Supervisory team
LSHTM
- Dr. Robert Moon, Rob.Moon@lshtm.ac.uk
https://www.lshtm.ac.uk/aboutus/people/moon.rob
Nagasaki University
- Lead: Dr. Kiyoshi Kita, kitak@nagasaki-u.ac.jp
https://www.tmgh.nagasaki-u.ac.jp/en/professors/kiyoshi-kita)
- Dr. Osamu Kaneko, okaneko@nagasaki-u.ac.jp
https://www.tmgh.nagasaki-u.ac.jp/en/professors/osamu-kaneko
- Dr. Shinya Miyazaki, smiyazaki@nagasaki-u.ac.jp
Project
Plasmodium falciparum is a mosquito-transmitted pathogenic parasite that causes many infections and deaths in tropical countries. After inoculation by mosquitoes to humans, P. falciparum multiplies once in the liver cell, then repeatedly replicates in erythrocytes (asexual blood stage). Some parasites in the erythrocytes differentiate into gametocytes, which are transformed into gametes in vector mosquitoes (sexual stage). Compared to the asexual blood stage, the biology of the sexual stage is poorly understood at the molecular level. To improve the malaria control strategy, a better understanding of the sexual stages is required.
While the parasite multiplies inside erythrocytes, some infected erythrocytes migrate from the peripheral blood to the microenvironment within the bone marrow, where they mature to gametocytes. The mature gametocytes migrate back into the peripheral blood and spread to other human hosts by mosquitoes. In the bone marrow, gametocyte maturation is speculated to occur by adhesion of Plasmodium-infected erythrocytes to human bone marrow mesenchymal stem cells (HBMMSCs). However, the parasite ligands involved in adhesion to the HBMMSCs have not been identified.
This project aims to identify the parasite ligands required for adhesion of infected erythrocytes using gene expression analysis, transgenic approaches and culture systems of immortalised HBMMSCs. Previous studies have shown that infected erythrocytes with both asexual blood- and sexual stages adhere to primary bone marrow cells isolated from human volunteers (Messina V et al. Front Cell Infect Microbiol. 2018). To overcome ethical issues, we have established a reliable and simple system of cytoadhesion assays using immortalised HBMMSCs and erythrocytes infected with asexual blood stage. Using this assay system, we established a P. falciparum strain that exhibits high cell adhesion to HBMMSCs. Pre-treatment of infected erythrocytes with trypsin abolished cytoadhesion, supporting the involvement of parasite ligands expressed on the surface of infected erythrocytes. We plan to conduct further molecular biological analyses based on the established systems and associated data. In particular, we aim to identify, by transcriptome analysis, a set of genes whose expression is upregulated in cytoadhesive lines compared to control lines. This approach has been exemplified by a study with P. knowlesi, which has identified a potential cytoadhesive ligand (SICA-HUVEC) (Chuang H et al. Sci Rep. 2022). Upregulated genes in cytoadhesive lines may cover putative ligands for cytoadhesion of erythrocytes infected with both asexual blood- and gametocyte stages. Subsequently, we will generate transgenic P. falciparum parasites that overexpress or knockdown the putative ligand molecules to low expression and examine the ability of these transgenic lines to adhere to HBMMSCs. In addition, we will examine whether the identified ligand is expressed and required for cytoadherence in sexual stages as well as asexual blood stages. P. knowlesi will also be examined for its activity to adhere to HBMMSCs and for the identification of potential ligands with similar approaches as described above. These approaches would aid in identifying the parasite's putative ligands required for adhesion to HBMMSCs in asexual blood- and sexual stages.
This research will provide clues for answering the question, "How do P. falciparum and P. knowlesi survive and differentiate in the human bone marrow?" This research will reveal new host-pathogen interactions, leading to the development of new transmission inhibitors with a mechanism of action that inhibits the adhesion of infected erythrocytes to bone marrow cells.
The role of LSHTM and NU in this collaborative project
Selected students will stay in Nagasaki most of the time and conduct research under active supervision by Profs. Kaneko and Miyazaki. The student will visit London occasionally and conduct some experiments.
Particular prior educational requirements for a student undertaking this project
Basic knowledge of molecular biology and skills such as PCR is appreciated. Cell culture experience (aseptic technique) is also appreciated, but this is not an absolute necessity.
Skills we expect a student to develop/acquire whilst pursuing this project
Skills in culturing malaria parasites and human cell lines, transfection and genome editing techniques (CRISPR/Cas9), and other advanced molecular biological techniques. Analysis of RNAseq expression data. Ability to critically discuss complex ideas based on a deep understanding of malaria cellular and molecular biology.