Male-Specific cAMP Signaling in the Hippocampus Controls Spatial Memory Deficits in a Mouse Model of Autism and Intellectual Disability

The promise of cyclic AMP modulation to restore cognitive function in neurodevelopmental disorders

Cyclic AMP (cAMP) is a key regulator of synaptic function and is dysregulated in both neurodevelopmental (NDD) and neurodegenerative disorders. Due to the ease of diffusion and promiscuity of downstream effectors, cAMP signaling is restricted within spatiotemporal domains to localize activation. Among the best-studied mechanisms is the feedback inhibition of cAMP-dependent protein kinase (PKA) activity by phosphodiesterases 4 (PDE4s) at synapses controlling neuronal plasticity, which is largely regulated by PDE4D. In fact, genetic variants in genes for multiple PKA subunits and PDE4D lead to NDDs. Here, we discuss the rationale for choosing PDE4D as a candidate for the design of selective allosteric inhibitors and the recent advances in clinical trials. These new compounds improve cognitive function in preclinical animal models due to improved selectivity and more physiological inhibition of the active enzyme. We also discuss opportunities for better understanding of PDE4D function in general, and for the development of next-generation inhibitors.

Oxytocin treatment rescues irritability-like behavior in Cc2d1a conditional knockout mice

Irritability, a state of excessive reactivity to negative emotional stimuli, is common in individuals with autism spectrum disorder (ASD). Although it has a significant negative impact of patients' disease severity and quality of life, the neural mechanisms underlying irritability in ASD remain largely unclear. We have previously demonstrated that male mice lacking the Coiled-coil and C2 domain containing 1a (Cc2d1a) in forebrain excitatory neurons recapitulate numerous ASD-like behavioral phenotypes, including impaired social behaviors and pronounced repetitive behaviors. Here, using the bottle-brush test (BBT) to trigger and evaluate aggressive and defensive responses, we show that Cc2d1a deletion increases irritability-like behavior in male but not female mice, which is correlated with reduced number of oxytocin (OXT)-expressing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Intranasal OXT administration or chemogenetic activation of OXT neurons in the PVN rescues irritability-like behavior in Cc2d1a conditional knockout (cKO) mice. Administration of a selective melanocortin receptor 4 agonist, RO27-3225, which potentiates endogenous OXT release, also alleviates irritability-like behavior in Cc2d1a cKO mice, an effect blocked by a specific OXT receptor antagonist, L-368,899. We additionally identify a projection connecting the posterior ventral segment of the medial amygdala (MeApv) and ventromedial nucleus of the ventromedial hypothalamus (VMHvl) for governing irritability-like behavior during the BBT. Chemogenetic suppression of the MeApv-VMHvl pathway alleviates irritability-like behavior in Cc2d1a cKO mice. Together, our study uncovers dysregulation of OXT system in irritability-like behavior in Cc2d1a cKO mice during the BBT and provide translatable insights into the development of OXT-based therapeutics for clinical interventions.

Autism-Related Cc2d1a Heterozygous Mice: Increased Levels of miRNAs Retained in DNA/RNA Hybrid Profiles (R-Loop)

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with a highly variable expression of phenotypes (restricted interest or activity and repetitive behavior in communication and social interactions), genes (mutation), markers (alteration of transcription) and pathways. Loss of function of the CC2D1A gene appears to primarily affect the brain, leading to a range of behavioral problems in humans. In our study published in 2020, we found that the expressions of miR-19a-3p, miR-361-5p, miR-150-5p, miR-3613-3p, miR-126-3p and miR-499a-5p were downregulated in the serum samples of autistic patients, their families and mouse models (Cc2d1a +/- and valproic acid treated males). Here, acquired non-Mendelian hereditary character in a genetically defined mouse model of autism (Cc2d1a +/-) correlates with the transcriptional alteration of five miRNAs. We seek to test the hypothesis that miRNA levels vary by changes in RNA/DNA structure during development, thereby creating transcription alteration and cell memory. Behavioral tests were conducted on the offspring of Cc2d1a (+/-) mutant and control mice, such as novel object, social interaction, marble burying and tail suspension behavior. Two RNA fractions were isolated from mouse hippocampal tissues and sperm cells via standard TRIzol extraction: free RNA and the fraction of RNA bound to DNA in the form of a DNA/RNA hybrid (R-loop). The expression levels of miR-19a-3p, miR-361-5p, miR-150-5p, miR-126-3p and miR-499a-5p were investigated by quantitative real-time RT-PCR. We report differences in the distribution of five miRNAs in the hippocampus between male and female mice, particularly in colonies of Cc2d1a (+/-) mice. Furthermore, the number of miRNAs engaged in the DNA/RNA hybrid fraction is generally higher in the mutant pedigree than in the control group. On the other hand, in sperm, both fractions are at lower levels than in controls. R-loops contribute to the physiology and pathology of organisms including human disease. Here, we report a variation in five miRNA levels between gender and tissue. Our results suggest that the transcription levels of these five miRNAs are directly regulated by their RNA.

