Postsynaptic clustering and activation of Pyk2 by PSD-95

Molecularly imprinted nanoparticles reveal regulatory scaffolding features in Pyk2 tyrosine kinase

Pyk2 is a multi-domain non-receptor tyrosine kinase that serves dual roles as a signaling enzyme and scaffold. Pyk2 activation involves a multi-stage cascade of conformational rearrangements and protein interactions initiated by autophosphorylation of a linker site. Linker phosphorylation recruits Src kinase, and Src-mediated phosphorylation of the Pyk2 activation loop confers full activation. The regulation and accessibility of the initial Pyk2 autophosphorylation site remains unclear. We employed peptide-binding molecularly imprinted nanoparticles (MINPs) to probe the regulatory conformations controlling Pyk2 activation. MINPs differentiating local structure and phosphorylation state revealed that the Pyk2 autophosphorylation site is protected in the autoinhibited state. Activity profiling of Pyk2 variants implicated FERM and linker residues responsible for constraining the autophosphorylation site. MINPs targeting each Src docking site disrupt the higher-order kinase interactions critical for activation complex maturation. Ultimately, MINPs targeting key regulatory motifs establish a useful toolkit for probing successive activational stages in the higher-order Pyk2 signaling complex.

Hippocampal Pyk2 regulates specific social skills: Implications for schizophrenia

Pyk2 has been shown previously to be involved in several psychological and cognitive alterations related to stress, Huntington's disease, and Alzheimer's disease. All these disorders are accompanied by different types of impairments in sociability, which has recently been linked to improper mitochondrial function. We hypothesize that Pyk2, which regulates mitochondria, could be associated with the regulation of mitochondrial dynamics and social skills. In the present manuscript, we report that a reduction of Pyk2 levels in mouse pyramidal neurons of the hippocampus decreased social dominance and aggressivity. Furthermore, social interactions induced robust Pyk2-dependent hippocampal changes in several oxidative phosphorylation complexes. We also observed that Pyk2 levels were increased in the CA1 pyramidal neurons of schizophrenic subjects, occurring alongside changes in different direct and indirect regulators of mitochondrial function including DISC1 and Grp75. Accordingly, overexpressing Pyk2 in hippocampal CA1 pyramidal cells mimicked some specific schizophrenia-like social behaviors in mice. In summary, our results indicate that Pyk2 might play a role in regulating specific social skills likely via mitochondrial dynamics and that there might be a link between Pyk2 levels in hippocampal neurons and social disturbances in schizophrenia.

Melanocortin-3 receptor expression in AgRP neurons is required for normal activation of the neurons in response to energy deficiency

The melanocortin-3 receptor (MC3R) is a negative regulator of the central melanocortin circuitry via presynaptic expression on agouti-related protein (AgRP) nerve terminals, from where it regulates GABA release onto secondary MC4R-expressing neurons. However, MC3R knockout (KO) mice also exhibit defective behavioral and neuroendocrine responses to fasting. Here, we demonstrate that MC3R KO mice exhibit defective activation of AgRP neurons in response to fasting, cold exposure, or ghrelin while exhibiting normal inhibition of AgRP neurons by sensory detection of food in the ad libitum-fed state. Using a conditional MC3R KO model, we show that the control of AgRP neuron activation by fasting and ghrelin requires the specific presence of MC3R within AgRP neurons. Thus, MC3R is a crucial player in the responsiveness of the AgRP soma to both hormonal and neuronal signals of energy need.

Activation loop phosphorylation tunes conformational dynamics underlying Pyk2 tyrosine kinase activation

Pyk2 is a multidomain non-receptor tyrosine kinase that undergoes a multistage activation mechanism. Activation is instigated by conformational rearrangements relieving autoinhibitory FERM domain interactions. The kinase autophosphorylates a central linker residue to recruit Src kinase. Pyk2 and Src mutually phosphorylate activation loops to confer full activation. While the mechanisms of autoinhibition are established, the conformational dynamics associated with autophosphorylation and Src recruitment remain unclear. We employ hydrogen/deuterium exchange mass spectrometry and kinase activity profiling to map the conformational dynamics associated with substrate binding and Src-mediated activation loop phosphorylation. Nucleotide engagement stabilizes the autoinhibitory interface, while phosphorylation deprotects both FERM and kinase regulatory surfaces. Phosphorylation organizes active site motifs linking catalytic loop with activation segment. Dynamics of the activation segment anchor propagate to EF/G helices to prevent reversion of the autoinhibitory FERM interaction. We employ targeted mutagenesis to dissect how phosphorylation-induced conformational rearrangements elevate kinase activity above the basal autophosphorylation rate.

Microglia PTK2B/Pyk2 in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a highly hereditary disease with complex genetic susceptibility factors. Extensive genome-wide association studies have established a distinct susceptibility link between the protein tyrosine kinase 2β (PTK2B) gene and late-onset Alzheimer's disease (LOAD), but the specific pathogenic mechanisms remain incompletely understood. PTK2B is known to be expressed in neurons, and recent research has revealed its more important significance in microglia. Elucidating the role of PTK2B high expression in microglia in AD's progression is crucial for uncovering novel pathogenic mechanisms of the disease. Our review of existing studies suggests a close relationship between PTK2B/proline-rich tyrosine kinase 2 (Pyk2) and tau pathology, and this process might be β-amyloid (Aβ) dependence. Pyk2 is hypothesized as a pivotal target linking Aβ and tau pathologies. Concurrently, Aβ-activated Pyk2 participates in the regulation of microglial activation and its proinflammatory functions. Consequently, it is reasonable to presume that Pyk2 in microglia contributes to amyloid-induced tau pathology in AD via a neuroinflammatory pathway. Furthermore, many things remain unclear, such as identifying the specific pathways that lead to the release of downstream inflammatory factors due to Pyk2 phosphorylation and whether all types of inflammatory factors can activate neuronal kinase pathways. Additionally, further in vivo experiments are essential to validate this hypothesized pathway. Considering PTK2B/Pyk2's potential role in AD pathogenesis, targeting this pathway may offer innovative and promising therapeutic approaches for AD.

Role of proline-rich tyrosine kinase 2 (Pyk2) in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is the most common form of dementia in the elderly. Two major pathological hallmarks have been identified for AD: extracellular amyloid plaques and intracellular neurofibrillary tangles (NFT). Recently, proline-rich tyrosine kinase 2 (Pyk2), which belongs to the focal adhesion kinase (FAK) non-receptor tyrosine kinase family, was recognized to contribute significantly towards the pathogenesis of AD. Pyk2 can influence the formation of amyloid plaques as well as NFTs. The kinase can directly phosphorylate tau, which is a significant component of NFTs and enhances tau pathology. Several competitive inhibitors have been developed for Pyk2, tested in several cancer models, as Pyk2 is known to be overexpressed under those conditions. The current review article discusses the possible mechanistic pathways by which Pyk2 can influence the pathogenesis of AD. Besides, it describes various inhibitors for Pyk2 and their potential role as therapeutics for AD in the future.

PYK2 senses calcium through a disordered dimerization and calmodulin-binding element

Multidomain kinases use many ways to integrate and process diverse stimuli. Here, we investigated the mechanism by which the protein tyrosine kinase 2-beta (PYK2) functions as a sensor and effector of cellular calcium influx. We show that the linker between the PYK2 kinase and FAT domains (KFL) encompasses an unusual calmodulin (CaM) binding element. PYK2 KFL is disordered and engages CaM through an ensemble of transient binding events. Calcium increases the association by promoting structural changes in CaM that expose auxiliary interaction opportunities. KFL also forms fuzzy dimers, and dimerization is enhanced by CaM binding. As a monomer, however, KFL associates with the PYK2 FERM-kinase fragment. Thus, we identify a mechanism whereby calcium influx can promote PYK2 self-association, and hence kinase-activating trans-autophosphorylation. Collectively, our findings describe a flexible protein module that expands the paradigms for CaM binding and self-association, and their use for controlling kinase activity.

Protein tyrosine kinase 2-beta is shown to function as a sensor and effector of cellular calcium influx through self-association.

