神经生长因子及其受体相关信号传导通路的研究进展

神经生长因子是神经营养因子家族成员之一,对不同时期神经元的存活、分化、生长及损伤后的修复和再生都有着十分重要的作用。不仅在神经系统中,随着人类的其他正常和肿瘤组织中同样也检测得到了NGF,神经生长因子在各方面的应用也得到了重视并均已得到了证实。NGF功能的发挥离不开与其受体的结合,根据NGF表面糖蛋白与凝集素结合能力的不同,其受体可被分为高亲和力受体酪氨酸激酶A和低亲和力受体p75。Trk A与NGF结合后所介导的信号通路主要有:1MAPK通路;2PLC-γ通路;3PI3K/PKB通路。而p75与NGF结合介导的信号传导通路主要包括:1NF-κB通路;2JNK-p53-Bax凋亡通路;3神经酰胺通路。Trk A一般介导的是正性信号,如促进神经细胞生长、维持神经细胞的存活等;而p75既可促进神经细胞存活,也可诱导神经细胞凋亡,但以后者为主。当Trk A与p75同时表达时,Trk A可抑制p75诱导细胞凋亡,使受损神经细胞大量增殖,所以其生物学总效应是促进神经细胞的生长和存活。     

HSV-1感染对神经胶质瘤细胞神经生长因子及其受体表达的影响

神经生长因子(NGF)主要由神经胶质细胞产生,通过特异的靶细胞表面的神经生长因子受体介导产生生物学效应,与神经细胞的生长发育、分化和凋亡等密切相关。单纯疱疹病毒1型(HSV-1)作为一种嗜神经病毒,易造成神经细胞、神经胶质细胞凋亡或死亡。本实验以U251人神经胶质瘤细胞为研究对象,观察HSV-1感染致U251细胞凋亡的过程中NGF及其受体的变化情况。结果发现U251细胞是HSV-1的容许细胞;HSV-1感染致U251细胞凋亡过程中,NGF及其低亲和力受体p75NTR出现表达强度随时间先增强后减弱的趋势,而高亲和受体Tr-kA持续低表达。推测HSV-1感染致神经细胞凋亡中可能调控了神经营养因子的表达。     

GDNF家族及其受体

神经营养因子对神经系统的发育和维持起着至关重要的作用。它们不但能够促进神经元的分化和存活 ,而且抑制与神经系统退行性疾病、神经损伤和神经毒相关的神经元的退化。最近被确认的ＧＤＮＦ家族是ＴＧＦ β家族成员的远亲。ＧＤＮＦ作为该家族的第一个成员 ,发现于 1 993年 ,由Ｌｉｎ等人[1] 由大鼠胶质细胞株Ｂ49中提纯到 ,发现它能促进胚胎中脑多巴胺能神经元的存活和形态分化 ,以及提高它们对高亲和性多巴胺的摄取。最近的研究发现 ,与其它神经营养因子相比 ,ＧＤＮＦ对多巴胺能神经元和去甲状腺能神经元有更强的促活能力[2 ] ,并且对…     

GDNF家族成员及其受体的研究进展

胶质细胞源性神经营养因子(GDNF)家族是一类结构上属于转化生长因子-β（TGF-β）超家族的神经营养因子,目前包括GDNF,neurturin(NTN)和persephin(PSP)三种因子,它们在体内有着广泛的作用.近年来发现GDNF和NTN的受体均为多组分结构,由不同的糖基磷脂酰肌醇（GPI）蛋白和共享的跨膜酪氨酸激酶受体Ret蛋白构成.有关这一家族的因子及其受体的研究正在不断深入.     

烟碱型乙酰胆碱受体及其神经保护作用

新近研究证实,神经元烟碱型乙酰胆碱受体(nAChR)激动后可起到一定的神经保护作用.目前,一些作用于烟碱受体的激动剂已被作为治疗神经退行性疾病如阿尔茨海默病(AD)和帕金森病(PD)的候选药物,但是关于烟碱受体激动后如何发挥神经保护作用及其潜在的分子机制还不清楚,其中有与Ca2+相关的信号转导假说以及神经营养因子等假说.本文就烟碱型乙酰胆碱受体及其神经保护作用的研究进展予以综述.     