PDE4D: A Multipurpose Pharmacological Target

Phosphodiesterase 4 (PDE4) enzymes catalyze cyclic adenosine monophosphate (cAMP) hydrolysis and are involved in a variety of physiological processes, including brain function, monocyte and macrophage activation, and neutrophil infiltration. Among different PDE4 isoforms, Phosphodiesterases 4D (PDE4Ds) play a fundamental role in cognitive, learning and memory consolidation processes and cancer development. Selective PDE4D inhibitors (PDE4Dis) could represent an innovative and valid therapeutic strategy for the treatment of various neurodegenerative diseases, such as Alzheimer's, Parkinson's, Huntington's, and Lou Gehrig's diseases, but also for stroke, traumatic brain and spinal cord injury, mild cognitive impairment, and all demyelinating diseases such as multiple sclerosis. In addition, small molecules able to block PDE4D isoforms have been recently studied for the treatment of specific cancer types, particularly hepatocellular carcinoma and breast cancer. This review overviews the PDE4DIsso far identified and provides useful information, from a medicinal chemistry point of view, for the development of a novel series of compounds with improved pharmacological properties.

A novel framework for functional annotation of variants of uncertain significance in ID/ASD risk gene CC2D1A

Intellectual disability (ID) and autism spectrum disorder (ASD) are genetically heterogeneous with hundreds of identified risk genes, most affecting only a few patients. Novel missense variants in these genes are being discovered as clinical exome sequencing is now routinely integrated into diagnosis, yet most of them are annotated as variants of uncertain significance (VUS). VUSs are a major roadblock in using patient genetics to inform clinical action. We developed a framework to characterize VUSs in Coiled-coil and C2 domain containing 1A (CC2D1A), a gene causing autosomal recessive ID with comorbid ASD in 40% of cases. We analyzed seven VUSs (p.Pro319Leu, p.Ser327Leu, p.Gly441Val, p.Val449Met, p.Thr580Ile, p.Arg886His and p.Glu910Lys) from four cases of individuals with ID and ASD. Variants were cloned and overexpressed in HEK293 individually and in their respective heterozygous combination. CC2D1A is a signaling scaffold that positively regulates PKA-CREB signaling by repressing phosphodiesterase 4D (PDE4D) to prevent cAMP degradation. After testing multiple parameters including direct interaction between PDE4D and CC2D1A, cAMP levels and CREB activation, we found that the most sensitive readout was CREB transcriptional activity using a luciferase assay. Compared to WT CC2D1A, five VUSs (p.Pro319Leu, p.Gly441Val, p.Val449Met, p.Thr580Ile, and p.Arg886His) led to significantly blunted response to forskolin induced CREB activation. This luciferase assay approach can be scaled up to annotate ~150 CC2D1A VUSs that are currently listed in ClinVar. Since CREB activation is a common denominator for multiple ASD/ID genes, our paradigm can also be adapted for their VUSs.

Defects in AMPAR trafficking and microglia activation underlie socio-cognitive deficits associated to decreased expression of phosphodiesterase 2 a

Phosphodiesterase 2 A (PDE2A) is an enzyme involved in the homeostasis of cAMP and cGMP and is the most highly expressed PDE in human brain regions critical for socio-cognitive behavior. In cerebral cortex and hippocampus, PDE2A expression level is upregulated in Fmr1-KO mice, a model of the Fragile X Syndrome (FXS), the most common form of inherited intellectual disability (ID) and autism spectrum disorder (ASD). Indeed, PDE2A translation is negatively modulated by FMRP, whose functional absence causes FXS. While the pharmacological inhibition of PDE2A has been associated to its pro-cognitive role in normal animals and in models of ID and ASD, homozygous PDE2A mutations have been identified in patients affected by ID, ASD and epilepsy. To clarify this apparent paradox about the role of PDE2A in brain development, we characterized here Pde2a+/- mice (homozygote animals being not viable) at the behavioral, cellular, molecular and electrophysiological levels. Pde2a+/- females display a milder form of the disorder with reduced cognitive performance in adulthood, conversely males show severe socio-cognitive deficits throughout their life. In males, these phenotypes are associated with microglia activation, elevated glutathione levels and increased externalization of Glutamate receptor (GluR1) in CA1, producing reduced mGluR-dependent Long-term Depression. Overall, our results reveal molecular targets of the PDE2A-dependent pathway underlying socio-cognitive performance. These results clarify the mechanism of action of pro-cognitive drugs based on PDE2A inactivation, which have been shown to be promising therapeutic approaches for Alzheimer's disease, schizophrenia, FXS as well as other forms of ASD.

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.

Heterozygous Cc2d1a mice show sex-dependent changes in the Beclin-1/p62 ratio with impaired prefrontal cortex and hippocampal autophagy

Autism Spectrum Disorders (ASD) are a group of neurodevelopmental disorders characterized by repetitive behaviors, lack of social interaction and communication. CC2D1A is identified in patients as an autism risk gene. Recently, we suggested that heterozygous Cc2d1a mice exhibit impaired autophagy in the hippocampus. We now report the analysis of autophagy markers (Lc3, Beclin and p62) in different regions hippocampus, prefrontal cortex, hypothalamus and cerebellum, with an overall decrease in autophagy and changes in Beclin-1/p62 ratio in the hippocampus. We observed sex-dependent variations in transcripts and protein expression levels. Moreover, our analyses suggest that alterations in autophagy initiated in Cc2d1a heterozygous parents are variably transmitted to offspring, even when the offspring's genotype is wild type. Aberration in the autophagy mechanism may indirectly contribute to induce synapse alteration in the ASD brain.

