Rapamycin prevents seizures after depletion of STRADA in a rare neurodevelopmental disorder

Clemizole and modulators of serotonin signalling suppress seizures in Dravet syndrome

Dravet syndrome is a catastrophic childhood epilepsy with early-onset seizures, delayed language and motor development, sleep disturbances, anxiety-like behaviour, severe cognitive deficit and an increased risk of fatality. It is primarily caused by de novo mutations of the SCN1A gene encoding a neuronal voltage-activated sodium channel. Zebrafish with a mutation in the SCN1A homologue recapitulate spontaneous seizure activity and mimic the convulsive behavioural movements observed in Dravet syndrome. Here, we show that phenotypic screening of drug libraries in zebrafish scn1 mutants rapidly and successfully identifies new therapeutics. We demonstrate that clemizole binds to serotonin receptors and its antiepileptic activity can be mimicked by drugs acting on serotonin signalling pathways e.g. trazodone and lorcaserin. Coincident with these zebrafish findings, we treated five medically intractable Dravet syndrome patients with a clinically-approved serotonin receptor agonist (lorcaserin, Belviq®) and observed some promising results in terms of reductions in seizure frequency and/or severity. Our findings demonstrate a rapid path from preclinical discovery in zebrafish, through target identification, to potential clinical treatments for Dravet syndrome.

DEPDC5 as a potential therapeutic target for epilepsy

INTRODUCTION

Dishevelled, Egl-10 and Pleckstrin (DEP) domain-containing protein 5 (DEPDC5) is a protein subunit of the GTPase-activating proteins towards Rags 1 (GATOR1) complex. GATOR1 is a recently identified modulator of mechanistic target of rapamycin (mTOR) activity. mTOR is a key regulator of cell proliferation and metabolism; disruption of the mTOR pathway is implicated in focal epilepsy, both acquired and genetic. Tuberous sclerosis is the prototypic mTOR genetic syndrome with epilepsy, however GATOR1 gene mutations have recently been shown to cause lesional and non-lesional focal epilepsy. Areas covered: This review summarizes the mTOR pathway, including regulators and downstream effectors, emphasizing recent developments in the understanding of the complex role of the GATOR1 complex. We review the epilepsy types associated with mTOR overactivity, including tuberous sclerosis, polyhydramnios megalencephaly symptomatic epilepsy, cortical dysplasia, non-lesional focal epilepsy and post-traumatic epilepsy. Currently available mTOR inhibitors are discussed, primarily rapamycin analogs and ATP competitive mTOR inhibitors. Expert opinion: DEPDC5 is an attractive therapeutic target in focal epilepsy, as effects of DEPDC5 agonists would likely be anti-epileptogenic and more selective than currently available mTOR inhibitors. Therapeutic effects might be synergistic with certain existing dietary therapies, including the ketogenic diet.

Proteomic Analysis After Status Epilepticus Identifies UCHL1 as Protective Against Hippocampal Injury

Brief, non-harmful seizures (preconditioning) can temporarily protect the brain against prolonged, otherwise injurious seizures. Following focal-onset status epilepticus (SE) in preconditioned (tolerance) and sham-preconditioned (injury) mice, we screened for protein changes using a proteomic approach and identified several putative candidates of epileptic tolerance. Among SE-induced changes to both proteomic screens, proteins clustered in key regulatory pathways, including protein trafficking and cytoskeletal regulation. Downregulation of one such protein, ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1), was unique to injury and not evident in tolerance. UCHL1 inhibition decreased hippocampal ubiquitin, disrupted UPS function, interfered with seizure termination and exacerbated seizure-induced cell death. Though UCHL1 transcription was maintained after SE, we observed downregulation of the pro-translational antisense Uchl1 (AsUchl1) and confirmed that both AsUchl1 and rapamycin can increase UCHL1 expression in vivo. These data indicate that the post-transcriptional loss of UCHL1 following SE is deleterious to neuronal survival and may contribute to hyperexcitability, and are suggestive of a novel modality of rapamycin therapy.

