Hydrophobic dipeptide Leu-Ile protects against neuronal death by inducing brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor synthesis

We investigated whether certain hydrophobic dipeptides, Leu-Ile, Leu-Pro, and Pro-Ile, which partially resemble the site on FK506 that binds to immunophilin, could stimulate glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) synthesis in cultured neurons and found only Leu-Ile to be an active dipeptide. Leu-Ile protected against the death of mesencephalic neurons from wild-type mice but not from mice lacking the BDNF or GDNF gene. Next, we examined the effects of i.p. or i.c.v. administration of Leu-Ile on BDNF and GDNF contents. Both types of administration increased the contents of BDNF and GDNF in the striatum of mice. Also, peripheral administration of Leu-Ile inhibited dopaminergic (DA) denervation caused by unilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum of mice. The number of rotations following a methamphetamine challenge was lower in the Leu-Ile-treated group than in the nontreated group. Next, we compared the calcineurin activity and immunosuppressant activity of Leu-Ile with those of FK506. Leu-Ile was not inhibitory toward calcineurin cellular activity in cultured neuronal cells. Furthermore, Leu-Ile did not suppress concanavalin A (ConA)-induced synthesis/secretion of interleukin-2 by cultured spleen cells, suggesting that the immunosuppressant activity of Leu-Ile may be negligible when used as a therapeutic tool for neurodegenerative diseases.     

Integrin beta1 is involved in the signaling of glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for the substantia nigra (SN) dopamine (DA) neurons. The transmembrane signaling of GDNF is mediated by a unique receptor system, including the ligand binding receptor GDNF family receptor alpha (GFRalpha) and the transmembrane signaling receptor Ret or neural cell adhesion molecule-140 (NCAM-140). Here, we found that another transmembrane cell adhesion molecule, integrin, a heterodimer consisting of alpha and beta subunits, also mediates the transmembrane signaling of GDNF. The results showed that the level of phosphorylated Src homology 2 domain containing (Shc), which was associated with the cytoplasmic domain of integrin beta1, increased after GDNF administration. Coimmunoprecipitation analysis demonstrated that integrin beta1 could form a complex with GFRalphal. The simulation of molecular modeling showed that four H-bonds were formed between integrin beta1 and GFRalpha. These data indicate that integrin beta1 is involved in the transmembrane signaling of GDNF and suggest that integrin beta1 may be an alternative signaling receptor for GDNF.     

Involvement of glial cell line-derived neurotrophic factor in activation processes of rodent macrophages

The physiological roles of glial cell line-derived neurotrophic factor (GDNF) expressed in the microglia/macrophages of the injured spinal cord have not yet been clarified. mRNA expression of chemokines, including monocyte chemoattractant protein (MCP)-1, was evoked within 1 hr after transection of the spinal cord, and GDNF mRNA expression was similarly up-regulated. Immunohistochemical analysis showed that GDNF was coexpressed with MCP-1 in the CD11b-positive cells. Therefore, we examined further the effects of GDNF on cultured rat peritoneal macrophages. GDNF enhanced the phagocytic activity of the macrophages via GFRalpha-1, glycosylphosphatidylinositol-anchored specific binding site of GDNF, in a c-Ret-independent manner. The influence of autocrine and/or paracrine GDNF synthesis was evaluated by performing activation experiments using macrophages cultured from heterozygous (+/-) GDNF gene-deficient mice or wild-type (+/+) mice. There were no morphological differences dependent on genetic types or stimulators. However, the GDNF mRNA level, but not the MCP-1 or GFRalpha-1 mRNA level, was substantially lower in the mutant macrophages than in the +/+ cells irrespective of stimulation with MCP-1 or lipopolysaccharide (LPS). The phagocytic activity enhanced by MCP-1 or LPS was significantly lower in the mutant cells (+/-) than in the +/+ ones, demonstrating the involvement of endogenous GDNF in the activation processes of macrophages in vitro and suggesting that not only neuroprotective function but also activation of macrophages is effected by the GDNF produced after a spinal cord injury.     

