New Perspectives of Dyrk1A Role in Neurogenesis and Neuropathologic Features of Down Syndrome

Characterizing executive functioning and associated behaviors in individuals with dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) syndrome

Introduction

DYRK1A, a protein kinase located on human chromosome 21, plays a role in postembryonic neuronal development and degeneration. Alterations to DYRK1A have been consistently associated with cognitive functioning and neurodevelopmental disorders (e.g., autism, intellectual disability). However, the broader cognitive and behavioral phenotype of DYRK1A syndrome requires further characterization. Specifically, executive functioning, or cognitive processes that are necessary for goal-directed behavior, has not yet been characterized in this population.

Methods

Individuals with DYRK1A variants (n = 29; ages 4 to 21 years) were assessed with a standardized protocol with multiple measures of executive functioning: Delis-Kaplan Executive Function Schedule, and chronologically age-appropriate caregiver-report forms of the Behavior Rating Inventory of Executive Function (BRIEF) and Achenbach System of Empirically Based Assessment (ASEBA). We first examined the feasibility and appropriateness of established executive functioning measures among participants with DYRK1A syndrome to inform selection of executive functioning tools in future research. We then characterized executive functioning among the group, including associations with other phenotypic features.

Results

Neurocognitive assessments of executive functioning were deemed infeasible due to cognitive and verbal functioning. Caregiver-report revealed elevated executive functioning concerns related to self-monitoring, working memory, and planning/organization on the BRIEF, and attention and ADHD on the CBCL. Only two participants had existing ADHD diagnoses; however, 5 participants (out of 10 participants with data) exceeded the cutoff on the BRIEF, 13 individuals (out of 27 with data) exceeded the cutoff on the ASEBA ADHD subscale, and 18 exceeded the cutoff on the ASEBA attention subscale. There was concordance between ADHD diagnosis and the ASEBA, but not BRIEF. Executive functioning was correlated with nonverbal IQ and autism traits.

Discussion

Objective measures of executive functioning are needed for individuals with intellectual disability who are nonverbal and/or have motor limitations. Diagnostic overshadowing, or the tendency to attribute all problems to intellectual disability and to leave other co-existing conditions, such as executive functioning challenges or ADHD, undiagnosed, is common. Phenotypic characterization of executive functioning is therefore important for our understanding of DYRK1A syndrome and for ensuring that caregivers' concerns are addressed, and individuals receive the clinical services that best meet their needs.

The cholinotrophic system in Down syndrome

Cholinergic basal forebrain (CBF) projection neurons within the nucleus basalis and striatal cholinergic interneurons degenerate in individuals with Down syndrome (DS). However, the neuropathobiology of these diverse cholinergic phenotypes remains underinvestigated. This review summarizes the alterations of cholinergic, neurotrophic survival and cell death factors as well as tau pathology and amyloidopathy, and their effects upon these cell types in DS. In trisomy, the developing cholinergic system remains stable, whereas the neurotrophic receptors are compromised between control and DS cases. Both cholinergic neuronal phenotypes display severe cellular degeneration in both adult and the aged people with DS. Although developing cholinergic striatal neurons display a similar morphology between phenotypes, cholinergic striatal neurons appear dystrophic in adults with DS. Both cholinergic cell types display tau tangle pathology in elders with DS. Novel findings suggest that alterations in plasma and cerebral spinal fluid levels of proNGF, NGF metabolites, and select classes of neuronal genes are potential biomarkers to distinguish nondemented from demented people with DS. Compounds that target cholinergic pathways, TrkA agonists, p75NTR/proNGF small molecular antagonists, NGF metabolites, and select gene ontology classes are potential targets to slow degeneration of the CBF memory connectome in DS with translation to AD.

Cholinergic System Structure and Function Changes in Individuals with Down Syndrome During the Development of Alzheimer's Disease

Adults with Down syndrome represent the population with the highest risk of developing Alzheimer's disease worldwide. The cholinergic system is known to decline in Alzheimer's disease, with this decline responsible for many of the cognitive deficits that develop. The integrity of the cholinergic system across the lifespan in individuals with Down syndrome is not well characterized. Small fetal and infant post-mortem studies suggest an intact cholinergic projection system with a potential reduction in cholinergic receptors, while post-mortem studies in adults with Down syndrome reveal an age-related decrease in cholinergic integrity. Advances in magnetic resonance imaging (MRI) and positron emission tomography (PET) over the last 20 years have allowed for studies investigating the changes in cholinergic integrity across aging and during the development of Alzheimer's disease. One large cross-sectional study demonstrated reduced cholinergic basal forebrain volume measured by MRI associated with increasing Alzheimer's disease pathology. In a small cohort of adults with Down syndrome, we have recently reported that PET measures of cholinergic integrity negatively correlated with amyloid accumulation. New disease-modifying treatments for Alzheimer's disease and treatments under development for Alzheimer's disease in Down syndrome have the potential to preserve the cholinergic system, while treatments targeting the cholinergic system directly may be used in conjunction with disease-modifying therapies to improve cognitive function further. A greater understanding of cholinergic neuronal and receptor integrity across the lifespan in individuals with Down syndrome will provide insights as to when targeting the cholinergic system is an appropriate therapeutic option and, in the future, maybe a valuable screening tool to identify individuals that would most benefit from cholinergic interventions.

DYRK1A interacts with the tuberous sclerosis complex and promotes mTORC1 activity

DYRK1A, a ubiquitously expressed kinase, is linked to the dominant intellectual developmental disorder, microcephaly, and Down syndrome in humans. It regulates numerous cellular processes such as cell cycle, vesicle trafficking, and microtubule assembly. DYRK1A is a critical regulator of organ growth; however, how it regulates organ growth is not fully understood. Here, we show that the knockdown of DYRK1A in mammalian cells results in reduced cell size, which depends on mTORC1. Using proteomic approaches, we found that DYRK1A interacts with the tuberous sclerosis complex (TSC) proteins, namely TSC1 and TSC2, which negatively regulate mTORC1 activation. Furthermore, we show that DYRK1A phosphorylates TSC2 at T1462, a modification known to inhibit TSC activity and promote mTORC1 activity. We also found that the reduced cell growth upon knockdown of DYRK1A can be rescued by overexpression of RHEB, an activator of mTORC1. Our findings suggest that DYRK1A inhibits TSC complex activity through inhibitory phosphorylation on TSC2, thereby promoting mTORC1 activity. Furthermore, using the Drosophila neuromuscular junction as a model, we show that the mnb, the fly homologs of DYRK1A, is rescued by RHEB overexpression, suggesting a conserved role of DYRK1A in TORC1 regulation.

Skeletal health in DYRK1A syndrome

DYRK1A syndrome results from a reduction in copy number of the DYRK1A gene, which resides on human chromosome 21 (Hsa21). DYRK1A has been implicated in the development of cognitive phenotypes associated with many genetic disorders, including Down syndrome (DS) and Alzheimer's disease (AD). Additionally, overexpression of DYRK1A in DS has been implicated in the development of abnormal skeletal phenotypes in these individuals. Analyses of mouse models with Dyrk1a dosage imbalance (overexpression and underexpression) show skeletal deficits and abnormalities. Normalization of Dyrk1a copy number in an otherwise trisomic animal rescues some skeletal health parameters, and reduction of Dyrk1a copy number in an otherwise euploid (control) animal results in altered skeletal health measurements, including reduced bone mineral density (BMD) in the femur, mandible, and skull. However, little research has been conducted thus far on the implications of DYRK1A reduction on human skeletal health, specifically in individuals with DYRK1A syndrome. This review highlights the skeletal phenotypes of individuals with DYRK1A syndrome, as well as in murine models with reduced Dyrk1a copy number, and provides potential pathways altered by a reduction of DYRK1A copy number, which may impact skeletal health and phenotypes in these individuals. Understanding how decreased expression of DYRK1A in individuals with DYRK1A syndrome impacts bone health may increase awareness of skeletal traits and assist in the development of therapies to improve quality of life for these individuals.

