Researchers track cholesterol in real time

Toronto, ON – Using a new method, scientists from the University of Toronto can now precisely track how cholesterol moves into blood vessel walls, a process that can lead to the formation of deadly plaque. It’s a discovery that could provide new insights into treating heart disease and stroke — two of the three leading causes of death in Canada.

For years, researchers knew that the first step in atherosclerosis, or hardening of the arteries, began when cholesterol moved through the endothelium, the inner lining of the blood vessel’s wall. But due to technical limitations, this process was poorly understood.

Previously, scientists believed that cholesterol broke through gaps in the damaged lining of the blood vessel’s wall. But autopsy studies on young people who died from car accidents, or other non-cardiac causes, showed that cholesterol could be detected under the lining of blood vessels, even when that lining was healthy and undamaged. 

“We’ve now shown that cholesterol can move through endothelial cells, even when the inner lining is perfectly intact and there are no gaps,” said Warren Lee, a professor in the Faculty of Medicine’s Department of Laboratory Medicine and Pathobiology.

Lee and his team used a newly applied technology, called total internal reflection fluorescence microscopy (TIRF), to track cholesterol moving through the inner lining in real time. They tagged cholesterol in human endothelial cells using fluorescent markers, and then measured flashes of light as the cholesterol moved through the cells. The technology is so accurate it can visualize the bottom 100 nanometres of an endothelial cell.

“Up to now, most researchers have studied blood vessels’ permeability using cells that are grown on a semi-permeable membrane in a plastic dish,” said Lee, who is also a clinician-scientist at St. Michael’s Hospital. “Those experiments are challenging because researchers can’t track how cholesterol moves. Our new method allows us to see the cholesterol moving through individual cells, and it’s a more powerful approach that will allow us to determine the specific molecules and regulatory pathways that are involved.”

At the beginning of the experiment, the team had difficulty tracking the thousands of fluorescent signals. Luckily, Lee met another researcher who created a mathematical script to track and analyze the experiment’s data.

“This computerized analysis is great because it’s unbiased. You give it terabytes of data and it gives you accurate and highly detailed answers,” said Lee.

During their research, Lee’s team discovered that a receptor, called SR-B1, helps to move cholesterol into the vessel wall. Their findings were recently published in Cardiovascular Research.

“We were really excited about our discovery,” said Michael Sugiyama, PhD student and co-lead author of the study. “Not only are we one of the only labs in the world to study cholesterol movement with this technology, but we’re also identifying ways to control this movement.”

Next, the researchers will search for other receptors that might play a similar role to SR-B1, finding other treatment targets for atherosclerosis.

“Our dream would be to stop cholesterol from moving into the vessel wall, or even to find a way to move previously deposited cholesterol back into the blood stream and out of the body,” said Lee. “Now that we understand how the process works, we can focus on finding ways to prevent heart attack and stroke.” 

Reported by Katie Babcock, University of Toronto