New Fluorescent Probes Could Revolutionize Neurodegenerative Disease Research
Cholesterol has many complex and crucial functions in the brain, and the scientists who want to make it easier to study it have their work cut out for them. Like most molecules, this essential lipid is practically invisible in cells, so they must design an easily detectable molecule that acts like cholesterol, ideally well enough to trick lipid transporters into shipping it around and between cells like the real thing.
In addition, it has to glow — the key element of fluorescent imaging that allows researchers to distinguish molecules inside cells.
“I don’t want to say impossible, but it’s very hard to do,” said Maciej J. Stawikowski, Ph.D., an assistant professor of chemistry and biochemistry at Florida Atlantic University’s Charles E. Schmidt College of Science.
But Stawikowski and his colleagues have gotten closer, developing a new class of fluorescent probes that mimic cholesterol closely enough to be taken up by a cell’s trafficking system while still fluorescing brightly enough to pinpoint their location under the right imaging techniques.
These new probes are “anticipated to impact the study of membrane biology, lipid dynamics and cellular targeting,” according to a recent paper published by the researchers in the journal Scientific Reports. “We expect that these compounds will enhance our understanding of cholesterol-related processes and cellular membrane dynamics and find applications in drug delivery systems and other areas of biomedical research.”
Fluorescent imaging of cholesterol isn’t a new idea, but previously developed probes have had their drawbacks. Some mimic cholesterol well but aren’t very bright, which can lead to lower-quality data collection. Some are bulky enough to disrupt how the tagged molecule would naturally move inside the cell.
Another probe that has become a major research tool fluoresces brightly and closely mimics cholesterol in many cases, but it doesn’t get transport between organelles of the cell quite right.
And some probes aren’t environmentally sensitive: They glow just as brightly in water as they do in cell membranes, where natural cholesterol resides.
Not only are the new probes environmentally sensitive, but their selective glowing properties can be tuned due to the modular structure. Its swappable head groups and linkers that connect the probe to cholesterol allow customization for specific experimental purposes.
For example, one head group is sensitive to pH changes. This could be useful for studying communication between synapses, Stawikowski said.
When neurons talk to each other through synapses, they use cholesterol to form vesicles to pack up and transport neurotransmitters. They emerge at the surface and release their cargo at the surface and then recycle back.
“During synapse communication, you have acidification of these synaptic vesicles,” Stawikowski said. “So, we can use the pH sensitivity of these probes for trafficking studies in synaptic vesicles.”
The probes could also be useful in studying lipid droplets, whose accumulation in the brain is increasingly linked to Alzheimer’s disease. Stawikowski’s lab is also working on developing fluorescent tags for other lipids stored in fat cells like diacylglycerols and triacylglycerols.
“We want to understand how these can interplay with cholesterol and especially lipid droplets,” Stawikowski said. “There’s a lot we still don’t understand about cholesterol and its involvement in neurodegeneration.”