Actions of seminal fluid signalling factors in the female reproductive tract and on pregnancy outcome.

Abstract

The cytokine environment of early pregnancy is known to be a key determinant of the development of the pre-implantation embryo, and its subsequent implantation and growth. Factors in male seminal fluid have been identified as regulators of the expression of cytokines in the female tract of mice, humans and other mammalian species, with insemination eliciting a cascade of molecular and cellular events, reminiscent of a classic inflammatory response. In humans, perturbations in seminal fluid signalling have been proposed to predispose to pathologies of pregnancy including implantation failure, recurrent miscarriage and pre-eclampsia. Seminal transforming growth factor-beta (TGFβ) is identified as one key molecule present in seminal fluid responsible for inducing the female post-mating cytokine response in mice. Research in humans however, has shown the seminal TGFβ content of fertile versus infertile couples to be similar, while the content of other known seminal constituents such as interferon-gamma (IFNγ), correlate with reproductive success. This project aimed to investigate the nature of active factors present in seminal fluid in mice, and their interactions in regulating the uterine cytokine environment during early pregnancy, utilising a variety of in vitro and in vivo experimental strategies. Further, the effect of perturbation in the peri-conception cytokine environment on short and long term pregnancy and postnatal outcomes was investigated. Evaluation of uterine fluids from estrous and mated mice showed a marked upregulation of a number of cytokines following mating, including granulocyte macrophage colony stimulating factor (GM-CSF), interleukin-6 (IL-6) and the chemokine KC (rodent IL-8 homologue). Increased production of factors such as GM-CSF and subsequent generation of a receptive uterine environment is thought to be crucial for optimal embryo development and placentation. It has previously been shown that seminal factors such as TGFβ contribute to the uterine post-mating inflammatory response, however other moieties present in seminal fluid, for instance cytokines induced in response to infection such as IFNγ or products from the mucosal microflora, may also play a regulatory role. Using uterine epithelial cells cultured in vitro, it was shown that a variety of immune modulators including the cytokines TGFβ and IFNγ, as well as bacterial products, gram negative lipopolysaccharide (LPS) and gram positive lipoteichoic acid (LTA), can alter basal cytokine production. IFNγ, a pro-inflammatory cytokine secreted by activated natural killer cells and T-cells, is known to interfere with TGFβ signalling in other contexts. Independently TGFβ, LPS and LTA stimulate GM-CSF production while differentially regulating IL-6 and KC production. Conversely IFNγ inhibits GM-CSF production, without effecting IL-6 or KC. Pair wise combinations of TGFβ, LPS and LTA resulted in additive stimulation of GM-CSF, while addition of IFNγ to cultures in conjunction with any of these molecules downregulated GM-CSF and KC stimulation. These in vitro studies indicate factor-specific interactions between seminal fluid constituents and highlight the complex nature of seminal fluid signalling. Consequently we propose that the relative ratio of seminal signalling factors is likely to be more important than the absolute concentration of various regulators, in determining the optimal female reproductive tract response. Using the mouse as an in vivo model, I have in addition demonstrated that LPS and LTA instilled into an estrous uterus can elicit cytokine production comparable to that observed following insemination. Further, these studies have shown that IFNγ instilled into the uterus of a recently mated mouse can reduce the post-copulatory GM-CSF and KC surge. However administration of IFNγ had no effect on near term pregnancy outcomes including fetal or placental weights, fetal crown-rump length, or implantation or resorption rates. The ‘developmental origins of adult disease hypothesis’ proposes the idea that the early uterine environment encountered by the conceptus contributes toward the risk of metabolic disorders in adulthood, hence a long term study of progeny conceived after IFNγ administration was also undertaken. Neo-natal outcomes, such as birth weight, litter size and gestation length were unaltered, as was growth trajectory to 22 weeks of age. Adult metabolic markers, glucose tolerance, organ weight, muscle weight, adiposity and systolic blood pressure were not affected by the perturbation of peri-conceptual cytokine parameters. This work has examined the potential regulatory role of a number of seminal fluid signalling agents in directing the post-mating cytokine response, and has furthermore shown the relatively resilient nature of the early cytokine environment to subtle perturbation. Delineating the identity and roles of seminal fluid factors in early pregnancy brings us closer to an understanding of the key physiological events of early pregnancy and assists in identifying potential risk factors for human pregnancy pathologies.