The long-range goal of this study is to understand the biology of apolipoproteins in the retina, particularly the mechanism by which specific apoE isoforms may exert (or lack) neuroprotective effects. The immediate goal of this 2-year exploratory project is to develop and characterize the requisite genetically altered mouse strains to pursue the long-range goal. ApoE is a protein involved in cholesterol metabolism and transport. In the brain, the apoES isoform is thought to be neuroprotective and to play an important role in recovery following CNS injury. In contrast, the apoE4 isoform is a risk factor for dementias, such as Alzheimer's disease. Paradoxically, the exact opposite trend seems to prevail in age-related macular degeneration (AMD), where apoE4 correlates with reduced incidence of disease. The reason for this paradox remains a mystery, and will require appropriate new model systems to elucidate the molecular mechanisms involved. As a first step toward that goal, we will develop novel mouse strains and assess whether apoE can modulate the severity and time course of hereditary retinal degeneration in an isoform-specific manner. Mutant mice harboring the rds (retinal degeneration slow) mutation and lacking the apoE gene will be cross-bred with mice that selectively express either the human apoES or apoE4 isoform. Genotype will be confirmed by PCR. ApoE expression will be assessed as a function of age using Western blot analysis and immunocytochemistry, in comparison with age-matched rds and non-transgenic (wild-type) control mice. Retinal degeneration will be assessed by light and electron microscopy; retinal function will be assessed by electroretinography (ERG). The clinical relevance of this study lies in the potential to modulate the expression of neuroprotective isoforms of apoE in the retina as a novel therapy to retard or ameliorate human retinal degenerations of various origins. As such, this project has the potential to impact several aspects of the NEI's mission: to help prevent and treat eye diseases and other disorders of vision; reduce visual impairment and blindness; improve the quality of life for people of all ages; and advance our knowledge of how the visual system functions in health and disease.