High-Fat Diet Exacerbates Autistic-Like Restricted Repetitive Behaviors and Social Abnormalities in CC2D1A Conditional Knockout Mice

Autism spectrum disorder (ASD) represents a heterogeneous group of neurodevelopmental disorders characterized by deficits in social communication, social interaction, and the presence of restricted repetitive behaviors. The cause of ASD involves complex interactions between genetic and environmental factors. Haploinsufficiency of the Coiled-coil and C2 domain containing 1A (Cc2d1a) gene is causally linked to ASD, and obesity has been associated with worse outcomes for ASD. High-fat diet (HFD) feeding leads to the development of obesity and metabolic dysfunction; however, the effect of HFD on pre-existing autistic-like phenotypes remains to be clarified. Here, we report that male Cc2d1a conditional knockout (cKO) mice fed with HFD, from weaning onwards and throughout the experimental period, show a marked aggravation in autistic-like phenotypes, manifested in increased restricted repetitive behaviors and impaired performance in the preference for social novelty, but not in sociability and cognitive impairments assessed using the object location memory, novel object recognition, and Morris water maze tests. HFD feeding also results in increased numbers of reactive microglia and astrocytes, and exacerbates reductions in dendritic complexity and spine density of hippocampal CA1 pyramidal neurons. Furthermore, we demonstrate that chronic treatment with minocycline, a semisynthetic tetracycline-derived antibiotic, rescues the observed behavioral and morphological deficits in Cc2d1a cKO mice fed with HFD. Collectively, these findings highlight an aggravating role of HFD in pre-existing autistic-like phenotypes and suggest that minocycline treatment can alleviate abnormal neuronal morphology and behavioral symptoms associated with ASD resulted from the interplay between genetic and environmental risk factors.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

Partial changes in apoptotic pathways in hippocampus and hypothalamus of Cc2d1a heterozygous

Alterations in the apoptosis pathway have been linked to changes in serotonin levels seen in autistic patients. Cc2d1a is a repressor of the HTR1A gene involved in the serotonin pathway. The hippocampus and hypothalamus of Cc2d1a ± mice were analyzed for the expression of apoptosis markers (caspase 3, 8 and 9). Gender differences were observed in the expression levels of the three caspases consistent with some altered activity in the open-field assay. The number of apoptotic cells was significantly increased. We concluded that apoptotic pathways are only partially affected in the pathogenesis of the Cc2d1a heterozygous mouse model. A) Apoptosis is suppressed because the cell does not receive a death signal, or the receptor cannot activate the caspase 8 pathway despite the death signal. B) Since Caspase 8 and Caspase 3 expression is downregulated in our mouse model, the mechanism of apoptosis is not activated.

Effects of the Cc2d1a/Freud-1 Knockdown in the Hippocampus of BTBR Mice on the Autistic-Like Behavior, Expression of Serotonin 5-HT1A and D2 Dopamine Receptors, and CREB and NF-kB Intracellular Signaling

The mechanisms of autism are of extreme interest due to the high prevalence of this disorder in the human population. In this regard, special attention is given to the transcription factor Freud-1 (encoded by the Cc2d1a gene), which regulates numerous intracellular signaling pathways and acts as a silencer for 5-HT_1A serotonin and D2 dopamine receptors. Disruption of the Freud-1 functions leads to the development of various psychopathologies. In this study, we found an increase in the expression of the Cc2d1a/Freud-1 gene in the hippocampus of BTBR mice (model of autistic-like behavior) in comparison with C57Bl/6J mice and examined how restoration of the Cc2d1a/Freud-1 expression in the hippocampus of BTBR mice affects their behavior, expression of 5-HT_1A serotonin and D2 dopamine receptors, and CREB and NF-κB intracellular signaling pathways in these animals. Five weeks after administration of the adeno-associated viral vector (AAV) carrying the pAAV_H1-2_shRNA-Freud-1_Syn_EGFP plasmid encoding a small hairpin RNA (shRNA) that suppressed expression of the Cc2d1a/Freud-1 gene, we observed an elevation in the anxiety levels, as well as the increase in the escape latency and path length to the platform in the Morris water maze test, which was probably associated with a strengthening of the active stress avoidance strategy. However, the Cc2d1a/Freud-1 knockdown did not affect the spatial memory and phosphorylation of the CREB transcription factor, although such effect was found in C57Bl/6J mice in our previous study. These results suggest the impairments in the CREB-dependent effector pathway in BTBR mice, which may play an important role in the development of the autistic-like phenotype. The knockdown of Cc2d1a/Freud-1 in the hippocampus of BTBR mice did not affect expression of the 5-HT_1A serotonin and D2 dopamine receptors and key NF-κB signaling genes (Nfkb1 and Rela). Our data suggest that the transcription factor Freud-1 plays a significant role in the pathogenesis of anxiety and active stress avoidance in autism.

