Association study of the vesicular monoamine transporter 1 (VMAT1) gene with autism in an Iranian population

Mouse models for inherited monoamine neurotransmitter disorders

Several mouse models have been developed to study human defects of primary and secondary inherited monoamine neurotransmitter disorders (iMND). As the field continues to expand, current defects in corresponding mouse models include enzymes and a molecular co-chaperone involved in monoamine synthesis and metabolism (PAH, TH, PITX3, AADC, DBH, MAOA, DNAJC6), tetrahydrobiopterin (BH4) cofactor synthesis and recycling (adGTPCH1/DRD, arGTPCH1, PTPS, SR, DHPR), and vitamin B6 cofactor deficiency (ALDH7A1), as well as defective monoamine neurotransmitter packaging (VMAT1, VMAT2) and reuptake (DAT). No mouse models are available for human DNAJC12 co-chaperone and PNPO-B6 deficiencies, disorders associated with recessive variants that result in decreased stability and function of the aromatic amino acid hydroxylases and decreased neurotransmitter synthesis, respectively. More than one mutant mouse is available for some of these defects, which is invaluable as different variant-specific (knock-in) models may provide more insights into underlying mechanisms of disorders, while complete gene inactivation (knock-out) models often have limitations in terms of recapitulating complex human diseases. While these mouse models have common phenotypic traits also observed in patients, reflecting the defective homeostasis of the monoamine neurotransmitter pathways, they also present with disease-specific manifestations with toxic accumulation or deficiency of specific metabolites related to the specific gene affected. This review provides an overview of the currently available models and may give directions toward selecting existing models or generating new ones to investigate novel pathogenic mechanisms and precision therapies.

Genetic and neural mechanisms of sleep disorders in children with autism spectrum disorder: a review

Background

The incidence of sleep disorders in children with autism spectrum disorder (ASD) is very high. Sleep disorders can exacerbate the development of ASD and impose a heavy burden on families and society. The pathological mechanism of sleep disorders in autism is complex, but gene mutations and neural abnormalities may be involved.

Methods

In this review, we examined literature addressing the genetic and neural mechanisms of sleep disorders in children with ASD. The databases PubMed and Scopus were searched for eligible studies published between 2013 and 2023.

Results

Prolonged awakenings of children with ASD may be caused by the following processes. Mutations in the MECP2, VGAT and SLC6A1 genes can decrease GABA inhibition on neurons in the locus coeruleus, leading to hyperactivity of noradrenergic neurons and prolonged awakenings in children with ASD. Mutations in the HRH1, HRH2, and HRH3 genes heighten the expression of histamine receptors in the posterior hypothalamus, potentially intensifying histamine's ability to promote arousal. Mutations in the KCNQ3 and PCDH10 genes cause atypical modulation of amygdala impact on orexinergic neurons, potentially causing hyperexcitability of the hypothalamic orexin system. Mutations in the AHI1, ARHGEF10, UBE3A, and SLC6A3 genes affect dopamine synthesis, catabolism, and reuptake processes, which can elevate dopamine concentrations in the midbrain. Secondly, non-rapid eye movement sleep disorder is closely related to the lack of butyric acid, iron deficiency and dysfunction of the thalamic reticular nucleus induced by PTCHD1 gene alterations. Thirdly, mutations in the HTR2A, SLC6A4, MAOA, MAOB, TPH2, VMATs, SHANK3, and CADPS2 genes induce structural and functional abnormalities of the dorsal raphe nucleus (DRN) and amygdala, which may disturb REM sleep. In addition, the decrease in melatonin levels caused by ASMT, MTNR1A, and MTNR1B gene mutations, along with functional abnormalities of basal forebrain cholinergic neurons, may lead to abnormal sleep-wake rhythm transitions.

Conclusion

Our review revealed that the functional and structural abnormalities of sleep-wake related neural circuits induced by gene mutations are strongly correlated with sleep disorders in children with ASD. Exploring the neural mechanisms of sleep disorders and the underlying genetic pathology in children with ASD is significant for further studies of therapy.

