GFAP-Driven GFP Expression in Activated Mouse Muller Glial Cells Aligning Retinal Blood Vessels Following Intravitreal Injection of AAV2/6 Vectors

Background: Muller cell gliosis occurs in various retinal pathologies regardless of the underlying cellular defect. Because activated Muller glial cells span the entire retina and align areas of injury, they are ideal targets for therapeutic strategies, including gene therapy.Methodology/Principal Findings: We used adeno-associated viral AAV2/6 vectors to transduce mouse retinas. The transduction pattern of AAV2/6 was investigated by studying expression of the green fluorescent protein (GFP) transgene using scanning-laser ophthalmoscopy and immuno-histochemistry. AAV2/6 vectors transduced mouse Muller glial cells aligning the retinal blood vessels. However, the transduction capacity was hindered by the inner limiting membrane (ILM) and besides Muller glial cells, several other inner retinal cell types were transduced. To obtain Muller glial cell-specific transgene expression, the cytomegalovirus (CMV) promoter was replaced by the glial fibrillary acidic protein (GFAP) promoter. Specificity and activation of the GFAP promoter was tested in a mouse model for retinal gliosis. Mice deficient for Crumbs homologue 1 (CRB1) develop gliosis after light exposure. Light exposure of Crb1(-/-) retinas transduced with AAV2/6-GFAP-GFP induced GFP expression restricted to activated Muller glial cells aligning retinal blood vessels.Conclusions/Significance: Our experiments indicate that AAV2 vectors carrying the GFAP promoter are a promising tool for specific expression of transgenes in activated glial cells

Direct gene therapy for repair of the spinal cord

For regrowth of injured nerve fibers following spinal cord injury (SCI), the environment must be favorable for axonal growth. The delivery of a therapeutic gene, beneficial for axonal growth, into the central nervous system for repair can be accomplished in many ways. Perhaps the most simple and elegant strategy is the so-called direct gene therapy approach that uses a single injection for delivery of a gene therapy vehicle. Among the vectors that have been used to transduce neural tissue in vivo are non-viral, herpes simplex viral, adeno-associated viral, adenoviral, and lentiviral vectors, each with their own merits and limitations. Many studies have been undertaken using direct gene therapy, ranging from strategies for neuroprotection to axonal growth promotion at the injury site, dorsal root injury repair, and initiation of a growth-supporting genetic program. The limitations and successes of direct gene transfer for spinal cord repair are discussed in this review

Virally Mediated Overexpression of Glial-Derived Neurotrophic Factor Elicits Age- and Dose-Dependent Neuronal Toxicity and Hearing Loss

Contemporary cochlear implants (CI) are generally very effective for remediation of severe to profound sensorineural hearing loss, but outcomes are still highly variable. Auditory nerve survival is likely one of the major factors underlying this variability. Neurotrophin therapy therefore has been proposed for CI recipients, with the goal of improving outcomes by promoting improved survival of cochlear spiral ganglion neurons (SGN) and/or residual hair cells. Previous studies have shown that glial-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor, and neurotrophin-3 can rescue SGNs following insult. The current study was designed to determine whether adeno-associated virus vector serotype 5 (AAV-5) encoding either green fluorescent protein or GDNF can transduce cells in the mouse cochlea to express useful levels of neurotrophin and to approximate the optimum therapeutic dose(s) for transducing hair cells and SGN. The findings demonstrate that AAV-5 is a potentially useful gene therapy vector for the cochlea, resulting in extremely high levels of transgene expression in the cochlear inner hair cells and SGN. However, overexpression of human GDNF in newborn mice caused severe neurological symptoms and hearing loss, likely due to Purkinje cell loss and cochlear nucleus pathology. Thus, extremely high levels of transgene protein expression should be avoided, particularly for proteins that have neurological function in neonatal subjects

518. Long-term lentiviral vector-mediated transgene expression in neural progenitor cells following implantation into the injured rat spinal cord