神经生长因子

神经生长因子是一类能促进神经生长的多肽,近年来的研究表明它在非神经系统及肿瘤的发生中也有重要作用。本文综述了神经生长因子的结构、生物合成、作用机制及生理、病理作用等方面的研究进展。     

神经生长因子的研究

神经生长因子的研究湖南医科大学李叔庚神经生长因子（ｎｅｒｖｅｇｒｏｗｔｈｆａｃｔｏｒＮＧＦ）是神经系统最重要的生物活性分子之一,也是最早发现和最典型的神经营养因子,它影响外周和中枢神经系统某些神经元的存活和分化［１］。１９４８年Ｂｕｅｋｅｒ首次发现将...     

一个新的信号受体家族--Toll/IL-1R家族的研究进展

Ｔｏｌｌ受体最初是在研究果蝇胚胎腹背侧体轴的形成中发现的,由于它与ＩＬ－１受体在结构、功能、信号转导通路上的诸多相似,人们将它们归入一个大的信号受体ｏｌｌ／ＵＩＬ－１Ｒ家族。许多研究均证实,除与胚胎发育有关外,这一信号受体家族的成员在机体对抗外来病原体的天然免疫中起到了重要的作用,尤其是人类Ｔｏｌｌ蛋白在介导内毒素对细胞操作中的作用备受关注。     

Nerve Growth Factor Receptors in Human Neuroblastoma Cells

Receptors for the nerve growth factor protein (NGFR) present in the human neuroblastoma cell line LAN-1 were characterized. LAN-1 cells display high-affinity (type I, with KD value of 5.9 X 10(-11) M) and low-affinity (type II, with KD value of 9.2 X 10(-9) M) binding to NGF. NGFR were fractionated by preparative isoelectric focusing in a granulated gel (PEGG). High-affinity binding was found in the 5.9-6.2 pH region of the PEGG, and low-affinity binding in the 4.6-4.8 and 8.8-9.3 pH ranges. After further analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) we observed both 92.5- and 200-kDa molecular species associated with NGF binding activity. The 200-kDa protein was found in fractions displaying high-affinity NGF binding and the 92.5-kDa protein in fractions displaying low-affinity NGF binding. Equilibrium binding analysis of NGF in PEGG fractions confirmed the presence of two specific saturable binding sites with KD values similar to those observed for whole dissociated cells. When NGFR II activity from the acidic region of the PEGG chromatogram was incubated with NGFR II from the basic region of the PEGG chromatogram, there was no change in NGF binding or in the number of apparent NGF receptors. However, incubation of these same fractions with a fraction having only NGFR I showed an apparent increase in high-affinity NGF binding and a decrease in low-affinity NGF binding. Immunoprecipitation of this "mixed" fraction and analysis on SDS-PAGE under reduced and nonreduced conditions showed 200-kDa and 92.5-kDa proteins under nonreduced conditions and a 92.5-kDa protein under reduced conditions. Our findings are consistent with the hypothesis that there are two distinct NGF receptors in NGF-responsive cells. The interconvertibility of low- and high-affinity receptors and the possible existence of a modulator type protein or of "silent" type receptors are also in agreement with our findings.     

Disulfide Bond Formation Between Nerve Growth Factor and the Nerve Growth Factor Receptor from Embryonic Sensory Neurons

Recent studies with sympathetic neurons using radiolabeled nerve growth factor have indicated that a high-molecular-weight covalent complex is formed. This complex is between the nerve growth factor and the high-affinity (type I) receptor and occurs through the formation of a disulfide bond. Studies presented in the present article demonstrate a similar complex is formed on chicken embryonic sensory neurons. The formation of this complex is inhibited by the addition of unlabeled nerve growth factor, metabolic energy inhibitors (dinitrophenol and NaF), and of sulfhydryl reagents. On the other hand, formation of this complex is not inhibited by temperature, or by the addition of insulin or epidermal growth factor. The receptor involved in the covalent complex formation is the high-affinity (type I) receptor. The molecular weight of this complex is approximately 232,000 daltons. Evidence indicates that this covalent complex may be required for the biological activity of the nerve growth factor.     

