Progesterone induces scolex evagination of the human parasite Taenia solium: evolutionary implications to the host-parasite relationship

Abstract

Taenia solium cysticercosis is a health problem in underdeveloped and developed countries. Sex hormones are involved in cysticercosis prevalence in female and male pigs. Here, we evaluated the effects of progesterone and its antagonist RU486 on scolex evagination, which is the initial step in the development of the adult worm. Interestingly, progesterone increased T. solium scolex evagination and worm growth, in a concentration-independent pattern. Progesterone effects could be mediated by a novel T. solium progesterone receptor (TsPR), since RU486 inhibits both scolex evagination and worm development induced by progesterone. Using RT-PCR and western blot, sequences related to progesterone receptor were detected in the parasite. A phylogenetic analysis reveals that TsPR is highly related to fish and amphibian progesterone receptors, whereas it has a distant relation with birds and mammals. Conclusively, progesterone directly acts upon T. solium cysticerci, possibly through its binding to a progesterone receptor synthesized by the parasite.

Figure 1

Progesterone induced scolex evagination of Taenia solium in a concentration-independent pattern (a) maintained along the time (b). On the contrary, RU486 exerted a potent concentration-dependent evagination-inhibitory effect (a), even in presence of progesterone and during the total 20 days of in vitro culture (b). In concentration-response curves (panel a), cysticerci treated with vehicle are referred as concentration zero. Data are represented as mean +/− SD; **P < .05.

Figure 2

Progesterone stimulates worm growth in a concentration-independent pattern (a), reaching its maximum effect at 20 day of in vitro culture (b). In contrast, RU486 inhibits worm development with the lowest concentration (0.06 μM) (a) and during the whole culture time (b). Progesterone-treated parasites were motile and undamaged on the culture plate, typically distinct to those treated with RU486. Worm length was considered as the addition (mm) of scolex, neck, and strobila. In the concentration-response curves (panel a), cysticerci treated with vehicle are referred as concentration zero. Data are represented as mean +/− SD; **P < .05.

Figure 3

TsPR gene expression in T. solium. A single band of 206 bp, corresponding to the Taenia solium Progesterone Receptor (TsPR) was detected in T. solium and mouse uterus (a). Progesterone as well as RU486 increased TsPR expression in T. solium cysticerci. Densitometric analysis is shown in (b). β-actin was used as constitutive expression gene. Data are represented as mean +/− SD; **P < .05.

Figure 4

TsPR protein detection in T. solium. A main band of approximately 116 KDa, equivalent to TsPR was detected in T. solium (a). This TsPR matches to the molecular weight of PR-B isoform from rat uterus, but not to PR-A (~87 KDa), where no protein bands in the parasite were observed (a). TsPR protein was significantly up-regulated by RU486 alone, but not by progesterone and the combination between progesterone and RU486 (b). α-tubulin was used as control constitutive protein. Data are represented as mean +/− SD; **P < .05.

Figure 5

Neighbor Join Tree (NJT) for phylogenetic relation analysis. PRs from several species of fish, amphibian, reptilian, bird, and mammals were analyzed through a NJT for searching probable relationship to the T. solium PR identified and sequenced. TsPR showed close relation to PRs from fish and amphibian, but distant to their counterparts in mammals. Numbers on the NJT means bootstrap support ranging among analyzed species.