Autism-linked Cullin3 germline haploinsufficiency impacts cytoskeletal dynamics and cortical neurogenesis through RhoA signaling

Integrated multi-omic characterizations of the synapse reveal RNA processing factors and ubiquitin ligases associated with neurodevelopmental disorders

The molecular composition of the excitatory synapse is incompletely defined due to its dynamic nature across developmental stages and neuronal populations. To address this gap, we apply proteomic mass spectrometry to characterize the synapse in multiple biological models, including the fetal human brain and human induced pluripotent stem cell (hiPSC)-derived neurons. To prioritize the identified proteins, we develop an orthogonal multi-omic screen of genomic, transcriptomic, interactomic, and structural data. This data-driven framework identifies proteins with key molecular features intrinsic to the synapse, including characteristic patterns of biophysical interactions and cross-tissue expression. The multi-omic analysis captures synaptic proteins across developmental stages and experimental systems, including 493 synaptic candidates supported by proteomics. We further investigate three such proteins that are associated with neurodevelopmental disorders-Cullin 3 (CUL3), DEAD-box helicase 3 X-linked (DDX3X), and Y-box binding protein-1 (YBX1)-by mapping their networks of physically interacting synapse proteins or transcripts. Our study demonstrates the potential of an integrated multi-omic approach to more comprehensively resolve the synaptic architecture.

Cullin-RING Ubiquitin Ligases in Neurodevelopment and Neurodevelopmental Disorders

Ubiquitination is a dynamic and tightly regulated post-translational modification essential for modulating protein stability, trafficking, and function to preserve cellular homeostasis. This process is orchestrated through a hierarchical enzymatic cascade involving three key enzymes: the E1 ubiquitin-activating enzyme, the E2 ubiquitin-conjugating enzyme, and the E3 ubiquitin ligase. The final step of ubiquitination is catalyzed by the E3 ubiquitin ligase, which facilitates the transfer of ubiquitin from the E2 enzyme to the substrate, thereby dictating which proteins undergo ubiquitination. Emerging evidence underscores the critical roles of ubiquitin ligases in neurodevelopment, regulating fundamental processes such as neuronal polarization, axonal outgrowth, synaptogenesis, and synaptic function. Mutations in genes encoding ubiquitin ligases and the consequent dysregulation of these pathways have been increasingly implicated in a spectrum of neurodevelopmental disorders, including autism spectrum disorder, intellectual disability, and attention-deficit/hyperactivity disorder. This review synthesizes current knowledge on the molecular mechanisms underlying neurodevelopment regulated by Cullin-RING ubiquitin ligases-the largest subclass of ubiquitin ligases-and their involvement in the pathophysiology of neurodevelopmental disorders. A deeper understanding of these mechanisms holds significant promise for informing novel therapeutic strategies, ultimately advancing clinical outcomes for individuals affected by neurodevelopmental disorders.

The neurobiological mechanisms underlying the effects of exercise interventions in autistic individuals

Autism spectrum disorder is a pervasive and heterogeneous neurodevelopmental condition characterized by social communication difficulties and rigid, repetitive behaviors. Owing to the complex pathogenesis of autism, effective drugs for treating its core features are lacking. Nonpharmacological approaches, including education, social-communication, behavioral and psychological methods, and exercise interventions, play important roles in supporting the needs of autistic individuals. The advantages of exercise intervention, such as its low cost, easy implementation, and high acceptance, have garnered increasing attention. Exercise interventions can effectively improve the core features and co-occurring conditions of autism, but the underlying neurobiological mechanisms are unclear. Abnormal changes in the gut microbiome, neuroinflammation, neurogenesis, and synaptic plasticity may individually or interactively be responsible for atypical brain structure and connectivity, leading to specific autistic experiences and characteristics. Interestingly, exercise can affect these biological processes and reshape brain network connections, which may explain how exercise alleviates core features and co-occurring conditions in autistic individuals. In this review, we describe the definition, diagnostic approach, epidemiology, and current support strategies for autism; highlight the benefits of exercise interventions; and call for individualized programs for different subtypes of autistic individuals. Finally, the possible neurobiological mechanisms by which exercise improves autistic features are comprehensively summarized to inform the development of optimal exercise interventions and specific targets to meet the needs of autistic individuals.

Sex-specific effects of prenatal bisphenol A exposure on transcriptome-interactome profiles of autism candidate genes in neural stem cells from offspring hippocampus

Bisphenol A (BPA), an endocrine-disrupting chemical, is increasingly linked to the pathogenesis of autism spectrum disorder (ASD). This study investigates the effects of prenatal BPA exposure on neural stem cells (NSCs) from the hippocampi of rat offspring, a brain region critical for neurodevelopment and implicated in ASD. Pregnant rats were administered with BPA or vehicle control once daily via oral gavage from gestational day 1 until parturition. NSCs were isolated from the offspring's hippocampi on postnatal day 1, and RNA sequencing was performed to examine transcriptomic alterations. Differentially expressed genes (DEGs) were identified through RNA-seq and further analyzed using Ingenuity Pathway Analysis (IPA) to explore disrupted pathways. In addition, in vitro proliferation assays were conducted, utilizing immunofluorescence staining for Sox2, a stem cell marker, and BrdU to quantify proliferating NSCs. Our results revealed that prenatal BPA exposure induced sex-specific alterations in NSC gene expression, with ASD-related genes such as Atp1a3, Nefl, and Grin1 being particularly dysregulated in male offspring. Moreover, sex-specific changes in NSC proliferation were observed. The study underscores BPA's potential as an environmental risk factor for ASD, emphasizing the need for further research into its role in sex-specific neurodevelopmental effects.