Acute Regulation of the Epidermal Growth Factor Receptor in Response to Nerve Growth Factor

PC12 cells possess specific receptors for both nerve growth factor and epidermal growth factor, and by an unknown mechanism, nerve growth factor is able to attenuate the propagation of a mitogenic response to epidermal growth factor. The differentiation response of PC12 cells to nerve growth factor, therefore, predominates over the proliferative response to epidermal growth factor. We have observed that the addition of nerve growth factor to PC12 cells rapidly produces a decrease in surface 125I-epidermal growth factor binding capacity. Unlike previously described nerve growth factor effects on 125I-epidermal growth factor binding capacity, which required several days of nerve growth factor exposure, the decreases we report occur within minutes of nerve growth factor addition: A 50% decrease in 125I-epidermal growth factor binding capacity is evident at 10 min. This rapid nerve growth factor response is concentration dependent; inhibition of 125I-epidermal growth factor binding is detectable at nerve growth factor levels as low as 0.2 ng/ml and is maximal at approximately 50 ng/ml, consistent with known ranges of biological activity. No demonstrable differences in the rate of epidermal growth factor receptor synthesis or degradation were observed in cells acutely exposed to nerve growth factor. Scatchard analysis revealed that acute nerve growth factor treatment decreased the number of both high- and low-affinity 125I-epidermal growth factor binding sites, while the receptor affinity remained unchanged. We have also investigated the involvement of various potential intracellular mediators of nerve growth factor action and of known intracellular modulatory systems of the epidermal growth factor receptor for their capacity to participate in this nerve growth factor activity.     

Expression of Nerve Growth Factor and Nerve Growth Factor Receptor Genes in Human Tissues and in Prostatic Adenocarcinoma Cell Lines

Nerve growth factor (NGF) mRNAs were detected and quantified in a variety of normal and neoplastic human tissues by northern blot hybridization. Human heart contained the highest NGF mRNA levels, whereas lower but comparable levels were found in the placenta, prostate, and kidney. All tissues examined coexpressed the low-affinity NGF receptor (LNGFR), whereas none of these tissues expressed the high-affinity NGF receptor encoded by the trk protooncogene. The widespread distribution of the LNGFR suggests that it plays a role in the regulation of normal cell growth. No overexpression of NGF or LNGFR mRNA was detected in neoplastic tissues, whereas LNGFR-like immunoreactivity was localized outside of tumor cells. Transforming growth factor-alpha and protooncogene c-fos expression in these tissues did not show a systematic correlation with NGF/LNGFR expression. Furthermore, regulation of the human NGF gene was studied in DU145 cells, a prostatic adenocarcinoma cell line that synthesizes significant NGF mRNA levels. Serum induced, whereas dexamethasone inhibited, NGF mRNA synthesis in these cells. Serum induction was preceded by a rapid and transient activation of the c-fos protooncogene.     

Regulation by Interleukin-1 of Nerve Growth Factor Secretion and Nerve Growth Factor mRNA Expression in Rat Primary Astroglial Cultures

Primary cultures of neonatal rat cortical astrocytes contain low cellular levels (about 2 pg/mg of protein) of nerve growth factor (NGF), but secrete significant amounts of NGF into the culture medium (about 540 pg of NGF/mg of cell protein/38-h incubation). Incubation of astrocytes with interleukin-1 (IL-1) increased the cellular content of NGF and the amount secreted by about threefold. In comparison, cerebellar astrocytes secreted significant amounts of NGF, and the secretion was also stimulated by IL-1. The stimulatory action of IL-1 on astrocytes prepared from cortex was dose- and time-dependent. Concentrations of IL-1 causing half-maximal and maximal stimulation of NGF secretion were 1 and 10 U/ml, respectively). Maximal NGF secretion induced by IL-1 (10 U/ml) was seen following 38 h of incubation. The basal secretion of NGF was reduced by about 50% under Ca2(+)-free conditions; however, the percent stimulation of NGF secretion by IL-1 was the same in the absence or presence of Ca2+. The stimulatory action of IL-1 was specific, because other glial growth factors and cytokines were almost ineffective in stimulating NGF secretion from cortical astroglial cells. IL-1 treatment also increased cellular NGF mRNA content twofold. The results indicate that IL-1 specifically triggers a cascade of events, independent of cell growth, which regulate NGF mRNA content and NGF secretion by astrocytes.     

