Mark/Par-1 Marking the Polarity of Migrating Neurons

Doublecortin reinforces microtubules to promote growth cone advance in soft environments

Doublecortin (DCX) is a microtubule-associated protein critical for brain development. Although most highly expressed in the developing central nervous system, the molecular function of DCX in neuron morphogenesis remains unknown and controversial. We demonstrate that DCX function is intimately linked to its microtubule-binding activity. By using human induced pluripotent stem cell (hiPSC)- derived cortical i 3 Neurons genome engineered to express mEmerald-tagged DCX from the endogenous locus, we find that DCX-MT interactions become highly polarized very early during neuron morphogenesis. DCX becomes enriched only on straight microtubules in advancing growth cones with approximately 120 DCX molecules bound per micrometer of growth cone microtubule. At a similar saturation, microtubule-bound DCX molecules begin to impede lysosome transport, and thus can potentially control growth cone organelle entry. In addition, by comparing control, DCX-mEmerald and knockout DCX -/Y i 3 Neurons, we find that DCX stabilizes microtubules in the growth cone peripheral domain by reducing the microtubule catastrophe frequency and the depolymerization rate. DCX -/Y i 3 Neuron morphogenesis was inhibited in soft microenvironments that mimic the viscoelasticity of brain tissue and DCX -/Y neurites failed to grow toward brain-derived neurotrophic factor (BDNF) gradients. Together with high resolution traction force microscopy data, we propose a model in which DCX-decorated, rigid growth cone microtubules provide intracellular mechanical resistance to actomyosin generated contractile forces in soft physiological environments in which weak and transient adhesion-mediated forces in the growth cone periphery may be insufficient for productive growth cone advance. These data provide a new mechanistic understanding of how DCX mutations cause lissencephaly-spectrum brain malformations by impacting growth cone dynamics during neuron morphogenesis in physiological environments.

Many faces and functions of GSKIP: a temporospatial regulation view

Glycogen synthase kinase 3 (GSK3)-β (GSK3β) interaction protein (GSKIP) is one of the smallest A-kinase anchoring proteins that possesses a binding site for GSK3β. Recently, our group identified the protein kinase A (PKA)-GSKIP-GSK3β-X axis; knowledge of this axis may help us decipher the many roles of GSKIP and perhaps help explain the evolutionary reason behind the interaction between GSK3β and PKA. In this review, we highlight the critical and multifaceted role of GSKIP in facilitating PKA kinase activity and its function as a scaffolding protein in signaling pathways. We also highlight how these pivotal PKA and GSK3 kinases can control context-specific functions and interact with multiple target proteins, such as β-catenin, Drp1, Tau, and other proteins. GSKIP is a key regulator of multiple mechanisms because of not only its location at certain subcellular compartments but also its serial changes during the developmental process. Moreover, the involvement of critical upstream regulatory signaling pathways in GSKIP signaling in various cancers, such as miRNA (microRNA) and lncRNA (long noncoding RNA), may help in the identification of therapeutic targets in the era of precision medicine and personalized therapy. Finally, we emphasize on the model of the early stage of pathogenesis of Alzheimer Disease (AD). Although the model requires validation, it can serve as a basis for diagnostic biomarkers development and drug discovery for early-stage AD.

Progress in experimental research on SPRED protein family

The Sprouty-related Ena/vasodilator-stimulated phosphoprotein homology-1 (EVH-1) domain (SPRED) family of proteins was discovered in 2001. These Sprouty-related tyrosine kinase-binding proteins negatively regulate a variety of growth factor-induced Ras/ERK signaling pathways. In recent years, SPRED proteins have been found to regulate vital activities such as cell development, movement, and proliferation, and to participate in pathophysiological processes such as tumor metastasis, hematopoietic regulation, and allergic reactions. The findings of these studies have important implications regarding the involvement of SPRED proteins in disease. Early studies of SPRED proteins focused mainly on various tumors, cardiovascular diseases, and organ development. However, in recent years, great progress has been made in elucidating the role of SPRED proteins in neuropsychiatric, inflammatory, endocrine, and ophthalmic diseases. This article provides a review of the experimental studies performed in recent years on the SPRED proteins and their role in the pathogenesis of certain diseases.

