NEW YORK – New research suggests messenger RNAs (mRNA) found in the blood's extracellular vesicles can provide a look at the processes involved in cerebral malaria complications in children infected with Plasmodium falciparum.
"[W]e hypothesized that the RNA content of circulating [extracellular vesicles] could be used to study neuropathological processes during cerebral malaria, specifically the transcriptional profiles of the cerebral tissues," senior and corresponding author Abdirahman Abdi, a bioscience researcher affiliated with the KEMRI-Wellcome Trust Research Programme, the University of Oxford, and Pwani University in Kenya, and his colleagues wrote in a paper published in Science Advances on Friday.
The investigators isolated extracellular vesicles found in archived blood plasma from 76 children treated for cerebral malaria at the Kilifi County Hospital in Kenya or from eight unaffected, P. falciparum infection-free adult control individuals. From there, they used RNA sequencing and computational analyses to profile messenger RNAs found in the extracellular vesicles. The cerebral malaria patients included 30 children with retinal tissue involvement, or "retinopathy," and 46 without.
"The retina comprises brain-like tissues and shows [P. falciparum] parasite sequestration and pathology comparable to that in canonical brain tissues, but unlike the brain, the retina can be directly visualized," the authors wrote, noting that malaria retinopathy "can be used as a surrogate marker for parasite sequestration in the brain" in children.
While nearly 68 percent of the extracellular vesicle RNA (EV-RNA) found in individuals with cerebral malaria seemed to stem from whole blood cells, for example, the researchers noted that the remaining proportion of EV-RNA from blood plasma coincided with genes with enhanced expression in solid tissues such as the brain, peripheral nerve tissue, or the small intestine.
In both the retinopathy-positive and -negative cases of cerebral malaria, the team reported a rise in the relative number of brain and peripheral nerve transcripts in the EV-RNA samples, particularly when it came to RNA from genes with elevated expression in the brain's endothelial cells, microglia, or neuron cells.
Even so, the researchers' differential expression analyses highlighted 1,440 genes with enhanced or diminished expression in the cerebral malaria cases with or without retinopathy, while their disease progression modeling analyses suggested that the retinopathy-free forms of cerebral malaria can progress to a later stage of cerebral malaria with retinal involvement.
When they followed transcript dynamics in extracellular vesicles from blood plasma, meanwhile, the investigators detected a dip in transcripts, originating in neuronal cells over the course of the cerebral malaria process. Over the same time frame, they saw a rise in the prevalence of transcripts that appeared to originate in glial, endothelial, or immune type cells.
"Taking our findings together, we speculate that reduced microcirculatory flow resulting from parasite sequestration in the brain leads to suboptimal brain perfusion and neuronal hypofunction, evidenced by falling neuronal transcript levels," the authors explained. "This is associated with a progressive increase in glial activity … as well as brain adaptive processes."
The team cautioned that EV-RNA features found in children with cerebral malaria "may not be generalizable" to adults with the disease. Nevertheless, the new results underscored the possibility of using extracellular vesicles found in the blood as a window into molecular processes at play in the brain — a tissue type that cannot be sampled and tested directly.
"We demonstrate that the molecular sequence of neurovascular events in pediatric cerebral malaria is accessible antemortem via [extracellular vesicles] despite the inaccessibility of brain tissues to direct sampling," the authors concluded. "This will allow a more complete study of the pathogenesis of the illness, identification of biomarkers to predict disease progression, and design of therapeutic interventions."