The mitogen-activated protein kinase signaling pathways: role in megakaryocyte differentiation

Summary.  Megakaryopoiesis is a process by which bone marrow progenitor cells develop into mature megakaryocytes (MKs), which in turn produce platelets required for normal hemostasis. The mitogen-activated protein kinases (MAPKs) family comprises four main groups of proteins: extracellular signal-related kinases (ERKs) (ERK1/2 or p44/p42), ERK5, p38MAPKs (α, β, γ, δ) and c-Jun amino-terminal kinases (JNKs) (JNK 1, 2, 3). These intracellular signaling pathways play a pivotal role in many essential cellular processes including proliferation and differentiation. The purpose of this review is to summarize our current knowledge on the role of MAPKs in MKs, specifically regarding differentiation in immortalized cell lines and primary MKs. A critical role of the MEK (MAPK kinase)-ERK1/2 pathway in MK development has been demonstrated although the details remain controversial. There is at present no functional evidence for a role of p38MAPKs whereas the role of JNKs and ERK5 in MK development is not known. Characterization of these molecular event cascades remains crucial for the understanding of the megakaryopoiesis process.     

脊髓压迫性损伤后p3 8MAPK信号转导通路的时间变化规律

目的研究脊髓压迫性损伤后p38MAPK信号转导通路在其中的变化规律和可能的意义.方法制备脊髓压迫伤动物模型,用Westerm blot检测伤后0,30 min,6,24,72 h组织中p38MAPK的变化情况.结果脊髓损伤后局部组织中p38MAPK存在明显的变化规律30 min时出现明显表达上调,6 h达到高峰,以后逐渐下降,而正常脊髓组织中未检测出明确的表达.结论p38MAPK信号转导通路参与了脊髓损伤后的信号转导,其变化规律有可能对脊髓损伤的治疗具有参考意义.     

Lithium protection of phencyclidine-induced neurotoxicity in developing brain: the role of phosphatidylinositol-3 kinase/Akt and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase signaling pathways

Phencyclidine (PCP) and other N-methyl-D-aspartate (NMDA) receptor antagonists have been shown to be neurotoxic to developing brains and to result in schizophrenia-like behaviors later in development. Prevention of both effects by antischizophrenic drugs suggests the validity of PCP neurodevelopmental toxicity as a heuristic model of schizophrenia. Lithium is used for the treatment of bipolar and schizoaffective disorders and has recently been shown to have neuroprotective properties. The present study used organotypic corticostriatal slices taken from postnatal day 2 rat pups to investigate the protective effect of lithium and the role of the phosphatidylinositol-3 kinase (PI-3K)/Akt and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) pathways in PCP-induced cell death. Lithium pretreatment dose-dependently reduced PCP-induced caspase-3 activation and DNA fragmentation in layers II to IV of the cortex. PCP elicited time-dependent inhibition of the MEK/ERK and PI-3K/Akt pathways, as indicated by dephosphorylation of ERK1/2 and Akt. The proapoptotic factor glycogen synthase kinase (GSK)-3beta was also dephosphorylated at serine 9 and thus activated. Lithium prevented PCP-induced inhibition of the two pathways and activation of GSK-3beta. Furthermore, blocking either PI-3K/Akt or MEK/ERK pathway abolished the protective effect of lithium, whereas inhibiting GSK-3beta activity mimicked the protective effect of lithium. However, no cross-talk between the two pathways was found. Finally, specific GSK-3beta inhibition did not prevent PCP-induced dephosphorylation of Akt and ERK. These data strongly suggest that the protective effect of lithium against PCP-induced neuroapoptosis is mediated through independent stimulation of the PI-3K/Akt and ERK pathways and suppression of GSK-3beta activity.     

Up-regulation of endothelial nitric-oxide synthase by endothelium-derived hyperpolarizing factor involves mitogen-activated protein kinase and protein kinase C signaling pathways

