Integrin-mediated dendrite branch maintenance requires Abelson (Abl) family kinases

Neuroprotective Activity of a Non-Covalent Imatinib+TP10 Conjugate in HT-22 Neuronal Cells In Vitro

This study evaluated the probable relevance of a non-covalent conjugate of imatinib with TP10 in the context of a neuroprotective effect in Parkinson's disease. Through the inhibition of c-Abl, which is a non-receptor tyrosine kinase and an indicator of oxidative stress, imatinib has shown promise in preclinical animal models of this disease. The poor distribution of imatinib within the brain tissue triggered experiments in which a conjugate was obtained by mixing the drug with TP10, which is known for exhibiting high translocation activity across the cell membrane. The conjugate was tested on the HT-22 cell line with respect to its impact on MPP+-induced oxidative stress, apoptosis, necrosis, cytotoxicity, and mortality. Additionally, it was checked whether the conjugate activated the ABCB1 protein. The experiments indicated that imatinib+PEG4+TP10 reduced the post-MPP+ oxidative stress, apoptosis, and mortality, and these effects were more prominent than those obtained after the exposition of the HT-22 cells to imatinib alone. Its cytotoxicity was similar to that of imatinib itself. In contrast to imatinib, the conjugate did not activate the ABCB1 protein. These favorable qualities of imatinib+PEG4+TP10 make it a potential candidate for further in vivo research, which would confirm its neuroprotective action in PD-affected brains.

Glutamate Receptors and C-ABL Inhibitors: A New Therapeutic Approach for Parkinson's Disease

Parkinson's disease (PD) is the second-most prevalent central nervous system (CNS) neurodegenerative condition. Over the past few decades, suppression of BCR-Abelson tyrosine kinase (c-Abl), which serves as a marker of -synuclein aggregation and oxidative stress, has shown promise as a potential therapy target in PD. c-Abl inhibition has the potential to provide neuroprotection against PD, as shown by experimental results and the first-in-human trial, which supports the strategy in bigger clinical trials. Furthermore, glutamate receptors have also been proposed as potential therapeutic targets for the treatment of PD since they facilitate and regulate synaptic neurotransmission throughout the basal ganglia motor system. It has been noticed that pharmacological manipulation of the receptors can change normal as well as abnormal neurotransmission in the Parkinsonian brain. The review study contributes to a comprehensive understanding of the approach toward the role of c-Abl and glutamate receptors in Parkinson's disease by highlighting the significance and urgent necessity to investigate new pharmacotherapeutic targets. The article covers an extensive insight into the concept of targeting, pathophysiology, and c-Abl interaction with α-synuclein, parkin, and cyclin-dependent kinase 5 (Cdk5). Furthermore, the concepts of Nmethyl- D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPA) receptor, and glutamate receptors are discussed briefly. Conclusion: This review article focuses on in-depth literature findings supported by an evidence-based discussion on pre-clinical trials and clinical trials related to c-Abl and glutamate receptors that act as potential therapeutic targets for PD.

Lactoferrin/sialic acid prevents adverse effects of intrauterine growth restriction on neurite length: investigations in an in vitro rabbit neurosphere model

Introduction

Intrauterine growth restriction (IUGR) is a well-known cause of impaired neurodevelopment during life. In this study, we aimed to characterize alterations in neuronal development underlying IUGR and discover strategies to ameliorate adverse neurodevelopment effects by using a recently established rabbit in vitro neurosphere culture.

Methods

IUGR was surgically induced in pregnant rabbits by ligation of placental vessels in one uterine horn, while the contralateral horn remained unaffected for normal growth (control). At this time point, rabbits were randomly assigned to receive either no treatment, docosahexaenoic acid (DHA), melatonin (MEL), or lactoferrin (LF) until c-section. Neurospheres consisting of neural progenitor cells were obtained from control and IUGR pup's whole brain and comparatively analyzed for the ability to differentiate into neurons, extend neurite length, and form dendritic branching or pre-synapses. We established for the very first time a protocol to cultivate control and IUGR rabbit neurospheres not only for 5 days but under long-term conditions up to 14 days under differentiation conditions. Additionally, an in vitro evaluation of these therapies was evaluated by exposing neurospheres from non-treated rabbits to DHA, MEL, and SA (sialic acid, which is the major lactoferrin compound) and by assessing the ability to differentiate neurons, extend neurite length, and form dendritic branching or pre-synapses.

Results

We revealed that IUGR significantly increased the neurite length after 5 days of cultivation in vitro, a result in good agreement with previous in vivo findings in IUGR rabbits presenting more complex dendritic arborization of neurons in the frontal cortex. MEL, DHA, and SA decreased the IUGR-induced length of primary dendrites in vitro, however, only SA was able to reduce the total neurite length to control level in IUGR neurospheres. After prenatal in vivo administration of SAs parent compound LF with subsequent evaluation in vitro, LF was able to prevent abnormal neurite extension.

Discussion

We established for the first time the maintenance of the rabbit neurosphere culture for 14 days under differentiation conditions with increasing complexity of neuronal length and branching up to pre-synaptic formation. From the therapies tested, LF or its major compound, SA, prevents abnormal neurite extension and was therefore identified as the most promising therapy against IUGR-induced changes in neuronal development.

Abl2 Kinase Differentially Regulates iGluRs Current Activity and Synaptic Localization

Abelson non-receptor tyrosine kinases (Abl1 and Abl2) are established cellular signaling proteins, implicated in cytoskeletal reorganization essential for modulation of cell morphology and motility. During development of the central nervous system, Abl kinases play fundamental roles in neurulation and neurite outgrowth, relaying information from axon guidance cues and growth factor receptors to promote cytoskeletal rearrangements. In mature neurons, Abl kinases localize to pre- and postsynaptic compartments and are involved in regulation of synaptic stability and plasticity. Although emerging evidence indicates interchangeability of these isoforms in managing of cellular functions, in healthy adult neurons, Abl1 contribution is less elucidated, while Abl2 is required for optimal synaptic functioning. Our previous study demonstrated compartmentalization of Abl1 to the presynapse and Abl2 to the postsynapse and characterized their modulatory effect on spontaneous excitatory synaptic transmission. Here, we further delineate the role of Abl2 on regulation of the postsynaptic component of miniature excitatory postsynaptic current (mEPSC). Our findings show that both acute and prolonged activation of Abl2, in line with reduction of mEPSC amplitude, also decrease AMPA and NMDA current amplitudes. In contrast with the current-detrimental effect, prolonged Abl2 activity stabilizes spines, particularly contributing to maintenance of active synapses at distal (perhaps apical) segments of dendrites. Hence, we propose that attenuation of ion currents via ionotropic glutamatergic receptors by Abl2 kinase derives from either reduction of the receptor sensitivity for glutamate or is due to alteration of channel gating mechanisms. Abl2 and excitatory postsynapses: Abl2 expression level affects active excitatory synapse density on distal dendrites, while Abl2 activity impacts current density through AMPA and NMDA receptors.

The Potential Role of Integrin Signaling in Memory and Cognitive Impairment

Dementia currently has no cure and, due to the increased prevalence and associated economic and personal burden of this condition, current research efforts for the development of potential therapies have intensified. Recently, targeting integrins as a strategy to ameliorate dementia and other forms of cognitive impairment has begun to gain traction. Integrins are major bidirectional signaling receptors in mammalian cells, mediating various physiological processes such as cell-cell interaction and cell adhesion, and are also known to bind to the extracellular matrix. In particular, integrins play a critical role in the synaptic transmission of signals, hence their potential contribution to memory formation and significance in cognitive impairment. In this review, we describe the physiological roles that integrins play in the blood-brain barrier (BBB) and in the formation of memories. We also provide a clear overview of how integrins are implicated in BBB disruption following cerebral pathology. Given that vascular contributions to cognitive impairment and dementia and Alzheimer's' disease are prominent forms of dementia that involve BBB disruption, as well as chronic inflammation, we present current approaches shown to improve dementia-like conditions with integrins as a central focus. We conclude that integrins are vital in memory formation and that their disruption could lead to various forms of cognitive impairment. While further research to understand the relationships between integrins and memory is needed, we propose that the translational relevance of research efforts in this area could be improved through the use of appropriately aged, comorbid, male and female animals.

