Immunosuppressant FK506 affects multiple signaling pathways and modulates gene expression in astrocytes

Combinatory Treatment of Canavanine and Arginine Deprivation Efficiently Targets Human Glioblastoma Cells via Pleiotropic Mechanisms

Glioblastomas are the most frequent and aggressive form of primary brain tumors with no efficient cure. However, they often exhibit specific metabolic shifts that include deficiency in the biosynthesis of and dependence on certain exogenous amino acids. Here, we evaluated, in vitro, a novel combinatory antiglioblastoma approach based on arginine deprivation and canavanine, an arginine analogue of plant origin, using two human glioblastoma cell models, U251MG and U87MG. The combinatory treatment profoundly affected cell viability, morphology, motility and adhesion, destabilizing the cytoskeleton and mitochondrial network, and induced apoptotic cell death. Importantly, the effects were selective toward glioblastoma cells, as they were not pronounced for primary rat glial cells. At the molecular level, canavanine inhibited prosurvival kinases such as FAK, Akt and AMPK. Its effects on protein synthesis and stress response pathways were more complex and dependent on exposure time. We directly observed canavanine incorporation into nascent proteins by using quantitative proteomics. Although canavanine in the absence of arginine readily incorporated into polypeptides, no motif preference for such incorporation was observed. Our findings provide a strong rationale for further developing the proposed modality based on canavanine and arginine deprivation as a potential antiglioblastoma metabolic therapy independent of the blood-brain barrier.

Csf1 Deficiency Dysregulates Glial Responses to Demyelination and Disturbs CNS White Matter Remyelination

Remyelination, a highly efficient central nervous system (CNS) regenerative process, is performed by oligodendrocyte progenitor cells (OPCs), which are recruited to the demyelination sites and differentiate into mature oligodendrocytes to form a new myelin sheath. Microglia, the specialized CNS-resident phagocytes, were shown to support remyelination through secretion of factors stimulating OPC recruitment and differentiation, and their pharmacological depletion impaired remyelination. Macrophage colony-stimulating factor (Csf1) has been implicated in the control of recruitment and polarization of microglia/macrophages in injury-induced CNS inflammation. However, it remains unclear how Csf1 regulates a glial inflammatory response to demyelination as well as axonal survival and new myelin formation. Here, we have investigated the effects of the inherent Csf1 deficiency in a murine model of remyelination. We showed that remyelination was severely impaired in Csf1-/- mutant mice despite the fact that reduction in monocyte/microglia accumulation affects neither the number of OPCs recruited to the demyelinating lesion nor their differentiation. We identified a specific inflammatory gene expression signature and found aberrant astrocyte activation in Csf1-/- mice. We conclude that Csf1-dependent microglia activity is essential for supporting the equilibrium between microglia and astrocyte pro-inflammatory vs. regenerative activation, demyelinated axons integration and, ultimately, reconstruction of damaged white matter.

Impact of immunosuppressive therapy on brain derived cytokines after liver transplantation

BACKGROUND

While acute neurotoxic side effects of calcineurin inhibitors (CNI) are well-known, data upon long-term effects on brain structure and function are sparse. We hypothesize that long-term CNI therapy affects the neuroimmune system, thereby, increasing the risk of neurodegeneration. Here, we measured the impact of CNI therapy on plasma levels of brain- and T cell-derived cytokines in a cohort of patients after liver transplantation (LT).

METHODS

Levels of T cell-mediated cytokines (e.g. Interferon-γ (IFN-γ)) and brain-derived cytokines (e.g. brain derived neurotrophic factor (BDNF), platelet derived growth factor (PDGF)) were measured by multiplex assays in plasma of 82 patients about 10 years after LT (17 with CNI free, 35 with CNI low dose, 30 with standard dose CNI immunosuppression) and 33 healthy controls. Data were related to psychometric test results and parameters of cerebral magnetic resonance imaging.

RESULTS

IFN-γ levels were significantly higher in the CNI free LT patient group (p=0.027) compared to healthy controls. BDNF levels were significantly lower in LT patients treated with CNI (CNI low: p<0.001; CNI standard: p=0.016) compared to controls. PDGF levels were significantly lower in the CNI low dose group (p=0.004) and for PDGF-AB/BB also in the CNI standard dose group (p=0.029) compared to controls. BDNF and PDGF negatively correlated with cognitive function and brain volume (p<0.05) in the CNI low dose group.

CONCLUSION

Our results imply that long-term treatment with CNI suppresses BDNF and PDGF expression, both crucial for neuronal signaling, cell survival and synaptic plasticity and thereby may lead to cognitive dysfunction and neurodegeneration.

Recent Topics on The Mechanisms of Immunosuppressive Therapy-Related Neurotoxicities

Although transplantation procedures have been developed for patients with end-stage hepatic insufficiency or other diseases, allograft rejection still threatens patient health and lifespan. Over the last few decades, the emergence of immunosuppressive agents such as calcineurin inhibitors (CNIs) and mammalian target of rapamycin (mTOR) inhibitors have strikingly increased graft survival. Unfortunately, immunosuppressive agent-related neurotoxicity commonly occurs in clinical practice, with the majority of neurotoxicity cases caused by CNIs. The possible mechanisms through which CNIs cause neurotoxicity include increasing the permeability or injury of the blood–brain barrier, alterations of mitochondrial function, and alterations in the electrophysiological state. Other immunosuppressants can also induce neuropsychiatric complications. For example, mTOR inhibitors induce seizures, mycophenolate mofetil induces depression and headaches, methotrexate affects the central nervous system, the mouse monoclonal immunoglobulin G2 antibody (used against the cluster of differentiation 3) also induces headaches, and patients using corticosteroids usually experience cognitive alteration. Therapeutic drug monitoring, individual therapy based on pharmacogenetics, and early recognition of symptoms help reduce neurotoxic events considerably. Once neurotoxicity occurs, a reduction in the drug dosage, switching to other immunosuppressants, combination therapy with drugs used to treat the neuropsychiatric manifestation, or blood purification therapy have proven to be effective against neurotoxicity. In this review, we summarize recent topics on the mechanisms of immunosuppressive drug-related neurotoxicity. In addition, information about the neuroprotective effects of several immunosuppressants is also discussed.

Analysis of FK506-mediated functional recovery and neuroprotection in a rat model of spinal cord injury indicates that EGF is modulated in astrocytes

The present study aimed to evaluate whether the application of tacrolimus (FK506) could improve functional recovery in spinal cord injury (SCI) rat models by activating astrocytes, and to further investigate the underlying mechanisms of this action. Male Sprague-Dawley rats (n=56) were used to establish moderate SCI models, which were induced at the T10 spinal segment by dropping a 10-g weight from a height of 25 mm using a New York University Impactor device. The rats were randomly separated into the FK506 or control group (n=28 per group). Rats were treated with FK506 (0.5 mg/kg) or saline intravenously 30 min after sustaining the injury. Functional recovery was evaluated over 42 days following the injury, and epidermal growth factor (EGF) levels were detected. The astrocytes were treated with FK506 in vitro, and the EGF mRNA and protein expression levels were analyzed using reverse transcription-quantitative polymerase chain reaction and ELISA, respectively. DNA microarray analysis was also performed to evaluate the genes in astrocytes. Rats in the FK506 group had improved locomotor functional recovery compared with those of control group. Furthermore, FK506 upregulated EGF expression of astrocytes both in vivo and in vitro. Subsequent to treatment with FK506-conditioned medium (CM), the length of neuronal cells increased 61.06% on the first day, and increased 56.4% on the third day compared with those of C-CM group. Furthermore, addition of anti-EGF neutralizing antibodies could interrupt the promotion of neurite outgrowth by FK506-CM. The present study indicates that astrocytes have an important role as mediators of FK506-improved spinal cord function recovery, and this partially clarifies the role of cell-cell interaction through modulating EGF in this process.

