Microglial signaling by amyloid beta protein through mitogen-activated protein kinase mediating phosphorylation of MARCKS

Myristoylated alanine-rich C kinase substrate (MARCKS), an acidic protein associated with cell motility and phagocytosis, is activated upon phosphorylation by protein kinase C (PKC) and proline-directed protein kinases. In Alzheimer disease (AD), activated microglia expressing MARCKS migrates around senile plaques. We reported that amyloid beta protein (A beta), a major component of senile plaques, activated MARCKS through a tyrosine kinase and PKC-delta. We have now identified another A beta signaling pathway through a mitogen-activated protein kinase (MAPK) involved in the phosphorylation of MARCKS and analysed cross-talk between PKC and MAPK pathways in primary cultured rat microglia. A selective inhibitor for MAPK kinase, PD098059, significantly inhibited the phosphorylation of MARCKS induced by A beta. Extracellulary regulated kinases, the activities of which were induced by A beta, directly phosphorylated a recombinant MARCKS in vitro. The MAPK pathway was sensitive to wortmannin, but not to a PKC inhibitor or to tyrosine kinase inhibitors. The activation of PKC by A beta was not sensitive to wortmannin. Our findings suggest involvement of the MAPK pathway through phosphoinositol 3-kinase in the phosphorylation of MARCKS in rat cultured microglia, an event may be associated with mechanisms activating microglia in AD.     

Regulation of the phosphoinositide-3 kinase and mitogen-activated protein kinase signaling pathways by progesterone and its reduced metabolites in the rat brain

Several growth factors, such as vascular endothelial growth factor, brain-derived neurotrophic factor, and insulin-like growth factor-I are involved in the actions of progesterone in the central nervous system. Previous studies in neuronal and glial cultures have shown that progesterone may regulate growth factor signaling, increasing the phosphorylation of extracellular-signal regulated kinase (ERK) and the phosphorylation of Akt, components of the mitogen-activated protein kinase (MAPK) and the phosphoinositide-3 kinase (PI3K) signaling pathways, respectively. In this study, we have evaluated whether progesterone and its reduced metabolites, dihydroprogesterone and tetrahydroprogesterone, regulate PI3K and MAPK signaling in the brain of ovariectomized rats in vivo. Significant increases in the phosphorylation of ERK, in the expression of the catalytic (p110) and the regulatory (p85) subunits of PI3K and in the phosphorylation of Akt were observed in the hypothalamus, the hippocampus, and the cerebellum 24 hr after progesterone administration. Progesterone metabolites partially mimicked the effect of progesterone and had a stronger effect on MAPK and PI3K signaling in the hypothalamus than in the other brain regions. These findings suggest that progesterone regulates MAPK and PI3K signaling pathways in the central nervous system in vivo by direct hormonal actions and by mechanisms involving progesterone metabolites.     

Interleukin-1 beta induces corticotropin-releasing factor-41 release from cultured hypothalamic cells through protein kinase C and cAMP-dependent protein kinase pathways.

Interleukin-1 beta (IL-1 beta) induces a dose-dependent increase in the release of corticotropin-releasing factor-41 (CRF) from dispersed rat fetal hypothalamic cells in culture. This release of CRF could be inhibited by the protein kinase C inhibitor H-7, and by the protein kinase A inhibitor IP-20. This suggests that both protein kinase C and protein kinase A-dependent pathways are involved in the response of CRF to IL-1 beta. Dexamethasone also blocked the CRF response to IL-1 beta, indicating that activated glucocorticoid receptors can inhibit the response of CRF to IL-1 beta.     

Interleukin-1 beta and interleukin-6 mRNA are expressed in human glioblastoma and neuroblastoma cells respectively.

We report the expression of different interleukins (IL) in four human glioblastoma and neuroblastoma cell lines. The glioblastoma cell line LI, expresses IL-1 beta and IL-6 mRNA, though not IL-2 and IL-4. The expression of the former gene is modulated by retinoic acid. Two cell clones [BE(2)-C and BE(2)-M17] as well as the neuroblastoma cell line SK-N-BE(2), from which both clones were derived, express IL-6 mRNA, but not IL-1 beta, IL-2 or IL-4. Both IL-1 beta and IL-6 cytokines are known to increase hypothalamic CRH mRNA, a gene reported to be expressed in all these cell lines. The production of both cytokines and neuropeptides indicates a complex dialogue between tumour cells and anti-tumour immunity.     

