Phosphorylation of β-Tubulin by the Down Syndrome Kinase, Minibrain/DYRK1a, Regulates Microtubule Dynamics and Dendrite Morphogenesis

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.

How cells exploit tubulin diversity to build functional cellular microtubule mosaics

Cellular microtubules are mosaic polymers assembled from multiple αβ-tubulin isoforms bearing chemically diverse posttranslational modifications. This tubulin diversity constitutes a combinatorial code that regulates microtubule interactions with cellular effectors and alters their intrinsic dynamic and mechanical properties. Cells generate stereotyped and complex tubulin modification patterns that are important for their specialized functions. Here we give a brief overview of the tubulin genetic and chemical diversity and highlight recent advances in our understanding of how the tubulin code regulates essential biological processes ranging from intracellular cargo transport, to cell division and cardiomyocyte contraction. Finally, we speculate on the molecular mechanisms for the generation and maintenance of the complex stereotyped modification patterns that form cellular microtubule mosaics.

Recent advances in branching mechanisms underlying neuronal morphogenesis

Proper neuronal wiring is central to all bodily functions, sensory perception, cognition, memory, and learning. Establishment of a functional neuronal circuit is a highly regulated and dynamic process involving axonal and dendritic branching and navigation toward appropriate targets and connection partners. This intricate circuitry includes axo-dendritic synapse formation, synaptic connections formed with effector cells, and extensive dendritic arborization that function to receive and transmit mechanical and chemical sensory inputs. Such complexity is primarily achieved by extensive axonal and dendritic branch formation and pruning. Fundamental to neuronal branching are cytoskeletal dynamics and plasma membrane expansion, both of which are regulated via numerous extracellular and intracellular signaling mechanisms and molecules. This review focuses on recent advances in understanding the biology of neuronal branching.

Correction of cognitive deficits in mouse models of Down syndrome by a pharmacological inhibitor of DYRK1A

Growing evidence supports the implication of DYRK1A in the development of cognitive deficits seen in Down syndrome (DS) and Alzheimer's disease (AD). We here demonstrate that pharmacological inhibition of brain DYRK1A is able to correct recognition memory deficits in three DS mouse models with increasing genetic complexity [Tg(Dyrk1a), Ts65Dn, Dp1Yey], all expressing an extra copy of Dyrk1a Overexpressed DYRK1A accumulates in the cytoplasm and at the synapse. Treatment of the three DS models with the pharmacological DYRK1A inhibitor leucettine L41 leads to normalization of DYRK1A activity and corrects the novel object cognitive impairment observed in these models. Brain functional magnetic resonance imaging reveals that this cognitive improvement is paralleled by functional connectivity remodelling of core brain areas involved in learning/memory processes. The impact of Dyrk1a trisomy and L41 treatment on brain phosphoproteins was investigated by a quantitative phosphoproteomics method, revealing the implication of synaptic (synapsin 1) and cytoskeletal components involved in synaptic response and axonal organization. These results encourage the development of DYRK1A inhibitors as drug candidates to treat cognitive deficits associated with DS and AD.

Design and synthesis of conformationally constraint Dyrk1A inhibitors by creating an intramolecular H-bond involving a benzothiazole core

We present the development of conformationally pre-organised Dyrk1A inhibitors based on the hydroxybenzothiazole urea scaffold. The modifications introduced to the discovered hit (AHS-211) proved the crucial role of the urea linker to preserve the bioactive conformation and led to the development of compound b5 as a promising selective Dyrk1A inhibitor.

The tubulin code in neuronal polarity

Cells depend on the asymmetric distribution of their components for homeostasis, differentiation and movement. In no other cell type is this requirement more critical than in the neuron where complex structures are generated during process growth and elaboration and cargo is transported over distances several thousand times the cell body diameter. Microtubules act both as dynamic structural elements and as tracks for intracellular transport. Microtubules are mosaic polymers containing multiple tubulin isoforms functionalized with abundant posttranslational modifications that are asymmetrically distributed in neurons. An increasing body of evidence supports the hypothesis that the combinatorial information expressed through tubulin genetic and chemical diversity controls microtubule dynamics, mechanics and interactions with microtubule effectors and thus constitutes a 'tubulin code'. Here we give a brief overview of tubulin isoform usage and posttranslational modifications in the neuron, and highlight recent progress in understanding the molecular mechanisms of the tubulin code.