DHA upregulates FADS2 expression in primary cortical astrocytes exposed to vitamin A

The fads2 gene encoding delta6-desaturase, the rate-limiting enzyme of the LCPUFA biosynthesis is expressed in astrocytes. Dietary fatty acids, which cross the blood-brain barrier, may regulate the transcription of lipogenic enzymes through activation of transcription factors such as peroxisome proliferator-activated receptors (PPARs). The PPARs form the transcription complex with retinoid X receptors (RXRs) that are activated by 9-cis retinoic acid, a metabolite of vitamin A (VA). The study examines whether challenge of astrocytes with VA, prior 24-h treatment with palmitic acid (PA), alpha-linolenic acid (ALA) or docosahexaenoic acid (DHA) has the effect on the FADS2 expression. RT-qPCR showed that in astrocytes not challenged with VA, PA increased fads2 gene expression and DHA decreased it. However, in VA-primed astrocytes, PA doubled the FADS2 mRNA levels, while DHA increased fads2 gene expression, oppositely to non-primed cells. Furthermore, similar changes were seen in VA-primed astrocytes with regard to delta6-desaturase protein levels following PA and DHA treatment. ALA did not have any effect on the FADS2 mRNA and protein levels in either VA-primed or non-primed astrocytes. These findings indicate that in the presence of vitamin A, DHA upregulates fads2 gene expression in astrocytes.

Repair of Neurological Function in Response to FK506 Through CaN/NFATc1 Pathway Following Traumatic Brain Injury in Rats

Tacrolimus (FK506), an immunophilin ligand, has been widely shown to be neuroprotective in a posttraumatic period. The nuclear factor of activated T cells (NFATc1) pathway plays an important role in regenerating neurological function following traumatic brain injury (TBI), but the precise mechanism underlying FK506-induced repair of neurological functions remains unclear. In the present study, a total of 210 SD rats were enrolled and randomly divided into sham group, TBI group and FK506 group. The rats in the TBI and FK506 groups were inflicted with moderate TBI left lateral fluid percussion impact. A modified neurological severity score (mNSS) system was used to evaluate the severity of effects on nerve function. mNSS levels were significantly lower in the FK506 group than in the TBI group. The zaccumulation of cerebral water content was lower, cerebral Aquaporin 4 (AQP4) mRNA level was lower, the number of growth-associated protein-43 (GAP-43)-positive cells was higher, and the distribution of vesicles containing excitatory neurotransmitters was altered in the injured cortex in the FK506 group. Moreover, the cortical mRNA and serum protein expression levels of interleukin-2 (IL-2) and interferon-γ (IFN-γ) were decreased in FK506 group, especially at 6 h and at 1 day after TBI. At days 1-28 after TBI, the expression of cleaved-caspase 3, which indicates apoptosis, was lower in the FK506 group than in the TBI group. Mechanistically, FK506 significantly down-regulated the mRNA and protein levels of calcium-regulated phosphatase (calcineurin, CaN) and inhibited the activation of NFATc1. These results demonstrate that FK506 relieved inflammatory responses by regulating the NFATc1 signaling pathway and promoting the synaptic reconstruction of neurons and glial cells by regulating cell apoptosis, thereby facilitated improvements in neurological function.

Interaction of myosin VI and its binding partner DOCK7 plays an important role in NGF-stimulated protrusion formation in PC12 cells

DOCK7 (dedicator of cytokinesis 7) is a guanidine nucleotide exchange factor (GEF) for Rac1 GTPase that is involved in neuronal polarity and axon generation as well in Schwann cell differentiation and myelination. Recently, we identified DOCK7 as the binding partner of unconventional myosin VI (MVI) in neuronal-lineage PC12 cells and postulated that this interaction could be important in vivo [Majewski et al. (2012) Biochem Cell Biol., 90:565-574]. Herein, we found that MVI-DOCK7 interaction takes also place in other cell lines and demonstrated that MVI cargo domain via its RRL motif binds to DOCK7 C-terminal M2 and DHR2 domains. In MVI knockdown cells, lower Rac1 activity and a decrease of DOCK7 phosphorylation on Tyr1118 were observed, indicating that MVI could contribute to DOCK7 activity. MVI and DOCK7 co-localization was maintained during NGF-stimulated PC12 cell differentiation and observed also in the outgrowths. Also, during differentiation an increase in phosphorylation of DOCK7 as well as of its downstream effector JNK kinase was detected. Interestingly, overexpression of GFP-tagged MVI cargo domain (GFP-GT) impaired protrusion formation indicating that full length protein is important for this process. Moreover, a transient increase in Rac activity observed at 5min of NGF-stimulated differentiation of PC12 cells (overexpressing either GFP or GFP-MVI) was not detected in cells overexpressing the cargo domain. These data indicate that MVI-DOCK7 interaction could have functional implications in the protrusion outgrowth, and full length MVI seems to be important for delivery and maintenance of DOCK7 along the protrusions, and exerting its GEF activity.

Identification of new scaffolds with anti-tumor action toward human glioblastoma cells

Compounds containing an isothiazolonaphthoquinone core and HDAC inhibitors with an indolyl-substituted biphenyl-4-yl-acrylohydroxamic acid are promising drug candidates against malignant brain tumors, glioblastomas.

Isolation of vascular endothelial cells from intact and injured murine brain cortex-technical issues and pitfalls in FACS analysis of the nervous tissue

CNS endothelial cells (CNS-ECs), one of the main non-neural CNS cell populations, play a vital role in physiology, pathology, and regeneration of the nervous system. Therefore, there is an urgent need to enhance our knowledge on their biology to elucidate mechanisms responsible for the blood brain barrier function in normal and pathological conditions, interaction between brain endothelium and neural stem cells in the neurogenic niche, the paracrine processes in the brain and spinal cord, etc. Here, we described a novel, simple, and efficient protocol for isolation of endothelial, vessel-forming cells from the murine CNS, which is based on Sca-1 expression. Using this newly described protocol we were able to detect and sort viable, highly pure CNS-ECs with minimal contamination by cells of non-endothelial origin. This method will increase the availability of CNS-ECs for in vitro research. Moreover, we compared phenotype of CNS-ECs isolated from neonatal mice and adult intact and injured brain looking for the cells of endothelial precursor characteristic, such as those found in the bone marrow and circulating in the bloodstream after organ injuries. We have found that neonatal brain capillaries contain proportion of endothelial precursor cells (Sca-1(+) , CD45(-) , c-Kit(+) ). Such precursors were also found in adult brain cortex, both in intact and injured brain. Finally, we discuss several crucial technical issues concerning CNS tissue preparation for flow cytometry analysis and cell sorting as well as nonspecific antibody binding caused by inflammatory microglia/macrophages which should be avoided in order to reliable isolation of pure CNS cells for downstream procedures including cell transplantation-based translational studies.