Linking Cell Polarity to Cortical Development and Malformations

Cell polarity refers to the asymmetric distribution of signaling molecules, cellular organelles, and cytoskeleton in a cell. Neural progenitors and neurons are highly polarized cells in which the cell membrane and cytoplasmic components are compartmentalized into distinct functional domains in response to internal and external cues that coordinate polarity and behavior during development and disease. In neural progenitor cells, polarity has a prominent impact on cell shape and coordinate several processes such as adhesion, division, and fate determination. Polarity also accompanies a neuron from the beginning until the end of its life. It is essential for development and later functionality of neuronal circuitries. During development, polarity governs transitions between multipolar and bipolar during migration of postmitotic neurons, and directs the specification and directional growth of axons. Once reaching final positions in cortical layers, neurons form dendrites which become compartmentalized to ensure proper establishment of neuronal connections and signaling. Changes in neuronal polarity induce signaling cascades that regulate cytoskeletal changes, as well as mRNA, protein, and vesicle trafficking, required for synapses to form and function. Hence, defects in establishing and maintaining cell polarity are associated with several neural disorders such as microcephaly, lissencephaly, schizophrenia, autism, and epilepsy. In this review we summarize the role of polarity genes in cortical development and emphasize the relationship between polarity dysfunctions and cortical malformations.

PAR3-PAR6-atypical PKC polarity complex proteins in neuronal polarization

Polarity is a fundamental feature of cells. Protein complexes, including the PAR3-PAR6-aPKC complex, have conserved roles in establishing polarity across a number of eukaryotic cell types. In neurons, polarity is evident as distinct axonal versus dendritic domains. The PAR3, PAR6, and aPKC proteins also play important roles in neuronal polarization. During this process, either aPKC kinase activity, the assembly of the PAR3-PAR6-aPKC complex or the localization of these proteins is regulated downstream of a number of signaling pathways. In turn, the PAR3, PAR6, and aPKC proteins control various effector molecules to establish neuronal polarity. Herein, we discuss the many signaling mechanisms and effector functions that have been linked to PAR3, PAR6, and aPKC during the establishment of neuronal polarity.

Regulation of Polarity Protein Levels in the Developing Central Nervous System

In the course of their development from neuroepithelial cells to mature neurons, neuronal progenitors proliferate, delaminate, differentiate, migrate, and extend processes to form a complex neuronal network. In addition to supporting the morphology of the neuroepithelium and radial glia, polarity proteins contribute to the remodeling of processes and support the architectural reorganizations that result in axon extension and dendrite formation. While a good amount of evidence highlights a rheostat-like regulation by signaling events leading to local activation and/or redistribution of polarity proteins, recent studies demonstrate a new paradigm involving a switch-like regulation directly controlling the availability of polarity protein at specific stage by transcriptional regulation and/or targeted ubiquitin proteasome degradation. During the process of differentiation, most neurons will adopt a morphology with reduced polarity which suggests that polarity complex proteins are strongly repressed during key step of development. Here we review the different mechanisms that directly impact the levels of polarity complex proteins in neurons in relation to the polarization context and discuss why this transient loss of polarity is essential to understand neural development and how this knowledge could be relevant for some neuropathy.

Proteomic Analysis of Mouse Cortex Postsynaptic Density following Neonatal Brain Hypoxia-Ischemia