Gastrodin Ameliorates Post-Stroke Depressive-Like Behaviors Through Cannabinoid-1 Receptor-Dependent PKA/RhoA Signaling Pathway

Post-stroke depression (PSD) is a significant complication in stroke patients, increases long-term mortality, and exaggerates ischemia-induced brain injury. However, the underlying molecular mechanisms and effective therapeutic targets related to PSD have remained elusive. Here, we employed an animal behavioral model of PSD by combining the use of middle cerebral artery occlusion (MCAO) followed by spatial restraint stress to study the molecular underpinnings and potential therapies of PSD. Interestingly, we found that sub-chronic application of gastrodin (Gas), a traditional Chinese medicinal herb Gastrodia elata extraction, relieved depression-related behavioral deficits, increased the impaired expression of synaptic transmission-associated proteins, and restored the altered spine density in hippocampal CA1 of PSD animals. Furthermore, our results indicated that the anti-PSD effect of Gas was dependent on membrane cannabinoid-1 receptor (CB1R) expression. The contents of phosphorated protein kinase A (p-PKA) and phosphorated Ras homolog gene family member A (p(ser188)-RhoA) were decreased in the hippocampus of PSD-mice, which was reversed by Gas treatment, and CB1R depletion caused a diminished efficacy of Gas on p-PKA and p-RhoA expression. In addition, the anti-PSD effect of Gas was partially blocked by PKA inhibition or RhoA activation, indicating that the anti-PSD effect of Gas is associated with the CB1R-mediated PKA/RhoA signaling pathway. Together, our findings revealed that Gas treatment possesses protective effects against the post-stroke depressive-like state; the CB1R-involved PKA/RhoA signaling pathway is critical in mediating Gas's anti-PSD potency, suggesting that Gas application may be beneficial in the prevention and adjunctive treatment of PSD.

The Cul3 ubiquitin ligase engages Insomniac as an adaptor to impact sleep and synaptic homeostasis

Mutations of the Cullin-3 (Cul3) E3 ubiquitin ligase are associated with autism and schizophrenia, neurological disorders characterized by sleep disturbances and altered synaptic function. Cul3 engages dozens of adaptor proteins to recruit hundreds of substrates for ubiquitination, but the adaptors that impact sleep and synapses remain ill-defined. Here we implicate Insomniac (Inc), a conserved protein required for normal sleep and synaptic homeostasis in Drosophila, as a Cul3 adaptor. Inc binds Cul3 in vivo, and mutations within the N-terminal BTB domain of Inc that weaken Inc-Cul3 associations impair Inc activity, suggesting that Inc function requires binding to the Cul3 complex. Deletion of the conserved C-terminus of Inc does not alter Cul3 binding but abolishes Inc activity in the context of sleep and synaptic homeostasis, indicating that the Inc C-terminus has the properties of a substrate recruitment domain. Mutation of a conserved, disease-associated arginine in the Inc C-terminus also abolishes Inc function, suggesting that this residue is vital for recruiting Inc targets. Inc levels are negatively regulated by Cul3 in neurons, consistent with Inc degradation by autocatalytic ubiquitination, a hallmark of Cullin adaptors. These findings link Inc and Cul3 in vivo and support the notion that Inc-Cul3 complexes are essential for normal sleep and synaptic function. Furthermore, these results indicate that dysregulation of conserved substrates of Inc-Cul3 complexes may contribute to altered sleep and synaptic function in autism and schizophrenia associated with Cul3 mutations.

Familial Hyperkalemic Hypertension

The rare disease Familial Hyperkalemic Hypertension (FHHt) is caused by mutations in the genes encoding Cullin 3 (CUL3), Kelch-Like 3 (KLHL3), and two members of the With-No-Lysine [K] (WNK) kinase family, WNK1 and WNK4. In the kidney, these mutations ultimately cause hyperactivation of NCC along the renal distal convoluted tubule. Hypertension results from increased NaCl retention, and hyperkalemia by impaired K + secretion by downstream nephron segments. CUL3 and KLHL3 are now known to form a ubiquitin ligase complex that promotes proteasomal degradation of WNK kinases, which activate downstream kinases that phosphorylate and thus activate NCC. For CUL3, potent effects on the vasculature that contribute to the more severe hypertensive phenotype have also been identified. Here we outline the in vitro and in vivo studies that led to the discovery of the molecular pathways regulating NCC and vascular tone, and how FHHt-causing mutations disrupt these pathways. Potential mechanisms for variability in disease severity related to differential effects of each mutation on the kidney and vasculature are described, and other possible effects of the mutant proteins beyond the kidney and vasculature are explored. © 2024 American Physiological Society. Compr Physiol 14:5839-5874, 2024.