Pyk2 Regulates MAMs and Mitochondrial Dynamics in Hippocampal Neurons

Pyk2 is a non-receptor tyrosine kinase enriched in hippocampal neurons, which can be activated by calcium-dependent mechanisms. In neurons, Pyk2 is mostly localised in the cytosol and dendritic shafts but can translocate to spines and/or to the nucleus. Here, we explore the function of a new localisation of Pyk2 in mitochondria-associated membranes (MAMs), a subdomain of ER-mitochondria surface that acts as a signalling hub in calcium regulation. To test the role of Pyk2 in MAMs’ calcium transport, we used full Pyk2 knockout mice (Pyk2^−/−) for in vivo and in vitro studies. Here we report that Pyk2^−/− hippocampal neurons present increased ER-mitochondrial contacts along with defective calcium homeostasis. We also show how the absence of Pyk2 modulates mitochondrial dynamics and morphology. Taken all together, our results point out that Pyk2 could be highly relevant in the modulation of ER-mitochondria calcium efflux, affecting in turn mitochondrial function.

Oligomeric Aβ25-35 induces the tyrosine phosphorylation of PSD-95 by SrcPTKs in rat hippocampal CA1 subfield

PURPOSE

Although amyloid-β (Aβ) is one of the neuropathological hallmarks of Alzheimer's Disease (AD), the mechanisms of Aβ neurotoxicity remain to be clarified. This study was aimed to evaluate the effect of Aβ on postsynaptic density-95 (PSD-95) tyrosine phosphorylation. Elucidating the regulatory mechanisms underlying it may be a promising therapy in AD.

METHODS

Aβ25-35 oligomers (20 μg/rat) were administered intracerebroventricularly in adult male Sprague-Dawley rats. PSD-95 tyrosine phosphorylation was assessed using immunoprecipitation followed by immunoblot analysis. Immunoblot was applied for measuring the protein levels of PSD-95 and β-actin.

RESULTS

Following 3, 7, 14, 21 days after oligomeric Aβ25-35 treatment, the tyrosine phosphorylation of PSD-95 increased significantly, and peaked at 3 days after oligomeric Aβ25-35 treatment in hippocampal CA1 subfield. Src family protein tyrosine kinases (SrcPTKs) specific inhibitor PP2 attenuated the tyrosine phosphorylation of PSD-95 induced by Aβ25-35. Amantadine [N-methyl-D-aspartate (NMDA) receptor noncompetitive antagonist], NVP-AAM077 (GluN2A-containing NMDA receptor selective inhibitor) and Ro25-6981 (GluN2B-containing NMDA receptor selective inhibitor) also suppressed the Aβ25-35-induced PSD-95 tyrosine phosphorylation.

CONCLUSION

These results suggest that Aβ oligomers induce the tyrosine phosphorylation of PSD-95 by SrcPTKs, which is mediated by the activation of GluN2A- and GluN2B-containing NMDA receptors.

The Non-receptor Tyrosine Kinase Pyk2 in Brain Function and Neurological and Psychiatric Diseases

Pyk2 is a non-receptor tyrosine kinase highly enriched in forebrain neurons. Pyk2 is closely related to focal adhesion kinase (FAK), which plays an important role in sensing cell contacts with extracellular matrix and other extracellular signals controlling adhesion and survival. Pyk2 shares some of FAK’s characteristics including recruitment of Src-family kinases after autophosphorylation, scaffolding by interacting with multiple partners, and activation of downstream signaling pathways. Pyk2, however, has the unique property to respond to increases in intracellular free Ca²⁺, which triggers its autophosphorylation following stimulation of various receptors including glutamate NMDA receptors. Pyk2 is dephosphorylated by the striatal-enriched phosphatase (STEP) that is highly expressed in the same neuronal populations. Pyk2 localization in neurons is dynamic, and altered following stimulation, with post-synaptic and nuclear enrichment. As a signaling protein Pyk2 is involved in multiple pathways resulting in sometimes opposing functions depending on experimental models. Thus Pyk2 has a dual role on neurites and dendritic spines. With Src family kinases Pyk2 participates in postsynaptic regulations including of NMDA receptors and is necessary for specific types of synaptic plasticity and spatial memory tasks. The diverse functions of Pyk2 are also illustrated by its role in pathology. Pyk2 is activated following epileptic seizures or ischemia-reperfusion and may contribute to the consequences of these insults whereas Pyk2 deficit may contribute to the hippocampal phenotype of Huntington’s disease. Pyk2 gene, PTK2B, is associated with the risk for late-onset Alzheimer’s disease. Studies of underlying mechanisms indicate a complex contribution with involvement in amyloid toxicity and tauopathy, combined with possible functional deficits in neurons and contribution in microglia. A role of Pyk2 has also been proposed in stress-induced depression and cocaine addiction. Pyk2 is also important for the mobility of astrocytes and glioblastoma cells. The implication of Pyk2 in various pathological conditions supports its potential interest for therapeutic interventions. This is possible through molecules inhibiting its activity or increasing it through inhibition of STEP or other means, depending on a precise evaluation of the balance between positive and negative consequences of Pyk2 actions.

Pyk2 suppresses contextual fear memory in an autophosphorylation-independent manner

Clustered protocadherins (Pcdhs) are a large family of cadherin-like cell adhesion proteins that are central for neurite self-avoidance and neuronal connectivity in the brain. Their downstream non-receptor tyrosine kinase Pyk2 (proline-rich tyrosine kinase 2, also known as Ptk2b, Cakb, Raftk, Fak2, and Cadtk) is predominantly expressed in the hippocampus. We constructed Pyk2 null mouse lines and found that these mutant mice showed enhancement in contextual fear memory, without any change in auditory-cued and spatial-referenced learning and memory. In addition, by preparing Y402F mutant mice, we observed that Pyk2 suppressed contextual fear memory in an autophosphorylation-independent manner. Moreover, using high-throughput RNA sequencing, we found that immediate early genes, such as Npas4, cFos, Zif268/Egr1, Arc, and Nr4a1, were enhanced in Pyk2 null mice. We further showed that Pyk2 disruption affected pyramidal neuronal complexity and spine dynamics. Thus, we demonstrated that Pyk2 is a novel fear memory suppressor molecule and Pyk2 null mice provide a model for understanding fear-related disorders. These findings have interesting implications regarding dysregulation of the Pcdh‒Pyk2 axis in neuropsychiatric disorders.

Noncanonical Metabotropic Glutamate Receptor 5 Signaling in Alzheimer's Disease

Metabotropic glutamate receptor 5 (mGluR5) is ubiquitously expressed in brain regions responsible for memory and learning. It plays a key role in modulating rapid changes in synaptic transmission and plasticity. mGluR5 supports long-term changes in synaptic strength by regulating the transcription and translation of essential synaptic proteins. β-Amyloid 42 (Aβ42) oligomers interact with a mGluR5/cellular prion protein (PrP^C) complex to disrupt physiological mGluR5 signal transduction. Aberrant mGluR5 signaling and associated synaptic failure are considered an emerging pathophysiological mechanism of Alzheimer's disease (AD). Therefore, mGluR5 represents an attractive therapeutic target for AD, and recent studies continue to validate the efficacy of various mGluR5 allosteric modulators in improving memory deficits and mitigating disease pathology. However, sex-specific differences in the pharmacology of mGluR5 and activation of noncanonical signaling downstream of the receptor suggest that its utility as a therapeutic target in female AD patients needs to be reconsidered. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Synaptic tau: A pathological or physiological phenomenon?

In this review, we discuss the synaptic aspects of Tau pathology occurring during Alzheimer's disease (AD) and how this may relate to memory impairment, a major hallmark of AD. Whilst the clinical diagnosis of AD patients is a loss of working memory and long-term declarative memory, the histological diagnosis is the presence of neurofibrillary tangles of hyperphosphorylated Tau and Amyloid-beta plaques. Tau pathology spreads through synaptically connected neurons to impair synaptic function preceding the formation of neurofibrillary tangles, synaptic loss, axonal retraction and cell death. Alongside synaptic pathology, recent data suggest that Tau has physiological roles in the pre- or post- synaptic compartments. Thus, we have seen a shift in the research focus from Tau as a microtubule-stabilising protein in axons, to Tau as a synaptic protein with roles in accelerating spine formation, dendritic elongation, and in synaptic plasticity coordinating memory pathways. We collate here the myriad of emerging interactions and physiological roles of synaptic Tau, and discuss the current evidence that synaptic Tau contributes to pathology in AD.

