Research team led by Professor Zhijun Zhao from the College of Biology and Environment worked with the research team led by Professor John Roger Speakman from Chinese Academy of Sciences Shenzhen Institute of Advanced Technology and made new progress in the study of energy metabolism and aging and lifespan in animals. In the “Body temperature is a more important modulator of lifespan than metabolic rate in two small mammals” published in Nature Metabolism online on 15 March 2022, they stated that lifespan may be related to metabolic rate.” Some animal studies show that higher metabolic rate lead to shorter lifespan as higher metabolic rate may cause increased production of free radicals, which will intensify the oxidative damage to organism tissues, cause faster aging and therefore shorten the lifespan. However other research shows that lifespan is not related to metabolic rate. For example, in some species with higher metabolic rate (such as birds) usually have quite long lifespan, whereas some species with lower metabolic rate (such as marsupial animals) have shorter lifespan. Therefore, the correlation between metabolic rate and lifespan may be based on individual level rather than at interspecific level. Animals under food restriction not only indicate lower metabolic rate but also have lower body temperature. Body temperature drop is often achieved by reducing metabolic rate as they are closely related. Therefore lower metabolic rate and lower body temperature may be both the key factors affecting aging and lifespan. However, as changes in metabolic rate often are accompanied by changes in body temperature, it is difficult to tell exactly the individual impact of the two factors on aging and lifespan.

The thermoneutral zone (TNZ) refers to the stable metabolic zone in which the oxygen consumption level of endotherms is the lowest within a certain range of ambient temperature. When internal body heat production is stable, a range of cooling methods including conduction, convection, radiation, and evaporation can change the body’s heat conductivity to maintain body temperature. When small mammals are domesticated at upper critical temperatures (UCT) at TNZ, dropped heat conductivity tend to push body temperature higher. Then the metabolic rate is maintained at a low level to reduce heat production and avoid hyperthermia. Under such ambient temperature, the change pattern of body temperature and metabolic rate of the two may be opposite, which allows us to distinguish the influence of the two alone on aging and lifespan.

In this study, the Cricetulus barabensis and Mus musculus were domesticated under UCT environment for a long time, and results showed that most of the body components had not changed significantly, however the metabolic rate was reduced significantly and body temperature was increased. Aging of both animals accelerated and lifespan was significantly shortened, which therefore was able to distinguish the effect of body temperature and metabolism on aging and lifespan alone. When animals under UCT environment are exposed to the breeze, wind acclimation did not significantly affect metabolic rate, but instead significantly increased thermal conductivity, promoted body heat dissipation, and significantly reduced body temperature. Both animals showed delayed aging and extended lifespan, thus reversing the adverse impact of high temperature on lifespan. Research results show that under certain conditions, body temperature adjustment has a greater impact on lifespan and lowering body temperature is beneficial to delay aging and prolong life expectancy.

In this study, UCT environment domestication was used to increase animal’s body temperature while maintaining metabolic rate at a low level; wind acclimation was used to increase heat conductivity and increase heat dissipation efficiency, which significantly reduced body temperature without significantly affecting metabolic rate and thus successfully distinguished the effects of metabolic rate and body temperature alone on aging and lifespan. This study also has its limitations. For example, the causes of aging and natural death in animals are still not known, body temperature and metabolic rate have not been consistently measured across different ages, and the effects of UCT environment and wind acclimation on other species are also unknown.

Wenzhou University is the first signatory of this research and the cooperating partners include Liaocheng University, Chinese Academy of Sciences Shenzhen Institute of Advanced Technology, Aberdeen University of UK, and Chinese Academy of Sciences Institute of Genetics and Developmental Biology. Zhijun Zhao is the first author of this paper.Zhijun Zhao and John Roger Speakman are joint corresponding authors. This project is supported by the National Natural Science Foundation of China and various other programs.