Structural and Lipidomic Alterations of Striatal Myelin in 16p11.2 Deletion Mouse Model of Autism Spectrum Disorder

The "don't eat me" signal CD47 is associated with microglial phagocytosis defects and autism-like behaviors in 16p11.2 deletion mice

Various pathological characteristics of autism spectrum disorder (ASD) stem from abnormalities in brain resident immune cells, specifically microglia, to prune unnecessary synapses or neural connections during early development. Animal models of ASD exhibit an abundance of synapses in different brain regions, which is strongly linked to the appearance of ASD behaviors. Overexpression of CD47 on neurons acts as a "don't eat me" signal, safeguarding synapses from inappropriate pruning by microglia. Indeed, CD47 overexpression occurs in 16p11.2 deletion carriers, causing decreased synaptic phagocytosis and the manifestation of ASD characteristics. However, the role of CD47 in synaptic pruning impairment leading to ASD phenotypes in the 16p11.2 deletion mouse model is unclear. Moreover, whether blocking CD47 can alleviate ASD mice's behavioral deficits remains unknown. Here, we demonstrate a strong link between increased CD47 expression, decreased microglia phagocytosis capacity, and increased impairment in social novelty preference in the 16p11.2 deletion mice. The reduction in microglia phagocytosis caused a rise in excitatory synapses and transmission in the prefrontal cortex of 16p11.2 deletion mice. Importantly, blocking CD47 using a specific CD47 antibody or reducing CD47 expression using a specific short hairpin RNA (shRNA) enhanced the microglia phagocytosis and reduced excitatory transmission. Reduction in CD47 expression improved social novelty preference deficits in 16p11.2 mice. These findings demonstrate that CD47 is associated with the ASD phenotypes in the 16p11.2 deletion mice and could be a promising target for the development of treatment for ASD.

Gut microbial GABA imbalance emerges as a metabolic signature in mild autism spectrum disorder linked to overrepresented Escherichia

Gut microbiota (GM) alterations have been implicated in autism spectrum disorder (ASD), yet the specific functional architecture remains elusive. Here, employing multi-omics approaches, we investigate stool samples from two distinct cohorts comprising 203 children with mild ASD or typical development. In our screening cohort, regression-based analysis for metabolomic profiling identifies an elevated γ-aminobutyric acid (GABA) to glutamate (Glu) ratio as a metabolic signature of ASD, independent of age and gender. In the validating cohort, we affirm the GABA/Glu ratio as an ASD diagnostic indicator after adjusting for geography, age, gender, and specific food-consuming frequency. Integrated analysis of metabolomics, 16S rRNA sequencing, and metagenomics reveals a correlation between overrepresented Escherichia and disrupted GABA metabolism. Furthermore, we observe social behavioral impairments in weaning mice transplanted with E. coli, suggesting a potential link to ASD symptomatology. Collectively, these findings provide insights into potential diagnostic and therapeutic strategies aimed at evaluating and restoring gut microbial neurotransmitter homeostasis.

Mice with 16p11.2 Deletion and Duplication Show Alterations in Biological Processes Associated with White Matter

Deletion and duplication in the human 16p11.2 chromosomal region are closely linked to neurodevelopmental disorders, specifically autism spectrum disorder. Data from neuroimaging studies suggest white matter microstructure aberrations across these conditions. In 16p11.2 deletion and duplication carriers, potential gene dosage effects may impact white matter organisation, contributing to phenotypes including impaired cognition. However, the biological mechanisms underlying this white matter pathology remain unclear. To bridge this knowledge gap, we utilised mouse models of 16p11.2 deletion and duplication to explore changes in corpus callosum oligodendrocytes, myelination, axon caliber, and astrocytes. Immunofluorescence staining was employed to measure lineage and mature oligodendrocyte numbers, as well as myelin basic protein and glial fibrillary acidic protein fluorescence intensity. Transmission electron microscopy was utilised to evaluate axonal structural alterations related to myelin, such as myelinated axon percentage, diameter, myelin thickness, and g-ratio. Our findings reveal changes in the number of mature oligodendrocytes, myelination levels, axon diameter, and astrocytes in the corpus callosum of mice with 16p11.2 deletion and duplication. Deletion mice displayed a tendency toward reduced counts of mature oligodendrocytes and myelination levels, while duplication mice exhibited a notable increase. Axon diameter variations included a significant increase in axon diameter and myelin thickness in both deletion and duplication mice, but with irregular structure in duplication mice. Variances in astrocytes between genotypes showed significant early increases in development for both deletion and duplication mice compared to wild-type mice, with this rise sustained in duplication mice but significantly diminished in deletion mice at a later stage. Our research reveals changes in the biological mechanisms impacting white matter. Comparison of reciprocal trends in 16p11.2 deletion and duplication mice with wild-type mice suggests the possibility of gene dosage effects. Identification of these mechanisms offers an initial step in unveiling therapeutic targets for associated neurodevelopmental disorder phenotypes.

