Role of extracellular signal regulated kinase 5 in neuronal survival

Bone and Extracellular Signal-Related Kinase 5 (ERK5)

Bones are vital for anchoring muscles, tendons, and ligaments, serving as a fundamental element of the human skeletal structure. However, our understanding of bone development mechanisms and the maintenance of bone homeostasis is still limited. Extracellular signal-related kinase 5 (ERK5), a recently identified member of the mitogen-activated protein kinase (MAPK) family, plays a critical role in the pathogenesis and progression of various diseases, especially neoplasms. Recent studies have highlighted ERK5's significant role in both bone development and bone-associated pathologies. This review offers a detailed examination of the latest research on ERK5 in different tissues and diseases, with a particular focus on its implications for bone health. It also examines therapeutic strategies and future research avenues targeting ERK5.

Over-expression of miR-3584-5p Represses Nav1.8 Channel Aggravating Neuropathic Pain caused by Chronic Constriction Injury

Nav1.8, a tetrodotoxin-resistant voltage-gated sodium channels (VGSCs) subtype encoded by SCN10A, which plays an important role in the production and transmission of peripheral neuropathic pain signals. Studies have shown that VGSCs may be key targets of MicroRNAs (miRNAs) in the regulation of neuropathic pain. In our study, bioinformatics analysis showed that the targeting relationship between miR-3584-5p and Nav1.8 was the most closely. The purpose of this study was to investigate the roles of miR-3584-5p and Nav1.8 in neuropathic pain. The effects of miR-3584-5p on chronic constriction injury (CCI)-induced neuropathic pain in rats was investigated by intrathecal injection of miR-3584-5p agomir (an agonist, 20 μM, 15 μL) or antagomir (an antagonist, 20 μM, 15 μL). The results showed that over-expression of miR-3584-5p aggravated neuronal injury by hematoxylin-eosin (H&E) staining and mechanical/thermal hypersensitivity in CCI rats. MiR-3584-5p indirectly inhibited the expression of Nav1.8 by up-regulating the expression of key proteins in the ERK5/CREB signaling pathway, and also inhibited the current density of the Nav1.8 channel, changed its channel dynamics characteristic, thereby accelerating the transmission of pain signals, and further aggravating pain. Similarly, in PC12 and SH-SY5Y cell cultures, miR-3584-5p increased the level of reactive oxygen species (ROS) and inhibited mitochondrial membrane potential (Δψm) in the mitochondrial pathway, decreased the ratio of apoptosis-related factor Bcl-2/Bax, and thus promoted neuronal apoptosis. In brief, over-expression of miR-3584-5p aggravates neuropathic pain by directly inhibiting the current density of Nav1.8 channel and altering its channel dynamics, or indirectly inhibiting Nav1.8 expression through ERK5/CREB pathway, and promoting apoptosis through mitochondrial pathway.

Novel trajectories of the NK1R antagonist aprepitant in rotenone-induced Parkinsonism-like symptoms in rats: Involvement of ERK5/KLF4/p62/Nrf2 signaling axis

Regulation of the interplay between autophagy and oxidative stress is vital in maintaining neuronal homeostasis during neurotoxicity. The interesting involvement of NK1 receptor (NK1R) in neurodegeneration has highlighted the value of investigating the neuroprotective effect of aprepitant (Aprep), an NK1R antagonist in Parkinson's disease (PD). This study was conducted to disclose Aprep's ability to modulate extracellular signal-regulated kinase 5/Krüppel-like factor 4 (ERK5/KLF4) cue as molecular signaling implicated in regulating autophagy and redox signaling in response to rotenone neurotoxicity. Rotenone (1.5 mg/kg) was administered on alternate days, and rats were given Aprep simultaneously with or without PD98059, an ERK inhibitor, for 21 days. Aprep ameliorated motor deficits as verified by restored histological features, and intact neurons count in SN and striata along with tyrosine hydroxylase immunoreactivity in SN. The molecular signaling of Aprep was illustrated by the expression of KLF4 following the phosphorylation of its upstream target, ERK5. Nuclear factor erythroid 2-related factor 2 (Nrf2) was up-regulated, shifting the oxidant/antioxidant balance towards the antioxidant side, as evidenced by elevated GSH and suppressed MDA levels. In parallel, Aprep noticeably reduced phosphorylated α-synuclein aggregates due to autophagy induction as emphasized by marked LC3II/LC3I elevation and p62 level reduction. These effects were diminished upon PD98059 pre-administration. In conclusion, Aprep showed neuroprotective effects against rotenone-induced PD, which may be partially attributed to the activation of the ERK5/KLF4 signaling pathway. It modulated p62-mediated autophagy and Nrf2 axis which act cooperatively to counter rotenone-associated neurotoxicity pointing to Aprep's prospect as a curious candidate in PD research.

Protective Effect of GIP against Monosodium Glutamate-Induced Ferroptosis in Mouse Hippocampal HT-22 Cells through the MAPK Signaling Pathway

The effect of glucose-dependent insulinotropic polypeptide (GIP) on cells under oxidative stress induced by glutamate, a neurotransmitter, and the underlying molecular mechanisms were assessed in the present study. We found that in the pre-treatment of HT-22 cells with glutamate in a dose-dependent manner, intracellular ROS were excessively generated, and additional cell damage occurred in the form of lipid peroxidation. The neurotoxicity caused by excessive glutamate was found to be ferroptosis and not apoptosis. Other factors (GPx-4, Nrf2, Nox1 and Hspb1) involved in ferroptosis were also identified. In other words, it was confirmed that GIP increased the activity of sub-signalling molecules in the process of suppressing ferroptosis as an antioxidant and maintained a stable cell cycle even under glutamate-induced neurotoxicity. At the same time, in HT-22 cells exposed to ferroptosis as a result of excessive glutamate accumulation, GIP sustained cell viability by activating the mitogen-activated protein kinase (MAPK) signalling pathway. These results suggest that the overexpression of the GIP gene increases cell viability by regulating mechanisms related to cytotoxicity and reactive oxygen species production in hippocampal neuronal cell lines.

The MEK5/ERK5 Pathway in Health and Disease

The MEK5/ERK5 mitogen-activated protein kinases (MAPK) cascade is a unique signaling module activated by both mitogens and stress stimuli, including cytokines, fluid shear stress, high osmolarity, and oxidative stress. Physiologically, it is mainly known as a mechanoreceptive pathway in the endothelium, where it transduces the various vasoprotective effects of laminar blood flow. However, it also maintains integrity in other tissues exposed to mechanical stress, including bone, cartilage, and muscle, where it exerts a key function as a survival and differentiation pathway. Beyond its diverse physiological roles, the MEK5/ERK5 pathway has also been implicated in various diseases, including cancer, where it has recently emerged as a major escape route, sustaining tumor cell survival and proliferation under drug stress. In addition, MEK5/ERK5 dysfunction may foster cardiovascular diseases such as atherosclerosis. Here, we highlight the importance of the MEK5/ERK5 pathway in health and disease, focusing on its role as a protective cascade in mechanical stress-exposed healthy tissues and its function as a therapy resistance pathway in cancers. We discuss the perspective of targeting this cascade for cancer treatment and weigh its chances and potential risks when considering its emerging role as a protective stress response pathway.

