Kevin C. Ess, M.D./Ph.D - US grants

[unreadable] DESCRIPTION (PROVIDED BY APPLICANT): The goals of this proposal are to 1) define mechanisms used by the TSC genes to control the generation of neurons and then glia from neural progenitor cells and 2) determine how defects in these processes result in cortical malformations in Tuberous Sclerosis Complex (TSC). TSC is caused by mutation of either the TSC1 or TSC2 genes and is the most common genetic cause of epilepsy and autism. These features are very likely due to cortical brain malformations (tubers) that are found in almost all patients. Previous work has demonstrated severe laminar disruptions within tubers with abnormal glia, dysmorphic neurons, and "giant" cells expressing neuronal as well as glia markers. These findings suggest that the TSC genes play a critical role during the generation of specific neuronal populations as well as the switch from neuronal to glia production by neural progenitor cells. Mechanisms that normally control this process are not well understood but appear linked to cell cycle exit and the length of G1. Proliferation, total cell cycle length, and G1 duration are mediated by cyclins, cyclin-dependent kinases (cdk), and cdk inhibitors such as p27kip1 (p27). Notably, while Tsc1 or Tsc2-deficient fibroblasts have decreased levels and activity of p27, similar alterations in Tsc1 or Tsc2-deficient neural progenitor cells have not been reported. Our Specific Aims are: 1) Determine the role of the Tsd gene on the timing of neuronal and glia production from neural progenitor cells, 2) determine G1 duration and proliferation in 7sc1-deficient neural progenitor cells, and 3) determine p27 expression, subcellular localization, and function in 7sc7-deficient neural progenitor cells. We will achieve these aims by studying 7sc1-deficient neural progenitor cells both in vivo and in vitro. The ability of these neural progenitor cells to differentiate will be determined using lineage specific markers. In addition, we will use S phase tracers to measure cell cycle length, G1 duration, and the proportion of cells that are actively proliferating in mice with Tsc1-deficient neural progenitor cells. Finally, p27 expression, subcellular localization, and function will be determined. The candidate will utilize this K08 Award to gain expertise in developmental neurobiology though interactions with his mentor, the Neuroscience research community at Vanderbilt University, and active involvement with national and international leaders in Developmental Neurobiology. Overall, this award should position him to become an independent physician-scientist who will successfully compete for future extramural NIH funding. Relevance: Tuberous Sclerosis Complex (TSC) is a genetic disease whose manifestations include seizure disorders, brain tumors, autism and developmental delay. This proposal seeks to understand the role of abnormal neural progenitor cells to TSC. These findings will likely have broad therapeutic implications for individuals with TSC as well as non-TSC patients with seizure disorders and autism. [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Tuberous Sclerosis Complex (TSC) is a genetic disease caused by mutation of the TSC1 or TSC2 genes. Patients frequently have severe CNS manifestations including epilepsy, intellectual disabilities and autism. Cortical malformations (tubers) in the brains of patients with TSC are generally accepted as responsible for these severe neurological manifestations. Previous studies using human tissues and transgenic mouse and zebrafish models have led our focus on neural progenitor/stem cells. Abnormalities of neural progenitor cells may readily explain the increased cell number, atypical differentiation and ectopic position of neurons seen within the brain of patients with TSC. Several signaling pathways are known to be dysregulated in TSC though control of the mTOR kinase appears most critical. Recent findings support abnormalities of mTOR within two distinct protein complexes, mTORC1 and mTORC2. These alterations differ as we have found that Tsc1- deficient mouse neural progenitor cells appear to have increased mTORC1 but decreased mTORC2 signaling. However, the relative contribution of mTORC1 and mTORC2 signaling during the pathogenesis of TSC remains poorly understood. The overarching goal of this proposal is to determine the role of mTORC1 and mTORC2 signaling in the pathogenesis of TSC. This goal directly addresses the NINDS Strategic Plan by seeking to increase our knowledge of how the normal brain and nervous system develop, how these processes are subverted in disease and whether this information can lead to better treatments of neurological disorders. To achieve this goal we will use both transgenic mouse models featuring the inactivation of the mouse Tsc1 gene as well as induced pluripotent stem cells (iPSC) we have generated from patients with TSC due to loss of function mutations of the TSC1 or TSC2 genes. The direct comparison of mouse and human neural progenitor cells is a key aspect of this proposal as fundamental differences in the control of mTOR signaling in the brain likely arose during evolution. The Specific Aims of this project are to 1) Determine if TSC1/2-mutant human and Tsc1-deficient mouse neural progenitor cells generate excessive numbers of neurons; 2) Determine if neurons generated from TSC1-deficient and TSC2-deficient human and Tsc1-deficient mouse neural progenitors are able to acquire lower or upper layer identity and whether inhibition of mTORC1 signaling can restore these identities; 3). Determine if decreased mTORC2 signaling alone is sufficient to cause abnormal differentiation of mouse and human neural progenitor cells. These studies should greatly increase our understanding of the function of the mouse Tsc1 and human TSC genes. Our proposal is expected to define abnormal mTORC1 and mTORC2 signaling pathways in mouse and human cells and lead to the development of much more effective therapies for patients with TSC.