Mnb/Dyrk1A orchestrates a transcriptional network at the transition from self-renewing neurogenic progenitors to postmitotic neuronal precursors

The Down syndrome and microcephaly related gene Mnb/Dyrk1A encodes an evolutionary conserved protein kinase subfamily that plays important roles in neurodevelopment. minibrain (mnb) mutants of Drosophila melanogaster (Dm) exhibit reduced adult brains due to neuronal deficits generated during larval development. These deficits are the consequence of the apoptotic cell death of numerous neuronal precursors that fail to properly exit the cell cycle and differentiate. We have recently found that in both the Dm larval brain and the embryonic vertebrate central nervous system (CNS), a transient expression of Mnb/Dyrk1A promotes the cell cycle exit of newborn neuronal precursors by upregulating the expression of the cyclin-dependent kinase inhibitor p27kip1 (called Dacapo in Dm). In the larval brain, Mnb performs this action by regulating the expression of three transcription factors, Asense (Ase), Deadpan (Dpn) and Prospero (Pros), which are key regulators of the self-renewal, proliferation, and terminal differentiation of neural progenitor cells. We have here studied in detail the cellular/temporal expression pattern of Ase, Dpn, Pros and Mnb, and have analyzed possible regulatory effects among them at the transitions from neurogenic progenitors to postmitotic neuronal precursors in the Dm larval brain. The emerging picture of this analysis reveals an intricate regulatory network in which Mnb appears to play a pivotal role helping to delineate the dynamics of the expression patterns of Ase, Dpn and Pros, as well as their specific functions in the aforementioned transitions. Our results also show that Ase, Dpn and Pros perform several cross-regulatory actions and contribute to shape the precise cellular/temporal expression pattern of Mnb. We propose that Mnb/Dyrk1A plays a central role in CNS neurogenesis by integrating molecular mechanisms that regulate progenitor self-renewal, cell cycle progression and neuronal differentiation.

DYRK1A-haploinsufficiency in mice causes autistic-like features and febrile seizures

Mutations and copy number variants affecting DYRK1A gene encoding the dual-specificity tyrosine phosphorylation-regulated kinase 1A are among the most frequent genetic causes of neurodevelopmental disorders including autism spectrum disorder (ASD) associated with microcephaly, febrile seizures and severe speech acquisition delay. Here we developed a mouse model harboring a frame-shift mutation in Dyrk1a resulting in a protein truncation and elimination of its kinase activity site. Dyrk1a+/- mice showed significant impairments in cognition and cognitive flexibility, communicative ultrasonic vocalizations, and social contacts. Susceptibility to hyperthermia-induced seizures was also significantly increased in these mice. The truncation leading to haploinsufficiency of DYRK1A in mice thus recapitulates the syndromic phenotypes observed in human patients and constitutes a useful model for further investigations of the mechanisms leading to ASD, speech delay and febrile seizures.

Microtubule dynamics: moving toward a multi-scale approach

Microtubule self-assembly dynamics serve to facilitate many vital cellular functions, such as chromosome segregation during mitosis and synaptic plasticity. However, the detailed atomistic basis of assembly dynamics has remained an unresolved puzzle. A key challenge is connecting together the vast range of relevant length-time scales, events happening at time scales ranging from nanoseconds, such as tubulin molecular interactions (Å-nm), to minutes-hours, such as the cellular response to microtubule dynamics during mitotic progression (μm). At the same time, microtubule interactions with associated proteins and binding agents, such as anti-cancer drugs, can strongly affect this dynamic process through atomic-level mechanisms that remain to be elucidated. New high-resolution technologies for investigating these interactions, including cryo-electron microscopy (EM) techniques and total internal reflection fluorescence (TIRF) microscopy, are yielding important new insights. Here, we focus on recent studies of microtubule dynamics, both theoretical and experimental, and how these findings shed new light on this complex phenomenon across length-time scales, from Å to μm and from nanoseconds to minutes.

