Mitogen- and stress-activated protein kinase 1: convergence of the ERK and p38 pathways in Alzheimer's disease

Microcurrent therapy as the nonpharmacological new protocol against Alzheimer's disease

Introduction

Alzheimer's disease (AD) poses an increasing global health challenge and is marked by gradual cognitive deterioration, memory impairment, and neuroinflammation. Innovative therapeutic approaches as non-pharmacological protocol are urgently needed with side effect risk of drugs. Microcurrent therapy, a non-invasive modality involving low-level electrical currents, has emerged as a potential solution to address AD's complex pathogenesis. This study investigates the optimal application of microcurrent therapy as a clinical protocol for AD, utilizing a comprehensive approach that integrates behavioral assessments and neuroinflammation evaluation in a mouse model of dementia.

Methods and results

The results reveal that microcurrent therapy holds promise in ameliorating memory impairment and reducing neuroinflammation in AD. Behavioral assessments, including the Novel Object Recognition Test (NOR) and Radial Arm Maze Test (RAM), demonstrated improved cognitive function following microcurrent therapy. Furthermore, microcurrent therapy inhibited expression of neuroinflammatory proteins, including ionized calcium binding adaptor molecule 1 (Iba1), and glial fibrillary acidic protein (GFAP) in current-treated group. Mechanistic insights suggest that microcurrent therapy may modulate neuroinflammation through the regulation of MAPK signaling pathways.

Conclusion

This study emphasizes the prospect of microcurrent therapy as a safe and efficacious non-pharmacological strategy for Alzheimer's disease (AD), providing optimism to the countless individuals impacted by this debilitating ailment. These results contribute to the developments of an innovative clinical protocol for AD and recovery from neurological injury, underscoring the significance of investigating unconventional therapeutic approaches for addressing this complex condition.

The Potential Neuroprotective Effects of Extracts from Oat Seedlings against Alzheimer's Disease

The physiological or dietary advantages of germinated grains have been the subject of numerous discussions over the past decade. Around 23 million tons of oats are consumed globally, making up a sizeable portion of the global grain market. Oat seedlings contain more protein, beta-glucan, free amino acids, and phenolic compounds than seeds. The progressive neurodegenerative disorder of Alzheimer's is accompanied by worsening memory and cognitive function. A key indicator of this disorder is the unusual buildup of amyloid-beta protein (or Aβ) in human brains. In this context, oat seedling extract (OSE) has been identified as a new therapeutic candidate for AD, due to its antioxidant activity and AD-specific mechanism of action. This study directly investigated how OSE affected AD and its impacts by examining the cognitive function and exploring the inflammatory response mechanism. The dried oat seedlings were grounded finely with a grinder, inserted with 50% fermented ethanol 10 times (w/v), and extracted by stirring for 10 h at 45 °C. After filtering the extract by 0.22 um filter, some of it was used for UHPLC analysis. The results indicated that the treatment with OSE protects against Aβ25-35-induced cytotoxicity in BV2 cells. Tg-5Xfad AD mice had strong deposition of Aβ throughout their brains, while WT mice did not exhibit any such deposition within their brains. A drastic reduction was observed in terms of numbers, as well as the size, of Aβ plaques within Tg-5Xfad AD mice exposed to OSE. This study indicated OSE's neuroprotective impacts against neurodegeneration, synaptic dysfunction, and neuroinflammation induced by amyloid-beta. Our results suggest that OSE acts as a neuroprotective agent to combat AD-specific apoptotic cell death, neuroinflammation, amyloid-beta accumulation, as well as synaptic dysfunction in AD mice's brains. Furthermore, the study indicated that OSE treatment affects JNK/ERK/p38 MAPK signaling, with considerable inhibition in p-JNK, p-p38, and p-ERK levels seen in the brain of OSE-treated Tg-5Xfad AD mice.