Inhibition of VMAT2 by β2-adrenergic agonists, antagonists, and the atypical antipsychotic ziprasidone

Vesicular monoamine transporter 2 (VMAT2) is responsible for packing monoamine neurotransmitters into synaptic vesicles for storage and subsequent neurotransmission. VMAT2 inhibitors are approved for symptomatic treatment of tardive dyskinesia and Huntington's chorea, but despite being much-studied inhibitors their exact binding site and mechanism behind binding and inhibition of monoamine transport are not known. Here we report the identification of several approved drugs, notably β2-adrenergic agonists salmeterol, vilanterol and formoterol, β2-adrenergic antagonist carvedilol and the atypical antipsychotic ziprasidone as inhibitors of rat VMAT2. Further, plausible binding modes of the established VMAT2 inhibitors reserpine and tetrabenazine and hit compounds salmeterol and ziprasidone were identified using molecular dynamics simulations and functional assays using VMAT2 wild-type and mutants. Our findings show VMAT2 as a potential off-target of treatments with several approved drugs in use today and can also provide important first steps in both drug repurposing and therapy development targeting VMAT2 function.

Genetic and molecular biology of autism spectrum disorder among Middle East population: a review

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disease, characterized by impaired social communication, executive dysfunction, and abnormal perceptual processing. It is more frequent among males. All of these clinical manifestations are associated with atypical neural development. Various genetic and environmental risk factors are involved in the etiology of autism. Genetic assessment is essential for the early detection and intervention which can improve social communications and reduce abnormal behaviors. Although, there is a noticeable ASD incidence in Middle East countries, there is still a lack of knowledge about the genetic and molecular biology of ASD among this population to introduce efficient diagnostic and prognostic methods.

MAIN BODY

In the present review, we have summarized all of the genes which have been associated with ASD progression among Middle East population. We have also categorized the reported genes based on their cell and molecular functions.

CONCLUSIONS

This review clarifies the genetic and molecular biology of ASD among Middle East population and paves the way of introducing an efficient population based panel of genetic markers for the early detection and management of ASD in Middle East countries.

IFNG/IFNG-AS1 expression level balance: implications for autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder associated with different epidemiological, genetic, epigenetic, and environmental factors. Although its etiology is not fully understood, immune dysfunction is implicated in this disease. Recently, a large number of genes encoding long noncoding RNAs (lncRNAs) were discovered which act as positive or negative regulators of neighboring target genes. The lncRNA, Interferon gamma-antisense RNA (IFNG-AS1), regulates expression levels of the Interferon gamma (IFNG) gene. In the present study, we investigated expression of IFNG and IFNG-AS1 in 50 children with ASD (15 females and 35 males, mean age: 6 ± 1.4 years) and 50 healthy controls (14 females and 36 males, mean age: 6 ± 1.74 years) by real time PCR technique. The results showed significant up-regulation of IFNG and down-regulation of IFNG-AS1 expression in children with ASD compared to controls (Fold change = 1.5, P < 0.0001; Fold change = -0.143, P = 0.013, respectively). The IFNG expression level increase was more pronounced in male ASD children (Fold change = 1.621; p < 0.0001). Our data reveal a functional disruption in the interactive network of IFNG/IFNG-AS1 regulation, which could be a contributing factor in the chronic inflammatory aspect of ASD. Our findings can help understanding the underlying contributors to ASD pathogenesis and find novel treatment options for children with ASD.

Association of human serotonin receptor 4 promoter methylation with autism spectrum disorder