Emerging targets signaling for inflammation in Parkinson's disease drug discovery

Parkinson's disease (PD) patients not only show motor features such as bradykinesia, tremor, and rigidity but also non-motor features such as anxiety, depression, psychosis, memory loss, attention deficits, fatigue, sexual dysfunction, gastrointestinal issues, and pain. Many pharmacological treatments are available for PD patients; however, these treatments are partially or transiently effective since they only decrease the symptoms. As these therapies are unable to restore dopaminergic neurons and stop the development of Parkinson's disease, therefore, the need for an effective therapeutic approach is required. The current review summarizes novel targets for PD, that can be utilized to identify disease-modifying treatments.

Ste20-like Kinase Is Critical for Inhibitory Synapse Maintenance and Its Deficiency Confers a Developmental Dendritopathy

The size and structure of the dendritic arbor play important roles in determining how synaptic inputs of neurons are converted to action potential output. The regulatory mechanisms governing the development of dendrites, however, are insufficiently understood. The evolutionary conserved Ste20/Hippo kinase pathway has been proposed to play an important role in regulating the formation and maintenance of dendritic architecture. A key element of this pathway, Ste20-like kinase (SLK), regulates cytoskeletal dynamics in non-neuronal cells and is strongly expressed throughout neuronal development. However, its function in neurons is unknown. We show that, during development of mouse cortical neurons, SLK has a surprisingly specific role for proper elaboration of higher, ≥ third-order dendrites both in male and in female mice. Moreover, we demonstrate that SLK is required to maintain excitation-inhibition balance. Specifically, SLK knockdown caused a selective loss of inhibitory synapses and functional inhibition after postnatal day 15, whereas excitatory neurotransmission was unaffected. Finally, we show that this mechanism may be relevant for human disease, as dysmorphic neurons within human cortical malformations revealed significant loss of SLK expression. Overall, the present data identify SLK as a key regulator of both dendritic complexity during development and inhibitory synapse maintenance.SIGNIFICANCE STATEMENT We show that dysmorphic neurons of human epileptogenic brain lesions have decreased levels of the Ste20-like kinase (SLK). Decreasing SLK expression in mouse neurons revealed that SLK has essential functions in forming the neuronal dendritic tree and in maintaining inhibitory connections with neighboring neurons.

WIP, YAP/TAZ and Actin Connections Orchestrate Development and Transformation in the Central Nervous System

YAP (Yes-associated protein) and TAZ (transcriptional coactivator with PDZ-binding motif) are transcription co-regulators that make up the terminal components of the Hippo signaling pathway, which plays a role in organ size control and derived tissue homeostasis through regulation of the proliferation, differentiation and apoptosis of a wide variety of differentiated and stem cells. Hippo/YAP signaling contributes to normal development of the nervous system, as it participates in self-renewal of neural stem cells, proliferation of neural progenitor cells and differentiation, activation and myelination of glial cells. Not surprisingly, alterations in this pathway underlie the development of severe neurological diseases. In glioblastomas, YAP and TAZ levels directly correlate with the amount of the actin-binding molecule WIP (WASP interacting protein), which regulates stemness and invasiveness. In neurons, WIP modulates cytoskeleton dynamics through actin polymerization/depolymerization and acts as a negative regulator of neuritogenesis, dendrite branching and dendritic spine formation. Our working hypothesis is that WIP regulates the YAP/TAZ pools using a Hippo-independent pathway. Thus, in this review we will present some of the data that links WIP, YAP and TAZ, with a focus on their function in cells from the central and peripheral nervous systems. It is hoped that a better understanding of the mechanisms involved in brain and nervous development and the pathologies that arise due to their alteration will reveal novel therapeutic targets for neurologic diseases.

Integrins protect sensory neurons in models of paclitaxel-induced peripheral sensory neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect from cancer treatment with no known method for prevention or cure in clinics. CIPN often affects unmyelinated nociceptive sensory terminals. Despite the high prevalence, molecular and cellular mechanisms that lead to CIPN are still poorly understood. Here, we used a genetically tractable Drosophila model and primary sensory neurons isolated from adult mouse to examine the mechanisms underlying CIPN and identify protective pathways. We found that chronic treatment of Drosophila larvae with paclitaxel caused degeneration and altered the branching pattern of nociceptive neurons, and reduced thermal nociceptive responses. We further found that nociceptive neuron-specific overexpression of integrins, which are known to support neuronal maintenance in several systems, conferred protection from paclitaxel-induced cellular and behavioral phenotypes. Live imaging and superresolution approaches provide evidence that paclitaxel treatment causes cellular changes that are consistent with alterations in endosome-mediated trafficking of integrins. Paclitaxel-induced changes in recycling endosomes precede morphological degeneration of nociceptive neuron arbors, which could be prevented by integrin overexpression. We used primary dorsal root ganglia (DRG) neuron cultures to test conservation of integrin-mediated protection. We show that transduction of a human integrin β-subunit 1 also prevented degeneration following paclitaxel treatment. Furthermore, endogenous levels of surface integrins were decreased in paclitaxel-treated mouse DRG neurons, suggesting that paclitaxel disrupts recycling in vertebrate sensory neurons. Altogether, our study supports conserved mechanisms of paclitaxel-induced perturbation of integrin trafficking and a therapeutic potential of restoring neuronal interactions with the extracellular environment to antagonize paclitaxel-induced toxicity in sensory neurons.

Abelson Kinases Mediate the Depression of Spontaneous Synaptic Activity Induced by Amyloid Beta 1-42 Peptides

Amyloid beta (Aβ) peptides represent one of the most studied etiological factors of Alzheimer's disease. Nevertheless, the effects elicited by different molecular forms of amyloid beta peptides widely vary between the studies, mostly depending on experimental conditions. Despite the enormous amount of accumulated evidences concerning the pathological effects of amyloid beta peptides, the exact identity of the amyloid beta species is still controversial, and even less is clear as regards to the downstream effectors that mediate the devastating impact of these peptides on synapses in the central nervous system. Recent publications indicate that some of the neurotoxic effects of amyloid beta peptides may be mediated via the activation of proteins belonging to the Abelson non-receptor tyrosine kinase (Abl) family, that are known to regulate actin cytoskeleton structure as well as phosphorylate microtubule-associated tau protein, a hallmark of Alzheimer's disease. By performing series of miniature excitatory postsynaptic currents (mEPSC) recordings in cultured hippocampal cells, we demonstrate that activation of Abl kinases by acute application of 42 amino acid-length monomeric amyloid beta (Aβ1-42) peptides reduces spontaneous synaptic release, while this effect can be rescued by pharmacologic inhibition of Abl kinase activity, or by reduction of Abl expression with small interfering RNAs. Our electrophysiological data are further reinforced by a subsequent biochemical analysis, showing enhanced phosphorylation of Abl kinase substrate CT10 Regulator of Kinase-homolog-Like (Crkl) upon treatment of hippocampal neurons with Aβ peptides. Thus, we conclude that Abl kinase activation may be involved in Aβ-induced weakening of synaptic transmission.

c-Abl Kinase Is Required for Satellite Cell Function Through Pax7 Regulation

Satellite cells (SCs) are tissue-specific stem cells responsible for adult skeletal muscle regeneration and maintenance. SCs function is critically dependent on two families of transcription factors: the paired box (Pax) involved in specification and maintenance and the Muscle Regulatory Factors (MRFs), which orchestrate myogenic commitment and differentiation. In turn, signaling events triggered by extrinsic and intrinsic stimuli control their function via post-translational modifications, including ubiquitination and phosphorylation. In this context, the Abelson non-receptor tyrosine kinase (c-Abl) mediates the activation of the p38 α/β MAPK pathway, promoting myogenesis. c-Abl also regulates the activity of the transcription factor MyoD during DNA-damage stress response, pausing differentiation. However, it is not clear if c-Abl modulates other key transcription factors controlling SC function. This work aims to determine the role of c-Abl in SCs myogenic capacity via loss of function approaches in vitro and in vivo. Here we show that c-Abl inhibition or deletion results in a down-regulation of Pax7 mRNA and protein levels, accompanied by decreased Pax7 transcriptional activity, without a significant effect on MRF expression. Additionally, we provide data indicating that Pax7 is directly phosphorylated by c-Abl. Finally, SC-specific c-Abl ablation impairs muscle regeneration upon acute injury. Our results indicate that c-Abl regulates myogenic progression in activated SCs by controlling Pax7 function and expression.

