Rapamycin Attenuates Acute Seizure-induced Astrocyte Injury in Mice in Vivo

Pharmacological mTOR inhibitors in ameliorating Alzheimer's disease: current review and perspectives

Traditionally, pharmacological mammalian/mechanistic targets of rapamycin (mTOR) kinase inhibitors have been used during transplantation and tumor treatment. Emerging pre-clinical evidence from the last decade displayed the surprising effectiveness of mTOR inhibitors in ameliorating Alzheimer's Disease (AD), a common neurodegenerative disorder characterized by progressive cognitive function decline and memory loss. Research shows mTOR activation as an early event in AD development, and inhibiting mTOR may promote the resolution of many hallmarks of Alzheimer's. Aberrant protein aggregation, including amyloid-beta (Aβ) deposition and tau filaments, and cognitive defects, are reversed upon mTOR inhibition. A closer inspection of the evidence highlighted a temporal dependence and a hallmark-specific nature of such beneficial effects. Time of administration relative to disease progression, and a maintenance of a functional lysosomal system, could modulate its effectiveness. Moreover, mTOR inhibition also exerts distinct effects between neurons, glial cells, and endothelial cells. Different pharmacological properties of the inhibitors also produce different effects based on different blood-brain barrier (BBB) entry capacities and mTOR inhibition sites. This questions the effectiveness of mTOR inhibition as a viable AD intervention strategy. In this review, we first summarize the different mTOR inhibitors available and their characteristics. We then comprehensively update and discuss the pre-clinical results of mTOR inhibition to resolve many of the hallmarks of AD. Key pathologies discussed include Aβ deposition, tauopathies, aberrant neuroinflammation, and neurovascular system breakdowns.

The Role of Resveratrol on Spinal Cord Injury: from Bench to Bedside

Spinal cord injury (SCI) is a severe and disabling injury of the central nervous system, with complex pathological mechanisms leading to sensory and motor dysfunction. Pathological processes, such as oxidative stress, inflammatory response, apoptosis, and glial scarring are important factors that aggravate SCI. Therefore, the inhibition of these pathological processes may contribute to the treatment of SCI. Currently, the pathogenesis of SCI remains under investigation as SCI treatment has not progressed considerably. Resveratrol, a natural polyphenol with anti-inflammatory and antioxidant properties, is considered a potential therapeutic drug for various diseases and plays a beneficial role in nerve damage. Preclinical studies have confirmed that signaling pathways are closely related to the pathological processes in SCI, and resveratrol is believed to exert therapeutic effects in SCI by activating the related signaling pathways. Based on current research on the pathways of resveratrol and its role in SCI, resveratrol may be a potentially effective treatment for SCI. This review summarizes the role of resveratrol in promoting the recovery of nerve function by regulating oxidative stress, inflammation, apoptosis, and glial scar formation in SCI through various mechanisms and pathways, as well as the deficiency of resveratrol in SCI research and the current and anticipated research trends of resveratrol. In addition, this review provides a background for further studies on the molecular mechanisms of SCI and the development of potential therapeutic agents. This information could also help clinicians understand the known mechanisms of action of resveratrol and provide better treatment options for patients with SCI.

Natural product-derived therapies for treating drug-resistant epilepsies: From ethnopharmacology to evidence-based medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Epilepsy is one of the most prevalent neurological human diseases, affecting 1% of the population in all age groups. Despite the availability of over 25 anti-seizure medications (ASMs), which are approved in most industrialized countries, approximately 30% of epilepsy patients still experience seizures that are resistant to these drugs. Since ASMs target only limited number of neurochemical mechanisms, drug-resistant epilepsy (DRE) is not only an unmet medical need, but also a formidable challenge in drug discovery.

AIM

In this review, we examine recently approved epilepsy drugs based on natural product (NP) such as cannabidiol (CBD) and rapamycin, as well as NP-based epilepsy drug candidates still in clinical development, such as huperzine A. We also critically evaluate the therapeutic potential of botanical drugs as polytherapy or adjunct therapy specifically for DRE.