Discovery of a novel chemotype as DYRK1A inhibitors against Alzheimer's disease: Computational modeling and biological evaluation

Dual-specificity tyrosine phosphorylation-regulated kinase 1 A (DYRK1A) plays an essential role in Tau and Aβ pathology closely related to Alzheimer's disease (AD). Accumulative evidence has demonstrated DYRK1A inhibition is able to reduce the pathological features of AD. Nevertheless, there is no approved DYRK1A inhibitor for clinical use as anti-AD therapy. This is somewhat due to the lack of effective and safe chemotypes of DYRK1A inhibitors. To address this issue, we carried out in silico screening, in vitro assays and in vivo efficacy evaluation with the aim to discover a new class of DYRK1A inhibitors for potential treatment of AD. By in silico screening, we selected and purchased 16 potential DYRK1A inhibitors from the Specs chemical library. Among them, compound Q17 (Specs ID: AO-476/40829177) potently inhibited DYRK1A. The hydrogen bonds between compound Q17 and two amino acid residues named GLU239 and LYS188, were uncovered by molecular docking and molecular dynamics simulation. The cell-based assays showed that compound Q17 could protect the SH-SY5Y human neuroblastoma cell line from okadaic acid (OA)-induced injury by targeting DYRK1A. More importantly, compound Q17 significantly improved cognitive dysfunction of 3 × Tg-AD mice, ameliorated pathological changes, and attenuated Tau hyperphosphorylation as well as Aβ deposition. In summary, our computational modeling strategy is effective to identify novel chemotypes of DYRK1A inhibitors with great potential to treat AD, and the identified compound Q17 in this study is worthy of further study.

Design, synthesis, and biological evaluation of some 2-(3-oxo-5,6-diphenyl-1,2,4-triazin-2(3H)-yl)-N-phenylacetamide hybrids as MTDLs for Alzheimer's disease therapy

Inspite of established symptomatic relief drug targets, a multi targeting approach is highly in demand to cure Alzheimer's disease (AD). Simultaneous inhibition of cholinesterase (ChE), β secretase-1 (BACE-1) and Dyrk1A could be promising in complete cure of AD. A series of 18 diaryl triazine based molecular hybrids were successfully designed, synthesized, and tested for their hChE, hBACE-1, Dyrk1A and Aβ aggregation inhibitory potentials. Compounds S-11 and S-12 were the representative molecules amongst the series with multi-targeted inhibitory effects. Compound S-12 showed hAChE inhibition (IC50 value = 0.486 ± 0.047 μM), BACE-1 inhibition (IC50 value = 0.542 ± 0.099 μM) along with good anti-Aβ aggregation effects in thioflavin-T assay. Only compound S-02 of the series has shown Dyrk1A inhibition (IC50 value = 2.000 ± 0.360 μM). Compound S-12 has also demonstrated no neurotoxic liabilities against SH-SY5Y as compared to donepezil. The in vivo behavioral studies of the compound S-12 in the scopolamine- and Aβ-induced animal models also demonstrated attanuation of learning and memory functions in rats models having AD-like characteristics. The ex vivo studies, on the rat hippocampal brain demonstrated reduction in certain biochemical markers of the AD brain with a significant increase in ACh level. The Western blot and Immunohistochemistry further revealed lower tau, APP and BACE-1 molecular levels. The drosophilla AD model also revealed improved eyephenotype after treatment with compound S-12. The molecular docking studies of the compounds suggested that compound S-12 was interacting with the ChE-PAS & CAS residues and catalytic dyad residues of the BACE-1 enzymes. The 100 ns molecular dynamics simulation studies of the ligand-protein complexed with hAChE and hBACE-1 also suggested stable ligand-protein confirmation throughout the simulation run.

Dual-specificity kinase DYRK3 phosphorylates p62 at the Thr-269 residue and promotes melanoma progression

Melanoma is a type of skin cancer that originates in melanin-producing melanocytes. It is considered a multifactorial disease caused by both genetic and environmental factors, such as UV radiation. Dual-specificity tyrosine-phosphorylation-regulated kinase (DYRK) phosphorylates many substrates involved in signaling pathways, cell survival, cell cycle control, differentiation, and neuronal development. However, little is known about the cellular function of DYRK3, one of the five members of the DYRK family. Interestingly, it was observed that the expression of DYRK3, as well as p62 (a multifunctional signaling protein), is highly enhanced in most melanoma cell lines. This study aimed to investigate whether DYRK3 interacts with p62, and how this affects melanoma progression, particularly in melanoma cell lines. We found that DYRK3 directly phosphorylates p62 at the Ser-207 and Thr-269 residue. Phosphorylation at Thr-269 of p62 by DYRK3 increased the interaction of p62 with tumor necrosis factor receptor-associated factor 6 (TRAF6), an already known activator of mammalian target of rapamycin complex 1 (mTORC1) in the mTOR-involved signaling pathways. Moreover, the phosphorylation of p62 at Thr-269 promoted the activation of mTORC1. We also found that DYRK3-mediated phosphorylation of p62 at Thr-269 enhanced the growth of melanoma cell lines and melanoma progression. Conversely, DYRK3 knockdown or blockade of p62-T269 phosphorylation inhibited melanoma growth, colony formation, and cell migration. In conclusion, we demonstrated that DYRK3 phosphorylates p62, positively modulating the p62-TRAF6-mTORC1 pathway in melanoma cells. This finding suggests that DYRK3 suppression may be a novel therapy for preventing melanoma progression by regulating the mTORC1 pathway.

Hsc70 phosphorylation patterns and calmodulin regulate AP2 Clathrin-Coated-Vesicle life span for cell adhesion protein transport

AP2 forms AP2 CCV with clathrin and over 60 additional coat proteins. Due to this complexity, we have a limited understanding of CCV life cycle regulation. Synapses contain canonical AP2 CCV, canCCV, and more stable, thereby longer lived, AP2 CCV. The more stable AP2 CCV can be distinguished from canCCV due to the stable binding of Hsc70 to clathrin. The AP1/σ1B complex knockout leads to impaired synaptic vesicle recycling and altered endosomal protein sorting. This causes as a secondary phenotype the twofold upregulation of endocytosis by canCCV and by more stable AP2 CCV. These stable CCV are more stabilized than their wt counterpart, hence stCCV. They have less of the uncoating proteins synaptojanin1 and Hsc70, and more of the coat stabilizing AAK1. Hsc70 clathrin dissociation activity is regulated by complex phosphorylation patterns. Two major groups of hyper- and of hypo-phosphorylated Hsc70 proteins are formed. The latter are enriched in wt stable CCV and stabilized stCCV. Hsc70 T265 phosphorylation regulates binding of CaM/Ca2+. CaM/Ca2+ binding to the T265 domain blocks Hsc70 homodimerization and its concentration in stCCV required for clathrin disassembly. Kinases DYRK1A and CaMK-IIδ can phosphorylate T265 preventing CaM/Ca2+ binding. Their and the levels of STK38L and STK39/Cab39, which are able to phosphorylate additional Hsc70 residues are reduced in stCCV. The stCCV pathway sorts specifically the cell adhesion proteins CHL1 and Neurocan, supporting our model of that the stCCV pathway fulfills specific functions in synaptic plasticity.

Sex-specific developmental alterations in DYRK1A expression in the brain of a Down syndrome mouse model

Aberrant neurodevelopment in Down syndrome (DS)-caused by triplication of human chromosome 21-is commonly attributed to gene dosage imbalance, linking overexpression of trisomic genes with disrupted developmental processes, with DYRK1A particularly implicated. We hypothesized that regional brain DYRK1A protein overexpression in trisomic mice varies over development in sex-specific patterns that may be distinct from Dyrk1a transcription, and reduction of Dyrk1a copy number from 3 to 2 in otherwise trisomic mice reduces DYRK1A, independent of other trisomic genes. DYRK1A overexpression varied with age, sex, and brain region, with peak overexpression on postnatal day (P) 6 in both sexes. Sex-dependent differences were also evident from P15-P24. Reducing Dyrk1a copy number confirmed that these differences depended on Dyrk1a gene dosage and not other trisomic genes. Trisomic Dyrk1a mRNA and protein expression were not highly correlated. Sex-specific patterns of DYRK1A overexpression during trisomic neurodevelopment may provide mechanistic targets for therapeutic intervention in DS.

Insights from the protein interaction Universe of the multifunctional "Goldilocks" kinase DYRK1A

Human Dual specificity tyrosine (Y)-Regulated Kinase 1A (DYRK1A) is encoded by a dosage-dependent gene located in the Down syndrome critical region of human chromosome 21. The known substrates of DYRK1A include proteins involved in transcription, cell cycle control, DNA repair and other processes. However, the function and regulation of this kinase is not fully understood, and the current knowledge does not fully explain the dosage-dependent function of this kinase. Several recent proteomic studies identified DYRK1A interacting proteins in several human cell lines. Interestingly, several of known protein substrates of DYRK1A were undetectable in these studies, likely due to a transient nature of the kinase-substrate interaction. It is possible that the stronger-binding DYRK1A interacting proteins, many of which are poorly characterized, are involved in regulatory functions by recruiting DYRK1A to the specific subcellular compartments or distinct signaling pathways. Better understanding of these DYRK1A-interacting proteins could help to decode the cellular processes regulated by this important protein kinase during embryonic development and in the adult organism. Here, we review the current knowledge of the biochemical and functional characterization of the DYRK1A protein-protein interaction network and discuss its involvement in human disease.