Down-Regulation of c-neu Receptors by Nerve Growth Factor in PC12 Cells

Abstract: A small number of p185^{c- neu} receptors have been found on PC12 cells. These receptors show some basal phosphorylation in quiescent cells. When the cells are treated with nerve growth factor (NGF) for a short time, some increase in phosphorylation is seen, mainly on serine and threonine residues, and this is accompanied by a slight shift in the apparent molecular weight. Epidermal growth factor (EGF) also increases the phosphorylation of p185^{c- neu} , in this case on tyrosine residues. Neither heregulin-β1 nor gp30 stimulates the tyrosine phosphorylation of p185^{c- neu} , and neither has a proliferative effect on the cells. Treatment of the cells with NGF for 5 days produces a 70–80% reduction in the number of p185^{c- neu} receptors. This down-regulation does not occur when PC12nnr5 cells, which lack the high-affinity NGF receptor, p140 ^trk , are treated with NGF.The level of p185^{c- neu} mRNA is not altered by NGF treatment, suggesting that the down-regulation is due to either a translational or a posttranslational alteration.     

Characteristics of Partially Purified Nerve Growth Factor Receptor

Receptors for the nerve growth factor protein (NGF) have been isolated from three cell types [embryonic chicken sensory neurons (dorsal root sensory ganglia; DRG), rat pheochromocytoma (PC12) and human neuroblastoma (LAN-1) cells] and have been shown to be similar with respect to equilibrium dissociation constants. The present results demonstrate that there are multiple molecular weight species for NGF receptors from DRG neurons and PC12 cells. NGF receptors can be isolated from DRG as four different molecular species of 228, 187, 125, and 112 kilodaltons, and PC12 cells as three molecular species of 203, 118, and 107 kilodaltons. The NGF receptors isolated from DRG show different pH-binding profiles for high- and low-affinity binding. High-affinity binding displays a bell-shaped pH profile with maximum binding between pH 7.0 and 7.9, whereas low-affinity binding is constant between pH 5.0 and 9.1, with a twofold greater binding at pH 3.6. At 22 degrees C, the association rate constant was found to be 9.5 +/- 1.0 X 10(6) M-1 s-1. Two dissociation rate constants were observed. The fast dissociating receptor has a dissociation rate constant of 3.0 +/- 1.5 X 10(-2) s-1, whereas the slow dissociating receptor constant was 2.4 +/- 1.0 X 10(-4) s-1. The equilibrium dissociation constants calculated from the ratio of dissociation to association rate constants are 2.5 X 109-11) M for the high-affinity receptor (type I) and 3.2 X 10(-9) M for the low-affinity receptor (type II). These values are the same as those determined by equilibrium experiments on the isolated receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

神经生长因子与冻干异体神经桥接大鼠神经缺损的研究

实验采用冻干处理的异体神经与外源性神经生长因子（ＮＧＦ）结合来桥接大鼠的坐骨神经１．０ｃｍ的缺损。用雄性Ｗｉｓｔａｒ大鼠进行的四组实验结果表明：冻干处理的异体神经可降低其抗原性,但处理后并不损害雪旺氏细胞（ＳＣ）基底膜的完整性,在移植后可能成为轴突再生的通道和支架;外源性ＮＧＦ与冻干神经结合形成的复合体,可为神经的再生提供一个较好的微环境,具有成为理想桥接材料的可能性     

神经生长因子的发光免疫分析法

介绍了一种灵敏的神经生长因子化学发光免疫测定方法。小鼠神经生长因子（ｍＮＧＦ）的抗体ＩｇＧ用亲和层析纯化并用吖啶酯标记。该法可用于大鼠组织中ＮＧＦ含量的测定。方法的灵敏度为１０ｐｇ／ｍＬＮＧＦ;批内批间变异系数分别为８．７％及１３．２％;回收率平均为１０３％。ｍＮＧＦ抗体对人的ＮＧＦ也有极强的交叉反应,故本方法也可能用于病人血清或脑脊液中ＮＧＦ含量的测定。