METHODS

Articles related to ethnopharmacological anti-epileptic medicines and NPs in treating all forms of epilepsy were collected from PubMed and Scopus using keywords related to epilepsy, DRE, herbal medicines, and NPs. The database clinicaltrials.gov was used to find ongoing, terminated and planned clinical trials using herbal medicines or NPs in epilepsy treatment.

RESULTS

A comprehensive review on anti-epileptic herbal drugs and natural products from the ethnomedical literature is provided. We discuss the ethnomedical context of recently approved drugs and drug candidates derived from NPs, including CBD, rapamycin, and huperzine A. Recently published studies on natural products with preclinical efficacy in animal models of DRE are summarized. Moreover, we highlight that natural products capable of pharmacologically activating the vagus nerve (VN), such as CBD, may be therapeutically useful to treat DRE.

CONCLUSIONS

The review highlights that herbal drugs utilized in traditional medicine offer a valuable source of potential anti-epileptic drug candidates with novel mechanisms of action, and with clinical promise for the treatment of drug-resistant epilepsy (DRE). Moreover, recently developed NP-based anti-seizure medications (ASMs) indicate the translational potential of metabolites of plant, microbial, fungal and animal origin.

Therapeutic potential of natural compounds from herbs and nutraceuticals in spinal cord injury: Regulation of the mTOR signaling pathway

Spinal cord injury (SCI) is a disease in which the spinal cord is subjected to various external forces that cause it to burst, shift, or, in severe cases, injure the spinal tissue, resulting in nerve injury. SCI includes not only acute primary injury but also delayed and persistent spinal tissue injury (i.e., secondary injury). The pathological changes post-SCI are complex, and effective clinical treatment strategies are lacking. The mammalian target of rapamycin (mTOR) coordinates the growth and metabolism of eukaryotic cells in response to various nutrients and growth factors. The mTOR signaling pathway has multiple roles in the pathogenesis of SCI. There is evidence for the beneficial effects of natural compounds and nutraceuticals that regulate the mTOR signaling pathways in a variety of diseases. Therefore, the effects of natural compounds on the pathogenesis of SCI were evaluated by a comprehensive review using electronic databases, such as PubMed, Web of Science, Scopus, and Medline, combined with our expertise in neuropathology. In particular, we reviewed the pathogenesis of SCI, including the importance of secondary nerve injury after the primary mechanical injury, the roles of the mTOR signaling pathways, and the beneficial effects and mechanisms of natural compounds that regulate the mTOR signaling pathway on pathological changes post-SCI, including effects on inflammation, neuronal apoptosis, autophagy, nerve regeneration, and other pathways. This recent research highlights the value of natural compounds in regulating the mTOR pathway, providing a basis for developing novel therapeutic strategies for SCI.

The role of Wnt/mTOR signaling in spinal cord injury

Spinal cord injury (SCI) is the most common disabling spinal injury, a complex pathologic process that can eventually lead to severe neurological dysfunction. The Wnt/mTOR signaling pathway is a pervasive signaling cascade that regulates a wide range of physiological processes during embryonic development, from stem cell pluripotency to cell fate. Numerous studies have reported that Wnt/mTOR signaling pathway plays an important role in neural development, synaptogenesis, neuron growth, differentiation and survival after the central nervous system (CNS) is damaged. Wnt/mTOR also plays an important role in regulating various pathophysiological processes after spinal cord injury (SCI). After SCI, Wnt/mTOR signal regulates the physiological and pathological processes of neural stem cell proliferation and differentiation, neuronal axon regeneration, neuroinflammation and pain through multiple pathways. Due to the characteristics of the Wnt signal in SCI make it a potential therapeutic target of SCI. In this paper, the characteristics of Wnt/mTOR signal, the role of Wnt/mTOR pathway on SCI and related mechanisms are reviewed, and some unsolved problems are discussed. It is hoped to provide reference value for the research field of the role of Wnt/mTOR pathway in SCI, and provide a theoretical basis for biological therapy of SCI.