Molecular and cellular mechanisms for differential effects of chronic social isolation stress in males and females

Chronic social isolation stress during adolescence induces susceptibility for neuropsychiatric disorders. Here we show that 5-week post-weaning isolation stress induces sex-specific behavioral abnormalities and neuronal activity changes in the prefrontal cortex (PFC), basal lateral amygdala (BLA), and ventral tegmental area (VTA). Chemogenetic manipulation, optogenetic recording, and in vivo calcium imaging identify that the PFC to BLA pathway is causally linked to heightened aggression in stressed males, and the PFC to VTA pathway is causally linked to social withdrawal in stressed females. Isolation stress induces genome-wide transcriptional alterations in a region-specific manner. Particularly, the upregulated genes in BLA of stressed males are under the control of activated transcription factor CREB, and CREB inhibition in BLA normalizes gene expression and reverses aggressive behaviors. On the other hand, neuropeptide Hcrt (Hypocretin/Orexin) is among the top-ranking downregulated genes in VTA of stressed females, and Orexin-A treatment rescues social withdrawal. These results have revealed molecular mechanisms and potential therapeutic targets for stress-related mental illness.

Loss-of-function variants in the schizophrenia risk gene SETD1A alter neuronal network activity in human neurons through the cAMP/PKA pathway

Heterozygous loss-of-function (LoF) mutations in SETD1A, which encodes a subunit of histone H3 lysine 4 methyltransferase, cause a neurodevelopmental syndrome and increase the risk for schizophrenia. Using CRISPR-Cas9, we generate excitatory/inhibitory neuronal networks from human induced pluripotent stem cells with a SETD1A heterozygous LoF mutation (SETD1A+/-). Our data show that SETD1A haploinsufficiency results in morphologically increased dendritic complexity and functionally increased bursting activity. This network phenotype is primarily driven by SETD1A haploinsufficiency in glutamatergic neurons. In accordance with the functional changes, transcriptomic profiling reveals perturbations in gene sets associated with glutamatergic synaptic function. At the molecular level, we identify specific changes in the cyclic AMP (cAMP)/Protein Kinase A pathway pointing toward a hyperactive cAMP pathway in SETD1A+/- neurons. Finally, by pharmacologically targeting the cAMP pathway, we are able to rescue the network deficits in SETD1A+/- cultures. Our results demonstrate a link between SETD1A and the cAMP-dependent pathway in human neurons.

Phosphodiesterase 2A inhibition corrects the aberrant behavioral traits observed in genetic and environmental preclinical models of Autism Spectrum Disorder

Pharmacological inhibition of phosphodiesterase 2A (PDE2A), which catalyzes the hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), has recently been proposed as a novel therapeutic tool for Fragile X Syndrome (FXS), the leading monogenic cause of Autism Spectrum Disorder (ASD). Here, we investigated the role of PDE2A in ASD pathogenesis using two rat models that reflect one of either the genetic or environmental factors involved in the human disease: the genetic Fmr1-Δexon 8 rat model and the environmental rat model based on prenatal exposure to valproic acid (VPA, 500 mg/kg). Prior to behavioral testing, the offspring was treated with the PDE2A inhibitor BAY607550 (0.05 mg/kg at infancy, 0.1 mg/kg at adolescence and adulthood). Socio-communicative symptoms were assessed in both models through the ultrasonic vocalization test at infancy and three-chamber test at adolescence and adulthood, while cognitive impairments were assessed by the novel object recognition test in Fmr1-Δexon 8 rats (adolescence and adulthood) and by the inhibitory avoidance test in VPA-exposed rats (adulthood). PDE2A enzymatic activity in VPA-exposed infant rats was also assessed. In line with the increased PDE2A enzymatic activity previously observed in the brain of Fmr1-KO animals, we found an altered upstream regulation of PDE2A activity in the brain of VPA-exposed rats at an early developmental age (p < 0.05). Pharmacological inhibition of PDE2A normalized the communicative (p < 0.01, p < 0.05), social (p < 0.001, p < 0.05), and cognitive impairment (p < 0.001) displayed by both Fmr1-Δexon 8 and VPA-exposed rats. Altogether, these data highlight a key role of PDE2A in brain development and point to PDE2A inhibition as a promising pharmacological approach for the deficits common to both FXS and ASD.

Insights into the potential of withanolides as Phosphodiesterase-4 (PDE4D) inhibitors

Medicinal herbs have been used as traditional medicines for centuries. The molecular mechanism of action of their bioactive molecules against various diseases or therapeutic targets is still being explored. Here, the active compounds (withanolides) of a well-known Indian medicinal herb, Ashwagandha (Withania somnifera), have been studied for their most potential therapeutic targets and their mechanism of action using ligand-based screening and receptor-based approaches. Ligand-based screening predicted the six top therapeutic targets, namely, Protein kinase C alpha (PRKCA), Protein kinase C delta (PRKCD), Protein kinase C epsilon (PRKCE), Androgenic Receptor (AR), Cycloxygenase-2 (PTGS-2) and Phosphodiesterase-4D (PDE4D). Further, when these predictions were validated using receptor-based studies, i.e. molecular docking, molecular dynamics simulation and free energy calculations, it was found that PDE4D was the most potent target for four withanolides, namely, Withaferin-A, 17-Hydroxywithaferin-A, 27-Hydroxywithanone and Withanolide-R. These compounds had a better binding affinity and similar interactions as that of an already known inhibitor (Zardaverine) of PDE4D. These results warrant further in-vitro and in-vivo investigations to examine their therapeutic potential as an inhibitor of PDE4D.Communicated by Ramaswamy H. Sarma.