Transfection of the glial cell line-derived neurotrophic factor gene promotes neuronal differentiation简

Glial cell line-derived neurotrophic factor recombinant adenovirus vector-transfected bone marrow mesenchymal stem cells were induced to differentiate into neuron-like cells using inductive medium containing retinoic acid and epidermal growth factor. Cell viability, micro- tubule-associated protein 2-positive cell ratio, and the expression levels of glial cell line-derived neurotrophic factor, nerve growth factor and growth-associated protein-43 protein in the su- pernatant were significantly higher in glial cell line-derived neurotrophic factor/bone marrow mesenchymal stem cells compared with empty virus plasmid-transfected bone marrow mes- enchymal stem cells. Furthermore, microtubule-associated protein 2, glial cell line-derived neurotrophic factor, nerve growth factor and growth-associated protein743 mRNA levels in cell pellets were statistically higher in glial cell line-derived neurotrophic factor/bone marrow mesen- chymal stem cells compared with empty virus plasmid-transfected bone marrow mesenchymal stem cells. These results suggest that glial cell line-derived neurotrophic factor/bone marrow mesenchymal stem cells have a higher rate of induction into neuron-like cells, and this enhanced differentiation into neuron-like cells may be associated with up-regulated expression of glial cell line-derived neurotrophic factor, nerve growth factor and growth-associated protein-43.     

Differential effects of lentiviral vector-mediated overexpression of nerve growth factor and glial cell line-derived neurotrophic factor on regenerating sensory and motor axons in the transected peripheral nerve

Even after reconstructive surgery, major functional impairments remain in the majority of patients with peripheral nerve injuries. The application of novel emerging therapeutic strategies, such as lentiviral (LV) vectors, may help to stimulate peripheral nerve regeneration at a molecular level. In the experiments described here, we examined the effect of LV vector-mediated overexpression of nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) on regeneration of the rat peripheral nerve in a transection/repair model in vivo. We showed that LV vectors can be used to locally elevate levels of NGF and GDNF in the injured rat peripheral nerve and this has profound and differential effects on regenerating sensory and motor neurons. For sensory neurons, increased levels of NGF and GDNF do not affect the number of regenerated neurons 1 cm distal to a lesion at 4 weeks post-lesion but do cause changes in the expression of markers for different populations of nociceptive neurons. These changes are accompanied by significant alterations in the recovery of nociceptive function. For motoneurons, overexpression of GDNF causes trapping of regenerating axons, impairing both long-distance axonal outgrowth and reinnervation of target muscles, whereas NGF has no effect on these parameters. These observations show the feasibility of combining surgical repair of the transected nerve with the application of viral vectors. Furthermore, they show a difference between the regenerative responses of motor and sensory neurons to locally increased levels of NGF and GDNF.     

AF5, a CNS cell line immortalized with an N-terminal fragment of SV40 large T: growth,differentiation, genetic stability,and gene expression

Central nervous system progenitor cells that are self-renewing in culture and also differentiate under controlled conditions are potentially useful for developmental studies and for cell-based therapies. We characterized growth and plasticity properties and gene expression in a rat mesencephalic cell line, AF5, that was immortalized with an N-terminal fragment of SV40 large T (T155g). For over 150 population doublings in culture, the growth rate of AF5 cells remained steady, the cells remained responsive to bFGF, and telomerase activity and telomere lengths were unchanged. While karyotype analyses revealed some chromosomal abnormalities, these were also unchanged over time; additionally, no mutations in p53 gene sequences were found, and wild-type p53 activation was normal. AF5 cells produced PDGF, TGFbeta1, TGFbeta2, and bFGF. Similar to primary progenitor cells, AF5 cells retained their plasticity in culture; they could be propagated in an undifferentiated state as "neurospheres" in serum-free media or as adherent cultures in serum-containing media, and they differentiated when allowed to become confluent. Adherent subconfluent actively growing cultures expressed a marker for immature neurons, nestin, while few cells expressed the mature neuronal cell marker betaIII-tubulin. Confluent cultures ceased growing, developed differentiated morphologies, contained few or no nestin-expressing cells, and acquired betaIII-tubulin expression. Global gene expression was examined using a 15,000 gene microarray, comparing exponential growth with and without bFGF stimulation, and the differentiated state. The AF5 cell line exhibited stable genetic and growth properties over extended periods of time, while retaining the ability to differentiate in vitro. These data suggest that the AF5 cell line may be useful as an in vitro model system for studies of neural differentiation.     

