In mice with conditional Arid1b haploinsufficiency in excitatory neurons, an increase in the rate of synaptic connectivity between excitatory neurons and reduced strength of excitatory synapses to parvalbumin (PV)-expressing inhibitory interneurons is found.
Abstract
Arid1b is a high confidence risk gene for autism spectrum disorder that encodes a subunit of a chromatin remodeling complex initially expressed in neuronal progenitors. Haploinsufficiency causes a broad range of social, behavioral, and intellectual disability phenotypes, including Coffin-Siris syndrome. Recent work suggests pathology is due to deficits in proliferation, survival, and synaptic development of cortical neurons. Here, we used transgenic mice to investigate how Arid1b dysfunction in cortical excitatory neurons impacts their intrinsic membrane properties, synaptic connectivity and physiology of local cortical circuits using paired whole-cell recordings, social behavior, and seizure susceptibility. We found that loss of both copies of Arid1b altered the proportions of different excitatory neuron cell-types in the superficial cortical layers; however, their intrinsic membrane properties were mostly unchanged. In mice with conditional Arid1b haploinsufficiency in excitatory neurons, we found an increase in the rate of synaptic connectivity between excitatory neurons and reduced strength of excitatory synapses to parvalbumin (PV)-expressing inhibitory interneurons. In the deep cortical layers, we found hyperpolarization of action potential threshold. Collectively, these data suggest an increase in the ratio of excitation to inhibition. However, we also found enhanced inhibition from PV interneurons to excitatory neurons that may rebalance this ratio. Indeed, Arid1b haploinsufficiency in excitatory neurons was insufficient to cause social deficits and seizure phenotypes observed in a preclinical germline haploinsufficient mouse model. Our data suggest that while excitatory neurons likely contribute to autistic phenotypes, pathology in these cells is not the primary cause.
ANK3, encoding the scaffolding protein ankyrin-G, is a major risk gene for bipolar disorder and schizophrenia, but its cellular and circuit-level mechanisms remain poorly defined. Here, we demonstrate that deletion of Ank3 in forebrain excitatory neurons-either prenatally (Ank3-/-:Emx1-Cre) or in adolescence (Ank3-/-:CaMKIIα-Cre) leads to convergent behavioral phenotypes in adulthood, including hyperactivity, reduced anxiety-like behavior, and decreased depression-like responses. Calcium imaging in cultured neurons and acute brain slices revealed that ankyrin-G loss reduces both spontaneous and evoked neuronal activity. Quantitative proteomic profiling of membrane-enriched cortical fractions uncovered widespread remodeling of the synaptic proteome, including upregulation of the kinase Taok2 and unexpected downregulation of myelin basic protein (Mbp), a structural component of oligodendrocyte-derived myelin. Importantly, chronic lithium treatment, known to reverse behavioral abnormalities in Ank3-deficient mice, also restored Mbp expression. Together, our findings identify ankyrin-G as a molecular bridge between excitatory neuronal activity, synaptic structure, and myelin-associated protein expression, revealing a pathway by which ANK3 variants may contribute to neuropsychiatric disease.
Sehyoun Yoon, M. D. Dos Santos, Natalia Khalatyan et al.· Proceedings of the National...· 0 citations
These findings establish DLG4 haploinsufficiency as a shared consequence of pathogenic DLG4 variants, while revealing additional variant-associated effects on neuronal structure and activity, rescued by AAV9-mediated neuronal restoration.
Dania Abdellatif, Mustafa Obeid, Rami I. Aqeilan· bioRxiv· 0 citations
Schizophrenia (SCZ) is characterized by heterogeneous symptoms including abnormal perception, social withdrawal, and cognitive deficits. Parvalbumin-positive (PV+) interneurons are particularly vulnerable in SCZ; however, the underlying cellular basis remains unclear. In this study, we found that selective deletion of the SCZ risk gene Foxg1 in PV+ interneurons of mice recapitulated aspects of the disease phenotype, including impaired sensorimotor gating, anxiety-like behavior, social deficits, and cognitive impairments. Foxg1 deficiency caused dendritic simplification, reduced spine density, and impaired synaptic transmission in PV+ interneurons of the prelimbic cortex. Our findings indicate that FOXG1 directly drives a set of SCZ risk genes that encode synaptic receptors, adhesion molecules, scaffolding proteins, transporters, ion channels, and vesicle-trafficking proteins, thereby orchestrating PV+ interneuron synaptic function. Notably, FOXG1 activates the transcription of metabotropic glutamate receptor 3 (mGluR3), and pharmacological potentiation of mGluR3 activity alleviates behavioral deficits in Foxg1 conditional knockout mice. In conclusion, our findings identify a novel role for Foxg1 in PV+ interneurons, providing new mechanistic insights into their vulnerability to SCZ.
