Malaria remains a pervasive global health burden. More than 241 million cases and 627,000 deaths were reported in 2020. The vast majority of those impacted reside in sub–Saharan Africa. More than 90% of fatalities from malaria are caused by infection with the mosquito-borne parasite Plasmodium falciparum.
One particularly severe form of P. falciparum malaria is known as cerebral malaria, a condition marked by blockages in blood vessels that can lead to serious neurological dysfunction, brain swelling, seizures, and coma. While cerebral malaria is treatable with rapid intervention, mortality rates can be as high as 20%.
In the 1890s, two Italian pathologists named Ettore Marchiafava and Amico Bignami discovered that cerebral malaria resulted from the adhesion of parasitized red blood cells to vascular endothelium in the brain. As infected red blood cells begin to accumulate in the brain blood vessel walls, the interaction of these infected cells with healthy endothelial cells triggers a complex inflammatory reaction that can damage the linings of the microvasculature that is essential for normal functioning. However, the ability of clinicians and scientists to model these “hidden events” taking place in the blood vessels of the brain has been limited.
Much of what is known about inflammation associated with cerebral malaria has been derived from postmortem studies of children who died from cerebral malaria and from laboratory investigations that use a mouse model. Although observations in living systems can offer insights that apply to humans, the pathology of the mouse model is markedly different from humans with little or no intracerebral sequestration of parasitized red blood cells. This is where new approaches in bioengineered blood vessel models were used to address questions raised by Marchiafava and Bignami’s seminal discovery from over one hundred years ago.
Ying Zheng, PhD is an associate professor of bioengineering and a faculty member in the Institute for Stem Cell and Regenerative Medicine (ISCRM). Zheng has previously used her expertise in tissue engineering to help malaria researchers study how the disease affects small vessels like capillaries. Now, a new paper from the Zheng Lab, published in Cell Reports, unveils a technique for probing cerebral malaria inflammation in 3D engineered human brain microvessels.
The study is the latest product of an ongoing collaboration between the Zheng Lab and Joe Smith, PhD, a Professor at the Seattle Children’s Research Institute’s Center for Global Infectious Disease Research where his lab studies parasite-host binding interactions in malaria. The first author of the paper is Caitlin Howard, a former PhD student in the Zheng Lab.
In the investigation, the researchers used endothelial cells isolated from the brain to construct a three-dimensional platform that mimics the in vivo human brain blood vessels. This novel research platform allowed the researchers to perfuse parasitized red blood cells and inflammatory cytokines in a controlled laboratory setting and gather data. The researchers combined imaging, ultrastructural and transcriptional analysis, and functional assays like leukocyte perfusion to study brain microvessel inflammation.
Notably, transcriptional analysis and imaging tools revealed that parasite and host inflammatory factors combined to inflict damage to brain endothelial cells. On their own, parasites induced a stress response in the 3D brain microvessel model and caused some endothelial cells to undergo a form of cell suicide, called apoptosis. By comparison, the inflammatory cytokine TNF-alpha induced a highly pro-adhesive phenotype on the blood vessel wall, which may contribute to attracting immune cells to the location of sequestered red blood cells. Additionally, the combined effect of TNF-alpha activation and infected red blood cells compounded the inflammatory effect and also slowed the recovery of 3D brain microvessel model back to its resting state.
Zheng emphasizes the dual contributions of the paper. One, the findings detailed in the article offer new information about the interplay of P. falciparum and the body’s inflammatory response to infection. Two, the study serves as a proof-of-concept for a modeling tool capable of helping other investigators identify and test new strategies for treating cerebral malaria.
“I am most excited that we were able to see the maturation of the parasites in our microvessels, that the microvessels had a unique response to parasite binding, and that we saw in our model that parasites can in fact have a combinatorial effect with TNF alpha,” says Zheng. “This opens up opportunities for us to use microvessel models cultured in vitro in perfusion for understanding vascular injuries and recoveries with time after single or multiple insults of infections and inflammation. And the spatiotemporal changes of the vessels will be valuable information for us to understand potential vessel vulnerability after diseases.”
Smith speaks to the potential of the modeling tool to yield further insights. “This novel 3D brain microvessel platform provides a unique window into the blood-brain barrier. It holds enormous potential to unravel secrets related to cerebral malaria disease and other infections that target the brain blood vessels.”