Proteomics of the synapses and postsynaptic densities (PSDs) have provided a deep understanding of protein composition and signal networks in the adult brain, which underlie neuronal plasticity and neurodegenerative or psychiatric disorders. However, there is a paucity of knowledge about the architecture and organization of PSDs in the immature brain, and how it is modified by brain injury in an early developing stage. Mass spectrometry (MS)-based proteomic analysis was performed on PSDs prepared from cortices of postnatal day 9 naïve mice or pups which had suffered hypoxic-ischemic (HI) brain injury. 512 proteins of different functional groups were identified from PSDs collected 1 h after HI injury, among which 60 have not been reported previously. Seven newly identified proteins involved in neural development were highlighted. HI injury increased the yield of PSDs at early time points upon reperfusion, and multiple proteins were recruited into PSDs following the insult. Quantitative analysis was performed using spectral counting, and proteins whose relative expression was more than 50% up- or downregulated compared to the sham animals 1 h after HI insult were reported. Validation with Western blotting demonstrated changes in expression and phosphorylation of the N-methyl-D-aspartate receptor, activation of a series of postsynaptic protein kinases and dysregulation of scaffold and adaptor proteins in response to neonatal HI insult. This work, along with other recent studies of synaptic protein profiling in the immature brain, builds a foundation for future investigation on the molecular mechanisms underlying developing plasticity. Furthermore, it provides insights into the biochemical changes of PSDs following early brain hypoxia-ischemia, which is helpful for understanding not only the injury mechanisms, but also the process of repair or replenishment of neuronal circuits during recovery from brain damage.

Regulation of Cell Polarity by PAR-1/MARK Kinase

PAR-1/MARK kinases are conserved serine/threonine kinases that are essential regulators of cell polarity. PAR-1/MARK kinases localize and function in opposition to the anterior PAR proteins to control the asymmetric distribution of factors in a wide variety polarized cells. In this review, we discuss the mechanisms that control the localization and activity of PAR-1/MARK kinases, including their antagonistic interactions with the anterior PAR proteins. We focus on the role PAR-1 plays in the asymmetric division of the Caenorhabditis elegans zygote, in the establishment of the anterior/posterior axis in the Drosophila oocyte and in the control of microtubule dynamics in mammalian neurons. In addition to conserved aspects of PAR-1 biology, we highlight the unique ways in which PAR-1 acts in these distinct cell types to orchestrate their polarization. Finally, we review the connections between disruptions in PAR-1/MARK function and Alzheimer's disease and cancer.

Novel pharmaceutical treatments for minimal traumatic brain injury and evaluation of animal models and methodologies supporting their development

BACKGROUND

The need for effective pharmaceuticals within animal models of traumatic brain injury (TBI) continues to be paramount, as TBI remains the major cause of brain damage for children and young adults. While preventative measures may act to reduce the incidence of initial blunt trauma, well-tolerated drugs are needed to target the neurologically damaging internal cascade of molecular mechanisms that follow. Such processes, known collectively as the secondary injury phase, include inflammation, excitotoxicity, and apoptosis among other changes still subject to research. In this article positive treatment findings to mitigate this secondary injury in rodent TBI models will be overviewed, and include recent studies on Exendin-4, N-Acetyl-l-cycteine, Salubrinal and Thrombin.

CONCLUSIONS

These studies provide representative examples of methodologies that can be combined with widely available in vivo rodent models to evaluate therapeutic approaches of translational relevance, as well as drug targets and biochemical cascades that may slow or accelerate the degenerative processes induced by TBI. They employ well-characterized tests such as the novel object recognition task for assessing cognitive deficits. The application of such methodologies provides both decision points and a gateway for implementation of further translational studies to establish the feasibility of clinical efficacy of potential therapeutic interventions.

Structural insight into the mechanism of synergistic autoinhibition of SAD kinases

The SAD/BRSK kinases participate in various important life processes, including neural development, cell cycle and energy metabolism. Like other members of the AMPK family, SAD contains an N-terminal kinase domain followed by the characteristic UBA and KA1 domains. Here we identify a unique autoinhibitory sequence (AIS) in SAD kinases, which exerts autoregulation in cooperation with UBA. Structural studies of mouse SAD-A revealed that UBA binds to the kinase domain in a distinct mode and, more importantly, AIS nestles specifically into the KD-UBA junction. The cooperative action of AIS and UBA results in an ‘αC-out' inactive kinase, which is conserved across species and essential for presynaptic vesicle clustering in C. elegans. In addition, the AIS, along with the KA1 domain, is indispensable for phospholipid binding. Taken together, these data suggest a model for synergistic autoinhibition and membrane activation of SAD kinases.