Ras, RhoA, and vascular pharmacology in neurodevelopment and aging

Small GTPases Ras, Rac, and RhoA are crucial regulators of cellular functions. They also act in dysregulated cell proliferation and transformation. Multiple publications have focused on illuminating their roles and mechanisms, including in immune system pathologies. Their functions in neurology-related diseases, neurodegeneration and neurodevelopment, are also emerging, as well as their potential as pharmacological targets in both pathologies. Observations increasingly suggest that these pathologies may relate to activation (or suppression) of signaling by members of the Ras superfamily, especially Ras, Rho, and Rac isoforms, and components of their signaling pathways. Germline (or embryonic) mutations that they harbor are responsible for neurodevelopmental disorders, such as RASopathies, autism spectrum disorder, and dilated cardiomyopathy. In aging, they promote neurodegenerative diseases, with Rho GTPase featuring in their pharmacology, as in the case of Alzheimer's disease (AD). Significantly, drugs with observed anti-AD activity, particularly those involved in cardiovascular systems, are associated with the RhoA signaling, as well as cerebral vasculature in brain development and aging. This leads us to suggest that anti-AD drugs could inform neurodevelopmental disorders, including pediatric low-grade gliomas pharmacology. Neurodevelopmental disorders associated with RhoA, like autism, are also connected with vascular systems, thus could be targets of vascular system-connected drugs.

Ubiquitin system mutations in neurological diseases

Neuronal ubiquitin balance impacts the fate of countless cellular proteins, and its disruption is associated with various neurological disorders. The ubiquitin system is critical for proper neuronal cell state transitions and the clearance of misfolded or aggregated proteins that threaten cellular integrity. This article reviews the state of and recent advancements in our understanding of the disruptions to components of the ubiquitin system, in particular E3 ligases and deubiquitylases, in neurodevelopmental and neurodegenerative diseases. Specific focus is on enzymes with recent progress in their characterization, including identifying enzyme-substrate pairs, the use of stem cell and animal models, and the development of therapeutics for ubiquitin-related diseases.

An Anti-Invasive Role for Mdmx through the RhoA GTPase under the Control of the NEDD8 Pathway

Mdmx (Mdm4) is established as an oncogene mainly through repression of the p53 tumour suppressor. On the other hand, anti-oncogenic functions for Mdmx have also been proposed, but the underlying regulatory pathways remain unknown. Investigations into the effect of inhibitors for the NEDD8 pathway in p53 activation, human cell morphology, and in cell motility during gastrulation in Xenopus embryos revealed an anti-invasive function of Mdmx. Through stabilisation and activation of the RhoA GTPase, Mdmx is required for the anti-invasive effects of NEDDylation inhibitors. Mechanistically, through its Zn finger domain, Mdmx preferentially interacts with the inactive GDP-form of RhoA. This protects RhoA from degradation and allows for RhoA targeting to the plasma membrane for its subsequent activation. The effect is transient, as prolonged NEDDylation inhibition targets Mdmx for degradation, which subsequently leads to RhoA destabilisation. Surprisingly, Mdmx degradation requires non-NEDDylated (inactive) Culin4A and the Mdm2 E3-ligase. This study reveals that Mdmx can control cell invasion through RhoA stabilisation/activation, which is potentially linked to the reported anti-oncogenic functions of Mdmx. As inhibitors of the NEDD8 pathway are in clinical trials, the status of Mdmx may be a critical determinant for the anti-tumour effects of these inhibitors.

Autism-associated CHD8 controls reactive gliosis and neuroinflammation via remodeling chromatin in astrocytes

Reactive changes of glial cells during neuroinflammation impact brain disorders and disease progression. Elucidating the mechanisms that control reactive gliosis may help us to understand brain pathophysiology and improve outcomes. Here, we report that adult ablation of autism spectrum disorder (ASD)-associated CHD8 in astrocytes attenuates reactive gliosis via remodeling chromatin accessibility, changing gene expression. Conditional Chd8 deletion in astrocytes, but not microglia, suppresses reactive gliosis by impeding astrocyte proliferation and morphological elaboration. Astrocyte Chd8 ablation alleviates lipopolysaccharide-induced neuroinflammation and septic-associated hypothermia in mice. Astrocytic CHD8 plays an important role in neuroinflammation by altering the chromatin landscape, regulating metabolic and lipid-associated pathways, and astrocyte-microglia crosstalk. Moreover, we show that reactive gliosis can be directly mitigated in vivo using an adeno-associated virus (AAV)-mediated Chd8 gene editing strategy. These findings uncover a role of ASD-associated CHD8 in the adult brain, which may warrant future exploration of targeting chromatin remodelers in reactive gliosis and neuroinflammation in injury and neurological diseases.

Autism risk gene Cul3 alters neuronal morphology via caspase-3 activity in mouse hippocampal neurons

Autism Spectrum Disorders (ASDs) are neurodevelopmental disorders (NDDs) in which children display differences in social interaction/communication and repetitive stereotyped behaviors along with variable associated features. Cul3, a gene linked to ASD, encodes CUL3 (CULLIN-3), a protein that serves as a key component of a ubiquitin ligase complex with unclear function in neurons. Cul3 homozygous deletion in mice is embryonic lethal; thus, we examine the role of Cul3 deletion in early synapse development and neuronal morphology in hippocampal primary neuronal cultures. Homozygous deletion of Cul3 significantly decreased dendritic complexity and dendritic length, as well as axon formation. Synaptic spine density significantly increased, mainly in thin and stubby spines along with decreased average spine volume in Cul3 knockouts. Both heterozygous and homozygous knockout of Cul3 caused significant reductions in the density and colocalization of gephyrin/vGAT puncta, providing evidence of decreased inhibitory synapse number, while excitatory synaptic puncta vGulT1/PSD95 density remained unchanged. Based on previous studies implicating elevated caspase-3 after Cul3 deletion, we demonstrated increased caspase-3 in our neuronal cultures and decreased neuronal cell viability. We then examined the efficacy of the caspase-3 inhibitor Z-DEVD-FMK to rescue the decrease in neuronal cell viability, demonstrating reversal of the cell viability phenotype with caspase-3 inhibition. Studies have also implicated caspase-3 in neuronal morphological changes. We found that caspase-3 inhibition largely reversed the dendrite, axon, and spine morphological changes along with the inhibitory synaptic puncta changes. Overall, these data provide additional evidence that Cul3 regulates the formation or maintenance of cell morphology, GABAergic synaptic puncta, and neuronal viability in developing hippocampal neurons in culture.