HOP protein expression in the hippocampal dentate gyrus is acutely downregulated in a status epilepticus mouse model

Status epilepticus (SE) is a neurological emergency, and delayed management can lead to higher morbidity and mortality. It is thought that prolonged seizures stimulate stem cells in the hippocampus and that epileptogenesis may arise from aberrant connections formed by newly born cells, while others have suggested that the acute neuroinflammation and gliosis often seen in epileptic hippocampi contribute to hyperexcitability and epilepsy development. Previous studies have identified the expression of homeodomain-only protein (HOP) in the hippocampal dentate gyrus (HDG) and the heart. HOP was found to be a regulator of cell proliferation and differentiation during heart development, while it maintains the 'heart conduction system' in adulthood. However, little is known about HOP function in the adult HDG, particularly in the SE setting. Here, a HOP immunohistochemical profile in an SE mouse model was established. A total of 24 adult mice were analyzed 3-10 days following the SE episode, the 'acute phase'. Our findings demonstrate a significant downregulation of HOP and BLBP protein expression in the SE group following SE episodes, while HOP/Ki67 coexpression did not remarkably differ. Furthermore, coexpression of HOP/S100β and HOP/Prox1 was not observed, although we noticed insignificant HOP/DCX coexpression level. The findings of this study show no compelling evidence of proliferation, and newly added neurons were not identified during the acute phase following SE, although HOP protein expression was significantly decreased in the HDG. Similar to its counterpart in the adult heart, this suggests that HOP seems to play a key role in regulating signal conduction in adult hippocampus. Moreover, acute changes in HOP expression following SE could be part of an inflammatory response that could subsequently influence epileptogenicity.

Cell death of hippocampal CA1 astrocytes during early epileptogenesis

OBJECTIVE

Growing evidence suggests that dysfunctional astrocytes are crucial players in the development of mesial temporal lobe epilepsy (MTLE). Using a mouse model closely recapitulating key alterations of chronic human MTLE with hippocampal sclerosis, here we asked whether death of astrocytes contributes to the initiation of the disease and investigated potential underlying molecular mechanisms.

METHODS

Antibody staining was combined with confocal imaging and semiquantitative real-time polymerase chain reaction analysis to identify markers of different cellular death mechanisms between 4 h and 3 days after epilepsy induction.

RESULTS

Four hours after kainate-mediated induction of status epilepticus (SE), we found a significant reduction in the density of astrocytes in the CA1 stratum radiatum (SR) of the ipsilateral hippocampus. This reduction was transient, as within the next 3 days, astrocyte cell numbers recovered to the initial values, which was accompanied by enhanced proliferation. Four hours after SE induction, a small proportion of astrocytes in the ipsilateral CA1 SR expressed autophagy-related genes and proteins, whereas we did not find astrocytes positive for cleaved caspase 3 or terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick-end labeling, ruling out apoptosis-related astrocytic death. Importantly, at the same early time point post-SE, many astrocytes in the ipsilateral CA1 SR showed strong expression of genes encoding pro-necroptosis factors, including receptor-interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Phosphorylation of MLKL (pMLKL), formation of necrosome complexes composed of RIPK3 and pMLKL, and translocation of pMLKL to the nucleus and to the plasma membrane were often observed in astrocytes of the ipsilateral hippocampus 4 h post-SE.

SIGNIFICANCE

The present study revealed that astrocytes die shortly after induction of SE. Our expression data and immunohistochemistry suggest that necroptosis and autophagy contribute to astrocytic death. These findings help to better understand how dysfunctional and pathological remodeling of astrocytes contributes to the initiation of temporal lobe epilepsy.

