Local translation of the Down syndrome cell adhesion molecule (DSCAM) mRNA in the vertebrate central nervous system

Synaptic cell adhesion molecules contribute to the pathogenesis and progression of fragile X syndrome

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and a monogenic cause of autism spectrum disorders. Deficiencies in the fragile X messenger ribonucleoprotein, encoded by the FMR1 gene, lead to various anatomical and pathophysiological abnormalities and behavioral deficits, such as spine dysmorphogenesis and learning and memory impairments. Synaptic cell adhesion molecules (CAMs) play crucial roles in synapse formation and neural signal transmission by promoting the formation of new synaptic contacts, accurately organizing presynaptic and postsynaptic protein complexes, and ensuring the accuracy of signal transmission. Recent studies have implicated synaptic CAMs such as the immunoglobulin superfamily, N-cadherin, leucine-rich repeat proteins, and neuroligin-1 in the pathogenesis of FXS and found that they contribute to defects in dendritic spines and synaptic plasticity in FXS animal models. This review systematically summarizes the biological associations between nine representative synaptic CAMs and FMRP, as well as the functional consequences of the interaction, to provide new insights into the mechanisms of abnormal synaptic development in FXS.

Integrated analysis of plasma proteome and cortex single-cell transcriptome reveals the novel biomarkers during cortical aging

Background

With the increase of age, multiple physiological functions of people begin gradually degenerating. Regardless of natural aging or pathological aging, the decline in cognitive function is one of the most obvious features in the process of brain aging. Brain aging is a key factor for several neuropsychiatric disorders and for most neurodegenerative diseases characterized by onset typically occurring late in life and with worsening of symptoms over time. Therefore, the early prevention and intervention of aging progression are particularly important. Since there is no unified conclusion about the plasma diagnostic biomarkers of brain aging, this paper innovatively employed the combined multi-omics analysis to delineate the plasma markers of brain aging.

Methods

In order to search for specific aging markers in plasma during cerebral cortex aging, we used multi-omics analysis to screen out differential genes/proteins by integrating two prefrontal cortex (PFC) single-nucleus transcriptome sequencing (snRNA-seq) datasets and one plasma proteome sequencing datasets. Then plasma samples were collected from 20 young people and 20 elder people to verify the selected differential genes/proteins with ELISA assay.

Results

We first integrated snRNA-seq data of the post-mortem human PFC and generated profiles of 65,064 nuclei from 14 subjects across adult (44-58 years), early-aging (69-79 years), and late-aging (85-94 years) stages. Seven major cell types were classified based on established markers, including oligodendrocyte, excitatory neurons, oligodendrocyte progenitor cells, astrocytes, microglia, inhibitory neurons, and endotheliocytes. A total of 93 cell-specific genes were identified to be significantly associated with age. Afterward, plasma proteomics data from 2,925 plasma proteins across 4,263 young adults to nonagenarians (18-95 years old) were combined with the outcomes from snRNA-seq data to obtain 12 differential genes/proteins (GPC5, CA10, DGKB, ST6GALNAC5, DSCAM, IL1RAPL2, TMEM132C, VCAN, APOE, PYH1R, CNTN2, SPOCK3). Finally, we verified the 12 differential genes by ELISA and found that the expression trends of five biomarkers (DSCAM, CNTN2, IL1RAPL2, CA10, GPC5) were correlated with brain aging.

Conclusion

Five differentially expressed proteins (DSCAM, CNTN2, IL1RAPL2, CA10, GPC5) can be considered as one of the screening indicators of brain aging, and provide a scientific basis for clinical diagnosis and intervention.

The Challenging Pathway of Treatment for Neurogenesis Impairment in Down Syndrome: Achievements and Perspectives