Abelson kinase's intrinsically disordered region plays essential roles in protein function and protein stability

Background

The non-receptor tyrosine kinase Abelson (Abl) is a key player in oncogenesis, with kinase inhibitors serving as paradigms of targeted therapy. Abl also is a critical regulator of normal development, playing conserved roles in regulating cell behavior, brain development and morphogenesis. Drosophila offers a superb model for studying Abl’s normal function, because, unlike mammals, there is only a single fly Abl family member. In exploring the mechanism of action of multi-domain scaffolding proteins like Abl, one route is to define the roles of their individual domains. Research into Abl’s diverse roles in embryonic morphogenesis revealed many surprises. For instance, kinase activity, while important, is not crucial for all Abl activities, and the C-terminal F-actin binding domain plays a very modest role. This turned our attention to one of Abl’s least understood features—the long intrinsically-disordered region (IDR) linking Abl’s kinase and F-actin binding domains. The past decade revealed unexpected, important roles for IDRs in diverse cell functions, as sites of posttranslational modifications, mediating multivalent interactions and enabling assembly of biomolecular condensates via phase separation. Previous work deleting conserved regions in Abl’s IDR revealed an important role for a PXXP motif, but did not identify any other essential regions.

Methods

Here we extend this analysis by deleting the entire IDR, and asking whether Abl∆IDR rescues the diverse roles of Abl in viability and embryonic morphogenesis in Drosophila.

Results

This revealed that the IDR is essential for embryonic and adult viability, and for cell shape changes and cytoskeletal regulation during embryonic morphogenesis, and, most surprisingly, revealed a role in modulating protein stability.

Conclusion

Our data provide new insights into the role of the IDR in an important signaling protein, the non-receptor kinase Abl, suggesting that it is essential for all aspects of protein function during embryogenesis, and revealing a role in protein stability. These data will stimulate new explorations of the mechanisms by which the IDR regulates Abl stability and function, both in Drosophila and also in mammals. They also will stimulate further interest in the broader roles IDRs play in diverse signaling proteins.

The Rac-GEF Tiam1 Promotes Dendrite and Synapse Stabilization of Dentate Granule Cells and Restricts Hippocampal-Dependent Memory Functions

The dentate gyrus (DG) controls information flow into the hippocampus and is critical for learning, memory, pattern separation, and spatial coding, while DG dysfunction is associated with neuropsychiatric disorders. Despite its importance, the molecular mechanisms regulating DG neural circuit assembly and function remain unclear. Here, we identify the Rac-GEF Tiam1 as an important regulator of DG development and associated memory processes. In the hippocampus, Tiam1 is predominantly expressed in the DG throughout life. Global deletion of Tiam1 in male mice results in DG granule cells with simplified dendritic arbors, reduced dendritic spine density, and diminished excitatory synaptic transmission. Notably, DG granule cell dendrites and synapses develop normally in Tiam1 KO mice, resembling WT mice at postnatal day 21 (P21), but fail to stabilize, leading to dendrite and synapse loss by P42. These results indicate that Tiam1 promotes DG granule cell dendrite and synapse stabilization late in development. Tiam1 loss also increases the survival, but not the production, of adult-born DG granule cells, possibly because of greater circuit integration as a result of decreased competition with mature granule cells for synaptic inputs. Strikingly, both male and female mice lacking Tiam1 exhibit enhanced contextual fear memory and context discrimination. Together, these results suggest that Tiam1 is a key regulator of DG granule cell stabilization and function within hippocampal circuits. Moreover, based on the enhanced memory phenotype of Tiam1 KO mice, Tiam1 may be a potential target for the treatment of disorders involving memory impairments.SIGNIFICANCE STATEMENT The dentate gyrus (DG) is important for learning, memory, pattern separation, and spatial navigation, and its dysfunction is associated with neuropsychiatric disorders. However, the molecular mechanisms controlling DG formation and function remain elusive. By characterizing mice lacking the Rac-GEF Tiam1, we demonstrate that Tiam1 promotes the stabilization of DG granule cell dendritic arbors, spines, and synapses, whereas it restricts the survival of adult-born DG granule cells, which compete with mature granule cells for synaptic integration. Notably, mice lacking Tiam1 also exhibit enhanced contextual fear memory and context discrimination. These findings establish Tiam1 as an essential regulator of DG granule cell development, and identify it as a possible therapeutic target for memory enhancement.

Scrap and Build for Functional Neural Circuits: Spatiotemporal Regulation of Dendrite Degeneration and Regeneration in Neural Development and Disease

Dendrites are cellular structures essential for the integration of neuronal information. These elegant but complex structures are highly patterned across the nervous system but vary tremendously in their size and fine architecture, each designed to best serve specific computations within their networks. Recent in vivo imaging studies reveal that the development of mature dendrite arbors in many cases involves extensive remodeling achieved through a precisely orchestrated interplay of growth, degeneration, and regeneration of dendritic branches. Both degeneration and regeneration of dendritic branches involve precise spatiotemporal regulation for the proper wiring of functional networks. In particular, dendrite degeneration must be targeted in a compartmentalized manner to avoid neuronal death. Dysregulation of these developmental processes, in particular dendrite degeneration, is associated with certain types of pathology, injury, and aging. In this article, we review recent progress in our understanding of dendrite degeneration and regeneration, focusing on molecular and cellular mechanisms underlying spatiotemporal control of dendrite remodeling in neural development. We further discuss how developmental dendrite degeneration and regeneration are molecularly and functionally related to dendrite remodeling in pathology, disease, and aging.

Timely Inhibitory Circuit Formation Controlled by Abl1 Regulates Innate Olfactory Behaviors in Mouse

More than one-half of the interneurons in a mouse olfactory bulb (OB) develop during the first week after birth and predominantly connect to excitatory tufted cells near the superficial granule cell layer (sGCL), unlike late-born interneurons. However, the molecular mechanisms underlying the temporal specification are yet to be identified. In this study, we determined the role of Abelson tyrosine-protein kinase 1 (Abl1) in the temporal development of early-born OB interneurons. Lentiviral knockdown of Abl1 disrupts the sGCL circuit of early-born interneurons through defects in function and circuit integration, resulting in olfactory hyper-sensitivity. We show that doublecortin (Dcx) is phosphorylated by Abl1, which contributes to the stabilization of Dcx, thereby regulating microtubule dynamics. Finally, Dcx overexpression rescues Abl1 knockdown-induced anatomic or functional defects. In summary, specific signaling by Abl1-Dcx in early-born interneurons facilitates the temporal development of the sGCL circuit to regulate innate olfactory functions, such as detection and sensitivity.

Current and emerging therapeutic targets for Parkinson's disease

Parkinson's disease (PD) is characterized by gradual neurodegeneration and forfeiture of dopamine neurons in substantia nigra pars compacta which ultimately leads to depletion of dopamine levels. PD patients not only display motor features such as rigidity, tremor, and bradykinesia but also non-motor features such as depression, anxiety, etc. Various treatments are available for PD patients such as dopamine replacement are well established but it is only partially or transiently effective. As these therapies not able to restore dopaminergic neurons and delay the development of Parkinson's disease, therefore, the need for an effective therapeutic approach is crucial. The present review discusses a comprehensive overview of current novel targets for PD which includes molecular chaperone, neuroinflammation, mitochondrial dysfunction, neuromelanin, Ubiquitin-proteasome system, protein Abelson, Synaptic vesicle glycoprotein 2C, and Cocaine-amphetamine-regulated transcript, etc. These approaches will help to identify new targets for the treatment of disease and may provide a ray of hope for PD patient treatment. Graphical abstract.

Beyond Axon Guidance: Roles of Slit-Robo Signaling in Neocortical Formation

The formation of the neocortex relies on intracellular and extracellular signaling molecules that are involved in the sequential steps of corticogenesis, ranging from the proliferation and differentiation of neural progenitor cells to the migration and dendrite formation of neocortical neurons. Abnormalities in these steps lead to disruption of the cortical structure and circuit, and underly various neurodevelopmental diseases, including dyslexia and autism spectrum disorder (ASD). In this review, we focus on the axon guidance signaling Slit-Robo, and address the multifaceted roles of Slit-Robo signaling in neocortical development. Recent studies have clarified the roles of Slit-Robo signaling not only in axon guidance but also in progenitor cell proliferation and migration, and the maturation of neocortical neurons. We further discuss the etiology of neurodevelopmental diseases, which are caused by defects in Slit-Robo signaling during neocortical formation.

