Sustained expression of functional nerve growth factor in primary septo-hippocampal cell cultures by liposome-mediated gene transfer

Liposome-Mediated Gene Transfer into Established CNS Cell Lines, Primary Glial Cells, and in Vivo

Sufficient gene transfer into CNS-derived cells is the most crucial step to develop strategies for gene therapy. In this study liposome-mediated gene transfer using a β-galactosidase (β-GAL) reporter gene was performed in vitro (C6 glioma cells, NT2 neuronal precursor cells, 3T3 fibroblasts, primary glial cells) and in vivo. Using Trypan blue exclusion staining, optimal lipid concentration was observed in the range of 10-12 μg/mL. Under optimal conditions (80,000 cells/16 mm well, incubation overnight, lipid/DNA ratio = 1:18) a high transfection rate was achieved (<9% for C6 cells; <1% for NT2 cells). In primary cultures of glial cells a fair amount of positive stained cells (glial cell) was found, but the transfection efficiency was lower (<0.1%). A “boost-lipofection” markedly increased (twice) lipofection efficiency in C6 cells. Expression of β-GAL reached a maximum after 3-5 days. When the liposome–DNA complexes were injected/infused directly into the brains of adult rats, several weakly stained cells could be observed in the brain region adjacent to the injection site. It is concluded that liposome-mediated gene transfer is an efficient method for gene transfer into CNS cells in vitro, but the transfection efficiency into the rat brain in vivo is far too low and therefore not applicable.

Liposome-mediated transfer of vascular endothelial growth factor cDNA augments survival of random-pattern skin flaps in the rat

Tissue engineering is an application for gene therapy that is in its infancy. We show that simple liposomal-mediated gene transfer could result in a potentially useful biological effect in the field of wound healing. cDNA encoding the 165 amino acid form of vascular endothelial growth factor complexed to commercially available liposomes was injected into rat skin 1 week before raising a random pattern 3 x 10 cm flap. The flap survival was enhanced by 14 percent, and was accomplished without accessing the arterial inflow of the territory. These results were statistically significant (p<0.002) and reproducible. No adverse effects were seen. Histological analysis of the angiogenesis localized much of the new vessel formation to the area around the hair follicles. Polymerase chain reaction amplification of extracted flap tissue confirmed the presence of the transgene.

A horseradish peroxidase-light and electron microscopic study of immunoliposomes utilized for intracellular delivery to the rat striatum

Liposomes can deliver plasmid DNA, viruses, antisense oligonucleotides, and pharmacological agents to the central nervous system. Conjugation of antibodies to liposomes increases delivery specificity. Immunoliposomes created with Thy 1.1 antibody have previously been shown to be effective for neuronal delivery. The intracellular delivery of these immunoliposomes is evaluated by light and electron microscopy. Thy 1.1 conjugated liposomes were loaded with horseradish peroxidase and stereotactically injected into rat striatum. On light microscopy, immunoliposomes were concentrated within 0.2 mm of the injection site 8 h following delivery but, 24 h post-operatively, had diffused more than 0.5 mm from the injection site. With transmission electron microscopy, immunoliposomes were observed entering numerous neurons and some astrocytes in a process distinct from the clathrin-coated pit mechanism. These findings suggest that Thy 1.1 immunoliposomes are effective for intracellular delivery in vivo and their endocytosis occurs independently of a coated pit process. The research has helped to elucidate alternative mechanisms for immunoliposomal delivery. A more fundamental understanding of these attributes is needed to achieve the therapeutic potential of immunoliposomes.