Down syndrome (DS), also known as trisomy 21, is a genetic disorder caused by triplication of Chromosome 21. Gene triplication may compromise different body functions but invariably impairs intellectual abilities starting from infancy. Moreover, after the fourth decade of life people with DS are likely to develop Alzheimer’s disease. Neurogenesis impairment during fetal life stages and dendritic pathology emerging in early infancy are thought to be key determinants of alterations in brain functioning in DS. Although the progressive improvement in medical care has led to a notable increase in life expectancy for people with DS, there are currently no treatments for intellectual disability. Increasing evidence in mouse models of DS reveals that pharmacological interventions in the embryonic and neonatal periods may greatly benefit brain development and cognitive performance. The most striking results have been obtained with pharmacotherapies during embryonic life stages, indicating that it is possible to pharmacologically rescue the severe neurodevelopmental defects linked to the trisomic condition. These findings provide hope that similar benefits may be possible for people with DS. This review summarizes current knowledge regarding (i) the scope and timeline of neurogenesis (and dendritic) alterations in DS, in order to delineate suitable windows for treatment; (ii) the role of triplicated genes that are most likely to be the key determinants of these alterations, in order to highlight possible therapeutic targets; and (iii) prenatal and neonatal treatments that have proved to be effective in mouse models, in order to rationalize the choice of treatment for human application. Based on this body of evidence we will discuss prospects and challenges for fetal therapy in individuals with DS as a potential means of drastically counteracting the deleterious effects of gene triplication.

[Differential expression profile of miRNAs in amniotic fluid exosomes from fetuses with Down syndrome]

OBJECTIVE

To investigate the role of miRNAs in amniotic fluid exosomes in growth and development of fetuses with Down syndrome (DS).

METHODS

Amniotic fluid were collected from 20 fetuses with DS and 20 normal fetuses (control) to extract amniotic exosome miRNA. MicroRNA sequencing technique was used to identify the differentially expressed miRNAs between the two groups, for which gene ontology (GO) and pathway analysis was performed. Three differentially expressed miRNAs with the strongest correlation with DS phenotype were selected for qPCR verification. Dual luciferase reporter assay was used to verify the activity of let-7d-5p for targeted regulation of BACH1.

RESULTS

We identified 15 differentially expressed miRNAs in DS as compared with the control group, among which 7 miRNAs were up-regulated and 8 were down-regulated. Target gene prediction results showed that the differentially expressed miRNAs targeted 17 DS-related genes. GO analysis revealed that the main functions of the target genes involved protein binding, protein transport, ATP binding, transferase activity and synapses. Pathway analysis revealed that the functional pathways were closely related with the development of the nervous system. qPCR results showed that the expression levels of miR-140-3p and let-7d-5p were significantly lower in DS group than in the control group (P < 0.05), as was consistent with miRNA sequencing results; the expression level of miR-4512 was significantly higher in DS group than in control group (P < 0.05), which was contrary to miRNA sequencing results. The results of double luciferase reporter gene assay confirmed that let-7d-5p was capable of targeted regulation of BACH1 expression.

CONCLUSION

Let-7d-5p in amniotic fluid exosomes may promote oxidative stress events in the brain of fetuses with DS by regulating BACH1 expression.

Role of DSCAM in the Development of Neural Control of Movement and Locomotion

Locomotion results in an alternance of flexor and extensor muscles between left and right limbs generated by motoneurons that are controlled by the spinal interneuronal circuit. This spinal locomotor circuit is modulated by sensory afferents, which relay proprioceptive and cutaneous inputs that inform the spatial position of limbs in space and potential contacts with our environment respectively, but also by supraspinal descending commands of the brain that allow us to navigate in complex environments, avoid obstacles, chase prey, or flee predators. Although signaling pathways are important in the establishment and maintenance of motor circuits, the role of DSCAM, a cell adherence molecule associated with Down syndrome, has only recently been investigated in the context of motor control and locomotion in the rodent. DSCAM is known to be involved in lamination and delamination, synaptic targeting, axonal guidance, dendritic and cell tiling, axonal fasciculation and branching, programmed cell death, and synaptogenesis, all of which can impact the establishment of motor circuits during development, but also their maintenance through adulthood. We discuss herein how DSCAM is important for proper motor coordination, especially for breathing and locomotion.

Dscam in immunity: A question of diversity in insects and crustaceans

In insects and crustaceans, thousands of Down syndrome cell adhesion molecules (Dscam) can be generated by alternative splicing of variable exons from a single-locus gene, Dscam-hv. This extraordinarily versatile gene (38,016 protein isoforms produced in Drosophila) was first proposed to be involved in exon guidance and subsequently implicated in immunity as a hypervariable immune molecule. Almost 20 y after discovery of Dscam-hv, there have been many studies in insects and crustaceans regarding roles of Dscam in immunity, with many similarities and concurrently, many differences. Here, we review the current status of Dscam-hv, presented as a comparison of similarities and differences in insects and crustaceans and discuss hypotheses of Dscam functions in immunity.