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

Alterations of the IKZF1-IKZF2 tandem in immune cells of schizophrenia patients regulate associated phenotypes

Schizophrenia is a complex multifactorial disorder and increasing evidence suggests the involvement of immune dysregulations in its pathogenesis. We observed that IKZF1 and IKZF2, classic immune-related transcription factors (TFs), were both downregulated in patients' peripheral blood mononuclear cells (PBMCs) but not in their brain. We generated a new mutant mouse model with a reduction in Ikzf1 and Ikzf2 to study the impact of those changes. Such mice developed deficits in the three dimensions (positive-negative-cognitive) of schizophrenia-like phenotypes associated with alterations in structural synaptic plasticity. We then studied the secretomes of cultured PBMCs obtained from patients and identified potentially secreted molecules, which depended on IKZF1 and IKZF2 mRNA levels, and that in turn have an impact on neural synchrony, structural synaptic plasticity and schizophrenia-like symptoms in in vivo and in vitro models. Our results point out that IKZF1-IKZF2-dependent immune signals negatively impact on essential neural circuits involved in schizophrenia.

Expansion of the neocortex and protection from neurodegeneration by in vivo transient reprogramming

Yamanaka factors (YFs) can reverse some aging features in mammalian tissues, but their effects on the brain remain largely unexplored. Here, we induced YFs in the mouse brain in a controlled spatiotemporal manner in two different scenarios: brain development and adult stages in the context of neurodegeneration. Embryonic induction of YFs perturbed cell identity of both progenitors and neurons, but transient and low-level expression is tolerated by these cells. Under these conditions, YF induction led to progenitor expansion, an increased number of upper cortical neurons and glia, and enhanced motor and social behavior in adult mice. Additionally, controlled YF induction is tolerated by principal neurons in the adult dorsal hippocampus and prevented the development of several hallmarks of Alzheimer's disease, including cognitive decline and altered molecular signatures, in the 5xFAD mouse model. These results highlight the powerful impact of YFs on neural proliferation and their potential use in brain disorders.

The PTK2B gene is associated with obesity, adiposity, and leptin levels in children and adolescents

Previous studies determined that Pyk2 is involved in several diseases in which the symptomatology presents alterations in energy balance. However, its role in obesity is poorly understood. To evaluate the metabolic role of the Pyk2 gene (PTK2B) in children and adolescents with obesity we measured its mRNA expression levels in peripheral blood mononuclear cells. For that we performed a cross-sectional study involving 130 Caucasian subjects that was divided into two groups according to BMI. Data showed increased PTK2B mRNA expression in children and adolescents with obesity. Interestingly, a positive correlation has been found between the levels of PTK2B with weight, BMI, BMI Z score, fat mass, waist circumference, waist to height ratio, diastolic blood pressure, and leptin. In addition, it is indicated that high levels of PTK2B gene expression might be a predictor of obesity development. This work provides important insights into the previously undescribed role of Pyk2 in obesity.

Single-nucleus RNA sequencing-based construction of a hippocampal neuron atlas in mice with epileptic cognitive impairment

The hippocampus plays a critical role in learning and memory, and mice with epileptic cognitive impairment exhibit hippocampal atrophy. However, there is still a lack of research on the hippocampal cell atlas related to these disorders. Here, we utilized snRNA-seq to characterize the transcriptomic changes in hippocampal neurons of drug-resistant epilepsy (DRE) cognitive-impaired mice. The intercellular heterogeneity of 20 subpopulations of neurons was analyzed, focusing on aspects such as cell communication, gene expressions, GO and KEGG enrichment analysis, and module gene set analysis. Based on the degree of relevance to synaptic biological functions, the subpopulations associated with cognitive impairment (ExN1, 3, 8 and InN1, 6) were preliminarily identified. We also identified some key biomarkers in DRE cognitive-impaired mice, such as Ptprz1 and Calb1. Finally, we integrate and validate our dataset using identified well-annotated marker genes in the hippocampal region, further supporting the functional annotation of neuronal subpopulations.

Neuroprotection by ADAM10 inhibition requires TrkB signaling in the Huntington's disease hippocampus

Synaptic dysfunction is an early pathogenic event leading to cognitive decline in Huntington's disease (HD). We previously reported that the active ADAM10 level is increased in the HD cortex and striatum, causing excessive proteolysis of the synaptic cell adhesion protein N-Cadherin. Conversely, ADAM10 inhibition is neuroprotective and prevents cognitive decline in HD mice. Although the breakdown of cortico-striatal connection has been historically linked to cognitive deterioration in HD, dendritic spine loss and long-term potentiation (LTP) defects identified in the HD hippocampus are also thought to contribute to the cognitive symptoms of the disease. The aim of this study is to investigate the contribution of ADAM10 to spine pathology and LTP defects of the HD hippocampus. We provide evidence that active ADAM10 is increased in the hippocampus of two mouse models of HD, leading to extensive proteolysis of N-Cadherin, which has a widely recognized role in spine morphology and synaptic plasticity. Importantly, the conditional heterozygous deletion of ADAM10 in the forebrain of HD mice resulted in the recovery of spine loss and ultrastructural synaptic defects in CA1 pyramidal neurons. Meanwhile, normalization of the active ADAM10 level increased the pool of synaptic BDNF protein and activated ERK neuroprotective signaling in the HD hippocampus. We also show that the ADAM10 inhibitor GI254023X restored LTP defects and increased the density of mushroom spines enriched with GluA1-AMPA receptors in HD hippocampal neurons. Notably, we report that administration of the TrkB antagonist ANA12 to HD hippocampal neurons reduced the beneficial effect of GI254023X, indicating that the BDNF receptor TrkB contributes to mediate the neuroprotective activity exerted by ADAM10 inhibition in HD. Collectively, these findings indicate that ADAM10 inhibition coupled with TrkB signaling represents an efficacious strategy to prevent hippocampal synaptic plasticity defects and cognitive dysfunction in HD.

A systems biology-based identification and in vivo functional screening of Alzheimer's disease risk genes reveal modulators of memory function

Genome-wide association studies (GWASs) have uncovered over 75 genomic loci associated with risk for late-onset Alzheimer's disease (LOAD), but identification of the underlying causal genes remains challenging. Studies of induced pluripotent stem cell (iPSC)-derived neurons from LOAD patients have demonstrated the existence of neuronal cell-intrinsic functional defects. Here, we searched for genetic contributions to neuronal dysfunction in LOAD using an integrative systems approach that incorporated multi-evidence-based gene mapping and network-analysis-based prioritization. A systematic perturbation screening of candidate risk genes in Caenorhabditis elegans (C. elegans) revealed that neuronal knockdown of the LOAD risk gene orthologs vha-10 (ATP6V1G2), cmd-1 (CALM3), amph-1 (BIN1), ephx-1 (NGEF), and pho-5 (ACP2) alters short-/intermediate-term memory function, the cognitive domain affected earliest during LOAD progression. These results highlight the impact of LOAD risk genes on evolutionarily conserved memory function, as mediated through neuronal endosomal dysfunction, and identify new targets for further mechanistic interrogation.

