NFATc4 Knockout Promotes Neuroprotection and Retinal Ganglion Cell Regeneration After Optic Nerve Injury

Retinal ganglion cells (RGCs), neurons transmitting visual information via the optic nerve, fail to regenerate their axons after injury. The progressive loss of RGC function underlies the pathophysiology of glaucoma and other optic neuropathies, often leading to irreversible blindness. Therefore, there is an urgent need to identify the regulators of RGC survival and the regenerative program. In this study, we investigated the role of the family of transcription factors known as nuclear factor of activated T cells (NFAT), which are expressed in the retina; however, their role in RGC survival after injury is unknown. Using the optic nerve crush (ONC) model, widely employed to study optic neuropathies and central nervous system axon injury, we found that NFATc4 is specifically but transiently up-regulated in response to mechanical injury. In the injured retina, NFATc4 immunolocalized primarily to the ganglionic cell layer. Utilizing NFATc4-/- and NFATc3-/- mice, we demonstrated that NFATc4, but not NFATc3, knockout increased RGC survival, improved retina function, and delayed axonal degeneration. Microarray screening data, along with decreased immunostaining of cleaved caspase-3, revealed that NFATc4 knockout was protective against ONC-induced degeneration by suppressing pro-apoptotic signaling. Finally, we used lentiviral-mediated NFATc4 delivery to the retina of NFATc4-/- mice and reversed the pro-survival effect of NFATc4 knockout, conclusively linking the enhanced survival of injured RGCs to NFATc4-dependent mechanisms. In summary, this study is the first to demonstrate that NFATc4 knockout may confer transient RGC neuroprotection and decelerate axonal degeneration after injury, providing a potent therapeutic strategy for optic neuropathies.

Calcium-Associated Proteins in Neuroregeneration

The dysregulation of intracellular calcium levels is a critical factor in neurodegeneration, leading to the aberrant activation of calcium-dependent processes and, ultimately, cell death. Ca2+ signals vary in magnitude, duration, and the type of neuron affected. A moderate Ca2+ concentration can initiate certain cellular repair pathways and promote neuroregeneration. While the peripheral nervous system exhibits an intrinsic regenerative capability, the central nervous system has limited self-repair potential. There is evidence that significant variations exist in evoked calcium responses and axonal regeneration among neurons, and individual differences in regenerative capacity are apparent even within the same type of neurons. Furthermore, some studies have shown that neuronal activity could serve as a potent regulator of this process. The spatio-temporal patterns of calcium dynamics are intricately controlled by a variety of proteins, including channels, ion pumps, enzymes, and various calcium-binding proteins, each of which can exert either positive or negative effects on neural repair, depending on the cellular context. In this concise review, we focus on several calcium-associated proteins such as CaM kinase II, GAP-43, oncomodulin, caldendrin, calneuron, and NCS-1 in order to elaborate on their roles in the intrinsic mechanisms governing neuronal regeneration following traumatic damage processes.

Targeting CaN/NFAT in Alzheimer's brain degeneration

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of cognitive functions. While the exact causes of this debilitating disorder remain elusive, numerous investigations have characterized its two core pathologies: the presence of β-amyloid plaques and tau tangles. Additionally, multiple studies of postmortem brain tissue, as well as results from AD preclinical models, have consistently demonstrated the presence of a sustained inflammatory response. As the persistent immune response is associated with neurodegeneration, it became clear that it may also exacerbate other AD pathologies, providing a link between the initial deposition of β-amyloid plaques and the later development of neurofibrillary tangles. Initially discovered in T cells, the nuclear factor of activated T-cells (NFAT) is one of the main transcription factors driving the expression of inflammatory genes and thus regulating immune responses. NFAT-dependent production of inflammatory mediators is controlled by Ca2+-dependent protein phosphatase calcineurin (CaN), which dephosphorylates NFAT and promotes its transcriptional activity. A substantial body of evidence has demonstrated that aberrant CaN/NFAT signaling is linked to several pathologies observed in AD, including neuronal apoptosis, synaptic deficits, and glia activation. In view of this, the role of NFAT isoforms in AD has been linked to disease progression at different stages, some of which are paralleled to diminished cognitive status. The use of classical inhibitors of CaN/NFAT signaling, such as tacrolimus or cyclosporine, or adeno-associated viruses to specifically inhibit astrocytic NFAT activation, has alleviated some symptoms of AD by diminishing β-amyloid neurotoxicity and neuroinflammation. In this article, we discuss the recent findings related to the contribution of CaN/NFAT signaling to the progression of AD and highlight the possible benefits of targeting this pathway in AD treatment.

