Thermoneutral housing is a critical factor for immune function and diet-induced obesity in C57BL/6 nude mice

Abstract

OBJECTIVES Obesity-related cancers represent public health burdens of the first order. Nevertheless, suitable mouse models to unravel molecular mechanisms linking obesity to human cancer are still not available. One translational model is the immunocompromised Foxn1 (winged-helix/forkead transcription factor) nude mouse transplanted with human tumor xenografts. However, most xenograft studies are conducted in nude mice on an in-bred BALB/c background that entails protection from diet-induced obesity. To overcome such resistance to obesity and its sequelae, we here propose the dual strategy of utilizing Foxn1 nude mice on a C57BL/6 background and housing them at their thermoneutral zone. METHODS C57BL/6 nude and corresponding wild-type mice, housed at 23 or 33 °C, were subjected to either low-fat diet or high-fat diet (HFD). Energy expenditure, locomotor activity, body core temperature, respiratory quotient as well as food and water intake were analyzed using indirect calorimetry. Immune function at different housing temperatures was assessed by using an in vivo cytokine capture assay. RESULTS Our data clearly demonstrate that conventional housing protects C57BL/6 nude mice from HFD-induced obesity, potentially via increased energy expenditure. In contrast, HFD-fed C57BL/6 nude mice housed at thermoneutral conditions develop adiposity, increased hepatic triglyceride accumulation, adipose tissue inflammation and glucose intolerance. Moreover, increased circulating levels of lipopolysaccharide-driven cytokines suggest a greatly enhanced immune response in C57BL/6 nude mice housed at thermoneutrality. CONCLUSION Our data reveals mild cold stress as a major modulator for energy and body weight homeostasis as well as immune function in C57BL/6 nude mice. Adjusting housing temperatures to the thermoneutral zone may ultimately be key to successfully study growth and progression of human tumors in a diet-induced obese environment.

Thermoneutrality, Mice, and Cancer: A Heated Opinion

“…Several groups have now shown that this unexpected lack of the predicted phenotype was because the mice were housed at ST, and when these mice are housed at TT (and are not burning energy through adaptive thermogenesis) they do become obese [61][62][63][64]. This effect of ST on obesity has been observed in other models as well [65][66][67], and it is clear that precise data on the linkage between diet, obesity, and cancer should be re-examined in the context of absence of cold stress. Interestingly, Koizumi and colleagues showed that the reported ability of dietary restriction to reduce the incidence of lymphoma in mice only occurred at ST, and that this effect was lost in mice housed at TT [68], again demonstrating a dichotomy of experimental results at ST versus TT.…”

“…The key to reproducibility is accurate reporting of these seemingly mundane details, which potentially have large effects ' [87]. Although housing temperature was not included as a factor in these analyses, studies are accumulating in which experimental outcomes differ depending on the ambient temperature; these are summarized in Figure 1 [7,10,11,19,27,28,40,42,44,46,48,63,66,67,70,79,84,[88][89][90][91][92][93][94] biomedical applications, and how this condition may influence decisions for translation to the clinic (see Outstanding Questions). It is likely that many, if not all, of the metabolic abnormalities noted previously in mouse models stem largely from chronic mild cold stress and the increase in adaptive thermogenesis.…”

“…In view of the fact that we found significant differences in the immune contexture of tumorbearing mice at ST and TT, further investigation into how ambient temperature may affect immune cell and cytokine/chemokine networks (profiles) is warranted. At least two studies have reported differences in the induction of cytokines in response to immune challenge [66,79]. Intriguingly, Straub et al [45] outline the possible relationships between chronic inflammatory diseases (which demand that increased energy resources are shifted to the immune response) and many metabolic abnormalities.…”

“…Sleep [79,94 ] Obesity [63,66,67 ] Insulin Produc Ɵon [46 ] Car diovasc ular [27,2 8] Organ Si ze, ta il length [29 ] Bas al Met abo lism [7,12,84 ] Metaboli sm of imm une cell s?…”

“…Comparisons of BAT by MRI could also prove to be a valuable and relevant biomarker of the degree of cold-stress in experimental mice at different ambient temperatures [40]. Sleep [79,94 ] Obesity [63,66,67 [7,10,12,[27][28][29]37,40,[42][43][44]46,47,63,66,67,70,71,79,84,89,93,94]). Several other conditions or phenomena that are modeled in mice and are likely to be influenced by housing temperature, but for which there is little or no published information are also listed (followed by ?).…”