Metformin ameliorates the status epilepticus- induced hippocampal pathology through possible mTOR modulation

The initial precipitating injury such as SE progresses to chronic epilepsy through multiple epileptogenic processes. Early epileptogenic events are generally characterized by neuroinflammation, neurodegeneration and abnormal neurogenesis in the hippocampus. Metformin has exhibited anti-inflammatory and neuroprotective properties in numerous studies. The current study attempts to investigate the effect of metformin on seizure-induced inflammation and neuronal degeneration, and the involvement of the mTOR pathway. Status epilepticus (SE) was induced in male Wistar rats with systemic administration of Lithium (127 mg/kg) and Pilocarpine (30 mg/kg). In test rats, Metformin 100 mg/kg or 200 mg/kg was administered orally for 7 days, followed by SE induction. Results indicate that metformin did not alter the SE profile significantly which was evident by the behavioural scoring and electroencephalogram (EEG) recordings. However, metformin 200 mg/kg attenuated the SE-induced glial activation (p < 0.01), up regulated mRNA levels of proinflammatory cytokines (p < 0.001) and chemokines (p < 0.001) and enhanced BBB permeability (p < 0.05). In addition, metformin ameliorated the insult-induced region-specific neuronal damage (p < 0.01) and restored the hippocampal neuronal density. Metformin significantly inhibited phosphorylated S6 ribosomal protein (phospho-S6rp) (p < 0.05), thus demonstrating that the beneficial effects might be partly mediated by the mTOR pathway. The study thus reiterates that mTOR signalling is one of the mechanisms involved in inflammation and neurodegeneration in early epileptogenesis following SE.

Chronic mTORC1 inhibition rescues behavioral and biochemical deficits resulting from neuronal Depdc5 loss in mice

DEPDC5 is now recognized as one of the genes most often implicated in familial/inherited focal epilepsy and brain malformations. Individuals with pathogenic variants in DEPDC5 are at risk for epilepsy, associated neuropsychiatric comorbidities and sudden unexplained death in epilepsy. Depdc5flox/flox-Syn1Cre (Depdc5cc+) neuronal-specific Depdc5 knockout mice exhibit seizures and neuronal mTORC1 hyperactivation. It is not known if Depdc5cc+ mice have a hyperactivity/anxiety phenotype, die early from terminal seizures or whether mTOR inhibitors rescue DEPDC5-related seizures and associated comorbidities. Herein, we report that Depdc5cc+ mice were hyperactive in open-field testing but did not display anxiety-like behaviors on the elevated-plus maze. Unlike many other mTOR-related models, Depdc5cc+ mice had minimal epileptiform activity and rare seizures prior to seizure-induced death, as confirmed by video-EEG monitoring. Treatment with the mTORC1 inhibitor rapamycin starting after 3 weeks of age significantly prolonged the survival of Depdc5cc+ mice and partially rescued the behavioral hyperactivity. Rapamycin decreased the enlarged brain size of Depdc5cc+ mice with corresponding decrease in neuronal soma size. Loss of Depdc5 led to a decrease in the other GATOR1 protein levels (NPRL2 and NPRL3). Rapamycin failed to rescue GATOR1 protein levels but rather rescued downstream mTORC1 hyperactivity as measured by phosphorylation of S6. Collectively, our data provide the first evidence of behavioral alterations in mice with Depdc5 loss and support mTOR inhibition as a rational therapeutic strategy for DEPDC5-related epilepsy in humans.

