How are the epileptogenesis clocks ticking?
The epileptogenesis process is associated with large-scale changes in gene expression, which contribute to the remodelling of brain networks permanently altering excitability. About 80% of the protein coding genes are under the influence of the circadian rhythms. These are 24-hour endogenous rhythms that determine a large number of daily changes in physiology and behavior in our bodies. In the brain, the master clock regulates a large number of pathways that are important during epileptogenesis and established-epilepsy, such as neurotransmission, synaptic homeostasis, inflammation, blood-brain barrier among others. In-depth mapping of the molecular basis of circadian timing in the brain is key for a complete understanding of the cellular and molecular events connecting genes to phenotypes.
Neuroinflammation in Epilepsy: what have we learned from human brain tissue specimens ?
Epileptogenesis is a gradual and dynamic process leading to difficult-to-treat seizures. Several cellular, molecular, and pathophysiologic mechanisms, including the activation of inflammatory processes. The use of human brain tissue represents a crucial strategy to advance our understanding of the underlying neuropathology and the molecular and cellular basis of epilepsy and related cognitive and behavioral comorbidities, The mounting evidence obtained during the past decade has emphasized the critical role of inflammation in the pathophysiological processes implicated in a large spectrum of genetic and acquired forms of focal epilepsies. Dissecting the cellular and molecular mediators of the pathological immune responses and their convergent and divergent mechanisms, is a major requisite for delineating their role in the establishment of epileptogenic networks. The role of small regulatory molecules involved in the regulation of specific pro- and anti-inflammatory pathways and the crosstalk between neuroinflammation and oxidative stress will be addressed. The observations supporting the activation of both innate and adaptive immune responses in human focal epilepsy will be discussed and elaborated, highlighting specific inflammatory pathways as potential targets for antiepileptic, disease-modifying therapeutic strategies.
Hidden nature of seizures
How seizures emerge from the abnormal dynamics of neural networks within the epileptogenic tissue remains an enigma. Are seizures random events, or do detectable changes in brain dynamics precede them? Are mechanisms of seizure emergence identical at the onset and later stages of epilepsy? Is the risk of seizure occurrence stable, or does it change over time? A myriad of questions about seizure genesis remains to be answered to understand the core principles governing seizure genesis. The last decade has brought unprecedented insights into the complex nature of seizure emergence. It is now believed that seizure onset represents the product of the interactions between the process of a transition to seizure, long-term fluctuations in seizure susceptibility, epileptogenesis, and disease progression. During the lecture, we will review the latest observations about mechanisms of ictogenesis operating at multiple temporal scales. We will show how the latest observations contribute to the formation of a comprehensive theory of seizure genesis, and challenge the traditional perspectives on ictogenesis. Finally, we will discuss how combining conventional approaches with computational modeling, modern techniques of in vivo imaging, and genetic manipulation open prospects for exploration of yet hidden mechanisms of seizure genesis.
Epileptogenesis in the developing brain:understanding a moving target
The origins, mechanisms and consequences of epilepsy in the developing brain are incompletely understood. Many developmental epilepsies have a genetic basis and their mechanisms stem from deficits in the function of one or numerous genes. Others, such as those that follow prolonged febrile seizures or severe birth asphyxia in a ‘normal’ brain may depend on the interaction of the insult with the rapidly evolving brain cells and circuits. Yet, how early-life insults may provoke epilepsy is unclear, and requires multiple levels of analysis: behavior, circuits, cells [neurons, glia] and molecules. Here we discuss developmental epileptogenesis, addressing some of its special features: the epilepsy phenotype, the effects insults on the maturation of brain circuits, the role of neuron-glia-neuron communication in cellular and circuit refinement, and how transient epileptogenic insults provoke enduring changes in the structure, connectivity and function of salient neuronal populations. We will highlight resolved questions- and the many unresolved issues that require tackling in 2022 and beyond.
Converging mechanisms of epileptogenesis after brain injury
Traumatic brain injury (TBI), a leading cause of acquired epilepsy, results in primary cellular injury as well as secondary neurophysiological and inflammatory responses which contribute to epileptogenesis. I will present our recent studies identifying a role for neuro-immune interactions, specifically, the innate immune receptor Toll-like receptor 4 (TLR4), in enhancing network excitability and cell loss in hippocampal dentate gyrus early after concussive brain injury. I will describe results indicating that the transient post-traumatic increases in dentate neurogenesis which occurs during the same early post-injury period augments dentate network excitability and epileptogenesis. I will provide evidence for the beneficial effects of targeting TLR4 and neurogenesis early after brain injury in limiting epileptogenesis. We will discuss potential mechanisms for convergence of the post-traumatic neuro-immune and neurogenic changes and the implications for therapies to reduce neurological deficits and epilepsy after brain injury.
Malformation of cortical development: the genesis of epileptogenic networks
Malformations of cortical development (MCDs) result from alterations of one or combined developmental steps, including progenitors proliferation, neuronal migration and differentiation. They are important cause of childhood epilepsy and frequently associate cognitive deficits and behavioral alterations. Though the genetic basis of MCDs have known prominent progress during the past decade, including the identification of somatic, mosaic mutations responsible for focal MCDs, the pathophysiological mechanisms linking malformations to epileptogenesis remain elusive. In this seminar I will present data from my team and from the literature addressing this topic in two different MCDs types, the subcortical band heterotopia as a model of cortical migration defect and mTOR- dependent MCDs , that characterize by cortical dyslamination and neuronal differentiation defects.
Sparks, flames, and inferno: epileptogenesis in the glioblastoma microenvironment
Glioblastoma cells trigger pharmacoresistant seizures that may promote tumor growth and diminish the quality of remaining life. To define the relationship between growth of glial tumors and their neuronal microenvironment, and to identify genomic biomarkers and mechanisms that may point to better prognosis and treatment of drug resistant epilepsy in brain cancer, we are analyzing a new generation of genetically defined CRISPR/in utero electroporation inborn glioblastoma (GBM) tumor models engineered in mice. The molecular pathophysiology of glioblastoma cells and surrounding neurons and untransformed astrocytes are compared at serial stages of tumor development. Initial studies reveal that epileptiform EEG spiking is a very early and reliable preclinical signature of GBM expansion in these mice, followed by rapidly progressive seizures and death within weeks. FACS-sorted transcriptomic analysis of cortical astrocytes reveals the expansion of a subgroup enriched in pro-synaptogenic genes that may drive hyperexcitability, a novel mechanism of epileptogenesis. Using a prototypical GBM IUE model, we systematically define and correlate the earliest appearance of cortical hyperexcitability with progressive cortical tumor cell invasion, including spontaneous episodes of spreading cortical depolarization, innate inflammation, and xCT upregulation in the peritumoral microenvironment. Blocking this glutamate exporter reduces seizure load. We show that the host genome contributes to seizure risk by generating tumors in a monogenic deletion strain (MapT/tau -/-) that raises cortical seizure threshold. We also show that the tumor variant profile determines epilepsy risk. Our genetic dissection approach sets the stage to broadly explore the developmental biology of personalized tumor/host interactions in mice engineered with novel human tumor mutations in specified glial cell lineages.