Early Developmental PMCA2b Expression Protects From Ketamine-Induced Apoptosis and GABA Impairments in Differentiating Hippocampal Progenitor Cells

PMCA2 is not expressed until the late embryonic state when the control of subtle Ca²⁺ fluxes becomes important for neuronal specialization. During this period, immature neurons are especially vulnerable to degenerative insults induced by the N-methyl-D-aspartate (NMDA) receptor blocker, ketamine. As H19-7 hippocampal progenitor cells isolated from E17 do not express the PMCA2 isoform, they constitute a valuable model for studying its role in neuronal development. In this study, we demonstrated that heterologous expression of PMCA2b enhanced the differentiation of H19-7 cells and protected from ketamine-induced death. PMCA2b did not affect resting [Ca²⁺]_c in the presence or absence of ketamine and had no effect on the rate of Ca²⁺ clearance following membrane depolarization in the presence of the drug. The upregulation of endogenous PMCA1 demonstrated in response to PMCA2b expression as well as ketamine-induced PMCA4 depletion were indifferent to the rate of Ca²⁺ clearance in the presence of ketamine. Yet, co-expression of PMCA4b and PMCA2b was able to partially restore Ca²⁺ extrusion diminished by ketamine. The profiling of NMDA receptor expression showed upregulation of the NMDAR1 subunit in PMCA2b-expressing cells and increased co-immunoprecipitation of both proteins following ketamine treatment. Further microarray screening demonstrated a significant influence of PMCA2b on GABA signaling in differentiating progenitor cells, manifested by the unique regulation of several genes key to the GABAergic transmission. The overall activity of glutamate decarboxylase remained unchanged, but Ca²⁺-induced GABA release was inhibited in the presence of ketamine. Interestingly, PMCA2b expression was able to reverse this effect. The mechanism of GABA secretion normalization in the presence of ketamine may involve PMCA2b-mediated inhibition of GABA transaminase, thus shifting GABA utilization from energetic purposes to neurosecretion. In this study, we show for the first time that developmentally controlled PMCA expression may dictate the pattern of differentiation of hippocampal progenitor cells. Moreover, the appearance of PMCA2 early in development has long-standing consequences for GABA metabolism with yet an unpredictable influence on GABAergic neurotransmission during later stages of brain maturation. In contrast, the presence of PMCA2b seems to be protective for differentiating progenitor cells from ketamine-induced apoptotic death.

Astrocytic Calcium and cAMP in Neurodegenerative Diseases

It is commonly accepted that the role of astrocytes exceeds far beyond neuronal scaffold and energy supply. Their unique morphological and functional features have recently brough much attention as it became evident that they play a fundamental role in neurotransmission and interact with synapses. Synaptic transmission is a highly orchestrated process, which triggers local and transient elevations in intracellular Ca²⁺, a phenomenon with specific temporal and spatial properties. Presynaptic activation of Ca²⁺-dependent adenylyl cyclases represents an important mechanism of synaptic transmission modulation. This involves activation of the cAMP-PKA pathway to regulate neurotransmitter synthesis, release and storage, and to increase neuroprotection. This aspect is of paramount importance for the preservation of neuronal survival and functionality in several pathological states occurring with progressive neuronal loss. Hence, the aim of this review is to discuss mutual relationships between cAMP and Ca²⁺ signaling and emphasize those alterations at the Ca²⁺/cAMP crosstalk that have been identified in neurodegenerative disorders, such as Alzheimer's and Parkinson's disease.

Hexachloronaphthalene (HxCN) impairs the dopamine pathway in an in vitro model of PC12 cells

Among polychlorinated naphthalenes (PCNs), listed by the Stockholm convention as Persistent Organic Pollutants (POPs), hexachloronaphthalenes are considered the most toxic and raise the highest concern. Of these, 1,2,3,5,6,7-hexachloronaphthalanene (PCN67) is considered the main congener affecting human health due to its hepatotoxicity and its ability to disturb the reproductive, endocrine, and hematological systems. It is also prevalent in human serum/plasma, milk, and adipose tissue. However, little is known about its neurotoxicity, despite the fact that anorectic effects have been observed in workers occupationally exposed to PCNs and in animal research on PCN67. Since dopamine is involved in many aspects of food intake, the aim of this study was to confirm whether PCN67 affects dopamine synthesis in differentiated PC12 cells, a widely used model of neurosecretion. Our results show that exposure to PCN67 resulted in diminished dopamine content and release. Moreover, PCN67 also affected the expression of tyrosine hydroxylase and lowered the expression of vesicular monoamine transporter 1 (VMAT1). In addition, significantly lower expression of antioxidant enzymes, including catalase, glutathione peroxidase and copper/zinc superoxide dismutase, was observed in comparison to the vehicle. In conclusion, PCN67 appears to disturb dopaminergic transmission by altering tyrosine hydroxylation, reducing VMAT1 expression and impairing antioxidant protection. Our study provides a potential mechanism for how PCN67 may cause dopamine deficiency and contribute to neuronal death by affecting cellular antioxidant potency; however, this conclusion requires further research.