Trio Haploinsufficiency Causes Neurodevelopmental Disease-Associated Deficits

Heterozygous coding mutations in TRIO are associated with neurodevelopmental disorders, including autism, schizophrenia, bipolar disorder, and epilepsy, and impair TRIO's biochemical activities. To model mutant alleles, we ablated one or both Trio alleles from excitatory neurons in the cortex and hippocampus of mice. Trio haploinsufficiency increases anxiety and impairs social preference and motor coordination. Trio loss reduces forebrain size and dendritic arborization but increases dendritic spine densities. Cortical synapses in Trio haploinsufficient mice are small, exhibit pre- and postsynaptic deficits, and cannot undergo long-term potentiation. Similar phenotypes are observed in Trio knockout mice. Overall, Trio haploinsufficiency causes severe disease-relevant deficits in behavior and neuronal structure and function. Interestingly, phosphodiesterase 4A5 (PDE4A5) levels are reduced and protein kinase A (PKA) signaling is increased when TRIO levels are reduced. Elevation of PDE4A5 and drug-based attenuation of PKA signaling rescue Trio haploinsufficiency-related dendritic spine defects, suggesting an avenue for therapeutic intervention for TRIO-related neurodevelopmental disorders.

Regulation of MT dynamics via direct binding of an Abl family kinase

Genetic studies revealed that Abl family kinases interact functionally with microtubules, but the mechanism by which Abl kinases regulate microtubules remains unclear. Hu et al. provide the first evidence that the Abl family kinase Abl2 directly binds microtubules to regulate microtubule dynamics.

Abl family kinases are essential regulators of cell shape and movement. Genetic studies revealed functional interactions between Abl kinases and microtubules (MTs), but the mechanism by which Abl family kinases regulate MTs remains unclear. Here, we report that Abl2 directly binds to MTs and regulates MT behaviors. Abl2 uses its C-terminal half to bind MTs, an interaction mediated in part through electrostatic binding to tubulin C-terminal tails. Using purified proteins, we found that Abl2 binds growing MTs and promotes MT polymerization and stability. In cells, knockout of Abl2 significantly impairs MT growth, and this defect can be rescued via reexpression of Abl2. Stable reexpression of an Abl2 fragment containing the MT-binding domain alone was sufficient to restore MT growth at the cell edge. These results show Abl2 uses its C-terminal half to bind MTs and directly regulate MT dynamics.

ABL kinase inhibition promotes lung regeneration through expansion of an SCGB1A1+ SPC+ cell population following bacterial pneumonia

Current therapeutic interventions for the treatment of respiratory infections are hampered by the evolution of multidrug resistance in pathogens as well as the lack of effective cellular targets. Despite the identification of multiple region-specific lung progenitor cells, the identity of molecules that might be therapeutically targeted in response to infections to promote activation of progenitor cell types remains elusive. Here, we report that loss of Abl1 specifically in SCGB1A1-expressing cells leads to a significant increase in the proliferation and differentiation of bronchiolar epithelial cells, resulting in dramatic expansion of an SCGB1A1+ airway cell population that coexpresses SPC, a marker for type II alveolar cells that promotes alveolar regeneration following bacterial pneumonia. Furthermore, treatment with an Abl-specific allosteric inhibitor enhanced regeneration of the alveolar epithelium and promoted accelerated recovery of mice following pneumonia. These data reveal a potential actionable target that may be exploited for efficient recovery after pathogen-induced infections.

Abl2 is recruited to ventral actin waves through cytoskeletal interactions to promote lamellipodium extension

Abl family nonreceptor tyrosine kinases regulate changes in cell shape and migration. Abl2 localizes to dynamic actin-rich protrusions, such as lamellipodia in fibroblasts and dendritic spines in neurons. Abl2 interactions with cortactin, an actin filament stabilizer, are crucial for the formation and stability of actin-rich structures, but Abl2:cortactin-positive structures have not been characterized with high spatiotemporal resolution in cells. Using total internal reflection fluorescence microscopy, we demonstrate that Abl2 colocalizes with cortactin at wave-like structures within lamellum and lamellipodium tips. Abl2 and cortactin within waves are focal and transient, extend to the outer edge of lamella, and serve as the base for lamellipodia protrusions. Abl2-positive foci colocalize with integrin β3 and paxillin, adhesive markers of the lamellum-lamellipodium interface. Cortactin-positive waves still form in Abl2 knockout cells, but the lamellipodium size is significantly reduced. This deficiency is restored following Abl2 reexpression. Complementation analyses revealed that the Abl2 C-terminal half, which contains domains that bind actin and microtubules, is necessary and sufficient for recruitment to the wave-like structures and to support normal lamellipodium size, while the kinase domain-containing N-terminal half does not impact lamellipodium size. Together, this work demonstrates that Abl2 is recruited with cortactin to actin waves through cytoskeletal interactions to promote lamellipodium extension.

Integrin activity in neuronal connectivity

The formation of correct synaptic structures and neuronal connections is paramount for normal brain development and a functioning adult brain. The integrin family of cell adhesion receptors and their ligands play essential roles in the control of several processes regulating neuronal connectivity - including neurite outgrowth, the formation and maintenance of synapses, and synaptic plasticity - that are affected in neurodevelopmental disorders, such as autism spectrum disorders (ASDs) and schizophrenia. Many ASD- and schizophrenia-associated genes are linked to alterations in the genetic code of integrins and associated signalling pathways. In non-neuronal cells, crosstalk between integrin-mediated adhesions and the actin cytoskeleton, and the regulation of integrin activity (affinity for extracellular ligands) are widely studied in healthy and pathological settings. In contrast, the roles of integrin-linked pathways in the central nervous system remains less well defined. In this Review, we will provide an overview of the known pathways that are regulated by integrin-ECM interaction in developing neurons and in adult brain. We will also describe recent advances in the identification of mechanisms that regulate integrin activity in neurons, and highlight the interesting emerging links between integrins and neurodevelopment.

Ndr2 Kinase Controls Neurite Outgrowth and Dendritic Branching Through α1 Integrin Expression

The serine/threonine kinase Ndr2 has been shown to control the inside-out activation of the β₁subunit of integrins and the formation of neurites in both primary neurons and neurally differentiated pheochromacytoma (PC12) cells. In this study, we demonstrate that Ndr2 kinase furthermore determines the substrate specificity of neurite extension in PC12 cells via expression of α₁β₁ integrins. We show that stable overexpression of Ndr2 in PC12 cells increases neurite growth and extension on poly-D-lysine substrate, likely involving an increased expression of active β₁ integrin in the growth tips of these cells. By contrast, the Ndr2 overexpressing cells do not show the α₁β₁ integrin-mediated enhancement of neurite growth on collagen IV substrate that can be seen in control cells. Moreover, they entirely fail to increase in response to activation of α₁β₁ integrins via a soluble KTS ligand and show a diminished accumulation of α₁ integrin in neurite tips, although the expression of this subunit is induced during differentiation to comparable levels as in control cells. Finally, we demonstrate that Ndr2 overexpression similarly inhibits the α₁β₁ integrin-dependent dendritic growth of primary hippocampal neurons on laminin 111 substrate. By contrast, lack of Ndr2 impairs the dendritic growth regardless of the substrate. Together, these results suggest that Ndr2 regulates α₁ integrin trafficking in addition to β₁ integrin subunit activation and thereby controls the neurite growth on different extracellular matrix (ECM) substrates.

The vascular endothelial specific IL-4 receptor alpha-ABL1 kinase signaling axis regulates the severity of IgE-mediated anaphylactic reactions

BACKGROUND

Severe IgE-mediated, food-induced anaphylactic reactions are characterized by pulmonary venous vasodilatation and fluid extravasation, which are thought to lead to the life-threatening anaphylactic phenotype. The underlying immunologic and cellular processes involved in driving fluid extravasation and the severe anaphylactic phenotype are not fully elucidated.

OBJECTIVE

We sought to define the interaction and requirement of IL-4 and vascular endothelial (VE) IL-4 receptor α chain (IL-4Rα) signaling in histamine-abelson murine leukemia viral oncogene homology 1 (ABL1)-mediated VE dysfunction and fluid extravasation in the severity of IgE-mediated anaphylactic reactions in mice.