Inflammation in Epileptic Encephalopathies

West syndrome (WS) is an infantile epileptic encephalopathy that manifests with infantile spasms (IS), hypsarrhythmia (in ~60% of infants), and poor neurodevelopmental outcomes. The etiologies of WS can be structural-metabolic pathologies (~60%), genetic (12%-15%), or of unknown origin. The current treatment options include hormonal treatment (adrenocorticotropic hormone and high-dose steroids) and the GABA aminotransferase inhibitor vigabatrin, while ketogenic diet can be given as add-on treatment in refractory IS. There is a need to identify new therapeutic targets and more effective treatments for WS. Theories about the role of inflammatory pathways in the pathogenesis and treatment of WS have emerged, being supported by both clinical and preclinical data from animal models of WS. Ongoing advances in genetics have revealed numerous genes involved in the pathogenesis of WS, including genes directly or indirectly involved in inflammation. Inflammatory pathways also interact with other signaling pathways implicated in WS, such as the neuroendocrine pathway. Furthermore, seizures may also activate proinflammatory pathways raising the possibility that inflammation can be a consequence of seizures and epileptogenic processes. With this targeted review, we plan to discuss the evidence pro and against the following key questions. Does activation of inflammatory pathways in the brain cause epilepsy in WS and does it contribute to the associated comorbidities and progression? Can activation of certain inflammatory pathways be a compensatory or protective event? Are there interactions between inflammation and the neuroendocrine system that contribute to the pathogenesis of WS? Does activation of brain inflammatory signaling pathways contribute to the transition of WS to Lennox-Gastaut syndrome? Are there any lead candidates or unexplored targets for future therapy development for WS targeting inflammation?

Increasing Cancer Screening Among Old Order Anabaptist Women Through Specialized Women's Health and Integrated Cancer Screening Interventions

Our objective was to develop, deliver, and evaluate a cancer screening intervention focused on rural Anabaptist communities in Ontario, Canada, to increase routine cancer screenings among women. We carried out three cancer prevention and screening interventions with Old Order Anabaptist women. Each intervention consisted of: transportation to the site, pre-arranged screening services, health teachings, fellowship and shopping, and an evaluative survey. Seventy five women total participated over three interventions. 85% of participants were under or never screened for cancer. This was the first breast screen for 26% of those who completed a mammogram and the first colon screen for 29% of the women who took home an FOBT collection kit. Reviews of the intervention were positive. Integration and community based planning were the primary reasons for the success of this cancer screening intervention. Intervention days were best timed in the early spring before planting or late fall after canning.

Long-term treatment of epilepsy with everolimus in tuberous sclerosis

OBJECTIVE

To evaluate the long-term benefit and safety of everolimus for the treatment of medically refractory epilepsy in patients with tuberous sclerosis complex (TSC).

METHODS

Everolimus was titrated over 4 weeks and continued an additional 8 weeks in a prospective, open-label, phase I/II clinical trial design. Participants demonstrating initial benefit continued treatment until study completion (48 months). The primary endpoint was percentage of patients with a ≥50% reduction in seizure frequency compared to baseline. Secondary endpoints assessed absolute seizure frequency, adverse events (AEs), behavior, and quality of life.

RESULTS

Of the 20 participants who completed the initial study phase, 18 continued extended treatment. Fourteen of 18 (78%) participants completed the study, all but 1 of whom reported ≥50% reduction in seizure frequency at 48 months. All participants reported at least 1 AE, the vast majority (94%) of which were graded mild or moderate severity. Improvements in behavior and quality of life were also observed, but failed to achieve statistical significance at 48 months.

CONCLUSIONS

Improved seizure control was maintained for 4 years in the majority of patients with TSC with medically refractory epilepsy treated with everolimus. Long-term treatment with everolimus is safe and well-tolerated in this population. Everolimus may be a therapeutic option for refractory epilepsy in TSC.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that for patients with TSC with medically refractory epilepsy everolimus improves seizure control.

Normalizing translation through 4E-BP prevents mTOR-driven cortical mislamination and ameliorates aberrant neuron integration

Hyperactive mammalian target of rapamycin complex 1 (mTORC1) is a shared molecular hallmark in several neurodevelopmental disorders characterized by abnormal brain cytoarchitecture. The mechanisms downstream of mTORC1 that are responsible for these defects remain unclear. We show that focally increasing mTORC1 activity during late corticogenesis leads to ectopic placement of upper-layer cortical neurons that does not require altered signaling in radial glia and is accompanied by changes in layer-specific molecular identity. Importantly, we found that decreasing cap-dependent translation by expressing a constitutively active mutant of the translational repressor eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) prevents neuronal misplacement and soma enlargement, while partially rescuing dendritic hypertrophy induced by hyperactive mTORC1. Furthermore, overactivation of translation alone through knockdown of 4E-BP2 was sufficient to induce neuronal misplacement. These data show that many aspects of abnormal brain cytoarchitecture can be prevented by manipulating a single intracellular process downstream of mTORC1, cap-dependent translation.

