Herpes simplex virus-thymidine kinase-based suicide gene therapy as a "molecular switch off" for nerve growth factor production in vitro

Tissue-engineered constructs offer a new hope to patients suffering from functional impairment after nerve injury. An effort has been made to focus on delivery, regulation, and "molecular shutoff" of nerve growth factor (NGF) in tissue-engineered constructs. We have previously demonstrated that human embryonic kidney (HEK-293) cells can be genetically modified to secrete NGF at varying time points upon up regulation with Ponasterone A (PonA) both in vitro and in vivo. In the present study, HEK-293 cells that stably and inducibly produce NGF were further stably transfected with herpes simplex virus-thymidine kinase gene as a suicide gene (hNGF-EcR-293-TK) in order to shut off the NGF secretion and kill the cells upon treatment with ganciclovir (GCV). These cells following induction with PonA secreted NGF levels of 6659.2 +/- 489.4 pg/mL at day 10 postbooster dose at day 5, which was significantly higher than the control noninduced cells. The NGF secreted by these cells was bioactive as determined by a rat adrenal pheochromocytoma (PC-12) cell bioassay. Treatment of these cells with GCV significantly reduced the NGF levels to 645.3 +/- 16.2 pg/mL at day 10 and live cell numbers dropped to 7.95 x 10(3) +/- 278 compared to 2.73 x 10(5) +/- 6.1 x 10(4). GCV-treated cell media when transferred to the PC-12 cell bioassay demonstrated less than 10% cells differentiating into neurite-like extensions. We conclude that hNGF-EcR-293-TK cells can inducibly secrete bioactive NGF when treated with the inducing agent and can also be killed upon treatment with GCV. This double-gene transfection for gene expression and molecular shutoff mechanism will be a useful tool in tissue-engineered nerve constructs.     

Muristerone A-induced nerve growth factor release from genetically engineered human dermal fibroblasts for peripheral nerve tissue engineering.

In this study, human dermal fibroblasts (hDFBs) were genetically modified to release human nerve growth factor (NGF) using an ecdysone-inducible system. NGF cDNA was inserted into the pIND vector and then hDFBs were cotransfected with pIND-NGF and pVgRXR. Muristerone A, an analog of ecdysone, was used as the inducing agent. NGF release from transfected hDFBs was assessed in vitro and in vivo. Transfected hDFBs in the presence of Muristerone A possessed a maximal in vitro release of 8.5 +/- 0.4 pg of NGF/mL per 10(3) cells, demonstrating significantly higher NGF levels compared to control hDFBs. The in vitro release rate curve for transfected hDFBs in the presence of Muristerone A exhibited a maximum of 5.1 +/- 0.2 ng NGF/10(6) cells/day. A PC-12 bioassay demonstrated that the in vitro NGF released is bioactive. When transfected hDFBs in the presence of Muristerone A were placed in vivo in nude rats, NGF levels reach 2074 +/- 257 pg/mL and 1620 +/- 132 pg/mL at 24 and 48 h, respectively. These levels were significantly higher than negative control and wound fluid levels. Results support further in vivo investigation of this molecular "on" switch for peripheral nerve regeneration.     

Nerve growth factor expression by PLG-mediated lipofection

Biomaterials capable of efficient gene delivery provide a fundamental tool for basic and applied research models, such as promoting neural regeneration. We developed a system for the encapsulation and sustained release of plasmid DNA complexed with a cationic lipid and investigated their efficacy using in vitro models of neurite outgrowth. Sustained lipoplex release was obtained for up to 50 days, with rates controlled by the fabrication conditions. Released lipoplexes retained their activity, transfecting 48.2+/-8.3% of NIH3T3 cells with luciferase activity of 3.97x10(7)RLU/mg. Expression of nerve growth factor (NGF) was employed in two models of neurite outgrowth: PC12 and primary dorsal root ganglia (DRG) co-culture. Polymer-mediated lipofection of PC12 produced bioactive NGF, eliciting robust neurite outgrowth. An EGFP/NGF dual-expression vector identified transfected cells (GFP-positive) while neurite outgrowth verified NGF secretion. A co-culture model examined the ability of NGF secretion by an accessory cell population to stimulate DRG neurite outgrowth. Polymer-mediated transfection of HEK293T with an NGF-encoding plasmid induced outgrowth by DRG neurons. This system could be fabricated as implants or nerve guidance conduits to support cellular and tissue regeneration. Combining this physical support with the ability to locally express neurotrophic factors will potentiate regeneration in nerve injury and disease models.     