Promotion of neurite outgrowth by protein kinase inhibitors and ganglioside GM1 in neuroblastoma cells involves MAP kinase ERK1/2

To investigate mechanisms of neurite outgrowth, murine Neuro-2a neuroblastoma cells were exposed to ganglioside GM1 in the presence or absence of specific protein kinase inhibitors. Isoquinolinesulfonamide (H-89), an inhibitor of cyclic AMP dependent protein kinase A (PKA), and bisindolylmaleimide I (BIM), which inhibits protein kinase C, each stimulated neurite outgrowth in a dose-dependent manner in the absence of exogenous GM1. Minimally effective (threshold) concentrations of H-89 or BIM potentiated outgrowth when they were used in combination with GM1. To search for a shared component in the mechanisms of GM1, H-89 and BIM, phosphorylation of ERK1/2 was examined. Inhibition of the activation of extracellular signal regulated kinases (ERK1/2) by U0126, prevented neuritogenesis of Neuro-2a by all the three agents. Pretreatment of serum-depleted Neuro-2a cultures with GM1 or BIM enhanced ERK1/2 phosphorylation when the serum level was restored to 10%. In contrast, H-89 did not alter the serum-mediated response. In cells exposed to GM1 or BIM without additional serum, a transitory decrease in ERK phosphorylation occurred. These data suggest that GM1 influences two neuritogenic pathways, one modulated by PKC and the other regulated by PKA. Therefore, GM1 may have the potential to stimulate alternate pathways resulting in outgrowth.     

Coupling of 5-HT1A autoreceptors to inhibition of mitogen-activated protein kinase activation via G beta gamma subunit signaling

The 5-HT1A receptor is expressed presynaptically as the primary somatodendritic autoreceptor on serotonergic raphe neurons, and postsynaptically in several brain regions. Signaling of the 5-HT1A autoreceptor was studied in RN46A cells, a model of serotonergic raphe neurons that express endogenous 5-HT1A receptors. In undifferentiated RN46A cells stably transfected with the wild-type 5-HT1A receptor, 5-HT1A receptor activation inhibited forskolin-induced cyclic adenosine monophosphate (cAMP) formation (by 50%), increased [Ca2+]i, and induced a novel inhibition (up to 60%) of phospho-p42/p44-mitogen-activated protein kinase (MAPK). Upon differentiation of non-transfected or 5-HT1A-transfected RN46A cells, agonist-mediated inhibition of MAPK was enhanced. These actions were blocked by pretreatment with pertussis toxin indicating mediation via Gi/Go proteins and the calcium response was blocked by preactivation of protein kinase C (PKC). In cells overexpressing the G beta gamma scavenger carboxyl-terminal domain of G protein receptor kinase 2 (GRK-CT), 5-HT1A receptor activation inhibited cAMP formation, but coupling to calcium mobilization and inhibition of MAPK was abolished. The activity of 5-HT1A receptors containing mutations of PKC sites in the second (i2: T149A) or third intracellular loop (i3: T229A/S253G/T343A) was tested. At comparable levels of receptor expression, the signaling of the 5-HT1A i3 mutant was similar to the 5-HT1A wild-type receptor, while the i2 and quadruple (i2/i3) mutants failed to couple to G beta gamma-mediated increase in [Ca2+]i or inhibition of MAPK, but did couple to G alpha i-mediated inhibition of cAMP. Thus, the i2-domain of the 5-HT1A autoreceptor is crucial for coupling to G beta gamma subunits and their subsequent responses (e.g. calcium mobilization and inhibition of MAPK activity).     

