title: The healing myocardium sequentially mobilizes two monocyte subsets with divergent and complementary functions.
abstract: Healing of myocardial infarction (MI) requires monocytes/macrophages. These mononuclear phagocytes likely degrade released macromolecules and aid in scavenging of dead cardiomyocytes, while mediating aspects of granulation tissue formation and remodeling. The mechanisms that orchestrate such divergent functions remain unknown. In view of the heightened appreciation of the heterogeneity of circulating monocytes, we investigated whether distinct monocyte subsets contribute in specific ways to myocardial ischemic injury in mouse MI. We identify two distinct phases of monocyte participation after MI and propose a model that reconciles the divergent properties of these cells in healing. Infarcted hearts modulate their chemokine expression profile over time, and they sequentially and actively recruit Ly-6C(hi) and -6C(lo) monocytes via CCR2 and CX(3)CR1, respectively. Ly-6C(hi) monocytes dominate early (phase I) and exhibit phagocytic, proteolytic, and inflammatory functions. Ly-6C(lo) monocytes dominate later (phase II), have attenuated inflammatory properties, and express vascular-endothelial growth factor. Consequently, Ly-6C(hi) monocytes digest damaged tissue, whereas Ly-6C(lo) monocytes promote healing via myofibroblast accumulation, angiogenesis, and deposition of collagen. MI in atherosclerotic mice with chronic Ly-6C(hi) monocytosis results in impaired healing, underscoring the need for a balanced and coordinated response. These observations provide novel mechanistic insights into the cellular and molecular events that regulate the response to ischemic injury and identify new therapeutic targets that can influence healing and ventricular remodeling after MI.
authors.affiliation: Center for Systems Biology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.
authors.forename: Matthias
authors.initials: M
authors.lastname: Nahrendorf
authors.forename: Filip K
authors.initials: FK
authors.lastname: Swirski
authors.forename: Elena
authors.initials: E
authors.lastname: Aikawa
authors.forename: Lars
authors.initials: L
authors.lastname: Stangenberg
authors.forename: Thomas
authors.initials: T
authors.lastname: Wurdinger
authors.forename: Jose-Luiz
authors.initials: JL
authors.lastname: Figueiredo
authors.forename: Peter
authors.initials: P
authors.lastname: Libby
authors.forename: Ralph
authors.initials: R
authors.lastname: Weissleder
authors.forename: Mikael J
authors.initials: MJ
authors.lastname: Pittet
mesh_terms: D000818:Animals; D005434:Flow Cytometry; D006335:Heart Injuries / Q000503:physiopathology*; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000145:classification / Q000502:physiology*; D009203:Myocardial Infarction / Q000503:physiopathology*; D009504:Neutrophils / Q000502:physiology*; D013997:Time Factors; D014945:Wound Healing