Pyk2 in dorsal hippocampus plays a selective role in spatial memory and synaptic plasticity

Pyk2 is a Ca²⁺-activated non-receptor tyrosine kinase enriched in the forebrain, especially in pyramidal neurons of the hippocampus. Previous reports suggested its role in hippocampal synaptic plasticity and spatial memory but with contradictory findings possibly due to experimental conditions. Here we address this issue and show that novel object location, a simple test of spatial memory induced by a single training session, is altered in Pyk2 KO mice and that re-expression of Pyk2 in the dorsal hippocampus corrects this deficit. Bilateral targeted deletion of Pyk2 in dorsal hippocampus CA1 region also alters novel object location. Long term potentiation (LTP) in CA1 is impaired in Pyk2 KO mice using a high frequency stimulation induction protocol but not with a theta burst protocol, explaining differences between previous reports. The same selective LTP alteration is observed in mice with Pyk2 deletion in dorsal hippocampus CA1 region. Thus, our results establish the role of Pyk2 in specific aspects of spatial memory and synaptic plasticity and show the dependence of the phenotype on the type of experiments used to reveal it. In combination with other studies, we provide evidence for a selective role of non-receptor tyrosine kinases in specific aspects of hippocampal neurons synaptic plasticity.

Impaired inhibitory GABAergic synaptic transmission and transcription studied in single neurons by Patch-seq in Huntington's disease

Transcriptional dysregulation in Huntington's disease (HD) causes functional deficits in striatal neurons. Here, we performed Patch-sequencing (Patch-seq) in an in vitro HD model to investigate the effects of mutant Huntingtin (Htt) on synaptic transmission and gene transcription in single striatal neurons. We found that expression of mutant Htt decreased the synaptic output of striatal neurons in a cell autonomous fashion and identified a number of genes whose dysregulation was correlated with physiological deficiencies in mutant Htt neurons. In support of a pivotal role for epigenetic mechanisms in HD pathophysiology, we found that inhibiting histone deacetylase 1/3 activities rectified several functional and morphological deficits and alleviated the aberrant transcriptional profiles in mutant Htt neurons. With this study, we demonstrate that Patch-seq technology can be applied both to better understand molecular mechanisms underlying a complex neurological disease at the single-cell level and to provide a platform for screening for therapeutics for the disease.

Pyk2 overexpression in postsynaptic neurons blocks amyloid β1-42-induced synaptotoxicity in microfluidic co-cultures

Recent meta-analyses of genome-wide association studies identified a number of genetic risk factors of Alzheimer's disease; however, little is known about the mechanisms by which they contribute to the pathological process. As synapse loss is observed at the earliest stage of Alzheimer's disease, deciphering the impact of Alzheimer's risk genes on synapse formation and maintenance is of great interest. In this article, we report a microfluidic co-culture device that physically isolates synapses from pre- and postsynaptic neurons and chronically exposes them to toxic amyloid β peptides secreted by model cell lines overexpressing wild-type or mutated (V717I) amyloid precursor protein. Co-culture with cells overexpressing mutated amyloid precursor protein exposed the synapses of primary hippocampal neurons to amyloid β_1-42 molecules at nanomolar concentrations and induced a significant decrease in synaptic connectivity, as evidenced by distance-based assignment of postsynaptic puncta to presynaptic puncta. Treating the cells with antibodies that target different forms of amyloid β suggested that low molecular weight oligomers are the likely culprit. As proof of concept, we demonstrate that overexpression of protein tyrosine kinase 2 beta-an Alzheimer's disease genetic risk factor involved in synaptic plasticity and shown to decrease in Alzheimer's disease brains at gene expression and protein levels-selectively in postsynaptic neurons is protective against amyloid β_1-42-induced synaptotoxicity. In summary, our lab-on-a-chip device provides a physiologically relevant model of Alzheimer's disease-related synaptotoxicity, optimal for assessing the impact of risk genes in pre- and postsynaptic compartments.

Systemic Mesenchymal Stem Cell Treatment Mitigates Structural and Functional Retinal Ganglion Cell Degeneration in a Mouse Model of Multiple Sclerosis

Purpose

The purpose of this study was to determine mesenchymal stem cell (MSC) therapy efficacy on rescuing the visual system in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS) and to provide new mechanistic insights.

Methods

EAE was induced in female C57BL6 mice by immunization with myelin oligodendrocyte glycoprotein (MOG)_35–55, complete Freund's adjuvant, and pertussis toxin. The findings were compared to sham-immunized mice. Half of the EAE mice received intraperitoneally delivered stem cells (EAE + MSC). Clinical progression was monitored according to a five-point EAE scoring scheme. Pattern electroretinogram (PERG) and retinal nerve fiber layer (RNFL) thickness were measured 32 days after induction. Retinas were harvested to determine retinal ganglion cell (RGC) density and prepared for RNA-sequencing.

Results

EAE animals that received MSC treatment seven days after EAE induction showed significantly lower motor-sensory impairment, improvement in the PERG amplitude, and preserved RNFL. Analysis of RNA-sequencing data demonstrated statistically significant differences in gene expression in the retina of MSC-treated EAE mice. Differentially expressed genes were enriched for pathways involved in endoplasmic reticulum stress, endothelial cell differentiation, HIF-1 signaling, and cholesterol transport in the MSC-treated EAE group.

Conclusions

Systemic MSC treatment positively affects RGC function and survival in EAE mice. Better cholesterol handling by increased expression of Abca1, the cholesterol efflux regulatory protein, paired with the resolution of HIF-1 signaling activation might explain the improvements seen in PERG of EAE animals after MSC treatment.

Translational Relevance

Using MSC therapy in a mouse model of MS, we discovered previously unappreciated biochemical pathways associated with RGC neuroprotection, which have the potential to be pharmacologically targeted as a new treatment regimen.

The non-receptor tyrosine kinase Pyk2 modulates acute locomotor effects of cocaine in D1 receptor-expressing neurons of the nucleus accumbens

The striatum is critical for cocaine-induced locomotor responses. Although the role of D1 receptor-expressing neurons is established, underlying molecular pathways are not fully understood. We studied the role of Pyk2, a non-receptor, calcium-dependent protein-tyrosine kinase. The locomotor coordination and basal activity of Pyk2 knock-out mice were not altered and major striatal protein markers were normal. Cocaine injection increased Pyk2 tyrosine phosphorylation in mouse striatum. Pyk2-deficient mice displayed decreased locomotor response to acute cocaine injection. In contrast, locomotor sensitization and conditioned place preference were normal. Cocaine-activated ERK phosphorylation, a signaling pathway essential for these late responses, was unaltered. Conditional deletion of Pyk2 in the nucleus accumbens or in D1 neurons reproduced decreased locomotor response to cocaine, whereas deletion of Pyk2 in the dorsal striatum or in A2A receptor-expressing neurons did not. In mice lacking Pyk2 in D1-neurons locomotor response to D1 agonist SKF-81297, but not to an anticholinergic drug, was blunted. Our results identify Pyk2 as a regulator of acute locomotor responses to psychostimulants. They highlight the role of tyrosine phosphorylation pathways in striatal neurons and suggest that changes in Pyk2 expression or activation may alter specific responses to drugs of abuse, or possibly other behavioral responses linked to dopamine action.