Pengfei Jiang, Mingzhao Su, Xue-lai Zhou et al.· Neuroscience Bulletin· 0 citations
Abstract β-catenin-coding gene CTNNB1 is a top-ranking risk gene for autism and intellectual disability. To better understand how CTNNB1 haploinsufficiency is involved in the pathophysiology of neurodevelopmental disorders, we generated a new mouse model that enables Ctnnb1 deletion in forebrain excitatory neurons starting at embryonic corticogenesis. Behavioural assays of the Ctnnb1 conditional knockout (cKO) mice revealed significant fear memory deficits, despite normal social preference, anxiety, spatial and recognition memory. Pyramidal neurons in prefrontal cortex (PFC) of Ctnnb1 cKO mice exhibited the significantly elevated intrinsic excitability but markedly decreased AMPA receptor-mediated synaptic response, while GABAA or NMDA receptor-mediated synaptic response was unchanged. Gene profiling revealed the significantly reduced mRNA level of Syp (encoding Synaptophysin) and Nlng2 (encoding Neuroligin-2) in PFC of Ctnnb1 cKO mice, while most of other screened genes were unchanged. These results suggest that β-catenin deficiency in forebrain excitatory neurons leads to fear conditioning impairment, which could be contributed by the diminished excitatory synaptic transmission in PFC resulting from disrupted synaptic gene expression.
Luis Gustavo Hernandez Carballo, Rachel Senek, Ksenia Novototskaya-Vlasova et al.· Brain Communications· 0 citations
Heterozygous loss-of-function variants in Neurabin I (PPP1R9A), responsible for encoding a cytoskeletal scaffolding protein essential for synaptic plasticity, are recurrently associated with neurodevelopmental and neuropsychiatric disorders, yet their direct effects on human neuronal maturation remain unclear. Here, we establish the first comprehensive human mechanistic model of PPP1R9A haploinsufficiency using an isogenic CRISPR/Cas9-engineered iPSC system differentiated into cortical neurons to define dosage-dependent functional consequences. PPP1R9A+/- neurons exhibited pronounced hyperspinogenesis and increased neuritic complexity, indicative of aberrant structural maturation; however, whole-cell patch-clamp recordings revealed impaired intrinsic excitability, including reduced action potential firing, altered waveform properties, and defective axo-somatic coupling, uncovering a striking dissociation between neuronal morphology and function. Long-read single-cell transcriptomics and quantitative proteomics identified coordinated downregulation of ion channel and synaptic transmission pathways, including genes essential for sodium channel function and glutamatergic signaling, together with disruption of synaptic vesicle cycling, axon guidance, and neurodevelopmental programs. Pseudotime trajectory analysis further demonstrated delayed neuronal differentiation, with mutant neurons accumulating at intermediate developmental states rather than acquiring mature cortical identities. Importantly, molecular rescue experiments confirmed causality, as restoration of full-length PPP1R9A expression robustly normalized transcriptional and synaptic signaling programs, whereas allele-specific antisense oligonucleotide-mediated suppression of the mutant transcript achieved only partial rescue. Taken together, these findings establish PPP1R9A haploinsufficiency as a driver of impaired molecular, electrophysiological, and developmental maturation in human cortical neurons, providing a human-specific mechanistic framework linking reduced Neurabin I dosage to neurodevelopmental and psychiatric disease risk.
The transcriptional mechanisms that maintain adult Parvalbumin (PV) interneuron function and cortical network stability remain poorly understood. We previously showed that the inactivation in GABAergic neurons of Dlx5/6, coding for transcription factors, disrupts social interaction and reduces PV interneuron density in the prefrontal cortex. Here, combining transcriptional and histological analyses with ex vivo electrophysiological and in vivo electroencephalographical (EEG) recordings, we show that Dlx5/6 regulate a molecular program controlling perineuronal net (PNN) homeostasis in the adult cortex. Dlx5/6 inactivation dysregulated the expression of multiple PNN-associated genes and induced region-specific remodelling of PNN mesh architecture in the prefrontal and somatosensory cortices. These structural changes were accompanied by alterations in excitatory and inhibitory synaptic organization and by a disrupted coupling between local PNN structure and synaptic properties. Ex vivo electrophysiological recordings revealed that fast-spiking interneurons displayed altered intrinsic properties and reduced excitatory synaptic drive in a region-specific manner, while EEG recordings during social interaction showed impaired recruitment of prefrontal gamma oscillations. Together, these findings identify Dlx5/6 as regulators of adult PV interneuron stability, linking extracellular matrix homeostasis to synaptic organization and cortical network dynamics. More broadly, it provides a new mechanistic framework connecting Dlx5/6 function to PV-related pathological phenotypes, including neuropsychiatric disorders. GRAPHICAL ABSTRACT