Proteomic analysis identifies HSP90AA1, PTK2B, and ANXA2 in the human entorhinal cortex in Alzheimer's disease: Potential role in synaptic homeostasis and Aβ pathology through microglial and astroglial cells

Alzheimer's disease (AD), the most prevalent neurodegenerative disorder worldwide, is clinically characterized by cognitive deficits. Neuropathologically, AD brains accumulate deposits of amyloid-β (Aβ) and tau proteins. Furthermore, these misfolded proteins can propagate from cell to cell in a prion-like manner and induce native proteins to become pathological. The entorhinal cortex (EC) is among the earliest areas affected by tau accumulation along with volume reduction and neurodegeneration. Neuron-glia interactions have recently come into focus; however, the role of microglia and astroglia in the pathogenesis of AD remains unclear. Proteomic approaches allow the determination of changes in the proteome to better understand the pathology underlying AD. Bioinformatic analysis of proteomic data was performed to compare ECs from AD and non-AD human brain tissue. To validate the proteomic results, western blot, immunofluorescence, and confocal studies were carried out. The findings revealed that the most disturbed signaling pathway was synaptogenesis. Because of their involvement in synapse function, relationship with Aβ and tau proteins and interactions in the pathway analysis, three proteins were selected for in-depth study: HSP90AA1, PTK2B, and ANXA2. All these proteins showed colocalization with neurons and/or astroglia and microglia and with pathological Aβ and tau proteins. In particular, ANXA2, which is overexpressed in AD, colocalized with amoeboid microglial cells and Aβ plaques surrounded by astrocytes. Taken together, the evidence suggests that unbalanced expression of HSP90AA1, PTK2B, and ANXA2 may play a significant role in synaptic homeostasis and Aβ pathology through microglial and astroglial cells in the human EC in AD.

Operant Training for Highly Palatable Food Alters Translating Messenger RNA in Nucleus Accumbens D2 Neurons and Reveals a Modulatory Role of Ncdn

BACKGROUND

Highly palatable food triggers behavioral responses including strong motivation. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the long-lasting effects of highly palatable food on feeding behavior are poorly understood.

METHODS

We studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral responses and dendritic spine modifications in the NAc. We compared the translating messenger RNA in NAc neurons identified by the type of dopamine receptors they express, depending on the kind of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn.

RESULTS

Operant conditioning for highly palatable food increased motivation for food even in well-fed mice. In wild-type mice, free choice between regular and highly palatable food increased weight compared with access to regular food only. Highly palatable food increased spine density in the NAc. In animals trained for highly palatable food, translating messenger RNAs were modified in NAc neurons expressing dopamine D2 receptors, mostly corresponding to striatal projection neurons, but not in neurons expressing D1 receptors. Knockout of Ncdn, an abundant downregulated gene, opposed the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting that downregulation may be a compensatory mechanism.

CONCLUSIONS

Our results emphasize the importance of messenger RNA alterations in D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

Homocysteine-induced sustained GluN2A NMDA receptor stimulation leads to mitochondrial ROS generation and neurotoxicity

Homocysteine, a sulfur-containing amino acid derived from methionine metabolism, is a known agonist of N-methyl-D-aspartate receptor (NMDAR) and is involved in neurotoxicity. Our previous findings showed that neuronal exposure to elevated homocysteine levels leads to sustained low-level increase in intracellular Ca2+, which is dependent on GluN2A subunit-containing NMDAR (GluN2A-NMDAR) stimulation. These studies further showed a role of ERK MAPK in homocysteine-GluN2A-NMDAR-mediated neuronal death. However, the intracellular mechanisms associated with such sustained GluN2A-NMDAR stimulation and subsequent Ca2+ influx have remained unexplored. Using live-cell imaging with Fluo3-AM and biochemical approaches, we show that homocysteine-GluN2A NMDAR-induced initial Ca2+ influx triggers sequential phosphorylation and subsequent activation of the proline rich tyrosine kinase 2 (Pyk2) and Src family kinases, which in turn phosphorylates GluN2A-Tyr1325 residue of GluN2A-NMDARs to maintain channel activity. The continuity of this cycle of events leads to sustained Ca2+ influx through GluN2A-NMDAR. Our findings also show that lack of activation of the regulatory tyrosine phosphatase STEP, which can limit Pyk2 and Src family kinase activity further contributes to the maintenance of this cycle. Additional studies using live-cell imaging of neurons expressing a redox-sensitive GFP targeted to the mitochondrial matrix show that treatment with homocysteine leads to a progressive increase in mitochondrial reactive oxygen species generation, which is dependent on GluN2A-NMDAR-mediated sustained ERK MAPK activation. This later finding demonstrates a novel role of GluN2A-NMDAR in homocysteine-induced mitochondrial ROS generation and highlights the role of ERK MAPK as the intermediary signaling pathway between GluN2A-NMDAR stimulation and mitochondrial reactive oxygen species generation.

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.

PYK2, a hub of signaling networks in breast cancer progression

Breast cancer (BC) involves complex signaling networks characterized by extensive cross-communication and feedback loops between and within multiple signaling cascades. Many of these signaling pathways are driven by genetic alterations of oncogene and/or tumor-suppressor genes and are influenced by various environmental cues. We describe unique roles of the non-receptor tyrosine kinase (NRTK) PYK2 in signaling integration and feedback looping in BC. PYK2 functions as a signaling hub in various cascades, and its involvement in positive and negative feedback loops enhances signaling robustness, modulates signaling dynamics, and contributes to BC growth, epithelial-to-mesenchymal transition (EMT), stemness, migration, invasion, and metastasis. We also discuss the potential of PYK2 as a therapeutic target in various BC subtypes.

Thalamic Foxp2 regulates output connectivity and sensory-motor impairments in a model of Huntington's Disease

BACKGROUND

Huntington's Disease (HD) is a disorder that affects body movements. Altered glutamatergic innervation of the striatum is a major hallmark of the disease. Approximately 30% of those glutamatergic inputs come from thalamic nuclei. Foxp2 is a transcription factor involved in cell differentiation and reported low in patients with HD. However, the role of the Foxp2 in the thalamus in HD remains unexplored.