Mevastatin-Induced AP-1-Dependent HO-1 Expression Suppresses Vascular Cell Adhesion Molecule-1 Expression and Monocyte Adhesion on Human Pulmonary Alveolar Epithelial Cells Challenged with TNF-α

Mevastatin (MVS) has been previously shown to induce heme oxygenase (HO)-1 expression through Nox/ROS-dependent PDGFRα/PI3K/Akt/Nrf2/ARE axis in human pulmonary alveolar epithelial cells (HPAEpiCs). However, alternative signaling pathways might involve in MVS-induced HO-1 expression. We found that tumor necrosis factor α (TNFα) induced vascular cell adhesion protein 1 (VCAM-1) expression and NF-κB p65 phosphorylation which were attenuated by pretreatment with MVS via up-regulation of HO-1, determined by Western blot and real-time qPCR. TNFα-induced VCAM-1 expression was attenuated by an NF-κB inhibitor, Bay117082. The inhibitory effects of MVS were reversed by tin protoporphyrin (SnPP)IX (an inhibitor of HO-1 activity). In addition, pretreatment with the inhibitor of pan-Protein kinase C (PKC) (GF109203X), PKCα (Gö6983), Pyk2 (PF431396), p38α MAPK (SB202190), JNK1/2 (SP600125), or AP-1 (Tanshinone IIA), and transfection with their respective siRNAs abolished MVS-induced HO-1 expression in HPAEpiCs. c-Jun (one of AP-1 subunits) was activated by PKCα, Pyk2, p38α MAPK, and JNK1/2, which turned on the transcription of the homx1 gene. The interaction between c-Jun and HO-1 promoter was confirmed by a chromatin immunoprecipitation (ChIP) assay, which was attenuated by these pharmacological inhibitors. These results suggested that MVS induces AP-1/HO-1 expression via PKCα/Pyk2/p38α MAPK- or JNK1/2-dependent c-Jun activation, which further binds with AP-1-binding site on HO-1 promoter and suppresses the TNFα-mediated inflammatory responses in HPAEpiCs. Thus, upregulation of the AP-1/HO-1 system by MVS exerts a potentially therapeutic strategy to protect against pulmonary inflammation.

Pyk2 is a Novel Tau Tyrosine Kinase that is Regulated by the Tyrosine Kinase Fyn

The protein tyrosine kinase Pyk2 is encoded by PTK2B, a novel Alzheimer’s disease (AD) susceptibility variant, with the PTK2B risk allele being associated with increased mRNA levels, suggestive of increased Pyk2 levels. However, the role of Pyk2, a member of the focal adhesion kinase (FAK) family, in AD pathology and its regulation are largely unknown. To address this, we generated mice with neuronal expression of human Pyk2. Because we had previously reported an association of Pyk2 and hyperphosphorylated tau (a hallmark feature of AD) in human tau transgenic pR5 mice, we also generated Pyk2/tau double-transgenic mice, which exhibit increased tyrosine phosphorylation and accumulation of tau. We further demonstrated that Pyk2 colocalizes, interacts with, and phosphorylates tau in vivo and in vitro. Importantly, although Pyk2 interacts with the established tyrosine-directed tau kinase Fyn, we identified an increased Pyk2 activity in mice which constitutively overexpress Fyn (FynCA), and a decreased activity in mice lacking Fyn (FynKO). Together, our study reveals a novel role for Pyk2 as a direct tyrosine kinase of tau that is active downstream of Fyn. Our analysis may enhance the understanding of how the PTK2B risk allele contributes to tauopathy.

BDNF increases synaptic NMDA receptor abundance by enhancing the local translation of Pyk2 in cultured hippocampal neurons

The effects of brain-derived neurotrophic factor (BDNF) in long-term synaptic potentiation (LTP) are thought to underlie learning and memory formation and are partly mediated by local protein synthesis. Here, we investigated the mechanisms that mediate BDNF-induced alterations in the synaptic proteome that are coupled to synaptic strengthening. BDNF induced the synaptic accumulation of GluN2B-containing NMDA receptors (NMDARs) and increased the amplitude of NMDAR-mediated miniature excitatory postsynaptic currents (mEPSCs) in cultured rat hippocampal neurons by a mechanism requiring activation of the protein tyrosine kinase Pyk2 and dependent on cellular protein synthesis. Single-particle tracking using quantum dot imaging revealed that the increase in the abundance of synaptic NMDAR currents correlated with their enhanced stability in the synaptic compartment. Furthermore, BDNF increased the local synthesis of Pyk2 at the synapse, and the observed increase in Pyk2 protein abundance along dendrites of cultured hippocampal neurons was mediated by a mechanism dependent on the ribonucleoprotein hnRNP K, which bound to Pyk2 mRNA and dissociated from it upon BDNF application. Knocking down hnRNP K reduced the BDNF-induced synaptic synthesis of Pyk2 protein, whereas its overexpression enhanced it. Together, these findings indicate that hnRNP K mediates the synaptic distribution of Pyk2 synthesis, and hence the synaptic incorporation of GluN2B-containing NMDARs, induced by BDNF, which may affect LTP and synaptic plasticity.

The Amyloid-β Oligomer Hypothesis: Beginning of the Third Decade

The amyloid-β oligomer (AβO) hypothesis was introduced in 1998. It proposed that the brain damage leading to Alzheimer’s disease (AD) was instigated by soluble, ligand-like AβOs. This hypothesis was based on the discovery that fibril-free synthetic preparations of AβOs were potent CNS neurotoxins that rapidly inhibited long-term potentiation and, with time, caused selective nerve cell death (Lambert et al., 1998). The mechanism was attributed to disrupted signaling involving the tyrosine-protein kinase Fyn, mediated by an unknown toxin receptor. Over 4,000 articles concerning AβOs have been published since then, including more than 400 reviews. AβOs have been shown to accumulate in an AD-dependent manner in human and animal model brain tissue and, experimentally, to impair learning and memory and instigate major facets of AD neuropathology, including tau pathology, synapse deterioration and loss, inflammation, and oxidative damage. As reviewed by Hayden and Teplow in 2013, the AβO hypothesis “has all but supplanted the amyloid cascade.” Despite the emerging understanding of the role played by AβOs in AD pathogenesis, AβOs have not yet received the clinical attention given to amyloid plaques, which have been at the core of major attempts at therapeutics and diagnostics but are no longer regarded as the most pathogenic form of Aβ. However, if the momentum of AβO research continues, particularly efforts to elucidate key aspects of structure, a clear path to a successful disease modifying therapy can be envisioned. Ensuring that lessons learned from recent, late-stage clinical failures are applied appropriately throughout therapeutic development will further enable the likelihood of a successful therapy in the near-term.

Pyk2 in the amygdala modulates chronic stress sequelae via PSD-95-related micro-structural changes

Major depressive disorder (MDD) is a common disorder with a variety of symptoms including mood alterations, anhedonia, sleep and appetite disorders, and cognitive disturbances. Stressful life events are among the strongest risk factors for developing MDD. At the cellular level, chronic stress results in the modification of dendritic spine morphology and density. Here, we study the role of Pyk2 in the development of depressive-like symptoms induced by a model of chronic unpredictable mild stress (CUMS). Pyk2 is a non-receptor calcium-dependent protein-tyrosine kinase highly expressed in the forebrain principal neurons and involved in spine structure and density regulation. We show that Pyk2 knockout mice are less affected to anxiety-like and anhedonia-like phenotypes induced by the CUMS paradigm. Using region-specific knockout, we demonstrate that this phenotype is fully recapitulated by selective Pyk2 inactivation in the amygdala. We also show that in the absence of Pyk2 the spine alterations, PSD-95 clustering, and NMDA receptors changes induced by the CUMS paradigm are prevented. Our results reveal a possible role for Pyk2 in the response to stress and in synaptic markers expression and spine density regulation in the amygdala. We suggest that Pyk2 contributes to stress-induced responses through micro-structural changes and that its deficit may contribute to the resilience to chronic stress.

Pyk2 Signaling through Graf1 and RhoA GTPase Is Required for Amyloid-β Oligomer-Triggered Synapse Loss

The intracellular tyrosine kinase Pyk2 (PTK2B) is related to focal adhesion kinase and localizes to postsynaptic sites in brain. Pyk2 genetic variation contributes to late onset Alzheimer's disease (AD) risk. We recently observed that Pyk2 is required for synapse loss and for learning deficits in a transgenic mouse model of AD. Here, we explore the cellular and biochemical basis for the action of Pyk2 tyrosine kinase in amyloid-β oligomer (Aβo)-induced dendritic spine loss. Overexpression of Pyk2 reduces dendritic spine density of hippocampal neurons by a kinase-dependent mechanism. Biochemical isolation of Pyk2-interacting proteins from brain identifies Graf1c, a RhoA GTPase-activating protein inhibited by Pyk2. Aβo-induced reductions in dendritic spine motility and chronic spine loss require both Pyk2 kinase and RhoA activation. Thus, Pyk2 functions at postsynaptic sites to modulate F-actin control by RhoA and regulate synapse maintenance of relevance to AD risk.SIGNIFICANCE STATEMENT Genetic variation at the Pyk2 locus is a risk for Alzheimer's disease. We have observed that Pyk2 is required for AD transgenic synapse loss and memory dysfunction. However, the cellular and biochemical basis for Pyk2 function related to AD is not defined. Here, we show that brain Pyk2 interacts with the RhoGAP protein Graf1 to alter dendritic spine stability via RhoA GTPase. Amyloid-β oligomer-induced dendritic spine loss requires the Pyk2/Graf1 pathway.