Human serotonin receptor 4 (HTR4) encodes a 5-HT4 receptor involved in learning, memory, depression, anxiety, and feeding behavior. The aim of this study was to investigate the association between the deoxyribonucleic acid (DNA) methylation of HTR4 promoter and autism spectrum disorder (ASD), a disease characterized by communication disorder and repetitive or restrictive behavior.Peripheral blood DNA was obtained from 61 ASD children and 66 healthy children, and the DNA methylation of HTR4 promoter was assessed by quantitative methylation-specific polymerase chain reaction. We used percentage of methylated reference (PMR) to represent DNA methylation level.Due to significant age differences between ASD cases and controls (3 [2, 5] years and 6 [5, 6] years, P = 3.34E-10), we used binary logistic regression analysis for adjustment. Our results showed that the DNA methylation levels of HTR4 promoter were significantly lower in children with ASD than in healthy children (median PMR: 66.23% vs 94.31%,P = .028, age-adjusted P = .034). In addition, the DNA methylation of HTR4 promoter was inversely associated with age in male ASD cases (total cases: r = -0.283, P = .027; male cases: r = -0.431, P = .002; female cases: r = -0.108, P = .752). Dual-luciferase reporter gene assay showed that the reporter gene expression in the strain with recombinant pGL3-promoter-HTR4 plasmid was significantly higher than that in the strain with pGL3-promoter plasmid (fold change = 2.01, P = .0065), indicating that the HTR4 promoter fragment may contain transcription factors to upregulate promoter activity.Our study suggested that hypomethylation of the HTR4 promoter is a potential biomarker for predicting the risk of male ASD.

Human-specific mutations in VMAT1 confer functional changes and multi-directional evolution in the regulation of monoamine circuits

BACKGROUND

Neurochemicals like serotonin and dopamine play crucial roles in human cognitive and emotional functions. Vesicular monoamine transporter 1 (VMAT1) transports monoamine neurotransmitters, and its variant (136Thr) is associated with various psychopathological symptoms and reduced monoamine uptake relative to 136Ile. We previously showed that two human-specific amino acid substitutions (Glu130Gly and Asn136Thr/Ile) of VMAT1 were subject to positive natural selection. However, the potential functional alterations caused by these substitutions (Glu130Gly and Asn136Thr) remain unclear. To assess functional changes in VMAT1 from an evolutionary perspective, we reconstructed ancestral residues and examined the role of these substitutions in monoamine uptake in vitro using fluorescent false neurotransmitters (FFN), which are newly developed substances used to quantitatively assay VMATs.

RESULTS

Immunoblotting confirmed that all the transfected YFP-VMAT1 variants are properly expressed in HEK293T cells at comparable levels, and no significant difference was seen in the density and the size of vesicles among them. Our fluorescent assays revealed a significant difference in FFN206 uptake among VMAT1 variants: 130Glu/136Asn, 130Glu/136Thr, and 130Gly/136Ile showed significantly higher levels of FFN206 uptake than 130Gly/136Asn and 130Gly/136Thr, indicating that both 130Glu and 136Ile led to increased neurotransmitter uptake, for which 136Thr and 136Asn were comparable by contrast.

CONCLUSIONS

These findings suggest that monoamine uptake by VMAT1 initially declined (from 130Glu/136Asn to 130Gly/136Thr) in human evolution, possibly resulting in higher susceptibility to the external environment of our ancestors.

Extreme enhancement or depletion of serotonin transporter function and serotonin availability in autism spectrum disorder

A variety of human and animal studies support the hypothesis that serotonin (5-hydroxytryptamine or 5-HT) system dysfunction is a contributing factor to the development of autism in some patients. However, many questions remain about how developmental manipulation of various components that influence 5-HT signaling (5-HT synthesis, transport, metabolism) persistently impair social behaviors. This review will summarize key aspects of central 5-HT function important for normal brain development, and review evidence implicating perinatal disruptions in 5-HT signaling in the pathophysiology of autism spectrum disorder. We discuss the importance, and relative dearth, of studies that explore the possible correlation to autism in the interactions between important intrinsic and extrinsic factors that may disrupt 5-HT homeostasis during development. In particular, we focus on exposure to 5-HT transport altering mechanisms such as selective serotonin-reuptake inhibitors or genetic polymorphisms in primary or auxiliary transporters of 5-HT, and how they relate to neurological stores of serotonin and its precursors. A deeper understanding of the many mechanisms by which 5-HT signaling can be disrupted, alone and in concert, may contribute to an improved understanding of the etiologies and heterogeneous nature of this disorder. We postulate that extreme bidirectional perturbations of these factors during development likely compound or synergize to facilitate enduring neurochemical changes resulting in insufficient or excessive 5-HT signaling, that could underlie the persistent behavioral characteristics of autism spectrum disorder.

