Scientists create light-controlled versions of cholesterol

High levels of cholesterol are linked to heart disease, stroke, and many other health problems. However, this complex and vital fatty, water insoluble molecule-a lipid-is found in every cell of the body and is not all bad news. It also regulates crucial processes that science has yet to map.

"Cholesterol helps build membranes and serves as the starting point for important hormones like estrone and testosterone, so it shapes many aspects of our health and disease," says Michael Zott, a Beckman Postdoctoral Fellow at the University of Pennsylvania. Studying its behavior is tricky because it is tiny and hard to track, Zott says.

These constraints mean scientists often rely on "functional derivatives," or molecules designed to mimic cholesterol but which include chemical tags so they can be seen and tracked.

In a paper published in the Journal of the American Chemical Society, Zott and a collaborate team led by his postdoctoral adviser Dirk Trauner have designed a new set of cholesterol proxies with light-sensitive compounds attached. Called "photocholesterols," these molecules change shape when exposed to light, allowing the researchers to toggle cholesterol's biological activity on or off.

This light-based system paves the way for advanced therapeutics, allowing drugs to be activated deep within the body where traditional controls fail. The team's ultimate goal is to enable wavelengths of light that can penetrate through the skin to reach organs targeted for medicine.

"The nice thing about using light to trigger these geometric changes in molecules we study is that certain forms of it can penetrate tissues quite deeply" says Trauner, co-senior author of the paper and a Penn Integrates Knowledge University Professor in the School of Arts & Sciences and the Perelman School of Medicine. "This allows for what we usually call spatiotemporal control. A person could take the medicine systemically, and then we could activate it at a precise time in a precise place using a focused beam of light to turn the molecule on in only a certain location."

They found that the photocholesterols they created did not behave identically.

"While we initially aimed to make a molecule that would work in every possible application-a 'pan cholesterol' mimic-we came upon a powerful, fortuitous result," Zott says.

Instead of behaving identically, some photocholesterols strongly preferred certain transport proteins over others, and one candidate turned out to be possibly the first selective inhibitor of two poorly understood sterol transport proteins: ORP1 and ORP2.

"The work has already led to new discovery," says co-senior author of the paper Luca Laraia of the Technical University of Denmark. "We now have the first 'photoswitchable' inhibitors of ORP1 and ORP2-proteins we know play a critical role in cholesterol balance but whose function we haven't fully elucidated. This will significantly help us understand their biological roles."

"By finding molecules that are selective for them, that means we can begin to develop tools to turn them off or turn on, selectively," adds Zott, "and that will help us uncover what their function is down the line."

For future work, the team plans to leverage the precision of light to map when and where key sterol transport proteins move cholesterol within complex cellular models under normal and disease-like conditions.

They also plan to adapt the same computational design strategy to build light-controlled versions of other lipids, with the long-term goal of optimizing lipid nanoparticle formulations for applications like light-controlled mRNA delivery and designing systemic therapies that can be activated locally using focused beams of light, providing precise spatiotemporal control.

"Cholesterol is at the center of biology and underlies cutting-edge tools like the lipid nanoparticles used in modern vaccine technology," says Zott. "By making a light-controlled version, we can begin to investigate, and potentially improve, all of these crucial processes."