Alzheimer's Disease Risk Factor Pyk2 Mediates Amyloid-β-Induced Synaptic Dysfunction and Loss

Dozens of genes have been implicated in late onset Alzheimer's disease (AD) risk, but none has a defined mechanism of action in neurons. Here, we show that the risk factor Pyk2 (PTK2B) localizes specifically to neurons in adult brain. Absence of Pyk2 has no major effect on synapse formation or the basal parameters of synaptic transmission in the hippocampal Schaffer collateral pathway. However, the induction of synaptic LTD is suppressed in Pyk2-null slices. In contrast, deletion of Pyk2 expression does not alter LTP under control conditions. Of relevance for AD pathophysiology, Pyk2^-/- slices are protected from amyloid-β-oligomer (Aβo)-induced suppression of LTP in hippocampal slices. Acutely, a Pyk2 kinase inhibitor also prevents Aβo-induced suppression of LTP in WT slices. Female and male transgenic AD model mice expressing APPswe/PSEN1ΔE9 require Pyk2 for age-dependent loss of synaptic markers and for impairment of learning and memory. However, absence of Pyk2 does not alter Aβ accumulation or gliosis. Therefore, the Pyk2 risk gene is directly implicated in a neuronal Aβo signaling pathway impairing synaptic anatomy and function.SIGNIFICANCE STATEMENT Genetic variation at the Pyk2 (PTK2B) locus is a risk for late onset Alzheimer's disease (AD), but the pathophysiological role of Pyk2 is not clear. Here, we studied Pyk2 neuronal function in mice lacking expression with and without transgenes generating amyloid-β (Aβ) plaque pathology. Pyk2 is not required for basal synaptic transmission or LTP, but participates in LTD. Hippocampal slices lacking Pyk2 are protected from AD-related Aβ oligomer suppression of synaptic plasticity. In transgenic AD model mice, deletion of Pyk2 rescues synaptic loss and learning/memory deficits. Therefore, Pyk2 plays a central role in AD-related synaptic dysfunction mediating Aβ-triggered dysfunction.

Postsynaptic localization and regulation of AMPA receptors and Cav1.2 by β2 adrenergic receptor/PKA and Ca2+/CaMKII signaling

The synapse transmits, processes, and stores data within its tiny space. Effective and specific signaling requires precise alignment of the relevant components. This review examines current insights into mechanisms of AMPAR and NMDAR localization by PSD-95 and their spatial distribution at postsynaptic sites to illuminate the structural and functional framework of postsynaptic signaling. It subsequently delineates how β2 adrenergic receptor (β2 AR) signaling via adenylyl cyclase and the cAMP-dependent protein kinase PKA is organized within nanodomains. Here, we discuss targeting of β2 AR, adenylyl cyclase, and PKA to defined signaling complexes at postsynaptic sites, i.e., AMPARs and the L-type Ca2+ channel Cav1.2, and other subcellular surface localizations, the role of A kinase anchor proteins, the physiological relevance of the spatial restriction of corresponding signaling, and their interplay with signal transduction by the Ca2+- and calmodulin-dependent kinase CaMKII How localized and specific signaling by cAMP occurs is a central cellular question. The dendritic spine constitutes an ideal paradigm for elucidating the dimensions of spatially restricted signaling because of their small size and defined protein composition.

Commentary on Giralt et al.: PTK2B/Pyk2 overexpression improves a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is the most common cause of dementia and the 6th leading cause of death. Although research has revealed significant information about AD, much is yet to be discovered about the precise biological changes that cause AD and how the disease could be prevented, slowed, or stopped. Accumulating evidence suggests the involvement of the non-receptor proline-rich tyrosine kinase 2 (Pyk2) in AD, but the downstream signaling events triggered by this protein and their implications on the pathology of the disease were unclear until recently. A recent paper by Giralt et al. used genetically depleted and overexpression mouse models to elucidate the role of Pyk2 in AD. Here, we discuss the findings presented in this paper in light of previous information and hypotheses, and suggest interpretations and explanations for this surprising and unexpected phenotype.

Endogenous Control Mechanisms of FAK and PYK2 and Their Relevance to Cancer Development

Focal adhesion kinase (FAK) and its close paralogue, proline-rich tyrosine kinase 2 (PYK2), are key regulators of aggressive spreading and metastasis of cancer cells. While targeted small-molecule inhibitors of FAK and PYK2 have been found to have promising antitumor activity, their clinical long-term efficacy may be undermined by the strong capacity of cancer cells to evade anti-kinase drugs. In healthy cells, the expression and/or function of FAK and PYK2 is tightly controlled via modulation of gene expression, competing alternatively spliced forms, non-coding RNAs, and proteins that directly or indirectly affect kinase activation or protein stability. The molecular factors involved in this control are frequently deregulated in cancer cells. Here, we review the endogenous mechanisms controlling FAK and PYK2, and with particular focus on how these mechanisms could inspire or improve anticancer therapies.

PTK2B/Pyk2 overexpression improves a mouse model of Alzheimer's disease

Pyk2 is a Ca²⁺-activated non-receptor tyrosine kinase enriched in forebrain neurons and involved in synaptic regulation. Human genetic studies associated PTK2B, the gene coding Pyk2, with risk for Alzheimer's disease (AD). We previously showed that Pyk2 is important for hippocampal function, plasticity, and spine structure. However, its potential role in AD is unknown. To address this question we used human brain samples and 5XFAD mice, an amyloid mouse model of AD expressing mutated human amyloid precursor protein and presenilin1. In the hippocampus of 5XFAD mice and in human AD patients' cortex and hippocampus, Pyk2 total levels were normal. However, Pyk2 Tyr-402 phosphorylation levels, reflecting its autophosphorylation-dependent activity, were reduced in 5XFAD mice at 8 months of age but not 3 months. We crossed these mice with Pyk2^-/- mice to generate 5XFAD animals devoid of Pyk2. At 8 months the phenotype of 5XFAD x Pyk2^-/- double mutant mice was not different from that of 5XFAD. In contrast, overexpression of Pyk2 in the hippocampus of 5XFAD mice, using adeno-associated virus, rescued autophosphorylated Pyk2 levels and improved synaptic markers and performance in several behavioral tasks. Both Pyk2^-/- and 5XFAD mice showed an increase of potentially neurotoxic Src cleavage product, which was rescued by Pyk2 overexpression. Manipulating Pyk2 levels had only minor effects on Aβ plaques, which were slightly decreased in hippocampus CA3 region of double mutant mice and increased following overexpression. Our results show that Pyk2 is not essential for the pathogenic effects of human amyloidogenic mutations in the 5XFAD mouse model. However, the slight decrease in plaque number observed in these mice in the absence of Pyk2 and their increase following Pyk2 overexpression suggest a contribution of this kinase in plaque formation. Importantly, a decreased function of Pyk2 was observed in 5XFAD mice, indicated by its decreased autophosphorylation and associated Src alterations. Overcoming this deficit by Pyk2 overexpression improved the behavioral and molecular phenotype of 5XFAD mice. Thus, our results in a mouse model of AD suggest that Pyk2 impairment may play a role in the symptoms of the disease.

The role of non-receptor protein tyrosine kinases in the excitotoxicity induced by the overactivation of NMDA receptors

Protein tyrosine phosphorylation is one of the primary modes of regulation of N-methyl-d-aspartate (NMDA) receptors. The non-receptor tyrosine kinases are one of the two types of protein tyrosine kinases that are involved in this process. The overactivation of NMDA receptors is a primary reason for neuron death following cerebral ischemia. Many studies have illustrated the important role of non-receptor tyrosine kinases in ischemia insults. This review introduces the roles of Src, Fyn, focal adhesion kinase, and proline-rich tyrosine kinase 2 in the excitotoxicity induced by the overactivation of NMDA receptors following cerebral ischemia.

