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1.  Gene Therapy Regenerates Protein Expression in Cone Photoreceptors in Rpe65R91W/R91W Mice 
PLoS ONE  2011;6(2):e16588.
Cone photoreceptors mediate visual acuity under daylight conditions, so loss of cone-mediated central vision of course dramatically affects the quality of life of patients suffering from retinal degeneration. Therefore, promoting cone survival has become the goal of many ocular therapies and defining the stage of degeneration that still allows cell rescue is of prime importance. Using the Rpe65R91W/R91W mouse, which carries a mutation in the Rpe65 gene leading to progressive photoreceptor degeneration in both patients and mice, we defined stages of retinal degeneration that still allow cone rescue. We evaluated the therapeutic window within which cones can be rescued, using a subretinal injection of a lentiviral vector driving expression of RPE65 in the Rpe65R91W/R91W mice. Surprisingly, when applied to adult mice (1 month) this treatment not only stalls or slows cone degeneration but, actually, induces cone-specific protein expression that was previously absent. Before the intervention only part of the cones (40% of the number found in wild-type animals) in the Rpe65R91W/R91W mice expressed cone transducin (GNAT2); this fraction increased to 64% after treatment. Correct S-opsin localization is also recovered in the transduced region. In consequence these results represent an extended therapeutic window compared to the Rpe65-/- mice, implying that patients suffering from missense mutations might also benefit from a prolonged therapeutic window. Moreover, cones are not only rescued during the course of the degeneration, but can actually recover their initial status, meaning that a proportion of altered cones in chromophore deficiency-related disease can be rehabilitated even though they are severely affected.
doi:10.1371/journal.pone.0016588
PMCID: PMC3033393  PMID: 21304899
2.  Spectral Domain Optical Coherence Tomography in Mouse Models of Retinal Degeneration 
Purpose
Spectral domain optical coherence tomography (SD-OCT) allows cross-sectional visualization of retinal structures in vivo. Here, we report the efficacy of a commercially available SD-OCT device to study mouse models of retinal degeneration.
Methods
C57BL/6 and BALB/c wild type mice and three different mouse models of hereditary retinal degeneration (Rho-/-, rd1, RPE65-/-) were investigated using confocal scanning laser ophthalmoscopy (cSLO) for en face visualization and SD-OCT for cross-sectional imaging of retinal structures. Histology was performed to correlate structural findings in SD-OCT with light microscopic data.
Results
In C57BL/6 and BALB/c mice, cSLO and SD-OCT imaging provided structural details of frequently used control animals (central retinal thickness, CRTC57BL/6 = 237±2μm and CRTBALB/c = 211±10μm). RPE65-/- mice at 11 months of age showed a significant reduction of retinal thickness (CRTRPE65 = 193±2μm) with thinning of the outer nuclear layer. Rho-/- mice at P28 demonstrated degenerative changes mainly in the outer retinal layers (CRTRho = 193±2μm). Examining rd1 animals before and after the onset of retinal degeneration allowed to monitor disease progression (CRTrd1 P11 = 246±4μm, CRTrd1 P28 = 143±4μm). Correlation of CRT assessed by histology and SD-OCT was high (r2 = 0.897).
Conclusion
We demonstrated cross sectional visualization of retinal structures in wild type mice and mouse models for retinal degeneration in vivo using a commercially available SD-OCT device. This method will help to reduce numbers of animals needed per study by allowing longitudinal study designs and facilitate characterization of disease dynamics and evaluation of putative therapeutic effects following experimental interventions.
doi:10.1167/iovs.09-3724
PMCID: PMC2800101  PMID: 19661229
optical coherence tomography; retinal degeneration; imaging; mouse models
3.  Constitutive Overexpression of Human Erythropoietin Protects the Mouse Retina against Induced But Not Inherited Retinal Degeneration 
Elevation of erythropoietin (Epo) concentrations by hypoxic preconditioning or application of recombinant human Epo (huEpo) protects the mouse retina against light-induced degeneration by inhibiting photoreceptor cell apoptosis. Because photoreceptor apoptosis is also the common path to cell loss in retinal dystrophies such as retinitis pigmentosa (RP), we tested whether high levels of huEpo would reduce apoptotic cell death in two mouse models of human RP. We combined the two respective mutant mouse lines with a transgenic line (tg6) that constitutively overexpresses huEpo mainly in neural tissues. Transgenic expression of huEpo caused constitutively high levels of Epo in the retina and protected photoreceptors against light-induced degeneration; however, the presence of high levels of huEpo did not affect the course or the extent of retinal degeneration in a light-independent (rd1) and a light-accelerated (VPP) mouse model of RP. Similarly, repetitive intraperitoneal injections of recombinant huEpo did not protect the retina in the rd1 and the VPP mouse. Lack of neuroprotection by Epo in the two models of inherited retinal degeneration was not caused by adaptational downregulation of Epo receptor. Our results suggest that apoptotic mechanisms during acute, light-induced photoreceptor cell death differ from those in genetically based retinal degeneration. Therapeutic intervention with cell death in inherited retinal degeneration may therefore require different drugs and treatments.
