Effects of social isolation on ehrlich tumor growth and tumor leukocyte infiltration in mice: evidence of participation of the submaxillary salivary gland

Stress alters the expression of cancer-related genes in the prostate

Background

Prostate cancer is a major contributor to mortality worldwide, and significant efforts are being undertaken to decipher specific cellular and molecular pathways underlying the disease. Chronic stress is known to suppress reproductive function and promote tumor progression in several cancer models, but our understanding of the mechanisms through which stress contributes to cancer development and progression is incomplete. We therefore examined the relationship between stress, modulation of the gonadotropin-releasing hormone (GnRH) system, and changes in the expression of cancer-related genes in the rat prostate.

Methods

Adult male rats were acutely or repeatedly exposed to restraint stress, and compared to unstressed controls and groups that were allowed 14 days of recovery from the stress. Prostate tissue was collected and frozen for gene expression analyses by PCR array before the rats were transcardially perfused; and brain tissues harvested and immunohistochemically stained for Fos to determine neuronal activation.

Results

Acute stress elevated Fos expression in the paraventricular nucleus of the hypothalamus (PVH), an effect that habituated with repeated stress exposure. Data from the PCR arrays showed that repeated stress significantly increases the transcript levels of several genes associated with cellular proliferation, including proto-oncogenes. Data from another array platform showed that both acute and repeated stress can induce significant changes in metastatic gene expression. The functional diversity of genes with altered expression, which includes transcription factors, growth factor receptors, apoptotic genes, and extracellular matrix components, suggests that stress is able to induce aberrant changes in pathways that are deregulated in prostate cancer.

Conclusions

Our findings further support the notion that stress can affect cancer outcomes, perhaps by interfering with neuroendocrine mechanisms involved in the control of reproduction.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3635-4) contains supplementary material, which is available to authorized users.

Social isolation induces autophagy in the mouse mammary gland: link to increased mammary cancer risk

Social isolation is a strong predictor of early all-cause mortality and consistently increases breast cancer risk in both women and animal models. Because social isolation increases body weight, we compared its effects to those caused by a consumption of obesity-inducing diet (OID) in C57BL/6 mice. Social isolation and OID impaired insulin and glucose sensitivity. In socially isolated, OID-fed mice (I-OID), insulin resistance was linked to reduced Pparg expression and increased neuropeptide Y levels, but in group-housed OID fed mice (G-OID), it was linked to increased leptin and reduced adiponectin levels, indicating that the pathways leading to insulin resistance are different. Carcinogen-induced mammary tumorigenesis was significantly higher in I-OID mice than in the other groups, but cancer risk was also increased in socially isolated, control diet-fed mice (I-C) and G-OID mice compared with that in controls. Unfolded protein response (UPR) signaling (GRP78; IRE1) was upregulated in the mammary glands of OID-fed mice, but not in control diet-fed, socially isolated I-C mice. In contrast, expression of BECLIN1, ATG7 and LC3II were increased, and p62 was downregulated by social isolation, indicating increased autophagy. In the mammary glands of socially isolated mice, but not in G-OID mice, mRNA expressions of p53 and the p53-regulated autophagy inducer Dram1 were upregulated, and nuclear p53 staining was strong. Our findings further indicated that autophagy and tumorigenesis were not increased in Atg7(+/-) mice kept in social isolation and fed OID. Thus, social isolation may increase breast cancer risk by inducing autophagy, independent of changes in body weight.

Chronic restraint stress attenuates p53 function and promotes tumorigenesis

Epidemiological studies strongly suggest that chronic psychological stress promotes tumorigenesis. However, its direct link in vivo and the underlying mechanisms that cause this remain unclear. This study provides direct evidence that chronic stress promotes tumorigenesis in vivo; chronic restraint, a well-established mouse model to induce chronic stress, greatly promotes ionizing radiation (IR)-induced tumorigenesis in p53(+/-) mice. The tumor suppressor protein p53 plays a central role in tumor prevention. Loss or attenuation of p53 function contriubutes greatly to tumorigenesis. We found that chronic restraint decreases the levels and function of p53 in mice, and furthermore, promotes the growth of human xenograft tumors in a largely p53-dependent manner. Our results show that glucocorticoids elevated during chronic restraint mediate the effect of chronic restraint on p53 through the induction of serum- and glucocorticoid-induced protein kinase (SGK1), which in turn increases MDM2 activity and decreases p53 function. Taken together, this study demonstrates that chronic stress promotes tumorigenesis in mice, and the attenuation of p53 function is an important part of the underlying mechanism, which can be mediated by glucocortcoids elevated during chronic restraint.