Neuroprotection of glial cell line-derived neurotrophic factor in damaged spinal cords following contusive injury

Glial cell line-derived neurotrophic factor (GDNF) acts as a potent survival factor for many neuronal populations, including spinal motoneurons, indicating the therapeutic promise of GDNF for neurological disorders. Injury to spinal cord (SCI) triggers processes destructive to ascending sensory and descending motor conduction and extends tissue loss, thereby leading to permanent behavioral dysfunction. In this study, we attempted to examine whether GDNF protects neurons from SCI and subsequently lessens locomotor deficit in SCI rats. We utilized the NYU weight-drop device developed at New York University to induce spinal cord contusion at the T9-10 spinal segment. After SCI, GDNF was administrated into the cord 1-2 mm rostral and caudal to the epicenter. Animals receiving GDNF treatment showed significant improvement over phosphate-buffered saline (PBS)-treated controls on the Basso Beattie Bresnahan (BBB) locomotor rating scale (P < 0.01-0.001). GDNF treatment increased the remaining neuronal fibers with calcitonin gene-related peptide, neurofilament, and growth-associated protein 43 immunoreactivity in injured spinal tissues compared with PBS-treated controls. Moreover, treatment with GDNF caused approximately 50% cell survival in the contused spinal cord tissues. Examination of signal transduction triggered by GDNF indicated that GDNF injection transiently induced activation of the mitogen-activated protein (MAP) kinase pathway in the spinal cord. Additionally, an up-regulation of anti-apoptotic Bcl-2 levels in the contusive center of the damaged spinal cord was observed 24 hr post-GDNF injection. Together our results show that GDNF exerts behavioral and anatomic neuroprotection following SCI. Additionally, GDNF-activated MAP kinase and Bcl-2 signaling may contribute to neuronal survival after spinal cord contusion.     

Dissociation between short-term increased graft survival and long-term functional improvements in Parkinsonian rats overexpressing glial cell line-derived neurotrophic factor

The present study was designed to analyse whether continuous overexpression of glial cell line-derived neurotrophic factor (GDNF) in the striatum by a recombinant lentiviral vector can provide improved cell survival and additional long-term functional benefits after transplantation of fetal ventral mesencephalic cells in Parkinsonian rats. A four-site intrastriatal 6-hydroxydopamine lesion resulted in an 80-90% depletion of nigral dopamine cells and striatal fiber innervation, leading to stable motor impairments. Histological analysis performed at 4 weeks after grafting into the GDNF-overexpressing striatum revealed a twofold increase in the number of surviving tyrosine hydroxylase (TH)-positive cells, as compared with grafts placed in control (green fluorescent protein-overexpressing) animals. However, in animals that were allowed to survive for 6 months, the numbers of surviving TH-positive cells in the grafts were equal in both groups, suggesting that the cells initially protected at 4 weeks failed to survive despite the continued presence of GDNF. Although cell survival was similar in both grafted groups, the TH-positive fiber innervation density was lower in the GDNF-treated grafted animals (30% of normal) compared with animals with control grafts (55% of normal). The vesicular monoamine transporter-2-positive fiber density in the striatum, by contrast, was equal in both groups, suggesting that long-term GDNF overexpression induced a selective down-regulation of TH in the grafted dopamine neurons. Behavioral analysis in the long-term grafted animals showed that the control grafted animals improved their performance in spontaneous motor behaviors to approximately 50% of normal, whereas the GDNF treatment did not provide any additional recovery.     

Intraspinal transplantation of motoneuron-like cell combined with delivery of polymer-based glial cell line-derived neurotrophic factor for repair of spinal cord contusion injury

To evaluate the effects of glial cell line-derived neurotrophic factor transplantation combined with adipose-derived stem cells-transdifferentiated motoneuron delivery on spinal cord con-tusion injury, we developed rat models of spinal cord contusion injury, 7 days later, injected adipose-derived stem cells-transdifferentiated motoneurons into the epicenter, rostral and caudal regions of the impact site and simultaneously transplanted glial cell line-derived neuro-trophic factor-gelfoam complex into the myelin sheath. Motoneuron-like cell transplantation combined with glial cell line-derived neurotrophic factor delivery reduced cavity formations and increased cell density in the transplantation site. The combined therapy exhibited superior promoting effects on recovery of motor function to transplantation of glial cell line-derived neurotrophic factor, adipose-derived stem cells or motoneurons alone. These ifndings suggest that motoneuron-like cell transplantation combined with glial cell line-derived neurotrophic factor delivery holds a great promise for repair of spinal cord injury.     