doi:10.1523/JNEUROSCI.1288-04.2004
PMCID: PMC2929919  PMID: 15215287
retinal degeneration; erythropoietin; apoptosis; neuroprotection; photoreceptor; transgene
4.  Noninvasive, In Vivo Assessment of Mouse Retinal Structure Using Optical Coherence Tomography 
PLoS ONE  2009;4(10):e7507.
Background
Optical coherence tomography (OCT) is a novel method of retinal in vivo imaging. In this study, we assessed the potential of OCT to yield histology-analogue sections in mouse models of retinal degeneration.
Methodology/Principal Findings
We achieved to adapt a commercial 3rd generation OCT system to obtain and quantify high-resolution morphological sections of the mouse retina which so far required in vitro histology. OCT and histology were compared in models with developmental defects, light damage, and inherited retinal degenerations. In conditional knockout mice deficient in retinal retinoblastoma protein Rb, the gradient of Cre expression from center to periphery, leading to a gradual reduction of retinal thickness, was clearly visible and well topographically quantifiable. In Nrl knockout mice, the layer involvement in the formation of rosette-like structures was similarly clear as in histology. OCT examination of focal light damage, well demarcated by the autofluorescence pattern, revealed a practically complete loss of photoreceptors with preservation of inner retinal layers, but also more subtle changes like edema formation. In Crb1 knockout mice (a model for Leber's congenital amaurosis), retinal vessels slipping through the outer nuclear layer towards the retinal pigment epithelium (RPE) due to the lack of adhesion in the subapical region of the photoreceptor inner segments could be well identified.
Conclusions/Significance
We found that with the OCT we were able to detect and analyze a wide range of mouse retinal pathology, and the results compared well to histological sections. In addition, the technique allows to follow individual animals over time, thereby reducing the numbers of study animals needed, and to assess dynamic processes like edema formation. The results clearly indicate that OCT has the potential to revolutionize the future design of respective short- and long-term studies, as well as the preclinical assessment of therapeutic strategies.
doi:10.1371/journal.pone.0007507
PMCID: PMC2759518  PMID: 19838301
5.  Analysis of the retinal gene expression profile after hypoxic preconditioning identifies candidate genes for neuroprotection 
BMC Genomics  2008;9:73.
Background
Retinal degeneration is a main cause of blindness in humans. Neuroprotective therapies may be used to rescue retinal cells and preserve vision. Hypoxic preconditioning stabilizes the transcription factor HIF-1α in the retina and strongly protects photoreceptors in an animal model of light-induced retinal degeneration. To address the molecular mechanisms of the protection, we analyzed the transcriptome of the hypoxic retina using microarrays and real-time PCR.
Results
Hypoxic exposure induced a marked alteration in the retinal transcriptome with significantly different expression levels of 431 genes immediately after hypoxic exposure. The normal expression profile was restored within 16 hours of reoxygenation. Among the differentially regulated genes, several candidates for neuroprotection were identified like metallothionein-1 and -2, the HIF-1 target gene adrenomedullin and the gene encoding the antioxidative and cytoprotective enzyme paraoxonase 1 which was previously not known to be a hypoxia responsive gene in the retina. The strongly upregulated cyclin dependent kinase inhibitor p21 was excluded from being essential for neuroprotection.
Conclusion
Our data suggest that neuroprotection after hypoxic preconditioning is the result of the differential expression of a multitude of genes which may act in concert to protect visual cells against a toxic insult.
doi:10.1186/1471-2164-9-73
PMCID: PMC2270833  PMID: 18261226
6.  Lentiviral Gene Transfer of Rpe65 Rescues Survival and Function of Cones in a Mouse Model of Leber Congenital Amaurosis 
PLoS Medicine  2006;3(10):e347.