Due to their self-renewal and multi-potency, stem cells represent an attractive source for cell replacement therapy in neurological disorders. Genetic manipulation of these cells may allow controlled release of therapeutic proteins, suppress immune rejection, or produce essential neurotransmitters. Furthermore, when the expression cassette is incorporated into the host genome ex vivo, this technique also may be used as a method to trace cells following implantation into tissues of interest. We explored the possibility of transducing pluripotent fetal rat cortical neural progenitor cells using lentiviral vectors encoding either the green fluorescent protein (GFP) or neurotrophic factors (NT-3, BDNF, GDNF and CNTF) under control of the CMV promoter and the Woodchuck post-transcriptional regulatory element. Following isolation and expansion of the cells at clonal density on poly-ornithine-fibronectin-coated dishes in the presence of bFGF, cells were collected, infected and replated on the dishes. Staining of these cells for neural markers (such as nestin, GFAP, Tuj-1 and RIP) after transduction did not reveal any significant difference from non-transduced cells. However, when they were transduced with a vector encoding CNTF, cells started expressing GFAP. Cells continued to express the transgene, including when bFGF was withdrawn and when cells started to differentiate into GFAP positive cells. Following delayed (1 week) implantation into the lesion site of the moderately contused spinal cord, transduced cells survived well up to 4 weeks post-implantation (the longest time point currently examined). Migration of the cells was mainly restricted to white matter on either side of the lesion. Currently, the therapeutic and axonal growth stimulating properties of the implanted cells are being investigated in injured rats

Viral vector-mediated gene transfer of neurotrophins to promote regeneration of the injured spinal cord

Injuries to the adult mammalian spinal cord often lead to severe damage to both ascending (sensory) pathways and descending (motor) nerve pathways without the perspective of complete functional recovery. Future spinal cord repair strategies should comprise a multi-factorial approach addressing several issues, including optimalization of survival and function of spared central nervous system neurons in partial lesions and the modulation of trophic and inhibitory influences to promote and guide axonal regrowth. Neurotrophins have emerged as promising molecules to augment neuroprotection and neuronal regeneration. Although intracerebroventricular, intrathecal and local protein delivery of neurotrophins to the injured spinal cord has resulted in enhanced survival and regeneration of injured neurons, there are a number of drawbacks to these methods. Viral vector-mediated transfer of neurotrophin genes to the injured spinal cord is emerging as a novel and effective strategy to express neurotrophins in the injured nervous system. Ex vivo transfer of neurotrophic factor genes is explored as a way to bridge lesions cavities for axonal regeneration. Several viral vector systems, based on herpes simplex virus, adenovirus, adeno-associated virus, lentivirus, and moloney leukaemia virus, have been employed. The genetic modification of fibroblasts, Schwann cells, olfactory ensheathing glia cells, and stem cells, prior to implantation to the injured spinal cord has resulted in improved cellular nerve guides. So far, neurotrophic factor gene transfer to the injured spinal cord has led to results comparable to those obtained with direct protein delivery, but has a number of advantages. The steady advances that have been made in combining new viral vector systems with a range of promising cellular platforms for ex vivo gene transfer (e.g., primary embryonic neurons, Schwann cells, olfactory ensheating glia cells and neural stem cells) holds promising perspectives for the development of new neurotrophic factor-based therapies to repair the injured nervous system

662. The Tracking of Exogenous Cells in the Injured Central Nervous System: Viral Vector Labeling Versus an Intrinsic Genetic Marker