METHODS

Mice deficient in VE IL-4Rα and models of passive and active oral antigen- and IgE-induced anaphylaxis were used to define the requirements of the VE IL-4Rα and ABL1 pathway in severe anaphylactic reactions. The human VE cell line (EA.hy926 cells) and pharmacologic (imatinib) and genetic (short hairpin RNA knockdown of IL4RA and ABL1) approaches were used to define the requirement of this pathway in VE barrier dysfunction.

RESULTS

IL-4 exacerbation of histamine-induced hypovolemic shock in mice was dependent on VE expression of IL-4Rα. IL-4- and histamine-induced ABL1 activation in human VE cells and VE barrier dysfunction was ABL1-dependent. Development of severe IgE-mediated hypovolemia and shock required VE-restricted ABL1 expression. Treatment of mice with a history of food-induced anaphylaxis with the ABL kinase inhibitor imatinib protected the mice from severe IgE-mediated anaphylaxis.

CONCLUSION

IL-4 amplifies IgE- and histamine-induced VE dysfunction, fluid extravasation, and the severity of anaphylaxis through a VE IL-4Rα/ABL1-dependent mechanism. These studies implicate an important contribution by the VE compartment in the severity of anaphylaxis and identify a new pathway for therapeutic intervention of IgE-mediated reactions.

Corticosteroid-induced dendrite loss and behavioral deficiencies can be blocked by activation of Abl2/Arg kinase

Stressor exposure induces neuronal remodeling in specific brain regions. Given the persistence of stress-related illnesses, key next steps in determining the contributions of neural structure to mental health are to identify cell types that fail to recover from stressor exposure and to identify "trigger points" and molecular underpinnings of stress-related neural degeneration. We evaluated dendrite arbor structure on hippocampal CA1 pyramidal neurons before, during, and following prolonged exposure to one key mediator of the stress response - corticosterone (cortisol in humans). Basal dendrite arbors progressively simplified during a 3-week exposure period, and failed to recover when corticosterone was withdrawn. Corticosterone exposure decreased levels of the dendrite stabilization factor Abl2/Arg nonreceptor tyrosine kinase and phosphorylation of its substrates p190RhoGAP and cortactin within 11days, suggesting that disruption of Arg-mediated signaling may trigger dendrite arbor atrophy and, potentially, behavioral abnormalities resulting from corticosterone exposure. To test this, we administered the novel, bioactive Arg kinase activator, 5-(1,3-diaryl-1H-pyrazol-4-yl)hydantoin, 5-[3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl]-2,4-imidazolidinedione (DPH), in conjunction with corticosterone. We found that repeated treatment corrected CA1 arbor structure, otherwise simplified by corticosterone. DPH also corrected corticosterone-induced errors in a hippocampal-dependent reversal learning task and anhedonic-like behavior. Thus, pharmacological compounds that target cytoskeletal regulators, rather than classical neurotransmitter systems, may interfere with stress-associated cognitive decline and mental health concerns.

The Abl-1 Kinase is Dispensable for NK Cell Inhibitory Signalling and is not Involved in Murine NK Cell Education

Natural killer (NK) cell responsiveness in the mouse is determined in an education process guided by inhibitory Ly49 and NKG2A receptors binding to MHC class I molecules. It has been proposed that inhibitory signalling in human NK cells involves Abl-1 (c-Abl)-mediated phosphorylation of Crk, lowering NK cell function via disruption of a signalling complex including C3G and c-Cbl, suggesting that NK cell education might involve c-Abl. Mice deficient in c-Abl expression specifically in murine NK cells displayed normal inhibitory and activating receptor repertoires. Furthermore, c-Abl-deficient NK cells fluxed Ca²⁺ normally after triggering of ITAM receptors, killed YAC-1 tumour cells efficiently and showed normal, or even slightly elevated, capacity to produce IFN-γ after activating receptor stimulation. Consistent with these results, c-Abl deficiency in NK cells did not affect NK cell inhibition via the receptors Ly49G2, Ly49A and NKG2A. We conclude that signalling downstream of murine inhibitory receptors does not involve c-Abl and that c-Abl plays no major role in NK cell education in the mouse.

Amplification of F-Actin Disassembly and Cellular Repulsion by Growth Factor Signaling

Extracellular cues that regulate cellular shape, motility, and navigation are generally classified as growth promoting (i.e., growth factors/chemoattractants and attractive guidance cues) or growth preventing (i.e., repellents and inhibitors). Yet, these designations are often based on complex assays and undefined signaling pathways and thus may misrepresent direct roles of specific cues. Here, we find that a recognized growth-promoting signaling pathway amplifies the F-actin disassembly and repulsive effects of a growth-preventing pathway. Focusing on Semaphorin/Plexin repulsion, we identified an interaction between the F-actin-disassembly enzyme Mical and the Abl tyrosine kinase. Biochemical assays revealed Abl phosphorylates Mical to directly amplify Mical Redox-mediated F-actin disassembly. Genetic assays revealed that Abl allows growth factors and Semaphorin/Plexin repellents to combinatorially increase Mical-mediated F-actin disassembly, cellular remodeling, and repulsive axon guidance. Similar roles for Mical in growth factor/Abl-related cancer cell behaviors further revealed contexts in which characterized positive effectors of growth/guidance stimulate such negative cellular effects as F-actin disassembly/repulsion.

Dendritic Actin Cytoskeleton: Structure, Functions, and Regulations

Actin is a versatile and ubiquitous cytoskeletal protein that plays a major role in both the establishment and the maintenance of neuronal polarity. For a long time, the most prominent roles that were attributed to actin in neurons were the movement of growth cones, polarized cargo sorting at the axon initial segment, and the dynamic plasticity of dendritic spines, since those compartments contain large accumulations of actin filaments (F-actin) that can be readily visualized using electron- and fluorescence microscopy. With the development of super-resolution microscopy in the past few years, previously unknown structures of the actin cytoskeleton have been uncovered: a periodic lattice consisting of actin and spectrin seems to pervade not only the whole axon, but also dendrites and even the necks of dendritic spines. Apart from that striking feature, patches of F-actin and deep actin filament bundles have been described along the lengths of neurites. So far, research has been focused on the specific roles of actin in the axon, while it is becoming more and more apparent that in the dendrite, actin is not only confined to dendritic spines, but serves many additional and important functions. In this review, we focus on recent developments regarding the role of actin in dendrite morphology, the regulation of actin dynamics by internal and external factors, and the role of F-actin in dendritic protein trafficking.

Differential expression of cytoskeletal regulatory factors in the adolescent prefrontal cortex: Implications for cortical development

The prevalence of depression, anxiety, schizophrenia, and drug and alcohol use disorders peaks during adolescence. Further, up to 50% of "adult" mental health disorders emerge in adolescence. During adolescence, the prefrontal cortex (PFC) undergoes dramatic structural reorganization, in which dendritic spines and synapses are refined, pruned, and stabilized. Understanding the molecular mechanisms that underlie these processes should help to identify factors that influence the development of psychiatric illness. Here we briefly discuss the anatomical connections of the medial and orbital prefrontal cortex (mPFC and OFC, respectively). We then present original findings suggesting that dendritic spines on deep-layer excitatory neurons in the mouse mPFC and OFC prune at different adolescent ages, with later pruning in the OFC. In parallel, we used Western blotting to define levels of several cytoskeletal regulatory proteins during early, mid-, and late adolescence, focusing on tropomyosin-related kinase receptor B (TrkB) and β1-integrin-containing receptors and select signaling partners. We identified regional differences in the levels of several proteins in early and midadolescence that then converged in early adulthood. We also observed age-related differences in TrkB levels, both full-length and truncated isoforms, Rho-kinase 2, and synaptophysin in both PFC subregions. Finally, we identified changes in protein levels in the dorsal and ventral hippocampus that were distinct from those in the PFC. We conclude with a general review of the manner in which TrkB- and β1-integrin-mediated signaling influences neuronal structure in the postnatal brain. Elucidating the role of cytoskeletal regulatory factors throughout adolescence may identify critical mechanisms of PFC development. © 2016 Wiley Periodicals, Inc.

