2-Decenoic acid ethyl ester, a derivative of unsaturated medium-chain fatty acids, facilitates functional recovery of locomotor activity after spinal cord injury

There is increasing evidence that omega-3 polyunsaturated fatty acids (PUFAs) have therapeutic potential in various animal models of neuronal injury. However, very few studies have examined the effect of medium-chain fatty acids (MCFAs) on neuronal injury. So in the present study we synthesized various MCFAs and their derivatives, and found that exposure to trans-2-decenoic acid ethyl ester (DAEE) markedly activated extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) in cultured cortical neurons. Therefore, we examined the effect of DAEE treatment on a rat model of spinal cord injury. DAEE (150 μg/kg body weight) administered after hemisection of the spinal cord resulted in improved functional recovery, decreased the lesion size, increased the activation of ERK1/2, and enhanced the expression of bcl-2 and brain-derived neurotrophic factor (BDNF) mRNA in the injury site of the spinal cord. Furthermore, it also increased neuronal survival after spinal cord injury. These results indicate that the possibility that DAEE will become a promising tool for reducing the secondary damage observed following primary physical injury to the spinal cord.     

Heptamethoxyflavone,a citrus flavonoid,enhances brain-derived neurotrophic factor production and neurogenesis in the hippocampus following cerebral global ischemia in mice

In the present study using a transient global ischemia mouse model, we showed that (1) a citrus flavonoid 3,5,6,7,8,3′,4′-heptamethoxyflavone (HMF) induced the phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) and cAMP response element-binding protein (CREB) in the hippocampus after ischemia; (2) HMF increased the expression of brain-derived neurotrophic factor (BDNF), a representative neurotrophic factor in the central nervous system, in the hippocampal dentate gyrus, and most BDNF-positive cells were also stained with anti-glial fibrillary acidic protein (one of the major intermediate filament proteins of mature astrocytes) and (3) HMF increased doublecortin positive neuronal precursor cells in the dentate gyrus subventricular zone or subgranular zone. These results suggest that HMF has the ability to induce BDNF production in astrocytes and enhance neurogenesis after brain ischemia, which may be mediated by activation of ERK1/2 and CREB.     

Oroxylin A increases BDNF production by activation of MAPK-CREB pathway in rat primary cortical neuronal culture

Oroxylin A (5,7-dihydroxy-6-methoxyfavone) is a flavonoid compound originated from the root of Scutellaria baicalensis Georgi. Our previous reports suggested that oroxylin A improves memory function in rat, at least in part, by its antagonistic effects on GABA(A) receptor. In addition, oroxylin A protects neurons from ischemic damage by mechanisms currently not clear. In this study we determined whether oroxylin A modulates the level of brain derived neurotrophic factor (BDNF) in primary rat cortical neuronal culture, which is well known for its role on neuronal survival, neurogenesis, differentiation of neurons and synapses and learning and memory. Treatment of oroxylin A for 3-48h increased BDNF expression which was analyzed by ELISA assay and Western blot analysis. Oroxylin A induced slow but sustained increases in intracellular calcium level and activated ERK1/2 mitogen activated protein kinase (MAPK). In addition, oroxylin A phosphorylated cyclic AMP response element binding protein (CREB) at Ser 133 in concentration and time dependent manner. Pretreatment with the MAPK inhibitor PD98059 (10μM) attenuated phosphorylation of ERK1/2 and CREB as well as BDNF production, which suggests that oroxylin A regulates BDNF production by activating MAPK-CREB pathway. GABA(A) antagonist bicuculline mimicked the effects of oroxylin A on BDNF production as well as MAPK-CREB pathway. Increase in intracellular Ca(2+) concentration, phosphorylation of ERK1/2 and CREB, and BDNF expression by oroxylin A was blocked by NMDA receptor inhibitor MK-801 (10μM) as well as tetrodotoxin (TTX, 0.5 and 1μM). The results from the present study suggest that the calcium and p-CREB dependent induction of BDNF expression, possibly via activation of synaptic NMDA receptor through the blockade of GABA(A) activity in cortical neuronal circuitry, might be responsible for the neuroprotective or memory enhancing effects of oroxylin A.     