Therapeutic success and efficacy of nonviral liposomal cDNA gene transfer to the skin in vivo is dose dependent

It is well documented that responses to growth factor treatment typically display bell-shaped dose responses that can significantly affect efficacy. Here we tested the hypothesis that nonviral liposomal gene delivery also displays this characteristic. We chose two different growth factors, keratinocyte growth factor (KGF) and insulin-like growth factor-I (IGF-I) CMV-driven transfecting constructs at three different concentrations and assessed efficacy on several physiological parameters that are descriptive of wound healing progress in a burn-wound healing model. Rats were given a 60% TBSA scald burn and randomly divided into one of seven groups to receive weekly subcutaneous injections of liposomes containing the cDNA for KGF (0.2 microg, 2.2 microg, or 22.2 microg), or liposomes containing the cDNA for IGF-I (0.2 microg, 2.2 microg, or 22.2 microg) at various concentrations, but constant liposome:DNA ratios and a LacZ gene (0.2 microg) CMV-driven construct for beta-galactosidase as vehicle and marker gene. Transfection was confirmed by histology for beta-galactosidase. Physiological efficacy was evaluated by measuring the wound healing parameters that define dermal and epidermal regeneration. Transfection products were found in the cytoplasm of rapidly dividing cells of the granulation tissue. Different doses of the nonviral cDNA gene transfer coding for KGF or IGF-I resulted in different outcomes for dermal and epidermal regeneration. There was a dose-dependent response to both growth factor gene transfers that was not dissimilar from that typically displayed by treatment with growth factor proteins. Both concentrations below and above the optimal concentration of DNA:liposomal preparations did not yield the results observed at the optimal concentration.

Efficient gene transfer and expression of biologically active glial cell line-derived neurotrophic factor in rat motoneurons transduced wit lentiviral vectors

Several studies have shown the ability of human immunodeficiency virus type 1 (HIV1)-based lentiviral vectors to infect nondividing brain and retinal neurons with high efficiency and long-term expression of the transduced gene. We show that purified embryonic motoneurons can be efficiently (>95%) transduced in culture using an HIV1-based lentiviral vector encoding LacZ. Expression of beta-galactosidase was observed for at least 9 days in these conditions. Furthermore, motoneurons transduced with a lentiviral vector expressing glial cell line-derived neurotrophic factor survived in the absence of additional trophic support, showing that the overexpressed protein was biologically active. Our results demonstrate the potential of lentiviral vectors in studying the biological effects of proteins expressed in motoneurons and in the development of future gene therapy for motoneuron diseases.

Liposome-mediated NGF gene transfection following neuronal injury: potential therapeutic applications

We have systematically investigated the therapeutic potential of cationic liposome-mediated neurotrophic gene transfer for treatment of CNS injury. Following determination of optimal transfection conditions, we examined the effects of dimethylaminoethane-carbamoyl-cholesterol (DC-Chol) liposome-mediated NGF cDNA transfection in injured and uninjured primary septo-hippocampal cell cultures and rat brains. In in vitro studies, we detected an increase of NGF mRNA in cultures 1 day after transfection. Subsequent ELISA and PC12 cell biological assays confirmed that cultured cells secreted soluble active NGF into the media from day 2 after gene transfection. Further experiments showed that such NGF gene transfection reduced the loss of chol- ine acetyltransferase (ChAT) activity in cultures following calcium-dependent depolarization injury. In in vivo studies, following intraventricular injections of NGF cDNA complexed with DC-Chol liposomes, ELISA detected nine- to 12-fold increases of NGF in rat CSF. Further studies showed that liposome/NGF cDNA complexes could attenuate the loss of cholinergic neuronal immunostaining in the rat septum after traumatic brain injury (TBI). Since deficits in cholinergic neurotransmission are a major consequence of TBI, our studies demonstrate for the first time that DC-Chol liposome-mediated NGF gene transfection may have therapeutic potential for treatment of brain injury.

Lipofectin-facilitated transfer of cholecystokinin gene corrects behavioral abnormalities of rats with audiogenic seizures

To evaluate the potential for lipofectin-mediated central nervous system gene transfer, the plasmid coding for cholecystokinin was administered intracerebroventricularly to rats, which have congenital audiogenic seizures and high responses to peripheral electric stimulation-induced analgesia. Previous studies had shown that low brain cholecystokinin levels may be the neurochemical variable of rat's audiogenic seizure and high responses to the analgesia because cholecystokinin is an anticonvulsant and anti-opioid neuropeptide. Gene transfer of cholecystokinin corrected the increased susceptibility to audiogenic seizures and the high responses to analgesia for about one week. Similar administration of plasmid expressing beta-galactosidase indicated that the vector mainly transfected ependymal cells lining the ventricle and pia mater cells. The increased cholecystokinin messenger RNA and immunoreactivity in the hippocampus following stereotactic intrahippocampal administration of cholecystokinin plasmid was also demonstrated with in situ hybridization and immunohistochemistry techniques. These results suggest that lipofectin-mediated gene transfer will be useful for studies of brain function, the modification of behavior and gene therapy for central nervous system disorders.

