title: Alternatively activated macrophages regulate extracellular levels of the hormone placental lactogen via receptor-mediated uptake and transcytosis.
abstract: Alternatively activated (M2) macrophages regulate immune responses and tissue remodelling. In many tissues including placenta, M2 express stabilin-1, a multidomain protein that exerts a dual role as a scavenger receptor for acetylated low density lipoprotein (acLDL) and SPARC (secreted protein acidic and rich in cysteine) and as an intracellular cargo carrier for SI-CLP. Using yeast two-hybrid screening, we identified the developmental hormone placental lactogen (PL) as a novel ligand of stabilin-1. In Chinese hamster ovary-stabilin-1 cells and M2, FACS and confocal microscopy demonstrated that stabilin-1 mediates internalization and endosomal sorting of PL. In M2 macrophages, PL was partially degraded in lysosomes; part of PL escaped degradation and was delivered to novel PL+ storage vesicles lacking endosomal/lysosomal markers. During formation, PL+ vesicles underwent transient interaction with the trans-Golgi network (TGN). Upon placement of PL-loaded M2 into PL-free medium, PL was secreted into the supernatant. Leupeptin, an inhibitor of lysosomal hydrolases, reduced PL degradation, enhanced sorting of PL into the TGN/storage vesicle pathway and increased PL secretion. Thus, processing of PL in M2 macrophages occurs either by the classical lysosomal pathway or by a novel TGN-associated trans-secretory pathway. Macrophages isolated from human placental villi efficiently endocytosed PL-FITC and transported it to the storage vesicles. Our data show that extracellular PL levels are determined by uptake, degradation, storage, and release in M2. During pregnancy PL concentration reaches 10 microg/ml in maternal circulation and stays below 0.5 microg/ml in fetal circulation. We propose that stabilin-1-positive macrophages determine the difference in PL levels between maternal and fetal circulation.
authors.affiliation: Department of Dermatology, Venerology and Allergology, University Medical Centre Mannheim, Ruprecht-Karls University of Heidelberg, Germany. julia.kzhyshkowska@haut.ma.uni-heidelberg.de
authors.forename: Julia
authors.initials: J
authors.lastname: Kzhyshkowska
authors.forename: Alexei
authors.initials: A
authors.lastname: Gratchev
authors.forename: Christina
authors.initials: C
authors.lastname: Schmuttermaier
authors.forename: Heike
authors.initials: H
authors.lastname: Brundiers
authors.forename: Liis
authors.initials: L
authors.lastname: Krusell
authors.forename: Srinivas
authors.initials: S
authors.lastname: Mamidi
authors.forename: Jingjing
authors.initials: J
authors.lastname: Zhang
authors.forename: Gail
authors.initials: G
authors.lastname: Workman
authors.forename: E Helene
authors.initials: EH
authors.lastname: Sage
authors.forename: Christine
authors.initials: C
authors.lastname: Anderle
authors.forename: Peter
authors.initials: P
authors.lastname: Sedlmayr
authors.forename: Sergij
authors.initials: S
authors.lastname: Goerdt
mesh_terms: D000818:Animals; D016466:CHO Cells; D015816:Cell Adhesion Molecules, Neuronal / Q000097:blood / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004705:Endocytosis / Q000235:genetics / Q000276:immunology*; D011992:Endosomes / Q000276:immunology / Q000378:metabolism; D005110:Extracellular Space / Q000276:immunology / Q000378:metabolism*; D005260:Female; D006801:Humans; D008024:Ligands; D008262:Macrophage Activation / Q000235:genetics / Q000276:immunology; D008264:Macrophages / Q000145:classification / Q000378:metabolism*; D008431:Maternal-Fetal Exchange / Q000276:immunology; D021041:Placental Circulation / Q000276:immunology; D010928:Placental Lactogen / Q000096:biosynthesis / Q000097:blood / Q000378:metabolism*; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000097:blood / Q000235:genetics / Q000502:physiology; D016201:Receptors, Lymphocyte Homing / Q000097:blood / Q000235:genetics / Q000502:physiology*; D014162:Transfection
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D008024:Ligands; D011257:Pregnancy Proteins; D016201:Receptors, Lymphocyte Homing; C449926:STAB1 protein, human; D010928:Placental Lactogen