Bsn conditional knockout mice provide strong evidence for a causal involvement of GABAergic synapses in the emergence of ASD-related behavioral and physiological phenotypes.
Abstract
Synaptic dysfunction and resulting imbalance of excitatory vs. inhibitory transmission are fundamental aspects of autism spectrum disorders (ASD). Here we addressed the role of inhibitory synapse disturbances in ASD employing mice with a conditional ablation in GABAergic forebrain interneurons of the presynaptic active zone scaffolding protein Bassoon (Bsn), a key factor in synaptic development, activity and maintenance. The conditional Bsn gene knockout resulted in a reduction of synaptic vesicles and reduced synaptic efficacy of affected inhibitory synapses as well as diminished GABAergic inhibition of hippocampal pyramidal neurons. Bsn mutants further displayed a reconfiguration of the hippocampal synaptic network in vivo, as seen in subfield-specific changes of inhibitory synaptic markers and reduced parvalbumin interneuron labeling, culminating in disturbance of hippocampal network activity patterns and profound mitochondrial and metabolic dysregulation. Importantly, the mutant mice developed behavioral abnormalities reminiscent of ASD including widespread social behavioral deficits and novelty-induced hyperarousal with altered motor behavior, increased anxiety and epileptiform activity. Bsn conditional knockout mice thus provide strong evidence for a causal involvement of GABAergic synapses in the emergence of ASD-related behavioral and physiological phenotypes.
Fragile X Syndrome (FXS) is a leading genetic cause of autism‐like symptoms and intellectual disability, resulting from epigenetic silencing of the Fragile X messenger ribonucleoprotein (Fmr1) gene. Recent observations in FXS models suggest abnormal GABAergic signaling and excitation/inhibition imbalance may underlie the pathophysiology of FXS. As most studies have focused on neuronal mechanisms, the role of astrocytes in mediating defective inhibition in FXS is largely unknown. Our previous study showed the effects of astrocyte‐specific Fmr1 conditional knockout (cKO) on cortical inhibitory circuit development using EEGs that were attributed to excess GABA synthesis by Fmr1 KO astrocytes. As the hippocampus plays an important role in spatial learning and social behaviors that are altered in FXS, in this study we focused on dissecting the mechanism of abnormal inhibition in the CA1 hippocampus using slice electrophysiology. While we observed a reduction in the expression of synaptic GABAA receptor subunits and overall density of perisomatic GABAergic synapses in cKO, the amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) was enhanced in pyramidal cells. In contrast to changes in phasic inhibition, astrocyte‐specific cKO did not affect tonic inhibition in pyramidal cells or the expression of extrasynaptic GABAA receptors, which were both impaired in global KO. Our study suggests that elevated levels of extracellular GABA due to abnormal GABA transport in cKO astrocytes may contribute to the enhanced power of sIPSCs and potentially affect parvalbumin (PV) cell activity. Acute inhibition of GABA transport in astrocytes enhanced PV expression and improved spatial memory and socialization in cKO mice. Our work supports astrocytes as key players in the development and regulation of hippocampal inhibitory circuits in FXS, potentially through GABA transport.
Victoria A. Wagner, Sarah Maples, Ritika Thapa et al.· Journal of Neurochemistry· 0 citations
Autism spectrum disorder (ASD) is a neurodevelopmental disorder with an unclear pathogenesis. Growing evidence implicates excitatory/inhibitory (E/I) imbalance in ASD pathophysiology, prompting an investigation into gamma-aminobutyric acid (GABA)-mediated inhibitory transmission. The transcription factor Paired Box 2 (Pax2), essential for GABAergic interneuron specification, participates in the regulation of neural developmental processes. Our previous work demonstrated an E/I imbalance in the neurotransmitter system and reduced GABAARα2-positive neurons in the prefrontal cortex (PFC) of Pax2 neuron-specific deletion mice, though the internal molecular regulatory mechanism remained elusive. In this study, we generated GABAergic neuron-specific Pax2 knockdown mice via injection of AAV-shPax2 virus and comprehensively evaluated ASD-related behaviors, revealing autism-like behaviors, such as impaired social novelty and repetitive behaviors. Molecular analysis revealed upregulation of Tcf7l2, a key downstream mediator of the Wnt/β-catenin signaling pathway. Functional assessment confirmed hyperactivation of the Wnt/β-catenin signaling pathway in GABAergic neuron Pax2 knockdown mice. Notably, pharmacological intervention with esculetin, an inhibitor of the Wnt/β-catenin pathway, ameliorated the observed autism-like behaviors. These findings establish a pathogenic axis wherein GABAergic neuron-specific Pax2 deficiency induces hyperactivation of the Wnt/β-catenin signaling pathway and disrupts E/I balance, ultimately driving autism-like behavioral phenotypes. Our results further identify inhibition of Wnt/β-catenin signaling as a promising therapeutic strategy for ASD.
It is demonstrated that ASD-related alterations are not static but evolve across adulthood, revealing a multi-level reorganization of behavioral, synaptic, and structural features.
Mathieu Thabault, Cloé Fernandes-Gomes, Cloé Alcaraz et al.· Neurobiology of Disease· 0 citations
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.
Alec H. Marshall, Meretta A. Hanson, Danielle J. Boyle et al.· Experimental Neurology· 0 citations
These 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, Marc Dos Santos, Natalia Khalatyan et al.· Proceedings of the National...· 0 citations
In autism spectrum disorder (ASD), children can exhibit a regressive phenotype with loss of previously acquired social and language skills in the first years of life. While the role of the GABAergic system in shaping neural circuits during development has been largely studied, its potential involvement in regressive phenotypes remains unclear. Here, we tracked the social and sensory development in Synapsin2 knockout (Syn2KO) mice, a model of ASD characterized by defective inhibitory tonic current, social deficits, and epilepsy in adulthood. We show that, after a transient early phase of impaired vocalization, young (PND 30) Syn2KO mice reached a normal social behavior. However, social behavior was regressively lost in adult (PND 120) mice, with the absence of vocalizations during the male-female interaction test associated with a drastic degeneration of the preoptic area-periaqueductal gray vocal GABAergic circuit. This deterioration began at earlier stages but was behaviorally latent. Adult Syn2KO mice also displayed sensory dysfunctions and dysregulation of the GABAergic system in the integrative posterior parietal cortex, with hyper-responsiveness of bimodal light- and sound-sensitive neurons that paralleled the social decline. Boosting tonic inhibition from birth with chronic treatment with the GABAA receptor agonist gaboxadol fully reversed social deficits, restored the integrity of vocal circuits, and the multimodal integration of sensory inputs. These results show that social regression in the Syn2KO model is a multiphase process characterized by early signs, a latent period of typical development, and a subsequent decline that can be reversed by enhancing tonic inhibition from development onward.
Lorenzo Ciano, Sebastian Sulis Sato, F. Galluzzi et al.· Molecular Psychiatry· 0 citations
