title: Nonclassical resident macrophages are important determinants in the development of myocardial fibrosis.
abstract: Macrophages are increasingly recognized as a potential therapeutic target in myocardial fibrosis via interactions with fibroblasts. We have characterized macrophage depletion and inhibition of nonclassical macrophage migration, in addition to direct interactions between nonclassical macrophages and fibroblasts in angiotensin II (AngII)-mediated, hypertensive myocardial fibrosis. Macrophage depletion was achieved by daily i.v. clodronate liposomes (-1 day to +3 days) during AngII infusion. Cx3cr1(-/-) mice were used to inhibit nonclassical macrophage migration. Macrophage phenotype (F4/80, CD11b, Ly6C) was characterized by immunofluorescence and flow cytometry. Collagen was assessed by Sirius Red/Fast Green. Quantitative real-time RT-PCR was performed for transcript levels. AngII/wild-type (WT) mice displayed significant infiltrate and fibrosis compared with saline/WT, which was virtually ablated by clodronate liposomes independent of hypertension. In vitro data supported M2 macrophages promoting fibroblast differentiation and collagen production. AngII/Cx3cr1(-/-) mice, however, significantly increased macrophage infiltrate and fibrosis relative to AngII/WT. AngII/Cx3cr1(-/-) mice also showed an M1 phenotypic shift relative to WT mice in, which the predominant phenotype was Ly6C(low), CD206(+) (M2). Myocardial IL-1β was significantly up-regulated, whereas transforming growth factor β down-regulated with this M1 shift. We demonstrated that infiltrating macrophages are critical to AngII-mediated myocardial fibrosis by preventing the development of fibrosis after liposomal depletion of circulating monocytes. Our findings also suggest that some macrophages, namely M2, may confer a protective myocardial environment that may prevent excessive tissue injury.
authors: Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Alec
authors: A
authors: Falkenham
authors: Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Roberto
authors: R
authors: de Antueno
authors: Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Nicole
authors: N
authors: Rosin
authors: Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Devin
authors: D
authors: Betsch
authors: Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada; Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada; Department of Surgery, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Timothy D G
authors: TD
authors: Lee
authors: Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors: Roy
authors: R
authors: Duncan
authors: Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada; Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada; Department of Surgery, Dalhousie University, Halifax, Nova Scotia, Canada. Electronic address: jean.legare@cdha.nshealth.ca.
authors: Jean-Francois
authors: JF
authors: Légaré
mesh_terms: D000199:Actins / Q000378:metabolism; D061605:Administration, Intravenous; D000804:Angiotensin II / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D000950:Antigens, Ly / Q000378:metabolism; D000073883:CX3C Chemokine Receptor 1; D004002:Clodronic Acid / Q000008:administration & dosage / Q000494:pharmacology; D003094:Collagen / Q000096:biosynthesis; D004562:Electrocardiography; D005355:Fibrosis; D018836:Inflammation Mediators / Q000378:metabolism; D008081:Liposomes / Q000008:administration & dosage / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D041681:NIH 3T3 Cells; D019707:Receptors, Chemokine / Q000172:deficiency / Q000378:metabolism
chemical_list: D000199:Actins; D000950:Antigens, Ly; D000073883:CX3C Chemokine Receptor 1; C471885:Cx3cr1 protein, mouse; D018836:Inflammation Mediators; D008081:Liposomes; C494192:Ly-6C antigen, mouse; D019707:Receptors, Chemokine; C544013:alpha-smooth muscle actin, mouse; D004002:Clodronic Acid; D000804:Angiotensin II; D003094:Collagen