For people with diabetes, regulating blood sugar is a big part of making it through everyday life. People with diabetes are always working to keep blood glucose as regulated as possible, to avoid hyperglycemia, and to improve insulin sensitivity. We’re told that these strategies are absolutely essential in allowing us to live long, healthy lives.
The same is not true for fish, apparently, or at least not for a species of blind cave fish in Mexico. These little fish have widely fluctuating blood sugar, high levels of insulin resistance, and are chubbier than their closely related, genetically similar, river-dwelling cousins.
So someone who understands the importance of regulating blood sugar would think that these cave dwellers deal with health problems and poor life expectancy. But they don’t, nor do they develop the advanced glycation end-products associated with many of the poor outcomes of diabetes. In other words, they live equally long, and healthier, fish lives. How do they get away with it? Something seems fishy.
Researchers are hoping that if they can better understand how this little fish, the Mexican tetra (Astyanax mexicanus), can thrive with poorly regulated blood sugar and insulin resistance, they may be able to help people with diabetes.
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The cavefish have a genetic mutation that causes insulin resistance. So it makes sense that the little tetras had higher post-meal blood glucose, and that their glucose levels stayed elevated for far longer, than related fish without the gene mutation. But the cavefish also have much lower glucose levels after prolonged periods of fasting, demonstrating that they deal with more dramatically fluctuating blood sugar overall.
The cavefish also have higher levels of body fat and lose weight more slowly in nutrient-poor environments than the river fish. They also have fatty livers.
Despite all this, the insulin-resistant cavefish live as long or longer than their cousins (over 14 years). The cavefish do not have the sugar-coated proteins that would be found in a human with chronic hyperglycemia, and they also exhibit fewer signs of aging than the river-dwelling fish. Near the end of their lifespan, the river-dwelling fish experience tattered fins, sunken skin, and humped backs. The cavefish do not, and they maintain better fertility as compared to the river fish. What’s their secret?
The cavefish live off algae, and they live a feast or famine lifestyle that forces them to go for long periods without food. But the tendency to gain weight, and not lose it, helps them survive times of scarcity, and they have ravenous appetites that help them store fat when there is abundant food.
Somehow, these fish that live in chronic darkness have found a way to make hyperglycemia and insulin resistance work for them. The published research puts it like this: “Cavefish may have evolved compensatory mechanisms enabling them to remain healthy despite potentially deleterious metabolic changes.”
Researchers hope that if they can understand how exactly these fish lives healthy lives despite traditionally negative health characteristics, they may be able to find ways to help humans cope with diabetes.
Nicolas Rohner, one of the study’s authors, said that the team can’t say for certain if studying the fish will lead to any breakthroughs, but he did say, “I think it would be silly not to look.”
We hope that the research is successful. Until then, it’s not all peaches and cream for these conundrum-causing fish—they do have to live eyeless lives in chronic darkness and endure long periods of scarcity. But if they held the answers to how to deal with hyperglycemia, these creepy tetras could be our new best friends.Whizzco