METHODS

We used two different mouse models of HD, the R6/1 and the HdhQ111 mice, to demonstrate a consistent thalamic Foxp2 reduction in the context of HD. We used in vivo electrophysiological recordings, microdialysis in behaving mice and rabies virus-based monosynaptic tracing to study thalamo-striatal and thalamo-cortical synaptic connectivity in R6/1 mice. Micro-structural synaptic plasticity was also evaluated in the striatum and cortex of R6/1 mice. We over-expressed Foxp2 in the thalamus of R6/1 mice or reduced Foxp2 in the thalamus of wild type mice to evaluate its role in sensory and motor skills deficiencies, as well as thalamo-striatal and thalamo-cortical connectivity in such mouse models.

RESULTS

Here, we demonstrate in a HD mouse model a clear and early thalamo-striatal aberrant connectivity associated with a reduction of thalamic Foxp2 levels. Recovering thalamic Foxp2 levels in the mouse rescued motor coordination and sensory skills concomitant with an amelioration of neuropathological features and with a repair of the structural and functional connectivity through a restoration of neurotransmitter release. In addition, reduction of thalamic Foxp2 levels in wild type mice induced HD-like phenotypes.

CONCLUSIONS

In conclusion, we show that a novel identified thalamic Foxp2 dysregulation alters basal ganglia circuits implicated in the pathophysiology of HD.

Integrative analyses highlight functional regulatory variants associated with neuropsychiatric diseases

Noncoding variants of presumed regulatory function contribute to the heritability of neuropsychiatric disease. A total of 2,221 noncoding variants connected to risk for ten neuropsychiatric disorders, including autism spectrum disorder, attention deficit hyperactivity disorder, bipolar disorder, borderline personality disorder, major depression, generalized anxiety disorder, panic disorder, post-traumatic stress disorder, obsessive-compulsive disorder and schizophrenia, were studied in developing human neural cells. Integrating epigenomic and transcriptomic data with massively parallel reporter assays identified differentially-active single-nucleotide variants (daSNVs) in specific neural cell types. Expression-gene mapping, network analyses and chromatin looping nominated candidate disease-relevant target genes modulated by these daSNVs. Follow-up integration of daSNV gene editing with clinical cohort analyses suggested that magnesium transport dysfunction may increase neuropsychiatric disease risk and indicated that common genetic pathomechanisms may mediate specific symptoms that are shared across multiple neuropsychiatric diseases.

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.

Arc protein, a remnant of ancient retrovirus, forms virus-like particles, which are abundantly generated by neurons during epileptic seizures, and affects epileptic susceptibility in rodent models

A product of the immediate early gene Arc (Activity-regulated cytoskeleton-associated protein or Arc protein) of retroviral ancestry resides in the genome of all tetrapods for millions of years and is expressed endogenously in neurons. It is a well-known protein, very important for synaptic plasticity and memory consolidation. Activity-dependent Arc expression concentrated in glutamatergic synapses affects the long-time synaptic strength of those excitatory synapses. Because it modulates excitatory-inhibitory balance in a neuronal network, the Arc gene itself was found to be related to the pathogenesis of epilepsy. General Arc knockout rodent models develop a susceptibility to epileptic seizures. Because of activity dependence, synaptic Arc protein synthesis also is affected by seizures. Interestingly, it was found that Arc protein in synapses of active neurons self-assemble in capsids of retrovirus-like particles, which can transfer genetic information between neurons, at least across neuronal synaptic boutons. Released Arc particles can be accumulated in astrocytes after seizures. It is still not known how capsid assembling and transmission timescale is affected by seizures. This scientific field is relatively novel and is experiencing swift transformation as it grapples with difficult concepts in light of evolving experimental findings. We summarize the emergent literature on the subject and also discuss the specific rodent models for studying Arc effects in epilepsy. We summarized both to clarify the possible role of Arc-related pseudo-viral particles in epileptic disorders, which may be helpful to researchers interested in this growing area of investigation.

Serotonin sensing by microglia conditions the proper development of neuronal circuits and of social and adaptive skills

The proper maturation of emotional and sensory circuits requires fine-tuning of serotonin (5-HT) level during early postnatal development. Consistently, dysfunctions of the serotonergic system have been associated with neurodevelopmental psychiatric diseases, including autism spectrum disorders (ASD). However, the mechanisms underlying the developmental effects of 5-HT remain partially unknown, one obstacle being the action of 5-HT on different cell types. Here, we focused on microglia, which play a role in brain wiring refinement, and we investigated whether the control of these cells by 5-HT is relevant for neurodevelopment and spontaneous behaviors in mice. Since the main 5-HT sensor in microglia is the 5-HT2B receptor subtype, we prevented 5-HT signaling specifically in microglia by conditional invalidation of the Htr2b gene in these cells. We observed that abrogating the serotonergic control of microglia during early postnatal development affects the phagolysosomal compartment of these cells and their proximity to dendritic spines and perturbs neuronal circuits maturation. Furthermore, this early ablation of microglial 5-HT2B receptors leads to adult hyperactivity in a novel environment and behavioral defects in sociability and flexibility. Importantly, we show that these behavioral alterations result from a developmental effect, since they are not observed when microglial Htr2b invalidation is induced later, at P30 onward. Thus, a primary alteration of 5-HT sensing in microglia, during a critical time window between birth and P30, is sufficient to impair social and flexibility skills. This link between 5-HT and microglia may explain the association between serotonergic dysfunctions and behavioral traits like impaired sociability and inadaptability to novelty, which are prominent in psychiatric disorders such as ASD.

Sevoflurane Exposure in Neonates Perturbs the Expression Patterns of Specific Genes That May Underly the Observed Learning and Memory Deficits

Exposure to commonly used anesthetics leads to neurotoxic effects in animal models-ranging from cell death to learning and memory deficits. These neurotoxic effects invoke a variety of molecular pathways, exerting either immediate or long-term effects at the cellular and behavioural levels. However, little is known about the gene expression changes following early neonatal exposure to these anesthetic agents. We report here on the effects of sevoflurane, a commonly used inhalational anesthetic, on learning and memory and identify a key set of genes that may likely be involved in the observed behavioural deficits. Specifically, we demonstrate that sevoflurane exposure in postnatal day 7 (P7) rat pups results in subtle, but distinct, memory deficits in the adult animals that have not been reported previously. Interestingly, when given intraperitoneally, pre-treatment with dexmedetomidine (DEX) could only prevent sevoflurane-induced anxiety in open field testing. To identify genes that may have been altered in the neonatal rats after sevoflurane and DEX exposure, specifically those impacting cellular viability, learning, and memory, we conducted an extensive Nanostring study examining over 770 genes. We found differential changes in the gene expression levels after exposure to both agents. A number of the perturbed genes found in this study have previously been implicated in synaptic transmission, plasticity, neurogenesis, apoptosis, myelination, and learning and memory. Our data thus demonstrate that subtle, albeit long-term, changes observed in an adult animal's learning and memory after neonatal anesthetic exposure may likely involve perturbation of specific gene expression patterns.

