Retinal plasticity in the context of a partially rescued retinitis pigmentosa mouse model

Retinitis pigmentosa (RP) is a major cause of hereditary blindness and visual disability. The prevalence of RP is estimated to be 1/4000, affecting approximately 2.5 million people worldwide. RP is a very slow-progressing disease, and its symptoms start usually during adolescence. Mutations in over 70 different genes can cause photoreceptor cell degeneration leading to retinitis pigmentosa. A common RP-related gene is PDE6B which encodes a β-subunit of PDE6-enzyme which has a crucial function in rod-mediated vision. No cure is available currently for RP patients. Treatment options are few, but the most promising one is gene therapy. Since retinal gene therapy is delivered by a single sub-retinal injection, it does not rescue all the diseased photoreceptor cells. The impact of the non-rescued photoreceptor cells on the rescued ones is not fully understood. This remains a challenge for the therapy. The project aimed to study the retinal morphology and the function of the retinal pigment epithelium (RPE) in 48-week-old diseased (RP) and partially rescued mice. Pde6bST/WT mice have a functional Pde6b allele and were used as a control in the experiments. Pde6bST/ST mice have a loxP-flanked stop cassette in the intron 1 of both loci of the Pde6b gene. The stop cassette contains multiple polyadenylation signals which prevent gene expression. Pde6bST/ST exhibit progressive rod degeneration. In Pde6bST/ST Pax6αCre mice, stop cassettes are partially removed by the Cre recombinase which is expressed under a Pax6α promoter. Both Pde6b alleles are functional in the distal retina whereas the non-recombined retina in the center remains mutant. Retinal sections were stained with multiple antibodies to study the retinal morphology. RPE morphology was studied by quantifying fluorescence images from RPE wholemounts. Apoptotic cell death in the RPE cells was studied by using a commercial TUNEL assay. In normal physiology, RPE cells phagocytose photoreceptor cell outer segments and this process was studied by using an ex vivo assay. According to the results, the partially rescued retina of Pde6bST/ST Pax6αCre showed signs of retinal remodelling. This can be seen as beneficial for the retinal gene therapies conducted by a single injection if the partially rescued retina can regenerate and expand the rescued area. The diseased retina of Pde6bST/ST showed large-scale retinal degeneration and revealed heterogeneity of the RPE

Automatic segmentation of pigment deposits in retinal fundus images of Retinitis Pigmentosa

Retinitis Pigmentosa is an eye disease that presents with a slow loss of vision and then evolves until blindness results. The automatic detection of the early signs of retinitis pigmentosa acts as a great support to ophthalmologists in the diagnosis and monitoring of the disease in order to slow down the degenerative process. A large body of literature is devoted to the analysis of Retinitis Pigmentosa. However, all the existing approaches work on Optical Coherence Tomography (OCT) data, while hardly any attempts have been made working on fundus images. Fundus image analysis is a suitable tool in daily practice for an early detection of retinal diseases and the monitoring of their progression. Moreover, the fundus camera represents a low-cost and easy-access diagnostic system, which can be employed in resource-limited regions and countries. The fundus images of a patient suffering from retinitis pigmentosa are characterized by an attenuation of the vessels, a waxy disc pallor and the presence of pigment deposits. Considering that several methods have been proposed for the analysis of retinal vessels and the optic disk, this work focuses on the automatic segmentation of the pigment deposits in the fundus images. The image distortions are attenuated by applying a local pre-processing. Next, a watershed transformation is carried out to produce homogeneous regions. Working on regions rather than on pixels makes the method very robust to the high variability of pigment deposits in terms of color and shape, so allowing the detection even of small pigment deposits. The regions undergo a feature extraction procedure, so that a region classification process is performed by means of an outlier detection analysis and a rule set. The experiments have been performed on a dataset of images of patients suffering from retinitis pigmentosa. Although the images present a high variability in terms of color and illumination, the method provides a good performance in terms of sensitivity, specificity, accuracy and the F-measure, whose values are 74.43, 98.44, 97.90, 59.04, respectively