TCF4 Mutations Disrupt Synaptic Function Through Dysregulation of RIMBP2 in Patient-Derived Cortical Neurons.

BACKGROUND: Genetic variation in the TCF4 (transcription factor 4) gene is associated with risk for a variety of developmental and psychiatric conditions, which includes a syndromic form of autism spectrum disorder called Pitt-Hopkins syndrome (PTHS). TCF4 encodes an activity-dependent transcription factor that is highly expressed during cortical development and in animal models has been shown to regulate various aspects of neuronal development and function. However, our understanding of how disease-causing mutations in TCF4 confer pathophysiology in a human context is lacking. METHODS: To model PTHS, we differentiated human cortical neurons from human induced pluripotent stem cells that were derived from patients with PTHS and neurotypical individuals. To identify pathophysiology and disease mechanisms, we assayed cortical neurons with whole-cell electrophysiology, Ca2+ imaging, multielectrode arrays, immunocytochemistry, and RNA sequencing. RESULTS: Cortical neurons derived from patients with TCF4 mutations showed deficits in spontaneous synaptic transmission, network excitability, and homeostatic plasticity. Transcriptomic analysis indicated that these phenotypes resulted in part from altered expression of genes involved in presynaptic neurotransmission and identified the presynaptic binding protein RIMBP2 as the most differentially expressed gene in PTHS neurons. Remarkably, TCF4-dependent deficits in spontaneous synaptic transmission and network excitability were rescued by increasing RIMBP2 expression in presynaptic neurons. CONCLUSIONS: Taken together, these results identify TCF4 as a critical transcriptional regulator of human synaptic development and plasticity and specifically identifies dysregulation of presynaptic function as an early pathophysiology in PTHS.

Psychiatric risk gene Transcription Factor 4 (TCF4) regulates the density and connectivity of distinct inhibitory interneuron subtypes.

Transcription factor 4 (TCF4) is a basic helix-loop-helix transcription factor that is implicated in a variety of psychiatric disorders including autism spectrum disorder (ASD), major depression, and schizophrenia. Autosomal dominant mutations in TCF4 are causal for a specific ASD called Pitt-Hopkins Syndrome (PTHS). However, our understanding of etiological and pathophysiological mechanisms downstream of TCF4 mutations is incomplete. Single cell sequencing indicates TCF4 is highly expressed in GABAergic interneurons (INs). Here, we performed cell-type specific expression analysis (CSEA) and cellular deconvolution (CD) on bulk RNA sequencing data from 5 different PTHS mouse models. Using CSEA we observed differentially expressed genes (DEGs) were enriched in parvalbumin expressing (PV+) INs and CD predicted a reduction in the PV+ INs population. Therefore, we investigated the role of TCF4 in regulating the development and function of INs in the Tcf4+/tr mouse model of PTHS. In Tcf4+/tr mice, immunohistochemical (IHC) analysis of subtype-specific IN markers and reporter mice identified reductions in PV+, vasoactive intestinal peptide (VIP+), and cortistatin (CST+) expressing INs in the cortex and cholinergic (ChAT+) INs in the striatum, with the somatostatin (SST+) IN population being spared. The reduction of these specific IN populations led to cell-type specific alterations in the balance of excitatory and inhibitory inputs onto PV+ and VIP+ INs and excitatory pyramidal neurons within the cortex. These data indicate TCF4 is a critical regulator of the development of specific subsets of INs and highlight the inhibitory network as an important source of pathophysiology in PTHS.

Promyelinating drugs promote functional recovery in an autism spectrum disorder mouse model of Pitt-Hopkins syndrome.