Cytochrome P450 (P450)-dependent metabolites of arachidonic acid, the epoxyeicosatrienoic acids (EETs), are proposed to be endothelium-derived hyperpolarizing factors (EDHF) that affect vascular tone; however, the effects of EDHF on endothelial-derived nitric oxide biosynthesis remain unknown. We examined the regulation of endothelial nitric-oxide synthase (eNOS) by EDHF and investigated the relevant signaling pathways involved. The P450 epoxygenases CYP102 F87V mutant, CYP2C11-CYPOR, and CYP2J2 were transfected into cultured bovine aortic endothelial cells, and the effects of endogenously formed or exogenously applied EETs on eNOS expression and activity were assessed. Transfection with the P450 epoxygenases led to increased eNOS protein expression, an effect that was attenuated by cotreatment with the P450 inhibitor 17-ODYA. Northern analysis demonstrated that P450 transfection led to increased eNOS mRNA levels consistent with an effect at the pretranslational level. P450 epoxygenase transfection resulted in increased eNOS activity as measured by the conversion of L-arginine to L-citrulline. Addition of synthetic EETs (50-200 nM) to the culture media also increased eNOS expression and activity. Treatment with mitogen-activated protein kinase (MAPK), MAPK kinase, and protein kinase C inhibitors apigenin, 2'-amino-3'-methoxyflavone (PD98059), and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), respectively, significantly inhibited the effects of P450 transfection on eNOS expression. Overexpression of P450 epoxygenases or addition of synthetic EETs increased Thr495 phosphorylation of eNOS, an effect that was inhibited by both apigenin and PD98059. Overexpression of P450 epoxygenases in rats resulted in increased aortic eNOS expression, providing direct evidence that EDHF can influence vascular eNOS levels in vivo. Based on this data, we conclude that EDHF up-regulates eNOS via activation of MAPK and protein kinase C signaling pathways.     

p38 and c-Jun N-terminal kinase mitogen-activated protein kinase signaling pathways play distinct roles in the response of organogenesis-stage embryos to a teratogen

Mitogen-activated protein kinase (MAPK) signaling plays an important role during embryo development. We hypothesize that MAPK activation is a determinant of the fate of organogenesis-stage embryos exposed to insult. To test this hypothesis, CD1 mice were exposed to a model teratogen, hydroxyurea, on gestational day 9. Hydroxyurea exposure triggered a dramatic, transient increase in the activation of p38 MAPKs and c-Jun N-terminal kinases (JNKs) in embryos, without activating extracellular signal-regulated kinases 1 and 2. Selectively blocking p38 MAPKs with 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580) enhanced hydroxyurea-induced fetal mortality without affecting growth retardation or the incidence of deformities among surviving fetuses. In contrast, selectively blocking JNKs with JNK peptide inhibitor 1, L-stereoisomer did not affect hydroxyurea-induced fetal death but increased the incidence of the hindlimb defects observed. Thus, p38 MAPKs and JNKs play distinct roles in protecting the conceptus against insult. Pharmacological inhibition of teratogen exposure induced MAPK activation has adverse consequences on the embryo.     

Perceptions of the nursing role in spinal cord injury rehabilitation

In the UK, over the last 50 years there have been many developments in the rehabilitation of spinal cord-injured people leading to improvements in outcomes. In spinal cord injury rehabilitation nurses work as members of a multiprofessional team but their role is not clearly defined and, unlike other professionals, they have a 24-hour relationship with patients. This article presents some findings from a larger ongoing ethnographic research study. The aim of this section of the study was to identify how nurses and patients perceive the nursing role in spinal cord injury rehabilitation. Semistructured interviews were carried out with 14 spinal cord-injured patients and 14 registered nurses. The findings suggest that patients value the nursing contribution as a means of emotional and physical support but that they do not necessarily see nursing input as rehabilitation. Nurses see their role as multifaceted but identify difficulties in crossing over from an acute care philosophy to a rehabilitation philosophy. The 24-hours close relationship with patients may be a source of imbalanced power relationships between nurses and patients and this causes distress to some patients. It is suggested that nurses need to develop their bedrock role in a way that empowers patients in spinal cord rehabilitation.     

Inhibition of mitogen-activated protein kinase and stimulation of Akt kinase signaling pathways: Two approaches with therapeutic potential in the treatment of neurodegenerative disease

The neurodegenerative diseases of adulthood, including Alzheimer's disease (AD) and Parkinson's disease (PD), pose an enormous and growing public health burden. Although effective symptomatic treatments exist for PD, and, to a lesser extent, for AD, there is no therapy for these disorders which will forestall their progression. With the rise of the concept of programmed cell death (PCD) came the realization that even in the absence of complete knowledge of proximate causes neuroprotection may nevertheless be possible by targeting the pathways of PCD. One set of signaling pathways that have been implicated in cell death are the mitogen-activated protein kinase (MAPK) pathways. The possibility of blocking these pathways and thereby providing neuroprotection has recently been put to the test in a clinical trial of a mixed lineage kinase inhibitor in the treatment of PD. Unfortunately, this trial failed to demonstrate a protective effect. Based on considerations related to the implementation of the trial, it would be premature to conclude that inhibition of MAPK signaling is a failed strategy. In spite of these negative results, the MAPK and related kinase pathways retain their importance as potential targets in PD. In relation to pathogenesis, the discovery of mutations in the mixed lineage kinase (MLK)-like kinase leucine-rich repeat kinase 2 (LRRK2) suggests a role for these kinases in regulating the viability of dopamine neurons. In relation to treatment, the survival signaling kinase Akt has been demonstrated in vivo to mediate striking neurotrophic and antiapoptotic effects. Thus, it is likely that therapeutic targets related to these kinase signaling pathways will emerge.     

