A new 3D imaging technique can quickly show cells how to respond to infection and possible treatments.
Science must move quickly to combat a pandemic. There are many promising COVID-19 treatments and safe vaccines that are now available. Biological research has accelerated significantly in the last two years.
Researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab) and Heidelberg University in Germany have increased the speed at which they can image infected cells with soft X-ray imaging. This microscopic imaging method can produce incredible detail in three-dimensional scans.
The scientists’ approach is quick and easy. This allows them to quickly analyze data that would have taken weeks to prepare and analyze with other methods. Scientists can also examine how cells react to SARS-CoV-2 or other pathogens.
“Before our imaging technology, one had to do the following: fix, slice, and stain the cells to get an electron microscopy analysis. Due to all the steps involved, it would take weeks to find the answer. It can be done in one day,” Carolyn Larabell (a Berkeley Lab faculty scientist working in the Biosciences Area) said. It speeds up diagnosing and treating patients with drugs that may cure or prevent disease.
Cellular freeze frames
Larabell is a professor in anatomy at UC San Francisco. She also directs the National Center for X-Ray Tomography (a facility based at Berkeley Lab’s Advanced Light Source (ALS). In the early 2000s, the facility staff developed soft X-ray tomography (SXT), which was used to fill in the gaps in other cellular imaging methods. The SXT is currently available to investigators worldwide and is constantly improving methods. She and three of her colleagues performed SXT using human lung cells prepared by colleagues from Heidelberg University and the German Center for Infection Research as part of a study published late last year in cell Reports Methods.
The German team was led by Venera Weinhardt and Ralf Bartenschlager, virologist. They then infected cells with SARS CoV-2 and chemically fixed them using aldehyde-based chemicals. This kills cells and keeps them immobile for at least 6 hours (and inactivates any remaining virus particles).
Despite chemical fixation, the team was thrilled when the 3D images produced had the same amazing detail and clarity as SXT. Their approach will enable many labs to image infected cells safely without the inherent risks and safety protocols associated with working with live cells.
Larabell stated that this is an important point as many dangerous organisms people cannot study. Not everyone has a BSL-3 lab (Biosafety Level 3). Berkeley Lab is not able to grow those cells in its lab. It opens up new avenues for experiments on pathogens we could not imagine before.
Valentina Loconte and Jian-Hua Ching, scientists in Larabell’s group, performed the image analysis and tomography sessions at the National Center for X-Ray Tomography. They were both pleasantly surprised at the high-resolution SXT images that captured changes in different organelles of lung cells. This was despite very little preparation time and no labelling or staining. These extra steps are sometimes necessary to create cell maps that clearly distinguish the internal components.
Loconte, a postdoctoral researcher, said that one thing that struck her was the large membrane compartment. This is likely the cell’s attempt to remove or recycle all the virus reproductive machinery. She pointed out that images of infected cells showed this compartment developing in almost all of them. Our technique made it very clear. It would have taken much longer to track a single organelle using a transmission electron microscope (TEM) because scientists using TEM must slice the cells and analyze each slice separately before reconstructing the area.
Spreading the news
The authors have demonstrated that whole-cell SXT can be used to image virus-infected cells. They believe their findings will aid the global scientific community in studying COVID-19 and possibly other diseases.
Larabell, Weinhardt and Bartenschlager have already put the technique to use. Bartenschlager, as part of his work at the German Center for Infection Research, has begun to use whole-cell SXT to study how human cells react to various experimental COVID-19-treating medications. The rapid turnaround of results is expected to help speed up drug development and allow more effective treatments to be available sooner. They also plan to use the technology to understand the progression of other viral infections.
