Conditional deletion of Stat3 in mammary epithelium impairs the acute phase response and modulates immune cell numbers during post‐lactational regression

Abstract

Mammary gland regression following weaning (involution) is associated with extensive cell death and the acquisition of an inflammatory signature. Characterizing the interplay between mammary epithelial cells, the re-emerging stroma and immune cells has implications for the understanding of the pathogenesis of pregnancy-associated breast cancer. Stat3 has a role in orchestrating cell death and involution, and we sought to determine whether expression of Stat3 by the mammary epithelium also influences the innate immune environment and inflammatory cell influx in the gland. We examined mice in which Stat3 is conditionally deleted only in the mammary epithelium. Distinct sets of genes associated with the acute phase response and innate immunity are markedly up-regulated during first phase involution in a Stat3-dependent manner. During second phase involution, chitinase 3-like 1, which has been associated with wound healing and chronic inflammatory conditions, is dramatically up-regulated by Stat3. Also at this time, the number of mammary macrophages and mast cells increases per unit area, and this increase is impaired in the absence of epithelial Stat3. Furthermore, expression of arginase-1 and Ym1, markers of alternatively activated macrophages, is significantly decreased in the absence of Stat3, whilst iNOS, a marker associated with classically activated macrophages, shows significantly increased expression in the Stat3-deleted glands. Thus, Stat3 is a key transcriptional regulator of genes associated with innate immunity and wound healing and influences mammary macrophage and mast cell numbers. The presence of epithelial Stat3 appears to polarize the macrophages and epithelial cells towards an alternatively activated phenotype, since in the absence of Stat3, the gland retains a phenotype associated with classically activated macrophages. These findings have relevance to the study of pregnancy-associated breast cancer and the role of Stat3 signalling in recruitment of alternatively activated tumour-associated macrophages in breast cancer. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Janus Kinase 1 Is Essential for Inflammatory Cytokine Signaling and Mammary Gland Remodeling

“…We further demonstrated that the deletion of JAK1 uncouples IL-6-class ligands from their downstream effector, STAT3. Consequently, this leads to the decreased expression of known STAT3 target genes that are associated with the acute-phase response, inflammation, and wound healing (42). The genome-wide expression analysis of JAK1-knockout mammary glands and control tissues revealed a number of novel target genes that were upregulated during involution in a JAK1-dependent manner.…”

Nucling, a Novel Apoptosis-associated Protein, Controls Mammary Gland Involution by Regulating NF-κB and STAT3

“…It may also be due to the inhibited activation of STAT3 in Nucling-KO mice. A previous study demonstrated that STAT3 activity directly or indirectly modulated M2 macrophage populations in postlactational mammary gland involution (27).…”

“…The Loss of Nucling Blocked STAT3 Activation by Repressing gp130 Expression-A recent study reported that STAT3 activity induced a M2 macrophage population during involution (27). Furthermore, the activation of STAT3 after weaning was required for normal mammary gland involution (7,8).…”

“…Therefore, we attempted to elucidate the contribution of Nucling to M2 macrophage recruitment during mammary gland involution. To achieve this, we examined the expression of Arginase-1 and Ym1, markers of M2 macrophages (14,27). At 36 h of involution, protein levels of Arginase-1 were similar in WT and Nucling-KO mice.…”

Apoptosis and Clearance of the Secretory Mammary Epithelium

“…Inhibition of mast cell-derived PKaI during postlactational involution impaired epithelial cell death, suggesting that mast cells are vital for triggering apoptosis in the post-lactational mammary gland. Interestingly, in the absence of STAT3 within the mammary epithelium, mast cells and macrophages are not recruited to the mammary gland during post-lactational involution [108], suggesting that recruitment of stromal cells to the involuting mammary gland is initiated by early apoptotic signaling events occurring within the epithelial compartment (Fig. 1). …”