Gene study explores polar bears’ weight-gain secret

When it comes to weight gain, nothing tops the polar bear. Yet the very fact that it remains fit and healthy despite half its entire bulk being pure fat could help us tackle heart disease in humans.

Irish researchers were deeply involved in an international study of the bears that focuses on their genes. Experts on genetic evolution at NUI Maynooth and Dublin City University analysed the genomes of 70 polar bears in a hunt for what it is that allows them to be so very fat yet completely healthy.

Beijing Genomics Institute, the largest of its kind in the world, led the international project. It provided the bear genomes, derived from tissue samples gathered by scientists from populations around the high Arctic. Science Foundation Ireland supported the labs here.

Largest project
"Outside of humans, this is the largest mammal genome project ever undertaken," said Prof James McInerney, an evolutionary biologist and professor in NUI Maynooth's department of biology.

“How is this study relevant to humans? This is the most extreme animal. A mature male will be 50 per cent fat. A human like this would be incredibly obese and unhealthy,” he said.

Many other labs were involved in the study, which is published this evening in the journal Cell.

“This is a really large international effort,” said Dr Mary O’Connell, a principal investigator in Dublin City University’s school of biotechnology.

“I took the genome data and tried to identify differences in the same gene across many species,” she said. “It is very exciting really; you start on these projects and you start digging and you don’t know what you are going to find.”

Bear genes
When they started to look for differences, out popped genes related to fat metabolism, what the bears do with their cholesterol and their cardiovascular function. Knowing how the bear genes work should provide a better understanding of how human genes differ and why our systems cannot tolerate so much fat.

One of the significant finds was how fast the polar bear genes evolved away from their brown bear origins. Earlier studies estimated polar bears could have evolved up to five million years ago. The international study revealed they evolved somewhere between 400,000 and 600,000 years ago representing just 60,000 generations.

“This is surprising because they are quite different to brown bears,” said Prof McInerney. “They must have evolved incredibly quickly. The hair colour is easy but not the metabolism and coping with their extreme life on the ice.”

The data should also help conserve these animals. There are only about 14 populations around the high Arctic and 10 are in decline, he said. The goal will be to protect the widest possible genetic diversity and avoid inbreeding that could bring an end to these amazing creatures.