The missing hallmark of health: psychosocial adaptation

The eight biological hallmarks of health that we initially postulated (Cell. 2021 Jan 7;184(1):33-63) include features of spatial compartmentalization (integrity of barriers, containment of local perturbations), maintenance of homeostasis over time (recycling & turnover, integration of circuitries, rhythmic oscillations) and an array of adequate responses to stress (homeostatic resilience, hormetic regulation, repair & regeneration). These hallmarks affect all eight somatic strata of the human body (molecules, organelles, cells, supracellular units, organs, organ systems, systemic circuitries and meta-organism). Here we postulate that mental and socioeconomic factors must be added to this 8×8 matrix as an additional hallmark of health ("psychosocial adaptation") and as an additional stratum ("psychosocial interactions"), hence building a 9×9 matrix. Potentially, perturbation of each of the somatic hallmarks and strata affects psychosocial factors and vice versa. Finally, we discuss the (patho)physiological bases of these interactions and their implications for mental health improvement.

Cullin-RING E3 ubiquitin ligase 4 regulates neurite morphogenesis during neurodevelopment

Neuritogenesis is crucial for establishing proper neuronal connections during brain development; its failure causes neurodevelopmental defects. Cullin-RING E3 ubiquitin ligase complexes participate in various neurodevelopmental processes by regulating protein stability. We demonstrated the regulatory function of Cullin-RING E3 ubiquitin ligase 4 (CRL4) in neurite morphogenesis during early neurodevelopment. Cul4a and Cul4b, the core scaffold proteins of CRL4, exhibit high expression and activation within the cytosol of developing neurons, regulated by neuronal stimulation through N-methyl D-aspartate (NMDA) receptor signaling. CRL4 also interacts with cytoskeleton-regulating proteins involved in neurite morphogenesis. Notably, genetic depletion and inhibition of cytosolic CRL4 enhance neurite extension and branching in developing neurons. Conversely, Cul4a overexpression suppresses basal and NMDA-enhanced neuritogenesis. Furthermore, CRL4 and its substrate adaptor regulate the polyubiquitination and proteasomal degradation of doublecortin protein. Collectively, our findings suggest that CRL4 ensures proper neurite morphogenesis in developing neurons by regulating cytoskeleton-regulating proteins.

Allosteric Activation of RhoA Complexed with p115-RhoGEF Deciphered by Conformational Dynamics

The Ras homologue family member A (RhoA) is a member of the Rho family, a subgroup of the Ras superfamily. RhoA interacts with the 115 kDa guanine nucleotide exchange factor (p115-RhoGEF), which assists in activation and binding with downstream effectors. Here, we use molecular dynamics (MD) simulations and essential dynamics analysis of the inactive RhoA-GDP and active RhoA-GTP, when bound to p115-RhoGEF to decipher the mechanism of RhoA activation at the structural level. We observe that inactive RhoA-GDP maintains its position near the catalytic site on the Dbl homology (DH) domain of p115-RhoGEF through the interaction of its Switch I region with the DH domain. We further show that the active RhoA-GTP is engaged in more interactions with the p115-RhoGEF membrane-bound Pleckstrin homology (PH) domain as compared to RhoA-GDP. We hypothesize that the role of the interactions between the active RhoA-GTP and the PH domain is to help release it from the DH domain upon activation. Our results support this premise, and our simulations uncover the beginning of this process and provide structural details. They also point to allosteric communication pathways that take part in RhoA activation to promote and strengthen the interaction between the active RhoA-GTP and the PH domain. Allosteric regulation also occurs among other members of the Rho superfamily. Collectively, we suggest that in the activation process, the role of the RhoA-GTP interaction with the PH domain is to release RhoA-GTP from the DH domain after activation, making it available to downstream effectors.

Neuronal knockdown of Cullin3 as a Drosophila model of autism spectrum disorder

Mutations in Cullin-3 (Cul3), a conserved gene encoding a ubiquitin ligase, are strongly associated with autism spectrum disorder (ASD). Here, we characterize ASD-related pathologies caused by neuron-specific Cul3 knockdown in Drosophila. We confirmed that neuronal Cul3 knockdown causes short sleep, paralleling sleep disturbances in ASD. Because sleep defects and ASD are linked to metabolic dysregulation, we tested the starvation response of neuronal Cul3 knockdown flies; they starved faster and had lower triacylglyceride levels than controls, suggesting defects in metabolic homeostasis. ASD is also characterized by increased biomarkers of oxidative stress; we found that neuronal Cul3 knockdown increased sensitivity to hyperoxia, an exogenous oxidative stress. Additional hallmarks of ASD are deficits in social interactions and learning. Using a courtship suppression assay that measures social interactions and memory of prior courtship, we found that neuronal Cul3 knockdown reduced courtship and learning compared to controls. Finally, we found that neuronal Cul3 depletion alters the anatomy of the mushroom body, a brain region required for memory and sleep. Taken together, the ASD-related phenotypes of neuronal Cul3 knockdown flies establish these flies as a genetic model to study molecular and cellular mechanisms underlying ASD pathology, including metabolic and oxidative stress dysregulation and neurodevelopment.