野生型和突变型GDF5蛋白表达及亚细胞定位的研究

目的研究人生长分化因子5基因(GDF5)c.1118T>G(p.L373R)突变对GDF5蛋白在HEK-293细胞系表达及其亚细胞定位的影响。方法构建pDsRed1-N1-GDF5-WT和pDsRed1-N1-GDF5-L373R载体,分别转染HEK-293细胞,细胞培养72h后通过荧光显微镜观察比较野生型和突变型GDF5蛋白荧光分布情况。结果 GDF5蛋白在HEK-293细胞中成功表达,在荧光显微镜下观察到转染野生型和突变型GDF5的细胞胞浆均匀发出红色荧光,而空载体组的红色荧光则弥散于全细胞,荧光强度均匀一致。结论野生型和突变型GDF5蛋白均定位于HEK-293细胞质。     

Increased metastatic potential in human prostate carcinoma cells by overexpression of arachidonate 12-lipoxygenase

Arachidonate 12-lipoxygenase (LOX) converts arachidonic acid to 12(S)-hydroxyeicosatetraenoic acid (HETE), a bioactive lipid implicated in tumor angiogenesis, growth, and metastasis. Alteration in 12-LOX expression or activity has been reported in various carcinomas including prostate carcinoma. However, little is known about the impact of the altered expression or activity of 12-LOX on tumor metastasis. In the present study, we examined whether or not an increase in 12-LOX expression in human prostate carcinoma cells can modulate their metastatic potential. We report that increased expression of 12-LOX in PC-3 cells caused a significant change in cell adhesiveness, spreading, motility, and invasiveness. Specifically 12-LOX transfected PC-3 cells were more adhesive toward vitronectin, type I and IV collagen, but not to fibronectin or laminin, than cells transfected with control vector. Increased spreading on vitronectin, fibronectin, collagen type I and IV also was observed in 12-LOX transfected PC-3 cells when compared to control PC-3 cells. The increased spreading of 12-LOX transfected PC-3 cells was blocked by treatment with 12-LOX inhibitors, baicalein and CDC. 12-LOX transfected PC-3 cells were more invasive through Matrigel than cells transfected with control vector. In vivo, tumor cell invasion to surrounding muscle or fat tissues was more frequent in nude mice bearing s.c. tumors from 12-LOX transfected PC-3 cells than in those from control vector transfected cells. When injected via the tail vein into SCID mice with implanted human bone fragments, there was an increase in tumor metastasis to human bone by 12-LOX transfected PC-3 cells in comparison to control vector transfected cells. Taken together, our data suggest that an increase in 12-LOX expression enhances the metastatic potential of human prostate cancer cells. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chemically-bound nerve growth factor for neural tissue engineering applications

In order to promote regeneration after spinal cord injury, growth factors have been applied in vivo to rescue ailing neurons and provide a path finding signal for regenerating neurites. We previously demonstrated that soluble growth factor concentration gradients can guide axons over long distances, but this model is inherently limited to in vitro applications. To translate the use of growth factor gradients to an implantible device for in vivo studies, we developed a photochemical method to bind nerve growth factor (NGF) to microporous poly(2-hydroxyethylmethacrylate) (PHEMA) gels and tested bioactivity in vitro. A cell adhesive photoreactive poly(allylamine) (PAA) was synthesized and characterized. This photoreactive PAA was applied to the surface of the PHEMA gels to provide both a cell adhesive layer and a photoreactive handle for further NGF immobilization. Using a direct ELISA technique, the amount of NGF immobilized on the surface of PHEMA after UV exposure was determined to be 5.65 +/- 0.82 ng/cm2 or 3.4% of the originally applied NGF. A cell-based assay was performed to determine the bioactivity of the immobilized NGF. Using pheochromocytoma (PC-12) cells, 30 +/- 7% of the cell population responded to bound NGF, a response statistically similar to that of cells cultured on collagen in the presence of 40 ng/ml soluble NGF of 39 +/- 12%. These results demonstrate that PHEMA with photochemically bound NGF is bioactive. This photochemical technique may be useful to spatially control the amount of NGF bound to PHEMA using light and thus build a stable concentration gradient.     