Neuroglia in autism spectrum disorders

Autism spectrum disorder (ASD) is characterized by difficulties in social interaction, communication, and repetitive behavior, typically diagnosed during early childhood and attributed to altered neuronal network connectivity. Several genetic and environmental risk factors contribute to ASD, including pre- or early life immune activation, which can trigger microglial and astroglial reactivity, impacting early neurodevelopment. In ASD, astrocytes show altered glutamate metabolism, directly influencing neuronal network activity, while microglia display impaired synaptic pruning, an essential developmental process for the refinement of neuronal connections. Additionally, reduced myelination in specific cortical and subcortical regions may affect brain connectivity in ASD, with white matter integrity correlating with the severity of the disorder, suggesting an important role for oligodendrocytes and myelin in ASD. This chapter provides an overview of current literature on the role of neuroglia cells in ASD, with a focus on immune activation, glutamate signaling, synaptic pruning, and myelination.

GPR158 in pyramidal neurons mediates social novelty behavior via modulating synaptic transmission in male mice

Impairment in social communication skills is a hallmark feature of autism spectrum disorder (ASD). The role of G-protein-coupled receptor 158 (GPR158) in ASD remains largely unexplored. In this study, we observed that both constitutive and cell-/tissue-specific knockouts of Gpr158 in pyramidal neurons or the medial prefrontal cortex (mPFC) result in impaired novelty preference, while sociability remains unaffected in male mice. Notably, the loss of GPR158 leads to a significant decline in excitatory synaptic transmission, characterized by a reduction in glutamate vesicles, as well as the expression and phosphorylation of GluN2B in the mPFC. We successfully rescue the phenotype of social novelty deficits either by reintroducing GPR158 in the mPFC of Gpr158 deficient mice or by chemogenetic activation of pyramidal neurons where Gpr158 is specifically ablated. Our findings indicate that GPR158 in pyramidal neurons plays a specific role in modulating social novelty and may represent a potential target for treating social disorders.

Discovering the gene-brain-behavior link in autism via generative machine learning

Autism is traditionally diagnosed behaviorally but has a strong genetic basis. A genetics-first approach could transform understanding and treatment of autism. However, isolating the gene-brain-behavior relationship from confounding sources of variability is a challenge. We demonstrate a novel technique, 3D transport-based morphometry (TBM), to extract the structural brain changes linked to genetic copy number variation (CNV) at the 16p11.2 region. We identified two distinct endophenotypes. In data from the Simons Variation in Individuals Project, detection of these endophenotypes enabled 89 to 95% test accuracy in predicting 16p11.2 CNV from brain images alone. Then, TBM enabled direct visualization of the endophenotypes driving accurate prediction, revealing dose-dependent brain changes among deletion and duplication carriers. These endophenotypes are sensitive to articulation disorders and explain a portion of the intelligence quotient variability. Genetic stratification combined with TBM could reveal new brain endophenotypes in many neurodevelopmental disorders, accelerating precision medicine, and understanding of human neurodiversity.

The gut metabolite indole-3-propionic acid activates ERK1 to restore social function and hippocampal inhibitory synaptic transmission in a 16p11.2 microdeletion mouse model

BACKGROUND

Microdeletion of the human chromosomal region 16p11.2 (16p11.2+ / - ) is a prevalent genetic factor associated with autism spectrum disorder (ASD) and other neurodevelopmental disorders. However its pathogenic mechanism remains unclear, and effective treatments for 16p11.2+ / -  syndrome are lacking. Emerging evidence suggests that the gut microbiota and its metabolites are inextricably linked to host behavior through the gut-brain axis and are therefore implicated in ASD development. Despite this, the functional roles of microbial metabolites in the context of 16p11.2+ / -  are yet to be elucidated. This study aims to investigate the therapeutic potential of indole-3-propionic acid (IPA), a gut microbiota metabolite, in addressing behavioral and neural deficits associated with 16p11.2+ / - , as well as the underlying molecular mechanisms.

RESULTS

Mice with the 16p11.2+ / -  showed dysbiosis of the gut microbiota and a significant decrease in IPA levels in feces and blood circulation. Further, these mice exhibited significant social and cognitive memory impairments, along with hyperactivation of hippocampal dentate gyrus neurons and reduced inhibitory synaptic transmission in this region. However, oral administration of IPA effectively mitigated the histological and electrophysiological alterations, thereby ameliorating the social and cognitive deficits of the mice. Remarkably, IPA treatment significantly increased the phosphorylation level of ERK1, a protein encoded by the Mapk3 gene in the 16p11.2 region, without affecting the transcription and translation of the Mapk3 gene.

CONCLUSIONS

Our study reveals that 16p11.2+ / -  leads to a decline in gut metabolite IPA levels; however, IPA supplementation notably reverses the behavioral and neural phenotypes of 16p11.2+ / -  mice. These findings provide new insights into the critical role of gut microbial metabolites in ASD pathogenesis and present a promising treatment strategy for social and cognitive memory deficit disorders, such as 16p11.2 microdeletion syndrome. Video Abstract.