Brain-derived neurotrophic factor activation of TrkB protects neurons from HIV-1/gp120-induced cell death

Patients with the human immunodeficiency virus type 1 (HIV-1) develop in the late phase of infection a complex of neurological signs termed Acquired Immune Deficiency Syndrome-Related Dementia (ADC). These patients exhibit cortical and subcortical atrophy. Considerable experimental data indicate that the HIV-1 envelope glycoprotein gp120 may be one of the agents causing neuronal cell death. Gp120 causes neuronal cell death both in vitro and in vivo by activating a caspase-dependent apoptotic pathway, and in particular caspase-3. The neurotrophin brain-derived neurotrophic factor (BDNF) has been shown to prevent gp120-mediated apoptosis of cerebellar granule cells by inhibiting caspase-3 activation. However, the signal transduction pathway that contributes to the neuroprotective effects of BDNF has not been determined. BDNF binds with high affinity to the tyrosine kinase receptor TrkB and activates different intracellular signaling cascade including the extracellular signal-related kinases (ERK) and the phosphatidylinositol 3-kinase (PI3-K). Pharmacological inhibition of TrkB or ERK1/2, but not PI3-K, greatly reduced the ability of BDNF to block gp120-mediated apoptosis of cerebellar granule cells. These findings suggest that TrkB-mediated activation of ERK1/2 is the main signaling pathway that contributes to neuroprotection against gp120.     

Cyclophosphamide promotes cell survival via activation of intracellular signaling in cultured cortical neurons

Cyclophosphamide (CP) has been used as an antitumour agent or immunosuppressant clinically, though the potential biological role of CP in the central nervous system (CNS) has not been clarified. In the present study, we found that pretreatment with CP prevented neuronal cell death caused by serum deprivation in cultured cortical neurons. Interestingly, CP stimulated activation of PI3K (phosphatidylinositol 3 kinase) and MAPK/ERK (mitogen-activated protein kinase/extracellular signal-regulated kinase) pathways, which are known as survival-promoting intracellular signalings. Furthermore, CP increased the expression of Bcl2, an anti-apoptotic factor. In the presence of inhibitors for PI3K or MAPK/ERK pathways, the CP-dependent neuronal survival and Bcl-2 up-regulation were both abolished. Importantly, significant increase in BDNF (brain-derived neurotrophic factor) expression was induced by CP application, implying that BDNF up-regulation is involved in the CP effect. We propose that CP has a protective effect on CNS neurons via the activation of intracellular signalings, and up-regulation of Bcl2 and BDNF.     

Activation of extracellular signal-regulated protein kinase in the dorsal root ganglion following inflammation near the nerve cell body

Inflammation of the primary afferent proximal to the dorsal root ganglion (DRG) and the DRG itself is known to produce radicular pain. Here, we examined pain-related behaviors and the activation of extracellular signal-regulated protein kinase (ERK) in the DRG after inflammation near the DRG somata. Inflammation of the L4/5 nerve roots and DRG induced by complete Freund's adjuvant (CFA) produced mechanical allodynia on the ipsilateral hindpaw and induced an increase in the phosphorylation of ERK, mainly in tyrosine kinase (trk) A-expressing small- and medium-size neurons. This CFA-induced increase in ERK phosphorylation was mediated through trk receptors, because intrathecal treatment with the tyrosine kinase inhibitor, K252a, reduced the activation of ERK. On the other hand, an increase in brain-derived neurotrophic factor (BDNF) mRNA/protein in the DRG concomitant with the ERK activation was also observed. Furthermore, we found that nerve growth factor (NGF) injection directly into the L4/5 nerve roots and DRG produced mechanical allodynia, and an increase in the phosphorylation of ERK and BDNF expression in the DRG, but the mitogen-activated protein kinase (MAPK) kinase1/2 inhibitor, U0126, inhibited the effects induced by NGF. Therefore, we suggest that after inflammation near the cell body, NGF synthesized within the nerve root and DRG induces BDNF expression through trkA receptors and intracellular ERK-MAPK. The activation of MAPK in the primary afferents may be involved in the pathophysiological mechanisms of inflammation-induced radiculopathy and MAPK pathways in the primary afferents may be potential targets for pharmacological intervention for neuropathic pain produced by inflammation near the DRG somata.     