Receptor-Dependent and Independent Regulation of Voltage-Gated Ca2+ Channels and Ca2+-Permeable Channels by Endocannabinoids in the Brain

The activity of specific populations of neurons in different brain areas makes decisions regarding proper synaptic transmission, the ability to make adaptations in response to different external signals, as well as the triggering of specific regulatory pathways to sustain neural function. The endocannabinoid system (ECS) appears to be a very important, highly expressed, and active system of control in the central nervous system (CNS). Functionally, it allows the cells to respond quickly to processes that occur during synaptic transmission, but can also induce long-term changes. The endocannabinoids (eCBs) belong to a large family of bioactive lipid mediators that includes amides, esters, and ethers of long-chain polyunsaturated fatty acids. They are produced “on demand” from the precursors located in the membranes, exhibit a short half-life, and play a key role as retrograde messengers. eCBs act mainly through two receptors, CB1R and CB2R, which belong to the G-protein coupled receptor superfamily (GPCRs), but can also exert their action via multiple non-receptor pathways. The action of eCBs depends on Ca²⁺, but eCBs can also regulate downstream Ca²⁺ signaling. In this short review, we focus on the regulation of neuronal calcium channels by the most effective members of eCBs-2-arachidonoylglycerol (2-AG), anandamide (AEA) and originating from AEA-N-arachidonoylglycine (NAGly), to better understand the contribution of ECS to brain function under physiological conditions.

Circulating glutathione peroxidase and superoxide dismutase levels in patients with epilepsy: A meta-analysis

PURPOSE

Glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) are assessed as oxidative stress markers to determine the impact of oxidation on the levels of GSH-Px and SOD in patients with epilepsy (PWE) and healthy controls.

METHODS

A meta-analysis was completed on twenty-nine published studies. A total of 636 PWE and 665 healthy controls, 303 PWE and 191 controls, and 22 PWE and 22 controls were included to study GSH-Px levels in erythrocytes, serum and plasma, respectively. For SOD studies, there were 610 PWE and 680 controls, 464 PWE and 382 controls, and 62 PWE with 77 controls for erythrocytes, serum and plasma, respectively.

RESULTS

Meta-analysis showed that the erythrocyte SOD level was significantly lower in PWE than in healthy controls (SMD =-1.96; 95% CI [-2.93, -0.99]; P<0.0001). Moreover, the meta-analysis demonstrated that in serum and plasma, SOD levels in PWE were significantly lower than those in healthy controls (SMD =-1.47; 95% CI [-2.47, -0.48]; P<0.0001). Erythrocyte GSH-Px levels had a tendency to decrease in PWE compared with healthy controls (SMD =-0.31; 95% CI [-1.48, 0.85]; P=0.598), but the results showed no significant difference.

CONCLUSION

Our results showed reduced SOD levels in erythrocytes, serum and plasma in PWE, which may be an indicator of oxidative damage in epilepsy. This is the first meta-analysis of circulating GSH-Px and SOD levels in PWE and healthy controls.

Cell death modulation by transient receptor potential melastatin channels TRPM2 and TRPM7 and their underlying molecular mechanisms

Transient receptor potential melastatin (TRPM) channels are members of the transient receptor potential (TRP) channels, a family of evolutionarily conserved integral membrane proteins. TRPM channels are nonselective cation channels, mediating the influx of various ions including Ca²⁺, Na⁺ and Zn²⁺. The function of TRPM channels is vital for cell proliferation, cell development and cell death. Cell death is a key procedure during embryonic development, organism homeostasis, aging and disease. The category of cell death modalities, beyond the traditionally defined concepts of necrosis, autophagy, and apoptosis, were extended with the discovery of pyroptosis, necroptosis and ferroptosis. As upstream signaling regulators of cell death, TRPM channels have been involved inrelevant pathologies. In this review, we introduced several cell death modalities, then summarized the contribution of TRPM channels (especially TRPM2 and TRPM7) to different cell death modalities and discussed the underlying regulatory mechanisms. Our work highlighted the possibility of TRPM channels as potential therapeutic targets in cell death-related diseases.

The Role of G Protein-Coupled Receptors (GPCRs) and Calcium Signaling in Schizophrenia. Focus on GPCRs Activated by Neurotransmitters and Chemokines

Schizophrenia is a common debilitating disease characterized by continuous or relapsing episodes of psychosis. Although the molecular mechanisms underlying this psychiatric illness remain incompletely understood, a growing body of clinical, pharmacological, and genetic evidence suggests that G protein-coupled receptors (GPCRs) play a critical role in disease development, progression, and treatment. This pivotal role is further highlighted by the fact that GPCRs are the most common targets for antipsychotic drugs. The GPCRs activation evokes slow synaptic transmission through several downstream pathways, many of them engaging intracellular Ca²⁺ mobilization. Dysfunctions of the neurotransmitter systems involving the action of GPCRs in the frontal and limbic-related regions are likely to underly the complex picture that includes the whole spectrum of positive and negative schizophrenia symptoms. Therefore, the progress in our understanding of GPCRs function in the control of brain cognitive functions is expected to open new avenues for selective drug development. In this paper, we review and synthesize the recent data regarding the contribution of neurotransmitter-GPCRs signaling to schizophrenia symptomology.

