Folate Receptor β (FRβ) Expression in Tissue-Resident and Tumor-Associated Macrophages Associates with and Depends on the Expression of PU.1

Abstract

As macrophages exhibit a huge functional plasticity under homeostasis and pathological conditions, they have become a therapeutic target for chronic inflammatory diseases. Hence, the identification of macrophage subset-specific markers is a requisite for the development of macrophage-directed therapeutic interventions. In this regard, the macrophage-specific Folate Receptor β (FRβ, encoded by the FOLR2 gene) has been already validated as a target for molecular delivery in cancer as well as in macrophage-targeting therapeutic strategies for chronic inflammatory pathologies. We now show that the transcriptome of human macrophages from healthy and inflamed tissues (tumor; rheumatoid arthritis, RA) share a significant over-representation of the “anti-inflammatory gene set”, which defines the gene profile of M-CSF-dependent IL-10-producing human macrophages (M-MØ). More specifically, FOLR2 expression has been found to strongly correlate with the expression of M-MØ-specific genes in tissue-resident macrophages, tumor-associated macrophages (TAM) and macrophages from inflamed synovium, and also correlates with the presence of the PU.1 transcription factor. In fact, PU.1-binding elements are found upstream of the first exon of FOLR2 and most M-MØ-specific- and TAM-specific genes. The functional relevance of PU.1 binding was demonstrated through analysis of the proximal regulatory region of the FOLR2 gene, whose activity was dependent on a cluster of PU.1-binding sequences. Further, siRNA-mediated knockdown established the importance of PU.1 for FOLR2 gene expression in myeloid cells. Therefore, we provide evidence that FRβ marks tissue-resident macrophages as well as macrophages within inflamed tissues, and its expression is dependent on PU.1.

Single cell analysis of endometriosis reveals a coordinated transcriptional program driving immunotolerance and angiogenesis across eutopic and ectopic tissues.

“…3e). Tissue resident LYVE1 + macrophages have been previously associated with angiogenesis 19,21 , arterial stiffness 27 and anti-inflammatory phenotypes 23 . In agreement, we found that endometriosis Mφ1-LYVE1 upregulate tolerogenic (IL10, VSIG4, RGS1, EGFL7) and angiogenesisrelated genes (THBS1, HBEGF, PDGFB, PDGFC, IGF1) (Fig.…”

Single cell analysis of endometriosis reveals a coordinated transcriptional program driving immunotolerance and angiogenesis across eutopic and ectopic tissues

“…We identified five Mf subpopulations, of which Mf1-LYVE1 and Mf3-APOE were previously identified by single cell analysis in other systems 8,21,22 . Tissue-resident macrophage subpopulations (Mf1-LYVE1, Mf2-peritoneal and Mf3-APOE) are distinguished by their expression of FOLR2-a gene associated with embryonic-derived tissue resident macrophages 19,23 . Mf2-peritoneal subpopulation is exclusive to peritoneal tissue and express ICAM2, a known marker for peritoneal macrophage 24 .…”

“…3e). Tissue resident LYVE1 + macrophages have been previously associated with angiogenesis 19,21 , arterial stiffness 27 and anti-inflammatory phenotypes 23 . In agreement, we found that endometriosis Mf1-LYVE1 upregulate tolerogenic (IL10, VSIG4, RGS1, EGFL7) and angiogenesis-related genes (THBS1, HBEGF, PDGFB, PDGFC, IGF1) (Fig.…”

LXR nuclear receptors prompt a pro-inflammatory gene and functional profile in human macrophages

“…To that end, we first evaluated whether LXR is involved in the macrophage polarizing ability of tumor-conditioned fluids, and specifically of ascitic fluids from tumors of various origins (Figure 7A). The M-CSF-induced expression of two functionally relevant markers of tumor-associated macrophages, IGF-1 (66, 67) and FOLR2 (63,68), was prevented in the presence of the LXR agonist GW3965 (Figure 7B). Moreover, the upregulation of both genes in the presence of ascitic fluids was also impaired by the LXR agonist (Figure 7B), implying that the polarizing ability of tumor-conditioned media is dependent on LXR activity.…”