Age-related changes in the basement membrane of the retinal pigment epithelium of Rpe65 ?/? and wild-type mice

Targeting senescent retinal pigment epithelial cells facilitates retinal regeneration in mouse models of age-related macular degeneration

Although age-related macular degeneration (AMD) is a multifactorial disorder with angiogenic, immune, and inflammatory components, the most common clinical treatment strategies are antiangiogenic therapies. However, these strategies are only applicable to neovascular AMD, which accounts for less than 20% of all AMD cases, and there are no FDA-approved drugs for the treatment of dry AMD, which accounts for ~ 80% of AMD cases. Here, we report that the elimination of senescent cells is a potential novel therapeutic approach for the treatment of all types of AMD. We identified senescent retinal pigment epithelium (RPE) cells in animal models of AMD and determined their contributions to retinal degeneration. We further confirmed that the clearance of senescent RPE cells with the MDM2-p53 inhibitor Nutlin-3a ameliorated retinal degeneration. These findings provide new insights into the use of senescent cells as a therapeutic target for the treatment of AMD.

The retinal pigment epithelium: Development, injury responses, and regenerative potential in mammalian and non-mammalian systems

Diseases that result in retinal pigment epithelium (RPE) degeneration, such as age-related macular degeneration (AMD), are among the leading causes of blindness worldwide. Atrophic (dry) AMD is the most prevalent form of AMD and there are currently no effective therapies to prevent RPE cell death or restore RPE cells lost from AMD. An intriguing approach to treat AMD and other RPE degenerative diseases is to develop therapies focused on stimulating endogenous RPE regeneration. For this to become feasible, a deeper understanding of the mechanisms underlying RPE development, injury responses and regenerative potential is needed. In mammals, RPE regeneration is extremely limited; small lesions can be repaired by the expansion of adjacent RPE cells, but large lesions cannot be repaired as remaining RPE cells are unable to functionally replace lost RPE tissue. In some injury paradigms, RPE cells proliferate but do not regenerate a morphologically normal monolayer, while in others, proliferation is pathogenic and results in further disruption to the retina. This is in contrast to non-mammalian vertebrates, which possess tremendous RPE regenerative potential. Here, we discuss what is known about RPE formation during development in mammalian and non-mammalian vertebrates, we detail the processes by which RPE cells respond to injury, and we describe examples of RPE-to-retina and RPE-to-RPE regeneration in non-mammalian vertebrates. Finally, we outline barriers to RPE-dependent regeneration in mammals that could potentially be overcome to stimulate a regenerative response from the RPE.

Egg yolk improves lipid profile, lipid peroxidation and retinal abnormalities in a murine model of genetic hypercholesterolemia

Carotenoids are believed to inhibit oxidative stress. We investigated the protective effect of lutein and egg yolk supplementation on systemic and retinal alterations in apolipoprotein E-deficient (apoE-/-) mice, an experimental model of hypercholesterolemia and cardiovascular disease. Three-month-old wild-type and apoE-/- mice received one of the following: vehicle, lutein (0.09 mg/kg per day) or egg yolk (0.8 g/kg per day), by gastroesophageal cannula for 3 months. Total cholesterol (TC), triacylglycerol (TG) and lipid peroxidation (TBARS) were measured in plasma. TBARS levels were also determined in retinal homogenates. Ultrastructural morphology was analyzed by electron microscopy. ApoE-/- mice, with increased TC and TG concentrations, had higher systemic (P<.05) and retinal (P<.01) levels of lipid peroxidation than wild-type strains. Electron microscopy showed ultrastructural alterations (basal laminar deposits, open intercellular junctions, increased cytoplasmic vacuoles) in the retinas from apoE-/- mice. Egg yolk significantly reduced plasma TG (P<.05) and, without changes in TC, decreased plasma lipid peroxidation (P<.05). Lutein supplementation marginally affected the parameters. Less severe retinal ultrastructural alterations were observed in apoE-/- mice receiving either egg yolk or lutein. In the apoE-/- mouse model, egg yolk improved the lipid profile and reduced systemic lipid peroxidation (P<.05). While lutein and egg yolk did not seem to reduce retinal lipid peroxidation, a reduction in retinal ultrastructural alterations was observed.

An ultrastructural study of the pathology of the retinal pigment epithelium, Bruch's membrane, and the choriocapillaris in the aged Fischer 344 rat

PURPOSE

The neural retinal degeneration in the aging Fischer 344 (F344) rat has been previously characterized. Here we describe the ultrastructural changes that occur in the retinal pigment epithelium (RPE), Bruch's membrane, and choriocapillaris in the periphery of the aged Fischer 344 rat.

METHODS

F344 eyes from 24-month-old animals (n = 4 animals, 8 eyes) were fixed and embedded for ultrastructural study. Serial mid-sagittal sections were taken from the superior peripheral retinas within 300 microm of the ora serrata. Pathology within the RPE, Bruch's membrane, and choriocapillaris was described.

RESULTS

Progressive changes were seen in the RPE/Bruch's/choriocapillaris complex, increasing anteriorly as the ora serrata was approached. Early pathology of the RPE included increased number of basal infoldings, increased number of phagolysosomes and lipofuscin deposits, attenuation, inclusion of vasculature, vesicle formation, and whirling extensions of the basement membrane into the cytoplasm. Bruch's membrane showed spots of considerable thinning, but most prominent was the nodular thickening. The choriocapillaris was found to have severe endothelial degeneration and transformation to fibrous tissue in the most severely affected regions. Lipofuscin was also found in areas of degenerated choriocapillaris.

CONCLUSIONS

Prior work focused on the neural retina, documented photoreceptor cell loss, and showed that Müller cell changes preceded that loss in the periphery of the F344 rat. It is now evident that the pathology in the RPE/Bruch's membrane/choriocapillaris complex may also be a critical component of the overall degenerative process. A possible mechanism for the extensive peripheral retinal degeneration in the F344 is presented.