Autophagy in the eye: implications for ocular cell health

Autophagy, a catabolic process by which a cell "eats" itself, turning over its own cellular constituents, plays a key role in cellular homeostasis. In an effort to maintain normal cellular function, autophagy is often up-regulated in response to environmental stresses and excessive organelle damage to facilitate aggregated protein removal. In the eye, virtually all cell types from those comprising the cornea in the front of the eye to the retinal pigment epithelium (RPE) providing a protective barrier for the retina at the back of the eye, rely on one or more aspects of autophagy to maintain structure and/or normal physiological function. In the lens autophagy plays a critical role in lens fiber cell maturation and the formation of the organelle free zone. Numerous studies delineating the role of Atg5, Vsp34 as well as FYCO1 in maintenance of lens transparency are discussed. Corneal endothelial dystrophies are also characterized as having elevated levels of autophagic proteins. Therefore, novel modulators of autophagy such as lithium and melatonin are proposed as new therapeutic strategies for this group of dystrophies. In addition, we summarize how corneal Herpes Simplex Virus (HSV-1) infection subverts the cornea's response to infection by inhibiting the normal autophagic response. Using glaucoma models we analyze the relative contribution of autophagy to cell death and cell survival. The cytoprotective role of autophagy is further discussed in an analysis of photoreceptor cell heath and function. We focus our analysis on the current understanding of autophagy in photoreceptor and RPE health, specifically on the diverse role of autophagy in rods and cones as well as its protective role in light induced degeneration. Lastly, in the RPE we highlight hybrid phagocytosis-autophagy pathways. This comprehensive review allows us to speculate on how alterations in various stages of autophagy contribute to glaucoma and retinal degenerations.