Stage-specific functions of Semaphorin7A during adult hippocampal neurogenesis rely on distinct receptors

The guidance protein Semaphorin7A (Sema7A) is required for the proper development of the immune and nervous systems. Despite strong expression in the mature brain, the role of Sema7A in the adult remains poorly defined. Here we show that Sema7A utilizes different cell surface receptors to control the proliferation and differentiation of neural progenitors in the adult hippocampal dentate gyrus (DG), one of the select regions of the mature brain where neurogenesis occurs. PlexinC1 is selectively expressed in early neural progenitors in the adult mouse DG and mediates the inhibitory effects of Sema7A on progenitor proliferation. Subsequently, during differentiation of adult-born DG granule cells, Sema7A promotes dendrite growth, complexity and spine development through β1-subunit-containing integrin receptors. Our data identify Sema7A as a key regulator of adult hippocampal neurogenesis, providing an example of how differential receptor usage spatiotemporally controls and diversifies the effects of guidance cues in the adult brain.

Ras and Rab interactor 1 controls neuronal plasticity by coordinating dendritic filopodial motility and AMPA receptor turnover

Ras and Rab interactor 1 (RIN1) is predominantly expressed in the nervous system. RIN1-knockout animals have deficits in latent inhibition and fear extinction in the amygdala, suggesting a critical role for RIN1 in preventing the persistence of unpleasant memories. At the molecular level, RIN1 signals through Rab5 GTPases that control endocytosis of cell-surface receptors and Abl nonreceptor tyrosine kinases that participate in actin cytoskeleton remodeling. Here we report that RIN1 controls the plasticity of cultured mouse hippocampal neurons. Our results show that RIN1 affects the morphology of dendritic protrusions and accelerates dendritic filopodial motility through an Abl kinase-dependent pathway. Lack of RIN1 results in enhanced mEPSC amplitudes, indicating an increase in surface AMPA receptor levels compared with wild-type neurons. We further provide evidence that the Rab5 GEF activity of RIN1 regulates surface GluA1 subunit endocytosis. Consequently loss of RIN1 blocks surface AMPA receptor down-regulation evoked by chemically induced long-term depression. Our findings indicate that RIN1 destabilizes synaptic connections and is a key player in postsynaptic AMPA receptor endocytosis, providing multiple ways of negatively regulating memory stabilization during neuronal plasticity.

c-Abl and Parkinson's Disease: Mechanisms and Therapeutic Potential

Although the etiology of Parkinson's disease (PD) is poorly understood, oxidative stress has long been implicated in the pathogenesis of the disease. However, multifaceted and divergent signaling cascades downstream of oxidative stress have posed challenges for researchers to identify a central component of the oxidative stress-induced pathways causing neurodegeneration in PD. Since 2010, c-Abl-a non-receptor tyrosine kinase and an indicator of oxidative stress-has shown remarkable potential as a future promising drug target in PD therapeutics. Although, the constitutively active form of c-Abl, Bcr-Abl, has a long history in chronic myeloid leukemia and acute lymphocytic leukemia, the role of c-Abl in PD and relevant neurodegenerative diseases was completely unknown. Recently, others and we have identified and validated c-Abl as an important pathogenic mediator of the disease, where activated c-Abl emerges as a common link to various PD-related inducers of oxidative stress relevant to both sporadic and familial forms of PD and α-synucleinopathies. This review discusses the role of c-Abl in PD and the latest advancement on c-Abl as a drug target and as a prospective biomarker.

A Sonic hedgehog coreceptor, BOC regulates neuronal differentiation and neurite outgrowth via interaction with ABL and JNK activation

Neurite outgrowth is a critical step for neurogenesis and remodeling synaptic circuitry during neuronal development and regeneration. An immunoglobulin superfamily member, BOC functions as Sonic hedgehog (Shh) coreceptor in canonical and noncanonical Shh signaling in neuronal development and axon outgrowth/guidance. However signaling mechanisms responsible for BOC action during these processes remain unknown. In our previous studies, a multiprotein complex containing BOC and a closely related protein CDO promotes myogenic differentiation through activation of multiple signaling pathways, including non-receptor tyrosine kinase ABL. Given that ABL and Jun. N-terminal kinase (JNK) are implicated in actin cytoskeletal dynamics required for neurogenesis, we investigated the relationship between BOC, ABL and JNK during neuronal differentiation. Here, we demonstrate that BOC and ABL are induced in P19 embryonal carcinoma (EC) cells and cortical neural progenitor cells (NPCs) during neuronal differentiation. BOC-depleted EC cells or Boc^-/- NPCs exhibit impaired neuronal differentiation with shorter neurite formation. BOC interacts with ABL through its putative SH2 binding domain and seems to be phosphorylated in an ABL activity-dependent manner. Unlike wildtype BOC, ABL-binding defective BOC mutants exhibit impaired JNK activation and neuronal differentiation. Finally, Shh treatment enhances JNK activation which is diminished by BOC depletion. These data suggest that BOC interacts with ABL and activates JNK thereby promoting neuronal differentiation and neurite outgrowth.

Multifunctional Abl kinases in health and disease

The Abelson tyrosine kinases were initially identified as drivers of leukemia in mice and humans. The Abl family kinases Abl1 and Abl2 regulate diverse cellular processes during development and normal homeostasis, and their functions are subverted during inflammation, cancer and other pathologies. Abl kinases can be activated by multiple stimuli leading to cytoskeletal reorganization required for cell morphogenesis, motility, adhesion and polarity. Depending on the cellular context, Abl kinases regulate cell survival and proliferation. Emerging data support important roles for Abl kinases in pathologies linked to inflammation. Among these are neurodegenerative diseases and inflammatory pathologies. Unexpectedly, Abl kinases have also been identified as important players in mammalian host cells during microbial pathogenesis. Thus, the use of Abl kinase inhibitors might prove to be effective in the treatment of pathologies beyond leukemia and solid tumors. In this Cell Science at a Glance article and in the accompanying poster, we highlight the emerging roles of Abl kinases in the regulation of cellular processes in normal cells and diverse pathologies ranging from cancer to microbial pathogenesis.

Integrin Activation Through the Hematopoietic Adapter Molecule ADAP Regulates Dendritic Development of Hippocampal Neurons

Integrin-mediated cell adhesion and signaling is of critical importance for neuronal differentiation. Recent evidence suggests that an “inside-out” activation of β1-integrin, similar to that observed in hematopoietic cells, contributes to the growth and branching of dendrites. In this study, we investigated the role of the hematopoietic adaptor protein adhesion and degranulation promoting adapter protein (ADAP) in these processes. We demonstrate the expression of ADAP in the developing and adult nervous hippocampus, and in outgrowing dendrites of primary hippocampal neurons. We further show that ADAP occurs in a complex with another adaptor protein signal-transducing kinase-associated phosphoprotein-homolog (SKAP-HOM), with the Rap1 effector protein RAPL and the Hippo kinase macrophage-stimulating 1 (MST1), resembling an ADAP/SKAP module that has been previously described in T-cells and is critically involved in “inside-out” activation of integrins. Knock down of ADAP resulted in reduced expression of activated β1-integrin on dendrites. It furthermore reduced the differentiation of developing neurons, as indicated by reduced dendrite growth and decreased expression of the dendritic marker microtubule-associated protein 2 (MAP2). Our data suggest that an ADAP-dependent integrin-activation similar to that described in hematopoietic cells contributes to the differentiation of neuronal cells.

A pre-metazoan origin of the CRK gene family and co-opted signaling network

CRK and CRKL adapter proteins play essential roles in development and cancer through their SRC homology 2 and 3 (SH2 and SH3) domains. To gain insight into the origin of their shared functions, we have investigated their evolutionary history. We propose a term, crk/crkl ancestral (crka), for orthologs in invertebrates before the divergence of CRK and CRKL in the vertebrate ancestor. We have isolated two orthologs expressed in the choanoflagellate Monosiga brevicollis, a unicellular relative to the metazoans. Consistent with its highly-conserved three-dimensional structure, the SH2 domain of M. brevicollis crka1 can bind to the mammalian CRK/CRKL SH2 binding consensus phospho-YxxP, and to the SRC substrate/focal adhesion protein BCAR1 (p130^CAS) in the presence of activated SRC. These results demonstrate an ancient origin of the CRK/CRKL SH2-target recognition specificity. Although BCAR1 orthologs exist only in metazoans as identified by an N-terminal SH3 domain, YxxP motifs, and a C-terminal FAT-like domain, some pre-metazoan transmembrane proteins include several YxxP repeats in their cytosolic region, suggesting that they are remotely related to the BCAR1 substrate domain. Since the tyrosine kinase SRC also has a pre-metazoan origin, co-option of BCAR1-related sequences may have rewired the crka-dependent network to mediate adhesion signals in the metazoan ancestor.