Over-expression of Dyrk1A affects bleeding by modulating plasma fibronectin and fibrinogen level in mice

Down syndrome is the most common chromosomal abnormality in humans. Patients with Down syndrome have hematologic disorders, including mild to moderate thrombocytopenia. In case of Down syndrome, thrombocytopenia is not associated with bleeding, and it remains poorly characterized regarding molecular mechanisms. We investigated the effects of overexpression of Dyrk1A, an important factor contributing to some major Down syndrome phenotypes, on platelet number and bleeding in mice. Mice overexpressing Dyrk1A have a decrease in platelet number by 20%. However, bleeding time was found to be reduced by 50%. The thrombocytopenia and the decreased bleeding time observed were not associated to an abnormal platelet receptors expression, to a defect of platelet activation by ADP, thrombin or convulxin, to the presence of activated platelets in the circulation or to an abnormal half-life of the platelets. To propose molecular mechanisms explaining this discrepancy, we performed a network analysis of Dyrk1A interactome and demonstrated that Dyrk1A, fibronectin and fibrinogen interact indirectly through two distinct clusters of proteins. Moreover, in mice overexpressing Dyrk1A, increased plasma fibronectin and fibrinogen levels were found, linked to an increase of the hepatic fibrinogen production. Our results indicate that overexpression of Dyrk1A in mice induces decreased bleeding consistent with increased plasma fibronectin and fibrinogen levels, revealing a new role of Dyrk1A depending on its indirect interaction with these two proteins.

Rapid effects of valproic acid on the fetal brain transcriptome: Implications for brain development and autism

There is an increased incidence of autism among the children of women who take the anti-epileptic, mood stabilizing drug, valproic acid (VPA) during pregnancy; moreover, exposure to VPA in utero causes autistic-like symptoms in rodents and non-human primates. Analysis of RNAseq data ob-tained from E12.5 fetal mouse brains 3 hours after VPA administration revealed that VPA significant-ly increased or decreased the expression of approximately 7,300 genes. No significant sex differ-ences in VPA-induced gene expression were observed. Expression of genes associated with neu-rodevelopmental disorders (NDDs) such as autism as well as neurogenesis, axon growth and syn-aptogenesis, GABAergic, glutaminergic and dopaminergic synaptic transmission, perineuronal nets, and circadian rhythms was dysregulated by VPA. Moreover, expression of 399 autism risk genes was significantly altered by VPA as was expression of 252 genes that have been reported to play fundamental roles in the development of the nervous system but are not otherwise linked to autism. The goal of this study was to identify mouse genes that are: (a) significantly up- or down-regulated by VPA in the fetal brain and (b) known to be associated with autism and/or to play a role in embryonic neurodevelopmental processes, perturbation of which has the potential to alter brain connectivity in the postnatal and adult brain. The set of genes meeting these criteria pro-vides potential targets for future hypothesis-driven approaches to elucidating the proximal underly-ing causes of defective brain connectivity in NDDs such as autism.

DYRK1A promotes viral entry of highly pathogenic human coronaviruses in a kinase-independent manner

Identifying host genes essential for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has the potential to reveal novel drug targets and further our understanding of Coronavirus Disease 2019 (COVID-19). We previously performed a genome-wide CRISPR/Cas9 screen to identify proviral host factors for highly pathogenic human coronaviruses. Few host factors were required by diverse coronaviruses across multiple cell types, but DYRK1A was one such exception. Although its role in coronavirus infection was previously undescribed, DYRK1A encodes Dual Specificity Tyrosine Phosphorylation Regulated Kinase 1A and is known to regulate cell proliferation and neuronal development. Here, we demonstrate that DYRK1A regulates ACE2 and DPP4 transcription independent of its catalytic kinase function to support SARS-CoV, SARS-CoV-2, and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) entry. We show that DYRK1A promotes DNA accessibility at the ACE2 promoter and a putative distal enhancer, facilitating transcription and gene expression. Finally, we validate that the proviral activity of DYRK1A is conserved across species using cells of nonhuman primate and human origin. In summary, we report that DYRK1A is a novel regulator of ACE2 and DPP4 expression that may dictate susceptibility to multiple highly pathogenic human coronaviruses.

DYRK3 phosphorylates SNAPIN to regulate axonal retrograde transport and neurotransmitter release

Among the five members of the dual-specificity tyrosine-phosphorylation-regulated kinase (DYRK) family, the cellular functions of DYRK3 have not been fully elucidated. Some studies have indicated limited physiological roles and substrates of DYRK3, including promotion of glioblastoma, requirement in influenza virus replication, and coupling of stress granule condensation with mammalian target of rapamycin complex 1 signaling. Here, we demonstrate that serum deprivation causes a decrease in intracellular DYRK3 levels via the proteolytic autophagy pathway, as well as the suppression of DYRK3 gene expression. To further demonstrate how DYRK3 affects cell viability, especially in neurons, we used a yeast two-hybrid assay and identified multiple DYRK3-binding proteins, including SNAPIN, a SNARE-associated protein implicated in synaptic transmission. We also found that DYRK3 directly phosphorylates SNAPIN at the threonine (Thr) 14 residue, increasing the interaction of SNAPIN with other proteins such as dynein and synaptotagmin-1. In central nervous system neurons, SNAPIN is associated with and mediate the retrograde axonal transport of diverse cellular products from the distal axon terminal to the soma and the synaptic release of neurotransmitters, respectively. Moreover, phosphorylation of SNAPIN at Thr-14 was found to positively modulate mitochondrial retrograde transport in mouse cortical neurons and the recycling pool size of synaptic vesicles, contributing to neuronal viability. In conclusion, the present study demonstrates that DYRK3 phosphorylates SNAPIN, positively regulating the dynein-mediated retrograde transport of mitochondria and SNARE complex-mediated exocytosis of synaptic vesicles within the neurons. This finding further suggests that DYRK3 affects cell viability and provides a novel neuroprotective mechanism.

DYRK1A and Activity-Dependent Neuroprotective Protein Comparative Diagnosis Interest in Cerebrospinal Fluid and Plasma in the Context of Alzheimer-Related Cognitive Impairment in Down Syndrome Patients

Down syndrome (DS) is a complex genetic condition due to an additional copy of human chromosome 21, which results in the deregulation of many genes. In addition to the intellectual disability associated with DS, adults with DS also have an ultrahigh risk of developing early onset Alzheimer's disease dementia. DYRK1A, a proline-directed serine/threonine kinase, whose gene is located on chromosome 21, has recently emerged as a promising plasma biomarker in patients with sporadic Alzheimer's disease (AD). The protein DYRK1A is truncated in symptomatic AD, the increased truncated form being associated with a decrease in the level of full-length form. Activity-dependent neuroprotective protein (ADNP), a key protein for the brain development, has been demonstrated to be a useful marker for symptomatic AD and disease progression. In this study, we evaluated DYRK1A and ADNP in CSF and plasma of adults with DS and explored the relationship between these proteins. We used mice models to evaluate the effect of DYRK1A overexpression on ADNP levels and then performed a dual-center cross-sectional human study in adults with DS in Barcelona (Spain) and Paris (France). Both cohorts included adults with DS at different stages of the continuum of AD: asymptomatic AD (aDS), prodromal AD (pDS), and AD dementia (dDS). Non-trisomic controls and patients with sporadic AD dementia were included for comparison. Full-form levels of DYRK1A were decreased in plasma and CSF in adults with DS and symptomatic AD (pDS and dDS) compared to aDS, and in patients with sporadic AD compared to controls. On the contrary, the truncated form of DYRK1A was found to increase both in CSF and plasma in adults with DS and symptomatic AD and in patients with sporadic AD with respect to aDS and controls. ADNP levels showed a more complex structure. ADNP levels increased in aDS groups vs. controls, in agreement with the increase in levels found in the brains of mice overexpressing DYRK1A. However, symptomatic individuals had lower levels than aDS individuals. Our results show that the comparison between full-length and truncated-form levels of DYRK1A coupled with ADNP levels could be used in trials targeting pathophysiological mechanisms of dementia in individuals with DS.