Operant training for highly palatable food alters translating mRNA in nucleus accumbens D2 neurons and reveals a modulatory role of Neurochondrin

BACKGROUND

Highly palatable food triggers behavioral alterations reminiscent of those induced by addictive drugs. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the effects of highly palatable food on feeding behavior are poorly understood.

METHODS

We studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral effects and dendritic spine modifications in the NAc. We compared the translating mRNA in NAc neurons identified by the type of dopamine receptors they express, depending on the type of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn (Neurochondrin).

RESULTS

Operant conditioning for highly palatable food increases motivation for food even in well-fed mice. In control mice, free access to regular or highly palatable food results in increased weight as compared to regular food only. Highly palatable food increases spine density in the NAc. In animals trained for highly palatable food, translating mRNAs are modified in NAc dopamine D2-receptor-expressing neurons, mostly corresponding to striatal projection neurons, but not in those expressing D1-receptors. Knock-out of Ncdn, an abundant down-regulated gene, opposes the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting down-regulation may be a compensatory mechanism.

CONCLUSIONS

Our results emphasize the importance of mRNA alterations D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

Ikzf1 as a novel regulator of microglial homeostasis in inflammation and neurodegeneration

In the last two decades, microglia have emerged as key contributors to disease progression in many neurological disorders, not only by exerting their classical immunological functions but also as extremely dynamic cells with the ability to modulate synaptic and neural activity. This dynamic behavior, together with their heterogeneous roles and response to diverse perturbations in the brain parenchyma has raised the idea that microglia activation is more diverse than anticipated and that understanding the molecular mechanisms underlying microglial states is essential to unravel their role in health and disease from development to aging. The Ikzf1 (a.k.a. Ikaros) gene plays crucial roles in modulating the function and maturation of circulating monocytes and lymphocytes, but whether it regulates microglial functions and states is unknown. Using genetic tools, here we describe that Ikzf1 is specifically expressed in the adult microglia in brain regions such as cortex and hippocampus. By characterizing the Ikzf1 deficient mice, we observed that these mice displayed spatial learning deficits, impaired hippocampal CA3-CA1 long-term potentiation, and decreased spine density in pyramidal neurons of the CA1, which correlates with an increased expression of synaptic markers within microglia. Additionally, these Ikzf1 deficient microglia exhibited a severe abnormal morphology in the hippocampus, which is accompanied by astrogliosis, an aberrant composition of the inflammasome, and an altered expression of disease-associated microglia molecules. Interestingly, the lack of Ikzf1 induced changes on histone 3 acetylation and methylation levels in the hippocampus. Since the lack of Ikzf1 in mice appears to induce the internalization of synaptic markers within microglia, and severe gliosis we then analyzed hippocampal Ikzf1 levels in several models of neurological disorders. Ikzf1 levels were increased in the hippocampus of these neurological models, as well as in postmortem hippocampal samples from Alzheimer's disease patients. Finally, over-expressing Ikzf1 in cultured microglia made these cells hyporeactive upon treatment with lipopolysaccharide, and less phagocytic compared to control microglia. Altogether, these results suggest that altered Ikzf1 levels in the adult hippocampus are sufficient to induce synaptic plasticity and memory deficits via altering microglial state and function.

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.

Activated PyK2 and Its Associated Molecules Transduce Cellular Signaling from the Cancerous Milieu for Cancer Metastasis

PyK2 is a member of the proline-rich tyrosine kinase and focal adhesion kinase families and is ubiquitously expressed. PyK2 is mainly activated by stimuli, such as activated Src kinases and intracellular acidic pH. The mechanism of PyK2 activation in cancer cells has been addressed extensively. The up-regulation of PyK2 through overexpression and enhanced phosphorylation is a key feature of tumorigenesis and cancer migration. In this review, we summarized the cancer milieu, including acidification and cancer-associated molecules, such as chemical reagents, interactive proteins, chemokine-related molecules, calcium channels/transporters, and oxidative molecules that affect the fate of PyK2. The inhibition of PyK2 leads to a beneficial strategy to attenuate cancer cell development, including metastasis. Thus, we highlighted the effect of PyK2 on various cancer cell types and the distribution of molecules that affect PyK2 activation. In particular, we underlined the relationship between PyK2 and cancer metastasis and its potential to treat cancer cells.

Exposure to a real traffic environment impairs brain cognition in aged mice

Traffic-related air pollution (TRAP) has been a common public health problem, which is associated with central nervous system dysfunction according to large-scale epidemiological studies. Current studies are mostly limited to artificial laboratory exposure environments and specific genetic mechanisms remain unclear. Therefore, we chose a real-world transportation environment to expose aged mice, transporting them from the laboratory to a 1-m-high dry platform inside the campus and tunnel, and the mice were exposed daily from 7 a.m. to 7 p.m. for 2, 4 and 12 weeks respectively. Compared with the control group (in campus), the memory function of mice in the experimental group (in tunnel) was significantly impaired in the Morris water maze test. TRAP exposure increased the number of activated microglia in the hippocampal DG, CA1, CA3 regions and dorsolateral prefrontal cortex (dPFC). And neuroinflammation and oxidative stress levels were up-regulated in both hippocampus and dPFC of aged mice. By screening the risk genes of Alzheimer's disease, we found the mRNA and protein levels of ABCA7 were down-regulated and those of PYK2 were up-regulated. The DNA methylation ratios increased in four CpG sites of abca7 promoter region and decreased in one CpG site of pyk2 promoter region, which were consistent with the altered expression of ABCA7 and PYK2. In conclusion, exposure to the real traffic environment impaired memory function and enhanced neuroinflammation and oxidative stress responses, which could be relevant to the altered expression and DNA methylation levels of ABCA7 and PYK2. Our work provides a new and promising understanding of the pathological mechanisms of cognitive impairment caused by traffic-related air pollution.

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.