17-β Estradiol Rescued Immature Rat Brain against Glutamate-Induced Oxidative Stress and Neurodegeneration via Regulating Nrf2/HO-1 and MAP-Kinase Signaling Pathway

Dysregulated glutamate signaling, leading to neuronal excitotoxicity and death, has been associated with neurodegenerative pathologies. 17β-estradiol (E2) is a human steroid hormone having a role in reproduction, sexual maturation, brain health and biological activities. The study aimed to explain the neuroprotective role of E2 against glutamate-induced ROS production, MAP kinase-dependent neuroinflammation, synaptic dysfunction and neurodegeneration in the cortex and hippocampus of postnatal day 7 rat brain. Biochemical and immunofluorescence analyses were applied. Our results showed that a single subcutaneous injection of glutamate (10 mg/kg) induced brain oxidative stress after 4 h by disturbing the homeostasis of glutathione (GSH) and revealed an upsurge in ROS and LPO levels and downregulated the expression of Nrf2 and HO-1 antioxidant protein. The glutamate-exposed P7 pups illustrated increased phosphorylation of stress-activated c-Jun N-terminal kinase (JNK) and p38 kinase (p38) and downregulated expression of P-Erk1/2. This was accompanied by pathological neuroinflammation as revealed by enhanced gliosis with upregulated expression of GFAP and Iba-1, and the activation of proinflammatory cytokines (TNF-α) in glutamate-injected P7 pups. Moreover, exogenous glutamate also reduced the expression of synaptic markers (PSD-95, SYP) and induced apoptotic neurodegeneration in the cortical and hippocampal regions by dysregulating the expression of Bax, Bcl-2 and caspase-3 in the developing rat brain. On the contrary, co-treatment of E2 (10 mg/kg) with glutamate significantly abrogated brain neuroinflammation, neurodegeneration and synapse loss by alleviating brain oxidative stress by upregulating the Nrf2/HO-1 antioxidant pathway and by deactivating pro-apoptotic P-JNK/P-p38 and activation of pro-survival P-Erk1/2 MAP kinase pathways. In brief, the data demonstrate the neuroprotective role of E2 against glutamate excitotoxicity-induced neurodegeneration. The study also encourages future studies investigating if E2 may be a potent neuroprotective and neurotherapeutic agent in different neurodegenerative diseases.

Inhibition of de novo ceramide biosynthesis affects aging phenotype in an in vitro model of neuronal senescence

Although aging is considered to be an unavoidable event, recent experimental evidence suggests that the process can be counteracted. Intracellular calcium (Ca²⁺_i) dyshomeostasis, mitochondrial dysfunction, oxidative stress, and lipid dysregulation are critical factors that contribute to senescence-related processes. Ceramides, a pleiotropic class of sphingolipids, are important mediators of cellular senescence, but their role in neuronal aging is still largely unexplored. In this study, we investigated the effects of L-cycloserine (L-CS), an inhibitor of thede novoceramide biosynthesis, on the aging phenotype of cortical neurons cultured for 22 days, a setting employed as anin vitromodel of senescence. Our findings indicate that, compared to control cultures, ‘aged’ neurons display dysregulation of [Ca²⁺]_ilevels, mitochondrial dysfunction, increased generation of reactive oxygen species (ROS), altered synaptic activity as well as the activation of neuronal death-related molecules. Treatment with L-CS positively affected the senescent phenotype, a result associated with recovery of neuronal [Ca²⁺]_isignaling and reduction of mitochondrial dysfunction and ROS generation. The results suggest that thede novoceramide biosynthesis represents a critical intermediate in the molecular and functional cascade leading to neuronal senescence and identify ceramide biosynthesis inhibitors as promising pharmacological tools to decrease age-related neuronal dysfunctions.

Neuroprotective effects of different frequency preconditioning exercise on neuronal apoptosis after focal brain ischemia in rats

OBJECTIVE

Preconditioning exercise can exert neuroprotective effects after stroke; however, the effects of exercise intensity, frequency, duration are unknown. We investigated the neuroprotective effect of different frequency preconditioning exercise on neuronal apoptosis after cerebral ischemia in rats.

METHODS

Rats were divided into the following five groups: 5 times a week of exercise (5/w-Ex) group, 3 times a week of exercise (3/w-Ex) group, once a week of exercise (1/w-Ex) group, no exercise (No-Ex) group, and intact control (control) group. Rats were made to run on a treadmill for 30 min per day at a speed of 25 m/min for 3 weeks. After the running program, the rats were subjected to 60-min left middle cerebral artery occlusion. Two days after ischemia, the cerebral infarct volume, neurological and motor function, Bcl-2-associated X protein (Bax)/B-cell lymphoma 2 (Bcl-2) ratio, expression of caspase-3, and TUNEL positive cells were examined in the cerebral cortex surrounding the ischemic zone.

RESULTS

The 3/w-Ex and 5/w-Ex groups showed significantly reduced infarct volumes compared with the No-Ex group, but the 1/w-Ex group did not. In addition, the 3/w-Ex and 5/w-Ex groups had improved neurological scores and sensorimotor function compared with the No-Ex group. The Bax/Bcl-2 ratio, expression of caspase-3, and TUNEL-positive cells significantly decreased in the penumbra area in the 3/w-Ex or 5/w-Ex groups compared with the No-Ex group.

DISCUSSION

Our findings suggested that three times or more per week of high-intensity preconditioning exercise exert neuroprotective effects through the downregulation of the Bax/Bcl-2 ratio and caspase-3 activation after stroke.

ABBREVIATIONS

TUNEL: terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick and labeling; MCAO:middle cerebral artery occlusion; BAX:Bcl-2-associated X protein; Bcl-2: B-cell lymphoma 2; TTC: 2,3,5-triphenyltetrazorlium chloride.

The Role of PI3K/Akt and ERK in Neurodegenerative Disorders

Disruption of Akt and Erk-mediated signal transduction significantly contributes in the pathogenesis of various neurodegenerative diseases (NDs), such as Parkinson's disease, Alzheimer's diseases, Huntington's disease, and many others. These regulatory proteins serve as the regulator of cell survival, motility, transcription, metabolism, and progression of the cell cycle. Therefore, targeting Akt and Erk pathway has been proposed as a reasonable approach to suppress ND progression. This review has emphasized on involvement of Akt/Erk cascade in the neurodegeneration. Akt has been reported to regulate neuronal toxicity through its various substrates like FOXos, GSK3β, and caspase-9 etc. Akt is also involved with PI3K in signaling pathway to mediate neuronal survival. ERK is another kinase which also regulates proliferation, differentiation, and survival of the neural cell. There has also been much progress in developing a therapeutic molecule targeting Akt and Erk signaling. Therefore, improved understanding of the molecular mechanism behind the regulatory aspect of Akt and Erk networks can make strong impact on exploration of the neurodegenerative disease pathogenesis.

Rutin hydrate ameliorates cadmium chloride-induced spatial memory loss and neural apoptosis in rats by enhancing levels of acetylcholine, inhibiting JNK and ERK1/2 activation and activating mTOR signalling

This study aimed at studying the potential neuroprotective effect of Rutin hydrate (RH) alone or in conjugation with α-tocopherol against cadmium chloride (CdCl₂)-induced neurotoxicity and cognitive impairment in rats and to investigate the mechanisms of action. Rats intoxicated with CdCl₂ were treated with the vehicle, RH, α-tocopherol or combined treatment were examined, and compared to control rats received vehicle or individual doses of either drug. Data confirmed that RH improves spatial memory function by increasing acetylcholine availability, boosting endogenous antioxidant potential, activating cell survival and inhibiting apoptotic pathways, an effect that is more effective when RH was conjugated with α-tocopherol. Mechanism of RH action includes activation of PP2A mediated inhibiting of ERK1/2 and JNK apoptotic pathways and inhibition of PTEN mediated activation of mTOR survival pathway. In conclusion, RH affords a potent neuroprotection against CdCl₂-induced brain damage and memory dysfunction and co-administration of α-tocopherol enhances its activity.