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) inhibitors: a survey of recent patent literature

INTRODUCTION

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a eukaryotic serine-threonine protein kinase belonging to the CMGC group. DYRK1A hyperactivity appears to contribute to the development of a number of human malignancies and to cognitive deficits observed in Down syndrome and Alzheimer's disease. As a result, the DYRK1A kinase represents an attractive target for the synthesis and optimization of pharmacological inhibitors of potential therapeutic interest. Like most tyrosine kinase inhibitors developed up to the market, DYRK1A inhibitors are essentially acting by competing with ATP for binding at the catalytic site of the kinase. Areas covered: This paper reviews patent activity associated with the discovery of synthetic novel heterocyclic molecules inhibiting the catalytic activity of DYRK1A. Expert opinion: Despite the important role of DYRK1A in biological processes and the growing interest in the design of new therapeutic drugs, there are only few patented synthetic DYRK1A inhibitors and most of them were and are still developed by academic research groups, sometimes with industrial partners.

ReMAPping the microtubule landscape: How phosphorylation dictates the activities of microtubule-associated proteins

Classical microtubule-associated proteins (MAPs) were originally identified based on their co-purification with microtubules assembled from mammalian brain lysate. They have since been found to perform a range of functions involved in regulating the dynamics of the microtubule cytoskeleton. Most of these MAPs play integral roles in microtubule organization during neuronal development, microtubule remodeling during neuronal activity, and microtubule stabilization during neuronal maintenance. As a result, mutations in MAPs contribute to neurodevelopmental disorders, psychiatric conditions, and neurodegenerative diseases. MAPs are post-translationally regulated by phosphorylation depending on developmental time point and cellular context. Phosphorylation can affect the microtubule affinity, cellular localization, or overall function of a particular MAP and can thus have profound implications for neuronal health. Here we review MAP1, MAP2, MAP4, MAP6, MAP7, MAP9, tau, and DCX, and how each is regulated by phosphorylation in neuronal physiology and disease. Developmental Dynamics 247:138-155, 2018. © 2017 Wiley Periodicals, Inc.

Tubulin Post-Translational Modifications and Microtubule Dynamics

Microtubules are hollow tube-like polymeric structures composed of α,β-tubulin heterodimers. They play an important role in numerous cellular processes, including intracellular transport, cell motility and segregation of the chromosomes during cell division. Moreover, microtubule doublets or triplets form a scaffold of a cilium, centriole and basal body, respectively. To perform such diverse functions microtubules have to differ in their properties. Post-translational modifications are one of the factors that affect the properties of the tubulin polymer. Here we focus on the direct and indirect effects of post-translational modifications of tubulin on microtubule dynamics.

Phosphorylation of Synaptojanin Differentially Regulates Endocytosis of Functionally Distinct Synaptic Vesicle Pools

The rapid replenishment of synaptic vesicles through endocytosis is crucial for sustaining synaptic transmission during intense neuronal activity. Synaptojanin (Synj), a phosphoinositide phosphatase, is known to play an important role in vesicle recycling by promoting the uncoating of clathrin following synaptic vesicle uptake. Synj has been shown to be a substrate of the minibrain (Mnb) kinase, a fly homolog of the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A); however, the functional impacts of Synj phosphorylation by Mnb are not well understood. Here we identify that Mnb phosphorylates Synj at S1029 in Drosophila We find that phosphorylation of Synj at S1029 enhances Synj phosphatase activity, alters interaction between Synj and endophilin, and promotes efficient endocytosis of the active cycling vesicle pool (also referred to as exo-endo cycling pool) at the expense of reserve pool vesicle endocytosis. Dephosphorylated Synj, on the other hand, is deficient in the endocytosis of the active recycling pool vesicles but maintains reserve pool vesicle endocytosis to restore total vesicle pool size and sustain synaptic transmission. Together, our findings reveal a novel role for Synj in modulating reserve pool vesicle endocytosis and further indicate that dynamic phosphorylation and dephosphorylation of Synj differentially maintain endocytosis of distinct functional synaptic vesicle pools.