Ca2+/calmodulin binding to PSD-95 mediates homeostatic synaptic scaling down

Postsynaptic density protein-95 (PSD-95) localizes AMPA-type glutamate receptors (AMPARs) to postsynaptic sites of glutamatergic synapses. Its postsynaptic displacement is necessary for loss of AMPARs during homeostatic scaling down of synapses. Here, we demonstrate that upon Ca²⁺ influx, Ca²⁺/calmodulin (Ca²⁺/CaM) binding to the N-terminus of PSD-95 mediates postsynaptic loss of PSD-95 and AMPARs during homeostatic scaling down. Our NMR structural analysis identified E17 within the PSD-95 N-terminus as important for binding to Ca²⁺/CaM by interacting with R126 on CaM. Mutating E17 to R prevented homeostatic scaling down in primary hippocampal neurons, which is rescued via charge inversion by ectopic expression of CaM^R126E, as determined by analysis of miniature excitatory postsynaptic currents. Accordingly, increased binding of Ca²⁺/CaM to PSD-95 induced by a chronic increase in Ca²⁺ influx is a critical molecular event in homeostatic downscaling of glutamatergic synaptic transmission.

Local substrates of non-receptor tyrosine kinases at synaptic sites in neurons

Several non-receptor tyrosine kinase (nRTK) members are expressed in neurons of mammalian brains. Among these neuron-enriched nRTKs, two Src family kinase members (Src and Fyn) are particularly abundant at synaptic sites and have been most extensively studied for their roles in the regulation of synaptic activity and plasticity. Increasing evidence shows that the synaptic subpool of nRTKs interacts with a number of local substrates, including glutamate receptors (both ionotropic and metabotropic glutamate receptors), postsynaptic scaffold proteins, presynaptic proteins, and synapse-enriched enzymes. By phosphorylating specific tyrosine residues in the intracellular domains of these synaptic proteins either constitutively or in an activity-dependent manner, nRTKs regulate these substrates in trafficking, surface expression, and function. Given the high sensitivity of nRTKs to changing synaptic input, nRTKs are considered to act as a critical regulator in the determination of the strength and efficacy of synaptic transmission.

Synaptotoxic Signaling by Amyloid Beta Oligomers in Alzheimer's Disease Through Prion Protein and mGluR5

Alzheimer's disease (AD) represents an impending global health crisis, yet the complexity of AD pathophysiology has so far precluded the development of any interventions to successfully slow or halt AD progression. It is clear that accumulation of Amyloid-beta (Aβ) peptide triggers progressive synapse loss to cause AD symptoms. Once initiated by Aβ, disease progression is complicated and accelerated by inflammation and by tau pathology. The recognition that Aβ peptide assumes multiple distinct states and that soluble oligomeric species (Aβo) are critical for synaptic damage is central to molecular understanding of AD. This knowledge has led to the identification of specific Aβo receptors, such as cellular prion protein (PrPC), mediating synaptic toxicity and neuronal dysfunction. The identification of PrPC as an Aβo receptor has illuminated an Aβo-induced signaling cascade involving mGluR5, Fyn, and Pyk2 that links Aβ and tau pathologies. This pathway provides novel potential therapeutic targets for disease-modifying AD therapy. Here, we discuss the methods by which several putative Aβo receptors were identified. We also offer an in-depth examination of the known molecular mechanisms believed to mediate Aβo-induced synaptic dysfunction, toxicity, and memory dysfunction.

Sperm-oocyte contact induces outside-in signaling via PYK2 activation

Fertilization is a multi-step process that begins with plasma membrane interactions that enable sperm - oocyte binding followed by fusion of the sperm and oocyte plasma membranes. Once membrane fusion has occurred, sperm incorporation involves actin remodeling events within the oocyte cortex that allow the sperm head to penetrate the cortical actin layer and gain access to the ooplasm. Despite the significance for reproduction, the control mechanisms involved in gamete binding, fusion, and sperm incorporation are poorly understood. While it is known that proline - rich tyrosine kinase 2 (PYK2 or PTK2b) kinase activity plays an important role in fertilization, its specific function has not been addressed. The present study made use of a zona-free mouse oocyte fertilization assay to investigate the relationship between PYK2 activity and sperm - oocyte binding and fusion, as well as localized changes in actin polymerization and sperm incorporation. In this assay, the majority of bound sperm had no apparent effect on the oocyte and only a few became incorporated into the ooplasm. However, a subset of bound sperm were associated with a localized response in which PYK2 was recruited to the oocyte cortex where it frequently co-localized with a ring or disk of f-actin. The frequency of sperm-oocyte binding sites that exhibited this actin response was reduced in pyk2-/- oocytes and the pyk2-/- oocytes proved less efficient at incorporating sperm, indicating that this protein kinase may have an important role in sperm incorporation. The response of PYK2 to sperm-oocyte interaction appeared unrelated to gamete fusion since PYK2 was recruited to sperm - binding sites under conditions where sperm - oocyte fusion was prevented and since PYK2 suppression or ablation did not prevent sperm - oocyte fusion. While a direct correlation between the PYK2 response in the oocyte and the successful incorporation of individual bound sperm remains to be established, these findings suggest a model in which the oocyte is not a passive participant in fertilization, but instead responds to sperm contact by localized PYK2 signaling that promotes actin remodeling events required to physically incorporate the sperm head into the ooplasm.

Sustained Gq-Protein Signaling Disrupts Striatal Circuits via JNK

The dorsal striatum is a major input structure of the basal ganglia and plays a key role in the control of vital processes such as motor behavior, cognition, and motivation. The functionality of striatal neurons is tightly controlled by various metabotropic receptors. Whereas the G_s/G_i-protein-dependent tuning of striatal neurons is fairly well known, the precise impact and underlying mechanism of G_q-protein-dependent signals remain poorly understood. Here, using different experimental approaches, especially designer receptor exclusively activated by designer drug (DREADD) chemogenetic technology, we found that sustained activation of G_q-protein signaling impairs the functionality of striatal neurons and we unveil the precise molecular mechanism underlying this process: a phospholipase C/Ca²⁺/proline-rich tyrosine kinase 2/cJun N-terminal kinase pathway. Moreover, engagement of this intracellular signaling route was functionally active in the mouse dorsal striatum in vivo, as proven by the disruption of neuronal integrity and behavioral tasks. To analyze this effect anatomically, we manipulated G_q-protein-dependent signaling selectively in neurons belonging to the direct or indirect striatal pathway. Acute G_q-protein activation in direct-pathway or indirect-pathway neurons produced an enhancement or a decrease, respectively, of activity-dependent parameters. In contrast, sustained G_q-protein activation impaired the functionality of direct-pathway and indirect-pathway neurons and disrupted the behavioral performance and electroencephalography-related activity tasks controlled by either anatomical framework. Collectively, these findings define the molecular mechanism and functional relevance of G_q-protein-driven signals in striatal circuits under normal and overactivated states.

SIGNIFICANCE STATEMENT

The dorsal striatum is a major input structure of the basal ganglia and plays a key role in the control of vital processes such as motor behavior, cognition, and motivation. Whereas the G_s/G_i-protein-dependent tuning of striatal neurons is fairly well known, the precise impact and underlying mechanism of G_q-protein-dependent signals remain unclear. Here, we show that striatal circuits can be "turned on" by acute G_q-protein signaling or "turned off" by sustained G_q-protein signaling. Specifically, sustained G_q-protein signaling inactivates striatal neurons by an intracellular pathway that relies on cJun N-terminal kinase. Overall, this study sheds new light onto the molecular mechanism and functional relevance of G_q-protein-driven signals in striatal circuits under normal and overactivated states.

Pyk2 modulates hippocampal excitatory synapses and contributes to cognitive deficits in a Huntington's disease model

The structure and function of spines and excitatory synapses are under the dynamic control of multiple signalling networks. Although tyrosine phosphorylation is involved, its regulation and importance are not well understood. Here we study the role of Pyk2, a non-receptor calcium-dependent protein-tyrosine kinase highly expressed in the hippocampus. Hippocampal-related learning and CA1 long-term potentiation are severely impaired in Pyk2-deficient mice and are associated with alterations in NMDA receptors, PSD-95 and dendritic spines. In cultured hippocampal neurons, Pyk2 has autophosphorylation-dependent and -independent roles in determining PSD-95 enrichment and spines density. Pyk2 levels are decreased in the hippocampus of individuals with Huntington and in the R6/1 mouse model of the disease. Normalizing Pyk2 levels in the hippocampus of R6/1 mice rescues memory deficits, spines pathology and PSD-95 localization. Our results reveal a role for Pyk2 in spine structure and synaptic function, and suggest that its deficit contributes to Huntington's disease cognitive impairments.