A role for mitogen-activated protein kinase activation by integrins in the pathogenesis of psoriasis

In normal epidermis, beta1 integrin expression is confined to the basal layer, whereas in hyperproliferative epidermis, integrins are also expressed in the suprabasal layers. Transgenic mice in which integrins are expressed suprabasally via the involucrin promoter have a sporadic psoriatic phenotype; however, the mechanism by which integrins contribute to the pathogenesis of psoriasis is unknown. We observed activation of mitogen-activated protein kinase (MAPK) in basal and suprabasal keratinocytes of human and transgenic mouse psoriatic lesions and healing mouse skin wounds, correlating in each case with suprabasal integrin expression. Phenotypically normal human and transgenic mouse epidermis did not contain activated MAPK. Transgene-positive keratinocytes produced more IL-1alpha than controls did, and keratinocyte MAPK could be activated by ligation of suprabasal integrins or treatment with IL-1alpha. Constitutive activation of MAPK increased the growth rate of human keratinocytes and delayed the onset of terminal differentiation, recreating many of the histological features of psoriatic epidermis. We propose that activation of MAPK by integrins, either directly or through increased IL-1alpha production, is responsible for epidermal hyperproliferation in psoriasis and wound healing, and that the sporadic phenotype of the transgenic mice may reflect the complex mechanisms by which IL-1 release and responsiveness are controlled in skin.     

Acetylation of mitogen-activated protein kinase phosphatase-1 inhibits Toll-like receptor signaling

The mitogen-activated protein kinase (MAPK) pathway plays a critical role in Toll-like receptor (TLR) signaling. MAPK phosphatase-1 (MKP-1) inhibits the MAPK pathway and decreases TLR signaling, but the regulation of MKP-1 is not completely understood. We now show that MKP-1 is acetylated, and that acetylation regulates its ability to interact with its substrates and deactivate inflammatory signaling. We found that LPS activates acetylation of MKP-1. MKP-1 is acetylated by p300 on lysine residue K57 within its substrate-binding domain. Acetylation of MKP-1 enhances its interaction with p38, thereby increasing its phosphatase activity and interrupting MAPK signaling. Inhibition of deacetylases increases MKP-1 acetylation and blocks MAPK signaling in wild-type (WT) cells; however, deacetylase inhibitors have no effect in cells lacking MKP-1. Furthermore, histone deacetylase inhibitors reduce inflammation and mortality in WT mice treated with LPS, but fail to protect MKP-1 knockout mice. Our data suggest that acetylation of MKP-1 inhibits innate immune signaling. This pathway may be an important therapeutic target in the treatment of inflammatory diseases.     

细胞凋亡在脊髓损伤中作用的实验研究

目的 探讨细胞凋亡在脊髓损伤发病机理中的作用。方法 采用原位末端标记法,对大鼠脊髓损伤不同时间脊髓组织中凋亡细胞的数目和部位进行观察和分析,并作正常对照。结果 损伤后灰质和白质均检测到凋亡细胞,神经元凋亡少见,胶质细胞凋亡多见。细胞凋亡发生在损伤后 12 h～ 4周,以 4d时达到高峰,至 4周时渐趋于正常。结论 大鼠脊髓损伤后神经元和胶质细胞均发生细胞凋亡,而以胶质细胞凋亡常见。     

PP2A regulates upstream members of the c-jun N-terminal kinase mitogen-activated protein kinase signaling pathway

