Investigating the role of androgens in myometrial biology during pregnancy
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Date
04/07/2015Author
Makieva, Sofia
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Abstract
Understanding the physiology of pregnancy enables effective management of
pregnancy complications that could otherwise be life threatening for both mother and
fetus. A functional uterus (a) retains the fetus in utero during pregnancy without
initiating stretch-induced contractions and (b) is able to dilate the cervix and contract
the myometrium at term to deliver the fetus. The onset of labour is associated with
successful cervical remodelling and contraction of myometrium, arising from
concomitant activation of uterine immune and endocrine systems. A large body of
evidence suggest that the action of local sex hormones may drive changes occurring
in the uterine microenvironment at term. Although there have been a number of
studies considering the potential role(s) played by progesterone and estrogens at the
time of parturition, the role of androgens has received less scrutiny.
The overarching aim of this thesis was to investigate the potential roles of androgens
in myometrial biology at the time of pregnancy. We examined both the genetranscription
dependent (genomic) and independent (non-genomic) action of
androgens on the uterine smooth muscle, employing in vitro, ex vivo, and in vivo
approaches.
We found that the androgen receptor (AR) mRNA was significantly increased in the
myometrium during labour when compared to the term non-labouring myometrium.
Our gene expression studies revealed that ligand-dependent AR signalling in the
myometrium might play a role in regulation of uterine smooth muscle cell
contractility. We explored the effect of androgens on contraction of uterine smooth
muscle strips obtained from both human myometrial biopsies collected at term and
murine uterine horns. We found that testosterone (T) and dihydrotestosterone (DHT)
in a range of 10-100 μM concentrations rapidly relaxed spontaneous and oxytocin-initiated
contractions. The relaxant effect was not mediated by the classical
intracellular AR nor was cell-surface initiated as shown by experiments employing a
specific AR antagonist (flutamide) and a cell-surface impermeable androgen (TBSA).
We investigated whether the relaxant effect was specific to androgens or a generic
effect of sex hormones. We demonstrated that both estradiol (E2) and progesterone
(P4) were also capable of relaxing the human and murine myometrium at the same
dose range. In addition, a sex hormone “cocktail” (all four sex hormones combined at
10 μM dose each) mimicked the relaxant effect that each individual sex hormone
elicited at a 40 μM dose, implying that the effect was possibly attributable to the
steroid structure of the sex hormones.
To study the underlying molecular events that mediate the relaxant effect of sex
hormones observed ex vivo, we employed two human myometrial cell lines namely
PHM1-41s and UtSMCs. We demonstrated that the androgen-induced relaxation in
vitro was not induced by cell death but was mediated by a physiological mechanism
whereby incubation with the androgen impaired the stimulated-Ca2+ entry into the
uterine myocytes, which in turn resulted in poor phosphorylation of myosin light
chain protein.
Finally, we conducted a pilot study to explore the hypothesis that administration of
androgen could relax the uterine muscle in vivo. We utilised a mouse model of
infection-induced preterm labour, where infection was induced by intrauterine
administration of liposaccharide (LPS) on day 17 of murine pregnancy. Our
preliminary data showed that intrauterine administration of DHT on day 17 did not
significantly reduce the rate of LPS-induced preterm birth in the doses tested in this
study.
In conclusion, the androgen-induced in vitro tocolysis appears to be sex hormone-specific
rather than androgen-specific. Therefore, sex hormones might have the
potential to be used for effective in vivo tocolysis to inhibit premature-initiated
contractions. Our investigation of the androgen-dependent signalling in the
myometrium contributed to the development of novel hypotheses regarding the role of
androgens in the regulation of the phenotypic transition of MSMCs during pregnancy.
These hypotheses remain to be confirmed in future studies.