The mTOR signalling cascade: paving new roads to cure neurological disease

Defining the multiple roles of the mechanistic (formerly 'mammalian') target of rapamycin (mTOR) signalling pathway in neurological diseases has been an exciting and rapidly evolving story of bench-to-bedside translational research that has spanned gene mutation discovery, functional experimental validation of mutations, pharmacological pathway manipulation, and clinical trials. Alterations in the dual contributions of mTOR - regulation of cell growth and proliferation, as well as autophagy and cell death - have been found in developmental brain malformations, epilepsy, autism and intellectual disability, hypoxic-ischaemic and traumatic brain injuries, brain tumours, and neurodegenerative disorders. mTOR integrates a variety of cues, such as growth factor levels, oxygen levels, and nutrient and energy availability, to regulate protein synthesis and cell growth. In line with the positioning of mTOR as a pivotal cell signalling node, altered mTOR activation has been associated with a group of phenotypically diverse neurological disorders. To understand how altered mTOR signalling leads to such divergent phenotypes, we need insight into the differential effects of enhanced or diminished mTOR activation, the developmental context of these changes, and the cell type affected by altered signalling. A particularly exciting feature of the tale of mTOR discovery is that pharmacological mTOR inhibitors have shown clinical benefits in some neurological disorders, such as tuberous sclerosis complex, and are being considered for clinical trials in epilepsy, autism, dementia, traumatic brain injury, and stroke.

Sending Mixed Signals: The Expanding Role of Molecular Cascade Mutations in Malformations of Cortical Development and Epilepsy

Advances in gene sequencing techniques have led to a dramatic increase in the number of signaling cascade and cytoskeletal assembly mutations associated with malformations of cortical development and epilepsy. At the forefront of this research are novel mutations found in regulators of the PI3K/AKT/mTOR cascade and tubulin-associated malformations of cortical development. However, there is limited understanding of the consequences of these newly discovered germline and somatic mutations on cellular function or how these changes in cell biology may lead to areas-large or small-of malformed cortex and recurrent spontaneous seizures. We summarize and discuss what is currently known in this field in an effort to shine light on vast gaps in our knowledge of relatively common causes of cortical malformations.

From Molecular Circuit Dysfunction to Disease: Case Studies in Epilepsy, Traumatic Brain Injury, and Alzheimer's Disease

Complex circuitry with feed-forward and feed-back systems regulate neuronal activity throughout the brain. Cell biological, electrical, and neurotransmitter systems enable neural networks to process and drive the entire spectrum of cognitive, behavioral, and motor functions. Simultaneous orchestration of distinct cells and interconnected neural circuits relies on hundreds, if not thousands, of unique molecular interactions. Even single molecule dysfunctions can be disrupting to neural circuit activity, leading to neurological pathology. Here, we sample our current understanding of how molecular aberrations lead to disruptions in networks using three neurological pathologies as exemplars: epilepsy, traumatic brain injury (TBI), and Alzheimer's disease (AD). Epilepsy provides a window into how total destabilization of network balance can occur. TBI is an abrupt physical disruption that manifests in both acute and chronic neurological deficits. Last, in AD progressive cell loss leads to devastating cognitive consequences. Interestingly, all three of these neurological diseases are interrelated. The goal of this review, therefore, is to identify molecular changes that may lead to network dysfunction, elaborate on how altered network activity and circuit structure can contribute to neurological disease, and suggest common threads that may lie at the heart of molecular circuit dysfunction.

Whole exome sequencing identifies the first STRADA point mutation in a patient with polyhydramnios, megalencephaly, and symptomatic epilepsy syndrome (PMSE)