神经生长因子在食管鳞癌细胞中的表达及分泌

目的 探讨神经生长因子（NGF)与食管鳞癌细胞分化的相关性。方法 采用有限稀释法分选出圆形和梭形单细胞克隆,采用无血清悬浮培养获得细胞球细胞, 贴壁的Eca109细胞分别在含血清和不含血清培养基中培养48h;分别采用反转录-聚合酶链式反应（RT-PCR)技术和免疫印迹法,检测NGF在食管鳞癌细胞中mRNA水平和蛋白水平的表达;免疫荧光技术检测NGF在食管鳞癌细胞中的表达定位;免疫组织化学法检测食管鳞癌组织中NGF的表达定位;用酶联免疫吸附法（ELISA）检测NGF在Eca109细胞培养基中的分泌情况。结果 在Eca109细胞中能检测到NGF的mRNA水平和蛋白水平的表达,其中NGF在细胞球细胞中的mRNA水平和蛋白水平的表达量最高。食管癌组织中检测到NGF表达于细胞质。Eca109细胞在无血清培养条件下能够分泌NGF,且明显高于含血清培养基中的含量。结论 食管癌细胞系Eca109表达并分泌NGF,并且食管癌组织中表达NGF,NGF可能在维持食管鳞状细胞癌的干细胞特性发挥了重要作用。     

Release characteristics and bioactivity of gelatin-tricalcium phosphate membranes covalently immobilized with nerve growth factors

The gelatin-tricalcium phosphate membranes were cross-linking with low concentration glutaraldehyde solution (GTG). This material has good mechanical property, biocompatibility, and is feasible for surgical manipulation. For axonal regeneration, nerve growth factors (NGF) were immobilized onto the composite (GTG) with carbodiimide. The purpose of this study was to evaluate the release characteristics and bioactivity of NGF after covalent immobilization onto the GTG membranes (GEN). NGF immobilized onto and released from the composite was quantified using ELISA method. PC 12 cells were cultured on the GTG and GEN composites. Cell survival, cytotoxicity, and cellular activity were evaluated by total protein content, LDH activity, and MTT assay respectively. Neurite outgrowth assay was used to evaluate the biological activity of NGF released from GEN composite. From ELISA measurement, the releasing curve for NGF showing two distinctive parts with different slopes indicated that NGF were released from the composite in diffusion-controlled mechanism and degradation-controlled mechanism respectively. While culturing with PC 12 cells, LDH leakage results implied that whether GTG composite cross-linked with NGF or not showed little cytotoxicity. The total protein content and cellular activity of PC 12 cells were lower on GTG and GEN membranes than control group. However, 56%+/-3.98 of PC 12 cells showed significant neurite outgrowth on GEN membranes which was statistically higher than GTG without NGF immobilization. In addition, sustained release of bioactive NGF for two months had been demonstrated by neurite outgrowth assay. From these experiments, it can be concluded that the technique used in the present study is capable of immobilizing NGF onto GTG membranes covalently and remaining the bioactivity of NGF. Therefore, GEN composite can be materials for sustained release of bioactive NGF and a candidate for future therapeutic application in nerve repair.     

Biologically active anti-nerve growth factor antibodies in commercial intravenous gammaglobulin

Neurotrophins are regulators of development, survival and function of neuronal and non-neuronal cells, one of the most important of which is nerve growth factor (NGF). Previous studies have demonstrated the presence of antibodies to NGF in normal human serum. It would therefore be predicted that antibodies to NGF would also be present in commercial intravenous gammaglobulin (IVIg). It has been shown in the present investigation that ELISA can detect anti-NGF antibodies in IVIg. The functional activity of these antibodies has been demonstrated after affinity purification, by their inhibitory effects upon (a) the proliferation of the NGF-responsive rat pheochromocytoma cell line PC-12, (b) the differentiation of PC-12 cells as determined by neurite outgrowth. All batches of commercially tested IVIg contained anti-NGF antibodies. Since NGF has an important role in the inflammatory immune response and in cell growth and differentiation, these findings may (a) facilitate our understanding of the mechanisms of action of IVIg, (b) indicate new disease states in which IVIg or its derivatives may exert beneficial effects.     