Novel Multitarget Directed Tacrine Hybrids as Anti-Alzheimer's Compounds Improved Synaptic Plasticity and Cognitive Impairment in APP/PS1 Transgenic Mice

Alzheimer's disease (AD) is a complex pathological neurodegenerative disease that seriously threatens human health. Therefore, how to effectively improve and treat AD is an urgent problem. In this study, a novel multitarget derivative based on tacrine (named 9i), which could work simultaneously on more than one pathological target, was used to treat AD model APP/PS1 transgenic mice. After 4 weeks of intragastric administration, cognitive function and synaptic plasticity were significantly improved and β-amyloid (Aβ) plaques that are main pathological hallmarks of AD were decreased in the APP/PS1 mice. On the one hand, 9i inhibited the excessive activation of the Raf/MEK/ERK signaling pathway to alleviate the loss of neurons, which provides a foundation for structural integrity. On the other hand, synaptic associated proteins and the density of synaptic spines were increased in APP/PS1 mice treated with 9i, which provides the basis for the improvement of synaptic plasticity and cognitive impairment. Interestingly, 9i also reduced Aβ plaques in the DG region, which is consistent with previous in vitro experiments showing that 9i inhibited the self-assembly of Aβ fibers, thus protecting neurons from Aβ plaque neurotoxicity. Our results suggest that 9i as a novel compound can effectively improve the cognitive function and the pathological changes of AD in APP/PS1 transgenic mice.

Kaposi's sarcoma-associated herpesvirus viral protein kinase phosphorylates extracellular signal-regulated kinase and activates MAPK/ERK signaling pathway

Open reading frame 36 (ORF36) of Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a serine/threonine-type viral protein kinase (vPK). Previous studies have examined the functions of KSHV vPK; however, its role in the activation of extracellular signal-regulated kinase (ERK1/2) has not yet been described to date. Using HEK 293 cell lines, we performed a human phospho-kinase array analysis to screen for MAPK signaling pathways kinases that are activated by KSHV vPK. In addition, we investigated the regulator protein phosphorylation of up/downstream ERK1/2 pathway; nuclear translocation of phosphorylated ERK1/2; and regulation of transcription factor, inflammatory cytokine, and pro-/anti-apoptotic factor by KSHV vPK transfection. Here, we demonstrated that KSHV vPK activates ERK1/2 signaling pathway and plays an important role in the activation of MAPK/ERK signaling pathway.

Suppression of Alzheimer's disease-related phenotypes by the heat shock protein 70 inducer, geranylgeranylacetone, in APP/PS1 transgenic mice via the ERK/p38 MAPK signaling pathway

HSP70 overexpression has a remedying effect in neurodegenerative diseases. In Alzheimer's disease (AD), the suppressive effects of HSP70 overexpression on AD-related phenotypes and the underlying mechanisms are unknown. In the current study, the effect of geranylgeranylacetone (GGA), a non-toxic inducer of heat shock protein (HSP)-70 expression, on cognitive function and other pathological phenotypes were evaluated in APP/PS1 mice. It was observed that all doses of orally administered GGA (200, 400, and 800 mg/kg/day) improved cognitive deficit (P<0.05) and lowered the levels of amyloid-β (Aβ) peptide (P<0.05) in APP/PS1 mice. GGA treatment also increased the levels of low density lipoprotein receptor-related protein 1 (LRP-1) (P<0.05), while the levels of p-glycoprotein and receptor for advanced glycation end products were unaltered. Significant decreases in the levels of inflammatory cytokines, namely tumor necrosis factor-α, interleukin-1β and cyclooxygenase-2, were also observed in the GGA-treated mice (P<0.05). Subsequent treatment with the HSP70 inhibitor quercetin caused significant decreases in the levels of phosphorylated (p)-p38 mitogen-activated protein kinase (p38 MAPK) and p-extracellular signal-regulated protein kinases (ERK; P<0.05), indicating that ERK/p38 MAPK signaling in AD-related phenotypes may be suppressed by oral administration of GGA. Finally, in APP/PS1 mice treated with GGA+SB-203580 (p38 inhibitor) and GGA+PD98059 (ERK inhibitor), it was observed that orally administered GGA led to the activation of ERK/p38 MAPK signaling (P<0.05) and increased LRP-1 expression (P<0.05), which subsequently aided the clearance of Aβ40 and Aβ42 (P<0.05) and alleviated AD-related phenotypes. These results indicate that oral administration of GGA in APP/PS1 mice alleviates AD-related phenotypes by regulation of the ERK/p38 MAPK signaling pathway. Thus, GGA may be a potential therapeutic for the treatment of AD.