We have previously demonstrated that inhibition of the serine-threonine phosphatase PP2A resulted in increased c-jun N-terminal kinase (JNK) activity, and that the regulatory subunit, A/alpha of PP2A, was physically associated with the JNK. Because there exists additional examples of phosphatases serving as negative regulators of multiple members of mitogen-activated protein kinase (MAPK) pathways in Drosophila and yeast, we hypothesized that PP2A may serve a homologous function in mammalian cells affording the regulation of additional upstream kinases in the JNK pathway. In human monocytes, activation of JNK by LPS proceeds through the MAPK kinase kinase MEKK-1 and, subsequently, the MAPK kinases MKK4 and/or MKK7. Using the human monocyte cell line THP-1, we show that pharmacological manipulation of the activity of PP2A seemed to regulate not only JNK but also the upstream kinases MKK4 and MEKK-1. Using coimmunoprecipitation, overexpression of tagged recombinant JNK, and bacterial two-hybrid strategies, evidence for physical interactions between the structural subunit, PP2A-A/alpha and MEKK-1, MKK4, and JNK was observed. These studies suggest that the target of regulation by PP2A includes upstream kinases in the JNK MAPK pathway. Furthermore, PP2A-A/alpha seems to serve as a structural protein to foster protein-protein interactions affording specificity of the regulation among members of this MAP kinase pathway.     

Glucose or diabetes activates p38 mitogen-activated protein kinase via different pathways

Hyperglycemia can cause vascular dysfunctions by multiple factors including hyperosmolarity, oxidant formation, and protein kinase C (PKC) activation. We have characterized the effect of hyperglycemia on p38 mitogen-activated protein (p38) kinase activation, which can be induced by oxidants, hyperosmolarity, and proinflammatory cytokines, leading to apoptosis, cell growth, and gene regulation. Glucose at 16.5 mM increased p38 kinase activity in a time-dependent manner compared with 5.5 mM in rat aortic smooth muscle cells (SMC). Mannitol activated p38 kinase only at or greater than 22 mM. High glucose levels and a PKC agonist activated p38 kinase, and a PKC inhibitor, GF109203X, prevented its activation. However, p38 kinase activation by mannitol or tumor necrosis factor-α was not inhibited by GF109203X. Changes in PKC isoform distribution after exposure to 16.5 mM glucose in SMC suggested that both PKC-β2 and PKC-δ isoforms were increased. Activities of p38 kinase in PKC-δ– but not PKC-β1–overexpressed SMC were increased compared with control cells. Activation of p38 kinase was also observed and characterized in various vascular cells in culture and aorta from diabetic rats. Thus, moderate hyperglycemia can activate p38 kinase by a PKC-δ isoform–dependent pathway, but glucose at extremely elevated levels can also activate p38 kinase by hyperosmolarity via a PKC-independent pathway.     

急性脊髓损伤后差异蛋白的表达

背景：在质谱分析中,任何一种同位素标记相对和绝对定量试剂标记的不同样本中的同一蛋白质表现为相同的质荷比,而在串联质谱中,信号离子表现为不同质荷EL（114—121）的峰,因此可以分析得到相关蛋白质的定量信息。目的：建立大鼠急性脊髓损伤后脊髓组织差异蛋白质谱,应用同位素标记相对和绝对定量技术联合LC．MS／MS质谱技术从分子水平来探索脊髓差异蛋白的表达情况。方法：取8只SD大鼠,参照Allen’s等方法建立大鼠急性脊髓损伤模型,随机分为脊髓损伤后0h组和8h组,每组各4只。损伤后取脊髓组织,用同位素标记相对和绝对定量技术分析大鼠急性脊髓损伤后脊髓组织的差异蛋白质。结果与结论：共鉴定到了220个差异表达的蛋白,上调的差异蛋白数是116个,下调的差异蛋白有104个。其中相关神经再生的差异蛋白12个,其中上调的有7个,下调的有5个。提示实验中检测到的多种差异蛋白及表达明显的神经生长因子可能作为急性脊髓损伤的生物标记物或可能作为临床管理监测急性脊髓损伤的损伤进程、靶向治疗及评估疗效的有力证据。     