Polyhydramnios, megalencephaly, and symptomatic epilepsy syndrome (PMSE) is an ultra rare neurodevelopmental disorder characterized by severe, infantile-onset intractable epilepsy, neurocognitive delay, macrocephaly, and craniofacial dysmorphism. The molecular diagnosis of this condition has thus far only been made in 16 Old Order Mennonite patients carrying a homozygous 7 kb founder deletion of exons 9-13 of STRADA. We performed clinical whole exome sequencing (WES) on a 4-year-old Indian male with global developmental delay, history of failure to thrive, infantile spasms, repetitive behaviors, hypotonia, low muscle mass, marked joint laxity, and dysmorphic facial features including tall forehead, long face, arched eyebrows, small chin, wide mouth, and tented upper lip. A homozygous single nucleotide duplication, c.842dupA (p.D281fs), in exon 10 of STRADA was identified. Sanger sequencing confirmed the mutation in the individual and identified both parents as carriers. In light of the molecular discoveries, the patient's clinical phenotype was considered to be a good fit for PMSE. We identified for the first time a homozygous point mutation in STRADA causing PMSE. Additional bi-allelic mutations related to PMSE thus far have not been observed in Baylor ∼6,000 consecutive clinical WES cases, supporting the rarity of this disorder. Our findings may have treatment implications for the patient since previous studies have shown rapamycin as a potential therapeutic agent for the seizures and cognitive problems in PMSE patients. © 2016 Wiley Periodicals, Inc.

Mutations in the mammalian target of rapamycin pathway regulators NPRL2 and NPRL3 cause focal epilepsy

OBJECTIVE

Focal epilepsies are the most common form observed and have not generally been considered to be genetic in origin. Recently, we identified mutations in DEPDC5 as a cause of familial focal epilepsy. In this study, we investigated whether mutations in the mammalian target of rapamycin (mTOR) regulators, NPRL2 and NPRL3, also contribute to cases of focal epilepsy.

METHODS

We used targeted capture and next-generation sequencing to analyze 404 unrelated probands with focal epilepsy. We performed exome sequencing on two families with multiple members affected with focal epilepsy and linkage analysis on one of these.

RESULTS

In our cohort of 404 unrelated focal epilepsy patients, we identified five mutations in NPRL2 and five in NPRL3. Exome sequencing analysis of two families with focal epilepsy identified NPRL2 and NPRL3 as the top candidate-causative genes. Some patients had focal epilepsy associated with brain malformations. We also identified 18 new mutations in DEPDC5.

INTERPRETATION

We have identified NPRL2 and NPRL3 as two new focal epilepsy genes that also play a role in the mTOR-signaling pathway. Our findings show that mutations in GATOR1 complex genes are the most significant cause of familial focal epilepsy identified to date, including cases with brain malformations. It is possible that deregulation of cellular growth control plays a more important role in epilepsy than is currently recognized.

Early rescue of interneuron disease trajectory in developmental epilepsies

The discovery of over 150 monogenic epilepsies and advances in early genetic diagnoses have launched a search for molecular strategies and developmental timetables to reverse or even prevent the course of these debilitating brain disorders. Orthologous rodent models of key disease genes are providing important examples of the range of targets, and serve as valuable test systems for perinatal therapeutic approaches. While gene-specific analyses of single rare 'orphan' diseases are each narrow in scope, they illuminate downstream pathways converging onto interneurons, and treatments that strengthen inhibition during cortical maturation may provide broad protection against these seemingly disparate gene errors. Several genes, even those linked to malformations, show promise for postnatal correction before the onset of their clinical phenotype.

mTOR in Brain Physiology and Pathologies

TOR (target of rapamycin) and its mammalian ortholog mTOR have been discovered in an effort to understand the mechanisms of action of the immunosuppressant drug rapamycin extracted from a bacterium of the Easter Island (Rapa Nui) soil. mTOR is a serine/threonine kinase found in two functionally distinct complexes, mTORC1 and mTORC2, which are differentially regulated by a great number of nutrients such as glucose and amino acids, energy (oxygen and ATP/AMP content), growth factors, hormones, and neurotransmitters. mTOR controls many basic cellular functions such as protein synthesis, energy metabolism, cell size, lipid metabolism, autophagy, mitochondria, and lysosome biogenesis. In addition, mTOR-controlled signaling pathways regulate many integrated physiological functions of the nervous system including neuronal development, synaptic plasticity, memory storage, and cognition. Thus it is not surprising that deregulation of mTOR signaling is associated with many neurological and psychiatric disorders. Preclinical and preliminary clinical studies indicate that inhibition of mTORC1 can be beneficial for some pathological conditions such as epilepsy, cognitive impairment, and brain tumors, whereas stimulation of mTORC1 (direct or indirect) can be beneficial for other pathologies such as depression or axonal growth and regeneration.

