Characterisation of micro-RNA changes in human primary endothelial cells after exposure to Plasmodium falciparum (Welch, 1897) and their derived extracellular vesicles

Abstract

Plasmodium falciparum is the most virulent cause of malaria, responsible for high mortality among children under five years and pregnant women. The parasite infects host erythrocytes, altering their morphology and impairing their normal function. This can lead to complications such as cerebral malaria, acute pulmonary disease, and kidney injury. Clinical outcomes range from fever and anaemia to organ failure, coma, and death. The pathogenesis involves antigenic variation through var gene expression and cytoadhesion to endothelial cells, both of which have been extensively studied. In contrast, the host transcriptional response, particularly at the mRNA level, is less well understood. This project aimed to establish a physiologically relevant in vitro model using primary endothelial cells exposed to P. falciparum-infected erythrocytes under laminar shear stress, a mechanical force experienced by endothelium in vivo, but which is often overlooked in vitro. The project primarily focused on microRNAs (miRNAs), which are small non-coding RNAs that regulate gene expression. miRNA profiles were screened in endothelial cells after parasite exposure and shear stress. Despite limited changes in endothelial mRNA or miRNA levels, 13 candidate miRNAs that may influence immune modulation, barrier integrity, and intercellular communication during infection were identified. Extracellular vesicles (EVs) derived from endothelial cells and infected erythrocytes were also analysed. EVs derived from activated endothelial cells carried distinct miRNA signatures, including miR-92b-3p and miR-424-5p, which in silico analyses linked to metabolism, transcription, and cytoskeletal regulation. Notably, EVs from infected erythrocytes contained human miRNAs, despite the parasite lacking the machinery for miRNA biogenesis, suggesting indirect host–parasite communication. These EVs were enriched in miRNAs such as miR-4306, miR-143-3p, and miR-454-3p, which could potentially modulate the function of target cells. This thesis demonstrates that the transcriptomic response in primary endothelial cells is more limited than has been reported for immortalized lines. This suggests that parasites may evade clearance by dampening endothelial activation. The findings also suggest that alternative pathways involving molecules released from infected erythrocytes, such as EVs, cytokines, or parasite-derived antigens, are central to the pathogenesis of severe malaria. Together, these results highlight the role of miRNAs and EVs as potential biomarkers and therapeutic targets for early diagnosis and prevention of severe malaria.