Arginine deprivation affects glioblastoma cell adhesion, invasiveness and actin cytoskeleton organization by impairment of β-actin arginylation

A deficit of exogenous arginine affects growth and viability of numerous cancer cells. Although arginine deprivation-based strategy is currently undergoing clinical trials, molecular mechanisms of tumor cells’ response to arginine deprivation are not yet elucidated. We have examined effects of arginine starvation on cell motility, adhesion and invasiveness as well as on actin cytoskeleton organization of human glioblastoma cells. We observed for the first time that arginine, but not lysine, starvation affected cell morphology, significantly inhibited their motility and invasiveness, and impaired adhesion. No effects on glia cells were observed. Also, arginine deprivation in glioblastoma evoked specific changes in actin assembly, decreased β-actin filament content, and affected its N-terminal arginylation. We suggest that alterations in organization of β-actin resulted from a decrease of its arginylation could be responsible for the observed effects of arginine deprivation on cell invasiveness and migration. Our data indicate that arginine deprivation-based treatment strategies could inhibit, at least transiently, the invasion process of highly malignant brain tumors and may have a potential for combination therapy to extend overall patient survival.

Umbilical cord blood mesenchymal stem cells co-modified by TERT and BDNF: a novel neuroprotective therapy for neonatal hypoxic-ischemic brain damage

Hypoxic-ischemic brain damage (HIBD), a leading cause of perinatal disability and death, has limited therapeutic options. Stem cell therapy has been demonstrated as a potential novel therapy for neurological disorders. Compared with other types of stem cells, umbilical cord blood mesenchymal stem cells (UCB-MSCs) have several unique characteristics, such as a higher rate of cell proliferation and clonality. However, the limited life span of UCB-MSCs hinders their clinical application. Therefore, efforts are urgently needed to circumvent this disadvantage. Telomerase reverse transcriptase (TERT), which promotes cell proliferation and survival, plays a protective role in hypoxic-ischemic (HI) brain injury. Thus, it is reasonable to propose that UCB-MSCs modified by exogenous TERT expression might have a longer lifespan and increased viability. Moreover, brain-derived neurotrophic factor (BDNF), a neurotrophin that regulates development, regeneration, survival and maintenance of neurons, facilitates post-injury recovery when administered by infusion or virus-mediated delivery. Therefore, TERT- and BDNF-modified UCB-MSCs may have a longer lifespan and also maintain neural differentiation, thus promoting the recovery of neurological function following hypoxic-ischemic brain damage (HIBD) and thereby representing a new effective strategy for HIBD in neonates.

Modulation of NMDAR subunit expression by TRPM2 channels regulates neuronal vulnerability to ischemic cell death

Neuronal vulnerability to ischemia is dependent on the balance between prosurvival and prodeath cellular signaling. In the latter, it is increasingly appreciated that toxic Ca(2+) influx can occur not only via postsynaptic glutamate receptors, but also through other cation conductances. One such conductance, the Transient receptor potential melastatin type-2 (TRPM2) channel, is a nonspecific cation channel having homology to TRPM7, a conductance reported to play a key role in anoxic neuronal death. The role of TRPM2 conductances in ischemic Ca(2+) influx has been difficult to study because of the lack of specific modulators. Here we used TRPM2-null mice (TRPM2(-/-)) to study how TRPM2 may modulate neuronal vulnerability to ischemia. TRPM2(-/-) mice subjected to transient middle cerebral artery occlusion exhibited smaller infarcts when compared with wild-type animals, suggesting that the absence of TRPM2 is neuroprotective. Surprisingly, field potentials (fEPSPs) recorded during redox modulation in brain slices taken from TRPM2(-/-) mice revealed increased excitability, a phenomenon normally associated with ischemic vulnerability, whereas wild-type fEPSPs were unaffected. The upregulation in fEPSP in TRPM2(-/-) neurons was blocked selectively by a GluN2A antagonist. This increase in excitability of TRPM2(-/-) fEPSPs during redox modulation depended on the upregulation and downregulation of GluN2A- and GluN2B-containing NMDARs, respectively, and on augmented prosurvival signaling via Akt and ERK pathways culminating in the inhibition of the proapoptotic factor GSK3β. Our results suggest that TRPM2 plays a role in downregulating prosurvival signals in central neurons and that TRPM2 channels may comprise a therapeutic target for preventing ischemic damage.

Upregulation of SYF2 is associated with neuronal apoptosis caused by reactive astrogliosis to neuroinflammation

SYF2, known as CCNDBP1-interactor or p29, is likely involved in pre-mRNA splicing and cell cycle progression. The present study was designed to elucidate dynamic changes in SYF2 expression and distribution in the cerebral cortex in a lipopolysaccharide (LPS)-induced neuroinflammation rat model. It was found that SYF2 expression was induced strongly in active astrocytes after LPS injection. In vitro studies showed that the upregulation of SYF2 might be involved in the activation of C6 cells after LPS challenge and the neuronal apoptosis after conditioned media challenge. In addition, with silencing of SYF2 in C6 and PC12 cells by siRNA, the results indicated that SYF2 was required for astrocyte activation and neuronal apoptosis induced by LPS. Our findings on the cellular signaling pathway may provide a new therapeutic strategy against neuroinflammation in the CNS.

Bone marrow stromal cells induce cell cycle arrest in reactive astrocytes in vitro

Transplantation of bone marrow stromal cells (BMSCs) reduces astrogliosis, decreases scar thickness and improves neurological functional recovery after brain damage. It is believed that transplanted BMSCs have a profound influence on astrocytes. To obtain the possible mechanism in their interaction, a co-culture system between BMSCs and astrocytes were set to investigate whether BMSCs could modulate cell cycle machinery in reactive astrocytes. The results obtained showed cell cycle regulatory proteins, cdk4 along with its activator cyclin D1, and PCNA increased while p27, an endogenous cyclin-dependent kinase inhibitor, deceased in glutamate-treated astrocytes in vitro. However, BMSCs influenced cell cycle elements in the cocultured astrocytes: cyclin D1, cdk 4 and PCNA were downregulated, while p27 was unregulated. Flow cytometry showed astrocytes in the S phase after glutamate incubation increased to 17.4±2.0% while restored to a level of 7.8±1.1% when cocultured with BMSCs. l-Canavanine, an inhibitor of inducible nitric oxide synthase, partially reversed the S phase to 11.3±0.4% in the cocultured astrocytes. These data indicated that BMSCs might inhibit the cell cycle control system in reactive astrocytes and nitric oxide signaling was involved in this process. The decline of astrogliosis conferred by BMSCs may derive from their effect of inhibiting the cell cycle progression in astrocytes.

Early steps of microglial activation are directly affected by neuroprotectant FK506 in both in vitro inflammation and in rat model of stroke

Neuroprotective and/or neuroregenerative activity of FK506, its derivatives, and to a lesser extent cyclosporin A (CsA) in animal models of neurodegenerative diseases of different etiology have been reported. Here, we verified a hypothesis that the most likely mechanism of their neuroprotective action is inhibition of the early steps of inflammatory activation of microglia by interference with mitogen-activated protein kinase (MAPK) signaling. The effect of immunosuppressants on lipopolysaccharide (LPS)-induced changes in morphology, proliferation, and motility of rat primary microglial cultures was evaluated. FK506 and CsA directly inhibited LPS-induced microglia activation and inflammatory responses. While both drugs efficiently reduced the expression of iNOS and the release of nitric oxide, only FK506 strongly inhibited the expression of Cox-2 and secretion of the mature form of IL-1β. FK506 strongly reduced LPS-induced activation of MAPK, and its downstream signaling crucial for inflammatory responses. Comparative analysis of global gene expression in rat ischemic brains and in LPS-stimulated microglial cultures revealed many genes and signaling pathways regulated in the same way in both systems. FK506 treatment blocked a majority of genes induced by an ischemic insult in the cortex, in particular inflammatory/innate immunity and apoptosis-related genes. Microglia-mediated inflammation is considered as one of the most important components of brain injury after trauma or stroke; thus, effective and multifaceted blockade of microglial activation by FK506 has clinical relevance and potential therapeutic implications.