单用或联用UDP-糖、GDNF和美金刚对脑白质损伤大鼠长期预后的改善作用

目的 探讨单用和联用尿苷二磷酸葡萄糖(UDP-糖)、胶质细胞源性神经营养因子(GDNF)和美金刚对脑室周围白质软化(PVL)新生大鼠体格发育、学习记忆和肢体运动功能的远期影响. 方法 5日龄SD新生大鼠按照随机数字表法分为对照组、PVL组、UDP-糖组和UDP-糖+GDNF+美金刚组(简称三联药组).对照组大鼠仅游离右侧颈总动脉,不接扎和缺氧;PVL组大鼠结扎颈总动脉和缺氧;UDP-糖组大鼠在缺血缺氧后给予腹腔注射UDP-糖;三联药组大鼠在缺血缺氧后给予颅内注射GDNF,同时腹腔注射UDP-糖和美金刚.每组大鼠造模前后称重并记录睁眼日龄,在PVL造模后21d进行水迷宫和斜板测试,记录各组大鼠逃逸潜伏期、游泳距离及在不同倾斜角度下的斜板得分. 结果 PVL组在各时段的体质量及睁眼日龄均显著低于其他3组,四象限的平均逃逸潜伏期值和游泳距离数值均显著长于其他3组,在45°和50°斜板上的得分均显著低于其他3组,差异有统计学意义(P＜0.05);两个用药组间以及两个用药组分别和对照组间大鼠体质量、睁眼日龄、逃逸潜伏期值、游泳距离以及斜板评分的差异均无统计学意义(P＞0.05). 结论 单用UDP-糖或联用UDP-糖、GDNF和美金刚能明显改善脑白质损伤大鼠的长期预后,三联药组的改善作用略微更明显.     

胶质细胞系源性神经营养因子对帕金森病大鼠黑质钙结合蛋白表达的影响

目的研究胶质细胞系源性神经营养因子(GDNF)对帕金森病(PD)大鼠黑质钙结合蛋白(CB)表达的影响,以及神经细胞黏附分子(NCAM)在其中的作用。方法制作PD模型大鼠36只,分为GD-NF组、NCAM阻断组和对照组,每组12只。采用免疫组化染色和免疫印迹法,检测各组大鼠黑质CB阳性细胞数和CB表达量。结果GDNF组黑质处CB阳性神经元数(46.50±6.28)及表达量(33770.60±6929.76)明显高于对照组[(27.00±8.60)、(18281.00±5266.78)](均P<0.05);与NCAM阻断组[(44.00±13.37)、(30857.00±7484.87)]相比差异无统计学意义(均P>0.05)。结论GDNF可上调PD大鼠黑质CB的表达,从而保护受损的多巴胺能神经元,NCAM对这一作用无明显影响。     

慢病毒介导的胶质细胞系源性神经营养因子在骨髓基质细胞中的表达及其对乳胞素干预PC12细胞的保护作用

目的 建立慢病毒介导的胶质细胞系源性神经营养因子(glial cellline-derived neurotrophic factor,GDNF)表达系统,体外感染骨髓基质细胞,检测过表达GDNF对蛋白酶抑制剂引起的PC12细胞损伤的神经保护作用.方法 经双酶切和T4连接酶构建pLenti6/V5-GDNF表达质粒,经293FT细胞包装产生高滴度病毒.用RT-PCR、ELISA和免疫细胞化学方法检测感染骨髓基质细胞(bone marrow stromal cells,BMSCs)后GDNF的表达,并检测过表达GDNF对蛋白酶抑制剂乳胞素(1actacystin)引起的PC12细胞损伤的保护作用.结果 成功构建pLenti6/V5-GDNF表达质粒,获得高滴度具有感染能力的病毒储存液(5.6×105 TU/mL).BMSCs体外被感染后能大量分泌GDNF(接近800 pg/mL),过表达GDNF能减轻乳胞素(10 μmol/L)引起的PC12细胞损伤.结论 慢病毒介导的GDNF转染骨髓基质细胞后能分泌具有生物学活性的GDNF,对蛋白酶体抑制剂引起的PC12细胞损伤有保护作用.     

