Analysis of the impact of CSF-1 administration in adult rats using a novel Csf1r-mApple reporter gene

Abstract

Macrophages are present in large numbers in every tissue in the body where they play critical roles in development and homeostasis. They exhibit remarkable phenotypic and functional diversity, underpinning their adaptation to specialized roles in each tissue niche. CSF1, signaling through the CSF1 Receptor (CSF1R), which is restricted to monocytemacrophage lineage cells in adults, is a critical growth factor controlling macrophage proliferation, differentiation and many aspects of mature macrophage function. We have generated a macrophage reporter rat, utilizing a construct containing elements of the mouse Csf1r promoter and the highly conserved Fms intronic regulatory element (FIRE) to drive mApple fluorescent protein expression. Csf1r-mApple was robustly expressed in monocytemacrophage lineage cells in rat bone marrow, peripheral blood and tissues, with detectable expression in granulocytes and B cells and no evidence of expression in hematopoietic precursors or non-hematopoietic cells. Here, we use the Csf1r-mApple transgene to highlight and dissect the abundance and heterogeneity of rat tissue macrophage populations, and to demonstrate parallel increases in blood monocytes and multiple tissue macrophage populations, including bone marrow, liver, spleen and lung, in response to CSF1 treatment in vivo. The Csf1r-mApple rat is a novel tool enabling analysis of rat macrophages in situ by direct imaging and providing an additional phenotypic marker to facilitate exploration of rat tissue macrophage phenotypic and functional heterogeneity.

Live Imaging of Monocyte Subsets in Immune Complex-Mediated Glomerulonephritis Reveals Distinct Phenotypes and Effector Functions

“…We have developed a novel WKY-hCD68-GFP monocyte/ macrophage reporter rat in which GFP expression occurs exclusively within monocytes and tissue macrophages and this complements another recently published CSF1r-mApple transgenic reporter rat. 27 In this model GFP expression was seen in neutrophils and B cells, as well as monocytemacrophage lineage cells. 27 We performed detailed phenotyping of monocyte subpopulations in WKY-hCD68-GFP rats, confirming for the first time that rat non-classical and classical monocytes are homologous to those identified in mice and humans, 10,11 on the basis of gene expression of key phenotypic markers.…”

“…27 In this model GFP expression was seen in neutrophils and B cells, as well as monocytemacrophage lineage cells. 27 We performed detailed phenotyping of monocyte subpopulations in WKY-hCD68-GFP rats, confirming for the first time that rat non-classical and classical monocytes are homologous to those identified in mice and humans, 10,11 on the basis of gene expression of key phenotypic markers. Moreover, WKY-hCD68-GFP rats had susceptibility to experimental GN comparable to wild-type WKY rats (Supplemental Figure 2).…”

“…We performed detailed phenotyping of monocytes in WKY-hCD68-GFP rats using flow cytometry to identify two main subpopulations on the basis of CD43 and HIS48 expression 26,27 (GFP pos CD43 hi HIS48 int non-classical and GFP pos CD43 lo HIS48 hi classical monocytes), and qPCR to confirm that their differential gene expression of phenotypic markers was homologous to the subpopulations identified in mice and humans 11,12,28,29 (Supplemental Figure 4).…”

The equine mononuclear phagocyte system: The relevance of the horse as a model for understanding human innate immunity

“…leads to a monocytosis as well as proliferative expansion of resident macrophage populations. [52][53][54][55] These findings, combined with the fact that macrophages of the liver and spleen are the main site of clearance of CSF1, led to the concept of homeostatic control of the entire MPS via the availability of CSF1. 37 The exception to this concept is the lung, where another growth factor, granulocyte-macrophage colony-stimulating factor 2 (CSF2, also known as GM-CSF), is uniquely required for both development and resident macrophage homeostasis.…”

Stable colony stimulating factor 1 fusion protein treatment increases HSC pool and enhances their mobilisation in mice

“…engineered a pig CSF1 molecule conjugated to the Fc (CH-3) region of pig immunoglobulin IgG1a that greatly increased its circulating half-life 15 . Pig CSF1 is equally active on mouse and human macrophages 16 and short term daily CSF1-Fc injection was well tolerated and effectively increased murine blood monocyte and tissue resident macrophage populations, including those in BM, in mice 15 , rats 17 and pigs 18 . However, the improved drug qualities of CSF1-Fc are associated with supraphysiologic pharmacokinetic properties 12,15,19 .…”