Effects of a Cc2d1a/Freud-1 Knockdown in the Hippocampus on Behavior, the Serotonin System, and BDNF

The serotonin 5-HT_1A receptor is one of the most abundant and widely distributed brain serotonin (5-HT) receptors that play a major role in the modulation of emotions and behavior. The 5-HT_1A receptor gene (Htr1a) is under the control of transcription factor Freud-1 (also known as Cc2d1a/Freud-1). Here, using adeno-associated virus (AAV) constructs in vivo, we investigated effects of a Cc2d1a/Freud-1 knockdown in the hippocampus of C57BL/6J mice on behavior, the brain 5-HT system, and brain-derived neurotrophic factor (BDNF). AAV particles carrying the pAAV_H1-2_shRNA-Freud-1_Syn_EGFP plasmid encoding a short-hairpin RNA targeting mouse Cc2d1a/Freud-1 mRNA had an antidepressant effect in the forced swim test 5 weeks after virus injection. The knockdown impaired spatiotemporal memory as assessed in the Morris water maze. pAAV_H1-2_shRNA-Freud-1_Syn_EGFP decreased Cc2d1a/Freud-1 mRNA and protein levels. Furthermore, the Cc2d1a/Freud-1 knockdown upregulated 5-HT and its metabolite 5-hydroxyindoleacetic acid but not their ratio. The Cc2d1a/Freud-1 knockdown failed to increase mRNA and protein levels of Htr1a but diminished a 5-HT_1A receptor functional response. Meanwhile, the Cc2d1a/Freud-1 knockdown reduced Creb mRNA expression and CREB phosphorylation and upregulated cFos mRNA. The knockdown enhanced the expression of a BDNF precursor (proBDNF protein), which is known to play a crucial part in neuroplasticity. Our data indicate that transcription factor Cc2d1a/Freud-1 is implicated in the pathogenesis of depressive disorders not only via the 5-HT_1A receptor and transcription factor CREB but also through an influence on BDNF.

Loss of CC2D1A in Glutamatergic Neurons Results in Autistic-Like Features in Mice

Biallelic loss-of-function mutations in Coiled-coil and C2 domain containing 1A (CC2D1A) cause autosomal recessive intellectual disability, sometimes comorbid with other neurodevelopmental disabilities, such as autism spectrum disorder (ASD) and seizures. We recently reported that conditional deletion of Cc2d1a in glutamatergic neurons of the postnatal mouse forebrain leads to impaired hippocampal synaptic plasticity and cognitive function. However, the pathogenic origin of the autistic features of CC2D1A deficiency remains elusive. Here, we confirmed that CC2D1A is highly expressed in the cortical zones during embryonic development. Taking advantage of Cre-LoxP-mediated gene deletion strategy, we generated a novel line of Cc2d1a conditional knockout (cKO) mice by crossing floxed Cc2d1a mice with Emx1-Cre mice, in which CC2D1A is ablated specifically in glutamatergic neurons throughout all embryonic and adult stages. We found that CC2D1A deletion leads to a trend toward decreased number of cortical progenitor cells at embryonic day 12.5 and alters the cortical thickness on postnatal day 10. In addition, male Cc2d1a cKO mice display autistic-like phenotypes including self-injurious repetitive grooming and aberrant social interactions. Loss of CC2D1A also results in decreased complexity of apical dendritic arbors of medial prefrontal cortex (mPFC) layer V pyramidal neurons and increased synaptic excitation/inhibition (E/I) ratio in the mPFC. Notably, chronic treatment with minocycline rescues behavioral and morphological abnormalities, as well as E/I changes, in male Cc2d1a cKO mice. Together, these findings indicate that male Cc2d1a cKO mice recapitulate autistic-like phenotypes of human disorder and suggest that minocycline has both structural and functional benefits in treating ASD.

Digging behavior discrimination test to probe burrowing and exploratory digging in male and female mice

Digging behavior is often used to test motor function and repetitive behaviors in mice. Different digging paradigms have been developed for behaviors related to anxiety and compulsion in mouse lines generated to recapitulate genetic mutations leading to psychiatric and neurological disorders. However, the interpretation of these tests has been confounded by the difficulty of determining the motivation behind digging in mice. Digging is a naturalistic mouse behavior that can be focused toward different goals, that is foraging for food, burrowing for shelter, burying objects, or even for recreation as has been shown for dogs, ferrets, and human children. However, the interpretation of results from current testing protocols assumes the motivation behind the behavior often concluding that increased digging is a repetitive or compulsive behavior. We asked whether providing a choice between different types of digging activities would increase sensitivity to assess digging motivation. Here, we present a test to distinguish between burrowing and exploratory digging in mice. We found that mice prefer burrowing when the option is available. When food restriction was used to promote a switch from burrowing to exploration, males readily switched from burrowing to digging outside, while females did not. In addition, when we tested a model of intellectual disability and autism spectrum disorder that had shown inconsistent results in the marble burying test, the Cc2d1a conditional knockout mouse, we found greatly reduced burrowing only in males. Our findings indicate that digging is a nuanced motivated behavior and suggest that male and female rodents may perform it differently.