Complement activation and atherosclerosis

Atherosclerosis is an inflammatory disease mediated through the action of monocyte/macrophages, complement and T-lymphocytes. C5a and monocyte chemotactic factor released during complement activation in the arterial wall may participate in the initial monocyte recruitment. Assembly of C5b-9 on cells of the arterial wall may also induce cell lysis. On the other hand, sublytic assembly of C5b-9 on smooth muscle cells (SMC) and endothelial cells (EC) induces cell activation and proliferation. Analysis of mitogen activated protein kinases (MAPK) pathways induced by C5b-9 in aortic SMC revealed that extracellular signal regulated kinase (ERK) 1, c-jun NH2-terminal kinase (JNK) 1, and p38 MAPK are all activated by C5b-9. ERK1 activity was inhibited by wortmannin suggesting that ERK1 pathway is activated through phosphatidyl inositol -3 (PI 3-) kinase. Sublytic C5b-9 assembly on the plasma membrane was also able to activate Janus kinase (JAK) 1, signal transducer and activator (STAT) 3 and STAT4 in EC. JAK1 but not STAT3 activation induced by C5b-9 is dependent on Gi protein activation. New evidence accumulated during the last decade support the role of complement activation in both initiation and progression of the atherosclerotic lesions. Complement system activation is a major component of the chronic inflammatory process associated with atherosclerosis.     

Mechanoregulation of monocyte chemoattractant protein-1 expression in rat vascular smooth muscle cells

The authors have previously shown that arterial wall strain mediates the development of vessel wall inflammation in experimental hypertension. The current studies explore the mechanoregulation of monocyte chemoattractant protein-1 (MCP-1), a potent pro-inflammatory chemokine, by mitogen-activated protein kinases (MAPK) and oxidative stress. Rat aortic smooth muscle (RASM) cells were subjected to cyclic strain on a uniform biaxial strain device. Strain rapidly activated both ERK1/2(MAPK) and p38(MAPK), with peak activation at 5 min. Strain induced a twofold increase in MCP-1 mRNA, which was attenuated by PD 98059, a specific ERK1/2(MAPK) inhibitor, and SB 203580, a specific p38(MAPK) inhibitor. Cyclic strain also increased production of superoxide anion via an NADPH oxidase-dependent mechanism. To assess the potential role of reactive oxygen species in MAPK activation, cells were stretched in the presence of N-acetylcysteine, which had no effect on p38(MAPK) activation, but significantly inhibited ERK1/2(MAPK) activation and MCP-1 expression. In conclusion, redox-sensitive activation of ERK1/2(MAPK) and redox-insensitive activation of p38(MAPK) regulate straininduced MCP-1 expression in RASM cells. These findings define a role for MAPK signal transduction in establishing a pro-inflammatory state in the arterial wall, and thus implicate a potential molecular link between arterial wall strain and atherosclerosis.     

Differential activation of mitogen‐activated protein kinase signalling pathways by isometric contractions in isolated slow‐ and fast‐twitch rat skeletal muscle

Activation of mitogen‐activated protein (MAP) kinases has been implicated in the signal transduction pathways linking exercise to adaptive changes of muscle protein expression. In the present study, we investigated whether contractions of isolated muscles induced phosphorylation of extracellular signal‐regulated kinase 1 and 2 (ERK1/2) and p38 MAPK in a fibre‐type dependent manner. Slow‐twitch (soleus) and fast‐twitch (epitrochlearis, extensor digitorum longus) rat skeletal muscles were exposed to intermittent tetanic stimulation. Compared with the contralateral non‐stimulated muscle, contractions increased ERK1/2 phosphorylation to the same extent in fast‐ and slow‐twitch muscles. Significant increase in phosphorylation of p38 MAPK was observed in the fast‐twitch muscles only. The total amount of ERK1/2 and p38 MAPK proteins was higher in the slow‐twitch soleus muscle. In conclusion, MAP kinase signalling pathways are differentially activated and expressed in slow‐ and fast‐twitch muscles. In addition, this activation is owing to muscle contraction per se and do not demand additional external influence.     

Interleukin-1 beta impairs brain derived neurotrophic factor-induced signal transduction

The expression of IL-1 is elevated in the CNS in diverse neurodegenerative disorders, including Alzheimer's disease. The hypothesis was tested that IL-1β renders neurons vulnerable to degeneration by interfering with BDNF-induced neuroprotection. In trophic support-deprived neurons, IL-1β compromised the PI3-K/Akt pathway-mediated protection by BDNF and suppressed Akt activation. The effect was specific as in addition to Akt, the activation of MAPK/ERK, but not PLCγ, was decreased. Activation of CREB, a target of these signaling pathways, was severely depressed by IL-1β. As the cytokine did not influence TrkB receptor and PLCγ activation, IL-1β might have interfered with BDNF signaling at the docking step conveying activation to the PI3-K/Akt and Ras/MAPK pathways. Indeed, IL-1β suppressed the activation of the respective scaffolding proteins IRS-1 and Shc; this effect might involve ceramide generation. IL-1-induced interference with BDNF neuroprotection and signal transduction was corrected, in part, by ceramide production inhibitors and mimicked by the cell-permeable C2-ceramide. These results suggest that IL-1β places neurons at risk by interfering with BDNF signaling involving a ceramide-associated mechanism.     

