This is a revised competitive renewal of a long-standing grant to understand the cellular basis for the formation of human age-related nuclear cataracts, the most common form of human cataract and a leading cause of worldwide blindness. In the last granting period significant progress was made in characterizing damage to fiber cell membranes, the distribution of crystallins in fiber cell cytoplasm and unique spherical particles containing a core of cytoplasm covered by multiple lipid bilayers, termed multi-lamellar bodies. Noteworthy contributions were made to the field by providing theoretical analyses of the predicted scattering from each type of cellular damage. These studies have led to an important modification to commonly held proposal that nuclear cataracts are caused by protein clumping into high molecular weight aggregates. Our results suggest that the fiber cell ultrastructure of early stage nuclear cataracts is nearly identical to aged transparent lenses, suggesting that initial protein modifications and associations are part of the natural aging process. Only after extensive protein modification in advanced cataracts from India, has it been possible to identify potential HMW aggregates using electron tomography. Our results suggest that multi-lamellar bodies make a major contribution to forward scatter that interferes with normal image formation at the fovea and this contribution to visual impairment increases with age and accumulation of cell damage caused mainly by oxidative stress. We propose to expand our ultrastructural studies employing scanning and transmission electron microscopy, electron tomography, cryo-electron microscopy and confocal/multi-photon light microscopy to characterize cellular damage in a variety of nuclear cataracts that can be compared to age-related nuclear cataracts. Improved preservation and resolution will yield valuable new information about the age-related transformations of crystallins and their associations with membranes. Quantitative structural data will be analyzed theoretically to evaluate their predicted contribution to lens scattering. Ou recent evidence shows, for the first time, that autophagy and mitophagy occur in the lens and that autophagy is most likely the source of multi-lamellar bodies. We propose to explore multi-lamellar body formation in humans of varying ages and in chick embryonic lenses as an animal model that will allow identification and regulation of genes involved in autophagy. Autophagy is enhanced by nutritional stress that could be important during early lens development. These ultrastructural studies and theoretical analyses are expected to lead to better understanding of the mechanisms of cell damage that produce excessive light scattering in nuclear cataract formation.
Cataracts are a major source of visual impairment throughout the world. Many patients can be effectively treated with surgery, although services may not be available or affordable. Moreover, the aging population is developing new cataracts at a significant rate. This research supports the search for the underlying cellular damage that leads to age-related cataracts and alternative treatment strategies for preventing or delaying the progression of cataracts.