CellGO: a novel deep learning-based framework and webserver for cell-type-specific gene function interpretation

Interpreting the function of genes and gene sets identified from omics experiments remains a challenge, as current pathway analysis tools often fail to consider the critical biological context, such as tissue or cell-type specificity. To address this limitation, we introduced CellGO. CellGO tackles this challenge by leveraging the visible neural network (VNN) and single-cell gene expressions to mimic cell-type-specific signaling propagation along the Gene Ontology tree within a cell. This design enables a novel scoring system to calculate the cell-type-specific gene-pathway paired active scores, based on which, CellGO is able to identify cell-type-specific active pathways associated with single genes. In addition, by aggregating the activities of single genes, CellGO extends its capability to identify cell-type-specific active pathways for a given gene set. To enhance biological interpretation, CellGO offers additional features, including the identification of significantly active cell types and driver genes and community analysis of pathways. To validate its performance, CellGO was assessed using a gene set comprising mixed cell-type markers, confirming its ability to discern active pathways across distinct cell types. Subsequent benchmarking analyses demonstrated CellGO's superiority in effectively identifying cell types and their corresponding cell-type-specific pathways affected by gene knockouts, using either single genes or sets of genes differentially expressed between knockout and control samples. Moreover, CellGO demonstrated its ability to infer cell-type-specific pathogenesis for disease risk genes. Accessible as a Python package, CellGO also provides a user-friendly web interface, making it a versatile and accessible tool for researchers in the field.

Dissecting the Relationship Between Neuropsychiatric and Neurodegenerative Disorders

Neurodegenerative diseases (NDDs) and neuropsychiatric disorders (NPDs) are two common causes of death in elderly people, which includes progressive neuronal cell death and behavioral changes. NDDs include Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, and motor neuron disease, characterized by cognitive defects and memory impairment, whereas NPDs include depression, seizures, migraine headaches, eating disorders, addictions, palsies, major depressive disorders, anxiety, and schizophrenia, characterized by behavioral changes. Mounting evidence demonstrated that NDDs and NPDs share an overlapping mechanism, which includes post-translational modifications, the microbiota-gut-brain axis, and signaling events. Mounting evidence demonstrated that various drug molecules, namely, natural compounds, repurposed drugs, multitarget directed ligands, and RNAs, have been potentially implemented as therapeutic agents against NDDs and NPDs. Herein, we highlighted the overlapping mechanism, the role of anxiety/stress-releasing factors, cytosol-to-nucleus signaling, and the microbiota-gut-brain axis in the pathophysiology of NDDs and NPDs. We summarize the therapeutic application of natural compounds, repurposed drugs, and multitarget-directed ligands as therapeutic agents. Lastly, we briefly described the application of RNA interferences as therapeutic agents in the pathogenesis of NDDs and NPDs. Neurodegenerative diseases and neuropsychiatric diseases both share a common signaling molecule and molecular phenomenon, namely, pro-inflammatory cytokines, γCaMKII and MAPK/ERK, chemokine receptors, BBB permeability, and the gut-microbiota-brain axis. Studies have demonstrated that any alterations in the signaling mentioned above molecules and molecular phenomena lead to the pathophysiology of neurodegenerative diseases, namely, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, and neuropsychiatric disorders, such as bipolar disorder, schizophrenia, depression, anxiety, autism spectrum disorder, and post-traumatic stress disorder.

Deficiency of Cullin 3, a Protein Encoded by a Schizophrenia and Autism Risk Gene, Impairs Behaviors by Enhancing the Excitability of Ventral Tegmental Area (VTA) DA Neurons

The dopaminergic neuromodulator system is fundamental to brain functions. Abnormal dopamine (DA) pathway is implicated in psychiatric disorders, including schizophrenia (SZ) and autism spectrum disorder (ASD). Mutations in Cullin 3 (CUL3), a core component of the Cullin-RING ubiquitin E3 ligase complex, have been associated with SZ and ASD. However, little is known about the function and mechanism of CUL3 in the DA system. Here, we show that CUL3 is critical for the function of DA neurons and DA-relevant behaviors in male mice. CUL3-deficient mice exhibited hyperactive locomotion, deficits in working memory and sensorimotor gating, and increased sensitivity to psychostimulants. In addition, enhanced DA signaling and elevated excitability of the VTA DA neurons were observed in CUL3-deficient animals. Behavioral impairments were attenuated by dopamine D2 receptor antagonist haloperidol and chemogenetic inhibition of DA neurons. Furthermore, we identified HCN2, a hyperpolarization-activated and cyclic nucleotide-gated channel, as a potential target of CUL3 in DA neurons. Our study indicates that CUL3 controls DA neuronal activity by maintaining ion channel homeostasis and provides insight into the role of CUL3 in the pathogenesis of psychiatric disorders.SIGNIFICANCE STATEMENT This study provides evidence that Cullin 3 (CUL3), a core component of the Cullin-RING ubiquitin E3 ligase complex that has been associated with autism spectrum disorder and schizophrenia, controls the excitability of dopamine (DA) neurons in mice. Its DA-specific heterozygous deficiency increased spontaneous locomotion, impaired working memory and sensorimotor gating, and elevated response to psychostimulants. We showed that CUL3 deficiency increased the excitability of VTA DA neurons, and inhibiting D2 receptor or DA neuronal activity attenuated behavioral deficits of CUL3-deficient mice. We found HCN2, a hyperpolarization-activated channel, as a target of CUL3 in DA neurons. Our findings reveal CUL3's role in DA neurons and offer insights into the pathogenic mechanisms of autism spectrum disorder and schizophrenia.