Activation of tyrosine kinase c-Abl contributes to α-synuclein-induced neurodegeneration

Aggregation of α-synuclein contributes to the formation of Lewy bodies and neurites, the pathologic hallmarks of Parkinson disease (PD) and α-synucleinopathies. Although a number of human mutations have been identified in familial PD, the mechanisms that promote α-synuclein accumulation and toxicity are poorly understood. Here, we report that hyperactivity of the nonreceptor tyrosine kinase c-Abl critically regulates α-synuclein-induced neuropathology. In mice expressing a human α-synucleinopathy-associated mutation (hA53Tα-syn mice), deletion of the gene encoding c-Abl reduced α-synuclein aggregation, neuropathology, and neurobehavioral deficits. Conversely, overexpression of constitutively active c-Abl in hA53Tα-syn mice accelerated α-synuclein aggregation, neuropathology, and neurobehavioral deficits. Moreover, c-Abl activation led to an age-dependent increase in phosphotyrosine 39 α-synuclein. In human postmortem samples, there was an accumulation of phosphotyrosine 39 α-synuclein in brain tissues and Lewy bodies of PD patients compared with age-matched controls. Furthermore, in vitro studies show that c-Abl phosphorylation of α-synuclein at tyrosine 39 enhances α-synuclein aggregation. Taken together, this work establishes a critical role for c-Abl in α-synuclein-induced neurodegeneration and demonstrates that selective inhibition of c-Abl may be neuroprotective. This study further indicates that phosphotyrosine 39 α-synuclein is a potential disease indicator for PD and related α-synucleinopathies.

Abelson kinase acts as a robust, multifunctional scaffold in regulating embryonic morphogenesis

The importance of Abl kinase activity, the F-actin–binding site, and scaffolding ability in Abl’s many cell biological roles during Drosophila morphogenesis is examined. Abl is a robust multidomain scaffold with different protein motifs and activities contributing differentially to diverse cellular behaviors.

Abelson family kinases (Abls) are key regulators of cell behavior and the cytoskeleton during development and in leukemia. Abl’s SH3, SH2, and tyrosine kinase domains are joined via a linker to an F-actin–binding domain (FABD). Research on Abl’s roles in cell culture led to several hypotheses for its mechanism of action: 1) Abl phosphorylates other proteins, modulating their activity, 2) Abl directly regulates the cytoskeleton via its cytoskeletal interaction domains, and/or 3) Abl is a scaffold for a signaling complex. The importance of these roles during normal development remains untested. We tested these mechanistic hypotheses during Drosophila morphogenesis using a series of mutants to examine Abl’s many cell biological roles. Strikingly, Abl lacking the FABD fully rescued morphogenesis, cell shape change, actin regulation, and viability, whereas kinase-dead Abl, although reduced in function, retained substantial rescuing ability in some but not all Abl functions. We also tested the function of four conserved motifs in the linker region, revealing a key role for a conserved PXXP motif known to bind Crk and Abi. We propose that Abl acts as a robust multidomain scaffold with different protein motifs and activities contributing differentially to diverse cellular behaviors.

Neuritic complexity of hippocampal neurons depends on WIP-mediated mTORC1 and Abl family kinases activities

INTRODUCTION

Neuronal morphogenesis is governed mainly by two interconnected processes, cytoskeletal reorganization, and signal transduction. The actin-binding molecule WIP (Wiskott-Aldrich syndrome protein [WASP]-interacting protein) was identified as a negative regulator of neuritogenesis. Although WIP controls activity of the actin-nucleation-promoting factor neural WASP (N-WASP) during neuritic differentiation, its implication in signal transduction remains unknown.

METHODS

Using primary neurons from WIP-deficient and wild-type mice we did an immunofluorescence, morphometric, and biochemical analysis of the signaling modified by WIP deficiency.

RESULTS

Here, we describe the WIP contribution to the regulation of neuritic elaboration and ramification through modification in phosphorylation levels of several kinases that participate in the mammalian target of rapamycin complex 1 (mTORC1)-p70S6K (phosphoprotein 70 ribosomal protein S6 kinase, S6K) intracellular signaling pathway. WIP deficiency induces an increase in the number of neuritic bifurcations and filopodial protrusions in primary embryonic neurons. This phenotype is not due to modifications in the activity of the phosphoinositide 3 kinase (PI3K)-Akt pathway, but to reduced phosphorylation of the S6K residues Ser(411) and Thr(389). The resulting decrease in kinase activity leads to reduced S6 phosphorylation in the absence of WIP. Incubation of control neurons with pharmacological inhibitors of mTORC1 or Abl, two S6K regulators, conferred a morphology resembling that of WIP-deficient neurons. Moreover, the preferential co-distribution of phospho-S6K with polymerized actin is altered in WIP-deficient neurons.

CONCLUSION

These experiments identify WIP as a member of a signaling cascade comprised of Abl family kinases, mTORC1 and S6K, which regulates neuron development and specifically, neuritic branching and complexity. Thus, we postulated a new role for WIP protein.

The Emerging Role of ABL Kinases in Solid Tumors

The Abelson (ABL) tyrosine kinases were identified as drivers of leukemia in mice and humans. Emerging data has shown a role for the ABL family kinases, ABL1 and ABL2, in the progression of several solid tumors. This review will focus on recent reports of the involvement of the ABL kinases in tumor progression using mouse models as well as recent data generated from genomic and proteomic studies linking enhanced expression and hyper-activation of the ABL kinases to some human cancers. Preclinical studies on small molecule inhibitors of the ABL kinases suggest that their use may have beneficial effects for the treatment of selected solid tumors.

Chronic Noise Exposure Acts Cumulatively to Exacerbate Alzheimer's Disease-Like Amyloid-β Pathology and Neuroinflammation in the Rat Hippocampus

A putative etiological association exists between noise exposure and Alzheimer’s disease (AD). Amyloid-β (Aβ) pathology is thought to be one of the primary initiating factors in AD. It has been further suggested that subsequent dysregulation of Aβ may play a mechanistic role in the AD-like pathophysiology associated with noise exposure. Here, we used ELISA, immunoblotting, cytokine arrays, and RT-PCR, to examine both hippocampal Aβ pathology and neuroinflammation in rats at different time points after noise exposure. We found that chronic noise exposure significantly accelerated the progressive overproduction of Aβ, which persisted for 7 to 14 days after the cessation of exposure. This effect was accompanied by up-regulated expression of amyloid precursor protein (APP) and its cleavage enzymes, β- and γ-secretases. Cytokine analysis revealed that chronic noise exposure increased levels of tumor necrosis factor-α and the receptor for advanced glycation end products, while decreasing the expression of activin A and platelet-derived growth factor- AA. Furthermore, we found persistent elevations of glial fibrillary acidic protein and ionized calcium-binding adapter molecule 1 expression that closely corresponded to the noise-induced increases in Aβ and neuroinflammation. These studies suggest that lifelong environmental noise exposure may have cumulative effects on the onset and development of AD.

Cross-talk between androgen receptor/filamin A and TrkA regulates neurite outgrowth in PC12 cells

Steroids and growth factors control neuronal development through their receptors under physiological and pathological conditions. We show that PC12 cells harbor endogenous androgen receptor (AR), whose inhibition or silencing strongly interferes with neuritogenesis stimulated by the nonaromatizable synthetic androgen R1881 or NGF. This implies a role for AR not only in androgen signaling, but also in NGF signaling. In turn, a pharmacological TrkA inhibitor interferes with NGF- or androgen-induced neuritogenesis. In addition, androgen or NGF triggers AR association with TrkA, TrkA interaction with PI3-K δ, and downstream activation of PI3-K δ and Rac in PC12 cells. Once associated with AR, filamin A (FlnA) contributes to androgen or NGF neuritogenesis, likely through its interaction with signaling effectors, such as Rac. This study thus identifies a previously unrecognized reciprocal cross-talk between AR and TrkA, which is controlled by β1 integrin. The contribution of FlnA/AR complex and PI3-K δ to neuronal differentiation by androgens and NGF is also novel. This is the first description of AR function in PC12 cells.

