Crosstalk between Hsp70 molecular chaperone, lysosomes and proteasomes in autophagy‐mediated proteolysis in human retinal pigment epithelial cells

Abstract

Abstract Purpose The pathogenesis of age‐related macular degeneration involves chronic oxidative stress, impaired degradation of membranous discs shed from photoreceptor outer segments and accumulation of lysosomal lipofuscin in retinal pigment epithelial (RPE) cells. It has been estimated that a major part of cellular proteolysis occurs in proteasomes, however the importance of proteasomes and the other proteolytic pathways including autophagy in RPE cells are poorly understood. In the present study the role of Hsp70 molecular chaperones, proteasomal and lysosomal proteolytic pathways were evaluated in human RPE cells (ARPE‐19). Methods The Hsp70 and ubiquitin protein levels and localization were analyzed by western blotting and immunofluorescense. Confocal and transmission electron microscopy were used to detect cellular organelles and to evaluate morphological changes. Results The proteasome inhibition evoked the accumulation of perinuclear lysosomal vesicles/residual bodies positive for ubiquitin and the lysosomal membrane protein LAMP‐2, and a robust accumulation of Hsp70 protein and ubiquitin‐protein conjugates. We found that the accumulation of lysosomal/residual bodies was reversible, a cessation of proteasome inhibition led to clearance of the deposits via a mechanism that probably includes autophagy. Conclusion We show novel connection of Hsp70 molecular chaperones, proteasomes and autophagy in regulation of protein turnover in human retinal pigment epithelial cells that may thus open new insights to understand degenerative processes in retina cell pathology.