mTOR-Related Cell-Clearing Systems in Epileptic Seizures, an Update

Recent evidence suggests that autophagy impairment is implicated in the epileptogenic mechanisms downstream of mTOR hyperactivation. This holds true for a variety of genetic and acquired epileptic syndromes besides malformations of cortical development which are classically known as mTORopathies. Autophagy suppression is sufficient to induce epilepsy in experimental models, while rescuing autophagy prevents epileptogenesis, improves behavioral alterations, and provides neuroprotection in seizure-induced neuronal damage. The implication of autophagy in epileptogenesis and maturation phenomena related to seizure activity is supported by evidence indicating that autophagy is involved in the molecular mechanisms which are implicated in epilepsy. In general, mTOR-dependent autophagy regulates the proliferation and migration of inter-/neuronal cortical progenitors, synapse development, vesicular release, synaptic plasticity, and importantly, synaptic clustering of GABA_A receptors and subsequent excitatory/inhibitory balance in the brain. Similar to autophagy, the ubiquitin–proteasome system is regulated downstream of mTOR, and it is implicated in epileptogenesis. Thus, mTOR-dependent cell-clearing systems are now taking center stage in the field of epilepsy. In the present review, we discuss such evidence in a variety of seizure-related disorders and models. This is expected to provide a deeper insight into the molecular mechanisms underlying seizure activity.

The antiepileptic effect of Gastrodiae Rhizoma through modulating overexpression of mTOR and attenuating astrogliosis in pilocarpine mice model

Objective

To investigate the effect of water extract of Gastrodiae Rhizoma (GR) on the development of acquired temporal lobe epilepsy (TLE) and on regulating the expression of the mammalian target of rapamycin (mTOR) and semaphorin 3F (SEMA3F).

Methods

A pilocarpine‐induced status epilepticus (SE) model was adopted to precipitate injury in the limbic systems. GR and carbamazepine (CBZ) treatments were given to mice for 14 days prior to SE induction to demonstrate the antiepileptic effects and continued for 5 more days to illustrate the effects on histologic studies.

Results

Our results consolidated that GR treatment (92.1 minutes) could delay the SE onset in comparison with the control group (61.5 minutes, P = .041). Fewer mice had reached SE with GR treatment (41.7%) when compared with the control group (83.3%, P = .044). GR treatment (2.1 hours/mouse) could suppress the number of acute seizures in post‐SE survival mice when compared with the control group (4.5 hours/mouse, P < .001). The effects of GR treatment were elucidated with the mechanism of actions. GR treatment reduced the overexpression of mTOR (0.27 vs 0.67 AU/mg protein, P = .047). GR treatment increased the underexpression of SEMA3F (0.51 vs 0.16 µg/mg protein, P = .034). In the histochemical study of microtubule‐associated protein 2 (MAP2) staining, our results showed that GR prevented neuronal loss in the GR treatment group (64.8% positively stained pixel area) as compared with the control group (59%, P = .014) in the hippocampus. In glial fibrillary acidic protein (GFAP) staining, the severity of astrogliosis was mitigated by the GR treatment (4.1% positively stained pixel area) when compared to the control group (5.6%, P = .047) in the hippocampus.

Significance

These results provide preclinical evidence to support the use of GR, which could suppress acute seizures and relieve pathological changes in pilocarpine‐induced TLE mice. We demonstrated that the antiepileptic effects of GR could be accompanied by mTOR reduction and astrogliosis attenuation.

Role of Elevated Thrombospondin-1 in Kainic Acid-Induced Status Epilepticus

Previous studies have suggested that thrombospondin-1 (TSP-1) regulates the transforming growth factor beta 1 (TGF-β1)/phosphorylated Smad2/3 (pSmad2/3) pathway. Moreover, TSP-1 is closely associated with epilepsy. However, the role of the TSP-1-regulated TGF-β1/pSmad2/3 pathway in seizures remains unclear. In this study, changes in this pathway were assessed following kainic acid (KA)-induced status epilepticus (SE) in rats. The results showed that increases in the TSP-1/TGF-β1/pSmad2/3 levels spatially and temporally matched the increases in glial fibrillary acidic protein (GFAP)/chondroitin sulfate (CS56) levels following KA administration. Inhibition of TSP-1 expression by small interfering RNA or inhibition of TGF-β1 activation with a Leu-Ser-Lys-Leu peptide significantly reduced the severity of KA-induced acute seizures. These anti-seizure effects were accompanied by decreased GFAP/CS56 expression and Smad2/3 phosphorylation. Moreover, inhibiting Smad2/3 phosphorylation with ponatinib or SIS3 also significantly reduced seizure severity, alongside reducing GFAP/CS56 immunoreactivity. These results suggest that the TSP-1-regulated TGF-β1/pSmad2/3 pathway plays a key role in KA-induced SE and astrogliosis, and that inhibiting this pathway may be a potential anti-seizure strategy.