The SAD kinases contain a UBA domain that binds to the kinase domain and has a role in autoinhibition and allosteric activation of the AMPK homoenzyme. Here, the authors identify an autoinhibitory sequence in SAD and show that the UBA domain synergistically functions as an autoinhibitory domain.

Expression of MMP-1/PAR-1 and patterns of invasion in oral squamous cell carcinoma as potential prognostic markers

Background

Matrix metalloproteinase (MMP)-1 degrades type I collagen of the extracellular matrix and also activates protease activated receptor (PAR)-1 to induce angiogenesis. The aims of this study were to evaluate microvessel density (MVD) and the expression of PAR-1 and MMP-1 in oral squamous cell carcinoma (SCC) specimens with different patterns of invasion (POI) and to evaluate their association with clinical outcomes.

Methods

Seventy-four surgically obtained oral SCC samples were classified by POI according to hematoxylin-eosin staining. MVD and the localization and intensity of PAR-1 and MMP-1 expression were detected by immunohistochemistry.

Results

Of the 74 oral SCC samples, 18, 5, 34, and 17 showed type I, II, III, and IV POI, respectively. MVD and expression levels of MMP-1 and PAR-1 differed between POI types I–II and POI types III–IV. Patients with low tumor expression of MMP-1 and PAR-1 and low MVD had a longer survival time than those with high tumor expression of MMP-1 and PAR-1. Moreover, the survival time of patients with POI types III–IV was shorter than that of patients with POI types I–II.

Conclusion

POI combined with expression levels of MMP-1 and PAR-1 may be a valuable tool for assessing the clinical prognosis of patients with oral SCC.

Canonical and noncanonical roles of Par-1/MARK kinases in cell migration

The partitioning defective gene 1 (Par-1)/microtubule affinity-regulating kinase (MARK) family of serine-threonine kinases have diverse cellular roles. Primary among these roles are the establishment and maintenance of cell polarity and the promotion of microtubule dynamics. Par-1/MARK kinases also regulate a growing number of cellular functions via noncanonical protein targets. Recent studies have demonstrated that Par-1/MARK proteins are required for the migration of multiple cell types. This review outlines the current evidence for regulation of cell migration by Par-1/MARK through both canonical and noncanonical roles. Par-1/MARK canonical control of microtubules during nonneuronal and neuronal migration is described. Next, regulation of cell polarity by Par-1/MARK and its dynamic effect on the movement of migrating cells are discussed. As examples of recent research that have expanded, the roles of the Par-1/MARK in cell migration, noncanonical functions of Par-1/MARK in Wnt signaling and actomyosin dynamics are described. This review also highlights questions and current challenges to further understanding how the versatile Par-1/MARK proteins function in cell migration during development, homeostatic processes, and cancer.

Protein phosphorylation in neurodegeneration: friend or foe?

Protein misfolding and aggregation is a common hallmark in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and fronto-temporal dementia (FTD). In these disorders, the misfolding and aggregation of specific proteins occurs alongside neuronal degeneration in somewhat specific brain areas, depending on the disorder and the stage of the disease. However, we still do not fully understand the mechanisms governing protein aggregation, and whether this constitutes a protective or detrimental process. In PD, alpha-synuclein (aSyn) forms protein aggregates, known as Lewy bodies, and is phosphorylated at serine 129. Other residues have also been shown to be phosphorylated, but the significance of phosphorylation in the biology and pathophysiology of the protein is still controversial. In AD and in FTD, hyperphosphorylation of tau protein causes its misfolding and aggregation. Again, our understanding of the precise consequences of tau phosphorylation in the biology and pathophysiology of the protein is still limited. Through the use of a variety of model organisms and technical approaches, we are now gaining stronger insight into the effects of phosphorylation in the behavior of these proteins. In this review, we cover recent findings in the field and discuss how targeting phosphorylation events might be used for therapeutic intervention in these devastating diseases of the nervous system.