Neurodevelopment of Tourette syndrome

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Tourette syndrome (TS) is a common disorder that afflicts as many as 1 in 150 children. Despite the high familiar recurrence rate, no significant causative or predisposing factor has yet emerged in TS. Neuroimaging and anatomical studies have implicated the striatum within the basal ganglia in TS. In postmortem brain tissue of patients with severe TS we found a decrease in striatal cholinergic neurons (CH/TAN) and two types of GABA interneurons, the parvalbumin+ (PV) and Somatostatin/Nitric Oxide Synthase /Neuropeptide Y+ (SST/NOS/NPY) by immunocytochemistry. Transcriptome profiling by RNA sequencing highlighted a decrease in synaptic neurotransmission and metabolism-related biofunctions in TS, as well as a prominent increase in inflammatory transcripts, as compared to matched normal controls (NC) brains. However, these signatures are an average of a complex cellular mixture and most likely miss changes occurring in cell subpopulations, particularly interneurons. We now seek to identify the transcriptome of striatal medium spiny neuron (MSN), interneuron (INT), astrocytes & microglia (AST/MICR) and oligodendrocytes (OLIG) cell subpopulations by fluorescence-activated nuclear sorting (FAN) as well as single neuronal nuclei in TS and NC postmortem brain tissue. Correspondingly, the epigenome of these cell types will be characterized by chromatin immunoprecipitation and sequencing (ChIP-seq) in the same cellular fractions. Differentially active enhancer regions will be mapped in the striatum of TS vs NC and a gene regulatory network encompassing changes in gene expression and corresponding enhancer activities will be built. Network modules differentially active in TS will be used to construct a model of dysfunctional striatal circuitry in TS. To understand the origin and potential causes of this network dysfunction, we will recapitulate early telencephalic development in vitro using a human induced pluripotent stem cell (iPSC) model of the disorder. Basal ganglia and cortical organoids from chronic TS patients, recovered TS patients and NC will be longitudinally analyzed and compared on the cellular, transcriptomic, epigenomic and electrophysiological levels to reveal cell fate, neuronal differentiation, molecular and functional abnormalities that underlie the disorder and its outcome. These complementary experiments will define the likely time of origin, pathophysiology, and molecular underpinnings of TS and provide a disease model where genetic and epigenetic changes can be perturbed to assess their neurobiological effects.