Naked mole-rats (Heterocephalus glaber) are rodents found in the hot tropical regions of the Horn of Africa. When he first described a naked mole-rat in 1842, the famous German naturalist Eduard Rüppell suspected he had encountered a diseased specimen—because the animal had no fur and permanently protruding teeth. Only after several more specimens had been collected did it become apparent that their weird appearance, variously described as resembling saber-toothed sausages or miniature walruses, was normal.
Naked mole-rats live in a maze of underground tunnels that may extend more than a mile in length and as deep as 8 feet beneath the soil surface. Their burrows contain both nest chambers, tended by sterile worker animals, and several toilets, which the animals use religiously to avoid contamination of their living space. To locate the roots, tubers, and small onion-like bulbs they eat, mole-rats must dig through the soil, expanding their tunnels using their chisel-like, ever-growing incisor teeth. They occasionally make an opening to the outside world to kick excavated soil to the surface, where it forms small volcano-shaped mounds—the only aboveground signs of the vast colonies below. Given this strictly subterranean existence, it is not surprising that naked mole-rats have evolved a set of characteristics highly suited to life in dark, dank burrows.
This is how the naked mole rat’s colony looks like. This excellent review in The Scientist by Thomas Park and Rochelle Buffenstein illustrates the complicated lives of these outstanding hairless animals: how they live under the ground in Africa, how they have the breeding Queen and worker-animals (just like the honey bees), how they don’t feel certain kinds of pain, how they are resistant to the lack of oxygen and toxic amounts of carbon dioxide in the air. But the coolest thing about the naked mole rats is that they basically live 9 times more than “they should”:
Although naked mole-rats are the size of a mouse, weighing only about 35–65 grams, in captivity these rodents live 9 times longer. With a recorded maximum lifespan of 32 years, they are the longest-lived rodents known. And remarkably, they appear able to maintain good health for most of their lives. At an age equivalent to a human age of 92 years, naked mole-rats show unchanged levels of activity and metabolic rate, as well as sustained muscle mass, fat mass, bone density, cardiac health, and neuron number.
So not only they are exceptionally long-lived, they are also very active and healthy even in the old age.
Somehow they delay the onset of aging and compress the period of decline into a small fraction of their overall lifespan.
They also have no cancer.
Naked mole rates are exceptions to several theories of aging. For example, the free radical theory states that aging happens, because of the extensive cellular damage from reactive oxygen species. However, naked mole rats show very high levels of oxidative damage from these free radicals and still their cells are perfectly functioning for years and years. Another hypothesis claims that aging is due to shortening of telomeres – DNA molecules caps, that shorten every time a cells undergoes division. Yet the naked mole rat has relatively short telomeres. Also the telomerase, protein that lengthens telomeres, is not really active in naked mole rats’ cells. So telomere maintenance is unlikely to explain the outstanding longevity in these animals.
So what are the reasons for these almost “magical” properties of the naked mole rat? Park and Buffenstein note:
1. Naked mole-rat tissues are better able to recognize abnormal cells, neutralize their tumorigenic properties, and repair their DNA. Should that fail, the cells are ushered into programmed cell death pathways. This means that errors in the DNA are constantly and effectively repaired or removed, before they give rise to cancer.
2. Many gene families in the mole-rat genome are involved in DNA repair and detoxification processes, and the expression of these genes remains unchanged as the animals age. So, stress resistance genes work perfectly well into the old age.
3. Proteasomes are more abundant and more efficient in degrading the damaged proteins within the cells. Same thing with autophagy – it occurs at a twofold greater rate in naked mole-rat cells than those of the mouse. These two enchanted mechanisms of cellular cleaning resist damage from toxins, heavy metals and DNA-damaging agents. In simple words: better housekeeping means longer life.
This supermodel for research is being studied only in a couple of labs in the world. This is such a shame. I wish more researchers included naked mole rats in their experiments. I wish there were more money for research in naked mole rats, because they may hold the keys to our understanding of the mechanisms responsible for life extension.