Release date: 2017-09-26
For months, a fish living in a dark cave in Mexico has no food. For a longer period of time - for thousands of years, they don't even have light, so their eyes degenerate during evolution and lose their skin pigmentation.
The researchers found that this strange creature has a quirk. In order to survive in a food-poor environment, they have evolved an extreme way of turning nutrients into energy. These characteristics form conditions such as large fluctuations in blood sugar, which is a precursor to type 2 diabetes in humans. But in these cave blind fish, this change is adaptive, not disease. These burrowing fish live a long and healthy life.
Cliff Tabin, a geneticist at Harvard Medical School in the United States, points out how these fish can stay healthy under these adverse conditions or contribute to the development of new therapies for treating diabetes in humans. Tabin studied these features and reported on the Pan American Evolutionary Biology Society in Calgary, a city in southwestern Canada, where he and his colleagues have gained clues about how burrowing fish have this ability.
In humans and other mammals, the first sign of type 2 diabetes is weaker glycemic control. This happens because the cells are resistant to insulin, a hormone that marks the cells's absorption of glucose from the blood. If the problem continues to develop, it will develop into comprehensive diabetes, making blood sugar levels reach 140 mg or more per 1/10 liter, leading to organ failure, vascular leakage, nerve damage, and high risk of stroke and heart disease. These diseases cause 3.4 million deaths worldwide each year. Diet, drugs, and insulin injections are current treatments, but they often don't work. (Body weight loss surgery has become another recent treatment option, but there is also a risk of surgery.)
This burrowing fish, the Mexican lycium, clearly indicates another treatment option. The fish was washed from the river into the cave about 1 million years ago. That is a huge environmental change. The river is full of food, but there are only seasonal floods in the caves – some small shellfish and decomposing substances and debris in the soil. There is no light in the cave, so there is no plant or photosynthesis, and there is very little oxygen in the water. But there are no predators of fish there. "The good news in the cave is that no predator will swallow you. The bad news is that you have nothing to eat," Tabin said.
Because the fish have no food for many months, the researchers suspect that they have evolved a metabolic way that can effectively store calories as fat. To test the idea, Tabin and the team compared the burrowing fish and river fish raised in a similar environment in the laboratory. They found that this burrowing fish did store more fat than its close relatives. They also have larger, fatter livers, similar to the fatty liver disease associated with diabetes in humans. "But you won't see the fish's liver damaged," Tabin said. "It's very strange."
The discovery of pre-diabetes in these healthy fish allowed Tabin to observe another aspect of their metabolism. Blood sugar control is one of them. When the river fish was fed with glucose, he saw that insulin began to control their blood sugar levels. However, the blood sugar level of burrowing fish has risen linearly. Then, during the hunger phase, the blood sugar level of the burrowing fish fell to a record level. "This causes diabetes in humans, but burrowing fish doesn't." Tabin said.
Further observation of the muscles of this fish (most of the blood sugar consumption) suggests that burrowing fish are resistant to insulin at both cellular and biochemical levels. After giving the same amount of insulin, the river fish muscle cells will absorb more glucose than the cave fish muscles.
Genetic analysis indicates the reason for its subsequent existence: the fish's insulin receptor gene has a unique mutation that helps it gain weight. Tabin and the team used genetic engineering methods to implant the insulin receptors of burrowing fish into common zebrafish. It turned out that those fish were healthier than ordinary zebrafish. “We found that many of the burrowing fish that have undergone natural selection are changing their metabolism.†Suzanne McGaugh of the University of Minnesota, who did not participate in the study, said he had studied the genome of burrowing fish.
These findings suggest that burrowing fish have evolved an extremely “thumpy†metabolic mechanism. But how do they escape the negative effects of food processing? Perhaps these fish have "co-evolution, and these factors make the problems associated with hypoglycemia control, fatty liver and insulin resistance ineffective." The former postdoctoral staff of Tabin Labs, head of the laboratory of the Stowes Medical Institute Nicolas Rohner said. In other words, the evolution of these burrowing fish has inspired potential therapies for diseases such as diabetes and obesity.
Source: Science Network
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