Modified hippocampal long-term potentiation in PKC gamma-mutant mice

Neurotransmitter imbalance and amygdala synaptic plasticity in lumbar disc herniation-induced chronic pain and related emotional Disturbances:A multi-omics analysis

Chronic pain due to lumbar disc herniation (LDH) significantly impairs quality of life and is often accompanied by emotional disturbances, such as anxiety and depression. Despite the recognition of these comorbidities, the underlying neural mechanisms remain unclear. This study investigates the role of neurotransmitter imbalances and key regulatory molecules in LDH-induced chronic pain and related emotional disturbances, with a focus on synaptic plasticity in the amygdala. A rat model of LDH was developed using male Sprague-Dawley rats. Behavioral assessments were conducted to evaluate pain hypersensitivity, anxiety, and depression-like behaviors. Cerebrospinal fluid (CSF) metabolomics and amygdala transcriptomics were employed to analyze neurotransmitter profiles and gene expression. In vitro experiments were conducted to explore the role of PRKCG in synaptic plasticity. Behavioral tests showed significant pain hypersensitivity and anxiety- and depression-like behavior in LDH rats. Metabolomic analysis revealed altered levels of glutamate and γ-aminobutyric acid (GABA) in the CSF, indicating neurotransmitter imbalances. Transcriptomic profiling identified changes in genes related to synaptic plasticity, including PRKCG. PRKCG knockdown led to reduced CAMKII phosphorylation and GRIA1 expression, supporting its role in modulating synaptic plasticity. This study provides evidence that neurotransmitter imbalances and alterations in synaptic plasticity within the amygdala may contribute to the persistence of chronic pain and associated emotional disturbances in LDH. PRKCG may represent a novel therapeutic target for treating both chronic pain and related emotional disturbances.

Sex specific disruptions in Protein Kinase Cγ signaling in a mouse model of Spinocerebellar Ataxia Type 14

Spinocerebellar Ataxia Type 14 (SCA14) is an autosomal dominant neurodegenerative disease caused by mutations in the gene encoding protein kinase C gamma (PKCγ), a Ca 2+ /diacylglycerol (DG)-dependent serine/threonine kinase dominantly expressed in cerebellar Purkinje cells. These mutations impair autoinhibitory constraints to increase the basal activity of the kinase, resulting in deficits in the cerebellum that are not observed upon simple deletion of the gene, and severe ataxia. To better understand the phenotypic impact of aberrant PKCγ signaling in disease pathology, we developed a knock-in murine model of the SCA14 mutation ΔF48 in PKCγ. This fully penetrant mutation is severe in humans and is mechanistically informative as it has high basal activity but is unresponsive to agonist stimulation. Genetic, behavioral, and molecular testing revealed that ΔF48 PKCγ SCA14 mice have ataxia related phenotypes and an altered cerebellar phosphoproteome, effects that are more severe in male mice. Analysis of existing human data reveal that SCA14 has a significantly earlier age of onset for males compared with females. Our data from this clinically relevant mutation suggest that enhanced basal activity of PKCγ is necessary and sufficient to cause ataxia and that treatment strategies to modulate aberrant PKCγ may be particularly beneficial in males.

Summary

New mouse model of Spinocerebellar Ataxia Type 14 containing a clinically relevant mutation in PKCγ identified underlying drivers of the disease and neuroprotection in females.

Protein kinase Cγ negatively regulates the intrinsic excitability in zebrin-negative cerebellar Purkinje cells

Protein kinase C γ (PKCγ), a neuronal isoform present exclusively in the central nervous system, is most abundantly expressed in cerebellar Purkinje cells (PCs). Targeted deletion of PKCγ causes a climbing fiber synapse elimination in developing PCs and motor deficit. However, physiological roles of PKCγ in adult mouse PCs are little understood. In this study, we aimed to unravel the roles of PKCγ in mature mouse PCs by deleting PKCγ from adult mouse PCs of PKCγfl/fl mice via cerebellar injection of adeno-associated virus (AAV) vectors expressing Cre recombinase under the control of the PC-specific L7-6 promoter. Whole cell patch-clamp recording of PCs showed higher intrinsic excitability in PCs virally lacking PKCγ [PKCγ-conditional knockout (PKCγ-cKO) PCs] than in wild-type (WT) mouse PCs in the zebrin-negative module, but not in the zebrin-positive module. AAV-mediated PKCγ re-expression in PKCγ-deficient mouse PCs in the zebrin-negative module restored the enhanced intrinsic excitability to a level comparable to that of wild-type mouse PCs. In parallel with higher intrinsic excitability, we found larger hyperpolarization-activated cyclic nucleotide-gated (HCN) channel currents in PKCγ-cKO PCs located in the zebrin-negative module, compared with those in WT mouse PCs in the same region. However, pharmacological inhibition of the HCN currents did not restore the enhanced intrinsic excitability in PKCγ-cKO PCs in the zebrin-negative module. These results suggested that PKCγ suppresses the intrinsic excitability in zebrin-negative PCs, which is likely independent of the HCN current inhibition.

Viewpoint: spinocerebellar ataxias as diseases of Purkinje cell dysfunction rather than Purkinje cell loss

Spinocerebellar ataxias (SCAs) are a group of hereditary neurodegenerative diseases mostly affecting cerebellar Purkinje cells caused by a wide variety of different mutations. One subtype, SCA14, is caused by mutations of Protein Kinase C gamma (PKCγ), the dominant PKC isoform present in Purkinje cells. Mutations in the pathway in which PKCγ is active, i.e., in the regulation of calcium levels and calcium signaling in Purkinje cells, are the cause of several other variants of SCA. In SCA14, many of the observed mutations in the PKCγ gene were shown to increase the basal activity of PKCγ, raising the possibility that increased activity of PKCγ might be the cause of most forms of SCA14 and might also be involved in the pathogenesis of SCA in related subtypes. In this viewpoint and review article we will discuss the evidence for and against such a major role of PKCγ basal activity and will suggest a hypothesis of how PKCγ activity and the calcium signaling pathway may be involved in the pathogenesis of SCAs despite the different and sometimes opposing effects of mutations affecting these pathways. We will then widen the scope and propose a concept of SCA pathogenesis which is not primarily driven by cell death and loss of Purkinje cells but rather by dysfunction of Purkinje cells which are still present and alive in the cerebellum.

The molecular memory code and synaptic plasticity: A synthesis

The most widely accepted view of memory in the brain holds that synapses are the storage sites of memory, and that memories are formed through associative modification of synapses. This view has been challenged on conceptual and empirical grounds. As an alternative, it has been proposed that molecules within the cell body are the storage sites of memory, and that memories are formed through biochemical operations on these molecules. This paper proposes a synthesis of these two views, grounded in a computational model of memory. Synapses are conceived as storage sites for the parameters of an approximate posterior probability distribution over latent causes. Intracellular molecules are conceived as storage sites for the parameters of a generative model. The model stipulates how these two components work together as part of an integrated algorithm for learning and inference.