Telomerase Reverse Transcriptase Upregulation Attenuates Astrocyte Proliferation and Promotes Neuronal Survival in the Hypoxic–Ischemic Rat Brain

Background and Purpose—

Telomerase reverse transcriptase (TERT) is tightly related to the resistance of cells to stress and injury. However, little is known about the roles of TERT in the nervous system. We try to investigate the effects of TERT on the function of astrocytes in developing rat brains subjected to hypoxia–ischemia.

Methods—

TERT expression was detected in rat brains with hypoxia–ischemia. In in vitro study, the function of astrocytes with TERT overexpression was measured, and the effects of astrocyte on neuronal apoptosis were examined. Moreover, overexpression or inhibition of TERT was conducted in vivo by gene transduction. Astrocyte proliferation was examined through Ki67 staining. Terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling staining and brain infarct volume calculation were used to detect neuronal injury.

Results—

Both TERT mRNA and protein were upregulated in neurons within 2 days but shifted to astrocytes at Day 3 after hypoxia–ischemia. Astrocyte proliferation was inhibited with TERT overexpression due to the upregulation of cell-cycle regulatory protein p15. Meanwhile, the apoptosis of neurons increased, whereas neurons were cocultured with conditioned media from astrocytes with TERT inhibition compared with TERT overexpression due to the decrease of neurotrophin-3 expression in astrocytes. Furthermore, Ki67-positive astrocytes and neuronal injury were found to be inhibited in TERT-overexpressing rat brains with hypoxia–ischemia.

Conclusions—

TERT attenuates astrocyte proliferation and promotes neuronal survival in the developing rat brain after hypoxia–ischemia, partly through its enhancement of p15 and neurotrophin-3 expression in astrocytes.

Differential roles for STIM1 and STIM2 in store-operated calcium entry in rat neurons

The interaction between Ca²⁺ sensors STIM1 and STIM2 and Ca²⁺ channel-forming protein ORAI1 is a crucial element of store-operated calcium entry (SOCE) in non-excitable cells. However, the molecular mechanism of SOCE in neurons remains unclear. We addressed this issue by establishing the presence and function of STIM proteins. Real-time polymerase chain reaction from cortical neurons showed that these cells contain significant amounts of Stim1 and Stim2 mRNA. Thapsigargin (TG) treatment increased the amount of both endogenous STIM proteins in neuronal membrane fractions. The number of YFP-STIM1/ORAI1 and YFP-STIM2/ORAI1 complexes was also enhanced by such treatment. The differences observed in the number of STIM1 and STIM2 complexes under SOCE conditions and the differential sensitivity to SOCE inhibitors suggest their distinct roles. Endoplasmic reticulum (ER) store depletion by TG enhanced intracellular Ca²⁺ levels in loaded with Fura-2 neurons transfected with YFP-STIM1 and ORAI1, but not with YFP-STIM2 and ORAI1, which correlated well with the number of complexes formed. Moreover, the SOCE inhibitors ML-9 and 2-APB reduced Ca²⁺ influx in neurons expressing YFP-STIM1/ORAI1 but produced no effect in cells transfected with YFP-STIM2/ORAI1. Moreover, in neurons transfected with YFP-STIM2/ORAI1, the increase in constitutive calcium entry was greater than with YFP-STIM1/ORAI1. Our data indicate that both STIM proteins are involved in calcium homeostasis in neurons. STIM1 mainly activates SOCE, whereas STIM2 regulates resting Ca²⁺ levels in the ER and Ca²⁺ leakage with the additional involvement of STIM1.

The hydrophobic dipeptide Leu-Ile inhibits immobility induced by repeated forced swimming via the induction of BDNF

Depression has recently become a serious problem in society worldwide. However, we lack appropriate therapeutic tools, since the causes of depression remain unclear. Degeneration of neuronal cells and a decrease in neurogenesis have been suggested recently as two of the factors responsible for depression-like behavior. Furthermore, brain-derived neurotrophic factor (BDNF) is also suggested to be an important factor in recovering from such behavior. We have previously demonstrated that the hydrophobic dipeptide leucyl-isoleucine (Leu-Ile) induces BDNF in cultured neuronal cells. We therefore investigated possible antidepressant-like effects of Leu-Ile in an animal model using the repeated forced swim test (FST). Mice were forced to swim for 6 min once a day in a cylinder containing water. The mice were treated with Leu-Ile s.c. or p.o. immediately after each FST. Five-day repeated Leu-Ile treatment significantly increased BDNF mRNA levels and activated the BDNF/Akt/mTOR signaling pathway in the hippocampi of the mice. While 2-week repeated FST increased immobility time, Leu-Ile treatment for 2 weeks offset this increase. In C57BL/6J-BDNF heterozygous knockout (BDNF(+/-)) mice, Leu-Ile failed to reduce the immobility time increased by repeated FST. We next investigated the extent of cell proliferation in the hippocampus as 5-bromo-2'-deoxy-uridine (BrdU) uptake into hippocampal cells. Repeated FST significantly reduced the number of BrdU-positive cells in the hippocampal dentate gyrus, while this deficit was prevented by repeated Leu-Ile treatment. These results suggest that Leu-Ile has an antidepressant-like effect, at least in part by supporting cell proliferation through the BDNF signaling pathway.

The effects of cyclosporin-A on axonal conduction deficits following traumatic brain injury in adult rats

Immunophilin ligands, including cyclosporin-A (CsA), have been shown to be neuroprotective in experimental models of traumatic brain injury (TBI) and to attenuate the severity of traumatic axonal injury. Prior studies have documented CsA treatment to reduce essential components of posttraumatic axonal pathology, including impaired axoplasmic transport, spectrin proteolysis, and axonal swelling. However, the effects of CsA administration on axonal function, following TBI, have not been evaluated. The present study assessed the effects of CsA treatment on compound action potentials (CAPs) evoked in corpus callosum of adult rats following midline fluid percussion injury. Rats received a 20 mg/kg bolus of CsA, or cremaphor vehicle, at either 15 min or 1 h postinjury, and at 24 h postinjury CAP recording was conducted in coronal brain slices. To elucidate how injury and CsA treatments affect specific populations of axons, CAP waveforms generated largely by myelinated axons (N1) were analyzed separately from the CAP signal, which predominantly reflects activity in unmyelinated axons (N2). CsA administration at 15 min postinjury resulted in significant protection of CAP area, and this effect was more pronounced in N1, than in the N2, CAP component. This treatment also significantly protected against TBI-induced reductions in high-frequency responding of the N1 CAP signal. In contrast, CsA treatment at 1 h did not significantly protect CAPs but was associated with atypical waveforms in N1 CAPs, including decreased CAP duration and reduced refractoriness. The present findings also support growing evidence that myelinated and unmyelinated axons respond differentially to injury and neuroprotective compounds.