The goal of this proposal is to establish in vitro tissue chip models of the closely related neurological disorders tuberous sclerosis complex (TSC) epilepsy, DEPDC5-associated epilepsy, and their associated cardiac dysfunction. The proposed research leverages emerging bioengineering technology for microphysiological systems developed at the Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE) with human induced pluripotent stem cell tools in regular use at Vanderbilt University Medical Center to ask probing questions about genetic disorders that afflict the heart and brain and about the drugs to treat them. The VIIBRE neurovascular unit (NVU)/blood-brain barrier and cardiac I-Wire organ-on-chip models will test the hypothesis that mTORC1 and mTORC2 signaling differentially affect neural and cardiac dysfunction in TSC- and DEPDC5-associated epilepsy. The primary and shared abnormality in patients with TSC and DEPDC5- associated epilepsy is dysregulation of the mTOR kinase complex 1 (mTORC1) signaling pathway. TSC also has abnormalities in mTORC2 signaling not seen in DEPDC5-associated epilepsy. A focus on mTOR signaling in these human mTORopathies has several advantages. First, rapamycin and related compounds are FDA- approved mTORC1 inhibitors and have been shown to have efficacy in some aspects of the disease manifestations of TSC. Second, TSC- and DEPDC5-associated epilepsy are both associated with neural and cardiac dysfunction. Third, the role for compensatory or differential mTORC2 activity is unclear and controversial. For patients with TSC, drugs targeting the mTORC1 signaling pathway have been associated with shrinkage of brain tumors, reduced seizures, and improved cardiac function. Thus, drug development for this group of diseases is well suited for study using both the NVU and I-Wire cardiac-tissue chips. In its first two years, the project will develop the NVU and I-Wire disease models, aimed at refining the TSC and DEPDC5 NVU model; applying the I-Wire model to TSC and DEPDC5 cardiomyocytes; and validating outcome methodologies in control and patient-derived NVU and I-Wire chips. The next three years aim to evaluate, for biomarker identification in control, TSC, and DEPDC5 NVU and I-Wire chips, changes in mTORC1 and mTORC2 signaling, protein markers of cellular health and toxicity, metabolites, functional measures and electrophysiological activity; and, use ion mobility-mass spectrometry to evaluate NVU and I-Wire outcome measures plus drug metabolites after treatment with mTORC1 inhibitor rapamycin, the seizure drug vigabatrin, and novel pre-clinical mTOR drug candidates. The NVU and I-Wire will assess the efficacy and toxicity of these agents and define TSC/DEPDC5 shared vs disease-specific effects. With this organ-on-chip/human induced pluripotent stem cell platform, it will be possible to address currently confounding mechanisms of pathogenesis, identify new disease biomarkers, quantify how drugs cross the normal and diseased blood-brain barrier, and ultimately develop effective therapies and hence enable bench-to-bedside translation.