Zinc Oxide Nanoparticles Induce Autophagy and Apoptosis via Oxidative Injury and Pro-Inflammatory Cytokines in Primary Astrocyte Cultures

The present study examined the potential toxic concentrations of zinc oxide nanoparticles (ZnO NPs) and associated autophagy and apoptosis-related injuries in primary neocortical astrocyte cultures. Concentrations of ZnO NPs ≥3 μg/mL induced significant toxicity in the astrocytes. At 24 h after exposure to the ZnO NPs, transmission electron microscopy revealed swelling of the endoplasmic reticulum (ER) and increased numbers of autophagolysosomes in the cultured astrocytes, and increased levels of LC3 (microtubule-associated protein 1 light chain 3)-mediated autophagy were identified by flow cytometry. Apoptosis induced by ZnO NP exposure was confirmed by the elevation of caspase-3/7 activity and 4′,6′-diamidino-2-phenylindole (DAPI) staining. Significant (p < 0.05) changes in the levels of glutathione peroxidase, superoxide dismutase, tumor necrosis factor (TNF-α), and interleukin-6 were observed by enzyme-linked immunoassay (ELISA) assay following the exposure of astrocyte cultures to ZnO NPs. Phosphatidylinositol 3-kinase (PI3K)/mitogen-activated protein kinase (MAPK) dual activation was induced by ZnO NPs in a dose-dependent manner. Additionally, the Akt (protein kinase B) inhibitor BML257 and the mTOR (mammalian target of rapamycin) inhibitor rapamycin contributed to the survival of astrocytes. Inhibitors of cyclooxygenase-2 and lipoxygenase attenuated ZnO NP-induced toxicity. Calcium-modulating compounds, antioxidants, and zinc/iron chelators also decreased ZnO NP-induced toxicity. Together, these results suggest that ZnO NP-induced autophagy and apoptosis may be associated with oxidative stress and the inflammatory process in primary astrocyte cultures.

Cerebral aquaporin-4 expression is independent of seizures in tuberous sclerosis complex

Astrocytes serve many functions in the human brain, many of which focus on maintenance of homeostasis. Astrocyte dysfunction in Tuberous Sclerosis Complex (TSC) has long been appreciated with activation of the mTORC1 signaling pathway resulting in gliosis and possibly contributing to the very frequent phenotype of epilepsy. We hypothesized that aberrant expression of the astrocyte protein aquaporin-4 (AQP4) may be present in TSC and contribute to disease pathology. Characterization of AQP4 expression in epileptic cortex from TSC patients demonstrated a diffuse increase in AQP4. To determine if this was due to exposure to seizures, we examined Aqp4 expression in mouse models of TSC in which Tsc1 or Tsc2 inactivation was targeted to astrocytes or glial progenitors, respectively. Loss of either Tsc1 or Tsc2 from astrocytes resulted in a marked increase in Aqp4 expression which was sensitive to mTORC1 inhibition with rapamycin. Our findings in both TSC epileptogenic cortex and in a variety of astrocyte culture models demonstrate for the first time that AQP4 expression is dysregulated in TSC. The extent to which AQP4 contributes to epilepsy in TSC is not known, though the similarities in AQP4 expression between TSC and temporal lobe epilepsy supports further studies targeting AQP4 in TSC.