Emerging Link between Alzheimer's Disease and Homeostatic Synaptic Plasticity

Alzheimer's disease (AD) is an irreversible brain disorder characterized by progressive cognitive decline and neurodegeneration of brain regions that are crucial for learning and memory. Although intracellular neurofibrillary tangles and extracellular senile plaques, composed of insoluble amyloid-β (Aβ) peptides, have been the hallmarks of postmortem AD brains, memory impairment in early AD correlates better with pathological accumulation of soluble Aβ oligomers and persistent weakening of excitatory synaptic strength, which is demonstrated by inhibition of long-term potentiation, enhancement of long-term depression, and loss of synapses. However, current, approved interventions aiming to reduce Aβ levels have failed to retard disease progression; this has led to a pressing need to identify and target alternative pathogenic mechanisms of AD. Recently, it has been suggested that the disruption of Hebbian synaptic plasticity in AD is due to aberrant metaplasticity, which is a form of homeostatic plasticity that tunes the magnitude and direction of future synaptic plasticity based on previous neuronal or synaptic activity. This review examines emerging evidence for aberrant metaplasticity in AD. Putative mechanisms underlying aberrant metaplasticity in AD will also be discussed. We hope this review inspires future studies to test the extent to which these mechanisms contribute to the etiology of AD and offer therapeutic targets.

Mitogen- and stress-activated Kinase 1 mediates Epstein-Barr virus latent membrane protein 1-promoted cell transformation in nasopharyngeal carcinoma through its induction of Fra-1 and c-Jun genes

Background

Mitogen- and Stress-Activated Kinase 1 (MSK1) is a nuclear kinase that serves as active link between extracellular signals and the primary response of gene expression. However, the involvement of MSK1 in malignant transformation and cancer development is not well understood. In this study, we aimed to explore the role of MSK1 in Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1)-promoted carcinogenesis of nasopharyngeal carcinoma (NPC).

Methods

The level of MSK1 phosphorylation at Thr581 was detected by the immunohistochemical analysis in NPC tissues and normal nasopharynx tissues, and its correlation with LMP1 was analyzed in NPC tissues and cell lines. Using MSK1 inhibitor H89 or small interfering RNA (siRNA)-MSK1, the effects of MSK1 on LMP1-promoted CNE1 cell proliferation and transformation were evaluated by CCK-8 assay, flow cytometry and focus-forming assay respectively. Furthermore, the regulatory role of MSK1-mediated histone H3 phosphorylation at Ser10 on the promoter activity and expression of Fra-1 or c-Jun was determined by reporter gene assay and western blotting analysis.

Results

Immunohistochemical analysis revealed that the level of MSK1 phosphorylation at Thr581 was significantly higher in the poorly differentiated NPC tissues than that in normal nasopharynx tissues (P < 0.001). Moreover, high level of phosphorylated MSK1 was positively correlated with the expression of LMP1 in NPC tissues (r = 0.393, P = 0.002) and cell lines. MSK1 inhibitor H89 or knockdown of MSK1 by siRNA dramatically suppressed LMP1-promoted CNE1 cell proliferation, which was associated with the induction of cell cycle arrest at G₀/G₁ phase. In addition, the anchorage-independent growth promoted by LMP1 was blocked in MSK1 knockdown cells. When the activity or expression of MSK1 was inhibited, LMP1-induced promoter activities of Fra-1 and c-Jun as well as their protein levels were greatly reduced. It was found that only H3 WT, but not mutant H3 S10A, dramatically increased LMP1 induction of Fra-1 and c-Jun genes compared with mock cells.

Conclusion

Increased MSK1 activity is critically important for LMP1-promoted cell proliferation and transformation in NPC, which may be correlated with its induction of Fra-1 and c-Jun through phosphorylation of histone H3 at Ser10.

Caffeine induces beneficial changes in PKA signaling and JNK and ERK activities in the striatum and cortex of Alzheimer's transgenic mice