Synaptic plasticity in hippocampal CA1 neurons of mice lacking inositol-1,4,5-trisphosphate receptor-binding protein released with IP3 (IRBIT)

In hippocampal CA1 neurons of wild-type mice, a short tetanus (15 or 20 pulses at 100 Hz) or a standard tetanus (100 pulses at 100 Hz) to a naive input pathway induces long-term potentiation (LTP) of the responses. Low-frequency stimulation (LFS; 1000 pulses at 1 Hz) 60 min after the standard tetanus reverses LTP (depotentiation [DP]), while LFS applied 60 min prior to the standard tetanus suppresses LTP induction (LTP suppression). We investigated LTP, DP, and LTP suppression of both field excitatory postsynaptic potentials and population spikes in CA1 neurons of mice lacking the inositol 1,4,5-trisphosphate (IP₃) receptor (IP₃R)-binding protein released with IP₃ (IRBIT). The mean magnitudes of LTP induced by short and standard tetanus were not different in mutant and wild-type mice. In contrast, DP and LTP suppression were attenuated in mutant mice, whereby the mean magnitude of responses after LFS or tetanus were significantly greater than in wild-type mice. These results suggest that, in hippocampal CA1 neurons, IRBIT is involved in DP and LTP suppression, but is not essential for LTP. The attenuation of DP and LTP suppression in mice lacking IRBIT indicates that this protein, released during or after priming stimulations, determines the direction of LTP expression after the delivery of subsequent stimulations.

Protein kinase Cγ in cerebellar Purkinje cells regulates Ca2+-activated large-conductance K+ channels and motor coordination

The cerebellum, the site where protein kinase C (PKC) was discovered, contains the highest amount of PKCγ in the central nervous system. PKCγ in the cerebellum is exclusively confined to Purkinje cells (PCs), sole outputs from the cerebellar cortex. Systemic PKCγ-knockout mice show impaired motor coordination; however, the cause of motor defects remains unknown. Here we show that activation of PKCγ suppresses the Ca²⁺-activated large-conductance K⁺ (BK) channels located along the PC dendrites. A consequential increase in the membrane resistance attenuates electrical signal decay during propagation, resulting in an altered complex spike waveform. Our results suggest that synaptically activated PKCγ in PCs plays a critical role in motor coordination by negative modulation of BK currents.

The cerebellum, the site where protein kinase C (PKC) was first discovered, contains the highest amount of PKC in the central nervous system, with PKCγ being the major isoform. Systemic PKCγ-knockout (KO) mice showed impaired motor coordination and deficient pruning of surplus climbing fibers (CFs) from developing cerebellar Purkinje cells (PCs). However, the physiological significance of PKCγ in the mature cerebellum and the cause of motor incoordination remain unknown. Using adeno-associated virus vectors targeting PCs, we showed that impaired motor coordination was restored by re-expression of PKCγ in mature PKCγ-KO mouse PCs in a kinase activity–dependent manner, while normal motor coordination in mature Prkcg^fl/fl mice was impaired by the Cre-dependent removal of PKCγ from PCs. Notably, the rescue or removal of PKCγ from mature PKCγ-KO or Prkcg^fl/fl mice, respectively, did not affect the CF innervation profile of PCs, suggesting the presence of a mechanism distinct from multiple CF innervation of PCs for the motor defects in PKCγ-deficient mice. We found marked potentiation of Ca²⁺-activated large-conductance K⁺ (BK) channel currents in PKCγ-deficient mice, as compared to wild-type mice, which decreased the membrane resistance, resulting in attenuation of the electrical signal during the propagation and significant alterations of the complex spike waveform. These changes in PKCγ-deficient mice were restored by the rescue of PKCγ or pharmacological suppression of BK channels. Our results suggest that PKCγ is a critical regulator that negatively modulates BK currents in PCs, which significantly influences PC output from the cerebellar cortex and, eventually, motor coordination.

Fluid markers of synapse degeneration in synucleinopathies

The abnormal accumulation of α-synuclein in the brain is a common feature of Parkinson's disease (PD), PD dementia (PDD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), and synucleinopathies that present with overlapping but distinct clinical symptoms that include motor and cognitive deficits. Synapse degeneration is the crucial neuropathological event in these synucleinopathies and the neuropathological correlate of connectome dysfunction. The cognitive and motor deficits resulting from the connectome dysfunction are currently measured by scalar systems that are limited in their sensitivity and largely subjective. Ideally, a marker of synapse degeneration would correlate with measures of cognitive or motor impairment, and could therefore be used as a more objective, surrogate biomarker of the core clinical features of these diseases. Furthermore, an objective surrogate biomarker that can detect and monitor the progression of synapse degeneration would improve patient management and clinical trial design, and could provide a measure of therapeutic response. Here, we review the published findings relating to candidate biomarkers of synapse degeneration in PD, PDD, DLB, and MSA patient-derived biofluids and discuss the findings in the context of the mechanisms associated with α-synuclein-mediated synapse degeneration. Understanding these mechanisms is essential not only for discovery of biomarkers, but also to improve our understanding of the earliest changes in disease pathogenesis of synucleinopathies.

Conventional protein kinase C in the brain: repurposing cancer drugs for neurodegenerative treatment?

Protein Kinase C (PKC) isozymes are tightly regulated kinases that transduce a myriad of signals from receptor-mediated hydrolysis of membrane phospholipids. They play an important role in brain physiology, and dysregulation of PKC activity is associated with neurodegeneration. Gain-of-function mutations in PKCα are associated with Alzheimer's disease (AD) and mutations in PKCγ cause spinocerebellar ataxia (SCA) type 14 (SCA14). This article presents an overview of the role of the conventional PKCα and PKCγ in neurodegeneration and proposes repurposing PKC inhibitors, which failed in clinical trials for cancer, for the treatment of neurodegenerative diseases.

Visualization of mandibular movement relative to the maxilla during mastication in mice: integration of kinematic analysis and reconstruction of a three-dimensional model of the maxillofacial structure

BACKGROUND

Mastication is one of the most fundamental functions for the conservation of human life. To clarify the pathogenetic mechanism of various oral dysfunctions, the demand for devices for evaluating stomatognathic function has been increasing. The aim of the present study was to develop a system to reconstruct and visualize 3-dimensional (3D) mandibular movements relative to the maxilla, including dynamic transition of occlusal contacts between the upper and lower dentitions during mastication in mice.

METHODS

First, mandibular movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, 3D models of maxillofacial structure were reconstructed from micro-computed tomography images. Movement trajectories of anatomical landmark points on the mandible were then reproduced by integrating the kinematic data of mandibular movements with the anatomical data of maxillofacial structures. Lastly, 3D surface images of the upper dentition with the surrounding maxillofacial structures were transferred to each of the motion capture images to reproduce mandibular movements relative to the maxilla. We also performed electromyography (EMG) of masticatory muscles associated with mandibular movements.

RESULTS

The developed system could reproduce the 3D movement trajectories of arbitrary points on the mandible, such as incisor, molars and condylar points with high accuracy and could visualize dynamic transitions of occlusal contacts between upper and lower teeth associated with mandibular movements.

CONCLUSIONS

The proposed system has potential to elucidate the mechanisms underlying motor coordination of masticatory muscles and to clarify their roles during mastication by taking advantage of the capability to record EMG data synchronously with mandibular movements. Such insights will enhance our understanding of the pathogenesis and diagnosis of oral motor disorders by allowing comparisons between normal mice and genetically modified mice with oral behavioral dysfunctions.

Protein Kinase C-Gamma Knockout Mice Show Impaired Hippocampal Short-Term Memory While Preserved Long-Term Memory

The brain encodes, stores, and retrieves relevant information in the form of memories that are classified as short-term (STM) and long-term memories (LTM) depending on the interval between acquisition and retrieval. It is classically accepted that STM undergo a consolidation process to form LTM, but the molecular determinants involved are not well understood. Among the molecular components relevant for memory formation, we focused our attention on the protein kinase C (PKC) family of enzymes since they control key aspects of the synaptic plasticity and memory. Within the different PKC isoforms, PKC-gamma has been specifically associated with learning and memory since mice lacking this isoform (PKC-gamma KO mice) showed mild cognitive impairment and deficits in hippocampal synaptic plasticity. We now reveal that PKC-gamma KO mice present a severe impairment in hippocampal-dependent STM using different memory tests including the novel object-recognition and novel place-recognition, context fear conditioning and trace fear conditioning. In contrast, no differences between genotypes were observed in an amygdala-dependent test, the delay fear conditioning. Strikingly, all LTM tasks that could be assessed 24 h after acquisition were not perturbed in the KO mice. The analysis of c-Fos expression in several brain areas after trace fear conditioning acquisition showed a blunted response in the dentate gyrus of PKC-gamma KO mice compared with WT mice, but such differences between genotypes were absent when the amygdala or the prefrontal cortex were examined. In the hippocampus, PKC-gamma was found to translocate to the membrane after auditory trace, but not after delay fear conditioning. Together, these results indicate that PKC-gamma dysfunction affects specifically hippocampal-dependent STM performance and disclose PKC-gamma as a molecular player differentially involved in STM and LTM processes.