A new factor derived from 1321N1 human astrocytoma cells causes differentiation of PC-12 cells mediated through mitogen-activated protein kinase cascade

Glial cells play an important role in maintaining neural function. In the present study, we examined the effects of a factor derived from human astrocytoma cells (1321N1) on differentiation of rat pheochromocytoma cells (PC-12). The conditioned medium which had been used for culture of 1321N1 cells caused the differentiation of PC-12 cells, suggesting that 1321N1 cells release a neurotrophic factor. The factor was apparently distinct from well-known neurotrophic factors, such as nerve growth factor (NGF), since it was resistant to boiling and trypsin treatment. The molecular size of the factor was assumed to be below 1000 through dialysis and ultrafiltration experiments. Furthermore, PC-12 cells were differentiated synergistically by the combined addition of NGF and the conditioned medium of 1321N1 cells. Partially purified fraction of the factor by Sephadex G-15 gel filtration column caused the prolonged activation of mitogen-activated protein kinase (MAPK). The differentiation of PC-12 cells induced by the fraction or NGF disappeared after the treatment with PD98059, a specific inhibitor of MAPK kinase (MEK), suggesting the involvement of MAPK in the differentiation. These results suggest that the new low-molecular factor derived from glial cells causes differentiation of PC-12 cells mediated through an activation of MAPK.     

Regulation of corticotropin-releasing factor receptor type 2beta messenger ribonucleic acid by interleukin-1beta in rat vascular smooth muscle cells

OBJECTIVE: Corticotropin-releasing factor receptor type 2 (CRF R2) messenger RNA (mRNA) expression in the rodent heart or vessels is modulated by exposure to urocortin and glucocorticoids. In addition, we previously found that incubation with a variety of cytokines, such as interleukin (IL)-1 and IL-6, and tumor necrosis factor-alpha also reduced CRF R2beta mRNA expression, with IL-1beta being the most effective. In this study, we further explored the regulation of CRF R2beta mRNA levels by IL-1beta in the rat vascular smooth muscle A7r5 cells. METHODS: A7r5 cells were incubated with IL-1beta, urocortin, or both for 6 h, after pre-incubating with or without anti-IL-1beta antibody (Ab) for 30 min, and then CRF R2beta mRNA levels were measured by RNase protection assay. Cells were incubated with lipopolysaccharides, IL-1beta, IL-6, dexamethasone, forskolin, or urocortin for 20 min, and then intracellular cAMP was measured by cAMP RIA. RESULTS: IL-1beta produced a significant time-dependent decrease in CRF R2beta mRNA levels. Combined urocortin and IL-1beta administration did not have synergistic effects on the decrease in CRF R2beta mRNA levels. IL-1beta Ab failed to block the ability of urocortin to regulate CRF R2beta mRNA levels, suggesting that urocortin regulated CRF R2beta mRNA levels via another pathway than IL-1beta production. Urocortin induced the intracellular cAMP production in A7r5 cells, while IL-1beta failed to induce it. CONCLUSION: The multifactorial regulation of CRF R2beta mRNA expression in the A7r5 cells serves to limit the inotropic and chronotropic effects of CRF R2 agonists such as urocortin during prolonged physical or immune challenge.     

Anoxic injury of endothelial cells causes divergent changes in protein kinase C and protein kinase A signaling pathways

Alterations in protein kinase C (PKC) and cAMP-dependent kinase have been documented in anoxic brain injury. However, the regulation of these signaling enzymes in the cerebrovasculature has not been explored. In this study, cultured brain endothelial cells exposed to anoxic injury (anoxia—20 min/reoxygenation—40 min) showed both a significant increase (p<0.001) in PKC and decrease (p<0.01) in cAMP-dependent kinase activity. Analysis of PKC by Western blot indicated an increase in kinase level in response to anoxic injury, whereas there was no change in the level of cAMP-dependent protein kinase, as measured by labeled cAMP binding. Inhibition of nitric oxide synthase did not affect these changes. Addition of the nitric oxide-releasing compound sodium nitroprusside caused a dose-dependent increase in the activity of both signaling systems in endothelial cells. These data demonstrate that anoxic injury of brain endothelial cells in culture causes significant and divergent changes in signaling kinase activity. Abnormalities in brain endothelial PKC and cAMP-dependent kinase could have important consequences for the blood-brain barrier in anoxic brain injury.     