Autism-Associated Variant in the SLC6A3 Gene Alters the Oral Microbiome and Metabolism in a Murine Model

Background: Altered dopamine (DA) signaling has been associated with autism spectrum disorder (ASD), a neurodevelopmental condition estimated to impact 1 in 54 children in the United States. There is growing evidence for alterations in both gastrointestinal function and oral microbiome composition in ASD. Recent work suggests that rare variants of the SLC6A3 gene encoding the DA transporter (DAT) identified in individuals with ASD result in structural and functional changes to the DAT. One such recently identified de novo mutation is a threonine to methionine substitution at position 356 of the DAT (DAT T356M). The DAT T356M variant is associated with ASD-like phenotypes in mice homozygous for the mutation (DAT T356M+/+), including social deficits, hyperactivity, and impaired DA signaling. Here, we determine the impact of this altered DA signaling as it relates to altered oral microbiota, and metabolic and gastrointestinal dysfunction. Methods: In the DAT T356M+/+ mouse, we determine the oral microbiota composition, metabolic function, and gastrointestinal (GI) function. We examined oral microbiota by 16S RNA sequencing. We measured metabolic function by examining glucose tolerance and we probed gastrointestinal parameters by measuring fecal dimensions and weight. Results: In the DAT T356M+/+ mouse, we evaluate how altered DA signaling relates to metabolic dysfunction and altered oral microbiota. We demonstrate that male DAT T356M+/+ mice weigh less (Wild type (WT) = 26.48 ± 0.6405 g, DAT T356M+/+ = 24.14 ± 0.4083 g) and have decreased body fat (WT = 14.89 ± 0.6206%, DAT T356M+/+ = 12.72 ± 0.4160%). These mice display improved glucose handling (WT = 32.60 ± 0.3298 kcal/g, DAT T356M+/+ = 36.97 ± 0.4910 kcal/g), and an altered oral microbiota. We found a significant decrease in Fusobacterium abundance. The abundance of Fusobacterium was associated with improved glucose handling and decreased body fat. Conclusions: Our findings provide new insights into how DAT dysfunction may alter gastrointestinal function, composition of the oral microbiota, and metabolism. Our data suggest that impaired DA signaling in ASD is associated with a number of metabolic and gastrointestinal changes which are common in individuals with ASD.

Structural interaction between DISC1 and ATF4 underlying transcriptional and synaptic dysregulation in an iPSC model of mental disorders

Psychiatric disorders are a collection of heterogeneous mental disorders arising from a contribution of genetic and environmental insults, many of which molecularly converge on transcriptional dysregulation, resulting in altered synaptic functions. The underlying mechanisms linking the genetic lesion and functional phenotypes remain largely unknown. Patient iPSC-derived neurons with a rare frameshift DISC1 (Disrupted-in-schizophrenia 1) mutation have previously been shown to exhibit aberrant gene expression and deficits in synaptic functions. How DISC1 regulates gene expression is largely unknown. Here we show that Activating Transcription Factor 4 (ATF4), a DISC1 binding partner, is more abundant in the nucleus of DISC1 mutant human neurons and exhibits enhanced binding to a collection of dysregulated genes. Functionally, overexpressing ATF4 in control neurons recapitulates deficits seen in DISC1 mutant neurons, whereas transcriptional and synaptic deficits are rescued in DISC1 mutant neurons with CRISPR-mediated heterozygous ATF4 knockout. By solving the high-resolution atomic structure of the DISC1-ATF4 complex, we show that mechanistically, the mutation of DISC1 disrupts normal DISC1-ATF4 interaction, and results in excessive ATF4 binding to DNA targets and deregulated gene expression. Together, our study identifies the molecular and structural basis of an DISC1-ATF4 interaction underlying transcriptional and synaptic dysregulation in an iPSC model of mental disorders.

Role of phosphodiesterases in the pathophysiology of neurodevelopmental disorders

Phosphodiesterases (PDEs) are enzymes involved in the homeostasis of both cAMP and cGMP. They are members of a family of proteins that includes 11 subfamilies with different substrate specificities. Their main function is to catalyze the hydrolysis of cAMP, cGMP, or both. cAMP and cGMP are two key second messengers that modulate a wide array of intracellular processes and neurobehavioral functions, including memory and cognition. Even if these enzymes are present in all tissues, we focused on those PDEs that are expressed in the brain. We took into consideration genetic variants in patients affected by neurodevelopmental disorders, phenotypes of animal models, and pharmacological effects of PDE inhibitors, a class of drugs in rapid evolution and increasing application to brain disorders. Collectively, these data indicate the potential of PDE modulators to treat neurodevelopmental diseases characterized by learning and memory impairment, alteration of behaviors associated with depression, and deficits in social interaction. Indeed, clinical trials are in progress to treat patients with Alzheimer's disease, schizophrenia, depression, and autism spectrum disorders. Among the most recent results, the application of some PDE inhibitors (PDE2A, PDE3, PDE4/4D, and PDE10A) to treat neurodevelopmental diseases, including autism spectrum disorders and intellectual disability, is a significant advance, since no specific therapies are available for these disorders that have a large prevalence. In addition, to highlight the role of several PDEs in normal and pathological neurodevelopment, we focused here on the deregulation of cAMP and/or cGMP in Down Syndrome, Fragile X Syndrome, Rett Syndrome, and intellectual disability associated with the CC2D1A gene.