Background
RPE65 is specifically expressed in the retinal pigment epithelium and is essential for the recycling of 11-cis-retinal, the chromophore of rod and cone opsins. In humans, mutations in RPE65 lead to Leber congenital amaurosis or early-onset retinal dystrophy, a severe form of retinitis pigmentosa. The proof of feasibility of gene therapy for RPE65 deficiency has already been established in a dog model of Leber congenital amaurosis, but rescue of the cone function, although crucial for human high-acuity vision, has never been strictly proven. In Rpe65 knockout mice, photoreceptors show a drastically reduced light sensitivity and are subject to degeneration, the cone photoreceptors being lost at early stages of the disease. In the present study, we address the question of whether application of a lentiviral vector expressing the Rpe65 mouse cDNA prevents cone degeneration and restores cone function in Rpe65 knockout mice.
Methods and Findings
Subretinal injection of the vector in Rpe65-deficient mice led to sustained expression of Rpe65 in the retinal pigment epithelium. Electroretinogram recordings showed that Rpe65 gene transfer restored retinal function to a near-normal pattern. We performed histological analyses using cone-specific markers and demonstrated that Rpe65 gene transfer completely prevented cone degeneration until at least four months, an age at which almost all cones have degenerated in the untreated Rpe65-deficient mouse. We established an algorithm that allows prediction of the cone-rescue area as a function of transgene expression, which should be a useful tool for future clinical trials. Finally, in mice deficient for both RPE65 and rod transducin, Rpe65 gene transfer restored cone function when applied at an early stage of the disease.
Conclusions
By demonstrating that lentivirus-mediated Rpe65 gene transfer protects and restores the function of cones in the Rpe65−/− mouse, this study reinforces the therapeutic value of gene therapy for RPE65 deficiencies, suggests a cone-preserving treatment for the retina, and evaluates a potentially effective viral vector for this purpose.
In theRpe65-/- mouse model of Leber congenital amaurosis, injection of a lentiviral vector expressing the Rpe65 mouse cDNA was able to prevent cone degeneration and restore cone function.
Editors' Summary
Background.
Leber congenital amaurosis (LCA) is the name of a group of hereditary diseases that cause blindness in infants and children. Changes in any one of a number of different genes can cause the blindness, which affects vision starting at birth or soon after. The condition was first described by a German doctor, Theodore Leber, in the 19th century, hence the first part of the name; “amaurosis” is another word for blindness. Mutations in one gene called retinal pigment epithelium-specific protein, 65 kDa (RPE65)—so called because it is expressed in the pigment epithelium, a cell layer adjacent to the light-sensitive cells, and is 65 kilodaltons in size—cause about 10% of cases of LCA. The product of this gene is essential for the recycling of a substance called 11-cis-retinal, which is necessary for the light-sensitive rods and cones of the retina to capture light. If the gene is abnormal, the sensitivity of the retina to light is drastically reduced, but it also leads to damage to the light-sensitive cells themselves.
Why Was This Study Done?
Potentially, eyes diseases such as this one could be treated by gene therapy, which works by replacing a defective gene with a normal functional one, usually by putting a copy of the normal gene into a harmless virus and injecting it into the affected tissue—in this case, the eye. The researchers here wanted to see whether expressing wild-type RPE65 using a particular type of gene vector that can carry large pieces of DNA transcript—a lentiviral vector—could prevent degeneration of cone cells and restore cone function in a mouse model of this type of LCA—mice who had had this Rpe65 gene genetically removed.
What Did the Researchers Do and Find?
Injection of the normal gene into the retina of Rpe65-deficient mice led to sustained expression of the protein RPE65 in the retinal pigment epithelium. Electrical recordings of the activity of the eyes in these mice showed that Rpe65 gene transfer restored retinal function to a near-normal level. In addition, Rpe65 gene transfer completely prevented cone degeneration until at least four months, an age at which almost all cones have degenerated in the untreated Rpe65-deficient mice.
What Do These Findings Mean?
These findings suggest that it is theoretically possible to treat this type of blindness by gene therapy. However, because this study was done in mice, many other steps need to be taken before it will be clear whether the treatment could work in humans. These steps include a demonstration that the virus is safe in humans, and experiments to determine what dose of virus would be needed and how long the effects of the treatment would last. Another question is whether it would be necessary (or even possible) to treat affected children during early childhood or when children start losing vision.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0030347.
The Foundation for Retinal Research has detailed information on Leber's congenital amaurosis
Contact a Family is a UK organization that aims to put families of children with illnesses in touch with each other
The Foundation for Fighting Blindness funds research into, and provides information about many types of blindness, including Leber's congenital amaurosis
This Web site provides information on gene therapy clinical trials, including those dedicated to cure eye diseases
This foundation provides information on diseases leading to blindness, including Leber's congenital amaurosis
doi:10.1371/journal.pmed.0030347
PMCID: PMC1592340  PMID: 17032058

Results 1-6 (6)