Characterization of a novel mouse model for deletion of a floxed gene in alternatively activated macrophages

Abstract

Abstract V-maf musculoaponeurotic fibrosarcoma oncogene family, protein B (MafB) promoter has been identified as macrophage-specific promoter, but it has never been characterized for pulmonary macrophages. Therefore, we hypothesized that MafB-driven Cre Recombinase expression will allow recombination in alveolar macrophages that contain floxed alleles. MafB-Cre+/− \Rosa-mTOMFlox/Flox/mEGFP (MafB-EGFP) mice was generated by crossbreeding MafB-Cre+/+ and Rosa-mTOMFlox/Flox/mEGFP parents. To determine the extent of macrophage-specific gene recombination, we performed bronchoalveolar lavage, fluorescent microscopy, and flow cytometry on BALF and lung digest of 42 days old MafB-EGFP mice. In addition, we assess the beneficial effect of in vitro and in vivo macrophage activation on recombination efficiency. Flow cytometry analyses on macrophages from MafB-EGFP offspring revealed that: 1) only 30–40% of the alveolar macrophages are amenable to the Cre-Lox mediated recombination, 2) majority of bone marrow-derived macrophages are amenable to the Cre-Lox mediated recombination, 3) Classical activation status did not affect the Cre-Lox recombination efficiency in freshly cultured alveolar macrophages. However, the alternative activation increased the recombination efficiency to ~80–90% in cultured alveolar macrophages. Intratracheal IL-33 treatment of MafB-EGFP mice also increased Cre-Lox mediated recombination of alveolar macrophages to ~80%. Our data suggest that while MafB-EGFP mice do not allow Cre-Lox recombination in the homeostatic lung and inflamed lungs with classically activated macrophages, these mice allow significant recombination in alternatively activated macrophages. Supported by NIEHS (R01, ES030125)