A mouse model of seizures in anti-N-methyl-d-aspartate receptor encephalitis

OBJECTIVE

Seizures develop in 80% of patients with anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis, and these represent a major cause of morbidity and mortality. Anti-NMDAR antibodies have been linked to memory loss in encephalitis; however, their role in seizures has not been established. We determined whether anti-NMDAR antibodies from autoimmune encephalitis patients are pathogenic for seizures.

METHODS

We performed continuous intracerebroventricular infusion of cerebrospinal fluid (CSF) or purified immunoglobulin (IgG) from the CSF of patients with anti-NMDAR encephalitis or polyclonal rabbit anti-NMDAR IgG, in male C57BL/6 mice. Seizure status during a 2-week treatment was assessed with video-electroencephalography. We assessed memory, anxiety-related behavior, and motor function at the end of treatment and assessed the extent of neuronal damage and gliosis in the CA1 region of hippocampus. We also performed whole-cell patch recordings from the CA1 pyramidal neurons in hippocampal slices of mice with seizures.

RESULTS

Prolonged exposure to rabbit anti-NMDAR IgG, patient CSF, or human IgG purified from the CSF of patients with encephalitis induced seizures in 33 of 36 mice. The median number of seizures recorded in 2 weeks was 13, 39, and 35 per mouse in these groups, respectively. We observed only 18 brief nonconvulsive seizures in 11 of 29 control mice (median seizure count of 0) infused with vehicle (n = 4), normal CSF obtained from patients with noninflammatory central nervous system (CNS) conditions (n = 12), polyclonal rabbit IgG (n = 7), albumin (n = 3), and normal human IgG (n = 3). We did not observe memory deficits, anxiety-related behavior, or motor impairment measured at 2 weeks in animals treated with CSF from affected patients or rabbit IgG. Furthermore, there was no evidence of hippocampal cell loss or astrocyte proliferation in the same mice.

SIGNIFICANCE

Our findings indicate that autoantibodies can induce seizures in anti-NMDAR encephalitis and offer a model for testing novel therapies for refractory autoimmune seizures.

Seizure Susceptibility Correlates with Brain Injury in Male Mice Treated with Hypothermia after Neonatal Hypoxia-Ischemia

Hypoxic-ischemic encephalopathy is a common neonatal brain injury associated with significant morbidity and mortality despite the administration of therapeutic hypothermia (TH). Neonatal seizures and subsequent chronic epilepsy are frequent in this patient population and current treatments are partially effective. We used a neonatal murine hypoxia-ischemia (HI) model to test whether the severity of hippocampal and cortical injury predicts seizure susceptibility 8 days after HI and whether TH mitigates this susceptibility. HI at postnatal day 10 (P10) caused hippocampal injury not mitigated by TH in male or female pups. TH did not confer protection against flurothyl seizure susceptibility at P18 in this model. Hippocampal (R2 = 0.33, p = 0.001) and cortical (R2 = 0.33, p = 0.003) injury directly correlated with seizure susceptibility in male but not female pups. Thus, there are sex-specific consequences of neonatal HI on flurothyl seizure susceptibility in a murine neonatal HI model. Further studies are necessary to elucidate the underlying mechanisms of sex dimorphism in seizure susceptibility after neonatal HI.

Longitudinal positron emission tomography imaging of glial cell activation in a mouse model of mesial temporal lobe epilepsy: Toward identification of optimal treatment windows

OBJECTIVE

Mesiotemporal lobe epilepsy is the most common type of drug-resistant partial epilepsy, with a specific history that often begins with status epilepticus due to various neurological insults followed by a silent period. During this period, before the first seizure occurs, a specific lesion develops, described as unilateral hippocampal sclerosis (HS). It is still challenging to determine which drugs, administered at which time point, will be most effective during the formation of this epileptic process. Neuroinflammation plays an important role in pathophysiological mechanisms in epilepsy, and therefore brain inflammation biomarkers such as translocator protein 18 kDa (TSPO) can be potent epilepsy biomarkers. TSPO is associated with reactive astrocytes and microglia. A unilateral intrahippocampal kainate injection mouse model can reproduce the defining features of human temporal lobe epilepsy with unilateral HS and the pattern of chronic pharmacoresistant temporal seizures. We hypothesized that longitudinal imaging using TSPO positron emission tomography (PET) with ¹⁸ F-DPA-714 could identify optimal treatment windows in a mouse model during the formation of HS.