Project Summary Genomic investigation has shown that the ATP1A3 gene has a very high intolerance of mutation. This is emerging clinically as a rapidly expanding spectrum of neurological and psychiatric disease. Several syndromes have been identified with a wide range of severity. These include severe infantile epilepsy; severe infantile hypotonia; alternating hemiplegia of childhood (AHC); rapid-onset dystonia-parkinsonism (RDP); relapsing encephalopathy with cerebellar ataxia (RECA); cerebellar ataxia, areflexia, pes cavus, optic nerve atrophy, and sensorimotor deafness (CAPOS); and early onset schizophrenia. Despite several distinct groups of mutations, many specific neurological symptoms as well as developmental delay appear on a continuum. Age of onset also has a wide range from birth to adulthood. Available treatments are minimal, not based on disease mechanism, and simply inadequate. On the positive side, the ATP1A3 encoded protein alpha 3 is a virtually neuron-specific isoform of Na,K-ATPase, and there is a substantial body of scientific knowledge related to its physiology and mechanism. This results in a very credible opportunity for cross-disciplinary interactions that could lead to effective therapies. A highly-interactive body of clinicians, geneticists, basic scientists, patient advocacy leaders, and parents of patients have met annually since 2012. This application is for funding for the 7th annual meeting, to be held in Chicago in 2018. The interdisciplinary format and the full participation of committed family members and advocates has produced very important insights and education at all levels. Consensus developments have shaped subsequent clinical and basic research, and forged new collaborations. Research topics discussed include new phenotypes; novel genetics; treatments of animal models; stem cell and cell model investigations; biochemical studies of mutations and phenotype correlations; planned clinical trials; clinical data repositories; and ideas for new treatments. The selection of a different geographical location for each meeting has facilitated the participation of local clinicians and parents. The meetings have been an outstanding learning environment for young investigators and clinical fellows that will continue in Chicago 2018.

Tuberous Sclerosis Complex (TSC) is a multi-organ disorder caused by mutations in the TSC1 or TSC2 genes. TSC is a challenging disease to approach as there are many involved organ systems, which have distinct profiles of symptom onset, disease progression, and in some cases even stability or regression of the benign tumors known as hamartomas. These multiple examples of distinct time courses in each organ system strongly suggest that the TSC1/TSC2 genes control cell signaling pathways that are tissue specific and developmentally regulated, resulting in lesions that present at different times in the lifetime of the patient. These pathways certainly include mTOR kinase signaling, but critical upstream and downstream regulators of this developmentally regulated process in specific tissues remain poorly understood. The neurological manifestations of TSC are typically severe at very early ages and include epilepsy, intellectual disability, autism, and behavioral/psychiatric disorders. Recent findings in human cell-derived model systems suggest that neural development is disrupted in TSC, and that proper regulation of mTOR signaling is especially important in human brain in comparison to other mammals. However, the cellular mechanisms connecting TSC1/2 mutation and the phenotypic outcomes of this mutation are not well understood. This project will use patient-derived cells and single-cell measurements of protein and RNA to measure altered signaling pathways in various cell types of the human brain and also address how these abnormalities impact specific developmental stages. Examined stages will span early neural progenitor cells to more mature neurons found in the postnatal brain. Human induced pluripotent stem cells (iPSCs) from patients carrying TSC2 mutations will be used to generate lineage-committed progenitors and differentiated neurons and glia. We will also use freshly resected human tubers as well as previously resected human tubers that have been fixed and stored, and will employ custom-designed computational pipelines to compare the developmental trajectories of TSC2-mutant cells to matched controls and larger published datasets. Using cutting edge cell imaging and analysis protocols, we will test the overarching hypothesis that tubers from patients with TSC and stem cell derivative neural cells and tissues have mTOR-dependent and mTOR- independent signaling abnormalities that are lineage- and temporally-restricted. Finally, we will quantitatively compare signaling dynamics in specific developmental stages and lineages between TSC2 mutant cells and cells derived from a second ?mTORopathy? with overlapping but non-identical clinical features, to dissect the function of different components of this pathway in neural development and pathogenesis and reveal compensatory signaling after treatment of cells carrying TSC2 or DEPDC5 mutations.