Reproducible high efficiency gene transfer into Y79 retinoblastoma cells using adenofection

In vitro Model Systems for Studies Into Retinal Neuroprotection

Therapy development for neurodegenerative diseases of the retina constitutes a major unmet medical need, and this may be particularly relevant for inherited diseases of the retina, which are largely untreatable to this day. Therapy development necessitates appropriate models to improve the understanding of the underlying degenerative mechanisms, as well as for the testing and evaluation of novel treatment approaches. This review provides an overview of various in vitro model systems used to study retinal neuroprotection. The in vitro methods and technologies discussed range from primary retinal cell cultures and cell lines, to retinal organoids and organotypic retinal explants, to the cultivation of whole eyeballs. The advantages and disadvantages of these methods are compared and evaluated, also in view of the 3R principles (i.e., the refinement, reduction, and replacement of live animal testing), to identify suitable in vitro alternatives for in vivo experimentation. The article further expands on the use of in vitro models to test and evaluate neuroprotective treatments and to aid the development of retinal drug delivery systems. Among the pharmacological agents tested and characterized in vitro are such that interfere with aberrant cyclic guanosine monophosphate (cGMP) -signaling or such that inhibit the activities of poly (ADP-ribose) polymerase (PARP), histone deacetylases (HDAC), calpain-type proteases, as well as unfolded protein response-related stress. We then introduce nanoparticle-based drug delivery systems and discuss how different in vitro systems may be used to assess their efficacy in the treatment of retinal diseases. The summary provides a brief comparison of available in vitro models and relates their advantages and limitations to the various experimental requirements, for instance, for studies into disease mechanisms, novel treatments, or retinal toxicity. In many cases, combinations of different in vitro models may be required to obtain a comprehensive view of the efficacy of a given retinal neuroprotection approach.

Polymeric vectors for ocular gene delivery

Gene therapy holds promise for the treatment of many inherited and acquired diseases of the eye. Successful ocular gene therapy interventions depend on efficient gene transfer to targeted cells with minimal toxicity. A major challenge is to overcome both intracellular and extracellular barriers associated with ocular gene delivery. Numerous viral and nonviral vectors were explored to improve transfection efficiency. Among nonviral delivery systems, polymeric vectors have gained significant attention in recent years owing to their nontoxic and non-immunogenic nature. Polyplexes or nanoparticles can be prepared by interaction of cationic polymers with DNA, which facilitate cellular uptake, endolysosomal escape and nuclear entry through active mechanisms. Chemical modification of these polymers allows for the generation of flexible delivery vectors with desirable properties. In this article several synthetic and natural polymeric systems utilized for ocular gene delivery are discussed.

Treatment with connexin 46 siRNA suppresses the growth of human Y79 retinoblastoma cell xenografts in vivo

Tumors with a hypoxic component, including human Y79 retinoblastoma cells, express a specific gap junction protein, Connexin 46 (Cx46), which is usually only found in naturally hypoxic tissues such as the differentiated lens. The aim of this study was to investigate if Cx46 downregulation would suppress Y79 tumor formation in vivo. Five-week old nude mice were subcutaneously implanted with human Y79 retinoblastoma cells and treated with intratumor siRNA injections of 30 μg Cx46 siRNA (n = 6), 30 μg non-silencing siRNA (n = 6), or no siRNA treatment (n = 6) every 2 days for a maximum of 10 treatments. Tumor volume (TV) was calculated from the recorded caliper measurements of length and width. Excised tumors were measured and weighed. Western blot analyses were performed to evaluate Cx46 and Cx43 expression in tumors which received Cx46 siRNA, non-silencing siRNA, or no siRNA treatment. Tumor histopathology was used to assess tumor features. Cx46 siRNA treated Y79 tumors had a reduced TV (287 mm(3) ± 77 mm(3)) when compared to the tumors of mice receiving the negative control siRNA (894 mm(3) ± 218 mm(3); P ≤ 0.03) or no siRNA (1068 mm(3) ± 192 mm(3); P ≤ 0.002). A 6-fold knockdown of Cx46 and a 3-fold rise in Cx43 protein expression was observed from western blots of tumors treated with Cx46 siRNA compared to mice treated with non-silencing siRNA. Knockdown of Cx46 with siRNA had an antitumor effect on human Y79 retinoblastoma tumors in the nude mouse model. The results suggest that anti-Cx46 therapy may be a potential target in the future treatment of retinoblastoma.

Freeze-drying of cationic polymer DNA complexes enables their long-term storage and reverse transfection of post-mitotic cells

WERI-Rb1 retinoblastoma (Rb) cell line, a human photoreceptor model, is notoriously difficult to transfect. Culturing of the WERI-Rb1 cells as a monolayer is complicated and cells are easily detached during transfection. Furthermore, transfection efficiencies in monolayer and in suspension are moderate at best which has limited the analysis of photoreceptor-specific promoters with low activity. To overcome these limitations, we developed a straightforward reverse transfection method for WERI-Rb1 cells wherein snap-frozen DNA/polyethylenimine complexes are freeze-dried on the surface of 48-well plates and stored in desiccator until cells are seeded for transfection. Comparing to conventional transfection, reverse transfection turned out to have equal or better transfection efficiency. In addition, while conventional transfection with cationic polymers requires serum-free conditions, reverse transfection can be performed in the presence of serum. Importantly, DNA/polyethylenimine complexes promote cell adhesion to the plates. This enables cell culturing as monolayers with concurrent complex uptake. Also, long-term storage of the plates did not reduce the transfection efficiency nor it had any effects on the cell toxicity. Because of the stability of complexes, reverse transfection enables large-scale transfection of hard-to-transfect retinoblastoma cells thus providing a reproducible, cost-effective and versatile tool for parallel screening of proteins and gene regulatory elements used in diverse applications.

