Jonathan Peterson ‘23
Executive Editor Emeritus
In my last article, I discussed many of the basic physical characteristics of naked mole-rats. Even those were bizarre, but the main focus of that article was on the infinitely more bizarre social structure of a naked mole-rat colony. These mammals live in groups which more closely resemble colonies of insects than the mammalian social structures we know. However, that article should not be taken to imply that the social structure of naked mole-rats is the craziest thing about these extraordinary little aliens. These mammals have been the subject of significant scientific research to discover both the “how” and the “why” of many of their physical characteristics.
Credit: BBC Science Focus
Thermoconformers
Mammals are notoriously thermoregulators—they maintain their body temperature within a specific and fairly narrow range. For instance, humans generally range from ninety-seven to ninety-nine degrees Fahrenheit. We expend energy to keep our body temperature within that range. This is how all mammals function—except for one.
Naked mole-rats are thermoconformers. This means that their body temperature conforms to the temperature of the environment around them. Because they live in burrows, the underground temperature is fairly consistent. Further, this adaptation is undeniably beneficial in their low-resource environment. Because their body temperature conforms to the temperature of their environment, they need not expend significant resources heating and cooling their bodies, like all other mammals.
Some argue that naked mole-rats are not true thermoconformers, but rather behavioral thermoregulators. This is based on evidence that, at temperatures above twenty-nine degrees Celsius, naked mole-rats will retreat deeper into the cooler areas of their burrows. And in cooler temperatures, naked mole-rats will huddle together, or congregate near the entrances to their burrow, where the sun is stronger.[1] So, some argue that they regulate their temperature through behaviors.
Pain Tolerance
In addition to being pink, hairless, and wrinkly, naked mole-rats are also immune to certain forms of pain. “[T]his superpower only works with specific chemical stimuli—acid and capsaicin—heat and pressure” are still painful to naked mole-rats.[2] This is because naked mole-rats do not have neurotransmitters in their cutaneous sensory fibers. Or, in English, their skin doesn’t have the nerves necessary to transmit the “pain” sensation.
One theory for why naked mole-rats have gained this adaptation is, again, related to the lack of resources in their environment. Having a less complex nervous system requires less energy—this makes naked mole-rats more efficient in their isolated environment.[3] Another theory posits that this adaptation developed in response to the naked mole-rat’s low oxygen and high carbon dioxide environment. The high levels of carbon dioxide can cause acid buildup in the body tissues of the rodents—this adaptation literally allows them to not experience the pain associated with this acid buildup.
Harnessing the power of this adaptation could help doctors to manage patient pain levels in treatments more effectively. This could be important for those suffering from cancer and arthritis. Acid buildup in the body is a significant contributor to chronic pain for both. If scientists could harness the ability of naked mole-rats to not experience pain resulting from acid, those suffering from cancer and arthritis could eliminate much of their chronic pain.[4]
Oxygen Deprivation
Naked mole-rats are also incredible at surviving in poorly ventilated, low-oxygen tunnels. For one, the hemoglobin in their blood is particularly efficient at oxygen uptake. Further, their respiratory and metabolic rates are far lower than other mammals their size—about 70 percent compared to a mouse—which allows for minimal oxygen use. Couple the two together and you have a rodent that is incredibly efficient at utilizing oxygen while simultaneously needing very little.
In fact, naked mole-rats can survive for at least five hours in an environment which contains only 5 percent oxygen. And they can survive indefinitely in an environment which contains 80 percent carbon dioxide and 20 percent oxygen. To put this into perspective, our atmosphere is 78.08 percent nitrogen, 20.95 percent oxygen, and 0.93 percent argon. Greenhouse gases like carbon dioxide, methane, nitrous oxide, and ozone collectively account for a mere 0.04 percent of our atmosphere.[5] So, carbon dioxide typically makes up only a portion of 0.04 percent of our atmosphere. Bump that up to 80 percent and leave oxygen at about 20 percent, and naked mole-rats would be content.
