In the December 2013 issue of the Proceedings of the National Academy of Sciences of the USA Kathleen Kokolus et al., from the Roswell Park Cancer Institute, Buffalo, NY and the US Environmental Protection Agency, NC, demonstrate that a cool ambient housing temperature may affect the outcome of a broad range of experimental endpoints, including antitumor immunity and experimental tumor growth in mice.
Experimental research with animal models can be affected by many factors but a variable that has received little attention is housing temperature in research facilities.
Research facilities use ‘standard’ housing temperatures for experimental animals around 20–26 °C. However, in nature, or natural ‘environments’, studies have shown that mice seek warm environments; and healthy mice usually select an ambient temperature of 30–31 °C.
The authors of this study have shown that mice housed at a standard temperature of ∼22–23 °C, when compared to mice kept at a thermoneutral temperature (∼30–31 °C), had not only less CD8+T cells (and more immune suppressive cells), but in the tumor microenvironment their T cells had suppressed interferon (IFN)-γ production. More importantly, these mice also had marked increase in tumor formation, g rowth rate and metastasis.
Kokolus et al., discuss that an increase in the activity of SNS/norepinephrine-driven cold stress response is most likely the underlying mechanism involved in their observations.
As mouse models may not correctly predict which new therapies will be effective in the clinic, this study, according to the authors, suggest that it is important to consider ambient temperature when cancer (and perhaps other disorders) are modeled in mice. Moreover, these results may also suggest that further studies on the interactions between (cold) stress, thermoregulation, and immune (antitumor) responses are warranted.
Source: Proc Natl Acad Sci U S A. 2013, 110:20176-81. doi: 10.1073/pnas.1304291110. Epub 2013 Nov 18.
Read more: pnas.org
A 2019 review by the group of Elizabeth Repasky discuss how mice in research facilities are chronically stressed at baseline because of environmental factors. Focusing on housing temperature, the authors suggest that the stress of cool housing temperatures contributes to the impact of other imposed experimental stressors and therefore has a confounding effect on mouse stress models.
The authors outline a growing number of papers reporting how choice of housing temperature impacts experimental outcomes and reproducibility in several mouse models. As discussed above, in their 2013 study they demonstrated that housing mice at 22˚C alone results in significant suppression of the anti-tumor immune response. The same authors went on to show that this difference is also lost when mice (housed at 22˚C) were treated with β-adrenergic receptor antagonists (β-blockers) confirming that the degree of adrenergic stress is a function of room temperature.
In a 2015 and 2017studies the group of Elizabeth Repasky found that the mild, but chronic cold stress that mice experience in 22˚C housing results in elevated levels of NE (the SNS neurotransmitter that drives nonshivering thermogenesis). These elevated NE levels are particularly concerning for preclinical tumor models because a growing literature in the last 15–20 years has developed demonstrating the tumor promoting effects of adrenergic stress signaling.
Additionally, it has become clear that adrenergic signaling suppresses immune responses and can skew the overall response away from a Th1 and CD8+ effector T-cell dependent immunity to a Th2 humoral response. Furthermore, effects of adrenergic stress on anti-tumor immunity have been reported mirroring the effects we have seen in response to 22˚C housing, that is, suppression of CD8+ T-cell proliferation, IFNγ expression, and cytotoxicity with a concurrent increase in pro-tumor immune suppressive cells, Tregs and MDSC.
In a 2022 study, Yajie Hu, Yang Liu and Shize Li established mice models of cold stress with different intensities were (cold exposure gradients were 22 ◦C, 16 ◦C, 10 ◦C and 4 ◦C). After the corresponding cold exposure treatment, blood samples were collected and used for the determination of corticosterone (Cort), corticotropin-releasing hormone (CRH), epinephrine (E), norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT). Following these experiments and measurements, these authors report that the hypothalamic–pituitary–adrenal (HPA) axis and locus coeruleus-noradrenergic (LC/NE) sympathetic nervous system were activated by cold stress and fluctuated with different intensities of cold exposure.