Down-regulation of the forkhead transcription factor Foxp1 is required for monocyte differentiation and macrophage function

Abstract

Down-regulation of the forkhead transcription factor Foxp1 by integrin engagement controls monocyte differentiation in vitro. To determine whether Foxp1 plays a critical role in monocyte differentiation and macrophage functions in vivo, we generated transgenic mice (macFoxp1tg) overexpressing human FOXP1 in monocyte/macrophage lineage cells using the CD68 promoter. Circulating blood mono-cytes from macFoxp1tg mice have reduced expression of the receptor for macrophage colony-stimulating factor (c-Fms/M-CSFR), impaired migratory capacity, and diminished accumulation as splenic macrophages. Macrophage functions, including cytokine production, phagocytosis, and respiratory burst were globally impaired in macFoxp1tg compared with wild-type cells. Osteoclastogenesis and bone resorption activity were also attenuated in macFoxp1tg mice. In models of chemical and bacterial peritonitis, macFoxp1tg mice exhibited reduced mac-rophage accumulation, bacterial clearance, and survival. Enforced overexpression of c-Fms/M-CSFR reversed the cytokine production and phagocytosis defects in macFoxp1tg macrophages, indicating that repression of c-fms/M-CSFR is likely the dominant mechanism responsible for Foxp1 action in monocyte differentiation and macrophage function. Taken together, these observations identify down-regulation of Foxp1 as critical for monocyte differentiation and macrophage functions in vivo. © 2008 by The American Society of Hematology.