Contribution of parasite proteins to altered mechanical properties of malaria-infected red blood cells

Abstract

Red blood cells (RBCs) parasitized byPlasmodium falciparum are rigid and poorly deformable and show abnormal circulatory behavior. During parasite development, knob-associated histidinerich protein (KAHRP) and P falciparum erythrocyte membrane protein 3 (PfEMP3) are exported from the parasite and interact with the RBC membrane skeleton. Using micropipette aspiration, the membrane shear elastic modulus of RBCs infected with transgenic parasites (with kahrp or pfemp3 genes deleted) was measured to determine the contribution of these proteins to the increased rigidity of parasitized RBCs (PRBCs). In the absence of either protein, the level of membrane rigidification was significantly less than that caused by the normal parental parasite clone. KAHRP had a significantly greater effect on rigidification than PfEMP3, contributing approximately 51% of the overall increase that occurs in PRBCs compared to 15% for PfEMP3. This study provides the first quantitative information on the contribution of specific parasite proteins to altered mechanical properties of PRBCs. IntroductionMalaria caused by Plasmodium falciparum remains the most serious and widespread parasitic disease of humans. Clinical symptoms of malaria occur during the asexual stage of the parasite's life cycle, when it multiplies within red blood cells (RBCs). The extreme virulence of P falciparum and the occurrence of severe, often fatal clinical complications is related to the ability of RBCs parasitized by mature forms of the parasite to accumulate in the microvasculature of a variety of organs. 1 This abnormal circulatory behavior for RBCs appears to be directly related to parasite-induced alteration of its mechanical and adhesive properties.During the last 2 decades, the altered adhesive properties of parasitized RBCs (PRBCs) have been studied intensively (see 2,3 for recent reviews). In contrast, alterations of their mechanical properties, and the molecular mechanisms underpinning these changes, have been relatively ignored. Previous studies have clearly demonstrated that the deformability of intact PRBCs is profoundly reduced. [4][5][6] The overall increase in red cell rigidity is due, in part, to the presence of the large, nondeformable intracellular parasite and to a number of stage-specific parasite-encoded proteins that associate with the RBC membrane skeleton. 3,5,6 Paulitschke and Nash 6 used micropipette aspiration to measure the rigidity of RBCs parasitized by a number of unrelated parasite lines of knobby and knobless phenotypes. In general, the membranes of knobby PRBCs were more rigid than those lacking knobs; however, there was considerable variation in rigidity, particularly between knobby lines, with some knobby PRBCs only slightly more rigid than others infected with knobless parasite lines. Unfortunately, in their study, there was no characterization of the parasite genotype or immunohistochemical analysis of the PRBCs to determine precisely which parasite proteins were or were not expressed in different parasite lines. As such, thoug...

Origin, composition, organization and function of the inner membrane complex of Plasmodium falciparum gametocytes

“…In agreement with previous reports, we found that asexual trophozoite-infected RBCs are highly undeformable (Nash et al, 1989). This loss of deformability is probably due to a combination of membrane rigidification and the presence of the large rigid intracellular parasite (Glenister et al, 2002;Nash et al, 1989). We found that stage III gametocytes have similar deformability properties to trophozoiteinfected RBCs; however, upon transition to stage IV the gametocytes show a significant increase in the elongation index measured under flow conditions.…”

“…P. falciparum is also unusual among human malaria parasites in that late stage asexual parasites drastically remodel the RBC through the export and insertion of parasite-derived proteins into and under the host RBC membrane . These modifications lead to a significant increase in cellular rigidity, which would make mature parasite-infected RBCs vulnerable to recognition and clearance within the spleen (Glenister et al, 2002;Safeukui et al, 2008). The parasite avoids these clearance mechanisms by cytoadhereing within the microvasculature of the host.…”

Protein trafficking in Plasmodium falciparum-infected red cells and impact of the expansion of exported protein families

“…Major changes that occur in the infected erythrocyte include the formation of small protrusions on the surface of the cell (knobs), alterations in ion channel behaviour (Decherf et al 2004;Staines et al 2007), the formation of novel channels for nutrient import (Saliba et al 1998;Desai et al 2000;Staines et al 2004), membrane rigidity and cell deformability (Glenister et al 2002) and altered behaviour of infected erythrocytes in the microcirculation (DiezSilva et al 2012). These modifications occur as a result of the export of various effector proteins in the infected erythrocyte.…”

Automated Micropipette Aspiration of Single Cells

“…The study of RBCs at the cellular level has shown that the infection of RBCs can impair their rheological properties [11][12][13][14][15][16][17][18][19][20].…”