Precise Regulation of the Basal PKCγ Activity by DGKγ Is Crucial for Motor Coordination

Diacylglycerol kinase γ (DGKγ) is a lipid kinase to convert diacylglycerol (DG) to phosphatidic acid (PA) and indirectly regulates protein kinase C γ (PKCγ) activity. We previously reported that the basal PKCγ upregulation impairs cerebellar long-term depression (LTD) in the conventional DGKγ knockout (KO) mice. However, the precise mechanism in impaired cerebellar LTD by upregulated PKCγ has not been clearly understood. Therefore, we first produced Purkinje cell-specific DGKγ KO (tm1d) mice to investigate the specific function of DGKγ in Purkinje cells and confirmed that tm1d mice showed cerebellar motor dysfunction in the rotarod and beam tests, and the basal PKCγ upregulation but not PKCα in the cerebellum of tm1d mice. Then, the LTD-induced chemical stimulation, K-glu (50 mM KCl + 100 µM, did not induce phosphorylation of PKCα and dissociation of GluR2 and glutamate receptor interacting protein (GRIP) in the acute cerebellar slices of tm1d mice. Furthermore, treatment with the PKCγ inhibitor, scutellarin, rescued cerebellar LTD, with the phosphorylation of PKCα and the dissociation of GluR2 and GRIP. In addition, nonselective transient receptor potential cation channel type 3 (TRPC3) was negatively regulated by upregulated PKCγ. These results demonstrated that DGKγ contributes to cerebellar LTD by regulation of the basal PKCγ activity.

Synthesis of hydrophilic caged DAG-lactones for chemical biology applications

The 6-bromo-7-hydroxy-coumarin-4-ylmethyl (Bhc) group has been used widely in cage chemistry because of its high molar absorptivity and photolytic efficiency. One of the drawbacks of coumarins however is their low aqueous solubility. Aqueous solubility is important in the behavior of caged compounds because hydrophobic caged compounds might be aggregated in physiological conditions and consequently the photocleavage would be impaired. The 8-azacoumarin-4-ylmethyl derivatives with bromine (8-aza-Bhc) or iodine (8-aza-Ihc), which were previously developed in this laboratory, have aqueous solubilities that are higher than those of related coumarins. Here, to improve the hydrophilicity and management of caged diacylglycerol lactones (DAG-lactones), 8-aza-Bhc and 8-aza-Ihc were introduced into the DAG-lactone structure. The synthesized caged compounds showed high hydrophilicity compared with the parent Bhc-caged DAG-lactone, and the 8-aza-Ihc-caged DAG-lactone (2) showed excellent photolytic efficiency, which allows rapid release of the DAG-lactone (1) by brief photoirradiation. The 8-aza-7-hydroxy-6-iodo-coumarin-4-ylmethyl group might be useful for caging of bioactive compounds, especially hydrophobic compounds.

Alterations of transcriptome signatures in head trauma-related neurodegenerative disorders

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease that is associated with repetitive traumatic brain injury (TBI). CTE is known to share similar neuropathological features with Alzheimer’s disease (AD), but little is known about the molecular properties in CTE. To better understand the neuropathological mechanism of TBI-related disorders, we conducted transcriptome sequencing analysis of CTE including AD and CTE with AD (CTE/AD) post-mortem human brain samples. Through weighted gene co-expression network analysis (WGCNA) and principal component analysis (PCA), we characterized common and unique transcriptome signatures among CTE, CTE/AD, and AD. Interestingly, synapse signaling-associated gene signatures (such as synaptotagmins) were commonly down-regulated in CTE, CTE/AD, and AD. Quantitative real-time PCR (qPCR) and Western blot analyses confirmed that the levels of synaptotagmin 1 (SYT1) were markedly decreased in CTE and AD compared to normal. In addition, calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase A (PKA), protein kinase C (PKC), and AMPA receptor genes that play a pivotal role in memory function, were down-regulated in head trauma-related disorders. On the other hand, up-regulation of cell adhesion molecules (CAMs) associated genes was only found in CTE. Our results indicate that dysregulation of synaptic transmission- and memory function-related genes are closely linked to the pathology of head injury-related disorder and AD. Alteration of CAMs-related genes may be specific pathological markers for the CTE pathology.

Proteomic analysis of synaptic protein turnover in the anterior cingulate cortex after nerve injury

Synaptic proteins play an important role for the regulation of synaptic plasticity. Numerous studies have identified and revealed individual synaptic protein functions using protein overexpression or deletion. In neuropathic pain nociceptive stimuli conveyed from the periphery repetitively stimulate neurons in the central nerve system, brain and spinal cord. Neuronal activities change the turnover (synthesis and degradation) rate of synaptic proteins. Thus, the analysis of synaptic protein turnover rather than just expression level change is critical for studying the role of synaptic proteins in synaptic plasticity. Here, we analyzed synaptosomal proteome in the anterior cingulate cortex (ACC) to identify protein turnover rate changes caused by peripheral nerve injury. Whereas PKCγ levels were not altered, we found that the protein’s turnover rate decreased after peripheral nerve injury. Our results suggest that postsynaptic PKCγ synthesized by neuronal activities in the ACC is translocated to the postsynaptic membrane with an extended half-life.

cPKCγ alleviates ischemic injury through modulating synapsin Ia/b phosphorylation in neurons of mice

Conventional protein kinase C (cPKC)γ and synapsin Ia/b have been implicated in the development of ischemic stroke, but their relationships and functions are unclear. In the present study, the oxygen-glucose deprivation (OGD)-induced ischemic insult in primary cultured cortical neurons in vitro and middle cerebral artery occlusion (MCAO)-induced ischemic stroke model in vivo were used to elucidate the function of cPKCγ and its modulation on synapsin Ia/b phosphorylation in ischemic stroke. We found that cPKCγ knockout significantly increased the infarct volume of mice after 1 h MCAO/72 h reperfusion by using triphenyltetrazolium chloride (TTC) staining. In the primarily cultured cortical neurons, cPKCγ knockout also aggravated the OGD-induced cell death and morphological damage of neurites, while cPKCγ restoration could alleviate the ischemic injury. Among the five phosphorylation sites of synapsin Ia/b, only the phosphorylation levels of Ser549 and 553 could be modulated by cPKCγ in neurons following 0.5 h OGD/24 h reoxygenation. In addition, we found that cPKCγ and synapsin Ia/b could be reciprocally co-immunoprecipitated in the cerebral cortex of MCAO mice. Taken together, we proposed that cPKCγ alleviates ischemic injury through modulating Ser549/553- synapsin Ia/b phosphorylation in neurons of mice.