Caffeine intake has been associated with a lower incidence of Alzheimer's disease (AD) in humans. In AD mouse models, caffeine significantly decreases senile plaques and amyloid beta (Aβ) levels while also protecting against or reversing cognitive impairment. To understand the mechanism(s) underlying the protective effects of caffeine against AD pathology, we investigated the effects of a two-week treatment with caffeine (3mg/day) in transgenic (APPswe) mice and non-transgenic (NT) mice on signaling factors involved in neuronal plasticity and survival. We evaluated cAMP-dependent protein kinase A (PKA), phospho-cyclic AMP response-element binding protein (phospho-CREB), and the pro-apoptotic protein kinases extracellular signal-regulated kinase 1/2 (phospho-ERK) and phospho-c-Jun N-terminal kinase 1 (phospho-JNK) in the striatum and frontal cortex of caffeine-treated mice. In the striatum, APPswe control mice exhibited a significant decrease in phospho-CREB, as well as significant increases in phospho-JNK and phospho-ERK in comparison to NT mice. Caffeine treatment stimulated PKA activity, increased phospho-CREB levels, and decreased phospho-JNK and phospho-ERK expression in the striatum of APPswe mice, all of which are thought to be beneficial changes for brain function. Even caffeine-treated NT mice exhibited some of these changes in striatum. In the frontal cortex, caffeine did not significantly increase phospho-CREB and PKA activity, but significantly reduced phospho-JNK and phospho-ERK expression in both APPswe and NT mice. These results suggest that caffeine shifts the balance between neurodegeneration and neuronal survival toward the stimulation of pro-survival cascades and inhibition of pro-apoptotic pathways in the striatum and/or cortex, which may contribute to its beneficial effects against AD.

Causes versus effects: the increasing complexities of Alzheimer's disease pathogenesis

Amyloid plaques and neurofibrillary tangles are the hallmarks of Alzheimer's disease and have been the focus of disease etiology and pathogenesis. However, in the larger picture of a complex disease, the precise etiology of the lesions per se, as well as the clinical disease, remain to be defined. In this regard, to date no single process has been identified as a useful target and treatment efforts have shown no meaningful progress. Therefore, alternative ideas that may lead to new and effective treatment options are much needed.

Targeting mitochondrial dysfunction in neurodegenerative disease: Part II

IMPORTANCE OF THE FIELD

With improvements in life expectancy over the past decades, the incidence of neurodegenerative disease has dramatically increased and new therapeutic strategies are urgently needed. One possible approach is to target mitochondrial dysfunction, which has been implicated in the pathogenesis of numerous neurodegenerative disorders.

AREAS COVERED IN THIS REVIEW

This review examines the role of mitochondrial dysfunction in neurodegeneration, drawing examples from common diseases such as Alzheimer's disease and rarer familial disorders such as Charcot-Marie-Tooth. The review is provided in two parts. In part I we discussed the mitochondrial defects which have been most extensively researched (oxidative stress, bioenergetic dysfunction, calcium mishandling). We focus now on those defects which have more recently been implicated in neurodegeneration; in mitochondrial fusion/fission, protein import, protein quality control, kinase signalling and opening of the permeability transition pore.

WHAT THE READER WILL GAIN

An examination of mitochondrial defects observed in neurodegeneration, and existing and possible future therapies to target these defects.

TAKE HOME MESSAGE

The mitochondrially-targeted therapeutics that have reached clinical trials so far have produced encouraging but largely inconclusive results. Increasing understanding of mitochondrial dysfunction has, however, led to preclinical work focusing on novel approaches, which has generated exciting preliminary data.

Estrogen and beta-amyloid toxicity: role of integrin and PI3-K

Beta-amyloid peptide (betaAP) induces apoptosis and down-regulation of alpha(1)beta(1) integrin in neuronal cells, indicating a relationship between betaAP neurotoxicity and modulation of integrin expression. Estrogen may play a role in protecting women from Alzheimer Disease (AD). It is here reported that both 17beta-estradiol (17betaE(2)) and its non-estrogenic stereoisomer 17alpha-estradiol (17alphaE(2)) rescue neuronal cells from betaAP-induced apoptosis. As cellular model, the human neuroblastoma cell line SK-N-BE was used, which responds to retinoic acid by growth arrest and differentiation toward the neuronal phenotype (RA-SK-N-BE). Estrogen receptor antagonist does not hinder estrogen protection. Inhibition of phosphatidylinositol 3-kinase (PI3-K), but not of tyrosine kinases or mitogen-activated protein kinases (MAPK) blocks 17betaE(2) protection against betaAP-induced apoptosis. 17betaE(2) up-regulates alpha(1)beta(1) integrin expression and completely abolishes betaAP-induced alpha(1)beta(1) down-regulation. Inadequate cell cycle control may contribute to neuronal death in AD. betaAP induces RA-SK-N-BE cells to enter cell cycle, which remains incomplete. 17betaE(2) induces betaAP-treated cells to complete cell cycle. Our data suggest that estrogen protects from betaAP neurotoxicity by restoring integrin expression and cell cycle control.

