In this study we demonstrated that within a complex tissue such as the mammary gland, the targeted deletion of
Sfrp1 resulted in changes to the mammary environment resulting in more macrophages and expression of
Arg1, a marker consistent with M2 polarization. An association between M2 related markers and Wnt3 exposure was also noted in human breast tissue. Our findings that Wnt3a drives M2 macrophage polarization in PDEs is supported by our previous findings that we can manipulate and polarize macrophages within benign human breast tissue PDEs towards M1 or M2 through the addition of IFNγ + LPS or IL-4 + IL-13 respectively [
17]. Treatment with the cytokines which drive M2 polarization (IL4 + IL-13) resulted in an increased expression of CD209 and CCL18. Both CD209 and CCL18 are involved in the regulation of immune response and tissue repair, which are key functions of M2 macrophages [
27,
28].
RNAseq validation revealed 3 key genes regulated by Wnt signaling and subsequent antagonism. Interestingly, MIR339 overexpression has been tied to the development of cancer by increasing cell viability and decreasing pro-apoptotic gene expression in stem cell leukemia/lymphoma cells [
29]. However, we were most intrigued by our
CCL11 and
CCL26 results because both of these chemokines are involved in promoting macrophage polarization and cancer metastasis [
30‐
32]. Tong et al. showed that high levels of CCL26 were found to be related with metastasis in differentiated thyroid cancer patients [
33]. Additionally, regenerated liver phosphatase 3 (PRL-3) has been found to promote the invasion and metastasis of colorectal cancer by upregulating CCL26 to induce TAMs infiltration [
32]. Levina et al. revealed that CCL11 potently stimulated proliferation and migration/invasion of ovarian carcinoma cell lines, and these effects were inhibited by neutralizing antibodies against its cognate receptors (CCR2, 3, and 5) [
34]. Furthermore, CCL11 has been shown to promote lung cancer metastasis by way of Epithelial to Mesenchymal Transition, a hallmark pro-metastatic pathway [
35]. Wang et al. demonstrated that the serum CCL11 level and the proportion of immunosuppressive T regulatory significantly increased in patients with breast cancer compared with healthy individuals and blockade of CCL11 in tumor bearing mice decreases immunosuppressive Tregs [
36]. Tian et al. reported that CCL11 is upregulated in glioblastomas and that CCL11 promotes proliferation, migration, and invasion in glioma cancer cell lines [
37]. Future work will be required to study the effects of CCL11 and CCL26 on M2 macrophage polarization and the subsequent effect on the migration and invasion of breast cancer cells. Our GSEA data unveiled that signaling pathways affected by Wnt stimulation/antagonism are involved in M2 macrophage polarization. Specifically, p38MAPK signaling is required for polarization in macrophages derived from murine bone marrow and PPAR signaling initiates the development of M2 macrophages by promoting the expression and ligation of
αvβ5 integrins [
25,
26]. Finally, our GO and KEGG enrichment data provide an exciting avenue to pursue going forward in terms of the effects of Wnt antagonism in breast tissue.
In conclusion, our data demonstrates that exposure of human benign breast tissue to Wnt is associated with changes in levels of genes and pathways affiliated macrophage polarization an global inflammation. These findings suggest that SFRP1 may be critical target to develop as a therapeutic strategy to help disrupt the tumor microenvironment.