Lattice Light-Sheet Microscopy Targets Malaria

With the help of a custom-built lattice light-sheet microscope, researchers at the Walter and Eliza Hall Institute (WEHI) captured high-resolution 3D video images of individual malaria parasites (Plasmodium falciparum) invading red blood cells in real time, and they observed the molecular and cellular changes that occurred throughout the very fast process.

Their use of lattice light-sheet microscopy (LLSM) provided views capable of providing new insight into malaria parasite biology that could have applications for the development of antimalarial medicines.

“In the past, the choice of microscope for an experiment had to be a compromise between capturing a lower-resolution video, which revealed dynamic processes like shape changes or movement, and capturing much higher-definition still images, which provided much more detail about how the cells and molecules are functioning,” said researcher Niall Geoghegan. “LLSM allows us to obtain high-resolution videos of cells, which has been a game-changer for many fields of biological research.”

Live parasites, such as those investigated in the work, are difficult to study; they are light-sensitive, making them difficult to study with light microscopy. Other challenges are the parasites’ small size, speed of cell invasion, and ability to hide within host cells.

Researchers Niall Geoghegan (left) and Lachlan Whitehead with the lattice light-sheet microscope. Courtesy of WEHI.
P. falciparum, the deadliest malaria-causing parasite, needs to export a large number of proteins into the infected cell in order to survive. This protein trafficking process provides a potential target for antimalarial drugs, but the mechanisms controlling it are poorly understood. The parasite’s invasion of the red blood cell, and the subsequent protein export, take place very quickly — within 10 to 20 s — and can only be captured using the fastest microscopes.

With LLSM, the researchers developed a method to track the invasion process through fast volumetric imaging. This gentle microscopy approach allowed the researchers to quantitatively characterize all stages of invasion, including the dynamics of parasite internalization and vacuole membrane formation.

“The videos we recorded showed the ‘push and pull’ interactions as the parasite landed on the red blood cell, and then entered the cell in an enclosed chamber — called a vacuole — where it grew and multiplied,” researcher Cindy Evelyn said. “There has long been contention in the field about whether the vacuole is derived from the parasite or the host cell. Our research resolved this question, revealing it was created from the red blood cell’s membrane.”

Kelly Rogers, head of the Centre for Dynamic Imaging, said that understanding how the parasite invades red blood cells could reveal new ways to stop this stage of the parasite’s life cycle. “By visualizing these processes in more detail, our research may contribute in several ways to the development of new antimalarial therapies,” she said. “For example, now that we know that the parasite vacuole relies on components of the red blood cell membrane, it might be possible to target these components with medicines to disrupt the parasite life cycle. This host-directed approach could be one way to bypass the malaria parasite’s propensity to rapidly develop drug resistance.

“LLSM may also have applications for observing the specific steps of parasite invasion that are blocked by potential new drugs — an area we are now very interested in pursuing,” Rogers said. Most existing therapies and vaccines target the initial binding of malaria to red blood cells.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-021-23626-7).