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Plasmodium falciparum-infected erythrocytes: a mutational analysis of cytoadherence via murine thrombomodulin
S Rabhi-Sabile1, M Steiner-Mosonyi, S Pollefeyt
1INSERM U 353, Hôpital Saint-Louis, Paris, France.
Abstract:
The pathophysiologic events leading to organ damage in Plasmodium falciparum malaria infections involve adhesion and sequestration of parasite-infected erythrocytes (PRBC) to the vascular endothelium and syncytiotrophoblast. Several potential receptors to which the PRBCs may bind have recently been identified, one of which is thrombomodulin (TM). TM has been implicated particularly in mediating sequestration of P. falciparum-infected erythrocytes in the placenta and brain, two sites of disease associated with high morbidity. In order to establish that binding of parasite-infected red blood cells to TM is dependent on its containing chondroitin-4-sulfate (CSA), we have mutated the CSA-attachment site of murine TM, and expressed this mutant form (TMsergly) in COS-7 cells. In cytoadhesion assays, we demonstrate that, in contrast to wild-type TM which contains CSA and supports the adhesion of 1466 PRBCs/mm2, TMser-gly does not contain CSA and adhesion of PRBCs to those cells expressing TMser-gly is entirely abrogated (200 PRBCs/mm2). These studies further confirm that the CSA of TM may play a role in the pathophysiology of malaria by providing a binding site for PRBCs.
Insights
Chondroitin-4-sulfate (CSA) on thrombomodulin (TM) mediates Plasmodium falciparum rosetting. Mutating the CSA-binding site on TM blocked parasite-infected red blood cell adhesion, confirming CSA
Area of Science:
- Molecular parasitology
- Vascular biology
- Pathophysiology of infectious diseases
Background:
- Plasmodium falciparum malaria causes organ damage via parasite-infected erythrocyte (PRBC) adhesion to endothelium.
- Thrombomodulin (TM) is a potential receptor mediating PRBC sequestration in critical organs like the placenta and brain.
- The role of chondroitin-4-sulfate (CSA) on TM in PRBC binding remains to be fully elucidated.
Purpose of the Study:
- To investigate whether the binding of P. falciparum-infected red blood cells (PRBCs) to thrombomodulin (TM) is dependent on its chondroitin-4-sulfate (CSA) moiety.
- To confirm the role of TM-bound CSA as a specific binding site for PRBCs in malaria pathophysiology.
Main Methods:
- Site-directed mutagenesis of the CSA-attachment site on murine thrombomodulin (TM) to create a mutant form (TMsergly).
- Expression of wild-type TM and TMsergly in COS-7 cells.
- Quantification of PRBC adhesion to cells expressing either wild-type TM or TMsergly using cytoadhesion assays.
Main Results:
- Wild-type TM, which contains CSA, supported significant adhesion of PRBCs (1466 PRBCs/mm2).
- The TMsergly mutant, lacking CSA, completely abrogated PRBC adhesion (200 PRBCs/mm2).
- These findings demonstrate a direct correlation between TM's CSA content and PRBC binding.
Conclusions:
- The chondroitin-4-sulfate (CSA) component of thrombomodulin (TM) is essential for the adhesion of Plasmodium falciparum-infected red blood cells (PRBCs).
- TM-bound CSA acts as a specific receptor mediating PRBC sequestration in malaria.
- Targeting the TM-CSA interaction could offer a novel therapeutic strategy for severe malaria.