Exenatide exerts cognitive effects by modulating the BDNF-TrkB neurotrophic axis in adult mice

Modulation of insulin-dependent signaling is emerging as a valuable therapeutic tool to target neurodegeneration. In the brain, the activation of insulin receptors promotes cell growth, neuronal repair, and protection. Altered brain insulin signaling participates in the cognitive decline seen in Alzheimer's disease patients and the aging brain. Glucagon-like peptide-1 (GLP-1) regulates insulin secretion and, along with GLP-1 analogues, enhances neurotrophic signaling and counteracts cognitive deficits in preclinical models of neurodegeneration. Moreover, recent evidence indicates that GLP-1 modulates the activity of the brain-derived neurotrophic factor (BDNF). In this study, in adult wild-type mice, here employed as a model of mid-life brain aging, we evaluated the effects of a 2-month treatment with exenatide, a GLP-1 analogue. We found that exenatide promotes the enhancement of long-term memory performances. Biochemical and imaging analyses show that the drug promotes the activation of the BDNF-TrkB neurotrophic axis and inhibits apoptosis by decreasing p75NTR-mediated signaling. The study provides preclinical evidence for the use of exenatide to delay age-dependent cognitive decline.

Analysis of Nkx3.1:Cre-driven Erk5 deletion reveals a profound spinal deformity which is linked to increased osteoclast activity

Extracellular signal-regulated protein kinase 5 (ERK5) has been implicated during development and carcinogenesis. Nkx3.1-mediated Cre expression is a useful strategy to genetically manipulate the mouse prostate. While grossly normal at birth, we observed an unexpected phenotype of spinal protrusion in Nkx3.1:Cre;Erk5 fl/fl (Erk5 fl/fl) mice by ~6-8 weeks of age. X-ray, histological and micro CT (µCT) analyses showed that 100% of male and female Erk5 fl/fl mice had a severely deformed curved thoracic spine, with an associated loss of trabecular bone volume. Although sex-specific differences were observed, histomorphometry measurements revealed that both bone resorption and bone formation parameters were increased in male Erk5 fl/fl mice compared to wild type (WT) littermates. Osteopenia occurs where the rate of bone resorption exceeds that of bone formation, so we investigated the role of the osteoclast compartment. We found that treatment of RANKL-stimulated primary bone marrow-derived macrophage (BMDM) cultures with small molecule ERK5 pathway inhibitors increased osteoclast numbers. Furthermore, osteoclast numbers and expression of osteoclast marker genes were increased in parallel with reduced Erk5 expression in cultures generated from Erk5 fl/fl mice compared to WT mice. Collectively, these results reveal a novel role for Erk5 during bone maturation and homeostasis in vivo.

Increased T-cell Infiltration Elicited by Erk5 Deletion in a Pten-Deficient Mouse Model of Prostate Carcinogenesis

Prostate cancer does not appear to respond to immune checkpoint therapies where T-cell infiltration may be a key limiting factor. Here, we report evidence that ablating the growth regulatory kinase Erk5 can increase T-cell infiltration in an established Pten-deficient mouse model of human prostate cancer. Mice that were doubly mutant in prostate tissue for Pten and Erk5 (prostate DKO) exhibited a markedly increased median survival with reduced tumor size and proliferation compared with control Pten-mutant mice, the latter of which exhibited increased Erk5 mRNA expression. A comparative transcriptomic analysis revealed upregulation in prostate DKO mice of the chemokines Ccl5 and Cxcl10, two potent chemoattractants for T lymphocytes. Consistent with this effect, we observed a relative increase in a predominantly CD4+ T-cell infiltrate in the prostate epithelial and stroma of tumors from DKO mice. Collectively, our results offer a preclinical proof of concept for ERK5 as a target to enhance T-cell infiltrates in prostate cancer, with possible implications for leveraging immune therapy in this disease. Cancer Res; 77(12); 3158-68. ©2017 AACR.

Research progress of the role and mechanism of extracellular signal-regulated protein kinase 5 (ERK5) pathway in pathological pain

Extracellular signal-regulated protein kinase 5 (ERK5), also known as big mitogen-activated protein kinase 1 (MAPK1), is an important member of ERK family, which is a subfamily of the large MAPK family. ERK5 is expressed in many tissues, including the dorsal root ganglion (DRG) neurons and the spinal cord. In this review, we focus on elaborating ERK5-associated pathway in pathological pain, in which the ERK5/CREB (cyclic adenosine monophosphate (cAMP)-response element-binding protein) pathway plays a crucial role in the transduction of pain signal and contributes to pain hypersensitivity. ERK5 activation in the spinal dorsal horn occurs mainly in microglia. The activation of ERK5 can be mediated by N-methyl-D-aspartate (NMDA) receptors. We also elaborate the relationship between ERK5 activation and nerve growth factor-tyrosine kinase A (NGF-TrkA), and the connection between ERK5 activation and brain-derived neurotrophic factor (BDNF) in pathological pain in detail.

Yeast genetic interaction screen of human genes associated with amyotrophic lateral sclerosis: identification of MAP2K5 kinase as a potential drug target

To understand disease mechanisms, a large-scale analysis of human–yeast genetic interactions was performed. Of 1305 human disease genes assayed, 20 genes exhibited strong toxicity in yeast. Human–yeast genetic interactions were identified by en masse transformation of the human disease genes into a pool of 4653 homozygous diploid yeast deletion mutants with unique barcode sequences, followed by multiplexed barcode sequencing to identify yeast toxicity modifiers. Subsequent network analyses focusing on amyotrophic lateral sclerosis (ALS)-associated genes, such as optineurin (OPTN) and angiogenin (ANG), showed that the human orthologs of the yeast toxicity modifiers of these ALS genes are enriched for several biological processes, such as cell death, lipid metabolism, and molecular transport. When yeast genetic interaction partners held in common between human OPTN and ANG were validated in mammalian cells and zebrafish, MAP2K5 kinase emerged as a potential drug target for ALS therapy. The toxicity modifiers identified in this study may deepen our understanding of the pathogenic mechanisms of ALS and other devastating diseases.

The role of erythropoietin in remote renal preconditioning on hippocampus ischemia/reperfusion injury

Remote ischemic preconditioning (RIPC) is an intriguing approach which exposes a remote organ/tissue to a non-lethal transient ischemia/reperfusion (I/R) in order to potentiate the resistance of the desired organ/tissue against the next unwanted I/R. It has been suggested that RIPC exerts its effect through neuronal and hormonal pathways. The underlying mechanisms of RIPC are obscure and should be elucidated. In this study, we induced RIPC in mice using 3 cycles of 5 min ischemia alternating with 5 min reperfusion of the left renal artery. Renal failure was induced in mice by intra-peritoneal (i.p.) injection of 200 mg/kg body weight of gentamicin twice per day for 4 consecutive days. Global hippocampal ischemia reperfusion (I/R) was performed by bilateral carotid artery occlusion for 20 min followed by reperfusion for 72 h. Moreover, the retention trial of passive avoidance test was determined 72 h after global ischemia. Histopathological changes of hippocampus neurons were observed using Nissl staining to detect neuronal loss. Finally, terminal deoxynucleotidyl transferase mediated dUTP nick end-labeling (TUNEL) was performed to assess the status of apoptotic cells in the hippocampus. The results of this study suggest that renal ischemic preconditioning is a good candidate for prevention of I/R-induced hippocampal injury. However, RRPC (remote renal preconditioning) failed to exert a neuroprotective effect in mice with renal failure (RF), indicating the probable role of a humoral factor which is released from kidneys in response to ischemia. In agreement with this hypothesis, treatment of mice with rhEPO (5000 IU/kg intraperitoneal) before induction of RRPC restored the neuroprotective effects of RRPC in RF mice. Accordingly, it is plausible to expect that erythropoietin is released from kidneys to act as a mediator for RRPC-induced neuroprotective effects. Renal ischemic preconditioning prevents I/R-induced hippocampal injury. In contrast, renal failure hampers protective effects of RRPC, while exogenous administration of erythropoietin (EPO) significantly prevents the inhibiting effects of renal failure.