Transplantation of exogenous cells into the injured central nervous system and subsequent examination of how these cells survive, integrate and perform physiological functions within the host environment requires that the cells be clearly identifiable from host cells. As many of the cells used for transplantation studies are derived from cultures of cells indistinguishable from the host using immunochemical approaches, numerous dyes or genetic markers have been devised and used for this purpose. These markers used to label and track these transplanted cells need to be specific, reliable, resistant to leakage or cellular transfer, and remain chemically stable once inside the host to allow long-term tracking. In the current study we compared two labeling methods for long-term tracking of cells following transplantation into the injured rat spinal cord; lentiviral vector transduction with green fluorescent protein (GFP) and DNA in situ hybridization for the Y chromosome after male cell transplantation in female rats. Examination of labeled cells at 12 wk post-injury demonstrated that both labels did not exhibit significant fading or loss of the signal due to instability over time. The visualization procedure for the DNA in situ reaction product was significantly more labor intensive than simple identification of GFP by fluorescent microscopy. Y chromosome positive cells were, however, easier to definitely count for assessment of cell survival than GFP labeled cells, due to the presence of the label as a single point within the nucleus rather than diffuse labeling throughout the entirety of the cell. The limited presence of the signal in Y chromosome positive cells though, made examination of their ability to integrate within the injured spinal cord, migrate and associate with axons impossible without additional immunochemical methods for labeling the entire cell. The combination of immunochemistry with DNA in situ however proved to be unsuccessful with the many antibody combinations tested. In conclusion GFP delivery by lentiviral vectors was far superior to DNA in situ detection of the Y chromosome for labeling of transplanted cells due to its rapid visualization and its applicability to a wide range of assessment techniques

Brain-derived neurotrophic factor released from engineered mesenchymal stem cells attenuates glutamate- and hydrogen peroxide-mediated death of staurosporine-differentiated RGC-5 cells.

The pupose of this study was to determine the viability of cell-based delivery of brain-derived neurotrophic factor (BDNF) from genetically modified mesenchymal stem cells (MSCs) for neuroprotection of RGC-5 cells. RGC-5 cells were differentiated with the protein kinase inhibitor staurosporine (SS) and exposed to the cellular stressors glutamate or H2O2. As a neuroprotective strategy, these cells were then co-cultured across a membrane insert with mesenchymal stem cells (MSCs) engineered with a lentiviral vector for production of BDNF (BDNF-MSCs). As a positive control, recombinant human BDNF (rhBDNF) was added to stressed RGC-5 cells. After SS differentiation RGC-5s developed neuronal-like morphologies, and a significant increase in the proportion of RGC-5s immunoreactive for TuJ-1 and Brn3a was observed. Differentiated RGC-5s also had prominent TrkB staining, demonstrating expression of the high-affinity BDNF receptor. Treatment of SS differentiated RGC-5s with glutamate or H2O2, produced significant cell death (56.0 ± 7.02 and 48.90 ± 4.58% of control cells, respectively) compared to carrier-solution treated cells. BDNF-delivery from MSCs preserved more RGC-5 cells after treatment with glutamate (80.0 ± 5.40% cells remaining) than control GFP expressing MSCs (GFP-MSCs, 57.29 ± 1.89%, p \u3c 0.01). BDNF-MSCs also protected more RGC-5s after treatment with H2O2 (65.6 ± 3.47%) than GFPMSCs (46.0 ± 4.20%, p \u3c 0.01). We have shown survival of differentiated RGC-5s is reduced by the cellular stressors glutamate and H2O2. Additionally, our results demonstrate that genetically modified BDNF-producing MSCs can enhance survival of stressed RGC-5 cells and therefore, may be effective vehicles to deliver BDNF to retinal ganglion cells affected by disease

Brain-derived neurotrophic factor released from engineered mesenchymal stem cells attenuates glutamate- and hydrogen peroxide-mediated death of staurosporine differentiated RGC-5 cells

