into BDNF-containing secretory granules in cortical neurons, and is secreted in response to membrane depolarization.

Elevated Expression of TRPC4 in Cortical Lesions of Focal Cortical Dysplasia II and Tuberous Sclerosis Complex

Focal cortical dysplasia type II (FCD II) and tuberous sclerosis complex (TSC) are well-known causes of chronic refractory epilepsy in children. Canonical transient receptor potential channels (TRPCs) are non-selective cation channels that are commonly activated by phospholipase C (PLC) stimulation. Previous studies found that TRPC4 may participate in the process of epileptogenesis. This study aimed to examine the expression and distribution of TRPC4 in FCD II (n = 24) and TSC (n = 11) surgical specimens compared with that in age-matched autopsy control samples (n = 12). We found that the protein levels of TRPC4 and its upstream factor, PLC delta 1 (PLCD1), were elevated in FCD II and TSC samples compared to those of control samples. Immunohistochemistry assays revealed that TRPC4 staining was stronger in malformed cells, such as dysmorphic neurons, balloon cells and giant cells. Moderate-to-strong staining of the upstream factor PLCD1 was also identified in abnormal neurons. Moreover, double immunofluorescence staining revealed that TRPC4 was colocalised with glutamatergic and GABAergic neuron markers. Taken together, our results indicate that overexpression of TRPC4 protein may be involved in the epileptogenesis of FCD II and TSC.