Temperature matters: the potential impact of thermoregulatory mechanisms in brain-body physiology.

Thermoregulation, responsible for maintaining a stable core temperature during wide fluctuations in external and internal thermal environments, is an iconic homeostatic process. However, we suggest that despite its fundamental physiological significance, the potential for required cool housing temperatures and thermoregulatory mechanisms to influence the interpretation of experimental data is not sufficiently appreciated. Moreover, although it is generally assumed that the major thermoregulatory pathways are well understood, here we discuss new research that suggests otherwise and reveals the emergence of a new wave of exciting ideas for this "old" field of research.

Housing temperature plays a critical role in determining gut microbiome composition in research mice: Implications for experimental reproducibility.

Preclinical mouse models are widely used for studying mechanisms of disease and responses to therapeutics, however there is concern about the lack of experimental reproducibility and failure to predict translational success. The gut microbiome has emerged as a regulator of metabolism and immunological processes in health and disease. The gut microbiome of mice differs by supplier and this affects experimental outcomes.

Using Mice to Model Human Disease: Understanding the Roles of Baseline Housing-Induced and Experimentally Imposed Stresses in Animal Welfare and Experimental Reproducibility.

Mice are the most common animal used to study disease, but there are real concerns about the reproducibility of many of these experiments. This review discusses how several different sources of chronic stress can directly impact experimental outcomes. Mandated housing conditions induce an underappreciated level of chronic stress but are not usually considered or reported as part of the experimental design.

Chronic Adrenergic Stress Contributes to Metabolic Dysfunction and an Exhausted Phenotype in T Cells in the Tumor Microenvironment.

Metabolic dysfunction and exhaustion in tumor-infiltrating T cells have been linked to ineffectual antitumor immunity and the failure of immune checkpoint inhibitor therapy. We report here that chronic stress plays a previously unrecognized role in regulating the state of T cells in the tumor microenvironment (TME). Using two mouse tumor models, we found that blocking chronic adrenergic stress signaling using the pan β-blocker propranolol or by using mice lacking the β2-adrenergic receptor (β2-AR) results in reduced tumor growth rates with significantly fewer tumor-infiltrating T cells that express markers of exhaustion, with a concomitant increase in progenitor exhausted T cells.

Comparing thermal stress reduction strategies that influence MDSC accumulation in tumor bearing mice.

Myeloid derived suppressor cells (MDSCs) are a diverse collection of immune cells that suppress anti-tumor immune responses. Decreasing MDSCs accumulation in the tumor microenvironment could improve the anti-tumor immune response and improve immunotherapy. Here, we examine the impact of physiologically relevant thermal treatments on the accumulation of MDSCs in tumors in mice.

Adrenergic stress constrains the development of anti-tumor immunity and abscopal responses following local radiation.

The abscopal effect following ionizing radiation therapy (RT) is considered to be a rare event. This effect does occur more frequently when combined with other therapies, including immunotherapy. Here we demonstrate that the frequency of abscopal events following RT alone is highly dependent upon the degree of adrenergic stress in the tumor-bearing host.

Temperature as a modulator of the gut microbiome: what are the implications and opportunities for thermal medicine?

There is substantial research being conducted on the relationships between the gut microbiome, the immune response and health and disease. Environmental temperature and heat stress are known to modify the gut microbiome. Changes in core temperature have been linked, in multiple phyla, to altered microbiome composition and function.

β2 adrenergic receptor-mediated signaling regulates the immunosuppressive potential of myeloid-derived suppressor cells.

Catecholamines released by sympathetic nerves can activate adrenergic receptors present on nearly every cell type, including myeloid-derived suppressor cells (MDSCs). Using in vitro systems, murine tumor models in wild-type and genetically modified (β2-AR-/-) mice, and adoptive transfer approaches, we found that the degree of β2-AR signaling significantly influences MDSC frequency and survival in tumors and other tissues. It also modulates their expression of immunosuppressive molecules such as arginase-I and PD-L1 and alters their ability to suppress the proliferation of T cells.

Adrenergic Receptor Signaling Regulates the Response of Tumors to Ionizing Radiation.

While ionizing radiation is a major form of cancer therapy, radioresistance remains a therapeutic obstacle. We have previously shown that the mandated housing temperature for laboratory mice (∼22°C) induces mild, but chronic, cold stress resulting in increased circulating norepinephrine, which binds to, and triggers activation of, beta-adrenergic receptors (β-AR) on tumor and immune cells. This adrenergic signaling increases tumor cell intrinsic resistance to chemotherapy and suppression of the anti-tumor immune response.

