Abstract
Defective clearance of apoptotic cells has emerged as an important contributing factor to the pathogenesis of many diseases. Although many efforts have been made to understand the machinery involved in the recognition between phagocytes and potential targets, little is known about the intracellular transport of phagosomes containing apoptotic cells within mammalian cells. We have, therefore, performed a detailed study on the maturation of phagosomes containing apoptotic cells in a non-professional phagocytic cell line. This process was compared with the maturation of IgG-opsonized particles, which are internalized via the Fcγ-receptor (Fcγ-R), one of the best characterized phagocytic receptor, in the same cell line stably expressing the Fcγ-RIIA. By comparing markers from different stages of phagosome maturation, we have found that phagosomes carrying apoptotic particles reach the lysosomes with a delay compared to those containing IgG-opsonized particles. Enrichment of the apoptotic particles in phosphatidylserine (PS) neither changed the kinetics of their engulfment nor the maturation process of the phagosome.
Highlights
Phagocytosis is a complex cellular event by which large particles are actively recognized, engulfed and degraded
RBCs are very good phagocytic models since they offer many advantages compared to other cell types: 1) RBCs cannot bind to phagocytes without previous modification on their surface; 2) they are induced to undergo an apoptotic-like process, termed eryptosis, mimicking senescent cells; 3) the plasma membrane levels of PS can be manipulated by incubating the cells with PSliposomes; 4) RBCs can be opsonized with antibodies and used to study Fc-mediated phagocytosis; and 5) by applying a hypotonic shock the distinction between attached RBCs and those that have been internalized is done
Once the phagocytic models were characterized, we looked at the effect of PS loading in the outer leaflet of aged human red blood cells (agRBC) in binding and phagocytosis as a function of time in the smooth muscle cell line
Summary
Phagocytosis is a complex cellular event by which large particles are actively recognized, engulfed and degraded. The predominant focus has been on the role in host defense, this process plays a critical role in removal of apoptotic cells that is essential for tissue remodeling and homeostasis [1,2,3,4]. This is important in diseases such as atherosclerosis and neurodegenerative diseases. In both cases, professional phagocytes are not the only players involved. In atherosclerosis, SMCs represent the major phagocytic population in the vessel wall besides macrophages [5,6,7]
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