PKCα integrates spatiotemporally distinct Ca2+ and autocrine BDNF signaling to facilitate synaptic plasticity

The Protein Kinase C (PKC) enzymes have long been established as critical for synaptic plasticity. However, it is unknown whether Ca²⁺-dependent PKC isozymes are activated in dendritic spines during plasticity, and if so, how this synaptic activity is encoded by PKC. Here, using newly-developed, isozyme-specific sensors, we demonstrate that classic isozymes are activated to varying degrees and with unique kinetics. PKCα is activated robustly and rapidly in stimulated spines and is the only isozyme required for structural plasticity. This specificity, depends on a PDZ-binding domain present only in PKCα. The activation of PKCα during plasticity requires both NMDAR Ca²⁺-flux and autocrine BDNF-TrkB signaling, two pathways that differ vastly in their spatiotemporal scales of signaling. Our results suggest that by integrating these signals, PKCα combines a measure of recent, nearby synaptic plasticity with local synaptic input, enabling complex cellular computations such as heterosynaptic facilitation of plasticity necessary for efficient hippocampal-dependent learning.

Non-canonical Opioid Signaling Inhibits Itch Transmission in the Spinal Cord of Mice

Chronic itch or pruritus is a debilitating disorder that is refractory to conventional anti-histamine treatment. Kappa opioid receptor (KOR) agonists have been used to treat chronic itch, but the underlying mechanism remains elusive. Here, we find that KOR and gastrin-releasing peptide receptor (GRPR) overlap in the spinal cord, and KOR activation attenuated GRPR-mediated histamine-independent acute and chronic itch in mice. Notably, canonical KOR-mediated Gαi signaling is not required for desensitizing GRPR function. In vivo and in vitro studies suggest that KOR activation results in the translocation of Ca2+-independent protein kinase C (PKC)δ from the cytosol to the plasma membrane, which in turn phosphorylates and inhibits GRPR activity. A blockade of phospholipase C (PLC) in HEK293 cells prevented KOR-agonist-induced PKCδ translocation and GRPR phosphorylation, suggesting a role of PLC signaling in KOR-mediated GRPR desensitization. These data suggest that a KOR-PLC-PKCδ-GRPR signaling pathway in the spinal cord may underlie KOR-agonists-induced anti-pruritus therapies.

Hippocampal expression of a virus-derived protein impairs memory in mice

The analysis of the biology of neurotropic viruses, notably of their interference with cellular signaling, provides a useful tool to get further insight into the role of specific pathways in the control of behavioral functions. Here, we exploited the natural property of a viral protein identified as a major effector of behavioral disorders during infection. We used the phosphoprotein (P) of Borna disease virus, which acts as a decoy substrate for protein kinase C (PKC) when expressed in neurons and disrupts synaptic plasticity. By a lentiviral-based strategy, we directed the singled-out expression of P in the dentate gyrus of the hippocampus and we examined its impact on mouse behavior. Mice expressing the P protein displayed increased anxiety and impaired long-term memory in contextual and spatial memory tasks. Interestingly, these effects were dependent on P protein phosphorylation by PKC, as expression of a mutant form of P devoid of its PKC phosphorylation sites had no effect on these behaviors. We also revealed features of behavioral impairment induced by P protein expression but that were independent of its phosphorylation by PKC. Altogether, our findings provide insight into the behavioral correlates of viral infection, as well as into the impact of virus-mediated alterations of the PKC pathway on behavioral functions.

Integrative Proteomics-Metabolomics Strategy for Pathological Mechanism of Vascular Depression Mouse Model

Vascular depression (VD), a subtype of depression, is caused by vascular diseases or cerebrovascular risk factors. Recently, the proportion of VD patients has increased significantly, which severely affects their quality of life. However, the current pathogenesis of VD has not yet been fully understood, and the basic research is not adequate. In this study, on the basis of the combination of LC-MS-based proteomics and metabolomics, we aimed to establish a protein metabolism regulatory network in a murine VD model to elucidate a more comprehensive impact of VD on organisms. We detected 44 metabolites and 304 proteins with different levels in the hippocampus samples from VD mice using a combination of metabolomic and proteomics analyses with an isobaric tags for relative and absolute quantification (iTRAQ) method. We constructed a protein-to-metabolic regulatory network by correlating and integrating the differential metabolites and proteins using ingenuity pathway analysis. Then we quantitatively validated the levels of the bimolecules shown in the bioinformatics analysis using LC-MS/MS and Western blotting. Validation results suggested changes in the regulation of neuroplasticity, transport of neurotransmitters, neuronal cell proliferation and apoptosis, and disorders of amino acids, lipids and energy metabolism. These proteins and metabolites involved in these dis-regulated pathways will provide a more targeted and credible direction to study the mechanism of VD. Therefore, this paper presents an approach and strategy that was applied in integrative proteomics and metabolomics for research and screening potential targets and biomarkers of VD, which could be more precise and credible in a field lacking adequate basic research.

PKCβ: Expanding role in hepatic adaptation of cholesterol homeostasis to dietary fat/cholesterol

Cholesterol homeostasis relies on an intricate network of cellular processes whose deregulation in response to Western type high-fat/cholesterol diets can lead to several life-threatening pathologies. Significant advances have been made in resolving the molecular identity and regulatory function of transcription factors sensitive to fat, cholesterol, or bile acids, but whether body senses the presence of both fat and cholesterol simultaneously is not known. Assessing the impact of a high-fat/cholesterol load, rather than an individual component alone, on cholesterol homeostasis is more physiologically relevant because Western diets deliver both fat and cholesterol at the same time. Moreover, dietary fat and dietary cholesterol are reported to act synergistically to impair liver cholesterol homeostasis. A key insight into the role of protein kinase C-β (PKCβ) in hepatic adaptation to high-fat/cholesterol diets was gained recently through the use of knockout mice. The emerging evidence indicates that PKCβ is an important regulator of cholesterol homeostasis that ensures normal adaptation to high-fat/cholesterol intake. Consistent with this function, high-fat/cholesterol diets induce PKCβ expression and signaling in the intestine and liver, while systemic PKCβ deficiency promotes accumulation of cholesterol in the liver and bile. PKCβ disruption results in profound dysregulation of hepatic cholesterol and bile homeostasis and imparts sensitivity to cholesterol gallstone formation. The available results support involvement of a two-pronged mechanism by which intestine and liver PKCβ signaling converge on liver ERK1/2 to dictate diet-induced cholesterol and bile acid homeostasis. Collectively, PKCβ is an integrator of dietary fat/cholesterol signal and mediates changes to cholesterol homeostasis.

Rubinstein-Taybi Syndrome and Epigenetic Alterations

Rubinstein-Taybi syndrome (RSTS) is a rare genetic disorder in humans characterized by growth and psychomotor delay, abnormal gross anatomy, and mild to severe mental retardation (Rubinstein and Taybi, Am J Dis Child 105:588-608, 1963, Hennekam et al., Am J Med Genet Suppl 6:56-64, 1990). RSTS is caused by de novo mutations in epigenetics-associated genes, including the cAMP response element-binding protein (CREBBP), the gene-encoding protein referred to as CBP, and the EP300 gene, which encodes the p300 protein, a CBP homologue. Recent studies of the epigenetic mechanisms underlying cognitive functions in mice provide direct evidence for the involvement of nuclear factors (e.g., CBP) in the control of higher cognitive functions. In fact, a role for CBP in higher cognitive function is suggested by the finding that RSTS is caused by heterozygous mutations at the CBP locus (Petrij et al., Nature 376:348-351, 1995). CBP was demonstrated to possess an intrinsic histone acetyltransferase activity (Ogryzko et al., Cell 87:953-959, 1996) that is required for CREB-mediated gene expression (Korzus et al., Science 279:703-707, 1998). The intrinsic protein acetyltransferase activity in CBP might directly destabilize promoter-bound nucleosomes, facilitating the activation of transcription. Due to the complexity of developmental abnormalities and the possible genetic compensation associated with this congenital disorder, however, it is difficult to establish a direct role for CBP in cognitive function in the adult brain. Although aspects of the clinical presentation in RSTS cases have been extensively studied, a spectrum of symptoms found in RSTS patients can be accessed only after birth, and, thus, prenatal genetic tests for this extremely rare genetic disorder are seldom considered. Even though there has been intensive research on the genetic and epigenetic function of the CREBBP gene in rodents, the etiology of this devastating congenital human disorder is largely unknown.