HSPA12A controls cerebral lactate homeostasis to maintain hippocampal neurogenesis and mood stabilization

Mood instability, a subjective emotional state defined as rapid mood oscillations of up and down, is a symptom that occurs in several psychiatric disorders, particularly major depressive disorder and bipolar disorder. Heat shock protein A12A (HSPA12A) shows decreased expression in the brains of schizophrenia patients. However, the causal effects of HSPA12A in any psychiatric disorders are completely unknown. To investigate whether HSPA12A affects mood stability, Hspa12a-knockout mice (Hspa12a-/-) and wild-type (WT) littermates were subjected to tests of open field, forced swimming, elevated plus maze, and sucrose preference. Cerebral lactate levels were measured in cerebrospinal fluid (CSF). Adult hippocampal neurogenesis (AHN) was assessed by BrdU labeling. We found that acute mood stress increased hippocampal HSPA12A expression and CSF lactate levels in mice. However, Hspa12a-/- mice exhibited behaviors of mood instability (anhedonia, lower locomotor activity, antidepression, and anxiety), which were accompanied by impaired AHN, decreased CSF lactate levels, and downregulated hippocampal glycolytic enzyme expression. By contrast, HSPA12A overexpression increased lactate production and glycolytic enzyme expression of primary hippocampal neurons. Intriguingly, lactate administration alleviated the mood instability and AHN impairment in Hspa12a-/- mice. Further analyses revealed that HSPA12A was necessary for sustaining cerebral lactate homeostasis, which could be mediated by inhibiting GSK3β in hippocampal neurons, to maintain AHN and mood stabilization. Taken together, HSPA12A is defined as a novel regulator of mood stability and exerts therapeutic potential for mood disorder. Our findings establish a framework for determining mood disorder and AHN relevance of cerebral lactate homeostasis. HSPA12A is a novel mood stabilizer through inhibiting GSK3β in hippocampal neurons, thereby sustaining glycolysis-generated lactate to maintain cerebral lactate homeostasis, which ultimately leading to maintenance of hippocampal neurogenesis and mood stabilization.

Current trends of high-risk gene Cul3 in neurodevelopmental disorders

Cul3 encodes Cullin-3, a core component of the ubiquitin E3 ligase that is involved in protein ubiquitination. Recent studies have identified Cul3 as a high-confidence risk gene in neurodevelopmental disorders (NDDs), especially autism spectrum disorder (ASD). Different strategies have been used to generate animal models with Cul3 deficiency in the central nervous system, including whole-brain knockout (KO), cell-type specific conditional KO (cKO), and brain region-specific knockdown. In this review, we revisited the basic properties of CUL3 and its function under physiological and pathological conditions. Recent clinical studies including case reports and large cohort sequencing studies related to CUl3 in NDDs have been summarized. Moreover, we characterized the behavioral, electrophysiological, and molecular changes in newly developed Cul3 deficiency models. This would guide further studies related to Cul3 in CNS and provide potential therapeutic targets for Cul3-deficiency-induced NDDs, including ASD.

Neurodevelopmental disorders, like cancer, are connected to impaired chromatin remodelers, PI3K/mTOR, and PAK1-regulated MAPK

Neurodevelopmental disorders (NDDs) and cancer share proteins, pathways, and mutations. Their clinical symptoms are different. However, individuals with NDDs have higher probabilities of eventually developing cancer. Here, we review the literature and ask how the shared features can lead to different medical conditions and why having an NDD first can increase the chances of malignancy. To explore these vital questions, we focus on dysregulated PI3K/mTOR, a major brain cell growth pathway in differentiation, and MAPK, a critical pathway in proliferation, a hallmark of cancer. Differentiation is governed by chromatin organization, making aberrant chromatin remodelers highly likely agents in NDDs. Dysregulated chromatin organization and accessibility influence the lineage of specific cell brain types at specific embryonic development stages. PAK1, with pivotal roles in brain development and in cancer, also regulates MAPK. We review, clarify, and connect dysregulated pathways with dysregulated proliferation and differentiation in cancer and NDDs and highlight PAK1 role in brain development and MAPK regulation. Exactly how PAK1 activation controls brain development, and why specific chromatin remodeler components, e.g., BAF170 encoded by SMARCC2 in autism, await clarification.

A novel splice site CUL3 variant in a patient with neurodevelopmental delay

BACKGROUND

CUL3-related neurodevelopmental disorder is a recently described rare genetic condition characterized by global developmental delay and intellectual disability. Five affected individuals have been reported worldwide. The molecular and phenotypic spectrum of the disorder has yet to be fully elucidated. Splice variants in CUL3 are a well-described cause of pseudohypoaldosteronism type IIE; however, splice variants have not been associated with the neurodevelopmental disorder. We report the first individual with a neurodevelopmental disorder attributed to a CUL3 splice site variant.

CASE REPORT

The patient presented with congenital developmental dysplasia of the hip and global developmental delay. A de novo splice site variant (c.379-2A > G) was identified in CUL3 and is predicted to abolish the acceptor splice site.