Synaptic Cytoskeletal Plasticity in the Prefrontal Cortex Following Psychostimulant Exposure

Addiction is characterized by maladaptive decision-making, a loss of control over drug consumption and habit-like drug seeking despite adverse consequences. These cognitive changes may reflect the effects of drugs of abuse on prefrontal cortical neurobiology. Here, we review evidence that amphetamine and cocaine fundamentally remodel the structure of excitatory neurons in the prefrontal cortex. We summarize evidence in particular that these psychostimulants have opposing effects in the medial and orbital prefrontal cortices ('mPFC' and 'oPFC', respectively). For example, amphetamine and cocaine increase dendrite length and spine density in the mPFC, while dendrites are impoverished and dendritic spines are eliminated in the oPFC. We will discuss evidence that certain cytoskeletal regulatory proteins expressed in the oPFC and implicated in postnatal (adolescent) neural development also regulate behavioral sensitivity to cocaine. These findings potentially open a window of opportunity for the identification of novel pharmacotherapeutic targets in the treatment of drug abuse disorders in adults, as well as in drug-vulnerable adolescent populations. Finally, we will discuss the behavioral implications of drug-related dendritic spine elimination in the oPFC, with regard to reversal learning tasks and tasks that assess the development of reward-seeking habits, both used to model aspects of addiction in rodents.

Structure of the ABL2/ARG kinase in complex with dasatinib

ABL2/ARG (ABL-related gene) belongs to the ABL (Abelson tyrosine-protein kinase) family of tyrosine kinases. ARG plays important roles in cell morphogenesis, motility, growth and survival, and many of these biological roles overlap with the cellular functions of the ABL kinase. Chronic myeloid leukemia (CML) is associated with constitutive ABL kinase activation resulting from fusion between parts of the breakpoint cluster region (BCR) and ABL1 genes. Similarly, fusion of the ETV6 (Tel) and ARG genes drives some forms of T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). Dasatinib is a tyrosine kinase inhibitor used for the treatment of CML by inhibiting ABL, and while it also inhibits ARG, there is currently no structure of ARG in complex with dasatinib. Here, the co-crystal structure of the mouse ARG catalytic domain with dasatinib at 2.5 Å resolution is reported. Dasatinib-bound ARG is found in the DFG-in conformation although it is nonphosphorylated on the activation-loop tyrosine. In this structure the glycine-rich P-loop is found in a relatively open conformation compared with other known ABL family-inhibitor complex structures.

Targeting Abl kinases to regulate vascular leak during sepsis and acute respiratory distress syndrome

The vascular endothelium separates circulating fluid and inflammatory cells from the surrounding tissues. Vascular leak occurs in response to wide-spread inflammatory processes, such as sepsis and acute respiratory distress syndrome, because of the formation of gaps between endothelial cells. Although these disorders are leading causes of mortality in the intensive care unit, no medical therapies exist to restore endothelial cell barrier function. Recent evidence highlights a key role for the Abl family of nonreceptor tyrosine kinases in regulating vascular barrier integrity. These kinases have well-described roles in cancer progression and neuronal morphogenesis, but their functions in the vasculature have remained enigmatic until recently. The Abl family kinases, c-Abl (Abl1) and Abl related gene (Arg, Abl2), phosphorylate several cytoskeletal effectors that mediate vascular permeability, including nonmuscle myosin light chain kinase, cortactin, vinculin, and β-catenin. They also regulate cell-cell and cell-matrix junction dynamics, and the formation of actin-based cellular protrusions in multiple cell types. In addition, both c-Abl and Arg are activated by hyperoxia and contribute to oxidant-induced endothelial cell injury. These numerous roles of Abl kinases in endothelial cells and the current clinical usage of imatinib and other Abl kinase inhibitors have spurred recent interest in repurposing these drugs for the treatment of vascular barrier dysfunction. This review will describe the structure and function of Abl kinases with an emphasis on their roles in mediating vascular barrier integrity. We will also provide a critical evaluation of the potential for exploiting Abl kinase inhibition as a novel therapy for inflammatory vascular leak syndromes.

Direct interactions with the integrin β1 cytoplasmic tail activate the Abl2/Arg kinase

Integrins are heterodimeric α/β extracellular matrix adhesion receptors that couple physically to the actin cytoskeleton and regulate kinase signaling pathways to control cytoskeletal remodeling and adhesion complex formation and disassembly. β1 integrins signal through the Abl2/Arg (Abl-related gene) nonreceptor tyrosine kinase to control fibroblast cell motility, neuronal dendrite morphogenesis and stability, and cancer cell invasiveness, but the molecular mechanisms by which integrin β1 activates Arg are unknown. We report here that the Arg kinase domain interacts directly with a lysine-rich membrane-proximal segment in the integrin β1 cytoplasmic tail, that Arg phosphorylates the membrane-proximal Tyr-783 in the β1 tail, and that the Arg Src homology domain then engages this phosphorylated region in the tail. We show that these interactions mediate direct binding between integrin β1 and Arg in vitro and in cells and activate Arg kinase activity. These findings provide a model for understanding how β1-containing integrins interact with and activate Abl family kinases.

Abl2/Abl-related gene stabilizes actin filaments, stimulates actin branching by actin-related protein 2/3 complex, and promotes actin filament severing by cofilin

Both Arp2/3 complex and the Abl2/Arg nonreceptor tyrosine kinase are essential to form and maintain diverse actin-based structures in cells, including cell edge protrusions in fibroblasts and cancer cells and dendritic spines in neurons. The ability of Arg to promote cell edge protrusions in fibroblasts does not absolutely require kinase activity, raising the question of how Arg might modulate actin assembly and turnover in the absence of kinase function. Arg has two distinct actin-binding domains and interacts physically and functionally with cortactin, an activator of the Arp2/3 complex. However, it was not known whether and how Arg influences actin filament stability, actin branch formation, or cofilin-mediated actin severing or how cortactin influences these reactions of Arg with actin. Arg or cortactin bound to actin filaments stabilizes them from depolymerization. Low concentrations of Arg and cortactin cooperate to stabilize filaments by slowing depolymerization. Arg stimulates formation of actin filament branches by Arp2/3 complex and cortactin. An Arg mutant lacking the C-terminal calponin homology actin-binding domain stimulates actin branch formation by the Arp2/3 complex, indicative of autoinhibition. ArgΔCH can stimulate the Arp2/3 complex even in the absence of cortactin. Arg greatly potentiates cofilin severing of actin filaments, and cortactin attenuates this enhanced severing. The ability of Arg to stabilize filaments, promote branching, and increase severing requires the internal (I/L)WEQ actin-binding domain. These activities likely underlie important roles that Arg plays in the formation, dynamics, and stability of actin-based cellular structures.

Adolescent cocaine exposure simplifies orbitofrontal cortical dendritic arbors

Cocaine and amphetamine remodel dendritic spines within discrete cortico-limbic brain structures including the orbitofrontal cortex (oPFC). Whether dendrite structure is similarly affected, and whether pre-existing cellular characteristics influence behavioral vulnerabilities to drugs of abuse, remain unclear. Animal models provide an ideal venue to address these issues because neurobehavioral phenotypes can be defined both before, and following, drug exposure. We exposed mice to cocaine from postnatal days 31–35, corresponding to early adolescence, using a dosing protocol that causes impairments in an instrumental reversal task in adulthood. We then imaged and reconstructed excitatory neurons in deep-layer oPFC. Prior cocaine exposure shortened and simplified arbors, particularly in the basal region. Next, we imaged and reconstructed orbital neurons in a developmental-genetic model of cocaine vulnerability—the p190rhogap+/– mouse. p190RhoGAP is an actin cytoskeleton regulatory protein that stabilizes dendrites and dendritic spines, and p190rhogap+/– mice develop rapid and robust locomotor activation in response to cocaine. Despite this, oPFC dendritic arbors were intact in drug-naïve p190rhogap+/– mice. Together, these findings provide evidence that adolescent cocaine exposure has long-term effects on dendrite structure in the oPFC, and they suggest that cocaine-induced modifications in dendrite structure may contribute to the behavioral effects of cocaine more so than pre-existing structural abnormalities in this cell population.