A roadmap for precision medicine in the epilepsies

Technological advances have paved the way for accelerated genomic discovery and are bringing precision medicine clearly into view. Epilepsy research in particular is well suited to serve as a model for the development and deployment of targeted therapeutics in precision medicine because of the rapidly expanding genetic knowledge base in epilepsy, the availability of good in-vitro and in-vivo model systems to efficiently study the biological consequences of genetic mutations, the ability to turn these models into effective drug-screening platforms, and the establishment of collaborative research groups. Moving forward, it is crucial that these collaborations are strengthened, particularly through integrated research platforms, to provide robust analyses both for accurate personal genome analysis and gene and drug discovery. Similarly, the implementation of clinical trial networks will allow the expansion of patient sample populations with genetically defined epilepsy so that drug discovery can be translated into clinical practice.

Impaired Reelin-Dab1 Signaling Contributes to Neuronal Migration Deficits of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is associated with neurodevelopmental abnormalities, including defects in neuronal migration. However, the alterations in cell signaling mechanisms critical for migration and final positioning of neurons in TSC remain unclear. Our detailed cellular analyses reveal that reduced Tsc2 in newborn neurons causes abnormalities in leading processes of migrating neurons, accompanied by significantly delayed migration. Importantly, we demonstrate that Reelin-Dab1 signaling is aberrantly regulated in TSC mouse models and in cortical tubers from TSC patients owing to enhanced expression of the E3 ubiquitin ligase Cul5, a known mediator of pDab1 ubiquitination. Likewise, mTORC1 activation by Rheb overexpression generates similar neuronal and Reelin-Dab1 signaling defects, and directly upregulates Cul5 expression. Inhibition of mTORC1 by rapamycin treatment or by reducing Cul5 largely restores normal leading processes and positioning of migrating neurons. Thus, disrupted Reelin-Dab1 signaling is critically involved in the neuronal migration defects of TSC.

Epileptic spasms are a feature of DEPDC5 mTORopathy

Objective:

To assess the presence of DEPDC5 mutations in a cohort of patients with epileptic spasms.

Methods:

We performed DEPDC5 resequencing in 130 patients with spasms, segregation analysis of variants of interest, and detailed clinical assessment of patients with possibly and likely pathogenic variants.

Results:

We identified 3 patients with variants in DEPDC5 in the cohort of 130 patients with spasms. We also describe 3 additional patients with DEPDC5 alterations and epileptic spasms: 2 from a previously described family and a third ascertained by clinical testing. Overall, we describe 6 patients from 5 families with spasms and DEPDC5 variants; 2 arose de novo and 3 were familial. Two individuals had focal cortical dysplasia. Clinical outcome was highly variable.

Conclusions:

While recent molecular findings in epileptic spasms emphasize the contribution of de novo mutations, we highlight the relevance of inherited mutations in the setting of a family history of focal epilepsies. We also illustrate the utility of clinical diagnostic testing and detailed phenotypic evaluation in characterizing the constellation of phenotypes associated with DEPDC5 alterations. We expand this phenotypic spectrum to include epileptic spasms, aligning DEPDC5 epilepsies more with the recognized features of other mTORopathies.

Catastrophic childhood epilepsy: a recent convergence of basic and clinical neuroscience

Advances in understanding the genetics and underlying pathology of the catastrophic childhood epilepsies are pointing toward treatments.

Focal Cortical Dysplasia

Focal cortical dysplasias are common malformations of cerebral cortical development and are highly associated with medically intractable epilepsy. They have been classified into neuropathological subtypes (type Ia, Ib, IIa, IIb, and III) based on the severity of cytoarchitectural disruption--tangential or radial dispersion, or loss of laminar structure--and the presence of unique cells types such as cytomegalic neurons or balloon cells. Most focal cortical dysplasias can be identified on neuroimaging and many require resective epilepsy surgery to cure refractory seizures. The pathogenesis of focal cortical dysplasias remains to be defined, although there is recent evidence to suggest that focal cortical dysplasias arise from de novo somatic mutations occurring during brain development. Some focal cortical dysplasia subtypes show a link to the mammalian target of rapamycin signaling cascade; this has now extended to other cortical malformations, including hemimegalencephaly.