Expression of the Vesicular Monoamine Transporter Gene Solute Carrier Family 18 Member 1 (SLC18A1) in Lung Cancer

BACKGROUND

One aspect of smoking and lung cancer that has not been closely examined, is that regarding genes that may predispose to tobacco dependence. Smoking and mental illness are tightly linked, apparently the result of smokers using cigarettes to self-medicate for mental problems. The gene for solute carrier family 18 member A1 (vesicular monoamine transporter; SLC18A1) is of particular interest in this regard because of its association with schizophrenia, autism and bipolar illness as well as with cancer. In the current study, the relationship of SLC18A1 expression with smoking and lung cancer was analyzed.

MATERIALS AND METHODS

The association between smoking, SLC18A1 expression and overall survival in the lung cancer dataset in The Cancer Genome Atlas was evaluated using the Genomic Data Commons Data Portal (https://portal.gdc.cancer.gov), as well as CbioPortal for Cancer Genomics (http://www.cbioportal.org) and the University of California Santa Cruz Xena browser (https://xenabrowser.net).

RESULTS

Increased expression of SLC18A1 was found to be associated with a significantly increased survival in patients with adenocarcinoma (p=0.0058), but not those with squamous carcinoma (p=0.96). Lifelong never-smokers had the highest SLC18A1 expression. In the Pan Cancer Atlas, increased expression of SLC18A1 places such a tumor in group C5, among immunologically-quiet tumors.

CONCLUSION

Most never-smokers with lung cancer do not respond to immune checkpoint inhibitors (ICIs). But for unknown reasons, a small proportion do show clinical benefit from the ICI pembrolizumab. Because of the good response of this group, it may be worthwhile assessing their SLC18A1 expression pre-treatment as a marker for potential clinical benefit. If SLC18A1 expression is low, a never-smoker may respond well to ICIs. High levels of expression would indicate a C5 tumor less likely to respond to ICIs. SLC18A1 might complement other biomarkers currently under study in relation to programmed cell death protein 1/programmed cell death protein ligand 1 inhibition.

Cytoplasmic FMRP interacting protein 1/2 (CYFIP1/2) expression analysis in autism

Cytoplasmic FMRP interacting proteins 1 and 2 (CYFIP1/2) have been previously shown to be associated with central nervous system (CNS) disorders such as autism spectrum disorder (ASD). Moreover, dysregulation of their expression levels results in disturbances in CNS maturation and neuronal interconnections. In the present study, we compared expression levels of CYFIP1/2 in peripheral blood of 30 ASD patients and 41 healthy subjects by means of real time PCR. Expression analysis showed significant over-expression of CYFIP1/2 in ASD patients compared with healthy subjects (Fold change = 3.252, P < 0.0001 and Fold change = 4.14, P = 0.001 respectively). Such over-expression was also seen for CYFIP1 in male and female patients when compared with the corresponding control subjects. In addition, a significant correlation was found between CYFIP1 transcript levels and age in female subjects. A significant correlation was detected between expression levels of these genes in control subjects. The current study provides further supports for contribution of CYFIP1/2 in the pathogenesis of ASD and potentiates it as a peripheral marker for ASD diagnosis. Future studies in larger sample sizes are needed to confirm the results of the current study.

Association Study of VMAT1 Polymorphisms and Suicide Behavior

Genetic association studies have linked suicide behavior with genes encoding transporters of monoamine. Variants in the vesicular monoamine transporter 1 (VMAT1) have been previously shown to be associated with several psychiatric disorders including schizophrenia and bipolar disorder. However, their association with suicide behavior has not been explored. In the present study, we genotyped three single-nucleotide polymorphisms (rs2270637, rs1390938, and rs2279709) within this gene in 100 individuals who attempted suicide, 236 suicide victims, and 300 control subjects without any history of psychiatric disorders or suicide ideation. We demonstrated no difference in genotype, allele, or haplotype frequencies of theses single-nucleotide polymorphisms between the study groups. Consequently, contribution of VMAT1 in risk of psychiatric disorders might be independent of suicide behavior. Future studies with larger sample sizes are needed to confirm our results.