The pupose of this study was to determine the viability of cell-based delivery of brain-derived neurotrophic factor (BDNF) from genetically modified mesenchymal stem cells (MSCs) for neuroprotection of RGC-5 cells. RGC-5 cells were differentiated with the protein kinase inhibitor staurosporine (SS) and exposed to the cellular stressors glutamate or H2O2. As a neuroprotective strategy, these cells were then co-cultured across a membrane insert with mesenchymal stem cells (MSCs) engineered with a lentiviral vector for production of BDNF (BDNF-MSCs). As a positive control, recombinant human BDNF (rhBDNF) was added to stressed RGC-5 cells. After SS differentiation RGC-5s developed neuronal-like morphologies, and a significant increase in the proportion of RGC-5s immunoreactive for TuJ-1 and Brn3a was observed. Differentiated RGC-5s also had prominent TrkB staining, demonstrating expression of the high-affinity BDNF receptor. Treatment of SS differentiated RGC-5s with glutamate or H2O2, produced significant cell death (56.0 ± 7.02 and 48.90 ± 4.58% of control cells, respectively) compared to carrier-solution treated cells. BDNF-delivery from MSCs preserved more RGC-5 cells after treatment with glutamate (80.0 ± 5.40% cells remaining) than control GFP expressing MSCs (GFP-MSCs, 57.29 ± 1.89%, p This is a manuscript from Experimental Eye Research 89 (2009): 538, doi: 10.1016/j.exer.2009.05.013. Posted with permission.</p

Rapid directional shift of mitochondrial DNA heteroplasmy in animal tissues by a mitochondrially targeted restriction endonuclease

Frequently, mtDNA with pathogenic mutations coexist with wild-type genomes (mtDNA heteroplasmy). Mitochondrial dysfunction and disease ensue only when the proportion of mutated mtDNAs is high, thus a reduction in this proportion should provide an effective therapy for these disorders. We developed a system to decrease specific mtDNA haplotypes by expressing a mitochondrially targeted restriction endonuclease, ApaLI, in cells of heteroplasmic mice. These mice have two mtDNA haplotypes, of which only one contains an ApaLI site. After transfection of cultured hepatocytes with mitochondrially targeted ApaLI, we found a rapid, directional, and complete shift in mtDNA heteroplasmy (2-6 h). We tested the efficacy of this approach in vivo, by using recombinant viral vectors expressing the mitochondrially targeted ApaLI. We observed a significant shift in mtDNA heteroplasmy in muscle and brain transduced with recombinant viruses. This strategy could prevent disease onset or reverse clinical symptoms in patients harboring certain heteroplasmic pathogenic mutations in mtDNA

Lentiviral vector-mediated transduction of neural progenitor cells before implantation into injured spinal cord and brain to detect their migration, deliver neurotrophic factors and repair tissue

Stem cells represent an attractive source for cell replacement therapy in neurological disorders due to their self-renewal and multi-potency. Genetic manipulation of these cells may allow controlled release of therapeutic proteins, suppress immune rejection, or produce essential neurotransmitters. Furthermore, when the expression cassette is incorporated into the host genome ex vivo, this technique also may be used as a method to trace cells following implantation into tissues of interest. We explored the possibility of transducing pluripotent fetal rat cortical neural progenitor cells (NPCs) using lentiviral vectors encoding the green fluorescent protein (GFP) or neurotrophic factors (BDNF, CNTF, D15A, GDNF, MNT and NT-3) prior to implanting these cells into the contused spinal cord or injured brain. In vitro staining of these cells for neural markers (such as nestin, GFAP, Tuj-1 and RIP) after transduction did not reveal any significant difference from non-transduced cells. When they were transduced with a vector encoding CNTF or MNT, however, cells started expressing GFAP in vitro. Following delayed (1 week) implantation into the lesion site of the moderately contused rat spinal cord or the injured brain, transduced cells survived up to 12 weeks post-implantation (the longest time point examined) and most of the NPCs turned into an astrocytic phenotype in the spinal cord, but not in the brain. Nestin and GFP positive cells were detected in the brain, but not in the spinal cord lesion. GFP positive cells in the spinal cord migrated rostrally and caudally from the lesion/implantation site towards uninjured tissue. Novel findings in this study are the longterm expression of a foreign gene in NPCs using lentiviral vectors; this enabled tracking of the cells following implantation. This expression also allowed the observation that NPCs developed differently in the injured spinal cord and brain. Moreover, NPCs could be transduced to overexpress neurotrophic factors. In sum, NPC survival and the long-term transgene expression that allows easy tracking of migrating cells make NPCs promising candidates for implantation into the injured spinal cord or brain and a potentially powerful tool to enhance regeneration when transduced ex vivo to produce therapeutic molecules