Manipulation of Ambient Housing Temperature To Study the Impact of Chronic Stress on Immunity and Cancer in Mice.

Mice are the preeminent research organism in which to model human diseases and study the involvement of the immune response. Rapidly accumulating evidence indicates a significant involvement of stress hormones in cancer progression, resistance to therapies, and suppression of immune responses. As a result, there has been a concerted effort to model human stress in mice.

Depression Stresses the Immune Response and Promotes Prostate Cancer Growth.

Depression induces secretion of neuropeptide Y from prostate cancer cells, which, in turn, recruits myeloid-derived suppressor cells (MDSC) to the tumor; tumor cells and MDSCs secrete IL6, which activates STAT3 within cancer cells. Prostate cancer samples from depressed patients reveal a similar phenotype, suggesting new treatment strategies based upon blockade of β2-adrenergic receptors and/or neuropeptide Y..

Mitochondrial DNA in the tumour microenvironment activates neutrophils and is associated with worse outcomes in patients with advanced epithelial ovarian cancer.

Background: Advanced cancer causes necrosis and releases damage-associated molecular patterns (DAMPs). Mitochondrial DAMPs activate neutrophils, including generation of neutrophil extracellular traps (NETs), which are injurious, thrombogenic, and implicated in metastasis. We hypothesised that extracellular mitochondrial DNA (mtDNA) in ascites from patients with epithelial ovarian cancer (EOC) would correlate with worse outcomes.

β-Adrenergic signaling blocks murine CD8 T-cell metabolic reprogramming during activation: a mechanism for immunosuppression by adrenergic stress.

Primary and secondary lymphoid organs are heavily innervated by the autonomic nervous system. Norepinephrine, the primary neurotransmitter secreted by post-ganglionic sympathetic neurons, binds to and activates β-adrenergic receptors expressed on the surface of immune cells and regulates the functions of these cells. While it is known that both activated and memory CD8 T-cells primarily express the β2-adrenergic receptor (β2-AR) and that signaling through this receptor can inhibit CD8 T-cell effector function, the mechanism(s) underlying this suppression is not understood.

An overview of the role of sympathetic regulation of immune responses in infectious disease and autoimmunity.

Stress in patients and pre-clinical research animals plays a critical role in disease progression Activation of the sympathetic nervous system (SNS) by stress results in secretion of the catecholamines epinephrine (Epi) and norepinephrine (NE) from the adrenal gland and sympathetic nerve endings. Adrenergic receptors for catecholamines are present on immune cells and their activity is affected by stress and the accompanying changes in levels of these neurotransmitters. In this short review, we discuss how this adrenergic stress impacts two categories of immune responses, infections and autoimmune diseases.

Adrenergic Signaling: A Targetable Checkpoint Limiting Development of the Antitumor Immune Response.

An immune response must be tightly controlled so that it will be commensurate with the level of response needed to protect the organism without damaging normal tissue. The roles of cytokines and chemokines in orchestrating these processes are well known, but although stress has long been thought to also affect immune responses, the underlying mechanisms were not as well understood. Recently, the role of nerves and, specifically, the sympathetic nervous system, in regulating immune responses is being revealed.

The Impact of Housing Temperature-Induced Chronic Stress on Preclinical Mouse Tumor Models and Therapeutic Responses: An Important Role for the Nervous System.

In the last 10-15 years, there has been a recognition that the catecholamines (norepinephrine, NE, and epinephrine, Epi) released by the sympathetic nervous system under stressful conditions promote tumor growth through a variety of mechanisms. Tumors recruit autonomic nerves during their development and NE is then released locally in the tumor microenvironment (TME). Acting through adrenergic receptors present on a variety of cells in the TME, NE and Epi induce proliferation, resistance to apoptosis, epithelial to mesenchymal transition, metastasis of tumor cells, angiogenesis, and inflammation in the TME.

β-Adrenergic Signaling in Mice Housed at Standard Temperatures Suppresses an Effector Phenotype in CD8 T Cells and Undermines Checkpoint Inhibitor Therapy.

The immune context of tumors has significant prognostic value and is predictive of responsiveness to several forms of therapy, including immunotherapy. We report here that CD8 T-cell frequency and functional orientation within the tumor microenvironment is regulated by β-adrenergic receptor (β-AR) signaling in host immune cells. We used three strategies-physiologic (manipulation of ambient thermal environment), pharmacologic (β-blockers), and genetic (β-AR knockout mice) to reduce adrenergic stress signaling in two widely studied preclinical mouse tumor models.

Pancreatic cancer stem cells in patient pancreatic xenografts are sensitive to drozitumab, an agonistic antibody against DR5.

