Functional Genomics of the Retina to Elucidate its Construction and Deconstruction

Shedding light on myopia by studying complete congenital stationary night blindness

Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare progressive and stationary inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in a variety of biological processes including eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signaling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON-bipolar cell signal transmission defect and is also associated with high myopia. Thus, it represents also an interesting model to identify myopia-related genes, as well as disease mechanisms. While the origin of night blindness is molecularly well established, further research is needed to elucidate the mechanisms of myopia development in subjects with cCSNB. Using whole transcriptome analysis on three different mouse models of cCSNB (in Gpr179^-/-, Lrit3^-/- and Grm6^-/-), we identified novel actors of the retinal signaling cascade, which are also novel candidate genes for myopia. Meta-analysis of our transcriptomic data with published transcriptomic databases and genome-wide association studies from myopia cases led us to propose new biological/cellular processes/mechanisms potentially at the origin of myopia in cCSNB subjects. The results provide a foundation to guide the development of pharmacological myopia therapies.

Clinical features associated with the atrophy of fellow eyes in patients with unilateral type 3 macular neovascularization

PURPOSE

We sought to investigate the clinical features of eyes with unilateral type 3 macular neovascularization (MNV) according to the degenerative features of fellow eyes.

METHODS

We retrospectively reviewed 55 patients with unilateral type 3 MNV and identified degenerative features including geographic atrophy (GA) in fellow eyes using multimodal imaging. Then, the clinical features of eyes with type 3 MNV at baseline and during follow-up with anti-vascular endothelial growth factor treatment and an as-needed regimen were compared according to the degenerative features of fellow eyes.

RESULTS

Eighteen patients (32.7%) had GA in fellow eyes; initial disease manifestations of type 3 MNV eyes including stage, best-corrected visual acuity, and choroidal thickness (CT) did not vary between groups (all P > 0.05). During follow-up, a rate of complete fluid resolution after three monthly loading injections was not associated with GA in fellow eyes (P = 0.703), while a lower rate of early recurrence within 3 months after loading treatment was associated with thinner CT in type 3 MNV eyes and GA over one disc area in fellow eyes (P = 0.025 and P = 0.021).

CONCLUSION

Degenerative features of fellow eyes in patients with unilateral type 3 MNV may be associated with the clinical characteristics of affected eyes.

A Splice Variant in SLC16A8 Gene Leads to Lactate Transport Deficit in Human iPS Cell-Derived Retinal Pigment Epithelial Cells

Age-related macular degeneration (AMD) is a blinding disease for which most of the patients remain untreatable. Since the disease affects the macula at the center of the retina, a structure specific to the primate lineage, rodent models to study the pathophysiology of AMD and to develop therapies are very limited. Consequently, our understanding relies mostly on genetic studies highlighting risk alleles at many loci. We are studying the possible implication of a metabolic imbalance associated with risk alleles within the SLC16A8 gene that encodes for a retinal pigment epithelium (RPE)-specific lactate transporter MCT3 and its consequences for vision. As a first approach, we report here the deficit in transepithelial lactate transport of a rare SLC16A8 allele identified during a genome-wide association study. We produced induced pluripotent stem cells (iPSCs) from the unique patient in our cohort that carries two copies of this allele. After in vitro differentiation of the iPSCs into RPE cells and their characterization, we demonstrate that the rare allele results in the retention of intron 2 of the SLC16A8 gene leading to the absence of MCT3 protein. We show using a biochemical assay that these cells have a deficit in transepithelial lactate transport.

Vitamin C- and Valproic Acid-Induced Fetal RPE Stem-like Cells Recover Retinal Degeneration via Regulating SOX2

Retinal pigment epithelial (RPE) cell replacement therapy has provided promising outcomes in the treatment of retinal degenerative diseases (RDDs), but the resulting limited visual improvement has raised questions about graft survival and differentiation. Through combined treatment with vitamin C and valproic acid (together, VV), we activated human fetal RPE (fRPE) cells to become highly proliferative fetal RPE stem-like cells (fRPESCs). In this study, we report that SOX2 (SRY-box 2) activation contributed to mesenchymal-epithelial transition and elevated the retinal progenitor and mesenchymal stromal markers expressions of fRPESCs. These fRPESCs could differentiate into RPE cells, rod photoreceptors, and mesenchymal lineage progenies under defined conditions. Finally, fRPESCs were transplanted into the subretinal space of an RDD mouse model, and a photoreceptor rescue benefit was demonstrated. The RPE and rod photoreceptor differentiation of transplanted fRPESCs may account for the neural retinal recovery. This study establishes fRPESCs as a highly proliferative, multi-lineage differentiation potential (including RPE, rod photoreceptor, and mesenchymal lineage differentiation), mesenchymal-to-epithelial-transitioned retinal stem-like cell source for cell-based therapy of RDDs.

Metabolic and Redox Signaling of the Nucleoredoxin-Like-1 Gene for the Treatment of Genetic Retinal Diseases

The loss of cone photoreceptor function in retinitis pigmentosa (RP) severely impacts the central and daily vision and quality of life of patients affected by this disease. The loss of cones follows the degeneration of rods, in a manner independent of the causing mutations in numerous genes associated with RP. We have explored this phenomenon and proposed that the loss of rods triggers a reduction in the expression of rod-derived cone viability factor (RdCVF) encoded by the nucleoredoxin-like 1 (NXNL1) gene which interrupts the metabolic and redox signaling between rods and cones. After providing scientific evidence supporting this mechanism, we propose a way to restore this lost signaling and prevent the cone vision loss in animal models of RP. We also explain how we could restore this signaling to prevent cone vision loss in animal models of the disease and how we plan to apply this therapeutic strategy by the administration of both products of NXNL1 encoding the trophic factor RdCVF and the thioredoxin enzyme RdCVFL using an adeno-associated viral vector. We describe in detail all the steps of this translational program, from the design of the drug, its production, biological validation, and analytical and preclinical qualification required for a future clinical trial that would, if successful, provide a treatment for this incurable disease.