Cationic lipid-mediated NGF gene transfection increases neurofilament phosphorylation

We examined the effect of cationic lipid-mediated gene transfection of nerve growth factor (NGF) in primary septo-hippocampal cell cultures. Rat NGF cDNA was subcloned into a pUC19-based plasmid containing a CMV promoter. Two days after NGF gene transfection in primary cell cultures, ELISA confirmed increases in NGF protein secretion from transfected cells. To study the biological effect of cationic lipid-mediated NGF gene transfection, we analyzed the amount of neurofilament protein from NGF-transfected cell cultures. Western blot and immunohistochemical analyses detected significant increases in the phosphorylated form of neurofilament proteins in the cultures after cationic lipid-mediated NGF cDNA transfection. Cationic lipid-mediated NGF cDNA transfection did rot cause significant changes in the total amount of neurofilament protein. Our studies suggest that cationic lipid-mediated NGF gene transfection can increase neurofilament phosphorylation but not total neurofilament protein.

The principles of gene therapy for the nervous system

Research pertaining to gene transfer into cells of the nervous system is one of the fastest growing fields in neuroscience. An important application of gene transfer is gene therapy, which is based on introducing therapeutic genes into cells of the nervous system by ex vivo or in vivo techniques. With the eventual development of efficient and safe vectors, therapeutic genes, under the control of a suitable promoter, can be targeted to the appropriate neurons or glial cells. Gene therapy is not only applicable to the treatment of genetic diseases of the nervous system and the control of malignant neoplasia, but it also has therapeutic potential for acquired degenerative encephalopathies (Alzheimer's disease, Parkinson's disease), as well as for promoting neuronal survival and regeneration in various pathological states.

Rescue of injury-induced neurofilament loss by BDNF gene transfection in primary septo-hippocampal cell cultures

We employed primary septo-hippocampal cell cultures to determine the ability of liposome-mediated BDNF gene transfection to facilitate recovery of neurofilament loss caused by depolarization injury. After BDNF gene transfection in uninjured cultures, RT-PCR and immunohistochemical staining confirmed increases in BDNF mRNA and protein in transfected cells. Three days after depolarization injury, Western blot and immunohistochemical analyses detected significant loss of neurofilament proteins in non-transfected cultures, while BDNF transfection produced marked increases in neurofilament proteins following either pre-injury transfection or transfection 24 h following injury. Immunohistochemical studies also detected enhanced immunolabeling of BDNF and total neurofilament protein (phosphorylated and non-phosphorylated) in injured neurons following BDNF transfection or administration of exogenous BDNF protein, compared to untransfected, injured controls.

Optimizing liposome-mediated gene transfer in primary rat septo-hippocampal cell cultures

Although liposomes have been widely employed to transfect DNA into a variety of cell types, no previous studies have systematically examined conditions producing optimal liposomal-mediated transfection of DNA into central nervous system (CNS) cells. Thus, we used the beta-galactosidase (beta-gal) reporter gene to examine factors influencing the efficiency of liposome-mediated gene transfection in CNS cell cultures. Our results indicate that without increasing the amounts of DNA, increased liposome concentrations within certain limits enhanced transfection efficiency. However, higher liposome levels could produce cell lysis. Without increasing liposome concentrations, increased amounts of DNA did not improve transfection efficiency. Employing the optimal concentration (1 microgram DNA/3 microliters liposomes/well), beta-gal gene expression was sustained for at least two weeks after transfection in primary septo-hippocampal cultures.