Background: Therapeutic resistance and tumor recurrence are two major hurdles in the treatment of pancreatic ductal adenocarcinoma. Recent findings suggest that both of these attributes are associated with a small subset of pancreatic tumor initiating cancer stem cells (CSCs). Here, we demonstrate that drozitumab, a human agonistic monoclonal antibody which binds the death receptor DR5, selectively eliminates CSCs, resulting in tumor growth inhibition and even regression of pancreatic tumors.

Thermoneutrality, Mice, and Cancer: A Heated Opinion.

The 'mild' cold stress caused by standard sub-thermoneutral housing temperatures used for laboratory mice in research institutes is sufficient to significantly bias conclusions drawn from murine models of several human diseases. We review the data leading to this conclusion, discuss the implications for research and suggest ways to reduce problems in reproducibility and experimental transparency caused by this housing variable. We have found that these cool temperatures suppress endogenous immune responses, skewing tumor growth data and the severity of graft versus host disease, and also increase the therapeutic resistance of tumors.

Tumor-Priming Smoothened Inhibitor Enhances Deposition and Efficacy of Cytotoxic Nanoparticles in a Pancreatic Cancer Model.

Most pancreatic adenocarcinoma patients present with unresectable disease and benefit little from chemotherapy. Poor tumor perfusion and vascular permeability limit drug deposition. Previous work showed that Smoothened inhibitors of hedgehog signaling (sHHI) promote neovascularization in spontaneous mouse models of pancreatic cancer (PaCA) and enhance tumor permeability to low-molecular weight compounds.

Tumor priming by Apo2L/TRAIL reduces interstitial fluid pressure and enhances efficacy of liposomal gemcitabine in a patient derived xenograft tumor model.

Interstitial fluid pressure (IFP) is elevated in tumors and high IFP, a negative cancer prognosticator, is known to limit the uptake and efficacy of anti-tumor therapeutics. Approaches that alter the tumor microenvironment and enhance uptake of therapeutics are collectively referred to as tumor "priming". Here we show that the cytotoxic biological therapy Apo2L/TRAIL can prime the tumor microenvironment and significantly lower IFP in three different human tumor xenograft models (Colo205, MiaPaca-2 and a patient gastrointestinal adenocarcinoma tumor xenograft).

Stress, metabolism and cancer: integrated pathways contributing to immune suppression.

The potential for immune cells to control cancers has been recognized for many decades, but only recently has real excitement begun to spread through the oncology community following clear evidence that therapeutic blockade of specific immune-suppressive mechanisms is enough to make a real difference in survival for patients with several different advanced cancers. However, impressive and encouraging as these new clinical data are, it is clear that more effort should be devoted toward understanding the full spectrum of factors within cancer patients, which have the potential to block or weaken antitumor activity by immune cells. The goal of this brief review is to highlight recent literature revealing interactive stress and metabolic pathways, particularly those mediated by the sympathetic nervous system, which may conspire to block immune cells from unleashing their full killing potential.

Defining immunological impact and therapeutic benefit of mild heating in a murine model of arthritis.

Traditional treatments, including a variety of thermal therapies have been known since ancient times to provide relief from rheumatoid arthritis (RA) symptoms. However, a general absence of information on how heating affects molecular or immunological targets relevant to RA has limited heat treatment (HT) to the category of treatments known as "alternative therapies". In this study, we evaluated the effectiveness of mild HT in a collagen-induced arthritis (CIA) model which has been used in many previous studies to evaluate newer pharmacological approaches for the treatment of RA, and tested whether inflammatory immune activity was altered.

Housing temperature-induced stress drives therapeutic resistance in murine tumour models through β2-adrenergic receptor activation.

Cancer research relies heavily on murine models for evaluating the anti-tumour efficacy of therapies. Here we show that the sensitivity of several pancreatic tumour models to cytotoxic therapies is significantly increased when mice are housed at a thermoneutral ambient temperature of 30 °C compared with the standard temperature of 22 °C. Further, we find that baseline levels of norepinephrine as well as the levels of several anti-apoptotic molecules are elevated in tumours from mice housed at 22 °C.

A nervous tumor microenvironment: the impact of adrenergic stress on cancer cells, immunosuppression, and immunotherapeutic response.

Long conserved mechanisms maintain homeostasis in living creatures in response to a variety of stresses. However, continuous exposure to stress can result in unabated production of stress hormones, especially catecholamines, which can have detrimental health effects. While the long-term effects of chronic stress have well-known physiological consequences, recent discoveries have revealed that stress may affect therapeutic efficacy in cancer.