Developmental Neuropathology and Neurodegeneration of Down Syndrome: Current Knowledge in Humans

Individuals with Down syndrome (DS) suffer from developmental delay, intellectual disability, and an early-onset of neurodegeneration, Alzheimer’s-like disease, or precocious dementia due to an extra chromosome 21. Studying the changes in anatomical, cellular, and molecular levels involved may help to understand the pathogenesis and develop target treatments, not just medical, but also surgical, cell and gene therapy, etc., for individuals with DS. Here we aim to identify key neurodevelopmental manifestations, locate knowledge gaps, and try to build molecular networks to better understand the mechanisms and clinical importance. We summarize current information about the neuropathology and neurodegeneration of the brain from conception to adulthood of foetuses and individuals with DS at anatomical, cellular, and molecular levels in humans. Understanding the alterations and characteristics of developing Down syndrome will help target treatment to improve the clinical outcomes. Early targeted intervention/therapy for the manifestations associated with DS in either the prenatal or postnatal period may be useful to rescue the neuropathology and neurodegeneration in DS.

Dyrk1a from Gene Function in Development and Physiology to Dosage Correction across Life Span in Down Syndrome

Down syndrome is the main cause of intellectual disabilities with a large set of comorbidities from developmental origins but also that appeared across life span. Investigation of the genetic overdosage found in Down syndrome, due to the trisomy of human chromosome 21, has pointed to one main driver gene, the Dual-specificity tyrosine-regulated kinase 1A (Dyrk1a). Dyrk1a is a murine homolog of the drosophila minibrain gene. It has been found to be involved in many biological processes during development and in adulthood. Further analysis showed its haploinsufficiency in mental retardation disease 7 and its involvement in Alzheimer's disease. DYRK1A plays a role in major developmental steps of brain development, controlling the proliferation of neural progenitors, the migration of neurons, their dendritogenesis and the function of the synapse. Several strategies targeting the overdosage of DYRK1A in DS with specific kinase inhibitors have showed promising evidence that DS cognitive conditions can be alleviated. Nevertheless, providing conditions for proper temporal treatment and to tackle the neurodevelopmental and the neurodegenerative aspects of DS across life span is still an open question.

Diabetic Kinome Inhibitors-A New Opportunity for β-Cells Restoration

Diabetes, and several diseases related to diabetes, including cancer, cardiovascular diseases and neurological disorders, represent one of the major ongoing threats to human life, becoming a true pandemic of the 21st century. Current treatment strategies for diabetes mainly involve promoting β-cell differentiation, and one of the most widely studied targets for β-cell regeneration is DYRK1A kinase, a member of the DYRK family. DYRK1A has been characterized as a key regulator of cell growth, differentiation, and signal transduction in various organisms, while further roles and substrates are the subjects of extensive investigation. The targets of interest in this review are implicated in the regulation of β-cells through DYRK1A inhibition-through driving their transition from highly inefficient and death-prone populations into efficient and sufficient precursors of islet regeneration. Increasing evidence for the role of DYRK1A in diabetes progression and β-cell proliferation expands the potential for pharmaceutical applications of DYRK1A inhibitors. The variety of new compounds and binding modes, determined by crystal structure and in vitro studies, may lead to new strategies for diabetes treatment. This review provides recent insights into the initial self-activation of DYRK1A by tyrosine autophosphorylation. Moreover, the importance of developing novel DYRK1A inhibitors and their implications for the treatment of diabetes are thoroughly discussed. The evolving understanding of DYRK kinase structure and function and emerging high-throughput screening technologies have been described. As a final point of this work, we intend to promote the term "diabetic kinome" as part of scientific terminology to emphasize the role of the synergistic action of multiple kinases in governing the molecular processes that underlie this particular group of diseases.

Importance of determining variations in the number of copies in newborns with autosomal aneuploidies

Introducción.

Las aneuploidías son trastornos genéticos frecuentes en la práctica clínica; sin embargo, se conoce poco sobre las otras variantes genéticas que modifican el fenotipo final.

Objetivo.

Determinar las variantes en el número de copias y las regiones con pérdida de heterocigosidad autosómica mayor de 0,5 % o de regiones mayores de 10 Mb en neonatos con aneuploidías autosómicas.

Materiales y métodos.

Se hizo el análisis cromosómico por micromatrices a los neonatos con aneuploidías autosómicas (n=7), trisomía 21 (n=5) y trisomía 18 (n=2) evaluados en los hospitales Antonio Lorena y Regional de Cusco, Perú, en el 2018.

Resultados.

En dos neonatos se encontraron variantes en el número de copias, patogénicas o probablemente patogénicas, en regiones diferentes al cromosoma 21 o al 18. Además, se observaron dos variantes del número de copias con más de 500 kpb de patogenia desconocida.

Conclusiones.

Si bien el número de pacientes era muy reducido, es importante resaltar que se encontraron otras variantes en el número de copias que se han descrito asociadas con trastornos del neurodesarrollo, varias anomalías congénitas, hipoacusia y talla baja o alta, entre otras, lo que probablemente influye negativamente en el fenotipo de este grupo de pacientes.

Nucleocytoplasmic transport of the RNA-binding protein CELF2 regulates neural stem cell fates

The development of the cerebral cortex requires balanced expansion and differentiation of neural stem/progenitor cells (NPCs), which rely on precise regulation of gene expression. Because NPCs often exhibit transcriptional priming of cell-fate-determination genes, the ultimate output of these genes for fate decisions must be carefully controlled in a timely fashion at the post-transcriptional level, but how that is achieved is poorly understood. Here, we report that de novo missense variants in an RNA-binding protein CELF2 cause human cortical malformations and perturb NPC fate decisions in mice by disrupting CELF2 nucleocytoplasmic transport. In self-renewing NPCs, CELF2 resides in the cytoplasm, where it represses mRNAs encoding cell fate regulators and neurodevelopmental disorder-related factors. The translocation of CELF2 into the nucleus releases mRNA for translation and thereby triggers NPC differentiation. Our results reveal that CELF2 translocation between subcellular compartments orchestrates mRNA at the translational level to instruct cell fates in cortical development.

TTC3-Mediated Protein Quality Control, A Potential Mechanism for Cognitive Impairment

The tetrapeptide repeat domain 3 (TTC3) gene falls within Down's syndrome (DS) critical region. Cognitive impairment is a common phenotype of DS and Alzheimer’s disease (AD), and overexpression of TTC3 can accelerate cognitive decline, but the specific mechanism is unknown. The TTC3-mediated protein quality control (PQC) mechanism, similar to the PQC system, is divided into three parts: it acts as a cochaperone to assist proteins in folding correctly; it acts as an E3 ubiquitin ligase (E3s) involved in protein degradation processes through the ubiquitin–proteasome system (UPS); and it may also eventually cause autophagy by affecting mitochondrial function. Thus, this article reviews the research progress on the structure, function, and metabolism of TTC3, including the recent research progress on TTC3 in DS and AD; the role of TTC3 in cognitive impairment through PQC in combination with the abovementioned attributes of TTC3; and the potential targets of TTC3 in the treatment of such diseases.

Molecular mechanisms that mediate dendrite morphogenesis

Neurons develop dendritic morphologies that bear cell type-specific features in dendritic field size and geometry, branch placement and density, and the types and distributions of synaptic contacts. Dendritic patterns influence the types and numbers of inputs a neuron receives, and the ways in which neural information is processed and transmitted in the circuitry. Even subtle alterations in dendritic structures can have profound consequences on neuronal function and are implicated in neurodevelopmental disorders. In this chapter, I review how growing dendrites acquire their exquisite patterns by drawing examples from diverse neuronal cell types in vertebrate and invertebrate model systems. Dendrite morphogenesis is shaped by intrinsic and extrinsic factors such as transcriptional regulators, guidance and adhesion molecules, neighboring cells and synaptic partners. I discuss molecular mechanisms that regulate dendrite morphogenesis with a focus on five aspects of dendrite patterning: (1) Dendritic cytoskeleton and cellular machineries that build the arbor; (2) Gene regulatory mechanisms; (3) Afferent cues that regulate dendritic arbor growth; (4) Space-filling strategies that optimize dendritic coverage; and (5) Molecular cues that specify dendrite wiring. Cell type-specific implementation of these patterning mechanisms produces the diversity of dendrite morphologies that wire the nervous system.

