Collagen VI assemblies in age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of incurable blindness in the developed world. Little is known about the pathogenesis of this condition, but deposits in Bruch's membrane and immediately beneath the retinal pigment epithelium are frequent findings associated with this disease. Within these deposits, molecular assemblies with an approximately 100-nm axial periodicity are seen. Two types of assembly are present: one exhibiting transverse double bands of protein density that are 30nm apart and repeat axially every approximately 100nm; the other with transverse double bands of protein density, 30nm apart and repeating axially every approximately 50nm. In this second type of assembly, more prominent pairs of bands alternate with less prominent ones. By comparison with analogous aggregates found in the vitreous of a patient with a full-thickness macular hole, collagen VI was singled out as the most probable protein constituent of the AMD aggregates. Possible models for the aggregation patterns of these assemblies are discussed in terms of collagen VI dimers and tetramers. Understanding the structure and chemical composition of the assemblies within the AMD basal deposits may prove of great help in understanding the pathophysiology of AMD itself.