Potentiation of Schaffer-Collateral CA1 Synaptic Transmission by eEF2K and p38 MAPK Mediated Mechanisms

The elongation factor 2 kinase (eEF2K), likewise known as CaMKIII, has been demonstrated to be involved in antidepressant responses of NMDA receptor antagonists. Even so, it remains open whether direct inhibition of eEF2K without altering up-stream or other signaling pathways affects hippocampal synaptic transmission and neuronal network synchrony. Inhibition of eEF2K by the selective and potent eEF2K inhibitor A-484954 induced a fast pre-synaptically mediated enhancement of synaptic transmission and synchronization of neural network activity. The eEF2K-inhibition mediated potentiation of synaptic transmission of hippocampal CA1 neurons is most notably independent of protein synthesis and does not rely on protein kinase C, protein kinase A or mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase 1/2. Moreover, the strengthening of synaptic transmission in the response to the inhibition of eEF2K was strongly attenuated by the inhibition of p38 MAPK. In addition, we show the involvement of barium-sensitive and more specific the TWIK-related potassium-1 (TREK-1) channels in the eEF2K-inhibition mediated potentiation of synaptic transmission. These findings reveal a novel pathway of eEF2K mediated regulation of hippocampal synaptic transmission. Further research is required to study whether such compounds could be beneficial for the development of mood disorder treatments with a fast-acting antidepressant response.

LysoPCs induce Hck- and PKCδ-mediated activation of PKCγ causing p47phox phosphorylation and membrane translocation in neutrophils

Lysophosphatidylcholines (lysoPCs) are effective polymorphonuclear neutrophil (PMN) priming agents implicated in transfusion-related acute lung injury (TRALI). LysoPCs cause ligation of the G2A receptor, cytosolic Ca²⁺ flux, and activation of Hck. We hypothesize that lysoPCs induce Hck-dependent activation of protein kinase C (PKC), resulting in phosphorylation and membrane translocation of 47 kDa phagocyte oxidase protein (p47^phox). PMNs, human or murine, were primed with lysoPCs and were smeared onto slides and examined by digital microscopy or separated into subcellular fractions or whole-cell lysates. Proteins were immunoprecipitated or separated by polyacrylamide gel electrophoresis and immunoblotted for proteins of interest. Wild-type (WT) and PKCγ knockout (KO) mice were used in a 2-event model of TRALI. LysoPCs induced Hck coprecipitation with PKCδ and PKCγ and the PKCδ:PKCγ complex also had a fluorescence resonance energy transfer (FRET)⁺ interaction with lipid rafts and Wiskott-Aldrich syndrome protein family verprolin-homologous protein 2 (WAVE2). PKCγ then coprecipitated with p47^phox Immunoblotting, immunoprecipitation (IP), specific inhibitors, intracellular depletion of PKC isoforms, and PMNs from PKCγ KO mice demonstrated that Hck elicited activation/Tyr phosphorylation (Tyr311 and Tyr525) of PKCδ, which became Thr phosphorylated (Thr507). Activated PKCδ then caused activation of PKCγ, both by Tyr phosphorylation (Τyr514) and Ser phosphorylation, which induced phosphorylation and membrane translocation of p47^phox In PKCγ KO PMNs, lysoPCs induced Hck translocation but did not evidence a FRET⁺ interaction between PKCδ and PKCγ nor prime PMNs. In WT mice, lysoPCs served as the second event in a 2-event in vivo model of TRALI but did not induce TRALI in PKCγ KO mice. We conclude that lysoPCs prime PMNs through Hck-dependent activation of PKCδ, which stimulates PKCγ, resulting in translocation of phosphorylated p47^phox.

Protective Role of Quercetin in Cadmium-Induced Cholinergic Dysfunctions in Rat Brain by Modulating Mitochondrial Integrity and MAP Kinase Signaling

With the increasing evidences of cadmium-induced cognitive deficits associated with brain cholinergic dysfunctions, the present study aimed to decipher molecular mechanisms involved in the neuroprotective efficacy of quercetin in rats. A decrease in the binding of cholinergic-muscarinic receptors and mRNA expression of cholinergic receptor genes (M1, M2, and M4) was observed in the frontal cortex and hippocampus on exposure of rats to cadmium (5.0 mg/kg body weight, p.o.) for 28 days compared to controls. Cadmium exposure resulted to decrease mRNA and protein expressions of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) and enhance reactive oxygen species (ROS) generation associated with mitochondrial dysfunctions, ultrastructural changes, and learning deficits. Enhanced apoptosis, as evidenced by alterations in key proteins involved in the pro- and anti-apoptotic pathway and mitogen-activated protein (MAP) kinase signaling, was evident on cadmium exposure. Simultaneous treatment with quercetin (25 mg/kg body weight, p.o.) resulted to protect cadmium-induced alterations in cholinergic-muscarinic receptors, mRNA expression of genes (M1, M2, and M4), and expression of ChAT and AChE. The protective effect on brain cholinergic targets was attributed to the antioxidant potential of quercetin, which reduced ROS generation and protected mitochondrial integrity by modulating proteins involved in apoptosis and MAP kinase signaling. The results exhibit that quercetin may modulate molecular targets involved in brain cholinergic signaling and attenuate cadmium neurotoxicity.

Protein kinase C and chemical-induced abnormal palate development

The protein kinase C (PKC) family of proteins mediates the action of growth factors and other ligands by activating a network of transcription factors that bind to TRE sequences in the promoters of many genes that regulate cell proliferation, differentiation, extracellular matrix synthesis, apoptosis and others in a cell type-, isozymeand context-specific manner. The critical role of PKC in embryonic development is indicated by early death of embryos in which one or more of these isozymes are inactivated. Our studies together with others show that palatal PKC signalling is functional and may be essential for normal palate development. Although single gene knockouts have failed to exhibit the cleft palate (CP) phenotype, owing to compensation by other kinases, many chemicals including the mycotoxin, secalonic acid D, disrupt palatal PKC signalling leading to altered palatal mesenchymal gene expression. The potential relevance of such effects to chemical-induced CP is discussed.

REVIEW ■ : LTP and LTD: Dynamic and Interactive Processes of Synaptic Plasticity

Long-lasting, activity-dependent changes in the efficacy of synaptic transmission are considered to be of fundamental importance for the storage of information and for the development of neural circuitry. The leading experimental model for such a change has been long-term potentiation (LTP), a long-lasting increase in synaptic strength. Intensive experimental analysis of LTP in the hippocampus has resulted in a detailed description of the initial steps responsible for its generation. Recently, a form of long-term depression (LTD) in the hippocampus has been described and examined. It shares several mechanistic features with LTP and appears to be able to reverse LTP. The intracellular second messenger systems that are required to generate and maintain LTP and LTD have been difficult to identify definitively. Leading candidates include diffusible intercellular messengers as well as protein kinases and protein phosphatases, the activities of which may converge at the level of specific phosphoproteins. In addition to delineating the cellular mechanisms under lying LTP and LTD, investigators also are beginning to clarify the roles they play in real learning and memory. The Neuroscientist 1:35-42, 1995

Territories of heterologous inputs onto Purkinje cell dendrites are segregated by mGluR1-dependent parallel fiber synapse elimination

