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.