Pathogenesis and new candidate treatments for infantile spasms and early life epileptic encephalopathies: A view from preclinical studies

Early onset and infantile epileptic encephalopathies (EIEEs) are usually associated with medically intractable or difficult to treat epileptic seizures and prominent cognitive, neurodevelopmental and behavioral consequences. EIEEs have numerous etiologies that contribute to the inter- and intra-syndromic phenotypic variability. Etiologies include structural and metabolic or genetic etiologies although a significant percentage is of unknown cause. The need to better understand their pathogenic mechanisms and identify better therapies has driven the development of animal models of EIEEs. Several rodent models of infantile spasms have emerged that recapitulate various aspects of the disease. The acute models manifest epileptic spasms after induction and include the NMDA rat model, the NMDA model with prior prenatal betamethasone or perinatal stress exposure, and the γ-butyrolactone induced spasms in a mouse model of Down syndrome. The chronic models include the tetrodotoxin rat model, the aristaless related homeobox X-linked (Arx) mouse models and the multiple-hit rat model of infantile spasms. We will discuss the main features and findings from these models on target mechanisms and emerging therapies. Genetic models have also provided interesting data on the pathogenesis of Dravet syndrome and proposed new therapies for testing. The genetic associations of many of the EIEEs have also been tested in rodent models as to their pathogenicity. Finally, several models have tested the impact of subclinical epileptiform discharges on brain function. The impact of these advances in animal modeling for therapy development will be discussed.

Genetic animal models of malformations of cortical development and epilepsy

Malformations of cortical development constitute a variety of pathological brain abnormalities that commonly cause severe, medically-refractory epilepsy, including focal lesions, such as focal cortical dysplasia, heterotopias, and tubers of tuberous sclerosis complex, and diffuse malformations, such as lissencephaly. Although some cortical malformations result from environmental insults during cortical development in utero, genetic factors are increasingly recognized as primary pathogenic factors across the entire spectrum of malformations. Genes implicated in causing different cortical malformations are involved in a variety of physiological functions, but many are focused on regulation of cell proliferation, differentiation, and neuronal migration. Advances in molecular genetic methods have allowed the engineering of increasingly sophisticated animal models of cortical malformations and associated epilepsy. These animal models have identified some common mechanistic themes shared by a number of different cortical malformations, but also revealed the diversity and complexity of cellular and molecular mechanisms that lead to the development of the pathological lesions and resulting epileptogenesis.

mTOR signaling in epilepsy: insights from malformations of cortical development

Over the past decade enhanced activation of the mammalian target of rapamycin (mTOR)-signaling cascade has been identified in focal malformations of cortical development (MCD) subtypes, which have been collectively referred to as "mTORopathies." Mutations in mTOR regulatory genes (e.g., TSC1, TSC2, AKT3, DEPDC5) have been associated with several focal MCD highly associated with epilepsy such as tuberous sclerosis complex (TSC), hemimegalencephaly (HME; brain malformation associated with dramatic enlargement of one brain hemisphere), and cortical dysplasia. mTOR plays important roles in the regulation of cell division, growth, and survival, and, thus, aberrant activation of the cascade during cortical development can cause dramatic alterations in cell size, cortical lamination, and axon and dendrite outgrowth often observed in focal MCD. Although it is widely believed that structural alterations induced by hyperactivated mTOR signaling are critical for epileptogenesis, newer evidence suggests that mTOR activation on its own may enhance neuronal excitability. Clinical trials with mTOR inhibitors have shown efficacy in the treatment of seizures associated with focal MCD.

mTOR inhibition in epilepsy: rationale and clinical perspectives

Despite a large number of available medical options, many individuals with epilepsy are refractory to existing therapies that mainly target neurotransmitter or ion channel activity. A growing body of preclinical data has uncovered a molecular pathway that appears crucial in many genetic and acquired epilepsy syndromes. The mammalian target of rapamycin (mTOR) pathway regulates a number of cellular processes required in the growth, metabolism, structure, and cell-cell interactions of neurons and glia. Rapamycin and similar compounds inhibit mTOR complex 1 and decrease seizures, delay seizure development, or prevent epileptogenesis in many animal models of mTOR hyperactivation. However, the exact mechanisms by which mTOR inhibition drives decreased seizure activity have not been completely determined. Nonetheless, these preclinical data have led to limited use in humans with epilepsy due to tuberous sclerosis complex and polyhydramnios, megalencephaly, and symptomatic epilepsy with promising results. Currently, larger controlled studies are underway using mTOR inhibitors in individuals with tuberous sclerosis complex and intractable epilepsy.