Functional Analysis of the Rod Photoreceptor cGMP Phosphodiesterase α-Subunit Gene Promoter

To understand the factors controlling expression of the cGMP phosphodiesterase type 6 (PDE6) genes, we have characterized the promoter of the human PDE6A gene that encodes the catalytic alpha-subunit. In vivo DNase I hypersensitivity assays revealed two sites immediately upstream of the PDE6A core promoter region. Transient transfection assay in Y79 cells of constructs containing varying lengths of the promoter region showed a decrease in promoter activity with increasing length. The most active segment contained a 177-bp upstream sequence including apparent Crx and Nrl transcription factor binding sites. Both Crx and Nrl transactivated the PDE6A promoter in HEK293 cells and showed a >100-fold increase when coexpressed. Coexpression of a dominant negative inhibitor of Nrl abolished Nrl transactivation but had no effect on Crx. DNase I footprinting assays identified three potential Crx binding sites within a 55-bp segment beginning 29 bp upstream of the transcription start point. Mutation of two of these sites reduced reporter gene activity by as much as 69%. Gel shifts showed that all three Crx sites required a TAAT sequence for efficient binding. Consistent with a requirement for Crx and Nrl in Pde6a promoter activity, Pde6a mRNA is reduced by 87% in the retina of Crx(-/-) mice and is undetectable in Nrl(-/-) mice at postnatal day 10. These results establish that both Nrl and Crx are required for full transcriptional activity of the PDE6A gene.

Retina-specific gene expression and improved DNA transfection in WERI-Rb1 retinoblastoma cells

We have studied retina-specific gene expression and gene promoter activity in WERI-Rb1 retinoblastoma cells. In general, the expression of endogenous genes matched the efficiency of promoter activity of the transfected gene: interphotoreceptor retinoid binding protein and phosphodiesterase-beta mRNAs and reporter activities were readily detected while other retina-specific messages were at or below the detection limit in WERI-Rb1 cells. Phosphodiesterase-beta promoter appeared active in all six cell lines tested. The viral SV40 promoter is very weak in WERI-Rb1 cells, which has implications for its use in gene constructs targeted to the photoreceptors. Our results also show that polyethyleneimine 25 is an efficient and simple carrier for DNA. The optimized transfection conditions permit the use of 24-well plates and low amounts of DNA for improved analysis of promoter activities, as compared to previous studies. Our results are expected to facilitate further research on retina-specific gene expression.

Derepression of HMGA2 gene expression in retinoblastoma is associated with cell proliferation

To assess whether retinoblastoma formation is associated with the expression of high mobility group (HMG) A2 protein, a transcription factor that is highly expressed during embryogenesis and completely repressed in normal adult tissues, we performed Northern and Western blots and RT-PCR analyses, and immunohistochemistry to test for HMGA2 expression. We used established retinoblastoma cell lines in tumors grown in nude mice and clinical retinoblastoma specimens, and contrasted these tumors with normal embryonic and adult retina. Adenoviral-mediated antisense experiments were conducted on the retinoblastoma cell lines to suppress HMGA2 expression and determine if cell proliferation is HMGA2-dependent. We also transfected a retinoblastoma cell line to identify cis-regulatory elements and transcription initiation sites on the HMGA2 gene promoter. HMGA2 gene expression was silenced in terminally differentiated retina of 6-wk-old mice, but it was detected in retina of a 13.5-d postcoitum embryo. Reactivation of HMGA2 gene expression was observed in the retinoblastoma cell lines Y79, WERI-Rb1, and TOTL-1, in tumors derived from some of these cells propagated in nude mice, and in a high frequency of retinoblastomas excised from human patients. This suggests that expression of HMGA2 gene in retinoblastoma cells involves a derepression process. By using an antisense approach to block HMGA2 expression, we observed a decrease in the number of proliferating retinoblastoma cells. As a 1st step toward understanding HMGA2 gene reactivation in retinoblastoma, we mapped the 2 transcription initiation sites and associated positive regulatory elements within the WERI-Rb1 cells. Our discovery of derepression of HMGA2 gene expression in retinoblastoma provides the 1st evidence that this protein might contribute to neoplastic transformation of retina cells.

Gene therapy for genetic and acquired retinal diseases

We present an overview of the current status of basic science and translational research being applied to gene therapy for eye disease, focusing on diseases of the retina. We discuss the viral and nonviral methods being used to transfer genes to the retina and retinal pigment epithelium, and the advantages and disadvantages of each approach. We review the various genetic and somatic treatment strategies that are being used for genetically determined and acquired diseases of the retina, including gene replacement, gene silencing by ribozymes and antisense oligonucleotides, suicide gene therapy, antiapoptosis, and growth factor therapies. The rationales for the specific therapeutic approaches to each disease are discussed. Schematics of gene transfer methods and therapeutic approaches are presented together with a glossary of gene transfer terminology.