Protein phosphatase PPM1B inhibits DYRK1A kinase through dephosphorylation of pS258 and reduces toxic tau aggregation

Down syndrome (DS) is mainly caused by an extra copy of chromosome 21 (trisomy 21), and patients display a variety of developmental symptoms, including characteristic facial features, physical growth delay, intellectual disability, and neurodegeneration (i.e., Alzheimer's disease; AD). One of the pathological hallmarks of AD is insoluble deposits of neurofibrillary tangles (NFTs) that consist of hyperphosphorylated tau. The human DYRK1A gene is mapped to chromosome 21, and the protein is associated with the formation of inclusion bodies in AD. For example, DYRK1A directly phosphorylates multiple serine and threonine residues of tau, including Thr212. However, the mechanism underpinning DYRK1A involvement in Trisomy 21-related pathological tau aggregation remains unknown. Here, we explored a novel regulatory mechanism of DYRK1A and subsequent tau pathology through a phosphatase. Using LC-MS/MS technology, we analyzed multiple DYRK1A-binding proteins, including PPM1B, a member of the PP2C family of Ser/Thr protein phosphatases, in HEK293 cells. We found that PPM1B dephosphorylates DYRK1A at Ser258, contributing to the inhibition of DYRK1A activity. Moreover, PPM1B-mediated dephosphorylation of DYRK1A reduced tau phosphorylation at Thr212, leading to inhibition of toxic tau oligomerization and aggregation. In conclusion, our study demonstrates that DYRK1A autophosphorylates Ser258, the dephosphorylation target of PPM1B, and PPM1B negatively regulates DYRK1A activity. This finding also suggests that PPM1B reduces the toxic formation of phospho-tau protein via DYRK1A modulation, possibly providing a novel cellular protective mechanism to regulate toxic tau-mediated neuropathology in AD of DS.

DYRK1A pathogenic variants in two patients with syndromic intellectual disability and a review of the literature

BACKGROUND

DYRK1A-Related Intellectual Disability Syndrome is a rare autosomal dominant condition characterized by intellectual disability, speech and language delays, microcephaly, facial dysmorphism, and feeding difficulties. Affected individuals represent simplex cases that result from de novo heterozygous pathogenic variants in DYRK1A (OMIM 614104), or chromosomal structural rearrangements involving the DYRK1A locus. Due to the rarity of DYRK1A-Related Intellectual Disability Syndrome, the spectrum of symptoms associated with this disease has not been completely defined.

METHODS AND RESULTS

We present two unrelated cases of DYRK1A-Related Intellectual Disability Syndrome resulting from variants in DYRK1A. Both probands presented to the National Institutes of Health (NIH) with multiple dysmorphic facial features, primary microcephaly, absent or minimal speech, feeding difficulties, and cognitive impairment; features that have been previously reported in individuals with DYRK1A. During NIH evaluation, additional features of enlarged cerebral subarachnoid spaces, retinal vascular tortuosity, and bilateral anomalous large optic discs with increased cup-to-disc ratio were identified in the first proband and multiple ophthalmologic abnormalities and sensorineural hearing loss were identified in the second proband.

CONCLUSION

We recommend that the workup of future of patients include a comprehensive eye exam. Early establishment of physical, occupational, and speech therapy may help in the management of ataxia, hypertonia, and speech impairments common in these patients.

Evaluation of the therapeutic potential of Epigallocatechin-3-gallate (EGCG) via oral gavage in young adult Down syndrome mice

Epigallocatechin-3-gallate (EGCG) is a candidate therapeutic for Down syndrome (DS) phenotypes based on in vitro inhibition of DYRK1A, a triplicated gene product of Trisomy 21 (Ts21). Consumption of green tea extracts containing EGCG improved some cognitive and behavioral outcomes in DS mouse models and in humans with Ts21. In contrast, treatment with pure EGCG in DS mouse models did not improve neurobehavioral phenotypes. This study tested the hypothesis that 200 mg/kg/day of pure EGCG, given via oral gavage, would improve neurobehavioral and skeletal phenotypes in the Ts65Dn DS mouse model. Serum EGCG levels post-gavage were significantly higher in trisomic mice than in euploid mice. Daily EGCG gavage treatments over three weeks resulted in growth deficits in both euploid and trisomic mice. Compared to vehicle treatment, EGCG did not significantly improve behavioral performance of Ts65Dn mice in the multivariate concentric square field, balance beam, or Morris water maze tasks, but reduced swimming speed. Furthermore, EGCG resulted in reduced cortical bone structure and strength in Ts65Dn mice. These outcomes failed to support the therapeutic potential of EGCG, and the deleterious effects on growth and skeletal phenotypes underscore the need for caution in high-dose EGCG supplements as an intervention in DS.

Modeling Down syndrome in animals from the early stage to the 4.0 models and next

The genotype-phenotype relationship and the physiopathology of Down Syndrome (DS) have been explored in the last 20 years with more and more relevant mouse models. From the early age of transgenesis to the new CRISPR/CAS9-derived chromosomal engineering and the transchromosomic technologies, mouse models have been key to identify homologous genes or entire regions homologous to the human chromosome 21 that are necessary or sufficient to induce DS features, to investigate the complexity of the genetic interactions that are involved in DS and to explore therapeutic strategies. In this review we report the new developments made, how genomic data and new genetic tools have deeply changed our way of making models, extended our panel of animal models, and increased our understanding of the neurobiology of the disease. But even if we have made an incredible progress which promises to make DS a curable condition, we are facing new research challenges to nurture our knowledge of DS pathophysiology as a neurodevelopmental disorder with many comorbidities during ageing.

Abnormalities of DYRK1A-Cytoskeleton Complexes in the Blood Cells as Potential Biomarkers of Alzheimer's Disease

BACKGROUND

DYRK1A is implicated in mental retardation and Alzheimer's disease (AD) dementia of Down syndrome (DS) individuals. The protein is associated with cytoskeleton and altered expression has been shown to impair the cytoskeletal network via dosage effect.

OBJECTIVE

Our original observations of marked reduction of cytoskeletal proteins associated with DYRK1A in brains and lymphoblastoid cell lines from DS and AD prompted an investigation whether cytoskeleton abnormalities could potentially be used as biomarkers of AD.

METHODS

Our assay relied on quantification of co-immunoprecipitated cytoskeletal proteins with DYRK1A (co-IP assay) and analysis of the profile of G- and F-actin fractions obtained by high-speed centrifugations (spin-down assay).

RESULTS

In co-IP assay, both DS and AD samples displayed reduced abundance of associated cytoskeletal proteins. In spin-down assay, G-actin fractions of controls displayed two closely spaced bands of actin in SDS-PAGE; while in AD and DS, only the upper band of the doublet was present. In both assays, alterations of actin cytoskeleton were present in DS, sporadic and familial AD cases, and in asymptomatic persons who later progressed to confirmed AD, but not in non-AD donors. In blind testing involving six AD and six controls, the above tests positively identified ten cases. Analysis of blood samples revealed the diversity of mild cognitive impairment (MCI) cases regarding the presence of the AD biomarker allowing distinction between likely prodromal AD and non-AD MCI cases.

CONCLUSIONS

Both brain tissue and lymphocytes from DS and AD displayed similar semi-quantitative and qualitative alterations of actin cytoskeleton. Their specificity for AD-type dementia and the presence before clinical onset of the disease make them suitable biomarker candidates for early and definite diagnosis of AD. The presence of alterations in peripheral tissue points to systemic underlying mechanisms and suggests that early dysfunction of cytoskeleton may be a predisposing factor in the development of AD.

DCAF7/WDR68 is required for normal levels of DYRK1A and DYRK1B

Overexpression of the Dual-specificity Tyrosine Phosphorylation-Regulated Kinase 1A (DYRK1A) gene contributes to the retardation, craniofacial anomalies, cognitive impairment, and learning and memory deficits associated with Down Syndrome (DS). DCAF7/HAN11/WDR68 (hereafter WDR68) binds DYRK1A and is required for craniofacial development. Accumulating evidence suggests DYRK1A-WDR68 complexes enable proper growth and patterning of multiple organ systems and suppress inappropriate cell growth/transformation by regulating the balance between proliferation and differentiation in multiple cellular contexts. Here we report, using engineered mouse C2C12 and human HeLa cell lines, that WDR68 is required for normal levels of DYRK1A. However, Wdr68 does not significantly regulate Dyrk1a mRNA expression levels and proteasome inhibition did not restore DYRK1A in cells lacking Wdr68 (Δwdr68 cells). Overexpression of WDR68 increased DYRK1A levels while overexpression of DYRK1A had no effect on WDR68 levels. We further report that WDR68 is similarly required for normal levels of the closely related DYRK1B kinase and that both DYRK1A and DYRK1B are essential for the transition from proliferation to differentiation in C2C12 cells. These findings reveal an additional role of WDR68 in DYRK1A-WDR68 and DYRK1B-WDR68 complexes.