The G Protein-Coupled Glutamate Receptors as Novel Molecular Targets in Schizophrenia Treatment-A Narrative Review

Schizophrenia is a severe neuropsychiatric disease with an unknown etiology. The research into the neurobiology of this disease led to several models aimed at explaining the link between perturbations in brain function and the manifestation of psychotic symptoms. The glutamatergic hypothesis postulates that disrupted glutamate neurotransmission may mediate cognitive and psychosocial impairments by affecting the connections between the cortex and the thalamus. In this regard, the greatest attention has been given to ionotropic NMDA receptor hypofunction. However, converging data indicates metabotropic glutamate receptors as crucial for cognitive and psychomotor function. The distribution of these receptors in the brain regions related to schizophrenia and their regulatory role in glutamate release make them promising molecular targets for novel antipsychotics. This article reviews the progress in the research on the role of metabotropic glutamate receptors in schizophrenia etiopathology.

Ketamine and Calcium Signaling-A Crosstalk for Neuronal Physiology and Pathology

Ketamine is a non-competitive antagonist of NMDA (N-methyl-D-aspartate) receptor, which has been in clinical practice for over a half century. Despite recent data suggesting its harmful side effects, such as neuronal loss, synapse dysfunction or disturbed neural network formation, the drug is still applied in veterinary medicine and specialist anesthesia. Several lines of evidence indicate that structural and functional abnormalities in the nervous system caused by ketamine are crosslinked with the imbalanced activity of multiple Ca²⁺-regulated signaling pathways. Due to its ubiquitous nature, Ca²⁺ is also frequently located in the center of ketamine action, although the precise mechanisms underlying drug’s negative or therapeutic properties remain mysterious for the large part. This review seeks to delineate the relationship between ketamine-triggered imbalance in Ca²⁺ homeostasis and functional consequences for downstream processes regulating key aspects of neuronal function.

The changes of serum zinc, copper, and selenium levels in epileptic patients: a systematic review and meta-analysis

INTRODUCTION

It is widely accepted that trace elements have been implicated in various metabolic processes. Valproic acid (VPA) is a remarkably safe and effective antiepileptic drug. There is no consensus option regarding the fluctuations in serum zinc (Zn), copper (Cu), and selenium (Se) in epileptic patients treated with VPA. We applied a meta-analysis to systematically assess the effects of VPA on serum ions in these patients.

AREAS COVERED

In this study, we performed a meta-analysis of the changes in serum Zn, Cu, and Se levels in human samples of healthy controls, epileptic patients, and patients treated with VPA. Twenty-two published analyzable studies were selected by searching the databases of PubMed, China National Knowledge Infrastructure (CNKI), Google Scholar, Web of Science, EMBASE, WAN FANG and Vip.

EXPERT OPINION

Serum Se levels in epileptic patients were decreased compared to healthy controls. Serum Zn levels in patients with VPA treatment were significantly lower than those in epileptic patients. The results of this meta-analysis are instructive for the intake of trace elements such as Zn, Cu, and Se in the diet balance of patients with epilepsy treated with VPA. Meanwhile, this study provides a theoretical basis for the combined use of other drugs that affect the intake and absorption of trace elements and VPA.

The Puzzling Role of Neuron-Specific PMCA Isoforms in the Aging Process

The aging process is a physiological phenomenon associated with progressive changes in metabolism, genes expression, and cellular resistance to stress. In neurons, one of the hallmarks of senescence is a disturbance of calcium homeostasis that may have far-reaching detrimental consequences on neuronal physiology and function. Among several proteins involved in calcium handling, plasma membrane Ca²⁺-ATPase (PMCA) is the most sensitive calcium detector controlling calcium homeostasis. PMCA exists in four main isoforms and PMCA2 and PMCA3 are highly expressed in the brain. The overall effects of impaired calcium extrusion due to age-dependent decline of PMCA function seem to accumulate with age, increasing the susceptibility to neurotoxic insults. To analyze the PMCA role in neuronal cells, we have developed stable transfected differentiated PC12 lines with down-regulated PMCA2 or PMCA3 isoforms to mimic age-related changes. The resting Ca²⁺ increased in both PMCA-deficient lines affecting the expression of several Ca²⁺-associated proteins, i.e., sarco/endoplasmic Ca²⁺-ATPase (SERCA), calmodulin, calcineurin, GAP43, CCR5, IP₃Rs, and certain types of voltage-gated Ca²⁺ channels (VGCCs). Functional studies also demonstrated profound changes in intracellular pH regulation and mitochondrial metabolism. Moreover, modification of PMCAs membrane composition triggered some adaptive processes to counterbalance calcium overload, but the reduction of PMCA2 appeared to be more detrimental to the cells than PMCA3.