川芎嗪干预转化生长因子β1诱导肝星状细胞结缔组织生长因子表达中p38丝裂酶原激活蛋白激酶的途径

背景：前期研究发现川芎嗪可通过抑制肝星状细胞的增殖和阻断Ⅰ,Ⅲ胶原的合成,下调结缔组织生长因子的表达等,发挥抗肝纤维化的作用,但具体机制尚不清楚。 目的：观察川芎嗪对体外培养肝星状细胞表达结缔组织生长因子的影响,以及p38丝裂酶原激活蛋白激酶(p38MAPK)信号通路在其中的作用。 方法：用5 μg/L转化生长因子β1诱导活化体外培养的肝星状细胞,用川芎嗪和p38MAPK特异阻断剂SB203580进行干预,以RT-PCR法检测结缔组织生长因子 mRNA和Ⅰ型胶原mRNA的表达,Western blot法检测磷酸化p38MAPK蛋白的表达。 结果与结论：经转化生长因子β1诱导后,肝星状细胞中结缔组织生长因子和Ⅰ型胶原mRNA表达显著增强(P < 0.01),用川芎嗪和SB203580干预后,结缔组织生长因子和Ⅰ型胶原mRNA的表达均出现不同程度的下降。但川芎嗪和川芎嗪+SB203580混合干预对这两者的基因表达抑制作用比单独的SB203580干预更强。川芎嗪和SB203580对磷酸化p38MAPK蛋白表达也都有明显的抑制作用(P < 0.01),但SB203580和川芎嗪+SB203580对其磷酸化蛋白表达抑制作用更明显,而SB203580与川芎嗪+SB203580无明显差异(P > 0.05)。因此,推测川芎嗪可能通过抑制转化生长因子β1诱导的结缔组织生长因子基因表达,阻断Ⅰ型胶原合成,其作用途径可能与抑制p38mapk信号通路有关,同时认为川芎嗪抗纤维化可能是多重作用靶点。     

Opposing influences of protein kinase activities on neurite outgrowth in human neuroblastoma cells: initiation by kinase A and restriction by kinase C.

The respective roles of cAMP-dependent protein kinase (protein kinase A [PKA]) and protein kinase C (PKC) in the early stages of neurite outgrowth were examined in SH-SY-5Y human neuroblastoma cells. Forskolin or dbcAMP, agents that increase intracellular cAMP levels, and intracellular delivery of PKA catalytic subunit induced neurite outgrowth. The PKA inhibitor, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), prevented the increases, and decreased further the percentage of cells possessing short, filopodia-like neurites in the absence of inducers. In contrast to effects on PKA activation, PKC activation by 12-0-tetradecanoylphorbol-13-acetate (TPA) reduced the percentage of filopodia-like neurites elaborated by otherwise untreated cells, and prevented neurite outgrowth induced by PKA activators. PKC inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), staurosporine, and sphingosine induced neurite outgrowth. Neurites induced by PKA activation contained higher levels of tubulin immunoreactivity than those induced by PKC inhibition. Furthermore, PKA-induced neurites rapidly retracted in the presence of colchicine, while those elaborated following PKC inhibition were more resistant. These data suggest that neurites elaborated in response to PKA activation are dependent upon microtubule polymerization, and that neurite induction following PKC inhibition is mediated by a different mechanism. PKA activators and PKC inhibitors exerted additive effects on neurite outgrowth, suggesting that the distinct pathways regulated by these two kinases function cooperatively during neuritogenesis.     

HIV-1-infected and/or immune-activated macrophages regulate astrocyte CXCL8 production through IL-1beta and TNF-alpha: involvement of mitogen-activated protein kinases and protein kinase R

Monocyte infiltration is an important pathogenic event in human immunodeficiency virus type one (HIV-1) associated dementia (HAD). CXCL8 (Interleukin 8, IL-8), a CXC chemokine that elicits chemotaxis of neutrophils, has recently been found to recruit monocytes or synergistically enhance CCL2-mediated monocyte migration. In this report, we demonstrate CXCL8 levels in the cerebrospinal fluid of HAD patients are higher than HIV-1 seropositive patients without neurological impairment. The underlying mechanisms regulating CXCL8 production during disease are not completely understood. We investigated the role of HIV-1-infected and immune-competent macrophages, the principal target cell and mediator of neuronal injury in HAD, in regulating astrocyte CXCL8 production. Immune-activated and HIV-1-infected human monocyte-derived-macrophages (MDM) conditioned media (MCM) induced production of CXCL8 by human astrocytes. This CXCL8 production was dependent on MDM IL-1β and TNF-α production following viral and immune activation. CXCL8 production was reduced by inhibitors for mitogen-activated protein kinases (MAPKs), including p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinases (ERK1/2). Moreover, prolonged IL-1β or TNF-α treatment activated double-stranded RNA-activated protein kinase (PKR). Inhibition of PKR prevented elevated CXCL8 production in astrocytes. We conclude that IL-1β and TNF-α, produced from HIV-1-infected and immune-competent macrophages, are critical in astrocyte CXCL8 production. Multiple protein kinases, including p38, JNK, ERK1/2, and PKR, participate in the inflammatory response of astrocytes. These observations will help to identify effective therapeutic strategies to reduce high-levels of CXCL8-mediated CNS inflammation during HAD.     

