Clearance of dying cells in the retina ‐ relevance to age‐related macula degeneration

Abstract

Abstract Purpose The retina is the place with the highest daily phagocytic turnover in the whole human body. Besides photoreceptor outer segments, retinal pigment epithelial (RPE) cells can engulf other dying cells as well (epithelial, neural, etc.). Failure to do so may result in accumulation of debris that could lead to development of age‐related macula degeneration (AMD). The in vitro dynamics of this clearance process can be modelled using human ARPE‐19 cells and macrophages. Methods Different death patterns were induced in vitro in ARPE‐19 cells: death through detachment from the extracellular matrix on polyHEMA coated surfaces known as anoikis, UV induced apoptosis and Argon‐laser induced necrosis. Two‐colored phagocytic assays were carried out where different phagocytes (living ARPE‐19 cells or human macrophages) engulfed different dying cells. Flow cytometry (FACS Calibur), fluorescent and time‐lapse microscopy (the later not shown) were used to quantify and visualize the phagocytic process. Results The clearance of the anoikic ARPE‐19 cells by the living ARPE‐19 cells (serving as a model for dry AMD) over 8 hours of co‐incubation proved efficient and increasing over time (at 8 hours, over 50% of the phagocytes contained engulfed anoikic ARPE‐19 cells inside). The human macrophages could also engulf the anoikic ARPE‐19 cells (serving as a model for wet AMD), although less efficiently at five times lower rate over the same period. Conclusion The clearance of the different dying ARPE‐19 cells can serve as a good in vitro model for studying AMD, both dry and wet type, as well as for testing different immunological and pharmacological aspects affecting this process.