SIGNIFICANCE STATEMENT

Synaptic vesicle endocytosis sustains communication between neurons during a wide range of neuronal activities by recycling used vesicle membrane and protein components. Here we identify that Synaptojanin, a protein with a known role in synaptic vesicle endocytosis, is phosphorylated at S1029 in vivo by the Minibrain kinase. We further demonstrate that the phosphorylation status of Synaptojanin at S1029 differentially regulates its participation in the recycling of distinct synaptic vesicle pools. Our results reveal a new role for Synaptojanin in maintaining synaptic vesicle pool size and in reserve vesicle endocytosis. As Synaptojanin and Minibrain perturbations are associated with various neurological disorders, such as Parkinson's, autism, and Down syndrome, understanding mechanisms modulating Synaptojanin function provides valuable insights into processes affecting neuronal communication.

Combined assessment of DYRK1A, BDNF and homocysteine levels as diagnostic marker for Alzheimer's disease

Early identification of Alzheimer's disease (AD) risk factors would aid development of interventions to delay the onset of dementia, but current biomarkers are invasive and/or costly to assess. Validated plasma biomarkers would circumvent these challenges. We previously identified the kinase DYRK1A in plasma. To validate DYRK1A as a biomarker for AD diagnosis, we assessed the levels of DYRK1A and the related markers brain-derived neurotrophic factor (BDNF) and homocysteine in two unrelated AD patient cohorts with age-matched controls. Receiver-operating characteristic curves and logistic regression analyses showed that combined assessment of DYRK1A, BDNF and homocysteine has a sensitivity of 0.952, a specificity of 0.889 and an accuracy of 0.933 in testing for AD. The blood levels of these markers provide a diagnosis assessment profile. Combined assessment of these three markers outperforms most of the previous markers and could become a useful substitute to the current panel of AD biomarkers. These results associate a decreased level of DYRK1A with AD and challenge the use of DYRK1A inhibitors in peripheral tissues as treatment. These measures will be useful for diagnosis purposes.

The X-Linked Intellectual Disability Protein IL1RAPL1 Regulates Dendrite Complexity

Mutations and deletions of the interleukin-1 receptor accessory protein like 1 (IL1RAPL1) gene, located on the X chromosome, are associated with intellectual disability (ID) and autism spectrum disorder (ASD). IL1RAPL1 protein is located at the postsynaptic compartment of excitatory synapses and plays a role in synapse formation and stabilization. Here, using primary neuronal cultures and Il1rapl1-KO mice, we characterized the role of IL1RAPL1 in regulating dendrite morphology. In Il1rapl1-KO mice we identified an increased number of dendrite branching points in CA1 and CA2 hippocampal neurons associated to hippocampal cognitive impairment. Similarly, induced pluripotent stem cell-derived neurons from a patient carrying a null mutation of the IL1RAPL1 gene had more dendrites. In hippocampal neurons, the overexpression of full-length IL1RAPL1 and mutants lacking part of C-terminal domains leads to simplified neuronal arborization. This effect is abolished when we overexpressed mutants lacking part of N-terminal domains, indicating that the IL1RAPL1 extracellular domain is required for regulating dendrite development. We also demonstrate that PTPδ interaction is not required for this activity, while IL1RAPL1 mediates the activity of IL-1β on dendrite morphology. Our data reveal a novel specific function for IL1RAPL1 in regulating dendrite morphology that can help clarify how changes in IL1RAPL1-regulated pathways can lead to cognitive disorders in humans.SIGNIFICANCE STATEMENT Abnormalities in the architecture of dendrites have been observed in a variety of neurodevelopmental, neurodegenerative, and neuropsychiatric disorders. Here we show that the X-linked intellectual disability protein interleukin-1 receptor accessory protein like 1 (IL1RAPL1) regulates dendrite morphology of mice hippocampal neurons and induced pluripotent stem cell-derived neurons from a patient carrying a null mutation of IL1RAPL1 gene. We also found that the extracellular domain of IL1RAPL1 is required for this effect, independently of the interaction with PTPδ, but IL1RAPL1 mediates the activity of IL-1β on dendrite morphology. Our data reveal a novel specific function for IL1RAPL1 in regulating dendrite morphology that can help clarify how changes in IL1RAPL1-regulated pathways can lead to cognitive disorders in humans.