In Purkinje cells (PCs) of the cerebellum, a single "winner" climbing fiber (CF) monopolizes proximal dendrites, whereas hundreds of thousands of parallel fibers (PFs) innervate distal dendrites, and both CF and PF inputs innervate a narrow intermediate domain. It is unclear how this segregated CF and PF innervation is established on PC dendrites. Through reconstruction of dendritic innervation by serial electron microscopy, we show that from postnatal day 9-15 in mice, both CF and PF innervation territories vigorously expand because of an enlargement of the region of overlapping innervation. From postnatal day 15 onwards, segregation of these territories occurs with robust shortening of the overlapping proximal region. Thus, innervation territories by the heterologous inputs are refined during the early postnatal period. Intriguingly, this transition is arrested in mutant mice lacking the type 1 metabotropic glutamate receptor (mGluR1) or protein kinase Cγ (PKCγ), resulting in the persistence of an abnormally expanded overlapping region. This arrested territory refinement is rescued by lentivirus-mediated expression of mGluR1α into mGluR1-deficient PCs. At the proximal dendrite of rescued PCs, PF synapses are eliminated and free spines emerge instead, whereas the number and density of CF synapses are unchanged. Because the mGluR1-PKCγ signaling pathway is also essential for the late-phase of CF synapse elimination, this signaling pathway promotes the two key features of excitatory synaptic wiring in PCs, namely CF monoinnervation by eliminating redundant CF synapses from the soma, and segregated territories of CF and PF innervation by eliminating competing PF synapses from proximal dendrites.

Induction of long-term potentiation and long-term depression is cell-type specific in the spinal cord

This study shows that the direction of synaptic plastic changes in the spinal cord is cell-type specific in response to nociceptive input.

The underlying mechanism of chronic pain is believed to be changes in excitability in spinal dorsal horn (DH) neurons that respond abnormally to peripheral input. Increased excitability in pain transmission neurons, and depression of inhibitory neurons, are widely recognized in the spinal cord of animal models of chronic pain. The possible occurrence of 2 parallel but opposing forms of synaptic plasticity, long-term potentiation (LTP) and long-term depression (LTD) was tested in 2 types of identified DH neurons using whole-cell patch-clamp recordings in mouse spinal cord slices. The test stimulus was applied to the sensory fibers to evoke excitatory postsynaptic currents in identified spinothalamic tract neurons (STTn) and GABAergic neurons (GABAn). Afferent conditioning stimulation (ACS) applied to primary afferent fibers with various stimulation parameters induced LTP in STTn but LTD in GABAn, regardless of stimulation parameters. These opposite responses were further confirmed by simultaneous dual patch-clamp recordings of STTn and GABAn from a single spinal cord slice. Both the LTP in STTn and the LTD in GABAn were blocked by an NMDA receptor antagonist, AP5, or an intracellular Ca²⁺ chelator, BAPTA. Both the pattern and magnitude of intracellular Ca²⁺ after ACS were almost identical between STTn and GABAn based on live-cell calcium imaging. The results suggest that the intense sensory input induces an NMDA receptor-dependent intracellular Ca²⁺ increase in both STTn and GABAn, but produces opposing synaptic plasticity. This study shows that there is cell type–specific synaptic plasticity in the spinal DH.

Extracellular ATP modulates synaptic plasticity induced by activation of metabotropic glutamate receptors in the hippocampus

Synaptic plasticity is believed to be a cellular mechanism for memory formation in the brain. It has been known that the metabotropic glutamate receptor (mGluR) is required for persistent forms of memory and induction of synaptic plasticity. Application of mGluR agonists induces synaptic plasticity in the absence of electrical conditioning stimulation, such as high or low frequency stimulation. The direction of the mGluR-induced synaptic plasticity, i.e., either long-term potentiation (LTP) or long-term-depression (LTD), is dependent on whether N-methyl-D-aspartate receptors (NMDARs) are co-activated with mGluRs. ATP has modulatory effects on neuronal functions and, in particular, there is increasing evidence that it plays a crucial role in synaptic plasticity. LTP can be induced by application of ATP, and this effect is inhibited by NMDAR antagonist. Although cooperative effects of NMDARs and mGluRs and of NMDARs and extracellular ATP in synaptic plasticity have been revealed, the effect of extracellular ATP on mGluR-induced synaptic plasticity is unknown. In this article, we summarize published data on mGluR- and ATP-induced synaptic plasticity, and present new data showing that extracellular ATP facilitates both the LTP and LTD induced by mGluR activation.

Absence of catalytic domain in a putative protein kinase C (PkcA) suppresses tip dominance in Dictyostelium discoideum

A number of organisms possess several isoforms of protein kinase C but little is known about the significance of any specific isoform during embryogenesis and development. To address this we characterized a PKC ortholog (PkcA; DDB_G0288147) in Dictyostelium discoideum. pkcA expression switches from prestalk in mound to prespore in slug, indicating a dynamic expression pattern. Mutants lacking the catalytic domain of PkcA (pkcA(-)) did not exhibit tip dominance. A striking phenotype of pkcA- was the formation of an aggregate with a central hollow, and aggregates later fragmented to form small mounds, each becoming a fruiting body. Optical density wave patterns of cAMP in the late aggregates showed several cAMP wave generation centers. We attribute these defects in pkcA(-) to impaired cAMP signaling, altered cell motility and decreased expression of the cell adhesion molecules - CadA and CsaA. pkcA(-) slugs showed ectopic expression of ecmA in the prespore region. Further, the use of a PKC-specific inhibitor, GF109203X that inhibits the activity of catalytic domain phenocopied pkcA(-).

A Knockout Experiment: Disciplinary Divides and Experimental Skill in Animal Behaviour Genetics

In the early 1990s, a set of new techniques for manipulating mouse DNA allowed researchers to 'knock out' specific genes and observe the effects of removing them on a live mouse. In animal behaviour genetics, questions about how to deploy these techniques to study the molecular basis of behaviour became quite controversial, with a number of key methodological issues dissecting the interdisciplinary research field along disciplinary lines. This paper examines debates that took place during the 1990s between a predominately North American group of molecular biologists and animal behaviourists around how to design, conduct, and interpret behavioural knockout experiments. Drawing from and extending Harry Collins's work on how research communities negotiate what counts as a 'well-done experiment,' I argue that the positions practitioners took on questions of experimental skill reflected not only the experimental traditions they were trained in but also their differing ontological and epistemological commitments. Different assumptions about the nature of gene action, eg., were tied to different positions in the knockout mouse debates on how to implement experimental controls. I conclude by showing that examining representations of skill in the context of a community's knowledge commitments sheds light on some of the contradictory ways in which contemporary animal behaviour geneticists talk about their own laboratory work as a highly skilled endeavour that also could be mechanised, as easy to perform and yet difficult to perform well.