Pre-ischemic exercise reduces apoptosis in hippocampal CA3 cells after cerebral ischemia by modulation of the Bax/Bcl-2 proteins ratio and prevention of caspase-3 activation

Ischemia induces physiological alterations in neurons that lead to cell death. This study investigated the effects of pre-ischemic exercise on CA3 neurons. Rats were divided into three groups. Animals in the exercise group were trained 5 days a week for 4 weeks. Ischemia was induced by occlusion of both common carotid arteries (CCAs) for 20 min. Apoptotic cell death was detected by TUNEL assay. Furthermore, expression of different proteins was determined by immunohistochemical staining. The number of TUNEL-positive cells was significantly increased in the ischemia group, but pre-ischemic exercise significantly reduced apoptotic cell death (P < 0.001). In addition, our results showed a significant increase in the Bax/Bcl-2 ratio in the ischemia group. Pre-ischemic exercise attenuated this ratio (P < 0.05). Furthermore, the number of active caspase-3-positive neurons was significantly increased in the ischemia group, which was reduced markedly by exercise preconditioning (P < 0.05). This study showed that pre-ischemic exercise can exert neuroprotective effects against ischemia in CA3 neurons.

ERK5 pathway regulates transcription factors important for monocytic differentiation of human myeloid leukemia cells

Mitogen-activated protein kinases (MAPKs) are important transducers of external signals for cell growth, survival, and other cellular responses including cell differentiation. Several MAPK cascades are known with the MEK1/2-ERK1/2, JNK, and p38MAPKs receiving most attention, but the role of MEK5-ERK5 in intracellular signaling deserves more scrutiny, as this pathway transmits signals that can complement ERK/2 signaling. We hypothesized that the ERK5 pathway plays a role in the control of monocytic differentiation, which is disturbed in myeloid leukemia. We therefore examined the cellular phenotype and key molecular events which occur when human myeloid leukemia cells, acute (AML) or chronic (CML), are forced to differentiate by vitamin D derivatives (VDDs). This study was performed using established cell lines HL60 and U937, and primary cultures of blasts from 10 patients with ML. We found that ERK5 and its direct downstream target transcription factor MEF2C are upregulated by 1,25D in parallel with monocytic differentiation. Further, inhibition of ERK5 activity by specific pharmacological agents BIX02189 and XMD8-92 alters the phenotype of these cells by reducing the abundance of the VDD-induced surface monocytic marker CD14, and concomitantly increasing surface expression of the general myeloid marker CD11b. Similar results were obtained when the expression of ERK5 was reduced by siRNA or short hairpin (sh) RNA. ERK5 inhibition resulted in an expected decrease in MEF2C activation. We also found that in AML cells the transcription factor C/EBPβ is positively regulated, while C/EBPα is negatively regulated by ERK5. These findings provide new understanding of dysregulated differentiation in human myeloid leukemia.

Genetic activation of ERK5 MAP kinase enhances adult neurogenesis and extends hippocampus-dependent long-term memory

Recent studies have shown that inhibition of adult neurogenesis impairs the formation of hippocampus-dependent memory. However, it is not known whether increasing adult neurogenesis affects the persistence of hippocampus-dependent long-term memory. Furthermore, signaling mechanisms that regulate adult neurogenesis are not fully defined. We recently reported that the conditional and targeted knock-out of ERK5 MAP kinase in adult neurogenic regions of the mouse brain attenuates adult neurogenesis in the hippocampus and disrupts several forms of hippocampus-dependent memory. Here, we developed a gain-of-function knock-in mouse model to specifically activate endogenous ERK5 in the neurogenic regions of the adult brain. We report that the selective and targeted activation of ERK5 increases adult neurogenesis in the dentate gyrus by enhancing cell survival, neuronal differentiation, and dendritic complexity. Conditional ERK5 activation also improves the performance of challenging forms of spatial learning and memory and extends hippocampus-dependent long-term memory. We conclude that enhancing signal transduction of a single signaling pathway within adult neural stem/progenitor cells is sufficient to increase adult neurogenesis and improve the persistence of hippocampus-dependent memory. Furthermore, activation of ERK5 may provide a novel therapeutic target to improve long-term memory.

Role of ERK1, 2, and 5 in dopamine neuron survival during aging

Extracellular signal-regulated kinases (ERKs) 1, 2, and 5 have been shown to play distinct roles in proliferation, differentiation, and neuronal viability. In this study, we examined ERK1, 2, and 5 expression and activation in the substantia nigra (SN), striatum (STR), and ventral tegmental area (VTA) during aging. An age-related decrease in phosphorylated ERK5 was observed in the SN and STR, whereas an increase in total ERK1 was observed in all 3 regions. In primary cultures of the SN and VTA, inhibition of ERK5 but not ERK1 and 2 decreased dopamine neuronal viability significantly. These data suggest that ERK5 is essential for the basal survival of SN and VTA dopaminergic neurons. This is the first study to examine ERK1, 2, and 5 expression and activation in the SN, STR, and VTA during aging, and the relative roles of ERK1, 2, and 5 in basal survival of SN and VTA dopaminergic neurons. These data raise the possibility that a decline in ERK5 signaling may play a role in age-related impairments in dopaminergic function.

MEK5/ERK5 signaling suppresses estrogen receptor expression and promotes hormone-independent tumorigenesis

Endocrine resistance and metastatic progression are primary causes of treatment failure in breast cancer. While mitogen activated protein kinases (MAPKs) are known to promote ligand-independent cell growth, the role of the MEK5-ERK5 pathway in the progression of clinical breast carcinoma remains poorly understood. Here, we demonstrated increased ERK5 activation in 30 of 39 (76.9%) clinical tumor samples, as well as across breast cancer cell systems. Overexpression of MEK5 in MCF-7 cells promoted both hormone-dependent and hormone-independent tumorigenesis in vitro and in vivo and conferred endocrine therapy resistance to previously sensitive breast cancer cells. Expression of MEK5 suppressed estrogen receptor (ER)α, but not ER-β protein levels, and abrogated downstream estrogen response element (ERE) transcriptional activity and ER-mediated gene transcription. Global gene expression changes associated with upregulation of MEK5 included increased activation of ER-α independent growth signaling pathways and promotion of epithelial-to-mesenchymal transition (EMT) markers. Taken together, our findings show that the MEK5-ERK5 pathway mediates progression to an ER(-), mesenchymal and endocrine therapy resistant phenotype. Given the need for new clinical therapeutic targets, our results demonstrate the therapeutic potential of targeting the MEK5-ERK5 pathway in breast cancer.

