Project description:The Xp22.11 locus that encompasses PTCHD1, DDX53, and the long noncoding RNA (lncRNA) PTCHD1-AS is frequently disrupted in males with autism spectrum disorder (ASD), but the functional consequences of these genetic risk factors for ASD are unknown. : iPSC-derived neurons from the ASD subjects exhibited reduced miniature excitatory post-synaptic current (mEPSC) frequency and NMDA receptor hypofunction. We found that 35 ASD-associated deletions mapping to the PTCHD1 locus disrupt exons of PTCHD1-AS. We also report a novel ASD-associated deletion of PTCHD1-AS exon 3, and we show exon 3 loss alters PTCHD1-AS splicing without affecting expression of the neighboring PTCHD1 coding gene. Finally, targeted disruption of PTCHD1-AS exon 3 recapitulated diminished mEPSC frequency, supporting a role for the lncRNA in the etiology of ASD. Our genetic findings provide strong evidence that PTCHD1-AS deletions are risk factors for ASD, and human iPSC-derived neurons implicate these deletions in the neurophysiology of excitatory synapses and in ASD-associated synaptic impairment.
Project description:The long non-coding (lnc) RNA PTCHD1-AS is frequently disrupted in males with autism spectrum disorder (ASD), but its role in neuron function is unknown. We generated induced pluripotent stem (iPS) cells from two ASD subjects with PTCHD1 locus microdeletions, and produced neurons that exhibited reduced miniature excitatory post-synaptic current (mEPSC) frequency and NMDA receptor hypofunction. Mutation of the lncRNA PTCHD1-AS had no impact on expression of the divergently transcribed neighboring PTCHD1 gene in cis, but 14 genes were differentially expressed. Alternative splicing patterns of the nuclear lncRNA were affected by exon 3 loss, and its importance was reinforced by discovery of a novel ASD-associated exon 3 deletion. Finally, genome editing of exon 3 in iPS cells recapitulated diminished mEPSC frequency in neurons. Our findings directly implicate PTCHD1-AS in excitatory synapse function, and reveal the first association of lncRNA deletion with neuronal under-connectivity in ASD.
Project description:Synapse development and neuronal activity represent fundamental processes for the establishment of cognitive function. Structural organization as well as signalling pathways from receptor stimulation to gene expression regulation are mediated by synaptic activity and misregulated in neurodevelopmental disorders such as autism spectrum disorder (ASD) and intellectual disability (ID). Deleterious mutations in the PTCHD1 (Patched domain containing 1) gene have been described in male patients with X-linked ID and/or ASD. The structure of PTCHD1 protein is similar to the Patched (PTCH1) receptor; however, the cellular mechanisms and pathways associated with PTCHD1 in the developing brain are poorly determined. Here we show that PTCHD1 displays a C-terminal PDZ-binding motif that binds to the postsynaptic proteins PSD95 and SAP102. We also report that PTCHD1 is unable to rescue the canonical sonic hedgehog (SHH) pathway in cells depleted of PTCH1, suggesting that both proteins are involved in distinct cellular signalling pathways. We find that Ptchd1 deficiency in male mice (Ptchd1-/y) induces global changes in synaptic gene expression, affects the expression of the immediate-early expression genes Egr1 and Npas4 and finally impairs excitatory synaptic structure and neuronal excitatory activity in the hippocampus, leading to cognitive dysfunction, motor disabilities and hyperactivity. Thus our results support that PTCHD1 deficiency induces a neurodevelopmental disorder causing excitatory synaptic dysfunction.
Project description:Heterozygous NRXN1 deletions constitute the most prevalent currently known single-gene mutation associated with schizophrenia, and predispose to multiple other neurodevelopmental disorders. Previous studies showed that engineered heterozygous NRXN1 deletions impaired neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. Utilizing this observation for drug discovery, however, requires confidence in its robustness and validity. Here, we describe a multi-center effort to test the generality of this pivotal observation, using independent analyses at two laboratories of patient-derived and newly engineered human neurons with heterozygous NRXN1 deletions. We show that in neurons that were trans-differentiated from induced pluripotent stem cells derived from three NRXN1-deletion patients, the same impairment in neurotransmitter release was observed as in engineered NRXN1-deficient neurons. This impairment manifested as a decrease in spontaneous synaptic events and in evoked synaptic responses, and an alteration in synaptic paired-pulse depression. Nrxn1-deficient mouse neurons generated from embryonic stem cells by the same method as human neurons did not exhibit impaired neurotransmitter release, suggesting a human-specific phenotype. NRXN1 deletions produced a reproducible increase in the levels of CASK, an intracellular NRXN1-binding protein, and were associated with characteristic gene expression changes. Thus, heterozygous NRXN1 deletions robustly impair synaptic function in human neurons regardless of genetic background, enabling future drug discovery efforts.