15-羟基二十碳四烯酸收缩慢性缺氧动脉环信号转导通路的部位：内皮细胞还是平滑肌

目的:观察15-羟基二十碳四烯酸(15-HETE)致慢性缺氧性大鼠肺动脉收缩的信号转导途径,阐明15-羟基二十碳四烯酸引起慢性缺氧性肺动脉收缩作用的可能机制。方法:实验于2006-03/2006-09在哈尔滨医科大学药学院进行。①实验材料:健康成年雄性Wistar大鼠,体质量220～240g,清洁级,由哈尔滨医科大学附属第二医院实验动物中心提供。②实验方法:取18只成年雄性Wistar大鼠连续缺氧9d(O2体积分数为0.12)制作大鼠缺氧模型,通过氧气监测控制器控制箱内氧气体积分数为0.12,9d后即成为缺氧大鼠模型。16只正常大鼠吸入正常空气(O2体积分数为0.21)作为对照。将大鼠麻醉后分离直径1.5mm肺内动脉,剪成2mm长动脉环置于组织浴槽中,记录血管张力变化。③实验评估:观察15-羟基二十碳四烯酸对缺氧模型组、正常组大鼠血管收缩作用,在此基础上,除去血管内皮细胞和使用丝裂素活化蛋白激酶的激酶抑制剂PD98059,明确血管内皮细胞和丝裂素活化蛋白激酶的激酶系统在15-羟基二十碳四烯酸收缩肺动脉中的作用。结果:34只大鼠均进入结果分析。①15-羟基二十碳四烯酸对正常组、缺氧模型组大鼠血管环均有收缩作用,呈浓度-效应正相关,但缺氧组收缩明显,与正常组比较,差异显著(P<0.01)。②丝裂素活化蛋白激酶的激酶抑制剂PD98059可明显阻断15-羟基二十碳四烯酸对缺氧大鼠肺动脉的收缩作用(P<0.05)。③去掉内皮的缺氧大鼠肺动脉,PD98059仍明显阻断15-羟基二十碳四烯酸的收缩作用(P<0.05)。结论:15-羟基二十碳四烯酸通过激活肺动脉平滑肌丝裂素活化蛋白激酶的激酶信号转导途径收缩慢性缺氧性大鼠肺动脉,作用部位主要位于血管平滑肌。     

大鼠脊髓损伤模型的改良及伤后再生基因-2蛋白的表达变化

目的:制备改良的大鼠脊髓损伤(SCI)动物模型,并探讨再生基因(Reg)-2蛋白在SCI后的表达规律。方法:采用36只SD大鼠。参考Allen法,使用自制打击装置致大鼠T13段脊髓中度损伤。以行为联合评分法(CBS)评定模型的可靠性。免疫印迹法和免疫组织化学(SABC)法对正常对照组、伤后第1天、第2天、第3天、第5天和第7天的大鼠脊髓组织中的Reg-2蛋白进行检测。结果:SCI后大鼠一般情况符合临床损伤特点,且稳定性强;各损伤组大鼠神经功能联合评分均呈明显下降趋势,与正常对照组比较差异具有显著性意义(P<0.05);在正常对照组大鼠脊髓神经元内有微量的Reg-2蛋白表达(阳性细胞数为17.3±2.6,Reg-2相对表达量为0.038±0.007)。SCI后1天,大鼠脊髓内Reg-2表达的免疫阳性细胞随着损伤时间的推移逐渐增多,至伤后第7天仍呈高水平表达(阳性细胞数为90.0±3.6,相对表达量为0.694±0.018),各组间比较差异具有显著性意义(P<0.05)。伤后3天内,Reg-2免疫阳性细胞以后角神经元为主,而伤后7天以前角神经元和胶质细胞为主。结论:本实验装置制作的大鼠SCI模型稳定、可靠;SCI后Reg-2蛋白表达开始升高,对受损神经起保护和修复作用。     

内皮素参与脊髓损伤后缺血

目的 :阐明内皮素 (ET)与脊髓损伤 (SCI)后缺血的关系。方法 :1鞘内注射 ET 110 ng,观察外源性ET 1对正常大鼠脊髓血流 (SCBF)的影响。 2 SCI前鞘内预先注射非选择性 ET受体拮抗剂 PD14 5 0 6 55 0 μg,观察阻断 ET生物学效应后伤区及邻近 SCBF的变化。采用激光多普勒血流仪监测血流。结果 :ET 1注射后 30分钟 ,SCBF降为基线的 (5 9.78± 8.80 ) % ,2小时为基线的 (5 8.6 0± 7.10 ) %。生理盐水组伤区 SCBF在 SCI后 5分钟即有明显下降 ,为基线的 (75 .5 7± 9.5 7) % ,2小时已降至基线的 (5 7.6 0± 7.6 0 ) % ,伤后 4小时仍未恢复 ;伤区邻近 SCBF下降较慢 ,伤后 30分钟降至基线的 (80 .74± 8.10 ) % ,2小时为基线的 (5 5 .2 6±5 .79) % ,伤后 4小时 SCBF仍未恢复。PD14 5 0 6 5明显改善了伤区 SCBF,损伤 5分钟及 30分钟后 ,伤区血流与生理盐水组比较差异均有显著性 (P均 <0 .0 1)。结论 :ET参与了 SCI后的缺血过程 ;PD14 5 0 6 5消除了伤区及邻近区 SCBF的下降。临床应用 ET受体拮抗剂对 SCI可能有治疗作用