The role of secretory autophagy and exosomes in the accumulation of drusen during the development of age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is the most common disease of the elderly that leads to the loss of sight. So far, no satisfactory therapy exists for this complex eye disease. The appearance of extracellular deposits, called drusen, on the outside of the retinal pigment epithelium (RPE) is considered to be the main clinical hallmark of AMD. Whilst the mechanisms of drusen formation are not well known, secreted material from the RPE, during its degeneration, is thought to contribute to the development of AMD. Various unconventional protein secretion (UPS) pathways are considered to be routes for the delivery of material which form the drusen. The two main forms of UPS are secretory autophagy, which is responsible for the cleansing of cellular debris from the RPE cells and endosomal secretion which carries material outside of the cell via exosomes. These pathways are unconventional in the sense that they comprise the delivery of material to the exterior of cells by bypassing the Golgi apparatus. Although secretory autophagy and exosome release are regarded as different routes by which cells exude material, they share similarities, such as common molecular participants and that their routes converge. Therefore, manipulation of these two processes might be useful in a therapy against AMD by diminishing the destructive drusen progression in the vicinity of the RPE.