Up-regulation of Ras/Raf/ERK1/2 signaling impairs cultured neuronal cell migration, neurogenesis, synapse formation, and dendritic spine development

The Ras/Raf/ERK1/2 signaling pathway controls many cellular responses such as cell proliferation, migration, differentiation, and death. In the nervous system, emerging evidence also points to a death-promoting role for ERK1/2 in both in vitro and in vivo models of neuronal death. Recent studies have suggested that abnormal apoptosis in the central nervous system may be involved in the pathogenesis of autism. Two studies reported that both a microdeletion and microduplication on chromosome 16, which includes the MAPK3 gene that encodes ERK1, are associated with autism. In addition, our recent work showed that Ras/Raf/ERK1/2 signaling activities were significantly up-regulated in the frontal cortex of autistic individuals and in the BTBR murine model of autism. To further investigate how Ras/Raf/ERK1/2 up-regulation may lead to the development of autism, we developed a cellular model of Raf/ERK up-regulation by over-expressing c-Raf in cultured cortical neurons (CNs) and cerebellar granule cells (CGCs). We found that Raf/ERK up-regulation stimulates the migration of both CNs and CGCs, and impairs the formation of excitatory synapses in CNs. In addition, we found that Raf/ERK up-regulation inhibits the development of mature dendritic spines in CNs. Investigating the possible mechanisms through which Raf/ERK up-regulation affects excitatory synapse formation and dendritic spine development, we discovered that Raf/ERK up-regulation suppresses the development and maturation of CNs. Together, these results suggest that the up-regulation of the Raf/ERK signaling pathway may contribute to the pathogenesis of autism through both its impairment of cortical neuron development and causing neural circuit imbalances.

ERK5: a novel IKKα-kinase in rat hippocampal neurons

BACKGROUND

Alzheimer's Disease (AD) is characterized in part by the increased presence of neurofibrillary tangles and amyloid beta (Aβ) plaques. Alzheimer's Disease is considered an inflammatory disease and, as such, nuclear factor-kappaB (NFκB) plays an important role in the pathophysiology of AD. Insulin acts as a neurotrophic factor. Yet, in the context of insulin resistance, concomitant hyperinsulinemia may contribute to the pathogenesis of AD.

METHODS

Rat Primmary Hippocampal Neurons (RPHN) were treated with insulin in the absence and presence of Wortmannin and ERK5 small inhibitory RNA and assayed for downstream effectors of activated ERK5.

RESULTS

Here we demonstrate that genetic inhibition of ERK5 blocks insulin stimulated (1) activation and translocation of ERK5 and NFκB, (2) phosphorylation of IKKα via association with ERK5, (3) increases in Aβ1-40 and Aβ1-42 soluble proteins 3-fold and 2.2-fold, respectively, and (4) increases in tau phosphorylation in RPHN.

CONCLUSIONS

ERK5 plays an active role in insulin signaling in neurons and may be a potential therapeutic target for neurodegenerative diseases.

Upregulation of Ras/Raf/ERK1/2 signaling and ERK5 in the brain of autistic subjects

Autism is a neurodevelopmental disorder characterized by impairments in social interaction, verbal communication and repetitive behaviors. A number of studies have shown that the Ras/Raf/ERK1/2 (extracellular signal-regulated kinase) signaling pathway plays important roles in the genesis of neural progenitors, learning and memory. Ras/Raf/ERK1/2 and ERK5 have also been shown to have death-promoting apoptotic roles in neural cells. Recent studies have shown a possible association between neural cell death and autism. In addition, two recent studies reported that a deletion of a locus on chromosome 16, which included the mitogen-activated protein kinase 3 (MAPK3) gene that encodes ERK1, is associated with autism. Most recently, our laboratory detected that Ras/Raf/ERK1/2 signaling activities were significantly enhanced in the brain of BTBR mice that model autism, as they exhibit many autism-like behaviors. We thus hypothesized that Ras/Raf/ERK1/2 signaling and ERK5 could be abnormally regulated in the brain of autistic subjects. In this study, we show that the expression of Ras protein was significantly elevated in the frontal cortex of autistic subjects. C-Raf phosphorylation was increased in the frontal cortex, while both C-Raf and A-Raf activities were enhanced in the cerebellum of autistic subjects. We also detected that both the protein expression and activities of ERK1/2 were significantly upregulated in the frontal cortex of autistic subjects, but not in the cerebellum. Furthermore, we showed that ERK5 protein expression is upregulated in both frontal cortex and cerebellum of autistic subjects. These results suggest that the upregulation of Ras/Raf/ERK1/2 signaling and ERK5 activities mainly found in the frontal cortex of autistic subjects may be critically involved in the pathogenesis of autism.

MEK5/ERK5/mef2: a novel signaling pathway affected by hepatitis C virus non-enveloped capsid-like particles

Hepatitis C virus (HCV) is an RNA positive strand virus, member of the Flaviviridae family. The viral particle is composed of a capsid containing the genome, surrounded by E1 and E2 proteins, however different forms of viral particles have been observed including non-enveloped particles. Previous reports have proposed that hepatitis C non-enveloped capsid-like particles (HCVne) enter cells of hepatic origin via clathrin-mediated endocytosis, during which different signaling events occur. In this report we show that HCVne particles are capable of inducing the recently discovered ERK5 pathway, in a dose dependent way. The ERK5 pathway can be activated by growth factors and other extracellular signals. This specific activation occurs through a well characterized upstream kinase, MEK5, and is capable of inducing gene regulation of mef2. In contrast, when HCV core structural and NS5A non-structural proteins were expressed endogenously no activation of this pathway was detected. These cell signaling events could be of critical importance and might give clues for the elucidation of cellular manifestations associated with HCV infection.

The MAP kinase signaling cascades: a system of hundreds of components regulates a diverse array of physiological functions

Sequential activation of kinases within the mitogen-activated protein (MAP) kinase (MAPK) cascades is a common, and evolutionary-conserved mechanism of signal transduction. Four MAPK cascades have been identified in the last 20 years and those are usually named according to the MAPK components that are the central building blocks of each of the cascades. These are the extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-Terminal kinase (JNK), p38, and ERK5 cascades. Each of these cascades consists of a core module of three tiers of protein kinases termed MAPK, MAPKK, and MAP3K, and often two additional tiers, the upstream MAP4K and the downstream MAPKAPK, which can complete five tiers of each cascade in certain cell lines or stimulations. The transmission of the signal via each cascade is mediated by sequential phosphorylation and activation of the components in the sequential tiers. These cascades cooperate in transmitting various extracellular signals and thus control a large number of distinct and even opposing cellular processes such as proliferation, differentiation, survival, development, stress response, and apoptosis. One way by which the specificity of each cascade is regulated is through the existence of several distinct components in each tier of the different cascades. About 70 genes, which are each translated to several alternatively spliced isoforms, encode the entire MAPK system, and allow the wide array of cascade's functions. These components, their regulation, as well as their involvement together with other mechanisms in the determination of signaling specificity by the MAPK cascade is described in this review. Mis-regulation of the MAPKs signals usually leads to diseases such as cancer and diabetes; therefore, studying the mechanisms of specificity-determination may lead to better understanding of these signaling-related diseases.

The proteasome-ubiquitin pathway in the Schistosoma mansoni egg has development- and morphology-specific characteristics

Schistosoma mansoni eggs, consisting of an ovum surrounded by nutritive vitelline cells packaged in a tanned protein shell, are produced by paired worms residing in the mesenteric veins of the human host. The vitelline cells are degraded as the larval miracidium matures, the fully developed egg either crossing the gut wall to escape the host or becoming lodged in the host's tissues where it dies and disintegrates, inducing a potentially pathological immune response. Thus, the egg is central to both the transmission of the parasite and the aetiology of the disease. Here we present the first study investigating protein turnover in the egg. We establish that the ubiquitin-proteasome pathway (UPP) changes with egg development and furthermore, that the morphological components of the fully developed egg (the miracidium and the subshell envelope) also exhibit different proteasome subunit expression profiles. We conclude that the UPP is responsible not only for degrading the vitelline cells but is also more highly developed in the envelope than in the miracidium. The envelope is involved in the defence of the miracidium and produces the proteins that the egg secretes, presumably to facilitate its escape from the host, so the UPP probably has a multi-faceted role in the egg's biology.