MTP18 is a Novel Regulator of Mitochondrial Fission in CNS Neuron Development, Axonal Growth, and Injury Responses

The process of mitochondrial fission-fusion has been implicated in diverse neuronal roles including neuronal survival, axon degeneration, and axon regeneration. However, whether increased fission or fusion is beneficial for neuronal health and/or axonal growth is not entirely clear, and is likely situational and cell type-dependent. In searching for mitochondrial fission-fusion regulating proteins for improving axonal growth within the visual system, we uncover that mitochondrial fission process 1,18 kDa (MTP18/MTFP1), a pro-fission protein within the CNS, is critical to maintaining mitochondrial size and volume under normal and injury conditions, in retinal ganglion cells (RGCs). We demonstrate that MTP18’s expression is regulated by transcription factors involved in axonal growth, Kruppel-like factor (KLF) transcription factors-7 and -9, and that knockdown of MTP18 promotes axon growth. This investigation exposes MTP18’s previously unexplored role in regulating mitochondrial fission, implicates MTP18 as a downstream component of axon regenerative signaling, and ultimately lays the groundwork for investigations on the therapeutic efficacy of MTP18 expression suppression during CNS axon degenerative events.

Calcium-engaged Mechanisms of Nongenomic Action of Neurosteroids

BACKGROUND

Neurosteroids form the unique group because of their dual mechanism of action. Classically, they bind to specific intracellular and/or nuclear receptors, and next modify genes transcription. Another mode of action is linked with the rapid effects induced at the plasma membrane level within seconds or milliseconds. The key molecules in neurotransmission are calcium ions, thereby we focus on the recent advances in understanding of complex signaling crosstalk between action of neurosteroids and calcium-engaged events.

METHODS

Short-time effects of neurosteroids action have been reviewed for GABAA receptor complex, glycine receptor, NMDA receptor, AMPA receptor, G protein-coupled receptors and sigma-1 receptor, as well as for several membrane ion channels and plasma membrane enzymes, based on available published research.

RESULTS

The physiological relevance of neurosteroids results from the fact that they can be synthesized and accumulated in the central nervous system, independently from peripheral sources. Fast action of neurosteroids is a prerequisite for genomic effects and these early events can significantly modify intracellular downstream signaling pathways. Since they may exert either positive or negative effects on calcium homeostasis, their role in monitoring of spatio-temporal Ca2+ dynamics, and subsequently, Ca2+-dependent physiological processes or initiation of pathological events, is evident.

CONCLUSION

Neurosteroids and calcium appear to be the integrated elements of signaling systems in neuronal cells under physiological and pathological conditions. A better understanding of cellular and molecular mechanisms of nongenomic, calcium-engaged neurosteroids action could open new ways for therapeutic interventions aimed to restore neuronal function in many neurological and psychiatric diseases.

Glutamate Deregulation in Ketamine-Induced Psychosis-A Potential Role of PSD95, NMDA Receptor and PMCA Interaction

Ketamine causes psychotic episodes and is often used as pharmacological model of psychotic-like behavior in animals. There is increasing evidence that molecular mechanism of its action is more complicated than just N-methyl-D-aspartic acid (NMDA) receptor antagonism and involves interaction with the components of calcium homeostatic machinery, in particular plasma membrane calcium pump (PMCA). Therefore, in this study we aimed to characterize brain region-specific effects of ketamine on PMCA activity, interaction with NMDA receptor through postsynaptic density protein 95 (PSD95) scaffolding proteins and glutamate release from nerve endings. In our study, ketamine induced behavioral changes in healthy male rats consistent with psychotic effects. In the same animals, we were able to demonstrate significant inhibition of plasma membrane calcium ATPase (PMCA) activity in cerebellum, hippocampus and striatum. The expression level and isoform composition of PMCAs were also affected in some of these brain compartments, with possible compensatory effects of PMCA1 substituting for decreased expression of PMCA3. Expression of the PDZ domain-containing scaffold protein PSD95 was induced and its association with PMCA4 was higher in most brain compartments upon ketamine treatment. Moreover, increased PSD95/NMDA receptor direct interaction was also reported, strongly suggesting the formation of multiprotein complexes potentially mediating the effect of ketamine on calcium signaling. We further support this molecular mechanism by showing brain region-specific changes in PSD95/PMCA4 spatial colocalization. We also show that ketamine significantly increases synaptic glutamate release in cortex and striatum (without affecting total tissue glutamate content), inducing the expression of vesicular glutamate transporters and decreasing the expression of membrane glutamate reuptake pump excitatory amino acid transporters 2 (EAAT2). Thus, ketamine-mediated PMCA inhibition, by decreasing total Ca²⁺ clearing potency, may locally raise cytosolic Ca²⁺ promoting excessive glutamate release. Regional alterations in glutamate secretion can be further driven by PSD95-mediated spatial recruitment of signaling complexes including glutamate receptors and calcium pumps, representing a novel mechanism of psychogenic action of ketamine.