CONCLUSION

This is the first report of an individual with a splice site variant causing CUL3-related neurodevelopmental disorder and expands our understanding of this rare condition.

Therapeutic strategies for autism: targeting three levels of the central dogma of molecular biology

The past decade has yielded much success in the identification of risk genes for Autism Spectrum Disorder (ASD), with many studies implicating loss-of-function (LoF) mutations within these genes. Despite this, no significant clinical advances have been made so far in the development of therapeutics for ASD. Given the role of LoF mutations in ASD etiology, many of the therapeutics in development are designed to rescue the haploinsufficient effect of genes at the transcriptional, translational, and protein levels. This review will discuss the various therapeutic techniques being developed from each level of the central dogma with examples including: CRISPR activation (CRISPRa) and gene replacement at the DNA level, antisense oligonucleotides (ASOs) at the mRNA level, and small-molecule drugs at the protein level, followed by a review of current delivery methods for these therapeutics. Since central nervous system (CNS) penetrance is of utmost importance for ASD therapeutics, it is especially necessary to evaluate delivery methods that have higher efficiency in crossing the blood-brain barrier (BBB).

Cholinergic neurons in the basal forebrain are involved in behavioral abnormalities associated with Cul3 deficiency: Role of prefrontal cortex projections in cognitive deficits

Loss-of-function mutations of the gene Cul3 have been identified as a risk factor for autism-spectrum disorder (ASD), but the pathogenic mechanisms are not well understood. Conditional Cul3 ablation in cholinergic neurons of mice (ChatCRECul3F/+) recapitulated ASD-like social and sensory gating phenotypes and caused significant cognitive impairments, with diminished activity of cholinergic neurons in the basal forebrain (BF). Chemogenetic inhibition of BF cholinergic neurons in healthy mice induced similar social and cognitive deficits. Conversely, chemogenetic stimulation of BF cholinergic neurons in ChatCRECul3F/+ mice reversed abnormalities in sensory gating and cognition. Cortical hypofunction was also found after ChAT-specific Cul3 ablation and stimulation of cholinergic projections from the BF to the prefrontal cortex (PFC) mitigated cognitive deficits. Overall, we demonstrate that cholinergic dysfunction due to Cul3 deficiency is involved in ASD-like behavioral abnormalities, and that BF cholinergic neurons are particularly critical for cognitive component through their projections to the PFC.

Cntnap2-dependent molecular networks in autism spectrum disorder revealed through an integrative multi-omics analysis

Autism spectrum disorder (ASD) is a major neurodevelopmental disorder in which patients present with core symptoms of social communication impairment, restricted interest, and repetitive behaviors. Although various studies have been performed to identify ASD-related mechanisms, ASD pathology is still poorly understood. CNTNAP2 genetic variants have been found that represent ASD genetic risk factors, and disruption of Cntnap2 expression has been associated with ASD phenotypes in mice. In this study, we performed an integrative multi-omics analysis by combining quantitative proteometabolomic data obtained with Cntnap2 knockout (KO) mice with multi-omics data obtained from ASD patients and forebrain organoids to elucidate Cntnap2-dependent molecular networks in ASD. To this end, a mass spectrometry-based proteometabolomic analysis of the medial prefrontal cortex in Cntnap2 KO mice led to the identification of Cntnap2-associated molecular features, and these features were assessed in combination with multi-omics data obtained on the prefrontal cortex in ASD patients to identify bona fide ASD cellular processes. Furthermore, a reanalysis of single-cell RNA sequencing data obtained from forebrain organoids derived from patients with CNTNAP2-associated ASD revealed that the aforementioned identified ASD processes were mainly linked to excitatory neurons. On the basis of these data, we constructed Cntnap2-associated ASD network models showing mitochondrial dysfunction, axonal impairment, and synaptic activity. Our results may shed light on the Cntnap2-dependent molecular networks in ASD.

In the pursuit of new social neurons. Neurogenesis and social behavior in mice: A systematic review

Social behaviors have become more relevant to our understanding of the human nervous system because relationships with our peers may require and modulate adult neurogenesis. Here, we review the pieces of evidence we have to date for the divergence of social behaviors in mice by modulation of adult neurogenesis or if social behaviors and the social environment can drive a change in neurogenic processes. Social recognition and memory are deeply affected by antimitotic drugs and irradiation, while NSC transgenic mice may run with lower levels of social discrimination. Interestingly, social living conditions can create a big impact on neurogenesis. Social isolation and social defeat reduce the number of new neurons, while social dominance and enrichment of the social environment increase their number. These new “social neurons” trigger functional modifications with amazing transgenerational effects. All of these suggest that we are facing two bidirectional intertwined variables, and the great challenge now is to understand the cellular and genetic mechanisms that allow this relationship to be used therapeutically.

Progress in magnetic resonance imaging of autism model mice brain

Autism spectrum disorder (ASD) is a neurodevelopmental disease characterized by social disorder and stereotypical behaviors with an increasing incidence. ASD patients are suffering from varying degrees of mental retardation and language development abnormalities. Magnetic resonance imaging (MRI) is a noninvasive imaging technology to detect brain structural and functional dysfunction in vivo, playing an important role in the early diagnosisbasic research of ASD. High-field, small-animal MRI in basic research of autism model mice has provided a new approach to research the pathogenesis, characteristics, and intervention efficacy in autism. This article reviews MRI studies of mouse models of autism over the past 20 years. Reduced gray matter, abnormal connections of brain networks, and abnormal development of white matter fibers have been demonstrated in these studies, which are present in different proportions in the various mouse models. This provides a more macroscopic view for subsequent research on autism model mice. This article is categorized under: Cognitive Biology > Genes and Environment Neuroscience > Computation Neuroscience > Genes, Molecules, and Cells Neuroscience > Development.