Matrix metalloproteinase-9 (MMP-9) expression and extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation in exercise-reduced neuronal apoptosis after stroke

Exercise preconditioning has been shown to reduce neuronal damage in ischemic/reperfusion (I/R) injury. ERK1/2 signaling in injury has been thought to modulate neuroprotection. In this study, we investigated the effects of ERK1/2 activation on the expression and activity of MMP-9 and downstream neuronal apoptosis. Adult male Sprague-Dawley rats were subjected to 30min of exercise on a treadmill for 3 weeks. Stroke was induced by a 2-h middle cerebral artery (MCA) occlusion using an intraluminal filament. Apoptotic protein caspase-3 and neuronal apoptosis in cortex and striatum was determined by Western blot at 24h reperfusion and TUNEL staining at 48h reperfusion in 5 I/R injury groups: no treatment, MMP-9 inhibitor (doxycycline), pre-ischemic exercise, exercised animals undergone ERK1/2 inhibition (U0126), and dual inhibition of ERK1/2 and MMP-9 in exercised ischemic rats. Cerebral MMP-9 expression in ischemic rats with different treatment was determined at 6, 12 and 24h reperfusion by real-time PCR for mRNA, Western blot for protein and zymography for enzyme activity. Exercise preconditioning significantly (p<0.05) reduced apoptosis determined by caspase-3 and TUNEL. In non-exercised rats, doxycycline treatment had significant (p<0.05) reductions in apoptosis after I/R injury. The dual ERK1/2-MMP-9 inhibited exercised animals had significantly (p<0.05) reduced neuronal apoptosis that was similar to that seen in exercised ischemic rats. MMP-9 expression in I/R injury was significantly (p<0.05) reduced in the exercised animals as compared to non-exercised controls. When ERK1/2 was inhibited, the reduced MMP-9 expression was reversed to the level seen in the non-exercised controls. This study has suggested that exercise-induced neuroprotection in I/R injury may be mediated by MMP-9 and ERK1/2 expression, leading to a reduction in neuronal apoptosis.

Identification of benzimidazole-based inhibitors of the mitogen activated kinase-5 signaling pathway

The MEK-signaling pathways are complex but critical signaling cascades that correlate an extracellular signaling event with internal cell processes. To date at least seven MEK isozymes have been identified. MEK5, in particular, is upregulated in multiple forms of tumors. Analysis of the EGF-induced MEK5 signaling cascade in cultured HEK cells has identified compounds that can inhibit MEK5 phosphorylation of ERK5; observed biological activity is dependent on chemical variation.

ERK5 and the regulation of endothelial cell function

ERK5 (extracellular-signal-regulated kinase 5), also termed BMK1 [big MAPK1 (mitogen-activated protein kinase 1)], is the most recently discovered member of the MAPK family. It is expressed in a variety of tissues and is activated by a range of growth factors, cytokines and cellular stresses. Targeted deletion of Erk5 in mice has revealed that the ERK5 signalling cascade is critical for normal cardiovascular development and vascular integrity. In vitro studies have revealed that in endothelial cells, ERK5 is required for preventing apoptosis, mediating shear-stress signalling, regulating hypoxia, tumour angiogenesis and cell migration. This review focuses on our current understanding of the role of ERK5 in regulating endothelial cell function.

The signaling pathway leading to extracellular signal-regulated kinase 5 (ERK5) activation via G-proteins and ERK5-dependent neurotrophic effects

Extracellular signal-regulated kinases (ERKs) or mitogen-activated protein kinases (MAPKs) are involved in cellular proliferation, differentiation, migration, and gene expression. The MAPK family includes ERK1/2, c-Jun NH(2)-terminal kinases 1, 2, and 3, p38MAPK alpha, beta, gamma, and -delta, and ERK5 as conventional MAPKs and ERK3, ERK4 NLK, and ERK7 as atypical MAPKs. Like other MAPKs, ERK5 is activated by variety of stimuli, including growth factors, G-protein-coupled receptor (GPCR) agonists, cytokines, and stress. However, the signaling pathway leading to ERK5 activation is not well understood compared with the other conventional MAPKs. For example, the pharmacological reagents that induce second messenger cAMP and Ca(2+) downstream of GPCRs do not activate ERK5 in neuronal cells. In addition, conflicting results have come from studies examining the involvement of small G-proteins in ERK5 activation by growth factors, and the details of the signaling pathway remain controversial. In addition, the physiological roles of ERK5 in neuronal cells have not been clarified. One reason was the lack of a selective ERK5 pharmacological inhibitor until the novel selective MEK5/ERK5 inhibitors BIX02188 and BIX02189 (Biochem Biophys Res Commun 377:120-125, 2008) reported last year. Another reason is that the use of interfering mutants is limited in neuronal cells because the transfection efficiency is low. Despite these difficulties, recent studies suggest that ERK5 mediates the promotion of neuronal survival and neuronal differentiation in vitro and in vivo. In this review, the signaling pathway leading to ERK5 activation through heterotrimeric and small G-proteins and the physiological roles of ERK5 in neuronal cells are summarized and discussed.

Insulin/PI3K signaling protects dentate neurons from oxygen-glucose deprivation in organotypic slice cultures

It is known that ischemia/reperfusion induces neurodegeneration in the hippocampus in a subregion-dependent manner. This study investigated the mechanism of selective resistance/vulnerability to oxygen-glucose deprivation (OGD) using mouse organotypic hippocampal cultures. Analysis of propidium iodide uptake showed that OGD-induced duration- and subregion-dependent neuronal injury. When compared with the CA1-3 subregions, dentate neuronal survival was more sensitive to inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt signaling under basal conditions. Dentate neuronal sensitivity to PI3K/Akt signaling activation was inversely related to its vulnerability to OGD-induced injury; insulin/insulin-like growth factor 1 pre-treatment conferred neuroprotection to dentate neurons via activation of PI3K/Akt signaling. In contrast, CA1 and CA3 neurons were less sensitive to disruptions of endogenous PI3K/Akt signaling and protective effects of insulin/insulin-like growth factor 1, but more vulnerable to OGD. OGD-induced injury in CA1 was reduced by inhibition of NMDA receptor or mitogen-activated protein kinase signaling, and was prevented by blocking NMDA receptor in the presence of insulin. The CA2 subregion was distinctive in its response to glutamate, OGD, and insulin, compared with other CA subregions. CA2 neurons were sensitive to the protective effects of insulin against OGD-induced injury, but more resistant to glutamate. Distinctive distribution of insulin receptor beta and basal phospho-Akt was detected in our slice cultures. Our results suggest a role for insulin signaling in subregional resistance/vulnerability to cerebral ischemia.

ERK and cell death: ERK1/2 in neuronal death

Extracellular signal-regulated kinase (ERK) is a versatile protein kinase that regulates many cellular functions. Growing evidence suggests that ERK1/2 plays a crucial role in promoting cell death in a variety of neuronal systems, including neurodegenerative diseases. It is believed that the magnitude and the duration of ERK1/2 activity determine its cellular function. In this review, we summarize recent evidence for a role of ERK1/2 in neuronal death. Furthermore, we discuss the mechanisms involved in ERK1/2 mediating neuronal death.

