Endogenous PGD₂ acting on DP2 receptor counter regulates Schistosoma mansoni infection-driven hepatic granulomatous fibrosis

by Giovanna N. Pezzella-Ferreira, Camila R. R. Pão, Isaac Bellas, Tatiana Luna-Gomes, Valdirene S. Muniz, Ligia A. Paiva, Natalia R. T. Amorim, Claudio Canetti, Patricia T. Bozza, Bruno L. Diaz, Christianne Bandeira-Melo

Identifying new molecular therapies targeted at the severe hepatic fibrosis associated with the granulomatous immune response to Schistosoma mansoni infection is essential to reduce fibrosis-related morbidity/mortality in schistosomiasis. In vitro cell activation studies suggested the lipid molecule prostaglandin D₂ (PGD₂) as a potential pro-fibrotic candidate in schistosomal context, although corroboratory in vivo evidence is still lacking. Here, to investigate the role of PGD₂ and its cognate receptor DP2 in vivo, impairment of PGD₂ synthesis by HQL-79 (an inhibitor of the H-PGD synthase) or DP2 receptor inhibition by CAY10471 (a selective DP2 antagonist) were used against the fibrotic response of hepatic eosinophilic granulomas of S. mansoni infection in mice. Although studies have postulated PGD₂ as a fibrogenic molecule, HQL-79 and CAY10471 amplified, rather than attenuated, the fibrotic response within schistosome hepatic granulomas. Both pharmacological strategies increased hepatic deposition of collagen fibers–an unexpected outcome accompanied by further elevation of hepatic levels of the pro-fibrotic cytokines TGF-β and IL-13 in infected animals. In contrast, infection-induced enhanced LTC₄ synthesis in the schistosomal liver was reduced after HQL-79 and CAY10471 treatments, and therefore, inversely correlated with collagen production in granulomatous livers. Like PGD₂-directed maneuvers, antagonism of cysteinyl leukotriene receptors CysLT1 by MK571 also promoted enhancement of TGF-β and IL-13, indicating a key down-regulatory role for endogenous LTC₄ in schistosomiasis-induced liver fibrosis. An ample body of data supports the role of S. mansoni-driven DP2-mediated activation of eosinophils as the source of LTC₄ during infection, including: (i) HQL-79 and CAY10471 impaired systemic eosinophilia, drastically decreasing eosinophils within peritoneum and hepatic granulomas of infected animals in parallel to a reduction in cysteinyl leukotrienes levels; (ii) peritoneal eosinophils were identified as the only cells producing LTC₄ in PGD₂-mediated S. mansoni-induced infection; (iii) the magnitude of hepatic granulomatous eosinophilia positively correlates with S. mansoni-elicited hepatic content of cysteinyl leukotrienes, and (iv) isolated eosinophils from S. mansoni-induced hepatic granuloma synthesize LTC₄ in vitro in a PGD₂/DP2 dependent manner. So, our findings uncover that granulomatous stellate cells-derived PGD₂ by activating DP2 receptors on eosinophils does stimulate production of anti-fibrogenic cysLTs, which endogenously down-regulates the hepatic fibrogenic process of S. mansoni granulomatous reaction–an in vivo protective function which demands caution in the future therapeutic attempts in targeting PGD₂/DP2 in schistosomiasis.