There are several ways to stay warm on a cold day. If you are human, you can turn up the heat in your home, put on a sweater, snuggle, and even produce body heat through shivering as well as non-shivering metabolic pathways – although the ability to produce heat metabolically typically declines with aging. If you are a small mammal, turning up the heat or putting on a sweater are not really viable options. Instead, these animals as well as newborn babies create their own body heat with the help of brown adipose tissue that generates heat without the need to shiver (i.e. non-shivering thermogenesis). Brown adipose tissue is rich with mitochondria that contain a special protein called uncoupling protein 1 (UCP1). When the mitochondria burn fats for fuel, they leak protons and produce heat.
Naked mole rats live in hypoxic burrows with fairly consistent temperatures throughout the year. Even though they avoid extreme temperature changes, they have brown adipose tissue between their shoulders that contains UCP1. Interestingly, researchers often say these animals are not very good at generating body heat in response to cold conditions. So, what is the UCP1 protein doing there?
A recent study published by Cheng et al., (2021) showed that naked mole rats actually can turn up the heat when they are in an environment with normal levels of oxygen (normoxic), but then lower UCP1 levels and hence, heat production, in hypoxic environments, like their burrow. So, rather than being activated by cold, UCP1 seems to be regulated by environmental oxygen. By reducing body heat in hypoxic environments, they can save energy.
Michael Gaudry and Dr. Martin Jastroch from Stockholm University are also interested in understanding how the UCP1 protein from naked mole rats differs from other mammals. At last month’s Experimental Biology conference in Philadelphia, they presented data comparing UCP1 from naked mole rats to other mammals to assess how the protein is evolving. Like Cheng et al., this new study found that UCP1 from naked mole rats can generated heat. They are now looking at various mutations in the naked mole rat UCP1 that may help explain its seemingly unique regulation of body heat.
H Cheng, R Rebaa, N Malholtra, B Lacost, Z El Hankouri, A Kirby, NC Bennett, B van Jaarsveld, DW Hart, GJ Tattersall, M-E Harper, ME Pamenter. Naked mole-rat brown fat thermogenesis is diminished during hypoxia through a rapid decrease in UCP1. Nature Communications. 12: 6801, 2021.
M Gaudry and M Jastroch. Insights into the evolution of non-shivering thermogenesis from UCP1 of the naked mole rat (Heterocephalus glaber). 2022 Experimental Biology conference abstracts.