Department of Human Health & Nutritional Sciences, University of Guelph, Guelph, ON, Canada.
Sunnybrook Research Institute, University of Toronto, Toronto, ON, Canada.
J Physiol. 2019 Sep;597(17):4581-4600. doi: 10.1113/JP278221. Epub 2019 Jul 11.
Mice are commonly housed at room temperatures below their thermoneutral zone meaning they are exposed to chronic thermal stress. Endurance exercise induces browning and mitochondrial biogenesis in white adipose tissue of rodents, but there are conflicting reports of this phenomenon in humans. We hypothesized that the ambient room temperature at which mice are housed could partially explain these discrepant reports between humans and rodents. We housed mice at room temperature or thermoneutrality and studied their physiological responses to acute and chronic exercise. We found that thermoneutral housing altered running behaviour and glucose homeostasis, and further, that exercise-induced markers of mitochondrial biogenesis and the browning of white adipose tissue were reduced in mice housed at thermoneutrality.
Mice are often housed at temperatures below their thermoneutral zone resulting in compensatory increases in thermogenesis. Despite this, many studies report housing mice at room temperature (RT), likely for the convenience of the researchers studying them. As such, the conflicting reports between humans and rodents regarding the ability of exercise to increase mitochondrial and thermogenic markers in white adipose tissue may be explained by the often-overlooked variable, housing temperature. To test this hypothesis, we housed male C57BL/6 mice at RT (22°C) or thermoneutrality (TN) (29°C) with or without access to a voluntary running wheel for 6 weeks or subjected them to an acute exhaustive bout of treadmill running. We examined the gene expression and protein content of select mitochondrial and thermogenic markers in skeletal muscle, epididymal white adipose tissue (eWAT), inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT). We also assessed adipocyte morphology and indices of glucose homeostasis. Housing temperature influenced glucose tolerance and insulin action in vivo, yet the beneficial effects of exercise, both acute and chronic, remained intact in eWAT, BAT and skeletal muscle irrespective of housing temperature. Housing mice at TN led to an attenuation of some of the effects of exercise on iWAT. Collectively, we present data characterizing the acute and chronic metabolic adaptations to exercise at different housing temperatures and demonstrate, for the first time, that temperature influences the ability of exercise to increase markers of mitochondrial biogenesis and the browning of white adipose tissue.
老鼠通常被安置在低于其热中性区的室温下，这意味着它们会长期受到热应激的影响。耐力运动可诱导啮齿动物白色脂肪组织的褐色化和线粒体生物发生，但在人类中对此现象的报道存在矛盾。我们假设，老鼠的环境室温可能部分解释了人类和啮齿动物之间的这些差异报告。我们将老鼠分别安置在室温或热中性温度下，并研究了它们对急性和慢性运动的生理反应。我们发现，热中性温度会改变老鼠的跑步行为和葡萄糖稳态，而且在热中性温度下饲养的老鼠，运动诱导的线粒体生物发生和白色脂肪组织褐色化的标志物减少。
老鼠通常被安置在低于其热中性区的室温下，这导致产热代偿性增加。尽管如此，许多研究报告还是将老鼠饲养在室温（RT）下，这可能是因为研究它们的研究人员方便。因此，人类和啮齿动物之间关于运动增加白色脂肪组织中线粒体和产热标志物的能力的相互矛盾的报告可能是由经常被忽视的变量——饲养温度来解释的。为了验证这一假设，我们将雄性 C57BL/6 老鼠分别饲养在室温（22°C）或热中性温度（29°C）下，同时或不提供自愿跑步轮，持续 6 周，或让它们进行急性剧烈的跑步机跑步。我们检测了骨骼肌、附睾白色脂肪组织（eWAT）、腹股沟白色脂肪组织（iWAT）和棕色脂肪组织（BAT）中选定的线粒体和产热标志物的基因表达和蛋白含量。我们还评估了脂肪细胞形态和葡萄糖稳态指数。饲养温度影响体内葡萄糖耐量和胰岛素作用，但无论饲养温度如何，急性和慢性运动的有益作用在 eWAT、BAT 和骨骼肌中仍然完好无损。将老鼠饲养在热中性温度下会导致运动对 iWAT 的一些影响减弱。总的来说，我们提供了数据来描述不同饲养温度下对运动的急性和慢性代谢适应，并首次证明温度会影响运动增加线粒体生物发生和白色脂肪组织褐色化的能力。