Pitt-Hopkins syndrome is an autism spectrum disorder caused by autosomal dominant mutations in the human transcription factor 4 gene (TCF4). One pathobiological process caused by murine Tcf4 mutation is a cell autonomous reduction in oligodendrocytes and myelination. In this study, we show that the promyelinating compounds, clemastine, sobetirome and Sob-AM2 are effective at restoring myelination defects in a Pitt-Hopkins syndrome mouse model. In vitro, clemastine treatment reduced excess oligodendrocyte precursor cells and normalized oligodendrocyte density. In vivo, 2-week intraperitoneal administration of clemastine also normalized oligodendrocyte precursor cell and oligodendrocyte density in the cortex of Tcf4 mutant mice and appeared to increase the number of axons undergoing myelination, as EM imaging of the corpus callosum showed a significant increase in the proportion of uncompacted myelin and an overall reduction in the g-ratio. Importantly, this treatment paradigm resulted in functional rescue by improving electrophysiology and behaviour. To confirm behavioural rescue was achieved via enhancing myelination, we show that treatment with the thyroid hormone receptor agonist sobetirome or its brain penetrating prodrug Sob-AM2, was also effective at normalizing oligodendrocyte precursor cell and oligodendrocyte densities and behaviour in the Pitt-Hopkins syndrome mouse model. Together, these results provide preclinical evidence that promyelinating therapies may be beneficial in Pitt-Hopkins syndrome and potentially other neurodevelopmental disorders characterized by dysmyelination.

TCF4 mutations disrupt synaptic function through dysregulation of RIMBP2 in patient-derived cortical neurons.

Genetic variation in the transcription factor 4 ( TCF4) gene is associated with risk for a variety of developmental and psychiatric conditions, which includes a syndromic form of ASD called Pitt Hopkins Syndrome (PTHS). TCF4 encodes an activity-dependent transcription factor that is highly expressed during cortical development and in animal models is shown to regulate various aspects of neuronal development and function. However, our understanding of how disease-causing mutations in TCF4 confer pathophysiology in a human context is lacking. Here we show that cortical neurons derived from patients with TCF4 mutations have deficits in spontaneous synaptic transmission, network excitability and homeostatic plasticity. Transcriptomic analysis indicates these phenotypes result from altered expression of genes involved in presynaptic neurotransmission and identifies the presynaptic binding protein, RIMBP2 as the most differentially expressed gene in PTHS neurons. Remarkably, TCF4-dependent deficits in spontaneous synaptic transmission and network excitability were rescued by increasing RIMBP2 expression in presynaptic neurons. Together, these results identify TCF4 as a critical transcriptional regulator of human synaptic development and plasticity and specifically identifies dysregulation of presynaptic function as an early pathophysiology in PTHS.

Molecular and Cellular Function of Transcription Factor 4 in Pitt-Hopkins Syndrome.

Transcription factor 4 (TCF4, also known as ITF2 or E2-2) is a type I basic helix-loop-helix transcription factor. Autosomal dominant mutations in TCF4 cause Pitt-Hopkins syndrome (PTHS), a rare syndromic form of autism spectrum disorder. In this review, we provide an update on the progress regarding our understanding of TCF4 function at the molecular, cellular, physiological, and behavioral levels with a focus on phenotypes and therapeutic interventions. We examine upstream and downstream regulatory networks associated with TCF4 and discuss a range of in vitro and in vivo data with the aim of understanding emerging TCF4-specific mechanisms relevant for disease pathophysiology. In conclusion, we provide comments about exciting future avenues of research that may provide insights into potential new therapeutic targets for PTHS.

A myelin-related transcriptomic profile is shared by Pitt-Hopkins syndrome models and human autism spectrum disorder.

Autism spectrum disorder (ASD) is genetically heterogeneous with convergent symptomatology, suggesting common dysregulated pathways. In this study, we analyzed brain transcriptional changes in five mouse models of Pitt-Hopkins syndrome (PTHS), a syndromic form of ASD caused by mutations in the TCF4 gene, but not the TCF7L2 gene. Analyses of differentially expressed genes (DEGs) highlighted oligodendrocyte (OL) dysregulation, which we confirmed in two additional mouse models of syndromic ASD (Ptenm3m4/m3m4 and Mecp2tm1.1Bird). The PTHS mouse models showed cell-autonomous reductions in OL numbers and myelination, functionally confirming OL transcriptional signatures. We also integrated PTHS mouse model DEGs with human idiopathic ASD postmortem brain RNA-sequencing data and found significant enrichment of overlapping DEGs and common myelination-associated pathways. Notably, DEGs from syndromic ASD mouse models and reduced deconvoluted OL numbers distinguished human idiopathic ASD cases from controls across three postmortem brain data sets. These results implicate disruptions in OL biology as a cellular mechanism in ASD pathology.