WDR68 is essential for the transcriptional activation of the PRC1-AUTS2 complex and neuronal differentiation of mouse embryonic stem cells

Recent studies on Polycomb repressive complexes (PRC) reveal a surprising role in transcriptional activation, yet the underlying mechanism remains poorly understood. We previously identified a type 1 PRC (PRC1) that contains Autism Susceptibility Candidate 2 (AUTS2), which positively regulates transcription of neuronal genes. However, the mechanism by which the PRC1-AUTS2 complex influences neurodevelopment is unclear. Here we demonstrate that WDR68 is not only an integral component of the PRC1-AUTS2 complex, but it is also required for PRC1-AUTS2-mediated transcription activation. Furthermore, deletion of Wdr68 in mouse embryonic stem cells leads to defects in neuronal differentiation without affecting self-renewal. Through transcriptomic analysis, we found that many genes responsible for neuronal differentiation are down-regulated in Wdr68 deficient neural progenitors. These genes include those targeted by the PRC1-AUTS2 complex. In summary, our studies uncovered a previously unknown but essential component of the active PRC1 complex and evidence of its role in regulating the expression of genes that are important for neuronal differentiation.

DYRK1A Kinase Positively Regulates Angiogenic Responses in Endothelial Cells

Angiogenesis is a highly regulated process essential for organ development and maintenance, and its deregulation contributes to inflammation, cardiac disorders, and cancer. The Ca2+/nuclear factor of activated T cells (NFAT) signaling pathway is central to endothelial cell angiogenic responses, and it is activated by stimuli like vascular endothelial growth factor (VEGF) A. NFAT phosphorylation by dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs) is thought to be an inactivating event. Contrary to expectations, we show that the DYRK family member DYRK1A positively regulates VEGF-dependent NFAT transcriptional responses in primary endothelial cells. DYRK1A silencing reduces intracellular Ca2+ influx in response to VEGF, which dampens NFAT activation. The effect is exerted at the level of VEGFR2 accumulation leading to impairment in PLCγ1 activation. Notably, Dyrk1a heterozygous mice show defects in developmental retinal vascularization. Our data establish a regulatory circuit, DYRK1A/ Ca2+/NFAT, to fine-tune endothelial cell proliferation and angiogenesis.

Functional characterization of DYRK1A missense variants associated with a syndromic form of intellectual deficiency and autism

Haploinsufficiency of DYRK1A is a cause of a neurodevelopmental syndrome termed mental retardation autosomal dominant 7 (MRD7). Several truncation mutations, microdeletions and missense variants have been identified and result in a recognizable phenotypic profile, including microcephaly, intellectual disability, epileptic seizures, autism spectrum disorder and language delay. DYRK1A is an evolutionary conserved protein kinase which achieves full catalytic activity through tyrosine autophosphorylation. We used a heterologous mammalian expression system to explore the functional characteristics of pathogenic missense variants that affect the catalytic domain of DYRK1A. Four of the substitutions eliminated tyrosine autophosphorylation (L245R, F308V, S311F, S346P), indicating that these variants lacked kinase activity. Tyrosine phosphorylation of DYRK1A-L295F in mammalian cells was comparable to wild type, although the mutant showed lower catalytic activity and reduced thermodynamic stability in cellular thermal shift assays. In addition, we observed that one variant (DYRK1A-T588N) with a mutation outside the catalytic domain did not differ from wild-type DYRK1A in tyrosine autophosphorylation, catalytic activity or subcellular localization. These results suggest that the pathogenic missense variants in the catalytic domain of DYRK1A impair enzymatic function by affecting catalytic residues or by compromising the structural integrity of the kinase domain.

This article has an associated First Person interview with the first author of the paper.

Summary: We have analyzed the functional consequences of amino acid substitutions in the protein kinase DYRK1A that have been identified as pathogenic in patients with microcephaly, intellectual disability and autism.

Normalizing the gene dosage of Dyrk1A in a mouse model of Down syndrome rescues several Alzheimer's disease phenotypes

The intellectual disability that characterizes Down syndrome (DS) is primarily caused by prenatal changes in central nervous system growth and differentiation. However, in later life stages, the cognitive abilities of DS individuals progressively decline due to accelerated aging and the development of Alzheimer's disease (AD) neuropathology. The AD neuropathology in DS has been related to the overexpression of several genes encoded by Hsa21 including DYRK1A (dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A), which encodes a protein kinase that performs crucial functions in the regulation of multiple signaling pathways that contribute to normal brain development and adult brain physiology. Studies performed in vitro and in vivo in animal models overexpressing this gene have demonstrated that the DYRK1A gene also plays a crucial role in several neurodegenerative processes found in DS. The Ts65Dn (TS) mouse bears a partial triplication of several Hsa21 orthologous genes, including Dyrk1A, and replicates many DS-like abnormalities, including age-dependent cognitive decline, cholinergic neuron degeneration, increased levels of APP and Aβ, and tau hyperphosphorylation. To use a more direct approach to evaluate the role of the gene dosage of Dyrk1A on the neurodegenerative profile of this model, TS mice were crossed with Dyrk1A KO mice to obtain mice with a triplication of a segment of Mmu16 that includes this gene, mice that are trisomic for the same genes but only carry two copies of Dyrk1A, euploid mice with a normal Dyrk1A dosage, and CO animals with a single copy of Dyrk1A. Normalizing the gene dosage of Dyrk1A in the TS mouse rescued the density of senescent cells in the cingulate cortex, hippocampus and septum, prevented cholinergic neuron degeneration, and reduced App expression in the hippocampus, Aβ load in the cortex and hippocampus, the expression of phosphorylated tau at the Ser202 residue in the hippocampus and cerebellum and the levels of total tau in the cortex, hippocampus and cerebellum. Thus, the present study provides further support for the role of the Dyrk1A gene in several AD-like phenotypes found in TS mice and indicates that this gene could be a therapeutic target to treat AD in DS.

Targeting trisomic treatments: optimizing Dyrk1a inhibition to improve Down syndrome deficits

Overexpression of Dual-specificity tyrosine-phosphorylated regulated kinase 1A (DYRK1A), located on human chromosome 21, may alter molecular processes linked to developmental deficits in Down syndrome (DS). Trisomic DYRK1A is a rational therapeutic target, and although reductions in Dyrk1a genetic dosage have shown improvements in trisomic mouse models, attempts to reduce Dyrk1a activity by pharmacological mechanisms and correct these DS-associated phenotypes have been largely unsuccessful. Epigallocatechin-3-gallate (EGCG) inhibits DYRK1A activity in vitro and this action has been postulated to account for improvement of some DS-associated phenotypes that have been reported in preclinical studies and clinical trials. However, the beneficial effects of EGCG are inconsistent and there is no direct evidence that any observed improvement actually occurs through Dyrk1a inhibition. Inconclusive outcomes likely reflect a lack of knowledge about the tissue-specific patterns of spatial and temporal overexpression and elevated activity of Dyrk1a that may contribute to emerging DS traits during development. Emerging evidence indicates that Dyrk1a expression varies over the life span in DS mouse models, yet preclinical therapeutic treatments targeting Dyrk1a have largely not considered these developmental changes. Therapies intended to improve DS phenotypes through normalizing trisomic Dyrk1a need to optimize the timing and dose of treatment to match the spatiotemporal patterning of excessive Dyrk1a activity in relevant tissues. This will require more precise identification of developmental periods of vulnerability to enduring adverse effects of elevated Dyrk1a, representing the concurrence of increased Dyrk1a expression together with hypothesized tissue-specific-sensitive periods when Dyrk1a regulates cellular processes that shape the long-term functional properties of the tissue. Future efforts targeting inhibition of trisomic Dyrk1a should identify these putative spatiotemporally specific developmental sensitive periods and determine whether normalizing Dyrk1a activity then can lead to improved outcomes in DS phenotypes.