A perspective on molecular signalling dysfunction, its clinical relevance and therapeutics in autism spectrum disorder

Intellectual disability (ID) and autism spectrum disorder (ASD) are neurodevelopmental disorders that have become a primary clinical and social concern, with a prevalence of 2-3% in the population. Neuronal function and behaviour undergo significant malleability during the critical period of development that is found to be impaired in ID/ASD. Human genome sequencing studies have revealed many genetic variations associated with ASD/ID that are further verified by many approaches, including many mouse and other models. These models have facilitated the identification of fundamental mechanisms underlying the pathogenesis of ASD/ID, and several studies have proposed converging molecular pathways in ASD/ID. However, linking the mechanisms of the pathogenic genes and their molecular characteristics that lead to ID/ASD has progressed slowly, hampering the development of potential therapeutic strategies. This review discusses the possibility of recognising the common molecular causes for most ASD/ID based on studies from the available models that may enable a better therapeutic strategy to treat ID/ASD. We also reviewed the potential biomarkers to detect ASD/ID at early stages that may aid in diagnosis and initiating medical treatment, the concerns with drug failure in clinical trials, and developing therapeutic strategies that can be applied beyond a particular mutation associated with ASD/ID.

Ubiquitin ligases: guardians of mammalian development

Mammalian development demands precision. Millions of molecules must be properly located in temporal order, and their function regulated, to orchestrate important steps in cell cycle progression, apoptosis, migration and differentiation, to shape developing embryos. Ubiquitin and its associated enzymes act as cellular guardians to ensure precise spatio-temporal control of key molecules during each of these important cellular processes. Loss of precision results in numerous examples of embryological disorders or even cancer. This Review discusses the crucial roles of E3 ubiquitin ligases during key steps of early mammalian development and their roles in human disease, and considers how new methods to manipulate and exploit the ubiquitin regulatory machinery - for example, the development of molecular glues and PROTACs - might facilitate clinical therapy.

Neurodevelopmental disorders, immunity, and cancer are connected

Immunity could be viewed as the common factor in neurodevelopmental disorders and cancer. The immune and nervous systems coevolve as the embryo develops. Immunity can release cytokines that activate MAPK signaling in neural cells. In specific embryonic brain cell types, dysregulated signaling that results from germline or embryonic mutations can promote changes in chromatin organization and gene accessibility, and thus expression levels of essential genes in neurodevelopment. In cancer, dysregulated signaling can emerge from sporadic somatic mutations during human life. Neurodevelopmental disorders and cancer share similarities. In neurodevelopmental disorders, immunity, and cancer, there appears an almost invariable involvement of small GTPases (e.g., Ras, RhoA, and Rac) and their pathways. TLRs, IL-1, GIT1, and FGFR signaling pathways, all can be dysregulated in neurodevelopmental disorders and cancer. Although there are signaling similarities, decisive differentiating factors are timing windows, and cell type specific perturbation levels, pointing to chromatin reorganization. Finally, we discuss drug discovery.

insomniac links the development and function of a sleep-regulatory circuit

Although many genes are known to influence sleep, when and how they impact sleep-regulatory circuits remain ill-defined. Here, we show that insomniac (inc), a conserved adaptor for the autism-associated Cul3 ubiquitin ligase, acts in a restricted period of neuronal development to impact sleep in adult Drosophila. The loss of inc causes structural and functional alterations within the mushroom body (MB), a center for sensory integration, associative learning, and sleep regulation. In inc mutants, MB neurons are produced in excess, develop anatomical defects that impede circuit assembly, and are unable to promote sleep when activated in adulthood. Our findings link neurogenesis and postmitotic development of sleep-regulatory neurons to their adult function and suggest that developmental perturbations of circuits that couple sensory inputs and sleep may underlie sleep dysfunction in neurodevelopmental disorders.

Cortical organoids model early brain development disrupted by 16p11.2 copy number variants in autism

Reciprocal deletion and duplication of the 16p11.2 region is the most common copy number variation (CNV) associated with autism spectrum disorders. We generated cortical organoids from skin fibroblasts of patients with 16p11.2 CNV to investigate impacted neurodevelopmental processes. We show that organoid size recapitulates macrocephaly and microcephaly phenotypes observed in the patients with 16p11.2 deletions and duplications. The CNV dosage affects neuronal maturation, proliferation, and synapse number, in addition to its effect on organoid size. We demonstrate that 16p11.2 CNV alters the ratio of neurons to neural progenitors in organoids during early neurogenesis, with a significant excess of neurons and depletion of neural progenitors observed in deletions. Transcriptomic and proteomic profiling revealed multiple pathways dysregulated by the 16p11.2 CNV, including neuron migration, actin cytoskeleton, ion channel activity, synaptic-related functions, and Wnt signaling. The level of the active form of small GTPase RhoA was increased in both, deletions and duplications. Inhibition of RhoA activity rescued migration deficits, but not neurite outgrowth. This study provides insights into potential neurobiological mechanisms behind the 16p11.2 CNV during neocortical development.