Learning and reaction times in mouse touchscreen tests are differentially impacted by mutations in genes encoding postsynaptic interacting proteins SYNGAP1, NLGN3, DLGAP1, DLGAP2 and SHANK2

The postsynaptic terminal of vertebrate excitatory synapses contains a highly conserved multiprotein complex that comprises neurotransmitter receptors, cell-adhesion molecules, scaffold proteins and enzymes, which are essential for brain signalling and plasticity underlying behaviour. Increasingly, mutations in genes that encode postsynaptic proteins belonging to the PSD-95 protein complex, continue to be identified in neurodevelopmental disorders (NDDs) such as autism spectrum disorder, intellectual disability and epilepsy. These disorders are highly heterogeneous, sharing genetic aetiology and comorbid cognitive and behavioural symptoms. Here, by using genetically engineered mice and innovative touchscreen-based cognitive testing, we sought to investigate whether loss-of-function mutations in genes encoding key interactors of the PSD-95 protein complex display shared phenotypes in associative learning, updating of learned associations and reaction times. Our genetic dissection of mice with loss-of-function mutations in Syngap1, Nlgn3, Dlgap1, Dlgap2 and Shank2 showed that distinct components of the PSD-95 protein complex differentially regulate learning, cognitive flexibility and reaction times in cognitive processing. These data provide insights for understanding how human mutations in these genes lead to the manifestation of diverse and complex phenotypes in NDDs.

Novel alterations of CC2D1A as a candidate gene in a Turkish sample of patients with autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with large genetic background, but identification of pathogenic variants has proceeded slowly because hundreds of loci are involved in this complex disorder. CC2D1A gene firstly associated with the intellectual disability (ID) in a family with a large deletion. We aimed to contribute to the literature by sequencing this gene and by this way we report novel CC2D1A variations in patients with ASD.

METHODS

Forty families who have a child with a diagnosis of ASD were enrolled to the study. DNA samples were obtained from each family member. Bidirectional CC2D1A gene sequencing was performed with CEQ Cycle Sequencing Kit, and the products were analyzed on the Beckman CEQ 8000. All of the genetic analysis was conducted in Erciyes University Genome and Stem Cell Center (GENKOK).

RESULTS

According to the sequencing results, we defined new alterations in this gene with two SNPs in exon 15 and 19 (rs747172992 and rs1364074600) in our patients. We found a pathogenic variant in one patient. This variant was located in the acceptor region. Six of the variants were missense mutations. Additionally, six different benign variants were detected in 30 patients; however, they were not associated with ASD. Two patients carried multiple rare variants.

CONCLUSION

In vitro and in vivo functional analysis with this gene will help to understand its contribution to ASD pathogenesis. Future studies may help to elucidate the underlying biological mechanisms of these variants leading to the autism phenotype.

Metformin therapy confers cardioprotection against the remodeling of gap junction in tachycardia-induced atrial fibrillation dog model

OBJECTIVE

Metformin, introduced in 1957, is widely used as an anti-diabetic drug and has considerable benefits in cardiovascular disease reportedly, dependent or independent on its glucose-lowering effects. Aim of this study was to investigate the effect of metformin on gap junction and the inducibility of AF.

METHODS

Beagle dogs were subjected to acute or chronic pacing at right atrial appendage by a pacemaker to develop an AF model and electrophysiological parameters were measured. In vitro study, a cell fast pacing model was developed by CardioExcyte 96. We performed Western blot, histology immunohistochemical staining and electron microscopy to detect the effect of metformin.

RESULTS

In chronic AF model, the inducibility and duration of AF increased obviously after pacing for 6 weeks compared with sham-operated group (Inducibility, 3.33 ± 5.77 vs. 85.33 ± 7.89%, P<0.0001; Duration, 0.8 ± 0.84 vs. 11 ± 2.67 ms, P<0.0001). Effective refractory periods (ERP) decreased at left and right left atrium and atrial appendages compared with sham-operated group (123.95 ± 6.57 vs. 89.96 ± 7.39 ms P<0.0001). Metformin attenuated the pacing-induced increase in EPR (89.96 ± 7.39 vs. 105.83 ± 7.45 ms, P<0.05), AF inducibility and AF duration (Inducibility, 85.33 ± 7.89 vs. 64.17 ± 7.36%, Duration, 11 ± 2.67 vs. 8.62 ± 1.15 ms, P<0.05). The expression of Cx43 shows a significant downregulation(about 38%, P<0.001) after chronic pacing and treating with metformin could alleviate this decrease(P<0.01). However, the effect of metformin in acute pacing model is limited. The immunohistochemical staining of cardiac tissue also shown that there is more lateralized Cx43 under pacing condition (87.67 ± 2.52 vs. 60.8 ± 9.13%, P<0.005). These pacing-induced lateralize Cx43 could be alleviated by the metformin (48.4 ± 8.62 vs. 60.8 ± 9.13%, P<0.05). Additionally, metformin could affect the interactions of ZO-1 with p-Src/Cx43 via decrease the abnormal cAMP level after pacing (84.04 ± 4.58 vs. 69.34 ± 4.5 nmol/L, P<0.001).

CONCLUSIONS

Metformin could alleviate the vulnerability of AF and attenuate the downregulation of gap junction under pacing condition via AMPK pathway and decreasing the P-Src level.