Pathological brain plasticity and cognition in the offspring of males subjected to postnatal traumatic stress

Traumatic stress in early-life increases the risk for cognitive and neuropsychiatric disorders later in life. Such early stress can also impact the progeny even if not directly exposed, likely through epigenetic mechanisms. Here, we report in mice that the offspring of males subjected to postnatal traumatic stress have decreased gene expression in molecular pathways necessary for neuronal signaling, and altered synaptic plasticity when adult. Long-term potentiation is abolished and long-term depression is enhanced in the hippocampus, and these defects are associated with impaired long-term memory in both the exposed fathers and their offspring. The brain-specific gamma isoform of protein kinase C (Prkcc) is one of the affected signaling components in the hippocampus. Its expression is reduced in the offspring, and DNA methylation at its promoter is altered both in the hippocampus of the offspring and the sperm of fathers. These results suggest that postnatal traumatic stress in males can affect brain plasticity and cognitive functions in the adult progeny, possibly through epigenetic alterations in the male germline.

mTOR signaling in tumorigenesis

mTOR (the mechanistic target of rapamycin) is an atypical serine/threonine kinase involved in regulating major cellular functions including growth and proliferation. Deregulation of the mTOR signaling pathway is one of the most commonly observed pathological alterations in human cancers. To this end, oncogenic activation of the mTOR signaling pathway contributes to cancer cell growth, proliferation and survival, highlighting the potential for targeting the oncogenic mTOR pathway members as an effective anti-cancer strategy. In order to do so, a thorough understanding of the physiological roles of key mTOR signaling pathway components and upstream regulators would guide future targeted therapies. Thus, in this review, we summarize available genetic mouse models for mTORC1 and mTORC2 components, as well as characterized mTOR upstream regulators and downstream targets, and assign a potential oncogenic or tumor suppressive role for each evaluated molecule. Together, our work will not only facilitate the current understanding of mTOR biology and possible future research directions, but more importantly, provide a molecular basis for targeted therapies aiming at key oncogenic members along the mTOR signaling pathway.

Comprehensive phosphoproteome analysis unravels the core signaling network that initiates the earliest synapse pathology in preclinical Alzheimer's disease brain

Using a high-end mass spectrometry, we screened phosphoproteins and phosphopeptides in four types of Alzheimer's disease (AD) mouse models and human AD postmortem brains. We identified commonly changed phosphoproteins in multiple models and also determined phosphoproteins related to initiation of amyloid beta (Aβ) deposition in the mouse brain. After confirming these proteins were also changed in and human AD brains, we put the proteins on experimentally verified protein-protein interaction databases. Surprisingly, most of the core phosphoproteins were directly connected, and they formed a functional network linked to synaptic spine formation. The change of the core network started at a preclinical stage even before histological Aβ deposition. Systems biology analyses suggested that phosphorylation of myristoylated alanine-rich C-kinase substrate (MARCKS) by overactivated kinases including protein kinases C and calmodulin-dependent kinases initiates synapse pathology. Two-photon microscopic observation revealed recovery of abnormal spine formation in the AD model mice by targeting a core protein MARCKS or by inhibiting candidate kinases, supporting our hypothesis formulated based on phosphoproteome analysis.

Protein kinase C gamma interneurons in the rat medullary dorsal horn: distribution and synaptic inputs to these neurons, and subcellular localization of the enzyme

The γ isoform of protein kinase C (PKCγ), which is concentrated in interneurons in the inner part of lamina II (IIi ) of the dorsal horn, has been implicated in the expression of tactile allodynia. Lamina IIi PKCγ interneurons were shown to be activated by tactile inputs and to participate in local circuits through which these inputs can reach lamina I, nociceptive output neurons. That such local circuits are gated by glycinergic inhibition and that A- and C-fibers low threshold mechanoreceptors (LTMRs) terminate in lamina IIi raise the general issue of synaptic inputs to lamina IIi PKCγ interneurons. Combining light and electron microscopic immunochemistry in the rat spinal trigeminal nucleus, we show that PKCγ-immunoreactivity is mostly restricted to interneurons in lamina IIi of the medullary dorsal horn, where they constitute 1/3 of total neurons. The majority of synapses on PKCγ-immunoreactive interneurons are asymmetric (likely excitatory). PKCγ-immunoreactive interneurons appear to receive exclusively myelinated primary afferents in type II synaptic glomeruli. Neither large dense core vesicle terminals nor type I synaptic glomeruli, assumed to be the endings of unmyelinated nociceptive terminals, were found on these interneurons. Moreover, there is no vesicular glutamate transporter 3-immunoreactive bouton, specific to C-LTMRs, on PKCγ-immunoreactive interneurons. PKCγ-immunoreactive interneurons contain GABAA ergic and glycinergic receptors. At the subcellular level, PKCγ-immunoreactivity is mostly concentrated on plasma membranes, close to, but not within, postsynaptic densities. That only myelinated primary afferents were found to contact PKCγ-immunoreactive interneurons suggests that myelinated, but not unmyelinated, LTMRs play a critical role in the expression of mechanical allodynia.

Calcium-dependent PKC isoforms have specialized roles in short-term synaptic plasticity

Posttetanic potentiation (PTP) is a widely observed form of short-term plasticity lasting for tens of seconds after high-frequency stimulation. Here we show that although protein kinase C (PKC) mediates PTP at the calyx of Held synapse in the auditory brainstem before and after hearing onset, PTP is produced primarily by an increased probability of release (p) before hearing onset, and by an increased readily releasable pool of vesicles (RRP) thereafter. We find that these mechanistic differences, which have distinct functional consequences, reflect unexpected differential actions of closely related calcium-dependent PKC isoforms. Prior to hearing onset, when PKCγ and PKCβ are both present, PKCγ mediates PTP by increasing p and partially suppressing PKCβ actions. After hearing onset, PKCγ is absent and PKCβ produces PTP by increasing RRP. In hearing animals, virally expressed PKCγ overrides PKCβ to produce PTP by increasing p. Thus, two similar PKC isoforms mediate PTP in distinctly different ways.

The "memory kinases": roles of PKC isoforms in signal processing and memory formation

The protein kinase C (PKC) isoforms, which play an essential role in transmembrane signal conduction, can be viewed as a family of "memory kinases." Evidence is emerging that they are critically involved in memory acquisition and maintenance, in addition to their involvement in other functions of cells. Deficits in PKC signal cascades in neurons are one of the earliest abnormalities in the brains of patients suffering from Alzheimer's disease. Their dysfunction is also involved in several other types of memory impairments, including those related to emotion, mental retardation, brain injury, and vascular dementia/ischemic stroke. Inhibition of PKC activity leads to a reduced capacity of many types of learning and memory, but may have therapeutic values in treating substance abuse or aversive memories. PKC activators, on the other hand, have been shown to possess memory-enhancing and antidementia actions. PKC pharmacology may, therefore, represent an attractive area for developing effective cognitive drugs for the treatment of many types of memory disorders and dementias.

Synaptic Signaling in Learning and Memory

Learning and memory require the formation of new neural networks in the brain. A key mechanism underlying this process is synaptic plasticity at excitatory synapses, which connect neurons into networks. Excitatory synaptic transmission happens when glutamate, the excitatory neurotransmitter, activates receptors on the postsynaptic neuron. Synaptic plasticity is a higher-level process in which the strength of excitatory synapses is altered in response to the pattern of activity at the synapse. It is initiated in the postsynaptic compartment, where the precise pattern of influx of calcium through activated glutamate receptors leads either to the addition of new receptors and enlargement of the synapse (long-term potentiation) or the removal of receptors and shrinkage of the synapse (long-term depression). Calcium/calmodulin-regulated enzymes and small GTPases collaborate to control this highly tuned mechanism.

Purinergic stimulation of K+-dependent Na+/Ca2+ exchanger isoform 4 requires dual activation by PKC and CaMKII

K⁺-dependent Na⁺/Ca²⁺-exchanger isoform 4 (NCXK4) is one of the most broadly expressed members of the NCKX (K⁺-dependent Na⁺/Ca²⁺-exchanger) family. Recent data indicate that NCKX4 plays a critical role in controlling normal Ca²⁺ signal dynamics in olfactory and other neurons. Synaptic Ca²⁺ dynamics are modulated by purinergic regulation, mediated by ATP released from synaptic vesicles or from neighbouring glial cells. Previous studies have focused on modulation of Ca²⁺ entry pathways that initiate signalling. Here we have investigated purinergic regulation of NCKX4, a powerful extrusion pathway that assists in terminating Ca²⁺ signals. NCKX4 activity was stimulated by ATP through activation of the P2Y receptor signalling pathway. Stimulation required dual activation of PKC (protein kinase C) and CaMKII (Ca²⁺/calmodulin-dependent protein kinase II). Mutating T312, a putative PKC phosphorylation site on NCKX4, partially prevented purinergic stimulation. These data illustrate how purinergic regulation can shape the dynamics of Ca²⁺ signalling by activating a signal damping and termination pathway.

