Methylprednisolone Acetate Induces, and Δ7-Dafachronic Acid Suppresses, Strongyloides Stercoralis Hyperinfection in NSG Mice
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Methylprednisolone acetate induces, and Δ7-dafachronic acid suppresses, Strongyloides stercoralis hyperinfection in NSG mice John B. Pattona,1, Sandra Bonne-Annéea,1, Jessica Deckmana, Jessica A. Hessa, April Torigiana, Thomas J. Nolanb, Zhu Wangc,d, Steven A. Kliewerc,e, Amy C. Durhamb, James J. Leef, Mark L. Eberhardg, David J. Mangelsdorfc,d,2, James B. Lokb,2, and David Abrahama,2 aDepartment of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, PA 19107; bDepartment of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104; cDepartment of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390; dHoward Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390; eDepartment of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390; fDivision of Pulmonary Medicine, Department of Biochemistry and Molecular Biology, Mayo Clinic, Scottsdale, AZ 85259; and gDivision of Parasitic Diseases and Malaria, Centers for Disease Control and Prevention, Atlanta, GA 30329 Contributed by David J. Mangelsdorf, October 30, 2017 (sent for review July 12, 2017; reviewed by Timothy G. Geary and James McKerrow) Strongyloides stercoralis hyperinfection causes high mortality rates are treated with the glucocorticoid methylprednisolone acetate in humans, and, while hyperinfection can be induced by immunosup- (MPA) (8). Wild-type (WT) mice are only susceptible to the early pressive glucocorticoids, the pathogenesis remains unknown. Since larval stages of the S. stercoralis life cycle and develop both innate immunocompetent mice are resistant to infection with S. stercoralis, and adaptive responses to control the infection. Multiple com- we hypothesized that NSG mice, which have a reduced innate im- ponents of the murine immune response, including neutrophils, mune response and lack adaptive immunity, would be suscepti- eosinophils, macrophages, and the complement cascade, contrib- ble to the infection and develop hyperinfection. Interestingly, ute to the immune control of S. stercoralis (9). Eosinophils can kill despite the presence of large numbers of adult and first-stage L3i in collaboration with complement factor C3b (10, 11) whereas larvae in S. stercoralis-infected NSG mice, no hyperinfection was ob- neutrophils require C3b and alternatively activated macrophages served even when the mice were treated with a monoclonal antibody PHARMACOLOGY to effectively kill S. stercoralis (9, 11–13). While WT mice are to eliminate residual granulocyte activity. NSG mice were then in- fected with third-stage larvae and treated for 6 wk with methylpred- resistant to the complete life cycle of S. stercoralis, severely nisolone acetate (MPA), a synthetic glucocorticoid. MPA treatment immune-compromised SCID mice support the development of of infected mice resulted in 50% mortality and caused a significant limited numbers of adult worms and L1 (14). This observation >10-fold increase in the number of parasitic female worms compared suggests that B and/or T cell responses are needed for complete with infected untreated mice. In addition, autoinfective third-stage clearance of the parasites from the tissue of WT mice (14). larvae, which initiate hyperinfection, were found in high numbers A highly immune-compromised strain of mouse, NOD.Cg- scid tm1Wjl in MPA-treated, but not untreated, mice. Remarkably, treatment Prkdc Il2rg /SzJ (NSG), has been developed, with pro- with Δ7-dafachronic acid, an agonist of the parasite nuclear receptor found defects in the adaptive and innate immune responses (15). Ss-DAF-12, significantly reduced the worm burden in MPA-treated mice undergoing hyperinfection with S. stercoralis. Overall, this study Significance provides a useful mouse model for S. stercoralis autoinfection and suggests a therapeutic strategy for treating lethal hyperinfection. The intestinal parasite Strongyloides stercoralis infects an estimated 100 million people. This nematode’s unique ability to Strongyloides stercoralis | hyperinfection | NSG mice | glucocorticoid | autoinfect its host enables it to persist for decades undetected and dafachronic acid to progress to a potentially fatal hyperinfection that often is in- duced by glucocorticoid treatment. We report a mouse model, he parasitic nematode, Strongyloides stercoralis, infects an involving the NSG strain, that recapitulates all forms of human Testimated 100 million people. Humans acquire infections strongyloidiasis. Even in severely immunocompromised NSG mice, through skin penetration by infective third-stage larvae (L3i), which glucocorticoid treatment was required for autoinfection, raising undergo development as they migrate to the intestine, where they intriguing questions about the mechanism of glucocorticoid ac- molt into parthenogenic female worms. Eggs released by female tion. Notably, administering a nematode-derived steroid, Δ7- wormshatchintheintestine,andfirst-stagelarvae(L1)maybere- dafachronic acid, which acts through a receptor within S. ster- leased in the feces, or they may develop into autoinfective third-stage coralis to regulate parasite development, significantly diminished larvae (L3a). L3a are able to penetrate the bowel and initiate a new autoinfection in glucocorticoid-treated NSG mice. This opens the infection cycle in the primary host (1). Autoinfection allows S. ster- possibility of new chemotherapy for hyperinfective strongyloidi- coralis infections to persist in an individual undetected for decades (2, asis, targeting the parasite’s own steroid hormone mechanisms. 