Fyn Signaling in Ischemia-Reperfusion Injury: Potential and Therapeutic Implications

Ischemic stroke caused by arterial occlusion is the most common type of stroke and is one of the leading causes of disability and death, with the incidence increasing each year. Fyn is a nonreceptor tyrosine kinase belonging to the Src family of kinases (SFKs), which is related to many normal and pathological processes of the nervous system, including neurodevelopment and disease progression. In recent years, more and more evidence suggests that Fyn may be closely related to cerebral ischemia-reperfusion, including energy metabolism disorders, excitatory neurotoxicity, intracellular calcium homeostasis, free radical production, and the activation of apoptotic genes. This paper reviews the role of Fyn in the pathological process of cerebral ischemia-reperfusion, including neuroexcitotoxicity and neuroinflammation, to explore how Fyn affects specific signal cascades and leads to cerebral ischemia-reperfusion injury. In addition, Fyn also promotes the production of superoxide and endogenous NO, so as to quickly react to produce peroxynitrite, which may also mediate cerebral ischemia-reperfusion injury, which is discussed in this paper. Finally, we revealed the treatment methods related to Fyn inhibitors and discussed its potential as a clinical treatment for ischemic stroke.

Sevoflurane exposure during the second trimester induces neurotoxicity in offspring rats by hyperactivation of PARP-1

RATIONALE

Fetal exposure to general anesthesia may cause noteworthy neurocognitive impairment, but the mechanisms are unclear.

OBJECTIVES

Our study designed to explore the potential mechanism of neurotoxicity in offspring rats after sevoflurane exposure to the pregnant rats during the second trimester.

METHODS

Pregnant rats (G14 day) were administrated with or without 3.5% sevoflurane, 40 mg/kg 3-aminobenzamide (3-AB), inhibitor of poly ADP ribose polymerase 1 (PARP-1), or 10 mg/kg TC-2153, inhibitor of striatal-enriched phosphatase 61 (STEP61). Afterwards, the effects on expression of β-tubulin (TUJ1), neurite outgrowth inhibitor A (Nogo-A), parthanatos-related and STEP61/proline-rich tyrosine kinase 2 (Pyk2) pathway-associated proteins, and reactive oxygen species (ROS) levels were examined by immunofluorescence staining, Western blot, and dihydroethidium (DHE) staining, respectively. Moreover, morphological changes in the hippocampal CA3 region and neuronal cell death were tested by glycine silver staining and TUNEL and immunofluorescence double staining, respectively. Furthermore, spatial learning and memory functions of rats on postnatal 28-33 days (PND 28-33) were evaluated by morris water maze (MWM).

RESULTS

Mid-pregnancy exposure to sevoflurane led to excessive PARP-1 activation, poly (ADP-ribose) (PAR) polymer accumulation, apoptosis-inducing factor (AIF) nuclear translocation, and Nogo-A accumulation. Besides, sevoflurane significantly inhibited neurite growth and increased cell death in the fetal rat brain. Additionally, sevoflurane activated STEP61/Pyk2 pathway and increased ROS levels. However, 3-AB or TC-2153 significantly alleviated cell death, promoted neurites growth, and improved sevoflurane-induced spatial learning and memory impairment.

CONCLUSION

This study proposes that sevoflurane exposure during the second trimester incudes neurotoxicity in offspring rats by hyperactivation of PARP-1 via STEP61/Pyk2 pathway.

Postnatal Foxp2 regulates early psychiatric-like phenotypes and associated molecular alterations in the R6/1 transgenic mouse model of Huntington's disease

Huntington's Disease (HD) is a devastating disorder characterized by a triad of motor, psychiatric and cognitive manifestations. Psychiatric and emotional symptoms appear at early stages of the disease which are consistently described by patients and caregivers among the most disabling. Here, we show for the first time that Foxp2 is strongly associated with some psychiatric-like disturbances in the R6/1 mouse model of HD. First, 4-week-old (juvenile) R6/1 mice behavioral phenotype was characterized by an increased impulsive-like behavior and less aggressive-like behavior. In this line, we identified an early striatal downregulation of Foxp2 protein starting as soon as at postnatal day 15 that could explain such deficiencies. Interestingly, the rescue of striatal Foxp2 levels from postnatal stages completely reverted the impulsivity-phenotype and partially the social impairments concomitant with a rescue of dendritic spine pathology. A mass spectrometry study indicated that the rescue of spine loss was associated with an improvement of several altered proteins related with cytoskeleton dynamics. Finally, we reproduced and mimicked the impulsivity and social deficits in wild type mice by reducing their striatal Foxp2 expression from postnatal stages. Overall, these results imply that early postnatal reduction of Foxp2 might contribute to the appearance of some of the early psychiatric symptoms in HD.

Pyk2 inhibition attenuates hypoxic-ischemic brain injury in neonatal mice

Newborns suffering from hypoxia-ischemia (HI) brain injury still lack effective treatment. Proline-rich tyrosine kinase 2 (Pyk2) is a non-receptor tyrosine kinase, which is highly correlated with transient ischemic brain injury in adult. In this study, we investigated the role of Pyk2 in neonatal HI brain injury. HI was induced in postnatal day 7 mouse pups by unilateral common carotid artery ligation followed by hypoxic exposure. Pyk2 interference lentivirus (LV-Pyk2 shRNA) was constructed and injected into unilateral cerebral ventricle of neonatal mice before HI. Infarct volume, pathological changes, and neurological behaviors were assessed on postnatal day 8-14. We showed that the phosphorylation level of Pyk2 was significantly increased in neonatal brain after HI, whereas LV-Pyk2 shRNA injection significantly attenuated acute HI brain damage and improved neurobehavioral outcomes. In oxygen-glucose deprivation-treated cultured cortical neurons, Pyk2 inhibition significantly alleviated NMDA receptor-mediated excitotoxicity; similar results were also observed in neonatal HI brain injury. We demonstrated that Pyk2 inhibition contributes to the long-term cerebrovascular recovery assessed by laser speckle contrast imaging, but cognitive function was not obviously improved as evaluated in Morris water maze and novel object recognition tests. Thus, we constructed lentiviral LV-HIF-Pyk2 shRNA, through which HIF-1α promoter-mediated interference of Pyk2 would occur during the anoxic environment. Intracerebroventricular injection of LV-HIF-Pyk2 shRNA significantly improved long-term recovery of cognitive function in HI-treated neonatal mice. In conclusion, this study demonstrates that Pyk2 interference protects neonatal brain from hypoxic-ischemic injury. HIF-1α promoter-mediated hypoxia conditional control is a useful tool to distinguish between hypoxic period and normal period. Pyk2 is a promising drug target for potential treatment of neonatal HI brain injury.