Phenotypes associated with inherited and developmental somatic mutations in genes encoding mTOR pathway components

Mutations affecting the genes that encode upstream components in the mammalian (or mechanistic) target of rapamycin signalling pathway are associated with a group of rare inherited and developmental disorders that show overlapping clinical features. These include predisposition to a variety of benign or malignant tumours, localized overgrowth, developmental abnormalities of the brain, neurodevelopmental disorders and epilepsy. Many of these features have been linked to hyperactivation of signalling via mammalian target of rapamycin complex 1, suggesting that inhibitors of this complex such as rapamycin and its derivatives may offer new opportunities for therapy. In this review we describe this group of inherited and developmental disorders and discuss recent progress in their treatment via mTORC1 inhibition.

Pathogenetic mechanisms of focal cortical dysplasia

Focal cortical dysplasias (FCDs) constitute a prevalent cause of intractable epilepsy in children, and is one of the leading conditions requiring epilepsy surgery. Despite recent advances in the cellular and molecular biology of these conditions, the pathogenetic mechanisms of FCDs remain largely unknown. The purpose if this work is to review the molecular underpinnings of FCDs and to highlight potential therapeutic targets. A systematic review of the literature regarding the histologic, molecular, and electrophysiologic aspects of FCDs was conducted. Disruption of the mammalian target of rapamycin (mTOR) signaling comprises a common pathway underlying the structural and electrical disturbances of some FCDs. Other mechanisms such as viral infections, prematurity, head trauma, and brain tumors are also posited. mTOR inhibitors (i.e., rapamycin) have shown positive results on seizure management in animal models and in a small cohort of patients with FCD. Encouraging progress has been achieved on the molecular and electrophysiologic basis of constitutive cells in the dysplastic tissue. Despite the promising results of mTOR inhibitors, large-scale randomized trials are in need to evaluate their efficacy and side effects, along with additional mechanistic studies for the development of novel, molecular-based diagnostic and therapeutic approaches.

Mechanisms of epileptogenesis in pediatric epileptic syndromes: Rasmussen encephalitis, infantile spasms, and febrile infection-related epilepsy syndrome (FIRES)

The mechanisms of epileptogenesis in pediatric epileptic syndromes are diverse, and may involve disturbances of neurodevelopmental trajectories, synaptic homeostasis, and cortical connectivity, which may occur during brain development, early infancy, or childhood. Although genetic or structural/metabolic factors are frequently associated with age-specific epileptic syndromes, such as infantile spasms and West syndrome, other syndromes may be determined by the effect of immunopathogenic mechanisms or energy-dependent processes in response to environmental challenges, such as infections or fever in normally-developed children during early or late childhood. Immune-mediated mechanisms have been suggested in selected pediatric epileptic syndromes in which acute and rapidly progressive encephalopathies preceded by fever and/or infections, such as febrile infection-related epilepsy syndrome, or in chronic progressive encephalopathies, such as Rasmussen encephalitis. A definite involvement of adaptive and innate immune mechanisms driven by cytotoxic CD8(+) T lymphocytes and neuroglial responses has been demonstrated in Rasmussen encephalitis, although the triggering factor of these responses remains unknown. Although the beneficial response to steroids and adrenocorticotropic hormone of infantile spasms, or preceding fever or infection in FIRES, may support a potential role of neuroinflammation as pathogenic factor, no definite demonstration of such involvement has been achieved, and genetic or metabolic factors are suspected. A major challenge for the future is discovering pathogenic mechanisms and etiological factors that facilitate the introduction of novel targets for drug intervention aimed at interfering with the disease mechanisms, therefore providing putative disease-modifying treatments in these pediatric epileptic syndromes.

STRAD pseudokinases regulate axogenesis and LKB1 stability

Background

Neuronal polarization is an essential step of morphogenesis and connectivity in the developing brain. The serine/threonine kinase LKB1 is a key regulator of cell polarity, metabolism, tumorigenesis, and is required for axon formation. It is allosterically regulated by two related and evolutionarily conserved pseudokinases, STe20-Related ADapters (STRADs) α and β. The roles of STRADα and STRADβ in the developing nervous system are not fully defined, nor is it known whether they serve distinct functions.

Results

We find that STRADα is highly spliced and appears to be the primal STRAD paralog. We report that each STRAD is sufficient for axogenesis and promoting cell survival in the developing cortex. We also reveal a reciprocal protein-stabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization.