Project description:16p13.11 copy number variants (CNVs) have been associated with autism, schizophrenia, psychosis, intellectual disability, and epilepsy. The majority of 16p13.11 deletions or duplications occur within three well-defined intervals, and despite growing knowledge of the functions of individual genes within these intervals, the molecular mechanisms that underlie commonly observed clinical phenotypes remain largely unknown. Patient-derived, induced pluripotent stem cells (iPSCs) provide a platform for investigating the morphological, electrophysiological, and gene-expression changes that result from 16p13.11 CNVs in human-derived neurons. Patient derived iPSCs with varying sizes of 16p13.11 deletions and familial controls were differentiated into cortical neurons for phenotypic analysis. High-content imaging and morphological analysis of patient-derived neurons demonstrated an increase in neurite branching in patients compared with controls. Whole-transcriptome sequencing revealed expression level changes in neuron development and synaptic-related gene families, suggesting a defect in synapse formation. Subsequent quantification of synapse number demonstrated increased numbers of synapses on neurons derived from early-onset patients compared to controls. The identification of common phenotypes among neurons derived from patients with overlapping 16p13.11 deletions will further assist in ascertaining common pathways and targets that could be utilized for screening drug candidates. These studies can help to improve future treatment options and clinical outcomes for 16p13.11 deletion patients.
Project description:The autism-associated synaptic-adhesion gene Neuroligin-4 (NLGN4) is poorly conserved evolutionarily, limiting conclusions from Nlgn4 mouse models for human cells. Here, we show that the cellular and subcellular expression of human and murine Neuroligin-4 differ, with human Neuroligin-4 primarily expressed in cerebral cortex and localized to excitatory synapses. Overexpression of NLGN4 in human neurons resulted in an increase in excitatory synapse numbers but a remarkable decrease in synaptic strength. Human neurons carrying the syndromic autism mutation NLGN4-R704C also formed more excitatory synapses but with increased functional synaptic transmission due to a postsynaptic mechanism, while genetic loss of NLGN4 did not significantly affect synapses in the human neurons analyzed. Thus, the NLGN4-R704C mutation represents a change of function mutation. Our work reveals contrasting roles of NLGN4 in human and mouse neurons, suggesting human evolution has impacted even fundamental cell biological processes generally assumed to be highly conserved.
Project description:Synaptic dysfunction represents a key pathophysiology in neurodevelopmental disorders such as autism spectrum disorder (ASD). Rare mutation R451C in human Neuroligin 3 (NLGN3, encoded by X-linked gene NLGN3), a cell adhesion molecule essential for synapse formation, has been linked to ASD. Despite success in recapitulating the social interaction behavioral deficits and the underlying synaptic abnormalities in mouse model, the impact of NLGN3 R451C on the human neuronal system remains elusive. Here, we generated isogenic knock-in human pluripotent stem cell lines harboring NLGN3 R451C allele and examined its impact on synaptic transmission. Analysis of co-cultured excitatory and inhibitory induced neurons (iNs) with mutation revealed an augmentation in excitatory synaptic strength comparing to isogenic control, but not in inhibitory synaptic transmission. Consistently, the augmentation in excitatory transmission was confirmed in iNs transplanted into mouse forebrain. Using single-cell RNA seq on co-cultured excitatory and inhibitory iNs, we identified differential expression genes (DEGs) and found NLGN3 R451C alters gene networks associated with synaptic transmission. Gene ontology and enrichment analysis revealed convergent gene networks associated with ASD and other mental disorders. Our finding suggests that the NLGN3 R451C mutation could preferentially impact excitatory neurons, which causes overall network properties changes and excitation-inhibition imbalance related to mental disorders.
Project description:Cortical layer 5 (L5) intratelencephalic (IT) and pyramidal tract (PT) neurons are embedded in distinct information processing pathways. The morphology, connectivity, electrophysiological properties, and role in behavior of these neurons have been extensively analyzed. However, the molecular composition of their synapses remains largely uncharacterized. Here, we dissect the protein composition of the excitatory postsynaptic compartment of L5 neurons in intact somatosensory circuits, using an optimized proximity biotinylation workflow with subsynaptic resolution. We find distinct synaptic signatures of L5 IT and PT neurons that are defined by proteins regulating synaptic organization and transmission, including cell-surface proteins (CSPs), neurotransmitter receptors and ion channels. In addition, we find a differential vulnerability to disease, with a marked enrichment of autism risk genes in the synaptic signature of L5 IT neurons compared to PT neurons. Our results align with human studies and suggest that the excitatory postsynaptic compartment of L5 IT neurons is notably susceptible in autism. Together, our analysis sheds light on the proteins that regulate synaptic organization and function of L5 neuron types and contribute to their susceptibility in disease. Our approach is versatile and can be broadly applied to other neuron types to create a protein-based, synaptic atlas of cortical circuits.