If that wasn’t crazy enough, naked mole-rats can take this a step further. “Their nerve cells can function for almost one hour in the complete absence of oxygen,”[6] and they seem to experience no negative side effects from being completely without oxygen for eighteen minutes.[7] They do this by switching from glucose to fructose for energy production within the body. Animals typically use glucose in an aerobic reaction—one which requires oxygen—to produce energy. Once a glucose molecule is broken into three smaller carbon molecules by glycolysis, the Krebs Cycle begins, and energy is produced. Naked mole-rats can, however, create energy through another means: fructose-driven glycolysis. Despite being far less efficient at creating energy than glucose-driven glycolysis, fructose-driven glycolysis is an anaerobic reaction, meaning no oxygen is required to produce the energy to keep vital bodily functions going. If this could be harnessed by scientists to aid humans, it could be used to prevent brain damage in patients suffering from strokes and other complications that restrict oxygen flow to the brain.[8]
Cancer Resistance
If the naked mole-rat isn’t your favorite animal by now, I don’t know what else I can say—besides the fact that they are almost entirely resistant to cancer.[9] Scientists aren’t fully sure what it is about naked mole-rats that makes them so cancer resistant, but there are a few theories. The first relates to what are known as “overcrowding” genes. Most mammals, including naked mole-rats, have the gene p27. This gene prevents cell division based on cell density—once cells come into contact with each other and reach a certain density, cell division will no longer occur. This prevents the unrestricted cell proliferation that is quintessential to cancer. While most mammals have the gene p27, naked mole-rats also have the gene p16. The two are both overcrowding genes; however, p16 functions at a much lower cell density than p27. This double layer of protection is believed to contribute to naked mole-rats’ cancer resistance.
In 2013, two other discoveries were made about naked mole-rats that may contribute to their cancer resistance. The first is that they have very high-molecular-mass hyaluronan molecules—five times larger than typical hyaluronan molecules.[10] Additionally, their ribosomes produce extremely error-free proteins, which contributes by limiting the number of mutations. Mutations are what lead to cells which exhibit unrestricted proliferation, so limiting the number of mutations reduces the risk of cancer.
Longevity
Finally, if you thought to yourself, “Maybe the naked mole-rat doesn’t get cancer because it doesn’t live very long,” you would be wrong. Naked mole-rats are the longest-living rodent and have a maximum recorded age of thirty-two years. And, unlike most mammals, their mortality rate does not increase with age.
Explanations for this include the naked mole-rat’s ability to lower its metabolism and the error-free proteins, both discussed above. Finally, both humans and naked mole-rats have higher levels of genes dedicated to repairing DNA than shorter-lived species, like mice.
Conclusion
I’ll keep it short: Naked mole-rats are crazy. They may not be beautiful, they may not be soft and cuddly, but they are incredibly interesting. And part of appreciating nature fully is appreciating things for more than their mere aesthetics. And loving nature is loving things despite their aesthetics. To me, naked mole-rats are ugly essentials, deserving of all the love they don’t receive.
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jtp4bw@virginia.edu
[1] As with the last article, assume all uncited information is supported by Wikipedia. https://en.wikipedia.org/wiki/Naked_mole-rat. I’m not entirely sure how this evidence is incompatible with the thermoconformer hypothesis. It seems to me that seeking out warmer or cooler environments to maintain a comfortable internal temperature is entirely consistent with maintaining an internal temperature consistent with the environment—otherwise known as thermoconforming.
[2] Ewan St. John Smith, Meet the Naked Mole-rat: Impervious to Pain and Cancer, and Lives Ten Times Longer than It Should (June 17, 2019) https://theconversation.com/meet-the-naked-mole-rat-impervious-to-pain-and-cancer-and-lives-ten-times-longer-than-it-should-118809. Capsaicin is what gives chili peppers their spiciness. It is a chemical irritant and neurotoxin for mammals.
[3] Elizabeth Pennisi, How Naked Mole Rats Conquered Pain—And What It Could Mean for Us (Oct. 11, 2016), https://www.science.org/content/article/how-naked-mole-rats-conquered-pain-and-what-it-could-mean-us#:~:text=Although%20it%20has%20a%20face,pain%20from%20injury%20and%20inflammation.
[4] Smith, supra note 2.
[5] Alan Buis, The Atmosphere: Getting a Handle on Carbon Dioxide, NASA (Oct. 9, 2019), https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/#:~:text=By%20volume%2C%20the%20dry%20air,methane%2C%20nitrous%20oxide%20and%20ozone.
[6] Smith, supra note 2.
[7] Park et al., Fructose-driven Glycolysis Supports Anoxia Resistance in the Naked Mole-rat, Science (Apr. 21, 2017), https://www.science.org/doi/10.1126/science.aab3896.
[8] Smith, supra note 2.
[9] They are also not my favorite animal, to be clear.
[10] I simply do not understand how this has an impact, but allegedly it does.