Declining phosphatases underlie aging-related hyperphosphorylation of neurofilaments

Cytoskeletal protein phosphorylation is frequently altered in neuropathologic states but little is known about changes during normal aging. Here we report that declining protein phosphatase activity, rather than activation of kinases, underlies aging-related neurofilament hyperphosphorylation. Purified PP2A or PP2B dephosphorylated the heavy neurofilament (NFH) subunit or its extensively phorphorylated carboxyl-terminal domain in vitro. In cultured primary hippocampal neurons, inhibiting either phosphatase induced NFH phosphorylation without activating known neurofilament kinases. Neurofilament phosphorylation in the mouse CNS, as reflected by levels of the RT-97 phosphoepitope associated with late axon maturation, more than doubled during the 12-month period after NFH expression plateaued at p21. This was accompanied by declines in levels and activity of PP2A but not PP2B, and no rise in activities of neurofilament kinases (Erk1,2, cdk5 and JNK1,2). Inhibiting PP2A in mice in vivo restored brain RT-97 to levels seen in young mice. Declining PP2A activity, therefore, can account for rising neurofilament phosphorylation in maturing brain, potentially compounding similar changes associated with adult-onset neurodegenerative diseases.

Down-regulation of aminolevulinate synthase, the rate-limiting enzyme for heme biosynthesis in Alzheimer's disease

Heme is an essential cell metabolite, intracellular regulatory molecule, and protein prosthetic group. Given the known alterations in heme metabolism and redox metal distribution and the up-regulation of heme oxygenase enzyme in Alzheimer's disease (AD), we hypothesized that heme dyshomeostasis plays a key role in the pathogenesis. To begin testing this hypothesis, we used qRT-PCR to quantify the expression of aminolevulinate synthase (ALAS1) and porphobilinogen deaminase (PBGD), rate-limiting enzymes in the heme biosynthesis pathway. The relative expression of ALAS1 mRNA, the first and rate-limiting enzyme for heme biosynthesis under normal physiological conditions, was significantly (p<0.05) reduced by nearly 90% in AD compared to control. Coordinately, the relative expression of PBGD mRNA, which encodes porphobilinogen deaminase, the third enzyme in the heme synthesis pathway and a secondary rate-limiting enzyme in heme biosynthesis, was also significantly (p<0.02) reduced by nearly 60% in AD brain compared to control and significantly related to apolipoprotein E genotype (p<0.005). In contrast, the relative expression of ALAD mRNA, which encodes aminolevulinate dehydratase, the second and a non-rate-limiting enzyme for heme biosynthesis, was unchanged between the two groups. Taken together, our results suggest regulation of cerebral heme biosynthesis is profoundly altered in AD and may contribute toward disease pathogenesis by affecting cell metabolism as well as iron homeostasis.

The effect of mGluR2 activation on signal transduction pathways and neuronal cell survival

In earlier studies, we found profound alterations in specific signal transduction pathways such as mitogen-activated protein kinase signal pathway that mirrored neuronal cell death in Alzheimer disease (AD). To further delineate the mechanism(s) involved in such aberrant signaling, we subsequently showed that mGluR2 is increased in pyramidal neurons in the hippocampus of AD and often co-localizes with neurofibrillary pathology. Based on these data, we suggested that selective neuronal degeneration in AD may arise through the differential expression and activation of specific receptor populations, such as, mGluR2. In this study, to examine the mechanistic relevance of the above-mentioned in vivo findings, we used cell culture models to show that the activation of mGluR2 leads to the activation of extracellular signal-related kinase (ERK) pathways. Importantly, attesting to the in vivo significance of our findings, this pro-survival signaling pathway is also found to be ectopically activated in AD. We also found that the activation of mGluR2 increases the phosphorylation of tau and that the specific activation of mGluR2 reduces oxidative stress mediated cytotoxicity in neuronal cells. Taken together our findings strongly suggest that mGluR2 may participate in mediating the survival of neurons in the face of selective neuronal dysfunction and degeneration in AD. Additionally, our findings lend support to the notion that tau phosphorylation is a neuroprotective antioxidant response to cellular insults.