Cell type-specific transcriptomics of hypothalamic energy-sensing neuron responses to weight-loss

Molecular and cellular processes in neurons are critical for sensing and responding to energy deficit states, such as during weight-loss. Agouti related protein (AGRP)-expressing neurons are a key hypothalamic population that is activated during energy deficit and increases appetite and weight-gain. Cell type-specific transcriptomics can be used to identify pathways that counteract weight-loss, and here we report high-quality gene expression profiles of AGRP neurons from well-fed and food-deprived young adult mice. For comparison, we also analyzed Proopiomelanocortin (POMC)-expressing neurons, an intermingled population that suppresses appetite and body weight. We find that AGRP neurons are considerably more sensitive to energy deficit than POMC neurons. Furthermore, we identify cell type-specific pathways involving endoplasmic reticulum-stress, circadian signaling, ion channels, neuropeptides, and receptors. Combined with methods to validate and manipulate these pathways, this resource greatly expands molecular insight into neuronal regulation of body weight, and may be useful for devising therapeutic strategies for obesity and eating disorders.

DOI:http://dx.doi.org/10.7554/eLife.09800.001

Humans and other animals must get adequate nutrition in order to survive. As a result, the body has several systems that work side by side to maintain a healthy body weight and ensure that enough food gets eaten to provide the energy that the body needs. Problems with these systems can contribute towards obesity and other eating disorders.

Certain types of cells in the brain play important roles in controlling weight and appetite, although the genes and cellular mechanisms that underlie these abilities are not well understood. When an animal is deprived of food, so-called AGRP neurons produce molecules that increase appetite and make it easier to gain weight. These neurons also go through structural changes and increase their electrical activity during weight loss. Another group of cells, called the POMC neurons, becomes less active when an animal is deprived of energy.

Using a technique called cell type-specific transcriptomics, Henry, Sugino et al. have now revealed that the expression of hundreds of genes in AGRP and POMC neurons changes depending on whether mice are well fed or food deprived. Food deprivation also affects more genes in AGRP neurons than has been seen in other types of brain cell, and the AGRP neurons are also more sensitive to a change in food intake than POMC neurons.

In the future, this gene expression data and knowledge of the pathways affected by the genes could help researchers to develop new treatments for obesity and other disorders that affect appetite. Henry, Sugino et al. then mapped how these changes in gene expression trigger molecular “pathways” in the neurons that alter how the cells work. These affect many parts of the cells, including ion channels, transcription factors, receptors, and secreted proteins. In addition, food deprivation activated pathways in AGRP neurons that protect the cells from damage and death caused by elevated neuron activity and also triggered signaling pathways that increase body weight.

In the future, this gene expression data and knowledge of the pathways affected by the genes could help researchers to develop new treatments for obesity and other disorders that affect appetite.

DOI:http://dx.doi.org/10.7554/eLife.09800.002

How to awaken your nanomachines: Site-specific activation of focal adhesion kinases through ligand interactions

The focal adhesion kinase (FAK) and the related protein-tyrosine kinase 2-beta (Pyk2) are highly versatile multidomain scaffolds central to cell adhesion, migration, and survival. Due to their key role in cancer metastasis, understanding and inhibiting their functions are important for the development of targeted therapy. Because FAK and Pyk2 are involved in many different cellular functions, designing drugs with partial and function-specific inhibitory effects would be desirable. Here, we summarise recent progress in understanding the structural mechanism of how the tug-of-war between intramolecular and intermolecular interactions allows these protein 'nanomachines' to become activated in a site-specific manner.

Fyn inhibition rescues established memory and synapse loss in Alzheimer mice

OBJECTIVE

Currently no effective disease-modifying agents exist for the treatment of Alzheimer disease (AD). The Fyn tyrosine kinase is implicated in AD pathology triggered by amyloid-ß oligomers (Aßo) and propagated by Tau. Thus, Fyn inhibition may prevent or delay disease progression. Here, we sought to repurpose the Src family kinase inhibitor oncology compound, AZD0530, for AD.

METHODS

The pharmacokinetics and distribution of AZD0530 were evaluated in mice. Inhibition of Aßo signaling to Fyn, Pyk2, and Glu receptors by AZD0530 was tested by brain slice assays. After AZD0530 or vehicle treatment of wild-type and AD transgenic mice, memory was assessed by Morris water maze and novel object recognition. For these cohorts, amyloid precursor protein (APP) metabolism, synaptic markers (SV2 and PSD-95), and targets of Fyn (Pyk2 and Tau) were studied by immunohistochemistry and by immunoblotting.

RESULTS

AZD0530 potently inhibits Fyn and prevents both Aßo-induced Fyn signaling and downstream phosphorylation of the AD risk gene product Pyk2, and of NR2B Glu receptors in brain slices. After 4 weeks of treatment, AZD0530 dosing of APP/PS1 transgenic mice fully rescues spatial memory deficits and synaptic depletion, without altering APP or Aß metabolism. AZD0530 treatment also reduces microglial activation in APP/PS1 mice, and rescues Tau phosphorylation and deposition abnormalities in APP/PS1/Tau transgenic mice. There is no evidence of AZD0530 chronic toxicity.

INTERPRETATION

Targeting Fyn can reverse memory deficits found in AD mouse models, and rescue synapse density loss characteristic of the disease. Thus, AZD0530 is a promising candidate to test as a potential therapy for AD.

Pyk2 and Src mediate signaling to CCL18-induced breast cancer metastasis

Pyk2 and Src phosphorylation is initiated by CCL18, which promotes breast cancer metastasis via its functional G protein-coupled receptor PITPNM3. However, the function of Pyk2 and Src in CCL18-induced breast cancer metastasis is poorly understood. Quantitative reverse-transcription polymerase chain reactions (qRT-PCRs), Western blot, boyden chamber assay, and adherence assay were performed to delineate the consequences of Pyk2/Src in CCL18-induced breast cancer cells. Co-immunoprecipitation and immunofluorescence were performed to analyze the interaction of proteins. Upon the binding of CCL18 to PITPNM3, Pyk2 translocates from the cytoplasm to the plasma membrane to form a stable complex with PITPNM3, subsequently activating Src kinase. Moreover, upon stimulation with CCL18, Pyk2 and Src become essential for integrin alpha5/beta1 clustering-dependent adherence, migration, and invasion. Pyk2 and Src are important in CCL18-induced breast cancer metastasis.

The upregulation of NR2A-containing N-methyl-D-aspartate receptor function by tyrosine phosphorylation of postsynaptic density 95 via facilitating Src/proline-rich tyrosine kinase 2 activation

The activation of postsynaptic N-methyl-D-aspartate (NMDA) receptors is required for long-term potentiation (LTP) of synaptic transmission. Postsynaptic density 95 (PSD-95) serves as a scaffold protein that tethers NMDA receptor subunits, kinases, and signal molecules. Our previous study proves that PSD-95 is a substrate of Src/Fyn and identifies Y523 on PSD-95 as a principal phosphorylation site. In this paper, we try to define an involvement and molecular consequences of PSD-95 phosphorylation by Src in NMDA receptor regulation. We found that either NMDA or chemical LTP induction leads to rapid phosphorylation of PSD-95 by Src in cultured cortical neurons. The phosphorylation of Y523 on PSD-95 potentiates NR2A-containing NMDA receptor current amplitude, implying an important role of Src-mediated PSD-95 phosphorylation in NMDA receptor activation. Comparing to wild-type PSD-95, overexpression of nonphosphorylatable mutant PSD-95Y523F attenuated the NMDA-stimulated NR2A tyrosine phosphorylation that enhances electrophysiological responses of NMDA receptor channels, while did not affect the membrane localization of NR2A subunits. PSD-95Y523D, a phosphomimetic mutant of PSD-95, induced NR2A tyrosine phosphorylation even if there was no NMDA treatment. In addition, the deficiency of Y523 phosphorylation on PSD-95 impaired the facilitatory effect of PSD-95 on the activation of Src and proline-rich tyrosine kinase 2 (Pyk2) and decreased the binding of Pyk2 with PSD-95. These results indicate that PSD-95 phosphorylation by Src facilitates the integration of Pyk2 to PSD-95 signal complex, the activation of Pyk2/Src, as well as the subsequent tyrosine phosphorylation of NR2A, which ultimately results in the upregulation of NMDA receptor function and synaptic transmission.

