The metastasis-associated protein-1 gene encodes a host permissive factor for schistosomiasis, a leading global cause of inflammation and cancer

Abstract

Schistosoma haematobium is responsible for two-thirds of the world's 200 million to 400 million cases of human schistosomiasis. It is a group 1 carcinogen and a leading cause of bladder cancer that occurs after years of chronic inflammation, fibrosis, and hyperproliferation in the host liver. The coevolution of blood flukes of the genus Schistosoma and their human hosts is paradigmatic of long-term parasite development, survival, and maintenance in mammals. However, the contribution of host genes, especially those discrete from the immune system, necessary for parasite establishment and development remains poorly understood. This study investigated the role of metastasis-associated protein-1 gene (Mta1) product in the survival of S. haematobium and productive infection in the host. Using a Mta-1 null mouse model, here we provide genetic evidence to suggest that MTA1 expression positively influences survival and/or maturation of schistosomes in the host to patency, as we reproducibly recovered significantly fewer S. haematobium worms and eggs from Mta1-/- mice than wild-type mice. In addition, we found a distinct loss of cytokine interdependence and aberrant Th1 and Th2 cytokine responses in the Mta1-/- mice compared to age-matched wild-type mice. Thus, utilizing this Mta1-null mouse model, we identified a distinct contribution of the mammalian MTA1 in establishing a productive host-parasite interaction and thus revealed a host factor critical for the optimal survival of schistosomes and successful parasitism. Moreover, MTA1 appears to play a significant role in driving inflammatory responses to schistosome egg-induced hepatic granulomata reactions, and thus offers a survival cue for parasitism as well as an obligatory contribution of liver in schistosomiasis.

Conclusion: These findings raise the possibility to develop intervention strategies targeting MTA1 to reduce the global burden of schistosomiasis, inflammation, and neoplasia.

Figure 1

MTA-1 is a requisite cellular cofactor for productive Schistosoma haematobium infection. Representative images of adult S. haematobium worms (top left panel) and eggs (bottom left panel) recovered from age matched WT Mta-1 (+ / +) mice by portal perfusion and KOH digestion of the liver. Right panel: Bar plots for total numbers of adult worms (1A) and eggs recovered (1B) at 12 weeks after infection.

Figure 2

ELISA for Schistosoma haematobium SWAP (soluble adult worm antigen preparation) and SEA (soluble egg antigen) reflect equivalent initial parasite burdens in both genotypes of the host mice but higher levels of mature infections in WT Mta-1(+/+) mice. (A) Bar plot showing results from ELISA against S. haematobium worm antigen using sera collected from Mta-1 WT and −/− (= KO, knockout) mice at increasing times after infection. (B) Bar plot showing the results from ELISA against S. haematobium egg antigen using sera collected from Mta-1 WT and KO at various time points during the course of infection. Data are presented as mean ± SD.

Figure 3

Impact of MTA-1 status on inflammatory and Th1/Th2 cytokines in response to Schistosoma haematobium infection. Cytokine responses in age matched WT and Mta1−/− mice at 2-, 5-, and 12-wk post-infection: panel A, MCP-1; B, IFN-γ; C, IL-2; D,IL-12p70; E, TNF-alpha; F, IL-10; G, IL-5; and H, IL-4. Serum samples were used to determine the levels of inflammatory and Th1/Th2 cytokines by cytokine bead array assays. Data are presented as mean ± SD.

Figure 4

Influence of MTA-1 on formation of granulomatous inflammatory lesions in liver. Paraffin embedded liver tissue sections from age-matched WT and Mta1−/− mice at 5 and 12 weeks after exposure to Schistosoma haematobium cercariae were stained with anti-cytokeratin-19 (Ck-19) antibody followed by hematoxylin and eosin (H & E). Stained slides were scored under phase contrast microscopy for hepatic granulomatous (HG) regions. Representative liver sections from uninfected, control mice (panel A, WT Mta1, panel B, Mta1−/−), infected mice at 12 weeks (C, D) after infection. Regions showing high infiltration of polymorphonuclear cells were scored as positive for inflammation. Percentage HG positive and CK19 positive zones from 20 fields were determined and represented as bar plot (panel F). Panel E shows an adult male S. haematobium in situ in a portal venule in a WT mouse 12 weeks after exposure to cercariae (H&E stain). Images were captured under a 20 × objective.

Figure 5

Mta1-WT mice show a higher degree of eosinophil infiltration in liver compared to age matched Mta1(−/−) mice 12 weeks post-infection. Liver tissue sections from infected WT and Mta1(−/−) mice were stained for eosinophils using EO-probe kit. Sections were scanned using Zeiss 710 confocal microscope and images were recorded using a 40× objective.

Figure 6

Liver cytokine expression reveals loss of cytokine interdependence in Mta1 (−/−) mice. Analysis of liver cytokine mRNA levels in Mta1-WT (+/+) and Mta1-KO (−/−) mice. 50 mg of liver tissue was used for RNA isolation and cDNA synthesis. Expression levels of Th1 and Th2 cytokine was assessed by Quantitative real-time PCR.* P <0.01 **P<0.001.

Figure 7

Mta1 is an early host-responsive gene following S. haematobium infection and regulates expression of CD4+ve T cell population. Expression levels of Mta1 (A), CD4 (B), was assessed by Quantitative real-time PCR.* P <0.01 **P<0.001.