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The low-dose mixture hypothesis of carcinogenesis proposes that exposure to an environmental chemical that is not individually oncogenic may nonetheless be capable of enabling carcinogenesis when it acts in concert with other factors. A class of ubiquitous environmental chemicals that are hypothesized to potentially function in this low-dose capacity are synthesized polybrominated diphenyl ethers (PBDEs). PBDEs can affect correlates of carcinogenesis that include genomic instability and inflammation. However, the effect of low-dose PBDE exposure on such correlates in mammary tissue has not been examined. In the present study, low-dose long-term (16 weeks) administration of PBDE to mice modulated transcriptomic indicators of genomic integrity and innate immunity in normal mammary tissue. PBDE increased transcriptome signatures for the Nuclear Factor Erythroid 2 Like 2 (NFE2L2) response to oxidative stress and decreased signatures for non-homologous end joining DNA repair (NHEJ). PBDE also decreased transcriptome signatures for the cyclic GMP-AMP Synthase - Stimulator of Interferon Genes (cGAS-STING) response, decreased indication of Interferon Stimulated Gene Factor 3 (ISGF3) and Nuclear Factor Kappa B (NF-κB) transcription factor activity, and increased digital cytometry estimates of immature dendritic cells (DCs) in mammary tissue. Replication of the PBDE exposure protocol in mice susceptible to mammary carcinogenesis resulted in greater tumor development. The results support the notion that ongoing exposure to low levels of PBDE can disrupt facets of genomic integrity and innate immunity in mammary tissue. Such effects affirm that synthesized PBDEs are a class of environmental chemicals that reasonably fit the low-dose mixture hypothesis.

The risk for breast cancer is significantly reduced in persons who engage in greater amounts of physical activity, and greater physical activity before or after diagnosis associates with reduced disease-specific mortality. Previous mechanistic studies indicate that components of innate immunity can mediate an inhibitory effect of physical activity on several types of tumor. However, in breast cancer specifically, the myeloid compartment of innate immunity is thought to exhibit high propensity for an immunosuppressive role that obstructs anti-tumor immunity. Thus, we tested the notion that greater physical activity alters mononuclear phagocytes in mammary tissue when inhibiting nascent tumor in a murine model of breast cancer. To model greater physical activity, we placed an angled running wheel in each mouse's home cage for two weeks before tumor engraftment with EO771 mammary cancer cells that express luciferase for bioluminescent detection. Fully immunocompetent mice and mice with compromised adaptive immunity showed significantly less mammary tumor signal when given access to running wheels, although the effect size was smaller in this latter group. To investigate the role of the myeloid compartment, mononuclear phagocytes were ablated by systemic injection of clodronate liposomes at 24 h before tumor engraftment and again at the time of tumor engraftment, and this treatment reversed the inhibition in wheel running mice. However, clodronate also inhibited mammary tumor signal in sedentary mice, in conjunction with an expected decrease in gene and protein expression of the myeloid antigen, F4/80 (Adgre1), in mammary tissue. Whole transcriptome digital cytometry with CIBERSORTx was used to analyze myeloid cell populations in mammary tissue following voluntary wheel running and clodronate treatment, and this approach found significant changes in macrophage and monocyte populations. In exploratory analyses, whole transcriptome composite scores for monocytic myeloid-derived suppressor cell (M-MDSC), macrophage lactate timer, and inflammation resolution gene expression programs were significantly altered. Altogether, the results support the hypothesis that physical activity inhibits nascent mammary tumor growth by enhancing the anti-tumor potential of mononuclear phagocytes in mammary tissue.

At the M2 terminal of the macrophage activation spectrum, expression of genes is regulated by transcription factors that include STAT6, CREB, and C/EBPβ. Signaling through β-adrenergic receptors drives M2 activation of macrophages, but little is known about the transcription factors involved. In the present study, we found that C/EBPβ regulates the signaling pathway between β-adrenergic stimulation and expression of Arg1 and several other specific genes in the greater M2 transcriptome. β-adrenergic signaling induced Cebpb gene expression relatively early with a peak at 1 h post-stimulation, followed by peak Arg1 gene expression at 8 h. C/EBPβ transcription factor activity was elevated at the enhancer region for Arg 1 at both 4 and 8 h after stimulation but not near the more proximal promoter region. Knockdown of Cebpb suppressed the β-adrenergic-induced peak in Cebpb gene expression as well as subsequent accumulation of C/EBPβ protein in the nucleus, which resulted in suppression of β-adrenergic-induced Arg1 gene expression. Analysis of genome-wide transcriptional profiles identified 20 additional M2 genes that followed the same pattern of regulation by β-adrenergic- and C/EBPβ-signaling. Promoter-based bioinformatic analysis confirmed enrichment of binding motifs for C/EBPβ transcription factor across these M2 genes. These findings pinpoint a mechanism that may be targeted to redirect the deleterious influence of β-adrenergic signaling on macrophage involvement in M2-related diseases such as cancer.

The end of the critical period for primary visual cortex (V1) coincides with the deposition of perineuronal nets (PNN) onto Parvalbumin (PV) inhibitory neurons. Recently, we found that transplantation of embryonic inhibitory neurons into adult V1 reinstates a new critical period. Here we used Wisteria Floribunda Agglutinin (WFA) staining to compare the deposition of PNNs onto neurons during normal development and following transplantation at equivalent cell ages. In accord with previous findings, PV and PNN expression increases from negligible levels at postnatal day 14 (P14) to mature levels by P70. In contrast to P14, PNNs are found on transplanted PV neurons by 21 days after transplantation and persist to 105 days after transplantation. This precocious deposition was specific to PV neurons and excluded transplanted neurons expressing Somatostatin. Notably, the onset of PV expression in transplanted inhibitory neurons follows the timing of PV expression in juvenile V1. Moreover, transplantation has no discernible effect on host PNNs. The precocious deposition of PNNs onto transplanted PV neurons suggests that PNN expression identified by WFA does not reflect neuronal maturity and may be an inaccurate marker for transplant-induced plasticity of cortical circuits.