3). Host symptoms are typically mild and nonspecific and include manifestations such as abdominal pain and diarrhea. However, in- Author contributions: J.B.P., S.B.-A., Z.W., S.A.K., D.J.M., J.B.L., and D.A. designed re- search; J.B.P., S.B.-A., J.D., J.A.H., A.T., T.J.N., Z.W., A.C.D., J.J.L., M.L.E., and J.B.L. per- fected individuals treated with glucocorticoids or coinfected with formed research; J.B.P., S.B.-A., Z.W., S.A.K., D.J.M., J.B.L., and D.A. analyzed data; and human T cell lymphotropic virus type 1 (HTLV-1), may develop J.B.P., S.B.-A., Z.W., S.A.K., D.J.M., J.B.L., and D.A. wrote the paper. hyperinfection syndrome. S. stercoralis hyperinfection is characterized Reviewers: T.G.G., McGill University; and J.M., University of California, San Diego. by significantly increased parasite burden, the presence of L3a, The authors declare no conflict of interest. widespread dissemination of parasites, and translocation of gut bac- Published under the PNAS license. teria as the L3a penetrate the intestinal walls. Hyperinfection can be 1J.B.P. and S.B-A. contributed equally to this work. – life threatening, with mortality reaching 87% when untreated (4 6). 2To whom correspondence may be addressed. Email: [email protected], S. stercoralis naturally infects humans, primates, and canines [email protected], or [email protected]. (7). Gerbils are susceptible to S. stercoralis infection, with all This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. parasitic stages developing. Hyperinfection ensues when gerbils 1073/pnas.1712235114/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1712235114 PNAS Early Edition | 1of6 Downloaded by guest on October 5, 2021 NSG mice are derived from the NOD\ShiLtJ background and AB carry multiple alleles reducing the function of the innate immune 80 * 1000 system, including defects in both macrophages and dendritic * 60 * 800 cells, as well as in the complement cascade (16, 17). The SCID 600 40 mutation confers loss of both T and B cell function (18). In * 400 addition, NSG mice have a null mutation of the common gamma 20 200 chain gene, which disrupts signaling of six different interleukins * L1 Recovered Adult Recovered (19). Monocytes and neutrophils are present in NSG mice al- 0 0 though their functional capacity is currently unknown. Both NOD SCID NSG NOD SCID NSG macrophages and dendritic cells are also found in NSG mice but C57BL/6J NOD/SCID C57BL/6J NOD/SCID are functionally compromised due to deficiencies in cytokine C D signaling and other genetic defects of the NOD\ShiLtJ back- 1500 ground (17, 20). Numbers of eosinophils in NSG mice have not * NSG been determined (15). 1000 * NOD/ The Caenorhabditis elegans nuclear receptor DAF-12, which SCID regulates the switch between dauer and continuous reproductive 500 SCID development (21), is conserved in S. stercoralis (22). The natural L3 Recovered 0 ligands of C. elegans DAF-12, the dafachronic acids (23), have 300 400 500 600 the capacity to signal through homologs of DAF-12 in S. stercoralis NOD SCID NSG μm and Ancylostoma caninum, stimulating resumption of development C57BL/6J NOD/SCID by L3i of these parasites (24, 25) and suppressing morphogenesis of S. stercoralis L3i in both the postparasitic and post–free-living Fig. 1. Susceptibility of immunodeficient mice to infection with Strong- generations (24, 25). The ability of Δ7-dafachronic acid (Δ7-DA) yloides stercoralis. Mice were infected with 5,000 S. stercoralis L3i, and, 6 wk postinfection, mice were necropsied and parasite recoveries in NOD (n = 7), to perturb L3i development in diverse clades of parasitic nema- SCID (n = 10), NOD/SCID (n = 10), and NSG (n = 10) mice were compared with todes bolsters the potential of the DAF-12 signaling pathway as a WT C57BL/6J mice (n = 8). Data presented are means ± SDs (*P ≤ 0.05) of chemotherapeutic target (24). total number of (A) adults, (B) L1, and (C) L3 recovered. (D) L3 recovered Based on the fact that SCID mice are somewhat susceptible to from the tissues of infected SCID, NOD/SCID, and NSG mice were fixed and S. stercoralis infection, it was hypothesized that NSG mice would measured. The experiment was performed twice with the same results. Data be fully susceptible to the infection. Susceptibility of NSG mice to presented are from both experiments. infection with S. stercoralis was compared in the present study with the susceptibility of B6.CB17-Prkdcscid/SzJ (SCID) (18), NOD/ ShiLtJ (NOD) (16, 21), and NOD.CB17-Prkdcscid/J (NOD/SCID) to destroy complement, parasite killing did not occur, indicating (17) mice.