Gene transfer of glial cell-derived neurotrophic factor and cardiotrophin-1 protects PC12 cells from injury: involvement of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase kinase pathways

Gene therapy for neurodegenerative diseases may utilize the expression of neurotrophic factors because of their potential to promote survival and regeneration of injured neuronal cells. Increasing numbers of these factors are being considered for gene transfer, but their specificity and efficacy in neuroprotection are greatly variable. The major aims of this study were to carry out gene transfer of various neurotrophic factors and investigate their mechanisms of action as well as their protective effects on the viability of rat pheochromocytoma (PC12) cells. We used glutamate, S-nitroso-N-acetyl-DL-penicillamine (SNAP), and staurosporine to induce excitatory damage, oxidative stress, and apoptosis, respectively, because these mechanisms are thought to participate in various disease processes leading to degeneration of cells. We utilized adenovirus vectors for efficient gene transfer of trophic factors (glial-cell derived neurotrophic factor [GDNF] and cardiotrophin-1 [CT-1]) or calbindin-D28k. We found that GDNF and CT-1 gene transfers were equally effective in saving PC12 cells from injury, but calbindin expression did not show any beneficial effects. GDNF gene transfer was much more efficient in protecting PC12 cells from damage than direct GDNF administration. The protection by GDNF expression against staurosporine was mediated through both phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase kinase (MAPK kinase; MEK) pathways, but only the MEK pathway was involved in the protection against SNAP. In contrast, the protective effect of GDNF against glutamate toxicity was independent of these RET-dependent signal transduction pathways.     

P38MAPK信号转导通路与血管细胞增殖及缺血再灌注的关系

丝裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)是广泛表达的丝氨酸/酪氨酸激酶,在真核生物细胞多种信号转导通路中起重要的作用,受多种因素的调控,作用底物多种多样。P38信号通路是MAPK通路中相当重要的一个分支,在炎症、细胞应激、凋亡、细胞周期和生长等多种生理、病理过程中起着重要作用。     

Saponins from Panax japonicus attenuate age-related neuroinflammation via regulation of the mitogen-activated protein kinase and nuclear factor kappa B signaling pathways

Neuroinflammation is recognized as an important pathogenic factor for aging and related cognitive disorders. Mitogen-activated protein kinase and nuclear factor kappa B signaling pathways may mediate neuroinflammation. Saponins from Panax japonicus are the most abundant and bioactive members in rhizomes of Panax japonicus, and show anti-inflammatory activity. However, it is not known whether saponin from Panax japonicus has an anti-inflammatory effect in the aging brain, and likewise its underlying mechanisms. Sprague-Dawley rats were divided into control groups(3-, 9-, 15-, and 24-month-old groups) and saponins from Panax japonicus-treated groups. Saponins from Panax japonicus-treated groups were orally administrated saponins from Panax japonicus at three doses of 10, 30, and 60 mg/kg once daily for 6 months until the rats were 24 months old. Immunohistochemical staining and western blot assay results demonstrated that many microglia were activated in 24-month-old rats compared with 3-and 9-month-old rats. Expression of interleukin-1β, tumor necrosis factor-α, cyclooxygenase-2, and inducible nitric oxide synthase increased. Each dose of saponins from Panax japonicus visibly suppressed microglial activation in the aging rat brain, and inhibited expression levels of the above factors. Each dose of saponins from Panax japonicus markedly diminished levels of nuclear factor kappa B, IκBα, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38. These results confirm that saponins from Panax japonicus can mitigate neuroinflammation in the aging rat brain by inhibition of the mitogen-activated protein kinase and nuclear factor kappa B signaling pathways.