Exercise pre-conditioning reduces brain inflammation in stroke via tumor necrosis factor-alpha, extracellular signal-regulated kinase 1/2 and matrix metalloproteinase-9 activity

OBJECTIVE

We sought to determine whether cerebral inflammation in ischemic rats was reduced by a neuroprotective action of pre-ischemic tumor necrosis factor-alpha up-regulation, which down-regulated matrix metalloproteinase-9 activity via extracellular signal-regulated kinase 1/2 phosphorylation.

MATERIAL AND METHODS

Adult male Sprague-Dawley rats were subjected to 30 minutes of exercise on a treadmill for 3 weeks. Stroke was induced by a 2 hour middle cerebral artery occlusion using an intraluminal filament. The exercised animals were treated with tumor necrosis factor-alpha antibody, UO126 (extracellular signal-regulated kinase 1/2 inhibitor), or both UO126 and doxycycline (matrix metalloproteinase-9 inhibitor). Brain infarct volume was assessed using Nissl staining. Leukocyte infiltration was evaluated using myeloperoxidase immunostaining. Intercellular adhesion molecule-1 and matrix metalloproteinase protein levels were determined by Western blot, and enzyme activity was evaluated using zymography.

RESULTS

There was a significant decrease in neurological deficits, brain infarct volume and leukocyte infiltration, in association with reduction in matrix metalloproteinase-9 and intercellular adhesion molecule-1 expression in exercised animals. Exercised animals treated with either tumor necrosis factor-alpha antibody or with UO126 showed a reversal of neurological outcome, infarct volume and leukocyte infiltration. Matrix metalloproteinase-9 activity was reversed, at least partially, but the intercellular adhesion molecule-1 expression was not. Neuroprotection remained when the exercised ischemic rats were treated with both UO126 and doxycycline.

CONCLUSION

These results suggest that exercise-induced up-regulation of tumor necrosis factor-alpha before stroke and extracellular signal-regulated kinase 1/2 phosphorylation play a role in decreasing brain inflammation by regulating matrix metalloproteinase-9 activity.

ERK5 activity is required for nerve growth factor-induced neurite outgrowth and stabilization of tyrosine hydroxylase in PC12 cells

Extracellular signal-regulated kinases (ERKs) play important physiological roles in proliferation, differentiation, and gene expression. ERK5 is approximately twice the size of ERK1/2, and its amino-terminal half contains the kinase domain that shares homology with ERK1/2 and TEY activation motif, whereas the carboxyl-terminal half is unique. In this study, we examined a physiological role of ERK5 in rat pheochromocytoma cells (PC12), comparing it with ERK1/2. Nerve growth factor (NGF) induced phosphorylation of both ERK5 and ERK1/2, whereas the cAMP analog dibutyryl cAMP (Bt(2)cAMP) caused only ERK1/2 phosphorylation. U0126, at 30 mum, that blocks ERK1/2 signaling selectively attenuated neurite outgrowth induced by NGF and Bt(2)cAMP, but BIX02188 and BIX02189, at 30 mum, that block ERK5 signaling and an ERK5 dominant-negative mutant suppressed only NGF-induced neurite outgrowth. Next, we examined the expression of tyrosine hydroxylase, a rate-limiting enzyme of catecholamine biosynthesis. Both NGF and Bt(2)cAMP increased tyrosine hydroxylase gene promoter activity in an ERK1/2-dependent manner but was ERK5-independent. However, when both ERK5 and ERK1/2 signalings were inhibited, tyrosine hydroxylase protein up-regulation by NGF and Bt(2)cAMP was abolished, because of the loss of stabilization of tyrosine hydroxylase protein by ERK5. Taking these results together, ERK5 is involved in neurite outgrowth and stabilization of tyrosine hydroxylase in PC12 cells, and ERK5, along with ERK1/2, plays essential roles in the neural differentiation process.

Differential roles of TLR2 and TLR4 in acute focal cerebral ischemia/reperfusion injury in mice

Recent studies have shown that Toll-like receptors (TLRs) are involved in cerebral ischemia/reperfusion (I/R) injury. This study was to investigate the role of TLR2 and TLR4 in acute focal cerebral I/R injury. Cerebral infarct size, neurological function and mortality were evaluated. NFsmall ka, CyrillicB binding activity, phosphorylation of Ismall ka, CyrillicBalpha, Akt and ERK1/2 were examined in ischemic cerebral tissue by EMSA and Western blots. Compared to wild type (WT) mice, in TLR4 knockout (TLR4KO) mice, brain infarct size was decreased (2.6+/-1.18% vs 11.6+/-1.97% of whole cerebral volume, p<0.05) and neurological function was maintained (7.3+/-0.79 vs 4.7+/-0.68, p<0.05). However, compared to TLR4KO mice, TLR2 knockout (TLR2KO) mice showed higher mortality (38.2% vs 13.0%, p<0.05), decreased neurological function (2.9+/-0.53 vs 7.3+/-0.79, p<0.05) and increased brain infarct size (19.1+/-1.33% vs 2.6+/-1.18%, p<0.05). NFsmall ka, CyrillicB activation and Ismall ka, CyrillicBalpha phosphorylation were attenuated in TLR4KO mice (1.09+/-0.02 and 1.2+/-0.04) compared to TLR2KO mice (1.31+/-0.02 and 2.2+/-0.32) after cerebral ischemia. Compared to TLR4KO mice, in TLR2KO mice, the phosphorylation of Akt (0.2+/-0.03 vs 0.9+/-0.16, p<0.05) and ERK1/2 (0.8+/-0.06 vs 1.3+/-0.17) evoked by cerebral I/R was attenuated. The present study demonstrates that TLR2 and TLR4 play differential roles in acute cerebral I/R injury. Specifically, TLR4 contributes to cerebral I/R injury, while TLR2 appears to be neuroprotective by enhancing the activation of protective signaling in response to cerebral I/R.

Myocyte enhancer factor 2A is transcriptionally autoregulated

MEF2 (myocyte enhancer factor 2) proteins are a small family of transcription factors that play pivotal roles in striated muscle differentiation, development, and metabolism, in neuron survival and synaptic formation, and in lymphocyte selection and activation. Products of the four mammalian MEF2 genes, MEF2A, MEF2B, MEF2C, and MEF2D, are expressed with overlapping but distinct temporospatial patterns. Toward analysis of MEF2A functions and the determinants of its regulated expression, we have mapped and begun studies of the transcriptional control regions of this gene. Heterogeneous 5'-untranslated regions of MEF2A mRNAs result from use of alternative promoters and splicing patterns. The two closely approximated TATA-less promoters are approximately 65 kb upstream of the exon containing the sole initiation codon. Ribonuclease protection and primer extension assays show that each promoter is active in various adult tissues. A canonical MEF2 site overlies the major promoter 1 transcription start site. This element specifically binds MEF2 factors, including endogenous nuclear MEF2A according to chromatin immunoprecipitation studies, and is critical to MEF2A transcription in myocytes. The site exerts reciprocal control of the alternative promoters, silencing promoter 1 and activating promoter 2 under some conditions. Erk5 and p38 MAPK signaling stimulate MEF2A expression by activating both promoters from the MEF2 element. MEF2A transcription is therefore subject to positive or negative regulation by its protein products, depending on signaling activities that influence MEF2 factor trans-activity. The sole MEF2 gene of the cephalochordate amphioxus has a similar regulatory region structure, suggesting that this mode of autoregulatory control is conserved among higher metazoan MEF2 genes.