Prolonged activation of ERK triggers glutamate-induced apoptosis of astrocytes: neuroprotective effect of FK506

Although, astrocytes are more resistant than neurons to ischemic injury, astrocyte death has been demonstrated in animal models of brain ischemia. Astrocytes death after ischemia/reperfusion may strongly affect neuronal survival because of the absence of their trophic and metabolic support to neurons, and astrocytic glutamate uptake. Early signals involved in astrocytes death are poorly understood. We demonstrated enhanced and mostly cytoplasmic activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) during glutamate-induced apoptosis of cultured astrocytes. Treatment with UO126, inhibitor of MEK1, threo-beta-benzyloxyaspartic acid, glutamate transporter inhibitor, and FK506, a cytoprotective drug prevented ERK activation and glutamate-induced apoptosis. Over-expression of ERK dual specificity phosphatases 5 and 6 reduced apoptosis in transfected astrocytes. Prolonged ERK1/2 activation was observed in ischemic brain: in the nucleus and cytoplasm of astrocytes in the cerebral cortex, and exclusively in the cytoplasm of astrocytes in the striatum. Global gene expression profiling in the cortex revealed that FK506 blocks middle cerebral artery occlusion-induced expression of numerous genes associated with ERK signaling pathway and apoptosis. The results demonstrate a pro-apoptotic role of sustained activation of ERK1/2 signaling in glutamate-induced death of astrocytes and the ability of FK506 to block both ERK activation and astrocytic cell death in vitro and in ischemic brains.

Molecular characterization of STAT signaling in inflammation and tumorigenesis

The Janus kinases (JAK) and signal transducer and activator of transcription (STAT) signaling are strongly activated in many tumors. STAT proteins are activated by phosphorylation at the tyrosine residue, then dimerize, translocate to the nucleus and bind DNA, initiating the transcription of target genes. Activation of JAK-STAT pathway is implicated in the regulation of cell growth, differentiation, survival and cross-talk between cancer and immune cells. The activation of STATs depends on phosphorylation on a single tyrosine residue (e.g., Tyr705 in STAT3 and Tyr694 in STAT5) in the C-terminal domain. Commercially available antibodies discriminate between total and specifically phosphorylated (active) forms of different STATs, which allows to measure directly STATs activation in crude cell extracts. Nuclear translocation and transcriptional activity of STATs can be measured in transfected cells using STAT dependent promoter driving reporter luciferase gene. STAT signaling pathway and STAT-dependent gene expression in cells can be specifically modulated using oligodeoxynucleotide (ODN) STAT decoy which is a double-stranded fragment of DNA containing an overlapping ISRE/GAS binding site.

Treatment modality affects allograft-derived Schwann cell phenotype and myelinating capacity

We used peripheral nerve allografts, already employed clinically to reconstruct devastating peripheral nerve injuries, to study Schwann cell (SC) plasticity in adult mice. By modulating the allograft treatment modality we were able to study migratory, denervated, rejecting, and reinnervated phenotypes in transgenic mice whose SCs expressed GFP under regulatory elements of either the S100b (S100-GFP) or nestin (Nestin-GFP) promoters. Well-differentiated SCs strongly expressed S100-GFP, while Nestin-GFP expression was stimulated by denervation, and in some cases, axons were constitutively labeled with CFP to enable in vivo imaging. Serial imaging of these mice demonstrated that untreated allografts were rejected within 20 days. Cold preserved (CP) allografts required an initial phase of SC migration that preceded axonal regeneration thus delaying myelination and maturation of the SC phenotype. Mice immunosuppressed with FK506 demonstrated mild subacute rejection, but the most robust regeneration of myelinated and unmyelinated axons and motor endplate reinnervation. While characterized by fewer regenerating axons, mice treated with the co-stimulatory blockade (CSB) agents anti-CD40L mAb and CTLAIg-4 demonstrated virtually no graft rejection during the 28 day experiment, and had significant increases in myelination, connexin-32 expression, and Akt phosphorylation compared with any other group. These results indicate that even with SC rejection, nerve regeneration can occur to some degree, particularly with FK506 treatment. However, we found that co-stimulatory blockade facilitate optimal myelin formation and maturation of SCs as indicated by protein expression of myelin basic protein (MBP), connexin-32 and phospho-Akt.

Analysis of FK506-mediated protection in an organotypic model of spinal cord damage: heat shock protein 70 levels are modulated in microglial cells

Functional loss after spinal cord injuries is originated by primary and secondary injury phases whose underlying mechanisms include massive release of excitatory amino acids to cytotoxic levels that contribute to neural death. Attenuation of this excitotoxicity is a key point for improving the functional outcome after injury. One of the drugs with potential neuroprotective actions is FK506, a molecule widely used as an immunosuppressant. FK506 may exert neuroprotection via inhibition of calcineurin by binding the FKBP12, or by binding other immunophilins such as FKBP52, leading to modulation of heat shock proteins (Hsp) 90 and 70. In the present study, we used an in vitro model of organotypic culture of rat spinal cord slices to assess whether FK506 is able to protect them against glutamate excitotoxicity. The results showed that FK506 promoted a significant protective effect on the spinal cord tissue at concentrations of 50 and 100 nM. Hsp70 induction was restricted to microglial cells in spinal cord slices treated with either glutamate or FK506. In contrast, the combination of both agents led to a transient reduction in Hsp70 levels in parallel to a marked reduction in IL-1beta precursor production by glial cells. The use of geldanamycin, which promotes persistent induction of Hsp70 in these cells as well as in motoneurons, did not produce tissue neuroprotection. These observations suggest that FK506 might protect spinal cord tissue by targeting on microglial cells and that transient downregulation of Hsp70 on these cells after excitotoxicity is a relevant mechanism of action of FK506.

Effect of ammonia, glutamine, and serum on calcineurin, p38MAPK-diP, GADD153/CHOP10, and CNTF in primary rat astrocyte cultures

Primary astrocyte cultures were subjected to different experimental schedules using several concentrations of ammonia (1, 3, and 5 mM ammonium chloride), serum (2.5%, 5%, and 12%), and glutamine (0.5, 1, and 3 mM) to analyze the involvement of calcineurin (CaN) in hyperammonemia and its relation with p38MAPK-diP and ciliary neurotrophic factor (CNTF). We demonstrated that exposure to ammonia affects CaN content, and confirmed the ammonia-induced reduction of CNTF expression; however, the involvement of CaN and p38MAPK-diP in CNTF reduction could not be confirmed. On the contrary, an inverse relationship between CaN and p38MAPK-diP contents was clearly demonstrated. GADD153/CHOP10 content was always higher under hyperammonemic conditions as well as under glutamine exposure, probably due to the osmotic stress provoked by glutamine accumulation, which was induced after exposure to ammonia. Statistical analysis demonstrated significant interactions of ammonia and serum for CaN, GADD153/CHOP10 and CNTF contents. The exposure to glutamine also induced changes in GADD153/CHOP10 and CaN; however, CNTF content was not affected. In conclusion, CaN content was affected by exposure to ammonia and glutamine; the serum content of the culture medium had a strong influence on the astroglial response to ammonium chloride, and glutamine exposure only reproduced some of the ammonia effects.

