Abstract
BackgroundSchistosomes are blood dwelling parasitic worms that cause the debilitating disease schistosomiasis. Here we examined the influence of the parasites on their external environment by monitoring the impact of adult Schistosoma mansoni worms on the murine plasma proteome in vitro and, in particular, on how the worms affect the blood coagulation protein high molecular weight kininogen (HK).MethodsFollowing the incubation of adult schistosomes in murine plasma, two-dimensional differential in-gel electrophoresis (2D-DIGE) was conducted to look for changes in the plasma proteome compared with control plasma. A major change to the blood protein kininogen (HK) was observed, and the interaction of Schistosoma mansoni parasite with this protein alone was then investigated by western blot analysis and activity assays. Finally, the generation of bradykinin from HK was monitored using a bradykinin detection kit.ResultsThe most striking change to the plasma proteome concerned HK; while the full-length protein was more abundant in control plasma, carboxyl-terminal truncated forms were more abundant in plasma that contained schistosomes. Incubating parasites in buffer with pure HK followed by Western blot analysis confirmed that human HK is degraded by the worms. The resulting digestion pattern differed from that brought about by kallikrein, a host serine protease that normally acts on HK to release the vasodilator bradykinin. We found that live schistosomes, while digesting HK, do not generate bradykinin nor do they cleave a chromogenic kallikrein substrate. Since the cleavage of HK by the worms is not impeded by the serine protease inhibitor PMSF but is blocked by the cysteine protease inhibitor E64c, we hypothesize that schistosome tegumental cysteine proteases are responsible for HK cleavage.ConclusionsSince proteomic and biochemical studies have revealed that the schistosome tegument contains two cysteine proteases belonging to the calpain family (SmCalp1 and SmCalp2) we conclude that these are likely responsible for the HK cleavage reported here. Schistosome cleavage of HK should help impede blood clotting and inflammation around the worms in vivo and so promote their ease of movement within the vasculature of their hosts.
Highlights
Schistosomes are blood dwelling parasitic worms that cause the debilitating disease schistosomiasis
All parasites were cultured in complete Dulbecco's Modified Eagle Medium/Nutrient Mixture F-12 (DMEM/F12) medium supplemented with 10% heat-inactivated fetal bovine serum, 200 U/ml penicillin and 200 μg/ml streptomycin, 0.2 μM Triiodo-lthyronine, 1 μM serotonin and 8 μg/ml human insulin and were maintained at 37 °C, in an atmosphere of 5% CO2 [16]
The 2D electrophoresis pattern of both plasma samples is shown in Fig. 1a where spots coloured red indicate proteins that are in greater relative abundance in the plasma sample that contained worms while spots coloured green are in greater abundance in the control plasma sample
Summary
Schistosomes are blood dwelling parasitic worms that cause the debilitating disease schistosomiasis. Schistosomes are parasitic flatworms that live in the vascular system of vertebrates, causing a chronic, debilitating disease called schistosomiasis. Three major species infect humans; these are Schistosoma mansoni, S. japonicum and S. haematobium [5]. Schistosomiasis is a water-borne disease, and infection occurs when freeswimming larval parasites called cercariae penetrate the skin. Schistosomula invade a blood vessel, migrate through the heart and lungs to the liver where the worms mature and males pair with females. S. mansoni and S. japonicum couples travel to the mesenteric veins, while S. haematobium pairs migrate to the vesicle venous plexus, where egg-laying occurs [6]
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