Mass Spectrometry Analysis of the Human Brain Sphingolipidome

In recent decades, mass spectrometry-based lipidomics has provided a fertile environment for scientific investigations of biochemical and mechanistic processes in biological systems. Notably, this approach has been used to characterize physiological and pathological processes relevant to the central nervous system by identifying changes in the sphingolipid content in the brain, cerebral spinal fluid, and blood plasma. However, despite a preponderance of studies identifying correlations between specific lipids and disease progression, this powerful resource has not yet substantively translated into clinically useful diagnostic assays. Part of this gap may be explained by insufficient depth of the lipidomic profiles in many studies, by lab-to-lab inconsistencies in methodology, and a lack of absolute quantification. These issues limit the identification of specific molecular species and the harmonization of results across independent studies. In this chapter, we contextualize these issues with recent reports identifying correlations between brain lipids and neurological diseases, and we describe the workflow our group has optimized for analysis of the blood plasma sphingolipidome, adapted to the characterization of the human brain tissue.

Neuroimaging Findings in Neurodevelopmental Copy Number Variants: Identifying Molecular Pathways to Convergent Phenotypes

Genomic copy number variants (CNVs) are associated with a high risk of neurodevelopmental disorders. A growing body of genetic studies suggests that these high-risk genetic variants converge in common molecular pathways and that common pathways also exist across clinically distinct disorders, such as schizophrenia and autism spectrum disorder. A key question is how common molecular mechanisms converge into similar clinical outcomes. We review emerging evidence for convergent cognitive and brain phenotypes across distinct CNVs. Multiple CNVs were shown to have similar effects on core sensory, cognitive, and motor traits. Emerging data from multisite neuroimaging studies have provided valuable information on how these CNVs affect brain structure and function. However, most of these studies examined one CNV at a time, making it difficult to fully understand the proportion of shared brain effects. Recent studies have started to combine neuroimaging data from multiple CNV carriers and identified similar brain effects across CNVs. Some early findings also support convergence in CNV animal models. Systems biology, through integration of multilevel data, provides new insights into convergent molecular mechanisms across genetic risk variants (e.g., altered synaptic activity). However, the link between such key molecular mechanisms and convergent psychiatric phenotypes is still unknown. To better understand this link, we need new approaches that integrate human molecular data with neuroimaging, cognitive, and animal model data, while taking into account critical developmental time points. Identifying risk mechanisms across genetic loci can elucidate the pathophysiology of neurodevelopmental disorders and identify new therapeutic targets for cross-disorder applications.

SHANK3 deficiency leads to myelin defects in the central and peripheral nervous system

Mutations or deletions of the SHANK3 gene are causative for Phelan–McDermid syndrome (PMDS), a syndromic form of autism spectrum disorders (ASDs). We analyzed Shank3Δ11(−/−) mice and organoids from PMDS individuals to study effects on myelin. SHANK3 was found to be expressed in oligodendrocytes and Schwann cells, and MRI analysis of Shank3Δ11(−/−) mice revealed a reduced volume of the corpus callosum as seen in PMDS patients. Myelin proteins including myelin basic protein showed significant temporal and regional differences with lower levels in the CNS but increased amounts in the PNS of Shank3Δ11(−/−) animals. Node, as well as paranode, lengths were increased and ultrastructural analysis revealed region-specific alterations of the myelin sheaths. In PMDS hiPSC-derived cerebral organoids we observed an altered number and delayed maturation of myelinating cells. These findings provide evidence that, in addition to a synaptic deregulation, impairment of myelin might profoundly contribute to the clinical manifestation of SHANK3 deficiency.

Microduplication of 16p11.2 locus Potentiates Hypertrophic Obesity in Association with Imbalanced Triglyceride Metabolism in White Adipose Tissue

SCOPE

Copy number variation (CNV) of 16p11.2 is a common genetic factor contributing to the etiology of abnormal weight status, while the underlying mechanism is not fully elucidated yet.

METHODS AND RESULTS

The 16p11.2 CNV mouse model with microduplication of the 7Slx1b-Sept1 region (dp/+) is evaluated under normal chow conditions. Compared to the wild type littermates (WT), the dp/+ mice exhibit obvious obese phenotype characterized by significant increase in body mass index, fat pad mass, and fat ratio, with visceral-dominant fat deposits at 12-week age. White adipose tissue (WAT), liver tissue, and plasma are sampled to assess the comorbid metabolic syndrome. In dp/+ mice, histopathologic analyses reveal hypertrophic adipocytes and hepatic steatosis; serological examinations show hyperlipemia and hyperinsulinemia. Further, by comparing lipidomic and transcriptomic profiling of epididymal WAT between dp/+ and WT mice, the study finds the triglyceride (TG) accumulation in dp/+ mice in association with the dysfunction of lipid droplets. Validation of TG-metabolism-associated genes in WAT and in primary cultured adipocytes show enhanced TG synthesis and declined TG hydrolysis in the dp/+ model.

CONCLUSION

This study elucidates that the imbalanced TG synthesis/hydrolysis in adipocytic lipid droplets may contribute to the hypertrophic obesity and metabolic disorders in mice with 16p11.2 microduplication.