Inhibiting cell cycle progression reduces reactive astrogliosis initiated by scratch injury in vitro and by cerebral ischemia in vivo

Astrogliosis occurs in a variety of neuropathological disorders and injuries, and excessive astrogliosis can be devastating to the recovery of neuronal function. In this study, we asked whether reactive astrogliosis can be suppressed in the lesion area by cell cycle inhibition and thus have therapeutic benefits. Reactive astrogliosis induced in either cultured astrocytes by hypoxia or scratch injury, or in a middle cerebral artery occlusion (MCAO) ischemia model were combined to address this issue. In the cultured astrocytes, hypoxia induced a cell cycle activation that was associated with upregulation of the proliferating cell nuclear marker (PCNA). Significantly, the cell cycle inhibitor, olomoucine, inhibited hypoxia-induced cell cycle activation by arresting the cells at G1/S and G2/M in a dose-dependent manner and also reversed hypoxia-induced upregulation of PCNA. Also in the cultured astrocytes, scratch injury induced reactive astrogliosis, such as hypertrophy and an increase in BrdU(+) astrocytes, both of which were ameliorated by olomoucine. In the MCAO ischemia mouse model, dense reactive glial fibrillary acidic protein and PCNA immunoreactivity were evident at the boundary zone of focal cerebral ischemia at days 7 and 30 after MCAO. We found that intraperitoneal olomoucine administration significantly inhibited these astrogliosis-associated changes. To demonstrate further that cell cycle regulation impacts on astrogliosis, cyclin D1 gene knockout mice (cyclin D1(-/-)) were subjected to ischemia, and we found that the percentage of Ki67-positive astrocytes in these mice was markedly reduced in the boundary zone. The number of apoptotic neurons and the lesion volume in cyclin D1(-/-) mice also decreased as compared to cyclin D1(+/+) and cyclin D1(+/-) mice at days 3, 7, and 30 after local cerebral ischemia. Together, these in vitro and in vivo results strongly suggest that astrogliosis can be significantly affected by cell cycle inhibition, which therefore emerges as a promising intervention to attenuate reactive glia-related damage to neuronal function in brain pathology.

Mitochondrial localization of P2Y1, P2Y2 and P2Y12 receptors in rat astrocytes and glioma C6 cells

We have previously shown that P2Y1, P2Y2 and P2Y12 nucleotide receptors are functionally expressed and active on the cell surface of rat glioma C6 cells. In the present study, we have immunocytochemically shown their sub-cellular colocalization with mitochondria in these cells. The same colocalization of above receptors has been found in rat astrocytes. Additionally, differences in intracellular distribution of examined receptors between both cell lines have been observed. This data indicates that P2Y1, P2Y2 and P2Y12 receptor proteins exist within mitochondria of astrocytes and C6 cells, although their role in these sub-cellular structures remains unclear.

Olfactory ensheathing glia graft in combination with FK506 administration promote repair after spinal cord injury

The aim of this study was to determine whether a combination of olfactory ensheathing cell (OEC) graft with the administration of FK506, two experimental approaches that have been previously reported to exert protective/regenerative effects after spinal cord injury, promotes synergic restorative effects after complete or partial spinal cord injuries. In partial spinal cord injury, combination of an OEC graft and FK506 reduced functional deficits evaluated by the BBB score, motor-evoked potentials (MEPs) and H reflex tests, diminished cavitation, astrogliosis and increased sparing/regeneration of raphespinal fibers compared to untreated and single-treatment groups of rats. After complete spinal cord transection, the combined treatment significantly improved functional outcomes, promoted axonal regeneration caudal to the lesion, and diminished astrogliosis compared only to non-transplanted animals. Slightly, but non-significant, better functional and histological results were found in OEC-grafted animals treated with FK506 than in those given saline after spinal cord transection. Nevertheless, the combined treatment increased the percentage of rats that recovered MEPs and promoted a significant reduction in astrogliosis. In conclusion, this study demonstrates that OEC grafts combined with FK506 promote additive repair of spinal cord injuries to those exerted by single treatments, the effect being more remarkable when the spinal cord is partially lesioned.

Neuroprotectant FK506 inhibits glutamate-induced apoptosis of astrocytes in vitro and in vivo

Neuron-astrocyte interactions are critical for signalling, energy metabolism, extracellular ion and glutamate homeostasis, volume regulation and neuroprotection in the CNS. Glutamate uptake by astrocytes may prevent excitotoxic glutamate elevation and determine neuronal survival. However, an excess of glutamate can cause the death of astrocytes. FK506, an inhibitor of calcineurin, and an immunosuppressive drug, is neuroprotective in animal models of neurologic diseases, including focal and global ischaemia. In the present work, we demonstrate that a single injection of FK506 60 min after a transient middle cerebral artery occlusion (MCAo) significantly decreases the number of terminal deoxynucleotidyl transferase nick-end labelling (TUNEL)-positive cells in the ischaemic cortex and striatum. Using 3-D confocal microscopy we found that, 24 h after MCAo, many TUNEL-positive cells in the ischaemic striatum and cortex are astrocytes. Furthermore, we demonstrate that exposure of cultured cortical astrocytes to 50-100 mM Glu for 24 h induces apoptotic alterations in nuclear morphology, DNA fragmentation, dissipation of mitochondrial transmembrane potential (DeltaPsi) and caspase activation. FK506 (1 muM) efficiently inhibits Glu-induced apoptosis of cultured astrocytes, DNA fragmentation and changes in mitochondrial DeltaPsi. Our findings suggest that modulation of glutamate-induced astrocyte death early after reperfusion may be a novel mechanism of FK506-mediated neuroprotection in ischaemia.

Calcineurin and Erk1/2-signaling pathways are involved in the antiapoptotic effect of cyclosporin A on astrocytes exposed to simulated ischemia in vitro

The present study focused on mechanisms involved in the anti-apoptotic effect of cyclosporin A (CsA) towards ischemic injured astrocytes in vitro [under combined oxygen glucose deprivation (OGD)]. We investigated whether this action might be mediated through activation of extracellular signal regulated kinases 1 and 2 (Erk1/2) or attenuation of calcineurin (CaN) by immunosuppressant in ischemic astrocytes. Additionally, the influence of CsA on phosphorylation of Akt kinase was determined. After 21 days of in vitro culture, astrocytes were subjected to OGD (for 8 h) and CsA (0.25-10 microM); 0.25 microM CsA distinctly stimulated the Erk1/2 pathway in astrocytes exposed to OGD. This protective effect of CsA was strongly associated with CaN inhibition, increased expression of anti-apoptotic factors such as Bcl-X(L) and NF-kappaB, as well as suppression of caspase-3 activity. Maximum p-Akt kinase expression was observed following treatment with 1 microM CsA. Finally, we also demonstrated that the beneficial effect of CsA at a concentration of 10 microM is related mainly to strong CaN inhibition. The results obtained suggest that, depending on the concentration used, CsA might act as a protective agent towards ischemia-injured astroglial cells through alternative intracellular pathways associated with increased p-Erk1/2 and p-Akt expression or CaN inactivation.