Activity of the K⁺-dependent Na⁺/Ca²⁺-exchanger, NCKX4, is stimulated by purinergic signals that depend on dual activation of two protein kinase pathways. This regulation provides a novel mechanism to shape Ca²⁺ signaling and thus to have important impact on neuronal processes.

G proteins Gαi1/3 are critical targets for Bordetella pertussis toxin-induced vasoactive amine sensitization

Pertussis toxin (PTX) is an AB5-type exotoxin produced by the bacterium Bordetella pertussis, the causative agent of whooping cough. In vivo intoxication with PTX elicits a variety of immunologic and inflammatory responses, including vasoactive amine sensitization (VAAS) to histamine (HA), serotonin (5-HT), and bradykinin (BDK). Previously, by using a forward genetic approach, we identified the HA H1 receptor (Hrh1/H1R) as the gene in mice that controls differential susceptibility to B. pertussis PTX-induced HA sensitization (Bphs). Here we show, by using inbred strains of mice, F1 hybrids, and segregating populations, that, unlike Bphs, PTX-induced 5-HT sensitivity (Bpss) and BDK sensitivity (Bpbs) are recessive traits and are separately controlled by multiple loci unlinked to 5-HT and BDK receptors, respectively. Furthermore, we found that PTX sensitizes mice to HA independently of Toll-like receptor 4, a purported receptor for PTX, and that the VAAS properties of PTX are not dependent upon endothelial caveolae or endothelial nitric oxide synthase. Finally, by using mice deficient in individual Gαi/o G-protein subunits, we demonstrate that Gαi1 and Gαi3 are the critical in vivo targets of ADP-ribosylation underlying VAAS elicited by PTX exposure.

Protein kinase C pharmacology: refining the toolbox

PKC (protein kinase C) has been in the limelight since the discovery three decades ago that it acts as a major receptor for the tumour-promoting phorbol esters. Phorbol esters, with their potent ability to activate two of the three classes of PKC isoenzymes, have remained the best pharmacological tool for directly modulating PKC activity. However, with the discovery of other phorbol ester-responsive proteins, the advent of various small-molecule and peptide modulators, and the need to distinguish isoenzyme-specific activity, the pharmacology of PKC has become increasingly complex. Not surprisingly, many of the compounds originally touted as direct modulators of PKC have subsequently been shown to hit many other cellular targets and, in some cases, not even directly modulate PKC. The complexities and reversals in PKC pharmacology have led to widespread confusion about the current status of the pharmacological tools available to control PKC activity. In the present review, we aim to clarify the cacophony in the literature regarding the current state of bona fide and discredited cellular PKC modulators, including activators, small-molecule inhibitors and peptides, and also address the use of genetically encoded reporters and of PKC mutants to measure the effects of these drugs on the spatiotemporal dynamics of signalling by specific isoenzymes.

The tail wagging the dog--regulation of lipid metabolism by protein kinase C

Upon their discovery almost 40 years ago, isoforms of the lipid-activated protein kinase C (PKC) family were initially regarded only as downstream effectors of the second messengers calcium and diacylglycerol, undergoing activation upon phospholipid hydrolysis in response to acute stimuli. Subsequently, several isoforms were found to be associated with the inhibitory effects of lipid over-supply on glucose homeostasis, especially the negative cross-talk with insulin signal transduction, observed upon accumulation of diacylglycerol in insulin target tissues. The PKC family has therefore attracted much attention in diabetes and obesity research, because intracellular lipid accumulation is strongly correlated with defective insulin action and the development of type 2 diabetes. Causal roles for various isoforms in the generation of insulin resistance have more recently been confirmed using PKC-deficient mice. However, during characterization of these animals, it became increasingly evident that the enzymes play key roles in the modulation of lipid metabolism itself, and may control the supply of lipids between tissues such as adipose and liver. Molecular studies have also demonstrated roles for PKC isoforms in several aspects of lipid metabolism, such as adipocyte differentiation and hepatic lipogenesis. While the precise mechanisms involved, especially the identities of protein substrates, are still unclear, the emerging picture suggests that the currently held view of the contribution of PKC isoforms to metabolism is an over-simplification. Although PKCs may inhibit insulin signal transduction, these enzymes are not merely downstream effectors of lipid accumulation, but in fact control the fate of fatty acids, thus the tail wags the dog.

PKCλ is critical in AMPA receptor phosphorylation and synaptic incorporation during LTP

Direct phosphorylation of GluA1 by PKC controls α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptor (AMPAR) incorporation into active synapses during long-term potentiation (LTP). Numerous signalling molecules that involved in AMPAR incorporation have been identified, but the specific PKC isoform(s) participating in GluA1 phosphorylation and the molecule triggering PKC activation remain largely unknown. Here, we report that the atypical isoform of PKC, PKCλ, is a critical molecule that acts downstream of phosphatidylinositol 3-kinase (PI3K) and is essential for LTP expression. PKCλ activation is required for both GluA1 phosphorylation and increased surface expression of AMPARs during LTP. Moreover, p62 interacts with both PKCλ and GluA1 during LTP and may serve as a scaffolding protein to place PKCλ in close proximity to facilitate GluA1 phosphorylation by PKCλ. Thus, we conclude that PKCλ is the critical signalling molecule responsible for GluA1-containing AMPAR phosphorylation and synaptic incorporation at activated synapses during LTP expression.

PKCγ participates in food entrainment by regulating BMAL1

Temporally restricted feeding (RF) can phase reset the circadian clocks in numerous tissues in mammals, contributing to altered timing of behavioral and physiological rhythms. However, little is known regarding the underlying molecular mechanism. Here we demonstrate a role for the gamma isotype of protein kinase C (PKCγ) in food-mediated entrainment of behavior and the molecular clock. We found that daytime RF reduced late-night activity in wild-type mice but not mice homozygous for a null mutation of PKCγ (PKCγ(-/-)). Molecular analysis revealed that PKCγ exhibited RF-induced changes in activation patterns in the cerebral cortex and that RF failed to substantially phase shift the oscillation of clock gene transcripts in the absence of PKCγ. PKCγ exerts effects on the clock, at least in part, by stabilizing the core clock component brain and muscle aryl hydrocarbon receptor nuclear translocator like 1 (BMAL1) and reducing its ubiquitylation in a deubiquitination-dependent manner. Taken together, these results suggest that PKCγ plays a role in food entrainment by regulating BMAL1 stability.

Diversity of the protein kinase C gene family Implications for cardiovascular disease

All eukaryotic cells are capable of responding to a changing intracellular environment and to extracellular stimuli. These functional responses are highly regulated by diverse means; one of the most common mechanisms of regulation requires the covalent phosphorylation of intracellular proteins, which when phosphorylated, mediate many functional events. The general class of enzymes that catalyzes the phosphorylation of effectors (substrates), the protein kinases, may be divided into two broad categories, depending on whether they phosphorylate serine and threonine residues or tyrosine residues. Evidence has accumulated that implicates abnormal activation of protein kinase C (PKC), which is one family of serine-threonine protein kinases, in cells and tissues from patients or models of cardiovascular disease. In this review, we present the molecular and biochemical basis for the diversity of the PKC family, and briefly summarize the evidence that PKC is implicated in cardiovascular pathology and the potential therapeutic implications and approaches.