Cross talk among PMCA, calcineurin and NFAT transcription factors in control of calmodulin gene expression in differentiating PC12 cells

Brain aging is characterized by progressive loss of plasma membrane calcium pump (PMCA) and its activator - calmodulin (CaM), but the mechanism of this phenomenon remains unresolved. CaM encoded by three genes Calm1, Calm2, Calm3, works to translate Ca²⁺ signal into changes in frequently opposite cellular activities. This unique function allows CaM to affect gene expression via stimulation of calcineurin (CaN) and its downstream target - nuclear factor of activated T-cells (NFAT) and to terminate Ca²⁺ signal by stimulation of its extrusion. PMCA, which exists in four isoforms PMCA1-4, may in turn shape the pattern of Ca²⁺ transients and control CaN activity by its direct binding. Therefore, the interplay between PMCA, CaM and CaN/NFAT is highly plausible. To verify that, we used differentiated PC12 cells with reduced expression of PMCA2 or PMCA3 to mimic the potential changes in aged brain. Manipulation in PMCAs level decreased CaM protein in PMCA2 or PMCA3-reduced lines that was accompanied by down-regulation of Calm1 and Calm2 in both lines, but Calm3 only in PMCA2-reduced cells. Further studies showed substantially higher NFATc2 nuclear accumulation and increased NFAT transcriptional activity. Blocking of CaN/NFAT signalling resulted in almost full CaM recovery, mainly due to up-regulation of Calm2 and Calm3 genes. Moreover, higher occupancy of Calm2 and Calm3 promoters by NFATc2 and increased expression of these genes in response to NFATc2 silencing were demonstrated in PMCA2 and PMCA3-reduced lines. Our results indicate that decrease in CaM level in response to PMCAs downregulation can be driven by CaN/NFAT pathway.

Regional brain dysregulation of Ca(2+)-handling systems in ketamine-induced rat model of experimental psychosis

Chronic N-methyl-D-aspartate receptor (NMDAR) antagonist treatment can provide valuable neurochemical and neuroanatomical models of experimental psychosis. One such antagonist, ketamine, with its short half-time and well-documented psychotomimetic action, has cognitive effects resembling various aspects of schizophrenia-like symptoms. In order to obtain insights into possible relationships between Ca(2+) homeostasis and schizophrenia-related symptoms, we investigate the effects of chronic ketamine administration on intracellular Ca(2+) levels in various brain regions and on the expression level of key members of the neuronal Ca(2+)-handling system in rats. We show increased intracellular [Ca(2+)] in all of the examined brain regions following ketamine treatment but an altered cytosolic Ca(2+) level correlated with hyperlocomotor activity was only established for the cortex and striatum. Our findings also suggest that an imbalance in the expression between the calcium "on" and "off" systems contributes to the deregulation of brain Ca(2+) homeostasis in our ketamine-induced model of experimental psychosis. Identification of the genes whose expression is affected by ketamine treatment indicates their involvement as putative etiological factors in schizophrenia.

Plasma membrane Ca(2+)-ATPase is a novel target for ketamine action

Ketamine, a high affinity uncompetitive antagonist of voltage-dependent NMDA receptor, has been used for years as a dissociative anesthetic. Although the drug is considered as safe and well-tolerable, it is now evident that it can exert dose-dependent multidirectional effects acting on different cellular targets and pathways. The latest clinical studies also demonstrated its promising antidepressant action. However, the widespread use of this drug in humans is largely limited by a broad range of cognitive adverse effects that resemble some core symptoms of schizophrenia. In line with the hypothesis of unifying role of calcium in schizophrenia symptomology, we used ketamine-induced rat model of experimental psychosis to study the effect of 5-day ketamine treatment (30 mg/kg, ip) on the activity of plasma membrane Ca(2+)-ATPase. Whereas no change in a total amount of the enzyme in cortical synaptosomal membranes was observed, a decrease by ∼50% in hydrolytic activity, as well as lowered phosphointermediate formation were detected. Moreover, ketamine action appeared to be isoform-independent. The experiments on intact Ca(2+)-ATPase purified from vehicle-treated rat cortex revealed dose-dependent inhibition of enzymatic activity. Furthermore, ketamine decreased, but not eliminated, the stimulation by calmodulin. The inhibitory effect, although much weaker, was also evident for truncated form of calcium pump obtained following digestion by trypsin. Our results indicate that plasma membrane Ca(2+)-ATPase is a novel target for ketamine and putative interaction sites may involve central catalytic loop and calmodulin-binding domain.