Oestradiol or genistein rescues neurons from amyloid beta-induced cell death by inhibiting activation of p38

Oestrogenic compounds have been postulated as neuroprotective agents. This prompted us to investigate their mechanism action in neurons in primary culture. Cells were pretreated with physiological concentrations of 17-beta estradiol (0.2 nm) or with nutritionally relevant concentrations of genistein (0.5 microm), and 48 h later treated with 5 microm of amyloid beta (Abeta) for 24 h. We found that Abeta increased oxidative stress, measured as peroxide levels or oxidized glutathione/reduced glutathione ratio, which in turn, caused phosphorylation of p38 MAP kinase. Amyloid beta subsequently induced neuronal death. Inhibiting the MAP kinase pathway prevented cell death, confirming the role of p38 in the toxic effect of Abeta. All these effects were prevented when cells were pretreated for 48 h with oestradiol or genistein. Therefore, oestrogenic compounds rescue neurons from Abeta-induced cell death by preventing oxidative stress, which in turn inhibits the activation of p38, protecting neurons from cell death. Because hormone replacement therapy with oestradiol could cause serious setbacks, the potential therapeutic effect of phyto-oestrogens for the prevention of Abeta-associated neurodegenerative disorders should be more carefully studied in clinical research.

Aging modifies brain region-specific vulnerability to experimental oxidative stress induced by low dose hydrogen peroxide

Our previous studies demonstrated a significant decline in brain function and behavior in Fischer 344 (F344) rats with age. The present study was designed to test the hypothesis that dysregulation in calcium homeostasis (as assessed through (45)Ca flux) may contribute to the increase in age-related vulnerability to oxidative stress in brain regions, and result in a deficit in behavior-mediated signaling. Crude membrane (P-2) and more purified synaptosomal fractions were isolated from the striatum, hippocampus, and frontal cortex of young (6 months) and old (22 months) F344 rats and were assessed for calcium flux and extracellular-regulated kinase activity 1 (ERK) under control and oxidative stress conditions induced by low dose hydrogen peroxide (final concentration 5 microM). The level of oxidative stress responses was monitored by measuring reactive oxygen species (ROS) and glutathione (GSH). The results showed a significant difference in oxidative stress responses between young and old rats in evaluated brain regions. Old rats showed higher sensitivity to oxidative stress than young rats. The present findings show the differential effects of oxidative stress on calcium flux in brain regions with age that are dependent upon the brain areas examined and the fraction assessed. The accumulation of ROS and the decrease in GSH in the frontal cortex were sufficient to decrease ERK activity in old rats. This is the first study, to our knowledge, that demonstrates age-related differential sensitivity to oxidative stress expressed as a function of behavior-mediated signaling and stress levels among different fractions isolated from brain regions controlling behavior.

The complex p25/Cdk5 kinase in neurofibrillary degeneration and neuronal death: the missing link to cell cycle

Emergence of the cell cycle hypothesis in neurodegenerative disease comes from the numerous lines of evidence showing a tight link between "cell cycle-like reactivation" and neuronal death. Terminally differentiated neurons remain in G0 phase and display, compared to proliferating cells, an opposite regulation pattern of cell cycle markers in that most of the key activators and inhibitors are respectively down- and up-regulated. It has been clearly established that any experimental attempt to force terminally differentiated neurons to divide ultimately leads to their death. Conversely, cell cycle blockade in experimental models of neuronal death is able to rescue neurons. Hence, cell cycle deregulation is certainly among mechanisms governing neuronal death. However, many questions remain unresolved, especially those related to which molecular mechanisms trigger cell cycle deregulation and how this deregulation leads to cell death. In the present review, we focus on neurodegeneration in Alzheimer's disease and discuss the cell cycle deregulation related to this neurodegenerative pathology. Finally, we emphasize the role of p25/Cdk5 kinase complex in this pathological process through retinoblastoma protein phosphorylation and derepression of E2F-responsive genes and other actors such as cdc2, cyclins, and MCM proteins.