Potential Role of Microtubule Stabilizing Agents in Neurodevelopmental Disorders

Neurodevelopmental disorders (NDDs) are characterized by neuroanatomical abnormalities indicative of corticogenesis disturbances. At the basis of NDDs cortical abnormalities, the principal developmental processes involved are cellular proliferation, migration and differentiation. NDDs are also considered “synaptic disorders” since accumulating evidence suggests that NDDs are developmental brain misconnection syndromes characterized by altered connectivity in local circuits and between brain regions. Microtubules and microtubule-associated proteins play a fundamental role in the regulation of basic neurodevelopmental processes, such as neuronal polarization and migration, neuronal branching and synaptogenesis. Here, the role of microtubule dynamics will be elucidated in regulating several neurodevelopmental steps. Furthermore, the correlation between abnormalities in microtubule dynamics and some NDDs will be described. Finally, we will discuss the potential use of microtubule stabilizing agents as a new pharmacological intervention for NDDs treatment.

Elucidating Pathogenic Mechanisms of Early-onset Alzheimer's Disease in Down Syndrome Patients

Down syndrome (DS) patients demonstrate the neuropathology of Alzheimer's disease (AD) characterized by the formation of senile plaques and neurofibrillary tangles by age 40-50 years. It has been considered for a number of years that 1.5-fold expression of the gene for the amyloid precursor protein (APP) located on chromosome 21 leading to overproduction of amyloid-β peptide (Aβ) results in the early onset of AD in adults with DS. However, the mean age of onset of familial AD with the Swedish mutation on APP which has high affinity for β-secretase associated with a dramatic increase in Aβ production is about 55 years. This paradox indicates that there is a poor correlation between average ages of AD onset and the theoretical amount of Aβ production and that there are factors exacerbating AD on chromosome 21. We therefore focused on dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), since overexpressing transgenic mice show AD-like brain pathology. The overexpression of DYRK1A caused suppression of the activity of neprilysin (NEP), which is a major Aβ-degrading enzyme in the brain, and phosphorylation at the NEP cytoplasmic domain. NEP activity was markedly reduced in fibroblasts derived from DS patients compared with that in fibroblasts derived from healthy controls. This impaired activity of NEP was rescued by DYRK1A inhibition. These results show that DYRK1A overexpression causes suppression of NEP activity through its phosphorylation in DS patients. Our results suggest that DYRK1A inhibitors could be effective against AD not only in adults with DS but also in sporadic AD patients.

DYRK1A, a Dosage-Sensitive Gene Involved in Neurodevelopmental Disorders, Is a Target for Drug Development in Down Syndrome

Down syndrome (DS) is one of the leading causes of intellectual disability, and patients with DS face various health issues, including learning and memory deficits, congenital heart disease, Alzheimer's disease (AD), leukemia, and cancer, leading to huge medical and social costs. Remarkable advances on DS research have been made in improving cognitive function in mouse models for future therapeutic approaches in patients. Among the different approaches, DYRK1A inhibitors have emerged as promising therapeutics to reduce DS cognitive deficits. DYRK1A is a dual-specificity kinase that is overexpressed in DS and plays a key role in neurogenesis, outgrowth of axons and dendrites, neuronal trafficking and aging. Its pivotal role in the DS phenotype makes it a prime target for the development of therapeutics. Recently, disruption of DYRK1A has been found in Autosomal Dominant Mental Retardation 7 (MRD7), resulting in severe mental deficiency. Recent advances in the development of kinase inhibitors are expected, in the near future, to remove DS from the list of incurable diseases, providing certain conditions such as drug dosage and correct timing for the optimum long-term treatment. In addition the exact molecular and cellular mechanisms that are targeted by the inhibition of DYRK1A are still to be discovered.

Disruptive de novo mutations of DYRK1A lead to a syndromic form of autism and ID

Dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1 A (DYRK1A) maps to the Down syndrome critical region; copy number increase of this gene is thought to have a major role in the neurocognitive deficits associated with Trisomy 21. Truncation of DYRK1A in patients with developmental delay (DD) and autism spectrum disorder (ASD) suggests a different pathology associated with loss-of-function mutations. To understand the phenotypic spectrum associated with DYRK1A mutations, we resequenced the gene in 7162 ASD/DD patients (2446 previously reported) and 2169 unaffected siblings and performed a detailed phenotypic assessment on nine patients. Comparison of our data and published cases with 8696 controls identified a significant enrichment of DYRK1A truncating mutations (P=0.00851) and an excess of de novo mutations (P=2.53 × 10(-10)) among ASD/intellectual disability (ID) patients. Phenotypic comparison of all novel (n=5) and recontacted (n=3) cases with previous case reports, including larger CNV and translocation events (n=7), identified a syndromal disorder among the 15 patients. It was characterized by ID, ASD, microcephaly, intrauterine growth retardation, febrile seizures in infancy, impaired speech, stereotypic behavior, hypertonia and a specific facial gestalt. We conclude that mutations in DYRK1A define a syndromic form of ASD and ID with neurodevelopmental defects consistent with murine and Drosophila knockout models.

DYRK1A overexpression enhances STAT activity and astrogliogenesis in a Down syndrome mouse model

Down syndrome (DS) arises from triplication of genes on human chromosome 21 and is associated with anomalies in brain development such as reduced production of neurons and increased generation of astrocytes. Here, we show that differentiation of cortical progenitor cells into astrocytes is promoted by DYRK1A, a Ser/Thr kinase encoded on human chromosome 21. In the Ts1Cje mouse model of DS, increased dosage of DYRK1A augments the propensity of progenitors to differentiate into astrocytes. This tendency is associated with enhanced astrogliogenesis in the developing neocortex. We also find that overexpression of DYRK1A upregulates the activity of the astrogliogenic transcription factor STAT in wild-type progenitors. Ts1Cje progenitors exhibit elevated STAT activity, and depletion of DYRK1A in these cells reverses the deregulation of STAT. In sum, our findings indicate that potentiation of the DYRK1A-STAT pathway in progenitors contributes to aberrant astrogliogenesis in DS.

Ten new cases further delineate the syndromic intellectual disability phenotype caused by mutations in DYRK1A

The dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) gene, located on chromosome 21q22.13 within the Down syndrome critical region, has been implicated in syndromic intellectual disability associated with Down syndrome and autism. DYRK1A has a critical role in brain growth and development primarily by regulating cell proliferation, neurogenesis, neuronal plasticity and survival. Several patients have been reported with chromosome 21 aberrations such as partial monosomy, involving multiple genes including DYRK1A. In addition, seven other individuals have been described with chromosomal rearrangements, intragenic deletions or truncating mutations that disrupt specifically DYRK1A. Most of these patients have microcephaly and all have significant intellectual disability. In the present study, we report 10 unrelated individuals with DYRK1A-associated intellectual disability (ID) who display a recurrent pattern of clinical manifestations including primary or acquired microcephaly, ID ranging from mild to severe, speech delay or absence, seizures, autism, motor delay, deep-set eyes, poor feeding and poor weight gain. We identified unique truncating and non-synonymous mutations (three nonsense, four frameshift and two missense) in DYRK1A in nine patients and a large chromosomal deletion that encompassed DYRK1A in one patient. On the basis of increasing identification of mutations in DYRK1A, we suggest that this gene be considered potentially causative in patients presenting with ID, primary or acquired microcephaly, feeding problems and absent or delayed speech with or without seizures.

Rescue of the abnormal skeletal phenotype in Ts65Dn Down syndrome mice using genetic and therapeutic modulation of trisomic Dyrk1a

Trisomy 21 causes skeletal alterations in individuals with Down syndrome (DS), but the causative trisomic gene and a therapeutic approach to rescue these abnormalities are unknown. Individuals with DS display skeletal alterations including reduced bone mineral density, modified bone structure and distinctive facial features. Due to peripheral skeletal anomalies and extended longevity, individuals with DS are increasingly more susceptible to bone fractures. Understanding the genetic and developmental origin of DS skeletal abnormalities would facilitate the development of therapies to rescue these and other deficiencies associated with DS. DYRK1A is found in three copies in individuals with DS and Ts65Dn DS mice and has been hypothesized to be involved in many Trisomy 21 phenotypes including skeletal abnormalities. Return of Dyrk1a copy number to normal levels in Ts65Dn mice rescued the appendicular bone abnormalities, suggesting that appropriate levels of DYRK1A expression are critical for the development and maintenance of the DS appendicular skeleton. Therapy using the DYRK1A inhibitor epigallocatechin-3-gallate improved Ts65Dn skeletal phenotypes. These outcomes suggest that the osteopenic phenotype associated with DS may be rescued postnatally by targeting trisomic Dyrk1a.

