4.7 Article

Alveolar macrophage development in mice requires L-plastin for cellular localization in alveoli

Journal

BLOOD
Volume 128, Issue 24, Pages 2785-2796

Publisher

AMER SOC HEMATOLOGY
DOI: 10.1182/blood-2016-03-705962

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Funding

  1. Basil O'Connor Starter Scholar Award
  2. Basic Research Grant from the American Lung Association
  3. American Heart Association
  4. Children's Discovery Institute [MD-FR-2010-83]
  5. National Institutes of Health, National Institute of Allergy and Infectious Diseases [R01-AI104732]
  6. Hope Center Transgenic Vectors Core at WUSM
  7. Speed Congenics Facility of the Rheumatic Diseases Core Center
  8. National Institutes of Health, National Institute of Arthritis and Musculoskeletal and Skin Diseases [P30-AR048335]

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Alveolar macrophages are lung-resident sentinel cells that develop perinatally and protect against pulmonary infection. Molecular mechanisms controlling alveolar macrophage generation have not been fully defined. Here, weshowthat the actin-bundling protein L-plastin (LPL) is required for the perinatal development of alveolar macrophages. Mice expressing a conditional allele of LPL (CD11c.Cre(pos)-LPLfl/fl) exhibited significant reductions in alveolar macrophages and failed to effectively clear pulmonary pneumococcal infection, showing that immunodeficiency results from reduced alveolar macrophage numbers. We next identified the phase of alveolar macrophage development requiring LPL. In mice, fetal monocytes arrive in the lungs during a late fetal stage, maturing to alveolar macrophages through a prealveolar macrophage intermediate. LPL was required for the transition from prealveolar macrophages to mature alveolar macrophages. The transition from prealveolar macrophage to alveolar macrophage requires the upregulation of the transcription factor peroxisome proliferatoractivated receptor-gamma (PPAR-gamma), which is induced by exposure to granulocyte-macrophage colony-stimulating factor (GM-CSF). Despite abundant lung GM-CSF and intact GM-CSF receptor signaling, PPAR-gamma was not sufficiently upregulated in developing alveolar macrophages in LPL-/- pups, suggesting that precursor cells were not correctly localized to the alveoli, where GM-CSF is produced. We found that LPL supports 2 actin-based processes essential for correct localizationof alveolar macrophage precursors: (1) transmigration into the alveoli, and (2) engraftment in the alveoli. We thus identify a molecular pathway governing neonatal alveolar macrophage development and show that genetic disruption of alveolar macrophage development results in immunodeficiency.

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