Downregulation of microsomal glutathione-S-transferase 1 modulates protective mechanisms in differentiated PC12 cells

Microsomal glutathione-S-transferase 1 (Mgst1) plays a specific role in protection of cells against oxidative stress. In this study, we assayed the effect of Mgst1 downregulation on cells behavior using differentiated PC12 line, a widely accepted neuronal model system. We have developed stable transfected cells with downregulated Mgst1 (PC12_M), which were differentiated with 1 mM dibutyryl-cAMP (db-cAMP). Mgst1 reduction induced necrosis, decreased ATP amount, and increased thiobarbituric acid reacting substances (TBARS) content. However, in PC12_M cell population, we detected more intensive neuritogenesis than that in mock-transfected cells. Interestingly, total glutathione as well as GSH level were significantly higher than those in control PC12 line. Real-time PCR and Western blot analyses showed elevated expression of enzymes involved in glutathione metabolism-a rate-limiting γ-glutamylcysteine ligase and glutathione reductase. The present study shows for the first time that under stress conditions induced by Mgst1 downregulation, a rescue pathway can be activated and thereby enables differentiated PC12 cells to survive. Since Mgst1expression was reported to decline with age, our results could represent a putative adaptive process during aging. It could also be an early mechanism protecting neuronal cells against some neurodegenerative insults.

Downregulation of PMCA2 or PMCA3 reorganizes Ca(2+) handling systems in differentiating PC12 cells

Changes in PMCA2 and PMCA3 expression during neuronal development are tightly linked to structural and functional modifications in Ca(2+) handling machinery. Using antisense strategy we obtained stably transfected PC12 lines with reduced level of PMCA2 or PMCA3, which were then subjected to dibutyryl-cAMP differentiation. Reduced level of neuron-specific PMCAs led to acceleration of differentiation and formation of longer neurites than in control PC12 line. Treatment with dibutyryl-cAMP was associated with retraction of growth cones and intensified formation of varicosities. In PMCA2-reduced cells development of apoptosis and DNA laddering were detected. Higher amounts of constitutive isoforms PMCA1 and PMCA4, their putative extended location to gaps left after partial removal of PMCA2 or PMCA3, together with increased SERCA may indicate the induction of compensatory mechanism in modified cells. Functional studies showed altered expression of certain types of VDCCs in PMCA-reduced cells, which correlated with their higher contribution to Ca(2+) influx. The cell response to PMCAs suppression suggests the interplay between transcription level of two opposite calcium-transporting systems i.e. voltage- and store depletion-activated channels facilitating Ca(2+) influx and calcium pumps responsible for Ca(2+) clearance, as well highlights the role of both neuron-specific PMCA isoforms in the control of PC12 cells differentiation.

[The role of calmodulin in calcium-dependent signalling in excitable cells]

Calmodulin (CaM) is a sensor protein, which takes part in calcium-dependent signaling, regulating processes like growth, differentiation, proliferation and motility. Calmodulin binds calcium ions during induction of intracellular signaling. It is also involved in silencing of calcium signal through activation of plasma membrane Ca(2+)-ATPase (directly) or SERCA pump (indirectly). Calmodulin may affect various channels, e.g. voltage gated calcium channels (VGCCs), transient receptor potential channels (TRPCs), NMDA receptors, calcium channels dependent on cyclic nucleotides or these located in endoplasmic reticulum (ryanodine receptors and all isoforms of IP3-dependent receptors).

Functional characteristic of PC12 cells with reduced microsomal glutathione transferase 1

Microsomal glutathione transferase 1 (MGST1) possesses glutathione transferase and peroxidase activities and is active in biotransformation of xenobiotics and in defense against oxidative stress. To assess MGST1 role in the development and functioning of PC12 cells, we constructed a cell line with reduced MGST1 (PC12_M). Real-time PCR and immunoblot assays showed MGST1 expression lowered to 60 % and immunocytochemical analyses demonstrated an altered concentration and distribution of the enzyme. PC12_M cells revealed a larger tendency to grow in clusters, weaker adhesion, irregular shape of bodies, short neurite outgrowth and higher percentage of necrotic cells (34 %). The total GSTs activity determined with non-specific substrate CDNB (1-chloro-2,4-dinitrobenzene) decreased by 15-20 %, whereas that with DCNB (2,4-dichloro-1-nitrobenzene), a substrate more specific for cytosolic GSTs, was similar to the one in control cells. This suggests that reduction of MGST1 cannot be compensated by other glutathione transferases. In PC12_M cells the total glutathione content was higher by 15-20 %, whereas the GSSG/GSH ratio was lower than in control cells. Moreover, the laminin-dependent migration rate was much faster in control cells than in PC12_M, suggesting some alterations in the metastatic potential of the line with suppressed MGST1. The amount of MAP kinases (p38, JNK, ERK1/2) was elevated in PC12_M cells but their phosphorylation level declined. Microarray analysis showed changed expression of several genes, which may be linked with differentiation and necrosis of PC12_M cells. Our data suggest that MGST1 could be an important regulator of PC12 cells development and might have significant effects on cell growth and proliferation, probably through altered expression of genes with different biological function.

