title: Physiologically aged red blood cells undergo erythrophagocytosis in vivo but not in vitro.
abstract: BACKGROUND
  The lifespan of red blood cells is terminated when macrophages remove senescent red blood cells by erythrophagocytosis. This puts macrophages at the center of systemic iron recycling in addition to their functions in tissue remodeling and innate immunity. Thus far, erythrophagocytosis has been studied by evaluating phagocytosis of erythrocytes that were damaged to mimic senescence. These studies have demonstrated that acquisition of some specific individual senescence markers can trigger erythrophagocytosis by macrophages, but we hypothesized that the mechanism of erythrophagocytosis of such damaged erythrocytes might differ from erythrophagocytosis of physiologically aged erythrocytes.
  
  
  METHODS
  To test this hypothesis we generated an erythrocyte population highly enriched in senescent erythrocytes by a hypertransfusion procedure in mice. Various erythrocyte-aging signals were analyzed and erythrophagocytosis was evaluated in vivo and in vitro.
  
  
  RESULTS
  The large cohort of senescent erythrocytes from hypertransfused mice carried numerous aging signals identical to those of senescent erythrocytes from control mice. Phagocytosis of fluorescently-labeled erythrocytes from hypertransfused mice injected into untreated mice was much higher than phagocytosis of labeled erythrocytes from control mice. However, neither erythrocytes from hypertransfused mice, nor those from control mice were phagocytosed in vitro by primary macrophage cultures, even though these cultures were able to phagocytose oxidatively damaged erythrocytes.
  
  
  CONCLUSIONS
  The large senescent erythrocyte population found in hypertransfused mice mimics physiologically aged erythrocytes. For effective erythrophagocytosis of these senescent erythrocytes, macrophages depend on some features of the intact phagocytosing tissue for support.
authors.affiliation: Laboratory for Molecular Nutrition, Faculty of Biotechnology and Food Engineering. Technion. Technion City, Haifa, Israel.
authors.forename: Yehonatan
authors.initials: Y
authors.lastname: Gottlieb
authors.forename: Orit
authors.initials: O
authors.lastname: Topaz
authors.forename: Lyora A
authors.initials: LA
authors.lastname: Cohen
authors.forename: Liat David
authors.initials: LD
authors.lastname: Yakov
authors.forename: Tom
authors.initials: T
authors.lastname: Haber
authors.forename: Abigail
authors.initials: A
authors.lastname: Morgenstern
authors.forename: Avital
authors.initials: A
authors.lastname: Weiss
authors.forename: Karen
authors.initials: K
authors.lastname: Chait Berman
authors.forename: Eitan
authors.initials: E
authors.lastname: Fibach
authors.forename: Esther G
authors.initials: EG
authors.lastname: Meyron-Holtz
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000032:analysis; D019921:Biotinylation; D004905:Erythrocyte Aging / Q000502:physiology*; D017707:Erythrocyte Transfusion; D004912:Erythrocytes / Q000166:cytology / Q000502:physiology*; D004920:Erythropoiesis / Q000502:physiology; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007501:Iron / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010084:Oxidation-Reduction; D010587:Phagocytosis / Q000502:physiology*; D061251:Primary Cell Culture; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D015415:Biomarkers; D017382:Reactive Oxygen Species; D007501:Iron