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A1051 - Deletion of Cannabinoid Receptor 1 (CB1R) in Myeloid Cells Prevents the Progression of Bleomycin-Induced Pulmonary Fibrosis in Mice
Author Block: N. J. Coffey1, J. K. Park1, T. Jourdan1, T. Yokoyama2, W. A. Gahl2, M. V. Malicdan2, R. Cinar1, G. Kunos1; 1Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, Rockville, MD, United States, 2Medical Genetics Branch, National Human Genome Research Institute, Bethesda, MD, United States.
RATIONALE: Pulmonary fibrosis (PF) is a chronic and deadly disease characterized by scarring of lung tissue. While its pathophysiology involves complex, multicellular interactions, the contribution of distinct cell populations to disease progression is not well understood. Recently, CB1R has emerged as a contributor to PF (Cinar et al., JCI Insight 2017 2(8):92281). Distinct cell populations of the lung, including macrophages, have been found to express CB1R, but the specific contribution of CB1R in myeloid cells to fibrosis progression has not been explored. Here we explored the potential pathogenic role of CB1R on myeloid cells in PF and the relationship between CB1R signaling and alveolar macrophage (AM) activation in the context of bleomycin-induced PF.
METHODS: PF was induced in wild-type (WT), Cnr1-/-, and myeloid cell-specific Cnr1-/- (myCnr1-/-) mice on a C57BL/6J background at 6-months of age by intratracheal instillation of bleomycin. Disease severity was assessed by gene expression profile, hydroxyproline content, and histological staining of lung tissue collected 14 days after bleomycin administration. Bronchoalveolar lavage fluid (BALF) was collected to investigate infiltrating immune cells and AMs phenotype by flow cytometry.
RESULTS: Compare to WT mice, the development of PF and associated weight loss was fully prevented in Cnr1-/- mice and partially attenuated in myCnr1-/- mice. Bleomycin induced similar increases in total BAL cell number in WT, Cnr1-/- and myCnr1-/- mice, but infiltration of GR1+neutrophils and CD19+, CD8a+ and CD4+ lymphocytes was almost completely absent in both Cnr1-/- and myCnr1-/- mice. In addition, deletion of Cnr1 globally or only in myeloid cells similarly attenuated the activation status of AMs following bleomycin treatment, as quantified by CD11b and CD206 cell surface expression intensity. Furthermore, bleomycin-induced elevated gene expressions of interferon regulatory factor 5 (IRF5) and chemokine (C-X-C motif) ligand 13 (CXCL13) in WT mice were similarly attenuated in Cnr1-/- and myCnr1-/- mice.
CONCLUSION: Activation of myeloid CB1Rs exacerbates fibrosis progression in bleomycin-induced PF in mice, and deletion of Cnr1 in myeloid cells prevents fibrosis progression. Notably, myeloid CB1Rs regulate AM phenotype and functionality by inducing a pro-inflammatory state after lung injury through increased expression of IRF5. Additionally, myeloid CB1Rs control the infiltration of lymphocytes and neutrophils by regulating their chemoattractant production. These findings establish myeloid CB1R as a therapeutic target in fibrosis, which could be engaged by peripherally restricted CB1R antagonists for therapeutic benefit, while minimizing the risk of central nervous system side effects that plague the use of globally acting antagonists.