PC-1基因表达诱导NIH3T3细胞恶性转化

目的 通过建立稳定表达外源PC-1基因的小鼠成纤维细胞株,初步探讨PC-1基因表达对肿瘤发生、发展的影响。方法 通过脂质体介导的方法,将真核表达载体pcDNA3、1(-)／myc-his-pc-1稳定转染NIH3T3细胞,之后利用PCR、逆转录PCR(RT-PCR)技术,确定外源PC-1基因在靶细胞染色体上的整合及在转录水平的表达。通过细胞形态学分析、MTT实验、细胞周期分析、软琼脂集落形成和裸鼠成瘤实验,观察PC-1基因表达对NIH3T3生物学特性的影响。结果建立了稳定转染PC-1基因的NIH3T3细胞株。PC-1基因表达的小鼠成纤维细胞NIH3T3生长速度加快,在软琼脂上生长并形成集落,接种裸鼠后可成瘤(6／6)。结论 PC-1基因在NIH3T3细胞中稳定表达具有诱导正常NIH3T3细胞发生恶性转化的重要生物功能。     

Controlled release of nerve growth factor from fibrin gel

Nerve growth factor (NGF) is known to promote the axonal regeneration in injured nerve system. Delivery of NGF for a long period in a controlled manner may enhance the regeneration efficacy. In this study, we investigated whether NGF can be released from fibrin gel for a long period in a controlled manner. We also investigated whether sustained delivery of NGF using fibrin gel can enhance the efficacy of NGF in vitro. The addition of heparin to fibrin gel decreased the rate of NGF release from the fibrin gel. As the concentrations of thrombin and fibrinogen in fibrin gel increased, the NGF release rate decreased significantly, and the initial release burst decreased. NGF was released for up to 14 days in vitro. The bioactivity of NGF released from fibrin gel was assessed by morphological changes of pheochromocytoma (PC12) cells cultured in the presence of NGF-containing fibrin gel. NGF released from fibrin gel exhibited significantly higher degrees of PC12 cell viability and differentiation than NGF added in a free form daily into the culture medium. This study demonstrates that fibrin gel can release NGF in a sustained, controlled manner and in a bioactive form.     

Contrasting neuroprotective and neurotoxic actions of respective metabolites of anti-Parkinson drugs rasagiline and selegiline

The anti-Parkinson selective irreversible monoamine oxidase B inhibitor drugs, rasagiline and selegiline, have been shown to possess neuroprotective activities in cell culture and in vivo models. While rasagiline is metabolized to its major metabolite aminoindan, selegiline gives rise to L-methamphetamine. Cultured PC-12 cells in absence of serum and nerve growth factor (NGF) die by an apoptotic process. Pretreatment of PC12 cells in absence of serum and NGF for 24 h with either rasagiline (1 microM) or selegiline (1 microM) is neuroprotective and anti-apoptotic as determined by ELISA and MTT tests. However, while aminoindan (1 microM), the major metabolite of rasagiline does not interfere with the neuroprotective activities of rasagiline or selegiline in PC-12 cells deprived of serum and NGF, the major metabolite of selegiline, L-methamphetamine (1 microM), inhibits them. In contrast to L-methamphetamine, aminoindan is itself is neuroprotective in this system. Recently it has been demonstrated that rasagiline directly activates PKC-MAP kinase pathway by a concentration and time dependent phosphorylation of p42 and p44 MAP kinase. In the present studies the neuroprotective activity of rasagiline is blocked by ERK inhibitor, PD98059 (20 microM), suggesting the involvement of PKC-MAP kinase pathway in the neuroprotection. These findings may have implication for the possible disease modifying action of rasagiline in treatment of Parkinson's disease.     

