UC Berkeley researchers are examining how species evolve and how they adapt to new environments by comparing the genome of the polar bear to that of the brown bear.

The research, which involved studying 89 bear genomes, revealed that even though polar bears have diets high in fat, they do not suffer from heart attacks or cardiac arrests. The team of researchers includes UC Berkeley professor of computational biology Rasmus Nielsen, Eline Lorenzen, a postdoctoral fellow who works in Nielsen’s lab, and Matteo Fumagalli, former postdoctoral scholar who also worked in Nielsen’s lab. The findings were released Thursday in the science journal Cell.

“We wanted to use nature’s own experiment to answer questions we might be interested in,” Nielsen said, adding that the study of polar bears might also answer some questions about human physiology.

The project is an international collaboration among researchers from the United States, Denmark and China and comprises four to five years of research. Researchers discovered that brown bears and polar bears evolved from the same ancestor less than 500,000 years ago. Since then, the mammals have taken on different lifestyles, with brown bears adapting a diet similar to humans and polar bears adapting a high-fat, carnivorous diet.
“We need to understand the genetic mechanisms that allow polar bears to live in the high Arctic,” Lorenzen said.

The project analyzed the genomes of 79 polar bears from Greenland and 10 brown bears across Sweden, Finland, Alaska and Montana. The team of researchers from Denmark acquired the blood and tissue samples, while the Chinese team sequenced the genomes and helped with the analysis, Lorenzen said.

UC Berkeley researchers then analyzed the sequenced genomes in an effort to understand how polar bears withstand an Arctic lifestyle and discovered that the gene APOB, which encodes a protein that binds to LDL cholesterol, has fewer variants in polar bears than in brown bears. LDL cholesterol is commonly known as bad cholesterol and can lead to heart attacks.

How mutations of APOB can change the function of the protein is still a work in progress, Lorenzen said.

“In the human sense, they’re profoundly obese,” Lorenzen said, referring to polar bears and their blubber-heavy diet.

Polar bears mainly eat marine mammals and have fat deposits underneath the skin that are usually four to six inches thick.

“But they don’t have a problem with it, because they can cope with high levels (of) LDL cholesterol,” Lorenzen said, adding that polar bears hydrate by breaking down fat, as water is a byproduct of metabolized fat.

The researchers worked with Inuits in Greenland to obtain the tissue and blood samples of polar bears. Lorenzen traveled to East Greenland in 2011 to obtain the samples. According to Lorenzen, the Inuits in Greenland have a set number of polar bears that they are allowed to kill every year, which simplified the process of obtaining the samples for research.

The researchers are interested in studying how cholesterol levels are moderated in polar bears and conducting further analysis of the genes that are responsible for allowing them to sustain their lifestyle. Researchers also hope to look at how climate change has affected polar bears by studying their population change.