Genetic Risk Models in Age-Related Macular Degeneration

Genetische Risiken und Therapieentwicklung bei Netzhautdegenerationen

Das Wissen um die genetischen Ursachen von Netzhautdegenerationen, ob monogen oder komplex, ist eine wichtige Voraussetzung, um grundlegende physiologische Prozesse der Krankheitsentwicklung zu verstehen und darauf aufbauend eine individualisierte, präzise auf den Patienten zugeschnittene Therapie entwickeln zu können. Diese Übersicht fasst zunächst den gegenwärtigen Wissensstand der Genetik von erblichen Netzhautdystrophien und von komplexen retinalen Degenerationen zusammen. Hieraus lassen sich ursächliche Mechanismen und molekulare Pathologien des klinisch und genetisch heterogenen Krankheitsbildes der Netzhautdegenerationen ableiten. Aufbauend auf diesen Kenntnissen lässt sich schließlich die Rolle der Genetik in der Therapieentwicklung beleuchten, die wesentlich die große Vielfalt von therapeutischen Strategien in diesem Bereich begründet. In weiteren Artikeln dieses Schwerpunktheftes werden solche Therapiestrategien an ausgewählten Beispielen veranschaulicht.

A decade of age-related macular degeneration risk models: What have we learned from them and where are we going?

The genomic revolution has revealed the complexity of multifactorial diseases, making the development of effective diagnostics extremely challenging. In turn, the prospect of precision medicine as applied through targeted therapeutic treatments continues to remain largely elusive. Age-related macular degeneration (AMD) as a complex disease falls under this category, despite it being one of the most well characterized multifactorial diseases. This reflects both the extent of identified genetic components and known environmental risk factors. Additional considerations in dissecting out the roles played by genetic and non-genetic risk factors arise through the rapid increase in prevalence of AMD with age and the varying time periods over which disease progression can occur, complicating efforts to discriminate between "progressors" and non-"progressors." As a consequence, extensive research into the aetiology of AMD is yet to realize a clinically acceptable predictive test. This review covers the current climate of risk models in late AMD but will focus mainly on genetic risk factors as well as the types of models that have currently been employed in the AMD modelling literature.

The genetics of age-related macular degeneration (AMD)--Novel targets for designing treatment options?

Age-related macular degeneration (AMD) is a progressive disease of the central retina and the main cause of legal blindness in industrialized countries. Risk to develop the disease is conferred by both individual as well as genetic factors with the latter being increasingly deciphered over the last decade. Therapeutically, striking advances have been made for the treatment of the neovascular form of late stage AMD while for the late stage atrophic form of the disease, which accounts for almost half of the visually impaired, there is currently no effective therapy on the market. This review highlights our current knowledge on the genetic architecture of early and late stage AMD and explores its potential for the discovery of novel, target-guided treatment options. We reflect on current clinical and experimental therapies for all forms of AMD and specifically note a persisting lack of efficacy for treatment in atrophic AMD. We further explore the current insight in AMD-associated genes and pathways and critically question whether this knowledge is suited to design novel treatment options. Specifically, we point out that known genetic factors associated with AMD govern the risk to develop disease and thus may not play a role in its severity or progression. Treatments based on such knowledge appear appropriate rather for prevention than treatment of manifest disease. As a consequence, future research in AMD needs to be greatly focused on approaches relevant to the patients and their medical needs.

Iron-induced Local Complement Component 3 (C3) Up-regulation via Non-canonical Transforming Growth Factor (TGF)-β Signaling in the Retinal Pigment Epithelium

Dysregulation of iron homeostasis may be a pathogenic factor in age-related macular degeneration (AMD). Meanwhile, the formation of complement-containing deposits under the retinal pigment epithelial (RPE) cell layer is a pathognomonic feature of AMD. In this study, we investigated the molecular mechanisms by which complement component 3 (C3), a central protein in the complement cascade, is up-regulated by iron in RPE cells. Modulation of TGF-β signaling, involving ERK1/2, SMAD3, and CCAAT/enhancer-binding protein-δ, is responsible for iron-induced C3 expression. The differential effects of spatially distinct SMAD3 phosphorylation sites at the linker region and at the C terminus determined the up-regulation of C3. Pharmacologic inhibition of either ERK1/2 or SMAD3 phosphorylation decreased iron-induced C3 expression levels. Knockdown of SMAD3 blocked the iron-induced up-regulation and nuclear accumulation of CCAAT/enhancer-binding protein-δ, a transcription factor that has been shown previously to bind the basic leucine zipper 1 domain in the C3 promoter. We show herein that mutation of this domain reduced iron-induced C3 promoter activity. In vivo studies support our in vitro finding of iron-induced C3 up-regulation. Mice with a mosaic pattern of RPE-specific iron overload demonstrated co-localization of iron-induced ferritin and C3d deposits. Humans with aceruloplasminemia causing RPE iron overload had increased RPE C3d deposition. The molecular events in the iron-C3 pathway represent therapeutic targets for AMD or other diseases exacerbated by iron-induced local complement dysregulation.

Nutritional supplements in age-related macular degeneration

Age-related macular degeneration (AMD) is the most frequent cause of blindness in the Western World. While with new therapies that are directed towards vascular endothelial growth factor (VEGF), a potentially efficient treatment option for the wet form of the disease has been introduced, a therapeutic regimen for dry AMD is still lacking. There is evidence from several studies that oral intake of supplements is beneficial in preventing progression of the disease. Several formulations of micronutrients are currently available. The present review focuses on the role of supplements in the treatment and prevention of AMD and sums up the current knowledge about the most frequently used micronutrients. In addition, regulatory issues are discussed, and future directions for the role of supplementation in AMD are highlighted.