Gene-modified mesenchymal stem cells express functionally active nerve growth factor on an engineered poly lactic glycolic acid (PLGA) substrate

Delivery of cellular and/or trophic factors to the site of injury may promote neural repair or regeneration and return of function after peripheral nerve or spinal cord injury. Engineered scaffolds provide a platform to deliver therapeutic cells and neurotrophic molecules. We have genetically engineered mesenchymal stem cells (MSCs) from the green rat (CZ-004 [SD TgN(act-EGFP)OsbCZ-004]) to express nerve growth factor (NGF) using an adenoviral vector. Cells maintained their stem cell phenotype as judged by expression of CD71 and CD172 markers, and absence of the hematopoietic marker CD45. Cells continued to express green fluorescent protein (GFP) on a long-term basis. Morphology, viability, and growth kinetics were maintained when cells were grown on a poly-lactic-co-glycolic acid (PLGA) polymer scaffold. Under appropriate growth conditions, they differentiated into chondrogenic, osteogenic, and adipogenic phenotypes, demonstrating that they retained their characteristics as MSCs. NGF was secreted from transduced MSCs at physiologically relevant levels ( approximately 25 ng/mL) measured by enzyme-linked immunoabsorbent assay (ELISA). Secreted NGF was functionally active in a neurite growth assay with PC12 cells. We conclude that MSCs are a good candidate for delivery of therapeutic factors into the injured nervous system. They are autologous, may be genetically modified to express neurotrophins, and are compatible with polymer surfaces that may be used as a potential delivery system.     

Transplants of NGF-secreting fibroblasts restore stimulus-evoked activity in barrel cortex of basal-forebrain-lesioned rats

Cholinergic nuclei in the basal forebrain supply the cerebral cortex with acetylcholine (ACh). Depletion of cholinergic fibers following basal forebrain lesion results in reduced stimulus-evoked functional activity in rat barrel cortex in response to whisker stimulation. We showed previously that exogenous delivery of nerve growth factor (NGF) to the lateral ventricle restores reduced functional activity toward normal despite persistent reductions in cortical cholinergic activity. Gene transfer of therapeutic peptides using genetically engineered cells allows for localized and biological delivery of compounds to the CNS, circumventing systemic administration or repetitive invasive surgery. In this study, we grafted genetically engineered fibroblasts that secrete NGF (NGF+) into three CNS loci of rats with unilateral basal forebrain lesions, along with control fibroblasts (NGF-) that did not secrete NGF. Only NGF+ fibroblasts grafted into ACh-depleted somatosensory cortex resulted in improvement of functional activity following cholinergic depletion. NGF+ fibroblast transplants into the lateral ventricle or basal forebrain did not improve functional activity nor did NGF- fibroblasts in any site. Similar to our previous experiments using intraventricular NGF injections, despite improvements in functional activity, the affected barrel cortex remained depleted of acetylcholinesterase-stained fibers following insertion of NGF+ fibroblasts. These data support the idea that NGF can act directly on the cerebral cortex following reductions in cholinergic innervation. The mechanism of NGF action is elusive, however, since the presence of its high-affinity receptor, trkA, in the cerebral cortex is controversial.     

Generation of recombinant Norovirus-like particles (VLP) in the human endothelial kidney cell line 293T

Summary. Noroviruses (NVs) are the major cause of non-bacterial outbreaks of gastroenteritis. Here we report a new alternative system to generate recombinant NV virus-like particles (rNV-VLP) in a human endothelial kidney cell line (HEK). Transfecting HEK-293T cells with an expression vector coding for the ORF-2 gene lead to the expression of the viral structural protein VP1 which spontaneously assembled into virus-like particles (VLP), as shown by electron microscopy. The transfected cells did not show a cytopathic effect and released rNV-VLP into the culture medium. The HEK-293T cell derived particles were morphologically indistinguishable to the rNV-VLP produced from baculovirus and the Venezuelan equine encephalitis virus (VEE)-replicon. The produced particles were stable for at least 2.5 months at 4 °C.     