Neuroimmunophilin ligands improve functional recovery and increase axonal growth after spinal cord hemisection in rats

We have previously shown that FK506 accelerates the rate of nerve regeneration in the peripheral nervous system (PNS) and increases regeneration of central nervous system (CNS) axons into a peripheral nerve graft. In the present study, we examined whether FK506 and a nonimmunosuppressive derivative (FK1706) improve functional recovery and long distance regeneration following a hemisection lesion of spinal cord at T10/T11. Rats were given daily subcutaneous injections of either FK506 (2 mg/kg/day), FK1706 (2 mg/kg/day), an equivalent volume of saline or 30% DMSO as vehicle, respectively. Functional recovery was assessed using a modified Tarlov/Klinger scale, walking along progressively narrower wooden beams (7.7-1.7 cm widths), and analysis of footprints obtained during walking. Compared to both control groups, FK506 and FK1706-treated animals demonstrated significant functional recovery 4 days (beam walking), 2 weeks (footprints), and 4 weeks (Tarlov/Klinger scale). By 11 weeks, FK506-treated and FK1706-treated animals were able to walk, albeit poorly, along even the narrowest (1.7 cm) beam. At 11 weeks, the spinal cords were re-exposed and a small piece of gel foam-soaked Fluoro-Gold was placed on the injured side 2-cm caudal to the first injury. Five days later, the animals were perfused and tissues prepared for fluorescence microscopy. FK506-treated and FK1706-treated rats demonstrate a significantly greater number of retrogradely labeled neurons in the red nucleus. The results implicate a nonimmunosuppressant mechanism in FK506's action and suggest that FK506 or a nonimmunosuppressant derivative may be useful for treatment of spinal cord injuries.

The carcinogenic potential of tacrolimus ointment beyond immune suppression: a hypothesis creating case report

Background

Since tacrolimus ointment was approved by the U.S. Food and Drug Administration (FDA) as a promising treatment for atopic dermatitis, it has been approved in more than 30 additional countries, including numerous European Union member nations. Moreover, in the current clinical routine the use of this drug is no longer restricted to the approved indication, but has been extended to a wide variety of inflammatory skin diseases including some with the potential of malignant transformation. So far, the side-effects reported from the topical use of tacrolimus have been relatively minor (e.g. burning, pruritus, erythema). Recently, however, the FDA reviewed the safety of topical tacrolimus, which resulted in a warning that the use of calcineurin inhibitors may be associated with an increased risk of cancer.

Case presentation

Oral lichen planus (OLP) was diagnosed in a 56-year-old women in February 1999. After several ineffective local and systemic therapeutic measures an off-label treatment of this recalcitrant condition using Tacrolimus 0.1% ointment was initiated in May 2002. After a few weeks of treatment most of the lesions ameliorated, with the exception of the plaques on the sides of the tongue. Nevertheless, the patient became free of symptoms which, however, reoccurred once tacrolimus was weaned, as a consequence treatment was maintained. In April 2005, the plaques on the left side of the tongue appeared increasingly compact and a biopsy specimen confirmed the suspected diagnosis of an oral squamous cell carcinoma.

Conclusion

The suspected causal relationship between topical use of tacrolimus and the development of a squamous cell carcinoma prompted us to test the notion that the carcinogenicity of tacrolimus may go beyond mere immune suppression. To this end, tacrolimus has been shown to have an impact on cancer signalling pathways such as the MAPK and the p53 pathway. In the given case, we were able to demonstrate that these pathways had also been altered subsequent to tacrolimus therapy.

Apparent presence of Ser133-phosphorylated cyclic AMP response element binding protein (pCREB) in brain mitochondria is due to cross-reactivity of pCREB antibodies with pyruvate dehydrogenase

Cyclic AMP response element binding protein (CREB) is a constitutive transcription factor that activates transcription following stimulus-dependent phosphorylation at Ser133, implicated in synaptic plasticity and neuronal survival pathways. The prevailing view that CREB is exclusively nuclear has been questioned by several studies, and, for example, mitochondrial localization has been reported. Using subcellular fractionation of rat brain cortex coupled with western immunoblotting with Ser133-phospho-CREB (pCREB) antibodies, we found a robust pCREB immunoreactivity (IR) in mitochondria-enriched fractions. The pCREB antibodies also stained the mitochondria, in addition to nuclei, of glial cells in primary cortical cultures. However, two CREB antibodies against different epitopes and gel shift assay detected the CREB protein mainly in the nuclear fraction. The two-dimensional electrophoretic mobility of mitochondrial pCREB IR differed markedly from the nuclear CREB/pCREB IR, indicating that the pCREB antibody cross-reacts with another mitochondrial protein. Immunoprecipitation of the mitochondrial pCREB IR produced three bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry as E2, E1 alpha-subunit, and E1 beta-subunit of pyruvate dehydrogenase complex. The cross-reacting epitope was identified as phospho-Ser300 of the alpha-subunit. In conclusion, this study confirms the presence of pCREB-like IR in brain mitochondria that, after careful scrutiny, turned out to be pyruvate dehydrogenase rather than authentic CREB.

MAPK signalling pathways as molecular targets for anti-inflammatory therapy--from molecular mechanisms to therapeutic benefits

Excessive inflammation is becoming accepted as a critical factor in many human diseases, including inflammatory and autoimmune disorders, neurodegenerative conditions, infection, cardiovascular diseases, and cancer. Cerebral ischemia and neurodegenerative diseases are accompanied by a marked inflammatory reaction that is initiated by expression of cytokines, adhesion molecules, and other inflammatory mediators, including prostanoids and nitric oxide. This review discusses recent advances regarding the detrimental effects of inflammation, the regulation of inflammatory signalling pathways in various diseases, and the potential molecular targets for anti-inflammatory therapy. Mitogen-activated protein kinases (MAPKs) are a family of serine/threonine protein kinases that mediate fundamental biological processes and cellular responses to external stress signals. Increased activity of MAPK, in particular p38 MAPK, and their involvement in the regulation of the synthesis of inflammation mediators at the level of transcription and translation, make them potential targets for anti-inflammatory therapeutics. Inhibitors targeting p38 MAPK and JNK pathways have been developed, and preclinical data suggest that they exhibit anti-inflammatory activity. This review discusses how these novel drugs modulate the activity of the p38 MAPK and JNK signalling cascades, and exhibit anti-inflammatory effects in preclinical disease models, primarily through the inhibition of the expression of inflammatory mediators. Use of MAPK inhibitors emerges as an attractive strategy because they are capable of reducing both the synthesis of pro-inflammatory cytokines and their signalling. Moreover, many of these drugs are small molecules that can be administered orally, and initial results of clinical trials have shown clinical benefits in patients with chronic inflammatory disease.

Neurotrophic Factor Expression after Focal Brain Ischemia Preceded by Different Preconditioning Strategies

BACKGROUND

Both prolonged brain ischemia and preconditioning (PC) induce expression of neurotrophic factors. However, the influence of PC on their expression after a long-term ischemia remains vague. Previously, we have found various effects of PC on mRNA levels of different cytokines after focal brain ischemia. Thus, we investigated mRNA expression of nerve growth factor, brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor after 90-min middle cerebral artery occlusion (MCAo) preceded by ischemic or chemical PC.

METHODS

MCAo was induced in rats using the suture method. PC had been carried out 3 days earlier. There were 4 experimental groups: MCAo alone; ischemic PC and MCAo; chemical PC and MCAo, and sham-operated rats. Expression of mRNAs in the ipsi- and contralateral cortex was studied by semiquantitative RT-PCR at 12 and 24 h after MCAo.

RESULTS

Despite clearly neuroprotective effects of both PC strategies, mRNA levels of neurotrophic factors were similar in tolerant and nontolerant rats. Only BDNF mRNA expression, 12 h after reperfusion, was lower when ischemic PC was applied prior to long-term ischemia.