Betagamma subunits of G(i/o) suppress EGF-induced ERK5 phosphorylation, whereas ERK1/2 phosphorylation is enhanced

Extracellular signal-regulated kinases (ERKs) play important physiological roles in proliferation, differentiation and gene expression. ERK5 is twice the size of ERK1/2, the amino-terminal half contains the kinase domain that shares the homology with ERK1/2 and TEY activation motif, whereas the carboxy-terminal half is unique. In this study, we examined the cross-talk mechanism between G-protein-coupled receptors (GPCRs) and receptor tyrosine kinases, focusing on ERK1/2 and 5. The pretreatment of rat pheochromocytoma cells (PC12) with pertussis toxin (PTX) specifically enhanced epidermal growth factor (EGF)-induced ERK5 phosphorylation. In addition, lysophosphatidic acid (LPA) attenuated the EGF-induced ERK5 phosphorylation in LPA(1) receptor- and G(i/o)-dependent manners. On the other hand, LPA alone activated ERK1/2 via Gbetagamma subunits and Ras and potentiated EGF-induced ERK1/2 phosphorylation at late time points. These results suggest G(i/o) negatively regulates ERK5, while it positively regulates ERK1/2. LPA did not affect cAMP levels after EGF treatment, and the reagents promoting cAMP production such as forskolin and cholera toxin also attenuated the EGF-induced ERK5 phosphorylation, indicating that the inhibitory effect of LPA on ERK5 inhibition via G(i/o) is not due to inhibition of adenylyl cyclase by Galpha(i/o). However, the inhibitory effect of LPA on ERK5 was abolished in PC12 cells stably overexpressing C-terminus of GPCR kinase2 (GRK2), and overexpression of Gbeta(1) and gamma(2) subunits also suppressed ERK5 phosphorylation by EGF. In response to LPA, Gbetagamma subunits interacted with EGF receptor in a time-dependent manner. These results strongly suggest that LPA negatively regulates the EGF-induced ERK5 phosphorylation through Gbetagamma subunits.

Concise review: MicroRNA expression in multipotent mesenchymal stromal cells

Mesenchymal stem cells, or multipotent mesenchymal stromal cells (MSC), isolated from various adult tissue sources have the capacities to self-renew and to differentiate into multiple lineages. Both of these processes are tightly regulated by genetic and epigenetic mechanisms. Emerging evidence indicates that the class of single-stranded noncoding RNAs known as microRNAs also plays a critical role in this process. First described in nematodes and plants, microRNAs have been shown to modulate major regulatory mechanisms in eukaryotic cells involved in a broad array of cellular functions. Studies with various types of embryonic as well as adult stem cells indicate an intricate network of microRNAs regulating key transcription factors and other genes, which in turn determine cell fate. In addition, expression of unique microRNAs in specific cell types serves as a useful diagnostic marker to define a particular cell type. MicroRNAs are also found to be regulated by extracellular signaling pathways that are important for differentiation into specific tissues, suggesting that they play a role in specifying tissue identity. In this review, we describe the importance of microRNAs in stem cells, focusing on our current understanding of microRNAs in MSC and their derivatives.

Aberrant extracellular signal-regulated kinase (ERK) 5 signaling in hippocampus of suicide subjects

Extracellular signal-regulated kinase 5 (ERK5), the newest member of the mitogen-activated protein (MAP) kinase family, is regulated differently than the other MAP kinases. Emerging evidence suggest the role of ERK5 signaling in promoting cell proliferation, differentiation, neuronal survival, and neuroprotection. The present study investigates whether suicide brain is associated with alterations in components of the ERK5 signaling cascade. In the prefrontal cortex (PFC) and hippocampus of suicide subjects (n=28) and nonpsychiatric control subjects (n=21), we examined the catalytic activities and protein levels of ERK5 and upstream MAP kinase kinase MEK5 in various subcellular fractions; mRNA levels of ERK5 in total RNA; and DNA-binding activity of myocyte enhancer factor (MEF)2C, a substrate of ERK5. In the hippocampus of suicide subjects, we observed that catalytic activity of ERK5 was decreased in cytosolic and nuclear fractions, whereas catalytic activity of MEK5 was decreased in the total fraction. Further, decreased mRNA and protein levels of ERK5, but no change in protein level of MEK5 were noted. A decrease in MEF2C-DNA-binding activity in the nuclear fraction was also observed. No significant alterations were noted in the PFC of suicide subjects. The observed changes were not related to a specific psychiatric diagnosis. Our findings of reduced activation and/or expression of ERK5 and MEK5, and reduced MEF2C-DNA-binding activity demonstrate abnormalities in ERK5 signaling in hippocampus of suicide subjects and suggest possible involvement of this aberrant signaling in pathogenic mechanisms of suicide.

Erk5 is activated and acts as a survival factor in mitosis

Erk5 is a recently discovered MAPK claimed to be responsible for some of the roles attributed to Erk1/2; here we report that it is activated in mitosis in comparison to G1/S. When Erk5 is inactivated pharmacologically or largely ablated by RNAi, cell survival in mitosis is diminished. We have previously shown Bim, a BH3-only protein of the Bcl-2 family, to be phosphorylated in mitosis, in a MEK-dependent manner (M. Grãos, A. D. Almeida, S. Chatterjee, Biochem. J. 388 (2005) 185). Inactivation of Erk5 in mitosis causes dephosphorylation of Bim. Bim is in the mitochondria in mitosis and when dephosphorylated interacts with Bax, inducing caspase activation. We also show that in mitosis Bim co-immunoprecipitates with Erk5 and Erk5 phosphorylates GST-Bim in in vitro kinase reaction. Taken together, our results identify a new target of the still largely mysterious Erk5 and suggest that Erk5 in mitosis may be a decisive step for the survival of proliferating cells.

Emerging role of mitogen-activated protein kinases in peripheral neuropathies

Among the different families of intracellular molecules that can be modulated during cell damage and repair, mitogen-activated protein kinases (MAPKs) are particularly interesting because they are involved in several intracellular pathways activated by injury and regeneration signals. Despite most of the studies have been performed in non-neurological models, recently a causal role for MAPKs has been postulated in central nervous system disorders. However, also in some peripheral neuropathies, MAPK changes can occur and these modifications might be relevant in the pathogenesis of the damage as well as during regeneration and repair. In this review, the current knowledge on the role of MAPKs in peripheral neuropathies will be discussed.

Protective effect of bone morphogenetic protein-6 on neurons from H2O2 injury

Bone morphogenetic protein-6 (BMP6) is a member of the TGF-beta superfamily. Expression of BMP6 and its receptors are increased when brain tissues of adult rats are injured, suggesting that BMP6 may have a neuroprotective function in the physiologic response to neurological damage. This research investigates the molecular mechanisms supporting a neuroprotective effect of BMP6 in neural cells traumatized by H(2)O(2). We demonstrate that presence of BMP6 either before or after H(2)O(2)-induced injury protects the cultured primary cortical cells from apoptosis. However, molecular mechanisms mediating the protective effects of either pre- or post-treatment with BMP6 are different. Cells pre-treated with BMP6 have attenuated MAPK activity induced by H(2)O(2), whereas the MAPK activity in cells post-treated with BMP6 remains unchanged. Further, pharmacological inhibitors of MAPKs, PD98059 and SB203580, block the protective effect of BMP6 in the cells pre-treated with BMP6 but not in the cells post-treated with BMP6. The protective effect of post-treatment with BMP6 appears to be mediated through regulation of p53 and Bax molecules, evidenced by decreased mRNA levels after BMP6 treatment. Taken together, these data suggest BMP6 protect cortical cells against oxidation stress induced by H(2)O(2) via two different mechanisms, where (1) pre-treatment with BMP6 acts through MAPK pathway and (2) post-treatment with BMP6 works by down-regulating p53 and Bax.