Structural Plasticity of the Hippocampus in Neurodegenerative Diseases

Neuroplasticity is the capacity of neural networks in the brain to alter through development and rearrangement. It can be classified as structural and functional plasticity. The hippocampus is more susceptible to neuroplasticity as compared to other brain regions. Structural modifications in the hippocampus underpin several neurodegenerative diseases that exhibit cognitive and emotional dysregulation. This article reviews the findings of several preclinical and clinical studies about the role of structural plasticity in the hippocampus in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In this study, literature was surveyed using Google Scholar, PubMed, Web of Science, and Scopus, to review the mechanisms that underlie the alterations in the structural plasticity of the hippocampus in neurodegenerative diseases. This review summarizes the role of structural plasticity in the hippocampus for the etiopathogenesis of neurodegenerative diseases and identifies the current focus and gaps in knowledge about hippocampal dysfunctions. Ultimately, this information will be useful to propel future mechanistic and therapeutic research in neurodegenerative diseases.

Meridianins Rescue Cognitive Deficits, Spine Density and Neuroinflammation in the 5xFAD Model of Alzheimer's Disease

Glycogen synthase kinase 3β (GSK3β) is a core protein, with a relevant role in many neurodegenerative disorders including Alzheimer’s disease. The enzyme has been largely studied as a potential therapeutic target for several neurological diseases. Unfortunately, preclinical and clinical studies with several GSK3β inhibitors have failed due to many reasons such as excessive toxicity or lack of effects in human subjects. We previously reported that meridianins are potent GSK3β inhibitors without altering neuronal viability. In the present work, we examine whether meridianins are capable to inhibit neural GSK3β in vivo and if such inhibition induces improvements in the 5xFAD mouse model of Alzheimer’s Disease. Direct administration of meridianins in the third ventricle of 5xFAD mice induced robust improvements of recognition memory and cognitive flexibility as well as a rescue of the synaptic loss and an amelioration of neuroinflammatory processes. In summary, our study points out meridianins as a potential compound to treat neurodegenerative disorders associated with an hyperactivation of GSK3β such as Alzheimer’s disease.

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.

Mouse Modeling Dissecting Macrophage-Breast Cancer Communication Uncovered Roles of PYK2 in Macrophage Recruitment and Breast Tumorigenesis

Macrophage infiltration in mammary tumors is associated with enhanced tumor progression, metastasis, and poor clinical outcome, and considered as target for therapeutic intervention. By using different genetic mouse models, the authors show that ablation of the tyrosine kinase PYK2, either in breast cancer cells, only in the tumor microenvironment, or in both, markedly reduces the number of infiltrating tumor macrophages and concomitantly inhibits tumor angiogenesis and tumor growth. Strikingly, PYK2 ablation only in macrophages is sufficient to induce similar effects. These phenotypic changes are associated with reduced monocyte recruitment and a substantial decrease in tumor-associated macrophages (TAMs). Mechanistically, the authors show that PYK2 mediates mutual communication between breast cancer cells and macrophages through critical effects on key receptor signaling. Specifically, PYK2 ablation inhibits Notch1 signaling and consequently reduces CCL2 secretion by breast cancer cells, and concurrently reduces the levels of CCR2, CXCR4, IL-4Rα, and Stat6 activation in macrophages. These bidirectional effects modulate monocyte recruitment, macrophage polarization, and tumor angiogenesis. The expression of PYK2 is correlated with infiltrated macrophages in breast cancer patients, and its effects on macrophage infiltration and pro-tumorigenic phenotype suggest that PYK2 targeting can be utilized as an effective strategy to modulate TAMs and possibly sensitize breast cancer to immunotherapy.

RTP801/REDD1 Is Involved in Neuroinflammation and Modulates Cognitive Dysfunction in Huntington's Disease

RTP801/REDD1 is a stress-regulated protein whose levels are increased in several neurodegenerative diseases such as Parkinson's, Alzheimer's, and Huntington's diseases (HD). RTP801 downregulation ameliorates behavioral abnormalities in several mouse models of these disorders. In HD, RTP801 mediates mutant huntingtin (mhtt) toxicity in in vitro models and its levels are increased in human iPSCs, human postmortem putamen samples, and in striatal synaptosomes from mouse models of the disease. Here, we investigated the role of RTP801 in the hippocampal pathophysiology of HD. We found that RTP801 levels are increased in the hippocampus of HD patients in correlation with gliosis markers. Although RTP801 expression is not altered in the hippocampus of the R6/1 mouse model of HD, neuronal RTP801 silencing in the dorsal hippocampus with shRNA containing AAV particles ameliorates cognitive alterations. This recovery is associated with a partial rescue of synaptic markers and with a reduction in inflammatory events, especially microgliosis. Altogether, our results indicate that RTP801 could be a marker of hippocampal neuroinflammation in HD patients and a promising therapeutic target of the disease.

Pyk2 Stabilizes Striatal Medium Spiny Neuron Structure and Striatal-Dependent Action

In day-to-day life, we often choose between pursuing familiar behaviors that have been rewarded in the past or adjusting behaviors when new strategies might be more fruitful. The dorsomedial striatum (DMS) is indispensable for flexibly arbitrating between old and new behavioral strategies. The way in which DMS neurons host stable connections necessary for sustained flexibility is still being defined. An entry point to addressing this question may be the structural scaffolds on DMS neurons that house synaptic connections. We find that the non-receptor tyrosine kinase Proline-rich tyrosine kinase 2 (Pyk2) stabilizes both dendrites and spines on striatal medium spiny neurons, such that Pyk2 loss causes dendrite arbor and spine loss. Viral-mediated Pyk2 silencing in the DMS obstructs the ability of mice to arbitrate between rewarded and non-rewarded behaviors. Meanwhile, the overexpression of Pyk2 or the closely related focal adhesion kinase (FAK) enhances this ability. Finally, experiments using combinatorial viral vector strategies suggest that flexible, Pyk2-dependent action involves inputs from the medial prefrontal cortex (mPFC), but not the ventrolateral orbitofrontal cortex (OFC). Thus, Pyk2 stabilizes the striatal medium spiny neuron structure, likely providing substrates for inputs, and supports the capacity of mice to arbitrate between novel and familiar behaviors, including via interactions with the medial-prefrontal cortex.

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.

Histone deacetylase-6 modulates amyloid beta-induced cognitive dysfunction rats by regulating PTK2B

The aim of this study was to investigate the effects of histone deacetylase-6 (HDAC6) on the functional and pathological changes of the amyloid beta (Aβ)-induced cognitive dysfunction rats by regulating protein tyrosine kinase 2 beta (PTK2B). Ninety Sprague Dawley rats were randomly divided into nine groups, consisting of five experimental groups and four control groups. In five experimental groups, Aβ1-42 was infused intracerebroventricularly and 3 days later, rats in each group were infused intracerebroventricularly with tubastatin A hydrochloride (TSA), the HDAC6-specific inhibitor (Aβ + TSA group), theophylline, the HDACs agonist (Aβ + Theo group), PF431396 (PF), the PTK2B inhibitor (Aβ + PF group), the combination of PF and theophylline (Aβ + PF + Theo group), and normal saline (Aβ + normal saline group), respectively. Rats in four control groups took normal saline that was equivalent to the volume of Aβ1-42, and 3 days later, TSA (TSA group), theophylline (Theo group), (PF group, or normal saline group) was given at a volume of 5 µL for rats in each group. Our results showed that HDAC6 may not only lead to the deterioration of learning and memory abilities but also elevate the levels of Aβo and Tau phosphorylation in Aβ-induced cognitive dysfunction rats via upregulating PTK2B.