Neuron-specific phosphorylation of mitogen- and stress-activated protein kinase-1 involved in cerebral hypoxic preconditioning of mice

Studies have demonstrated the involvement of mitogen-activated protein kinase (MAPK) cascade pathways in the development of cerebral ischemic/hypoxic preconditioning (I/HPC). However, the role of mitogen- and stress-activated protein kinase 1 (MSK1), an important downstream kinase of MAPK signaling pathways, in cerebral I/HPC is unclear. By using Western blot and immunostaining methods, we applied our unique "autohypoxia"-induced I/HPC mouse model to investigate the effects of repetitive hypoxic exposure (H0-H6, n=6 for each group) on phosphorylation and protein expression levels of MSK1 in the brain of mice. We found that the levels of phosphorylation on threonine 645 (Thr645) and serine 375 (Ser375) of MSK1, but not the protein expression, increased significantly both in hippocampus and in cortex of mice from H1-H6 groups (P<0.05) over that of the normoxic group (H0, n=6). Similarly, enhanced phosphorylations on Thr645 and Ser375 of MSK1 were also observed by immunostaining in both the cortex and the hippocampus of mice following three series of hypoxic exposures (H3). In addition, we found by using double-immunofluorescence labeling that phosphorylated Thr645-MSK1 colocalized with a neuron-specific protein, neurogranin, in both cortex and hippocampus of I/HPC mice (H3). These results suggest that the increased neuron-specific phosphorylation of MSK1 on Thr645 and Ser375, not protein expression, might be involved in the development of cerebral I/HPC in mice.

TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model

BACKGROUND

Previous studies have demonstrated reexpression of cell-cycle markers within postmitotic neurons in neurodegenerative tauopathies, including Alzheimer's disease (AD). However, the critical questions of whether cell-cycle activation is causal or epiphenomenal to tau-induced neurodegeneration and which signaling pathways mediate cell-cycle activation in tauopathy remain unresolved.

RESULTS

Cell-cycle activation accompanies wild-type and mutant tau-induced neurodegeneration in Drosophila, and genetically interfering with cell-cycle progression substantially reduces neurodegeneration. Our data support a role for cell-cycle activation downstream of tau phosphorylation, directly preceding apoptosis. We accordingly show that ectopic cell-cycle activation leads to apoptosis of postmitotic neurons in vivo. As in AD, TOR (target of rapamycin kinase) activity is increased in our model and is required for neurodegeneration. TOR activation enhances tau-induced neurodegeneration in a cell cycle-dependent manner and, when ectopically activated, drives cell-cycle activation and apoptosis in postmitotic neurons.

CONCLUSIONS

TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model, identifying TOR and the cell cycle as potential therapeutic targets in tauopathies and AD.

Involvement of JNKs and p38-MAPK/MSK1 pathways in H2O2-induced upregulation of heme oxygenase-1 mRNA in H9c2 cells

One of the most important challenges that cardiomyocytes experience is an increase in the levels of reactive oxygen species (ROS), i.e., during ischemia, reperfusion as well as in the failing myocardium. HOX-1 has been found to protect cells and tissues against oxidative damage; therefore, we decided to study the signalling cascades involved in its transcriptional regulation. HOX-1 mRNA levels were found to be maximally induced after 6h of treatment with 200 microM H2O2 and remained elevated for at least 24h. Inhibition of JNKs, p38-MAPK and MSK1 pathways, by pharmacological inhibitors, reduced HOX-1 mRNA levels in H2O2-treated H9c2 cells. In parallel, we observed that all three subfamilies of the mitogen-activated protein kinases (MAPKs) attained their maximal phosphorylation levels at 5-15 min of H2O2 treatment, with mitogen- and stress-activated-protein kinase 1 (MSK1) also being maximally phosphorylated at 15 min. H2O2-induced MSK1 phosphorylation was completely abrogated in the presence of the selective p38-MAPK inhibitor SB203580. In an effort to define possible substrates of MSK1, we found that ATF2 as well as cJun phosphorylation were equally induced after 30 min and 60 min, respectively, a response inhibited by SP600125 (JNKs inhibitor) and H89 (MSK1 inhibitor), indicating the involvement of these kinases in the observed response. This finding was further substantiated with the detection of a potential signalling complex composed of either p-MSK1 and p-cJun or p-MSK1 and p-ATF2 (co-immunoprecipitation). ATF2 and cJun are known AP1 components. Given the presence of an AP-1 site in HOX-1 promoter region, the activity of AP1 transcription factor was examined. Electrophoretic mobility shift assays performed showed a maximal upregulation of AP1 binding activity after 60 min of H2O2 treatment, which was significantly inhibited by SP600125 and H89. Our results show for the first time the potential role of JNKs, p38-MAPK and MSK1 in the mechanism of transducing the oxidative stress-signal to HOX-1, possibly promoting cell survival and preserving homeostasis.

