Autophagy
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Studies on human and animal models of retinal dystrophy have suggested that apoptosis may be the common pathway of photoreceptor cell death. Autophagy, the major cellular degradation process in animal cells, is important in normal development and tissue remodeling, as well as under pathological conditions. Previously we provided evidence that genes, whose products are involved in apoptosis and autophagy, may be coexpressed in photoreceptors undergoing degeneration. ⋯ In summary, the study first suggests that autophagy participates in photoreceptor cell death possibly by initiating apoptosis. Second, it confirms that cells that normally die by apoptosis will execute cell death by necrosis if the normal pathway is blocked. And third, these results argue that the up-stream regulators of autophagy need to be identified as potential therapeutic targets in photoreceptor degeneration.
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Chaperone-mediated autophagy (CMA) is a lysosomal pathway of proteolysis that is responsible for the degradation of 30% of cytosolic proteins under conditions of prolonged nutrient deprivation. Molecular chaperones in the cytosol and in the lysosomal lumen stimulate this proteolytic pathway. The molecular chaperones in the cytosol unfold substrate proteins prior to their translocation across the lysosomal membrane, while the chaperone in the lysosomal lumen is probably required to pull the substrate protein across the lysosomal membrane. ⋯ The reduced CMA in aging is due to reduced LAMP-2A in the lysosomal membrane. This reduction is caused by an age-related increased degradation of LAMP-2A and an age-related reduced ability of LAMP-2A to reinsert into the lysosomal membrane. These findings reveal a rich complexity of mechanisms to control CMA activity.