Conclusions

We demonstrate a novel role for STRADβ in axogenesis and also show for the first time in vivo that STRADα, but not STRADβ, is responsible for LKB1 protein stability.

A critical review of mTOR inhibitors and epilepsy: from basic science to clinical trials

Present medications for epilepsy have substantial limitations, such as medical intractability in many patients and lack of antiepileptogenic properties to prevent epilepsy. Drugs with novel mechanisms of action are needed to overcome these limitations. The mTOR signaling pathway has emerged as a possible therapeutic target for epilepsy. Preliminary clinical trials suggest that mTOR inhibitors reduce seizures in tuberous sclerosis complex (TSC) patients with intractable epilepsy. Furthermore, mTOR inhibitors have antiepileptogenic properties in preventing epilepsy in animal models of TSC. Besides TSC, accumulating preclinical data suggest that mTOR inhibitors may have antiseizure or antiepileptogenic actions in other types of epilepsy, including infantile spasms, neonatal hypoxic seizures, absence epilepsy and acquired temporal lobe epilepsy following brain injury, but these effects depend on a number of conditions. Future clinical and basic research is needed to establish whether mTOR inhibitors are an effective treatment for epilepsy.

mTOR complexes in neurodevelopmental and neuropsychiatric disorders

The mechanistic target of rapamycin (mTOR) acts as a highly conserved signaling "hub" that integrates neuronal activity and a variety of synaptic inputs. mTOR is found in two functionally distinct complexes, mTORC1 and mTORC2, that crucially control long-term synaptic efficacy and memory storage. Dysregulation of mTOR signaling is associated with neurodevelopmental and neuropsychiatric disorders. In this Review, we describe the most recent advances in studies of mTOR signaling in the brain and the possible mechanisms underlying the many different functions of the mTOR complexes in neurological diseases. In addition, we discuss the medical relevance of these findings.

Everolimus treatment of refractory epilepsy in tuberous sclerosis complex

OBJECTIVE

Epilepsy is a major manifestation of tuberous sclerosis complex (TSC). Everolimus is an mammalian target of rapamycin complex 1 inhibitor with demonstrated benefit in several aspects of TSC. We report the first prospective human clinical trial to directly assess whether everolimus will also benefit epilepsy in TSC patients.

METHODS

The effect of everolimus on seizure control was assessed using a prospective, multicenter, open-label, phase I/II clinical trial. Patients≥2 years of age with confirmed diagnosis of TSC and medically refractory epilepsy were treated for a total of 12 weeks. The primary endpoint was percentage of patients with a ≥50% reduction in seizure frequency over a 4-week period before and after treatment. Secondary endpoints assessed impact on electroencephalography (EEG), behavior, and quality of life.

RESULTS

Twenty-three patients were enrolled, and 20 patients were treated with everolimus. Seizure frequency was reduced by ≥50% in 12 of 20 subjects. Overall, seizures were reduced in 17 of the 20 by a median reduction of 73% (p<0.001). Seizure frequency was also reduced during 23-hour EEG monitoring (p=0.007). Significant reductions in seizure duration and improvement in parent-reported behavior and quality of life were also observed. There were 83 reported adverse events that were thought to be treatment-related, all of which were mild or moderate in severity.

INTERPRETATION

Seizure control improved in the majority of TSC patients with medically refractory epilepsy following treatment with everolimus. Everolimus demonstrated additional benefits on behavior and quality of life. Treatment was safe and well tolerated. Everolimus may be a therapeutic option for refractory epilepsy in this population.

Focal malformations of cortical development: new vistas for molecular pathogenesis

Focal malformations of cortical development (FMCD) are highly associated with several neurological disorders including intractable epilepsy and neurocognitive disabilities. Over the past decade, several FMCD subtypes have been linked to hyperactivation of the mammalian target of rapamycin (mTOR) signaling cascade. In view of the roles that mTOR plays in cell proliferation, size, motility, and stem cell phenotype, many of the features of FMCD such as cytomegaly, disorganized lamination, and expression of stem cell markers can be explained by enhanced mTOR signaling. FMCD result from several distinct and fascinating molecular mechanisms including biallelic gene inactivation, somatic mutation, and potentially, viral infection. These mechanisms have been directly linked to mTOR activation. Perhaps most compelling, pharmacological inhibition of mTOR has been implemented successfully in clinical trials for select FMCD and provides a new vista for treatment.