Capping of the N-terminus of PSD-95 by calmodulin triggers its postsynaptic release

Postsynaptic density protein-95 (PSD-95) is a central element of the postsynaptic architecture of glutamatergic synapses. PSD-95 mediates postsynaptic localization of AMPA receptors and NMDA receptors and plays an important role in synaptic plasticity. PSD-95 is released from postsynaptic membranes in response to Ca(2+) influx via NMDA receptors. Here, we show that Ca(2+)/calmodulin (CaM) binds at the N-terminus of PSD-95. Our NMR structure reveals that both lobes of CaM collapse onto a helical structure of PSD-95 formed at its N-terminus (residues 1-16). This N-terminal capping of PSD-95 by CaM blocks palmitoylation of C3 and C5, which is required for postsynaptic PSD-95 targeting and the binding of CDKL5, a kinase important for synapse stability. CaM forms extensive hydrophobic contacts with Y12 of PSD-95. The PSD-95 mutant Y12E strongly impairs binding to CaM and Ca(2+)-induced release of PSD-95 from the postsynaptic membrane in dendritic spines. Our data indicate that CaM binding to PSD-95 serves to block palmitoylation of PSD-95, which in turn promotes Ca(2+)-induced dissociation of PSD-95 from the postsynaptic membrane.

LTP: GluN2B on the go

LTP, the lasting increase in synaptic transmission following heightened activity, is viewed as the physiological basis of learning. In this issue of The EMBO Journal, Dupuis et al find that certain NMDARs diffuse away upon LTP. Antibodies against the NMDAR from patients with autoimmune synaptic encephalitis prevent this redistribution and LTP.

Competition between α-actinin and Ca²⁺-calmodulin controls surface retention of the L-type Ca²⁺ channel Ca(V)1.2

Regulation of neuronal excitability and cardiac excitation-contraction coupling requires the proper localization of L-type Ca²⁺ channels. We show that the actin-binding protein α-actinin binds to the C-terminal surface targeting motif of α11.2, the central pore-forming Ca(V)1.2 subunit, in order to foster its surface expression. Disruption of α-actinin function by dominant-negative or small hairpin RNA constructs reduces Ca(V)1.2 surface localization in human embryonic kidney 293 and neuronal cultures and dendritic spine localization in neurons. We demonstrate that calmodulin displaces α-actinin from their shared binding site on α11.2 upon Ca²⁺ influx through L-type channels, but not through NMDAR, thereby triggering loss of Ca(V)1.2 from spines. Coexpression of a Ca²⁺-binding-deficient calmodulin mutant does not affect basal Ca(V)1.2 surface expression but inhibits its internalization upon Ca²⁺ influx. We conclude that α-actinin stabilizes Ca(V)1.2 at the plasma membrane and that its displacement by Ca²⁺-calmodulin triggers Ca²⁺-induced endocytosis of Ca(V)1.2, thus providing an important negative feedback mechanism for Ca²⁺ influx.

Non-receptor-tyrosine kinases integrate fast glucocorticoid signaling in hippocampal neurons

Despite numerous descriptions of rapid effects of corticosterone on neuronal function, the intracellular mechanisms responsible for these changes remain elusive. The present comprehensive analysis reveals that signaling from a membrane-located G protein-coupled receptor activates PKC, Akt/PKB, and PKA, which subsequently trigger the phosphorylation of the tyrosine kinases Pyk2, Src, and Abl. These changes induce rapid cytoskeletal rearrangements (increased PSD-95 co-clustering) within the post-synaptic density; these events are accompanied by increased surface NMDA receptor expression, reflecting corticosterone-induced inhibition of NMDA receptor endocytosis. Notably, none of these signaling mechanisms require de novo protein synthesis. The observed up-regulation of ERK1/2 (downstream of NMDA receptor signaling) together with the fact that c-Abl integrates cytoplasmic and nuclear functions introduces a potential mechanism through which rapid signaling initiated at the plasma membrane may eventually determine the long term integrated response to corticosterone by impacting on the transcriptional machinery that is regulated by classical, nuclear mineralocorticoid, and glucocorticoid receptors.

Oxidative stress induced by P2X7 receptor stimulation in murine macrophages is mediated by c-Src/Pyk2 and ERK1/2

BACKGROUND

Activation of ATP-gated P2X7 receptors (P2X7R) in macrophages leads to production of reactive oxygen species (ROS) by a mechanism that is partially characterized. Here we used J774 cells to identify the signaling cascade that couples ROS production to receptor stimulation.

METHODS

J774 cells and mP2X7-transfected HEK293 cells were stimulated with Bz-ATP in the presence and absence of extracellular calcium. Protein inhibitors were used to evaluate the physiological role of various kinases in ROS production. In addition, phospho-antibodies against ERK1/2 and Pyk2 were used to determine activation of these two kinases.

RESULTS

ROS generation in either J774 or HEK293 cells (expressing P2X7, NOX2, Rac1, p47phox and p67phox) was strictly dependent on calcium entry via P2X7R. Stimulation of P2X7R activated Pyk2 but not calmodulin. Inhibitors of MEK1/2 and c-Src abolished ERK1/2 activation and ROS production but inhibitors of PI3K and p38 MAPK had no effect on ROS generation. PKC inhibitors abolished ERK1/2 activation but barely reduced the amount of ROS produced by Bz-ATP. In agreement, the amount of ROS produced by PMA was about half of that produced by Bz-ATP.

CONCLUSIONS

Purinergic stimulation resulted in calcium entry via P2X7R and subsequent activation of the PKC/c-Src/Pyk2/ERK1/2 pathway to produce ROS. This signaling mechanism did not require PI3K, p38 MAPK or calmodulin.

GENERAL SIGNIFICANCE

ROS is generated in order to kill invading pathogens, thus elucidating the mechanism of ROS production in macrophages and other immune cells allow us to understand how our body copes with microbial infections.

Inhibition of a novel specific neuroglial integrin signaling pathway increases STAT3-mediated CNTF expression

Background

Ciliary neurotrophic factor (CNTF) expression is repressed in astrocytes by neuronal contact in the CNS and is rapidly induced by injury. Here, we defined an inhibitory integrin signaling pathway.

Results

The integrin substrates laminin, fibronectin and vitronectin, but not collagen, thrombospondin or fibrinogen, reduced CNTF expression in C6 astroglioma cells. Antibodies against αv and β5, but not α6 or β1, integrin induced CNTF. Together, the ligand and antibody specificity suggests that CNTF is repressed by αvβ5 integrin. Antibodies against Thy1, an abundant neuronal surface protein whose function is unclear, induced CNTF in neuron-astrocyte co-cultures indicating that it is a neuroglial CNTF repressor. Inhibition of the integrin signaling molecule Focal Adhesion Kinase (FAK) or the downstream c-Jun N-terminal kinase (JNK), but not extracellular regulated kinase (ERK) or p38 MAPK, greatly induced CNTF mRNA and protein expression within 4 hours. This selective inhibitory pathway phosphorylated STAT3 on its inhibitory ser-727 residue interfering with activity of the pro-transcription Tyr-705 residue. STAT3 can activate CNTF transcription because it bound to its promoter and FAK antagonist-induced CNTF was reduced by blocking STAT3. Microinjection of FAK inhibitor directly into the brain or spinal cord in adult mice rapidly induced CNTF mRNA and protein expression. Importantly, systemic treatment with FAK inhibitors over 3 days induced CNTF in the subventricular zone and increased neurogenesis.

Conclusions

Neuron-astroglia contact mediated by integrins serves as a sensor to enable rapid neurotrophic responses and provides a new pharmacological avenue to exploit the neuroprotective properties of endogenous CNTF.