A Neurodevelopmental Perspective for Autism-Associated Gene Function

Large-scale genetic sequencing studies have identified a wealth of genes in which mutations are associated with autism spectrum disorder (ASD). Understanding the biological function of these genes sheds light onto the neurodevelopmental basis of ASD. To this end, we defined functional categories representing brain development - (1) Cell Division and Survival, (2) Cell Migration and Differentiation, (3) Neuronal Morphological Elaboration, (4) Development and Regulation of Cellular Excitability, and (5) Synapse Formation and Function - and place 100 high confidence ASD-associated genes yielding at least 50 published PubMed articles into these categories based on keyword searches. We compare the categorization of ASD genes to genes associated with developmental delay (DD) and systematically review the published literature on the function of these genes. We find evidence that ASD-associated genes have important functions that span the neurodevelopmental continuum. Further, examining the temporal expression pattern of these genes using the BrainSpan Atlas of the Developing Human Brain supports their function across development. Thus, our analyses and review of literature on ASD gene function support a model whereby differences in brain development - from very early stages of macroarchitectural patterning to late stages of activity-dependent sculpting of synaptic connectivity - may lead to ASD. It will be important to keep investigating potential points of mechanistic convergence which could explain a common pathophysiological basis of ASD behind this disparate array of genes.

The cellular basis of dendrite pathology in neurodegenerative diseases

One of the characteristics of the neurons that distinguishes them from other cells is their complex and polarized structure consisting of dendrites, cell body, and axon. The complexity and diversity of dendrites are particularly well recognized, and accumulating evidences suggest that the alterations in the dendrite structure are associated with many neurodegenerative diseases. Given the importance of the proper dendritic structures for neuronal functions, the dendrite pathology appears to have crucial contribution to the pathogenesis of neurodegenerative diseases. Nonetheless, the cellular and molecular basis of dendritic changes in the neurodegenerative diseases remains largely elusive. Previous studies in normal condition have revealed that several cellular components, such as local cytoskeletal structures and organelles located locally in dendrites, play crucial roles in dendrite growth. By reviewing what has been unveiled to date regarding dendrite growth in terms of these local cellular components, we aim to provide an insight to categorize the potential cellular basis that can be applied to the dendrite pathology manifested in many neurodegenerative diseases. [BMB Reports 2017; 50(1): 5-11].

Understanding the Multifaceted Role of Human Down Syndrome Kinase DYRK1A

The dual-specificity tyrosine (Y) phosphorylation-regulated kinase DYRK1A, also known as Down syndrome (DS) kinase, is a dosage-dependent signaling kinase that was originally shown to be highly expressed in DS patients as a consequence of trisomy 21. Although this was evident some time ago, it is only in recent investigations that the molecular roles of DYRK1A in a wide range of cellular processes are becoming increasingly apparent. Since initial knowledge on DYRK1A became evident through minibrain mnb, the Drosophila homolog of DYRK1A, this review will first summarize the scientific reports on minibrain and further expand on the well-established neuronal functions of mammalian and human DYRK1A. Recent investigations across the current decade have provided rather interesting and compelling evidence in establishing nonneuronal functions for DYRK1A, including its role in infection, immunity, cardiomyocyte biology, cancer, and cell cycle control. The latter part of this review will therefore focus in detail on the emerging nonneuronal functions of DYRK1A and summarize the regulatory role of DYRK1A in controlling Tau and α-synuclein. Finally, the emerging role of DYRK1A in Parkinson's disease will be outlined.