Social regulation of leukocyte homeostasis: the role of glucocorticoid sensitivity

Recent small-scale genomics analyses suggest that physiologic regulation of pro-inflammatory gene expression by endogenous glucocorticoids may be compromised in individuals who experience chronic social isolation. The present study assessed the relationship between leukocyte distributional sensitivity to glucocorticoid regulation and subjective social isolation in a large population-based sample of older adults. Initial analyses confirmed that circulating neutrophil percentages were elevated, and circulating lymphocyte and monocyte percentages were suppressed, in direct proportion to circulating cortisol levels. However, leukocyte distributional sensitivity to endogenous glucocorticoids was abrogated in individuals reporting either occasional or frequent experiences of subjective social isolation. This finding held in both non-parametric univariate analyses and in multivariate linear models controlling for a variety of biological, social, behavioral, and psychological confounders. The present results suggest that social factors may alter immune cell sensitivity to physiologic regulation by the hypothalamic-pituitary-adrenal axis in ways that could ultimately contribute to the increased physical health risks associated with social isolation.

Effects of social isolation stress on immune response and survival time of mouse with liver cancer

AIM: To investigate the effects of isolation stress on mouse with liver cancer and possible associated mechanisms.

METHODS: Transplantable murine hepatoma22 (H22) model was used to evaluate the effects of social isolation stress on murine liver cancer. Mice were immunized with sheep red blood cell (SRBC) and intraperitoneally inoculated with H22 cell, then divided into two groups, one reared individually as group (I) and the other reared in groups as group (G). Titer of antibody to SRBC and interleukin 2 (IL-2) in serum was monitored. The survival time of mouse with liver cancer was observed.

RESULTS: The titer of antibody to SRBC in group (G) was 1:24.5 and that in group (I) was 1:11.2. There was a significant difference between these two groups (t = 2.60, P = 0.02). A significant difference in IL-2 concentration was observed between group (G) (39.6 ng/L) and group (I) (47.1 ng/L, t = 2.14, P = 0.046). The survival time in group (G) (16.5 d) was markedly longer than that in group (I) (13.2 d, t = 3.46, P = 0.002).

CONCLUSION: Our study suggests that survival time of the mouse bearing H22 tumor is affected by the social isolation stress and the associated mechanism may be the immunological changes under the social isolation stress.

Effect of Atropa belladonna and Echinacea angustifolia in homeopathic dilution on experimental peritonitis

Atropa belladonna and Echinacea angustifolia have been used in homeopathy as modulators of inflammatory processes, in simple potency or 'accord of potencies', as recommended by homotoxicology. We evaluated their effects on leukocyte migration and macrophage activity induced by experimental peritonitis in vivo. Mice were injected (i.p.) with LPS (1.0mg/kg) and treated (0.3ml/10g/day, s.c.) with different commercial forms of these medicines. Echinacea angustifolia D4--a simple potency preparation--and Belladonna Homaccord, Belladonna Injeel, Belladonna Injeel Forte, Echinacea Injeel and Echinacea Injeel Forte--all in 'accord of potencies'--were tested. The association of A. belladonna and E. angustifolia in 'accord of potencies' produced an increase of polymorphonuclear cell migration (Kruskal-Wallis, P = 0.03) and a decrease of mononuclear cell percentages (Kruskal-Wallis, P < or = 0.04), when compared with control, mainly in preparations containing low potencies. The proportion of degenerate leukocytes was lower in the treated groups, compared to a control group (P < or = 0.05). The treated groups showed increased phagocytosis (P < or = 0.05), mainly in preparations containing high potencies. Our results suggest that A. belladonna and E. angustifolia, when prepared in 'accord of potencies', modulate peritoneal inflammatory reaction and have a cytoprotective action on leukocytes.

Cohabitation with a sick cage mate: consequences on behavior and on ehrlich tumor growth

The present study analyzed the effects of cohabitation for 11 days with a sick cage mate on behavior and Ehrlich tumor growth in mice. Pairs of female mice were divided into one control and one experimental group. One mouse of each control pair was kept undisturbed and called 'healthy companion' (HC). One animal of each experimental pair of mice was inoculated (i.p.) with 5 x 10(6) Ehrlich tumor cells, and the other, the object of this study, was called 'sick companion' (SC). The SC mice presented: (1) increased activity in an open field, (2) increased number of entries and of movements within the plus-maze open arms, (3) similar levels of plus-maze closed-arm exploration, (4) a decrease in the exploratory activity in a hole board, (5) a decrease in the number of white but not red blood cells, and (6) similar corticosterone serum levels. Eleven days after cohabitation with a conspecific, HC and SC mice were injected with 5 x10(6) Ehrlich tumor cells. Results showed that SC animals presented decreased resistance to the ascitic form of the Ehrlich tumor. The observed data provide experimental evidence that psychosocial stress induced by cohabitation with a sick cage mate changed at the same time some behavioral and physiological parameters, and decreased resistance to Ehrlich tumor. These data are discussed in the light of a possible neuroimmune system interaction.