Functional characteristic of PC12 cells with reduced microsomal glutathione transferase 1

Microsomal glutathione transferase 1 (MGST1) possesses glutathione transferase and peroxidase activities and is active in biotransformation of xenobiotics and in defense against oxidative stress. To assess MGST1 role in the development and functioning of PC12 cells, we constructed a cell line with reduced MGST1 (PC12_M). Real-time PCR and immunoblot assays showed MGST1 expression lowered to 60 % and immunocytochemical analyses demonstrated an altered concentration and distribution of the enzyme. PC12_M cells revealed a larger tendency to grow in clusters, weaker adhesion, irregular shape of bodies, short neurite outgrowth and higher percentage of necrotic cells (34 %). The total GSTs activity determined with non-specific substrate CDNB (1-chloro-2,4-dinitrobenzene) decreased by 15-20 %, whereas that with DCNB (2,4-dichloro-1-nitrobenzene), a substrate more specific for cytosolic GSTs, was similar to the one in control cells. This suggests that reduction of MGST1 cannot be compensated by other glutathione transferases. In PC12_M cells the total glutathione content was higher by 15-20 %, whereas the GSSG/GSH ratio was lower than in control cells. Moreover, the laminin-dependent migration rate was much faster in control cells than in PC12_M, suggesting some alterations in the metastatic potential of the line with suppressed MGST1. The amount of MAP kinases (p38, JNK, ERK1/2) was elevated in PC12_M cells but their phosphorylation level declined. Microarray analysis showed changed expression of several genes, which may be linked with differentiation and necrosis of PC12_M cells. Our data suggest that MGST1 could be an important regulator of PC12 cells development and might have significant effects on cell growth and proliferation, probably through altered expression of genes with different biological function.

Adaptation of microsomal glutathione transferase 1 in PC12 cells with modified PMCA isoforms composition

Microsomal glutathione transferase 1 (MGST1) is an integral homo-trimeric membrane protein with transferase and peroxidase activities. With glutathione as a co-substrate, it scavenges toxic compounds and may exert anti-apoptotic effect. We examined the effect of suppression of plasma membrane Ca(2+)-ATPase isoforms--PMCA2 or PMCA3 on MGST1 in PC12 cells. GSH level was significantly higher in PMCA2-reduced line, but similar GSSG/GSH ratios in all cell lines suggested an efficient protection or absence of oxidative stress. The ATP concentration decreased in both modified lines, although in PMCA2-suppressed cells the decrease was higher. Total GSTs activity in postmitochondrial fraction increased by 30% in the cells with reduced PMCA3. After treatment with MGST1 activator N-ethylmaleimide (NEM), the activity increased in both transfected lines by 30-40%. Real-time PCR also showed a higher mRNA expression of MGST1 in these lines. Staining with antibody recognizing all cytosolic and membrane-bound GSTs revealed the difference in oligomeric forms of GSTs, and specific anti-MGST1 antibody showed the presence of MGST1 hexamers in the transfected cells. Formation of similar hexamers was detected in the control line after treatment with peroxynitrite. Modification of MGST1 under reduced PMCAs amount may represent an adaptive mechanism that offers protection against the cytotoxicity mediated by increased Ca2+.

Structure and function of Bacillus subtilis YphP, a prokaryotic disulfide isomerase with a CXC catalytic motif

The DUF1094 family contains over 100 bacterial proteins, all containing a conserved CXC motif, with unknown function. We solved the crystal structure of the Bacillus subtilis representative, the product of the yphP gene. The protein shows remarkable structural similarity to thioredoxins, with a canonical alphabetaalphabetaalphabetabetaalpha topology, despite low amino acid sequence identity to thioredoxin. The CXC motif is found in the loop immediately downstream of the first beta-strand, in a location equivalent to the CXXC motif of thioredoxins, with the first Cys occupying a position equivalent to the first Cys in canonical thioredoxin. The experimentally determined reduction potential of YphP is E degrees' = -130 mV, significantly higher than that of thioredoxin and consistent with disulfide isomerase activity. Functional assays confirmed that the protein displays a level of isomerase activity that might be biologically significant. We propose a mechanism by which the members of this family catalyze isomerization using the CXC catalytic site.

Protein crystallization by surface entropy reduction: optimization of the SER strategy

A strategy of rationally engineering protein surfaces with the aim of obtaining mutants that are distinctly more susceptible to crystallization than the wild-type protein has previously been suggested. The strategy relies on replacing small clusters of two to three surface residues characterized by high conformational entropy with alanines. This surface entropy reduction (or SER) method has proven to be an effective salvage pathway for proteins that are difficult to crystallize. Here, a systematic comparison of the efficacy of using Ala, His, Ser, Thr and Tyr to replace high-entropy residues is reported. A total of 40 mutants were generated and screened using two different procedures. The results reaffirm that alanine is a particularly good choice for a replacement residue and identify tyrosines and threonines as additional candidates that have considerable potential to mediate crystal contacts. The propensity of these mutants to form crystals in alternative screens in which the normal crystallization reservoir solutions were replaced with 1.5 M NaCl was also examined. The results were impressive: more than half of the mutants yielded a larger number of crystals with salt as the reservoir solution. This method greatly increased the variety of conditions that yielded crystals. Taken together, these results suggest a powerful crystallization strategy that combines surface engineering with efficient screening using standard and alternate reservoir solutions.