Dyrk1A phosphorylates parkin at Ser-131 and negatively regulates its ubiquitin E3 ligase activity

Mutations of parkin are associated with the occurrence of autosomal recessive familial Parkinson's disease (PD). Parkin acts an E3 ubiquitin ligase, which ubiquitinates target proteins and subsequently regulates either their steady-state levels through the ubiquitin-proteasome system or biochemical properties. In this study, we identify a novel regulatory mechanism of parkin by searching for new regulatory factors. After screening human fetal brain using a yeast two hybrid assay, we found dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (Dyrk1A) as a novel binding partner of parkin. We also observed that parkin interacts and co-localizes with Dyrk1A in mammalian cells. In addition, Dyrk1A directly phosphorylated parkin at Ser-131, causing the inhibition of its E3 ubiquitin ligase activity. Moreover, Dyrk1A-mediated phosphorylation reduced the binding affinity of parkin to its ubiquitin-conjugating E2 enzyme and substrate, which could be the underlying inhibitory mechanism of parkin activity. Furthermore, Dyrk1A-mediated phosphorylation inhibited the neuroprotective action of parkin against 6-hydroxydopamine toxicity in dopaminergic SH-SY5Y cells. These findings suggest that Dyrk1A acts as a novel functional modulator of parkin. Parkin phosphorylation by Dyrk1A suppresses its E3 ubiquitin ligase activity potentially contributing to the pathogenesis of PD under PD-inducing pathological conditions. Mutations of parkin are linked to autosomal recessive forms of familial Parkinson's disease (PD). According to its functional relevance in abnormal protein aggregation and neuronal cell death, a number of post-translational modifications regulate the ubiquitin E3 ligase activity of parkin. Here we propose a novel inhibitory mechanism of parkin E3 ubiquitin ligase through dual-specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A)-mediated phosphorylation as well as its neuroprotective action against 6-hydroxydopamine (6-OHDA)-induced cell death. The present work suggests that parkin phosphorylation by Dyrk1A may affect the pathogenesis of PD under PD-inducing pathological conditions.

Selectivity Profiling and Biological Activity of Novel β-Carbolines as Potent and Selective DYRK1 Kinase Inhibitors

DYRK1A is a pleiotropic protein kinase with diverse functions in cellular regulation, including cell cycle control, neuronal differentiation, and synaptic transmission. Enhanced activity and overexpression of DYRK1A have been linked to altered brain development and function in Down syndrome and neurodegenerative diseases such as Alzheimer's disease. The β-carboline alkaloid harmine is a high affinity inhibitor of DYRK1A but suffers from the drawback of inhibiting monoamine oxidase A (MAO-A) with even higher potency. Here we characterized a series of novel harmine analogs with minimal or absent MAO-A inhibitory activity. We identified several inhibitors with submicromolar potencies for DYRK1A and selectivity for DYRK1A and DYRK1B over the related kinases DYRK2 and HIPK2. An optimized inhibitor, AnnH75, inhibited CLK1, CLK4, and haspin/GSG2 as the only off-targets in a panel of 300 protein kinases. In cellular assays, AnnH75 dose-dependently reduced the phosphorylation of three known DYRK1A substrates (SF3B1, SEPT4, and tau) without negative effects on cell viability. AnnH75 inhibited the cotranslational tyrosine autophosphorylation of DYRK1A and threonine phosphorylation of an exogenous substrate protein with similar potency. In conclusion, we have characterized an optimized β-carboline inhibitor as a highly selective chemical probe that complies with desirable properties of drug-like molecules and is suitable to interrogate the function of DYRK1A in biological studies.

Applications of Induced Pluripotent Stem Cells in Studying the Neurodegenerative Diseases

Neurodegeneration is the umbrella term for the progressive loss of structure or function of neurons. Incurable neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD) show dramatic rising trends particularly in the advanced age groups. However, the underlying mechanisms are not yet fully elucidated, and to date there are no biomarkers for early detection or effective treatments for the underlying causes of these diseases. Furthermore, due to species variation and differences between animal models (e.g., mouse transgenic and knockout models) of neurodegenerative diseases, substantial debate focuses on whether animal and cell culture disease models can correctly model the condition in human patients. In 2006, Yamanaka of Kyoto University first demonstrated a novel approach for the preparation of induced pluripotent stem cells (iPSCs), which displayed similar pluripotency potential to embryonic stem cells (ESCs). Currently, iPSCs studies are permeating many sectors of disease research. Patient sample-derived iPSCs can be used to construct patient-specific disease models to elucidate the pathogenic mechanisms of disease development and to test new therapeutic strategies. Accordingly, the present review will focus on recent progress in iPSC research in the modeling of neurodegenerative disorders and in the development of novel therapeutic options.

Advances in tetrahydropyrido[1,2-a]isoindolone (valmerins) series: Potent glycogen synthase kinase 3 and cyclin dependent kinase 5 inhibitors

An efficient synthetic strategy was developed to modulate the structure of the tetrahydropyridine isoindolone (Valmerin) skeleton. A library of more than 30 novel final structures was generated. Biological activities on CDK5 and GSK3 as well as cellular effects on cancer cell lines were measured for each novel compound. Additionally docking studies were performed to support medicinal chemistry efforts. A strong GSK3/CDK5 dual inhibitor (38, IC50 GSK3/CDK5 32/84 nM) was obtained. A set of highly selective GSK3 inhibitors was synthesized by fine-tuning structural modifications (29 IC50 GSK3/CDK5 32/320 nM). Antiproliferative effects on cells were correlated with the in vitro kinase activities and the best effects were obtained with lung and colon cell lines.

A cluster of protein kinases and phosphatases modulated in fetal Down syndrome (trisomy 21) brain

Down syndrome (DS; trisomy 21) is the most frequent cause of mental retardation with major cognitive and behavioral deficits. Although a series of aberrant biochemical pathways has been reported, work on signaling proteins is limited. It was, therefore, the aim of the study to test a selection of protein kinases and phosphatases known to be essential for memory and learning mechanisms in fetal DS brain. 12 frontal cortices from DS brain were compared to 12 frontal cortices from controls obtained at legal abortions. Proteins were extracted from brains and western blotting with specific antibodies was carried out. Primary results were used for networking (IntAct Molecular Interaction Database) and individual predicted pathway components were subsequently quantified by western blotting. Levels of calcium-calmodulin kinase II alpha, transforming growth factor beta-activated kinase 1 as well as phosphatase and tensin homolog (PTEN) were reduced in cortex of DS subjects and network generation pointed to interaction between PTEN and the dendritic spine protein drebrin that was subsequently determined and reduced levels were observed. The findings of reduced levels of cognitive-function-related protein kinases and the phosphatase may be relevant for interpretation of previous work and may be useful for the design of future studies on signaling in DS brain. Moreover, decreased drebrin levels may point to dendritic spine abnormalities.

DYRK1A-mediated phosphorylation of GluN2A at Ser(1048) regulates the surface expression and channel activity of GluN1/GluN2A receptors

N-methyl-D-aspartate glutamate receptors (NMDARs) play a pivotal role in neural development and synaptic plasticity, as well as in neurological disease. Since NMDARs exert their function at the cell surface, their density in the plasma membrane is finely tuned by a plethora of molecules that regulate their production, trafficking, docking and internalization in response to external stimuli. In addition to transcriptional regulation, the density of NMDARs is also influenced by post-translational mechanisms like phosphorylation, a modification that also affects their biophysical properties. We previously described the increased surface expression of GluN1/GluN2A receptors in transgenic mice overexpressing the Dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A), suggesting that DYRK1A regulates NMDARs. Here we have further investigated whether the density and activity of NMDARs were modulated by DYRK1A phosphorylation. Accordingly, we show that endogenous DYRK1A is recruited to GluN2A-containing NMDARs in the adult mouse brain, and we identify a DYRK1A phosphorylation site at Ser¹⁰⁴⁸ of GluN2A, within its intracellular C-terminal domain. Mechanistically, the DYRK1A-dependent phosphorylation of GluN2A at Ser¹⁰⁴⁸ hinders the internalization of GluN1/GluN2A, causing an increase of surface GluN1/GluN2A in heterologous systems, as well as in primary cortical neurons. Furthermore, GluN2A phosphorylation at Ser¹⁰⁴⁸ increases the current density and potentiates the gating of GluN1/GluN2A receptors. We conclude that DYRK1A is a direct regulator of NMDA receptors and we propose a novel mechanism for the control of NMDAR activity in neurons.