JAN 18, 2017 07:27 PM PST

Researchers Learn More About the Function of Cholesterol

WRITTEN BY: Carmen Leitch

While cholesterol is primarily found in the cell membrane, its role there is not well understood. Researchers at the University of Illinois at Chicago have used a powerful imaging technology to reveal more about the function of cholesterol. In a surprise to the investigators, cholesterol apparently acts to transmit signals across the membrane of cells. Their research has been reported in Nature Chemical Biology.

This is a diagram showing cholesterol's (red) predominance in the outer layer of the cell membrane. Cholesterol transport proteins (blue) can alter its distribution between the inner and outer layers. / Credit: UIC

"Cholesterol is a lipid that gets bad press because of its association with cardiovascular disease," said the leader of the study, Wonhwa Cho, a Professor of Chemistry at UIC. "It's been very well studied, but not much is known about its cellular function. What is its role? Is it a bad lipid? Absolutely not - for example, the brain is about half lipid, and cholesterol is the richest lipid in the brain," he said.

Previous work by Cho's team has investigated the various molecular interactions cholesterol has with a variety of molecules that govern cellular processes, but researchers had not considered a regulatory role for cholesterol itself. "We knew it could play an important role in cell regulation - for example, in proliferation or development. We know that high-fat diets, which boost cholesterol levels, have been linked to an elevated incidence of cancer. How, is not fully understood," Cho explained.

One reason that cholesterol is not considered regulatory is because such molecules are typically transitory signals. "But cholesterol is there all the time," Cho said. The majority of cholesterol in a cell, 90 percent, is found in the cell membrane, where cholesterol is a major component of membrane lipids. The cholesterol adds stability to the double-layered lipid membrane. Cholesterol coalesces as "rafts," and had been thought of as platforms used by signaling molecules. "But in this paper, we showed that a single cholesterol molecule can itself be the signal trigger," Cho explained.

It was thought that cholesterol was present in both layers of the membrane, Cho said, "maybe more in the inner layer. But we, for the first time, measured cholesterol levels in the inner and outer layers simultaneously in real time, in living cells. And we showed that cholesterol is predominantly in the outer layer."

In this work, the investigators report that cholesterol comprises around 40 percent of the membrane’s outer layer, while the inner layer only contains around 3 percent cholesterol. The various levels of cholesterol can be altered; the amount in the inner layer more than doubled and the level in the outer layer fell by that amount after a stimulation by the researchers.

They also determined that in cancerous cell, the normally low level of cholesterol in the inner layer jumps much higher. "We checked this in many different cell lines," Cho added.

Statin drugs, used to lower cholesterol, have the side effect of reducing the risk of cancer. Cho’s team determined that applying a statin to cells substantially lowered the amount of cholesterol in the inner layer, reducing cellular growth. This could potentially lead to new cancer treatment methods, Cho suggested.

"I think we're just scratching the surface of the regulatory role of cholesterol. We have many unpublished data indicating that cholesterol is involved in a wide variety of cellular processes and regulation," he said.

Cho added that cholesterol is a challenging molecule to study; lipids like cholesterol are "very nasty molecules to work with; unlike most biological chemicals, they are not soluble in water. "We had to devise a new strategy," Cho explained.

Cho and his team created an optical imaging technology six years ago, which enables the direct measurement of lipid levels in live cells. By adding a fluorescent tag to a lipid-binding protein molecule, the amount of free to bound lipid can be measured, as there is a change of color when the lipid is in specific locations within the membrane.

To learn more about the fluid mosaic model of the cell membrane, check out the video above from Khan Academy. The video below is a short lecture on glycolipids and cholesterol.

 

Sources: AAAS/Eurekalert! via UIC, Nature Chemical Biology

About the Author
  • Experienced research scientist and technical expert with authorships on 28 peer-reviewed publications, traveler to over 60 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
NOV 26, 2018
Genetics & Genomics
NOV 26, 2018
Researcher Claims to Have Genetically Engineered Human Babies
Shocking the scientific community, a Chinese scientist announced that he edited human embryos, and twins have been born....
NOV 26, 2018
Neuroscience
NOV 26, 2018
Most Rewarding Experiences Take The Top Spot In Memory
brain filters out neutral, inconsequential events, retaining only the memories that are useful to the future decisions....
NOV 28, 2018
Videos
NOV 28, 2018
Nanorobots That can Move Through the Eye
Researchers want to create tiny drug delivery systems that can move through biological tissue....
DEC 08, 2018
Cell & Molecular Biology
DEC 08, 2018
Regenerating Beta Cells to Cure Diabetes
Beta cells of the pancreas produce a critical hormone that controls blood sugar - insulin. But beta cells can die off....
DEC 10, 2018
Neuroscience
DEC 10, 2018
Researchers Found Future Choice Predictive Neural Activity In The Prefrontal Cortex
Uncertainty and Gambling go hand-in-hand; there is never a sure bet. Researchers have identified neuronal activity in the prefrontal cortex that encodes predictive action....
DEC 10, 2018
Neuroscience
DEC 10, 2018
Scientist found genes to promote spinal cord regeneration
lay out a path that neurons of the spinal cord might be able to follow - potentially leading to improved recovery for people paralyzed by spinal cord injuries....
Loading Comments...