Blind cavefish seem to ignore insulin without health consequences

Enlarge (credit: Zachary Zakibe)

The Mexican tetra comes in different flavors. In normal river habitats, it's a small, standard-looking, silvery fish. But some groups within the species have made their home in dark, food-scarce caves. Evolution has quickly rid these groups of their resource-hungry eyes and turned them into pinkish, chubby, blind cavefish-with a bunch of metabolic changes that help them survive in the extreme environment.

A paper in Nature this week reports that the cavefish are resistant to insulin, a condition that can cause damage on its own and is often a precursor to diabetes. But the fish somehow don't suffer the same kinds of tissue damage that humans do when we have insulin resistance. The authors of the paper, led by Harvard geneticist Misty Riddle, report on how they tried to get to the bottom of the genetic mutations that contribute to this metabolic mystery. Their results show just how much variety exists in how different species respond to insulin-and that studying these fish more could help our understanding of diabetes.

High blood sugar

After you eat something, your blood sugar rises, and your pancreas releases insulin to deal with the increase. The insulin binds to specialized receptors, found on the surfaces of muscle, fat, and liver cells, telling them to absorb glucose from the blood. In between meals when blood glucose levels drop, a different hormone (glucagon) prompts the liver to release its stored glucose back into the blood.

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