CONCLUSIONS

These results suggest that PC generally does not change the expression of neurotrophic factor expression after a long-term focal brain ischemia compared to the nontolerant state.

Increased Matrix Metalloproteinase-9 in Blood in Association with Activation of Interleukin-6 after Traumatic Brain Injury: Influence of Hypothermic Therapy

Recent experimental data have shown that levels of matrix metalloproteinase-9 (MMP-9) increase after traumatic brain injury (TBI), degrading components of the basal lamina disrupting the blood-brain barrier. However, the post-traumatic secretion patterns of MMP-9 in humans are unknown. We measured the concentration of MMP-9 in plasma after TBI at the same time as the concentration of interleukin-6 (IL-6) in serum. Levels of MMP-9 and IL-6 in systemic arterial and jugular venous blood from seven patients with TBI were measured on days 0 and 1 post-injury. All patients underwent hypothermia at 32-35 degrees C as soon as possible after admission. Before induction of hypothermia, levels of MMP-9 in arterial and internal jugular venous blood exceeded the normal range. Higher MMP-9 levels were detected in internal jugular venous blood than in arterial blood. After hypothermia had been induced, MMP-9 levels in arterial blood and internal jugular venous blood decreased significantly, to within the normal range. In addition to these changes, a significant correlation was seen between levels of MMP-9 and IL-6 in internal jugular venous blood during the investigation period. These results indicate that MMP-9 is elevated in patients with acute TBI, and may play an important role in traumatic brain damage. The elevation of MMP-9 is associated with inflammatory events following TBI. Hypothermic intervention may suppress the elevation of MMP-9 with suppression of the inflammatory response, affording neuroprotection in TBI.

Impairment of phosphatase 2A contributes to the prolonged MAP kinase phosphorylation in Alzheimer's disease fibroblasts

The serine/threonine phosphatase 2A (PP2A) has been implicated in the pathogenesis of Alzheimer's disease (AD) due to its important role in regulating dephosphorylation of the microtubule-associated protein tau and mitogen-activated protein (MAP) kinase. In the present study, we show that PP2A was responsible for dephosphorylation of the extracellular signal-regulated kinase 1/2 (Erk1/2) following its activation by BK stimulation. Abnormal gene and protein expressions of PP2A, as well as its activity, were found to contribute to the abnormally prolonged Erk1/2 phosphorylation in the AD fibroblasts. Inhibition of PP2A with okadiac acid produced enhanced and more lasting Erk1/2 phosphorylation after BK stimulation, whereas FK506, an inhibitor of PP2B and FK-binding protein, inhibited the BK-stimulated Erk1/2 phosphorylation. Furthermore, while the phosphorylated Erk1/2 was concentrated in the nucleus of AC cells, it was mainly distributed in the extranuclear compartments of AD cells. These results suggest that the delayed dephosphorylation of Erk1/2 in AD cells following its BK-stimulated activation may be due to deficits of PP2A activity and impaired nuclear translocation of phosphorylated Erk1/2.

Molecular mechanisms of neuroprotective action of immunosuppressants--facts and hypotheses

Cyclosporin A (CsA) and FK506 (Tacrolimus) are short polypeptides which block the activation of lymphocytes and other immune system cells. Immunosuppressants exert neuroprotective and neurotrophic action in traumatic brain injury, sciatic nerve injury, focal and global ischemia in animals. Their neuroprotective actions are not understood and many hypotheses have been formed to explain such effects. We discuss a role of drug target--calcineurin in neuroprotective action of immunosuppressants. Protein dephosphorylation by calcineurin plays an important role in neuronal signal transduction due to its ability to regulate the activity of ion channels, glutamate release, and synaptic plasticity. In vitro FK506 protects cortex neurons from NMDA-induced death, augments NOS phosphorylation inhibiting its activity and NO synthesis. However, in vivo experiments demonstrated that FK506 in neuroprotective doses did not block excitotoxic cell death nor did it alter NO production during ischemia/reperfusion. Tissue damage in ischemia is the result of a complex pathophysiological cascade, which comprises a variety of distinct pathological events. Resident non-neuronal brain cells respond rapidly to neuronal cell death and may have both deleterious and useful role in neuronal damage. There is increasing evidence that reactive gliosis and post-ischemic inflammation involving microglia contribute to ischemic damage. We have demonstrated that FK506 modulates hypertrophic/proliferative responses and proinflammatory cytokine expression in astrocytes and microglia in vitro and in focal transient brain ischemia. Our findings suggest that astrocytes and microglia are direct targets of FK506 and modulation of glial response and inflammation is a possible mechanism of FK506-mediated neuroprotection in ischemia.

A novel mechanism of FK506-mediated neuroprotection: Downregulation of cytokine expression in glial cells

Immunosuppressant FK506 is neuroprotective in experimental models of cerebral ischemia, but the molecular mechanisms underlying this neuroprotection remain unknown. We have demonstrated that FK506 inhibits the signaling pathways that regulate hypertrophic/proliferative responses in cultured astrocytes. Ischemia/reperfusion injury is associated with the proliferation and hypertrophy of astrocytes and with inflammatory responses. In the present work, we sought to determine whether FK506 neuroprotection after middle cerebral artery occlusion (MCAo) in rat is mediated via suppression of glia activation and changes in cytokine expression. Neurological deficits, infarct size, and astrocyte/microglial response were quantified in rats subjected to 90 min of MCAo. Changes in the mRNA expression of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha) in ipsilateral and contralateral cortices were determined by reverse transcription-polymerase chain reaction (RT-PCR). FK506 administered at 1 mg/kg, 60 min after MCAo, produced a significant improvement in neurological function and reduction of infarct volume. In FK506-treated rats, a significant reduction of IL-1beta, IL-6, and TNF-alpha expression was observed 12 h after reperfusion. FK506 neuroprotection was associated with a significant downregulation of IL-1beta expression in astrocytes and microglia in the injured side. FK506 selectively decreased the levels of TNF-alpha, and IL-1beta mRNAs in astrocytes in vitro, with no effect on transforming growth factor-beta 1 (TGF-beta1) and IL-6 expression. Moreover, FK506 inhibits lipopolysaccharide (LPS)-induced activation and cytokine expression in microglia in vitro. Our findings suggest that astrocytes and microglia are targets for FK506, and that modulation of glial response and inflammation may be a mechanism of FK506-mediated neuroprotection in ischemia.

T cell receptor-independent basal signaling via Erk and Abl kinases suppresses RAG gene expression

Signal transduction pathways guided by cellular receptors commonly exhibit low-level constitutive signaling in a continuous, ligand-independent manner. The dynamic equilibrium of positive and negative regulators establishes such a tonic signal. Ligand-independent signaling by the precursors of mature antigen receptors regulates development of B and T lymphocytes. Here we describe a basal signal that controls gene expression profiles in the Jurkat T cell line and mouse thymocytes. Using DNA microarrays and Northern blots to analyze unstimulated cells, we demonstrate that expression of a cluster of genes, including RAG-1 and RAG-2, is repressed by constitutive signals requiring the adapter molecules LAT and SLP-76. This TCR-like pathway results in constitutive low-level activity of Erk and Abl kinases. Inhibition of Abl by the drug STI-571 or inhibition of signaling events upstream of Erk increases RAG-1 expression. Our data suggest that physiologic gene expression programs depend upon tonic activity of signaling pathways independent of receptor ligation.

In the absence of basal signaling, RAG activity is high at a time during T cell development when it is otherwise normally suppressed