METHODS

The model was induced into the right dorsal hippocampus of male C57/Bl6 mice. Micro-PET/computed tomographic scanning was performed before model induction and along the development of the HS at 7 days, 14 days, 1 month, and 6 months. In vitro autoradiography and immunohistofluorescence were performed on additional mice at each time point.

RESULTS

TSPO PET uptake reached peak at 7 days and mostly related to microglial activation, whereas after 14 days, reactive astrocytes were shown to be the main cells expressing TSPO, reflected by a continuing increased PET uptake.

SIGNIFICANCE

TSPO-targeted PET is a highly potent longitudinal biomarker of epilepsy and could be of interest to determine the therapeutic windows in epilepsy and to monitor response to treatment.

Beneficial Effects of Resveratrol-Mediated Inhibition of the mTOR Pathway in Spinal Cord Injury

Spinal cord injury (SCI) causes a high rate of morbidity and disability. The clinical features of SCI are divided into acute, subacute, and chronic phases according to its pathophysiological events. The mammalian target of rapamycin (mTOR) signaling pathway plays an important role in cell death and inflammation in the acute phase and neuroregeneration in the subacute/chronic phases at different times. Resveratrol has the potential of regulating cell growth, proliferation, metabolism, and angiogenesis through the mTOR signaling pathway. Herein, we explicate the role of resveratrol in the repair of SCI through the inhibition of the mTOR signaling pathway. The inhibition of the mTOR pathway by resveratrol has the potential of serving as a neuronal restorative mechanism following SCI.

A mouse model of DEPDC5-related epilepsy: Neuronal loss of Depdc5 causes dysplastic and ectopic neurons, increased mTOR signaling, and seizure susceptibility

DEPDC5 is a newly identified epilepsy-related gene implicated in focal epilepsy, brain malformations, and Sudden Unexplained Death in Epilepsy (SUDEP). In vitro, DEPDC5 negatively regulates amino acid sensing by the mTOR complex 1 (mTORC1) pathway, but the role of DEPDC5 in neurodevelopment and epilepsy has not been described. No animal model of DEPDC5-related epilepsy has recapitulated the neurological phenotypes seen in patients, and germline knockout rodent models are embryonic lethal. Here, we establish a neuron-specific Depdc5 conditional knockout mouse by cre-recombination under the Synapsin1 promotor. Depdc5^flox/flox-Syn1^Cre (Depdc5cc+) mice survive to adulthood with a progressive neurologic phenotype that includes motor abnormalities (i.e., hind limb clasping) and reduced survival compared to littermate control mice. Depdc5cc+ mice have larger brains with increased cortical neuron size and dysplastic neurons throughout the cortex, comparable to the abnormal neurons seen in human focal cortical dysplasia specimens. Depdc5 results in constitutive mTORC1 hyperactivation exclusively in neurons as measured by the increased phosphorylation of the downstream ribosomal protein S6. Despite a lack of increased mTORC1 signaling within astrocytes, Depdc5cc+ brains show reactive astrogliosis. We observed two Depdc5cc+ mice to have spontaneous seizures, including a terminal seizure. We demonstrate that as a group Depdc5cc+ mice have lowered seizure thresholds, as evidenced by decreased latency to seizures after chemoconvulsant injection and increased mortality from pentylenetetrazole-induced seizures. In summary, our neuron-specific Depdc5 knockout mouse model recapitulates clinical, pathological, and biochemical features of human DEPDC5-related epilepsy and brain malformations. We thereby present an important model in which to study targeted therapeutic strategies for DEPDC5-related conditions.