Xanthophylls in the Retina of the Eye
Research project objectives/Hypothesis
Advanced molecular spectroscopy and imaging techniques will be applied (e.g. Fluorescence Lifetime Imaging Microscopy, Raman Imaging) in studies of xanthophyll-containing model lipid membranes and natural membranes of the retina. The main objective of the project is unveiling and understanding molecular mechanisms associated with the physiological activity of xanthophyll pigments, lutein, zeaxanthin, and meso-zeaxanthin, that are highly concentrated in the yellow spot of the retina of the human eye. The research will contribute to the understanding of etiology and prevention against AMD (age-related macular degeneration). The project is focused around three main hypotheses:
- The xanthophylls in the retina of the eye respond to increasing ight intensity by increase in the light absorption cross-section. This means that blue light filtering effect in the retina is dynamically modulated in response to the light intensity.
- An increase in the absorption cross-section of membrane bound xanthophylls is realized via xantophyll reorientation within the membrane, potentiated by a light-driven trans-to-cis molecular reconfiguration. Importantly, central cis xanthophylls substantially increase light absorption cross-section in the UV spectral region.
- Specific xanthophyll-binding proteins in the retina of the eye act permeanently as “isomerases” catalyzing the back cis-to-trans molecular reconfiguration of the macular xantophylls.
The research planned in this project is divided into five work packages. The first focuses on imaging of macula lutea tissues prepared post-mortem from the retina of human donor eyeballs with the application of Fluorescence Lifetime Imaging Microscopy (FLIM) and Raman imaging microscopy. Second, a detailed examination of the process of lutein and zeaxanthin photo-isomerization and related light-induced xanthophyll reorientation in single lipid bilayer systems composed of various lipid components, giving rise to different thickness of the hydrophobic core of the membrane and fluidity. These analyses will be performed with the application of Raman microscopy (supplemented with principle component analysis), FLIM, and fluorescence anisotropy determination and imaging. A strong focus will be put on mimicking retinal membranes with the lipid systems. The next work package is dedicated to molecular dynamic simulation of molecular organization and orientation of lutein and zeaxanthin in the all-trans, 9-cis, 15-15’-cis in lipid bilayer membranes at different lipid composition and different physical states. This research will be conducted under the supervision of our partner in the project Dr Jacek Czub, who is an expert in molecular dynamics of biomolecules embedded in lipid membranes. Another work package revolves around the examination of putative cis-to-trans isomerase enzymatic activity of the specific xanthophyll-binding proteins, GSTP1 in the case of zeaxanthin and StARD3 in the case of lutein. The last work package will examine the protective activity of lutein and zeaxanthin, based on singlet oxygen quenching, in a model lipid membrane system (GUV) and in natural tissues of the retina.
Research project impact
The planned research will provide answers for the hypothesis about the dynamic adjustment of blue-light-filtering photoprotective activity of the macular xanthophylls, in response to light intensity. Also, the project should unveil detailed photophysical and molecular mechanisms associated with the activity of xanthophyll’s in photoprotection of lipid-protein membranes of the retina of the eye.
Pioneering nature of the research project
Information on the role of retina xanthophylls will provide crucial information in the treatment and development of therapies for age-related macular degeneration.