Molecular causes of sex-specific deficits in rodent models of neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) such as intellectual disability and autism spectrum disorder consistently show a male bias in prevalence, but it remains unclear why males and females are affected with different frequency. While many behavioral studies of transgenic NDD models have focused only on males, the requirement by the National Institutes of Health to consider sex as a biological variable has promoted the comparison of male and female performance in wild-type and mutant animals. Here, we review examples of rodent models of NDDs in which sex-specific deficits were identified in molecular, physiological, and/or behavioral responses, showing sex differences in susceptibility to disruption of genes mutated in NDDs. Haploinsufficiency in genes involved in mechanisms such as synaptic function (GABRB3 and NRXN1), chromatin remodeling (CHD8, EMHT1, and ADNP), and intracellular signaling (CC2D1A and ERK1) lead to more severe behavioral outcomes in males. However, in the absence of behavioral deficits, females can still present with cellular and electrophysiological changes that could be due to compensatory mechanisms or differential allocation of molecular and cellular functions in the two sexes. By contrasting these findings with mouse models where females are more severely affected (MTHFR and AMBRA1), we propose a framework to approach the study of sex-specific deficits possibly leading to sex bias in NDDs.

Integrated Transcriptome Analyses Revealed Key Target Genes in Mouse Models of Autism

Genetic mutations are the major pathogenic factor of Autism Spectrum Disorder (ASD). In recent years, more and more ASD risk genes have been revealed, among which there are a group of transcriptional regulators. Considering the similarity of the core clinical phenotypes, it is possible that these different factors may regulate the expression levels of certain key targets. Identification of these targets could facilitate the understanding of the etiology and developing of novel diagnostic and therapeutic methods. Therefore, we performed integrated transcriptome analyses of RNA-Seq and microarray data in multiple ASD mouse models and identified a number of common downstream genes in various brain regions, many of which are related to the structure and function of the synapse components or drug addiction. We then established protein-protein interaction networks of the overlapped targets and isolated the hub genes by 11 algorithms based on the topological structure of the networks, including Sdc4, Vegfa, and Cp in the Cortex-Adult subgroup, Gria1 in the Cortex-Juvenile subgroup, and Kdr, S1pr1, Ubc, Grm2, Grin2b, Nrxn1, Pdyn, Grin3a, Itgam, Grin2a, Gabra2, and Camk4 in the Hippocampus-Adult subgroup, many of which have been associated with ASD in previous studies. Finally, we cross compared our results with human brain transcriptional data sets and verified several key candidates, which may play important role in the pathology process of ASD, including SDC4, CP, S1PR1, UBC, PDYN, GRIN2A, GABRA2, and CAMK4. In summary, by integrated bioinformatics analysis, we have identified a series of potentially important molecules for future ASD research. Autism Res 2020, 13: 352-368. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Abnormal transcriptional regulation accounts for a significant portion of Autism Spectrum Disorder. In this study, we performed transcriptome analyses of mouse models to identify common downstream targets of transcriptional regulators involved in ASD. We identified several recurrent target genes that are close related to the common pathological process of ASD, including SDC4, CP, S1PR1, UBC, PDYN, GRM2, NRXN1, GRIN3A, ITGAM, GRIN2A, GABRA2, and CAMK4. These results provide potentially important targets for understanding the molecular mechanism of ASD.

Protection from Amyloid β Peptide-Induced Memory, Biochemical, and Morphological Deficits by a Phosphodiesterase-4D Allosteric Inhibitor

Recent imaging studies of amyloid and tau in cognitively normal elderly subjects imply that Alzheimer's pathology can be tolerated by the brain to some extent due to compensatory mechanisms operating at the cellular and synaptic levels. The present study investigated the effects of an allosteric inhibitor of phosphodiesterase-4D (PDE4D), known as BPN14770 (2-(4-((2-(3-Chlorophenyl)-6-(trifluoromethyl)pyridin-4-yl)methyl)phenyl)acetic Acid), on impairment of memory, dendritic structure, and synaptic proteins induced by bilateral microinjection of oligomeric amyloid beta (Aβ _1-42 into the hippocampus of humanized PDE4D (hPDE4D) mice. The hPDE4D mice provide a unique and powerful genetic tool for assessing PDE4D target engagement. Behavioral studies showed that treatment with BPN14770 significantly improved memory acquisition and retrieval in the Morris water maze test and the percentage of alternations in the Y-maze test in the model of Aβ impairment. Microinjection of oligomeric Aβ _1-42 caused decreases in the number of dendrites, dendritic length, and spine density of pyramid neurons in the hippocampus. These changes were prevented by BPN14770 in a dose-dependent manner. Furthermore, molecular studies showed that BPN14770 prevented Aβ-induced decreases in synaptophysin, postsynaptic density protein 95, phosphorylated cAMP-response element binding protein (CREB)/CREB, brain-derived neurotrophic factor, and nerve growth factor inducible protein levels in the hippocampus. The protective effects of BPN14770 against Aβ-induced memory deficits, synaptic damage, and the alteration in the cAMP-meditated cell signaling cascade were blocked by H-89 (N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride), an inhibitor of protein kinase A. These results suggest that BPN14770 may activate compensatory mechanisms that support synaptic health even with the onset of amyloid pathology in Alzheimer's disease. SIGNIFICANCE STATEMENT: This study demonstrates that a phosphodiesterase-4D allosteric inhibitor, BPN14770, protects against memory loss and neuronal atrophy induced by oligomeric Aβ _1-42. The study provides useful insight into the potential role of compensatory mechanisms in Alzheimer's disease in a model of oligomeric Aβ _1-42 neurotoxicity.