Induction of the matrix metalloproteinase-2 activation system in arteries by tensile stress. Involvement of the p38 MAP-kinase pathway

Matrix metalloproteinases (MMPs) play an important role in vascular remodeling and cardiovascular diseases by degrading extracellular matrix. Regulation of MMPs can be mediated by mitogen-activated protein kinases (MAPKs). Effects of pressure application on the proteolytic activity of MMP-2 and MAPK pathways were investigated in an organ culture of porcine muscular arteries. Inhibition of MAPKs (ERK1/2 and p38 MAPK) was carried out to prove their effects on MMP-2 activation. After tensile stress, activity and gene expression of MMP-2 were increased (p<0.05) as shown by gelatinase assays and real-time PCR. Whereas protein expression of MMP-2 and TIMP-2 showed no changes, its regulator MT1-MMP decreased in Western blot (p<0.001) and immunohistochemistry. In addition, p38 and ERK1/2 were activated (p38, p<0.05; ERK1/2, p<0.001) by pressure. After inhibition of p38 and ERK1/2 with SB203580 or PD98059, only the inhibition of the p38 pathway had an inhibitory effect on MMP-2 gelatinolytic activity. Tensile stress activates the MMP-2 system in muscular arterial walls. This mechanical signal is mediated by p38 MAPK and can be attenuated by blocking the p38 signal pathway. The regulation of the vascular gelatinolytic system by MAP kinases suggests a therapeutic option against cardiovascular diseases at the level of MAPK signal transduction.     

三七皂苷Rg1抑制脂多糖诱导小胶质细胞激活的机制研究

目的:探讨中药有效成分三七皂苷Rg1(Ginsenoside Rg1,Rg1)对抑制脂多糖(lipopolysaccharide,LPS)诱导的小胶质细胞株BV-2细胞激活的机制。方法:用LPS刺激BV-2细胞构建激活模型,采用四甲基偶氮唑蓝比色法(MTT)检测Rg1对BV-2细胞的活力影响,蛋白质免疫印迹(Western Blot)方法检测不同浓度Rg1(10、20和40μmol/L)对磷酸化的核因子-κB抑制蛋白-α(inhibitorκB-α,IκB-α)和反应结合蛋白(cAMP-responseelement binding protein,CREB)以及促分裂原活化蛋白激酶(mitogen-activated protein kinases,MAPKs)家族的细胞外信号调节激酶(extracellular signal-regulated kinase 1/2,ERK1/2)、c-Jun氨基端激酶(c-Jun N-terminal kinase,JNK)和p38促分裂原活化蛋白激酶(p38 mitogen-activated protein kinase,p38 MAPK)等细胞信号通路蛋白的表达及其变化规律。结果:不同浓度的Rg1明显抑制了LPS诱导的磷酸化IκB-α和CREB蛋白表达以及MAPKs通路(ERK1/2,JNK,p38 MAPK)磷酸化蛋白表达,并且对p38 MAPK表达的影响呈剂量依赖性。结论:Rg1可能通过抑制MAPKs的磷酸化来调控LPS诱导的小胶质细胞株BV-2细胞激活,发挥其神经抗炎的作用。     

学习与记忆机制研究进展

学习与记忆是动物最具特色的高级神经活动之一，长时程增强(LTP)被认为是与学习记忆有关的神经元可塑性的理想模型，其分子机制涉及一个信号转导级联反应——谷氨酸释放、N-甲基-D-天(门)冬氨酸(N-Methyl-D-aspartic acid,NMDA)谷氨酸受体激活、Ca2+通道和Ca2+/钙调蛋白依赖性蛋白激酶（Ca2+/calmodulin-dependent protein kinases,CaM激酶）Ⅱ、Ⅳ和丝裂原蛋白激酶（mitogen-activated protein kinase,MAPK）激活。最后，CaM激酶Ⅱ使α-氨基羟甲基恶唑丙酸(α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid,AMPA)谷氨酸受体磷酸化而激活，引起突触后神经元Ca2+ 内流增加。CaM激酶Ⅳ和MAPK通过刺激基因表达促使环磷腺苷反应元件结合蛋白 (cyclic AMP response element binding protein, CREB)磷酸化水平升高，c-fos表达增加。