Role of MSK1 in the signaling pathway leading to VEGF-mediated PAF synthesis in endothelial cells

Vascular endothelial growth factor (VEGF) inflammatory effects require acute platelet-activating factor (PAF) synthesis by endothelial cells (EC). We previously reported that VEGF-mediated PAF synthesis involves the activation of VEGF receptor-2/Neuropilin-1 complex, which is leading to the activation of p38 and p42/44 mitogen-activated protein kinases (MAPKs) and group V secretory phospholipase A(2) (sPLA(2)-V). As the mechanisms regulating sPLA(2)-V remain unknown, we addressed the role of the mitogen- and stress-activated protein kinase-1 (MSK1), which can be rapidly and transiently activated by p38 or p42/44 MAPKs. In native bovine aortic endothelial cells (BAEC), we observed a constitutive protein interaction of MSK1 with p38, p42/44 MAPKs, and sPLA(2)-V. These protein interactions were maintained in BAEC transfected either with the empty vector pCDNA3.1, wild-type MSK1 (MSK1-WT) or N-terminal dead kinase MSK1 mutant (MSK1-D195A). However, in BAEC expressing C-terminal dead kinase MSK1 mutant (MSK1-D565A), the interaction between MSK1 and sPLA(2)-V was reduced by 82% and 90% under basal and VEGF-treated conditions as compared to native BAEC. Treatment with VEGF for 15 min increased basal PAF synthesis in native BAEC, pCDNA3.1, MSK1-WT, and MSK1-D195A by 166%, 139%, 125%, and 82%, respectively. In contrast, PAF synthesis was prevented in cells expressing MSK1-D565A mutant. These results demonstrate the essential role of the C-terminal domain of MSK1 for its constitutive interaction with sPLA(2)-V, which appears essential to support VEGF-mediated PAF synthesis.

Mitogen-activated protein kinases, adherens junction dynamics, and spermatogenesis: a review of recent data

Mitogen-activated protein kinases (MAPKs) are important regulators of many cellular processes. In mammalian testes, these kinases are involved in controlling cell division, differentiation, survival and death, and are therefore critical to spermatogenesis. Recent studies have also illustrated their involvement in junction restructuring in the seminiferous epithelium, especially at the ectoplasmic specialization (ES), a testis-specific adherens junction (AJ) type. ES contributes to the adhesion between Sertoli cells at the blood-testis barrier, as well as between Sertoli and developing spermatids (step 9 and beyond) at the adluminal compartment. MAPKs regulate AJ dynamics in the testis via their effects on the turnover of junction-associated protein complexes, the production of proteases and protease inhibitors, and the cytoskeleton structure. In this review, roles of the three major MAPK members, namely extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, in ES dynamics are critically discussed. An integrated model of how these three MAPKs regulate adhesion function in the seminiferous epithelium is also presented. This model will serve as the framework for future investigation in the field.

Vasoactive intestinal peptide upregulates MUC2 intestinal mucin via CREB/ATF1

VIP exerts a spectrum of effects as a potent anti-inflammatory factor. In addition, VIP increases expression of MUC2, a major intestinal secretory mucin. We therefore investigated the effects of VIP on the promoter activity of the 5'-flanking region of the MUC2 gene. VIP activated MUC2 transcription in human colonic epithelial cells via cAMP signaling to ERK and p38. cAMP/Epac/Rap1/B-Raf signaling was not involved in MUC2 reporter activation. Furthermore, activation of MUC2 transcription was independent of many of the reported downstream effectors of G protein-coupled receptors, such as PKC, Ras, Raf, Src, calcium, and phosphoinositide 3-kinase. VIP induced cAMP response element-binding protein (CREB)/ATF1 phosphorylation, and this was prevented by treatment with inhibitors of either MEK or p38 and by PKA and MSK1 inhibitor H89. CREB/ATF1 and c-Jun were shown to bind to an oligonucleotide encompassing a distal, conserved CREB/AP1 site in the 5'-flanking region of the MUC2 gene, and this cis element was shown to mediate promoter reporter activation by VIP. This study has identified a new, functional cis element within the MUC2 promoter and also a new pathway regulating MUC2 expression, thus providing further insight into the molecular mechanism of VIP action in the colon. These findings are relevant to the normal biology of the colonic mucosa as well as to the development of VIP as a therapeutic agent for treatment of inflammatory bowel disease.