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.

Distinct regulation of hippocampal neuroplasticity and ciliary genes by corticosteroid receptors

Glucocorticoid hormones (GCs) - acting through hippocampal mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) - are critical to physiological regulation and behavioural adaptation. We conducted genome-wide MR and GR ChIP-seq and Ribo-Zero RNA-seq studies on rat hippocampus to elucidate MR- and GR-regulated genes under circadian variation or acute stress. In a subset of genes, these physiological conditions resulted in enhanced MR and/or GR binding to DNA sequences and associated transcriptional changes. Binding of MR at a substantial number of sites however remained unchanged. MR and GR binding occur at overlapping as well as distinct loci. Moreover, although the GC response element (GRE) was the predominant motif, the transcription factor recognition site composition within MR and GR binding peaks show marked differences. Pathway analysis uncovered that MR and GR regulate a substantial number of genes involved in synaptic/neuro-plasticity, cell morphology and development, behavior, and neuropsychiatric disorders. We find that MR, not GR, is the predominant receptor binding to >50 ciliary genes; and that MR function is linked to neuronal differentiation and ciliogenesis in human fetal neuronal progenitor cells. These results show that hippocampal MRs and GRs constitutively and dynamically regulate genomic activities underpinning neuronal plasticity and behavioral adaptation to changing environments.

Huntingtin and the Synapse

Huntington disease (HD) is a monogenic disease that results in a combination of motor, psychiatric and cognitive symptoms. HD is caused by a CAG trinucleotide repeat expansion in the huntingtin (HTT) gene, which results in the production of a pathogenic mutant HTT protein (mHTT). Although there is no cure at present for HD, a number of RNA-targeting therapies have recently entered clinical trials which aim to lower mHTT production through the use of antisense oligonucleotides (ASOs) and RNAi. However, many of these treatment strategies are non-selective in that they cannot differentiate between non-pathogenic wild type HTT (wtHTT) and the mHTT variant. As HD patients are already born with decreased levels of wtHTT, these genetic therapies may result in critically low levels of wtHTT. The consequence of wtHTT reduction in the adult brain is currently under debate, and here we argue that wtHTT loss is not well-tolerated at the synaptic level. Synaptic dysfunction is an extremely sensitive measure of subsequent cell death, and is known to precede neurodegeneration in numerous brain diseases including HD. The present review focuses on the prominent role of wtHTT at the synapse and considers the consequences of wtHTT loss on both pre- and postsynaptic function. We discuss how wtHTT is implicated in virtually all major facets of synaptic neurotransmission including anterograde and retrograde transport of proteins to/from terminal buttons and dendrites, neurotransmitter release, endocytic vesicle recycling, and postsynaptic receptor localization and recycling. We conclude that wtHTT presence is essential for proper synaptic function.

Identification of Full-Length Wild-Type and Mutant Huntingtin Interacting Proteins by Crosslinking Immunoprecipitation in Mice Brain Cortex

Background:

Huntington’s disease is a neurodegenerative disorder caused by a CAG expansion in the huntingtin gene, resulting in a polyglutamine expansion in the ubiquitously expressed mutant huntingtin protein.

Objective:

Here we set out to identify proteins interacting with the full-length wild-type and mutant huntingtin protein in the mice cortex brain region to understand affected biological processes in Huntington’s disease pathology.

Methods:

Full-length huntingtin with 20 and 140 polyQ repeats were formaldehyde-crosslinked and isolated via their N-terminal Flag-tag from 2-month-old mice brain cortex. Interacting proteins were identified and quantified by label-free liquid chromatography-mass spectrometry (LC-MS/MS).

Results:

We identified 30 interactors specific for wild-type huntingtin, 14 interactors specific for mutant huntingtin and 14 shared interactors that interacted with both wild-type and mutant huntingtin, including known interactors such as F8a1/Hap40. Syt1, Ykt6, and Snap47, involved in vesicle transport and exocytosis, were among the proteins that interacted specifically with wild-type huntingtin. Various other proteins involved in energy metabolism and mitochondria were also found to associate predominantly with wild-type huntingtin, whereas mutant huntingtin interacted with proteins involved in translation including Mapk3, Eif3h and Eef1a2.

Conclusion:

Here we identified both shared and specific interactors of wild-type and mutant huntingtin, which are involved in different biological processes including exocytosis, vesicle transport, translation and metabolism. These findings contribute to the understanding of the roles that wild-type and mutant huntingtin play in a variety of cellular processes both in healthy conditions and Huntington’s disease pathology.

S-Palmitoylation of Synaptic Proteins as a Novel Mechanism Underlying Sex-Dependent Differences in Neuronal Plasticity

Although sex differences in the brain are prevalent, the knowledge about mechanisms underlying sex-related effects on normal and pathological brain functioning is rather poor. It is known that female and male brains differ in size and connectivity. Moreover, those differences are related to neuronal morphology, synaptic plasticity, and molecular signaling pathways. Among different processes assuring proper synapse functions are posttranslational modifications, and among them, S-palmitoylation (S-PALM) emerges as a crucial mechanism regulating synaptic integrity. Protein S-PALM is governed by a family of palmitoyl acyltransferases, also known as DHHC proteins. Here we focused on the sex-related functional importance of DHHC7 acyltransferase because of its S-PALM action over different synaptic proteins as well as sex steroid receptors. Using the mass spectrometry-based PANIMoni method, we identified sex-dependent differences in the S-PALM of synaptic proteins potentially involved in the regulation of membrane excitability and synaptic transmission as well as in the signaling of proteins involved in the structural plasticity of dendritic spines. To determine a mechanistic source for obtained sex-dependent changes in protein S-PALM, we analyzed synaptoneurosomes isolated from DHHC7-/- (DHHC7KO) female and male mice. Our data showed sex-dependent action of DHHC7 acyltransferase. Furthermore, we revealed that different S-PALM proteins control the same biological processes in male and female synapses.

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.