人重组腺病毒rAd-IL-23R的构建与功能鉴定

目的构建表达白介素23受体的人重组腺病毒(rAd-IL-23R),并探究该病毒对人子宫颈癌(HeLa)细胞系增殖的影响。方法采用AdEasyTM系统,将带有IL-23R的穿梭载体与腺病毒骨架载体进行同源重组,构建pAd-IL-23R,酶切消化鉴定,线性化的病毒质粒在HEK-293A细胞中进行病毒包装和扩增,TCID50法测定病毒滴度。CCK-8法检测rAd-IL-23R对HeLa细胞增殖的影响,流式细胞计量术分析和Western blot检测rAd-IL-23R对HeLa细胞凋亡的影响。结果pAd-IL-23R经PacⅠ酶切消化为约30 kb和3 kb的核酸片段,可诱导HEK-293A细胞产生细胞病变,并成功表达IL-23R蛋白;用不同滴度的rAd-IL-23R(0、1和2 MOI)感染HeLa细胞后,rAd-IL-23R对细胞增殖的抑制具有明显的剂量效应(P<0.05),随着MOI增加,细胞凋亡率显著增加(P<0.05),同时cleaved-caspase 3的蛋白表达水平增高。结论成功构建rAd-IL-23R,该重组腺病毒可抑制HeLa细胞增殖并促进凋亡发生。     

高亲和性神经生长因子受体对神经生长因子诱导神经母细胞瘤 …

观察人神经母细胞瘤细胞系ＩＭＲ－３２细胞在恢复高亲和性神经生长因子受体基因ｔｒｋＡ表达后对神经生长因子（ＮＧＦ）诱导分化的反应。方法应用基因重组技术构建含外源ｔｒｋＡ ｃＤＮＡ的逆转录病毒载体,经ＰＡ３１７细胞包装后感染靶细胞系ＩＭＲ－３２细胞,经Ｓｏｕｔｈｅｒｎ ｂｌｏｔ杂交,逆转录－聚合酶链反应（ＲＴ－ＰＣＲ）证实转化细胞系中含有外源基因的整合及稳定表达后,进行神经生长因子诱导分化实验。结果转     

Overexpression of BRCA1 attenuates the sensitivity of PC9 cells to gefitinib

Gefitinib is an orally active antitumor agent which inhibits uncontrolled cell proliferation by interrupting epidermal growth factor receptor (EGFR) signaling pathways. Various in vitro and in vivo studies have revealed that the upregulated expression of breast cancer susceptibility gene 1 (BRCA1) is associated with chemoresistance and reduced survival following chemotherapies. In this study, a gefitinib-highly-sensitive cell line, PC-9, was used to investigate the effect of BRCA1 expression on the sensitivity of PC-9 cells to gefitinib. PC-9 cells were stably transfected with BRCA-1 (HA-tagged). Transfected and untransfected PC-9 cells were treated with gefitinib, phosphorylated γH2AX was examined by western blot to determine the DNA damages. Following the treatment of gefitinib, the inhibition of proliferation of the PC-9 cells, PC-9-pcDNA3.1 cells, and BRCA1-transfected PC-9 cells were determined. Also, a comet assay was performed to determine the DNA damage caused by gefitinib. The treatment of geftinib for 6 hr, 12 h, and 24 hr significantly increased the cellular expression of phosphorylated γH2AX. With the treatment of gefitinib, the inhibition of proliferation of BRCA-1 overexpressed PC-9 cells was significantly lower than that of the non-transfected PC-9 cells, indicating the overexpression of BRCA1 plays a role in attenuating the sensitivity of PC-9 cells to gefitinib. The comet assay revealed that BRCA1 transfected cells showed a shorter comet tail, indicating the overexpression of BRCA1 attenuated the DNA damages caused by gefitinib. The overexpression of BRCA1 reduced the DNA damages, and enhanced DNA repair mechanisms. Also, gefitinib-mediated inhibition of cell proliferation is attenuated by the expression of BRCA1.     

神经生长因子转染骨髓间充质干细胞诱导分化成神经样细胞

目的探讨神经生长因子(NGF)转染大鼠骨髓间充质干细胞(MSCs)后的表达及其对MSCs分化成神经样细胞的影响。方法在体外低密度扩增大鼠骨髓MSCs。应用基因重组技术,构建pEGFP-NGF真核表达质粒,并将其转染至MSCs中。免疫荧光标记法检测中间神经丝蛋白(NF-M)和胶质纤维酸性蛋白(GFAP)的表达。在荧光显微镜下观察MSCs阳性荧光的表达率、细胞的形态变化和类型。结果MSCs阳性荧光的表达率约为30%。转染后,MSCs呈现多突起,且几个突起之间互相连接成网状,似神经元样的形态。免疫荧光标记法鉴定其中一部分细胞表达NF-M,另一部分细胞表达GFAP。结论转染的MSCs可表达NGF并在含有NGF的微环境中分化成神经样细胞。