多发性硬化、视神经脊髓炎患者血清及脑脊液中脑源性神经营养因子与胶质细胞源性神经营养因子水平

目的 探讨多发性硬化(MS)、视神经脊髓炎(NMO)患者血清及脑脊液中脑源性神经营养因子(BDNF)、胶质细胞源性神经营养因子(GDNF)水平及其神经保护作用.方法 对62例MS、NMO患者及21例对照者进行研究,患者组复发期进行扩展残疾状态量表(EDSS)评分、MRI检查及寡克隆带测定,液相芯片分析技术检测血清及脑脊液BDNF、GDNF浓度.结果 MS、NMO患者复发期血清及脑脊液BDNF(μg/L,MS患者:5.616±0.650、0.186±0.012;NMO患者6.584±0.929、0.176±0.006)、GDNF浓度(μg/L,MS患者:0.039、0.080;NMO患者0.029、0.050)与对照组(μg/L,血清:4.374±0.501、0.040;脑脊液:0.152±0.011、0.065)比较差异无统计学意义;脑脊液BDNF与GDNF浓度水平呈正相关(r=0.756,P=0.000),血清BDNF与GDNF浓度水平呈负相关(r=-0.329,P=0.018).血清及脑脊液BDNF、GDNF浓度与EDSS评分、血脑屏障指数、Delpech指数及Tourtellotte合成率无明显相关性.有或无脑萎缩的MS、NMO患者血清及腩脊液BDNF、GDNF浓度差异无统计学意义.结论 MS、NMO患者体内BDNF与GDNF水平相关,二者可能具有协同的神经保护作用.BDNF及GDNF与NMO、MS患者血脑屏障破坏及中枢神经系统内IgG合成无关,与神经功能残疾及脑萎缩的关系仍需研究.     

抗坏血酸联合胶质细胞源性神经营养因子诱导神经干细胞向多巴胺能神经元分化的研究

目的 研究抗坏血酸(AA)和胶质细胞源性神经营养因子(GDNF)对神经干细胞向多巴胺能神经元分化的影响.方法 从新生24h内的sD大鼠脑组织分离和培养神经干细胞,进行神经干细胞鉴定.第二代神经干细胞诱导培养基中分别给予AA或(和)GDNF,10d后终止诱导,进行DA能神经元特异性标记物酪氨酸羟化酶(TH)和多巴胺转运蛋白的免疫细胞化学检测和TH基因的RT-PCR检测.结果 各诱导组均检测到TH mRNA的表达;与对照组比较,AA及GDNF均能增加NSC向TH阳性细胞分化的比率(P<0.05);与单独运用100μmol/LAA或10ng/mlGDNF组比较,联合诱导组可明显提高NSCs向TH阳性细胞分化的比率(P<0.05).结论 AA和GDNF均能促进NSCs向DA能神经元分化,两者联合诱导后分化作用得到进一步加强.     

Secretion of nerve growth factor,brain-derived neurotrophic factor,and glial cell-line derived neurotrophic factor in co-culture of four cell types in cerebrospinal fluid-containing medium

The present study co-cultured human embryonic olfactory ensheathing cells, human Schwann cells, human amniotic epithelial cells and human vascular endothelial cells in complete culture medium- containing cerebrospinal fluid. Enzyme linked immunosorbent assay was used to detect nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor secretion in the supernatant of co-cultured cells. Results showed that the number of all cell types reached a peak at 7-10 days, and the expression of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor peaked at 9 days. Levels of secreted nerve growth factor were four-fold higher than brain-derived neurotrophic factor, which was three-fold higher than glial cell line-derived neurotrophic factor. Increasing concentrations of cerebrospinal fluid (10%, 20% and 30%) in the growth medium caused a decrease of neurotrophic factor secretion Results indicated co-culture of human embryonic olfactory ensheathing cells, human Schwann cells human amniotic epithelial cells and human vascular endothelial cells improved the expression of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor. The reduction of cerebrospinal fluid extravasation at the transplant site after spinal cord injury is beneficial for the survival and secretion of neurotrophic factors from transplanted cells.     

Glial cell line derived neurotrophic factor promotes the recovery of dopamine neurons damaged by 6-hydroxydopamine in vitro

Glial cell line derived neurotrophic factor (GDNF) has been shown to be a potent neurotrophic factor for dopamine neurons in culture and to prevent the loss of substantia nigra dopamine neurons following in vivo lesions with 6-hydroxydopamine (6-OHDA). In this study we used mesencephalic cultures containing both neurons and glia to examine whether GDNF protects dopamine neurons from 6-OHDA toxicity in vitro. Our data show that GDNF does not prevent the loss of dopamine neurons caused by treatment with 6-OHDA in vitro. However, continuous exposure to GDNF increases the high affinity dopamine uptake in cultures treated with 6-OHDA, suggesting that it enhances the growth of damaged dopamine neurons. We also show that in vitro treatment with 6-OHDA causes widespread cell death in mesencephalic cultures, which is not restricted to dopamine neurons. The lack of selectivity of 6-OHDA toxicity when applied in vitro may explain the inability of GDNF to prevent the loss of dopamine neurons in mesencephalic cultures. The stimulation of the growth of 6-OHDA damaged dopamine neurons by GDNF, observed in our study, suggests that it may prove beneficial in the treatment of injured dopamine neurons.