Genetic variants in glutamate-, Aβ-, and tau-related pathways determine polygenic risk for Alzheimer's disease

Synapse loss is an early event in late-onset Alzheimer's disease (LOAD). In this study, we have assessed the capacity of a polygenic risk score (PRS) restricted to synapse-encoding loci to predict LOAD. We used summary statistics from the International Genetics of Alzheimer's Project genome-wide association meta-analysis of 74,046 patients for model construction and tested the "synaptic PRS" in 2 independent data sets of controls and pathologically confirmed LOAD. The mean synaptic PRS was 2.3-fold higher in LOAD than that in controls (p < 0.0001) with a predictive accuracy of 72% in the target data set (n = 439) and 73% in the validation data set (n = 136), a 5%-6% improvement compared with the APOE locus (p < 0.00001). The model comprises 8 variants from 4 previously identified (BIN1, PTK2B, PICALM, APOE) and 2 novel (DLG2, MINK1) LOAD loci involved in glutamate signaling (p = 0.01) or APP catabolism or tau binding (p = 0.005). As the simplest PRS model with good predictive accuracy to predict LOAD, we conclude that synapse-encoding genes are enriched for LOAD risk-modifying loci. The synaptic PRS could be used to identify individuals at risk of LOAD before symptom onset.

Insight into the Role of the STriatal-Enriched Protein Tyrosine Phosphatase (STEP) in A2A Receptor-Mediated Effects in the Central Nervous System

The STriatal-Enriched protein tyrosine phosphatase STEP is a brain-specific tyrosine phosphatase that plays a pivotal role in the mechanisms of learning and memory, and it has been demonstrated to be involved in several neuropsychiatric diseases. Recently, we found a functional interaction between STEP and adenosine A_2A receptor (A_2AR), a subtype of the adenosine receptor family widely expressed in the central nervous system, where it regulates motor behavior and cognition, and plays a role in cell survival and neurodegeneration. Specifically, we demonstrated the involvement of STEP in A_2AR-mediated cocaine effects in the striatum and, more recently, we found that in the rat striatum and hippocampus, as well as in a neuroblastoma cell line, the overexpression of the A_2AR, or its stimulation, results in an increase in STEP activity. In the present article we will discuss the functional implication of this interaction, trying to examine the possible mechanisms involved in this relation between STEP and A_2ARs.

Super-resolution imaging reveals extrastriatal synaptic dysfunction in presymptomatic Huntington disease mice

Synaptic structure and function are compromised prior to cell death and symptom onset in a variety of neurodegenerative diseases. In Huntington disease (HD), a CAG repeat expansion in the gene encoding the huntingtin protein results in a presymptomatic stage that typically spans multiple decades and is followed by striking degeneration of striatal tissue and the progression of debilitating motor symptoms. Many lines of evidence demonstrate that the HD presymptomatic window is associated with injurious effects to striatal synapses, many of which appear to be prerequisites to subsequent cell death. While the striatum is the most vulnerable region in the HD brain, it is widely recognized that HD is a brain-wide disease, affecting numerous extrastriatal regions that contribute to debilitating non-motor symptoms including cognitive dysfunction. Currently, we have a poor understanding of the synaptic integrity, or lack thereof, in extrastriatal regions in the presymptomatic HD brain. If early therapeutic intervention seeks to maintain healthy synaptic function, it is important to understand early HD-associated synaptopathy at a brain-wide, rather than striatal-exclusive, level. Here, we focused on the hippocampus as this structure is generally thought to be affected only in manifest HD despite the subtle cognitive deficits known to emerge in prodromal HD. We used super-resolution microscopy and multi-electrode array electrophysiology as sensitive measures of excitatory synapse structure and function, respectively, in the hippocampus of presymptomatic heterozygous HD mice (Q175FDN model). We found clear evidence for enhanced AMPA receptor subunit clustering and hyperexcitability well before the onset of a detectable HD-like behavioral phenotype. In addition, activity-dependent re-organization of synaptic protein nanostructure, and functional measures of synaptic plasticity were impaired in presymptomatic HD mice. These data demonstrate that synaptic abnormalities in the presymptomatic HD brain are not exclusive to the striatum, and highlight the need to better understand the region-dependent complexities of early synaptopathy in the HD brain.

Gene expression in the striatum of cynomolgus monkeys after chronic administration of cocaine and heroin

Cocaine and heroin cause impairment of neural plasticity in the brain including striatum. This study aimed to identify genes differentially expressed in the striatum of cynomolgus monkeys in response to cocaine and heroin. After chronic administration of cocaine and heroin in the monkeys, we performed large-scale transcriptome profiling in the striatum using RNA-Seq technology and analysed functional annotation. We found that 547 and 1238 transcripts were more than 1.5-fold up- or down-regulated in cocaine- and heroin-treated groups, respectively, compared to the control group, and 3432 transcripts exhibited differential expression between cocaine- and heroin-treated groups. Functional annotation analysis indicated that genes associated with nervous system development (NAGLU, MOBP and TTL7) and stress granule disassembly (KIF5B and KLC1) were differentially expressed in the cocaine-treated group compared to the control group, whereas gene associated with neuron apoptotic process (ERBB3) was differentially expressed in the heroin-treated group. In addition, IPA network analysis indicated that genes (TRAF6 and TRAF3IP2) associated with inflammation were increased by the chronic administration of cocaine and heroin. These results provide insight into the correlated molecular mechanisms as well as the upregulation and down-regulation of genes in the striatum after chronic exposure to cocaine and heroin.

Roles of Pyk2 in signal transduction after gonadotropin-releasing hormone receptor stimulation

The receptor for gonadotropin-releasing hormone (GnRH) is highly expressed in hypothalamic neurons. It has been reported that GnRH treatment of cultured GnRH neurons (GT1-7 cells) activated proline-rich tyrosine kinase 2 (Pyk2), and Pyk2 was involved in the activation of extracellular signal-regulated protein kinase 1 (ERK1) and ERK2 (ERK1/2). In the present study, we first examined the possibility that GnRH treatment might activate epidermal growth factor receptor (EGFR). We found that activation of EGFR after GnRH treatment for 5 min was much less than after EGF or heparin-binding EGF treatment. Next, we examined whether or not Pyk2 bound to growth factor receptor-binding protein 2 (Grb2). We overexpressed FLAG-fused Pyk2 in GT1-7 cells, and immunoprecipitated Pyk2 using an anti-FLAG antibody. The binding of Pyk2 to Grb2 was detected only after GnRH treatment. In contrast, a site-directed mutant of Pyk2 wherein tyrosine 881 was mutated to phenylalanine did not bind to Grb2. Studies with small interfering RNA and inhibitors indicated that the activation of Grb2/Ras/Raf/MEK was a major pathway to ERK1/2 activation after the short-term treatment of GT1-7 cells with GnRH.

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.