Complex Interactions Between Sex Steroids and Cytokines in the Human Pregnant Myometrium: Evidence for an Autocrine Signaling System at Term*

Abstract

Little is known about the mechanisms controlling the expression of key proteins that regulate excitability and contractility in the human myometrium at term. However, evidence is accumulating to suggest that the cytokine transforming growth factor (TGF)beta may play a central role. TGFbeta1 and TGFbeta receptors are present in the myometrial cells, indicative of an autocrine signaling system. Furthermore, the levels of TGFbeta1 and the expression of its receptors increase in the myometrium at term suggesting that they are, in turn, regulated and form part of a physiological cascade of events involving a number of autocrine signaling associated proteins. The present experiments were done to identify factors that regulate the expression of TGFbeta1 and TGFbeta receptors and may form other elements of this cascade. Because IL-1 and IL-8 are found in the myometrium at term and have been implicated in the etiology in premature labor we focus on this cytokines. Receptors for IL-1 and IL-8 were detected in the myometrial cells. Using Western blot analysis, the levels of expression were found to vary. The expression of IL-1 receptor type I was highest in the nonpregnant tissue with lower levels in nonlaboring myometrium with a further reduction in the spontaneously laboring tissue. In contrast, the expression of IL-8 receptor type B was highest in the pregnant nonlaboring tissue with a lower level in the spontaneously laboring tissue. Using an in vitro model, TGFbeta1 and TGFbeta receptor expression was up-regulated by IL-8, IL-1, and TGFbeta1 itself. However, IL-8 receptor expression was decreased by IL-8 and TGFbeta1. This suggests that in a cascade IL-8 would feed forward to promote the TGFbeta system, whereas TGFbeta1 feeds back to inhibit responsiveness to IL-8. Estrogen and progesterone increased the release of TGFbeta1. However, at high concentrations, estrogen and progesterone (100 nM 17beta-estradiol or 200 nM progesterone) decreased the level of TGFbeta receptor expression. Thus, the progressive rise of steroid levels in vivo might account for the observed changes in TGFbeta1 and TGFbeta receptor expression in vivo. Taken together, these observations support the idea that there is a cascade of autocrine signals that may play a major role in the physiological processes preparing the myometrium for parturition at term.

Smooth Muscle

“…In the human myometrium in vitro, the levels of transforming growth factor-jn (TGF,81), interleukin (IL)-1 and IL-8 are found to increase in the myometrium during parturition (Hatthachote et al 1998;WinkleI' et al 1998). Recently, it has also been shown that TGF,81 production is increased in human myometrial smooth muscle cells in vitro by IL-1 and IL-S (Hatthachote & Gillespie, 1999). Therefore cytokines induced by other cytokines may be a key element in the complex signalling cascade that underlies the physiological process preparing the myometrium for term.…”

“…All samples of myometrium were obtained with ethical approval and informed consent, and cells prepared as previously described (Hatthachote & Gillespie, 1999). Myometrial cells were exposed to forskolin (5 fiM) in the presence of 10 % fetal calf serum for 24,48 and 72 h. Results are expressed as means ± S.E.M.…”

“…These data are consistent with the idea that GAP-43, under the regulation of NGF, may have a role to play in the cytoskeletal rearrangements as part of the hypertrophy of the pathologically altered detrusor smooth muscle. It has been proposed that, in normal pregnancy, a complex sequence of autocrine cytokine interactions may be involved in regulating the maturation of the human myometrium at term (Hatthachote & Gillespie, 1999). In the human myometrium in vitro, the levels of transforming growth factor-jn (TGF,81), interleukin (IL)-1 and IL-8 are found to increase in the myometrium during parturition (Hatthachote et al 1998;WinkleI' et al 1998).…”

“…TGFj11 and TpRI expression is up-regulated in late pregnancy and, in vitro, their expression can be regulated by cytokines and steroid hormones. Thus it has been suggested that, in vivo, there is a complex cascade of autocrine and endocrine signals that prepare the human myometrium for term (Hatthachote & Gillespie, 1999). At an earlier stage of pregnancy cAMP is thought to regulate gene expression and indirectly influence the contractile state of the uterus.…”

“…Therefore, it is possible that changes in cAMP levels might form part of this cascade and regulate the expression of SAPs. In this study, myometrial smooth muscle cells cultured from non-pregnant myometrium were used to study this hypothesis.All samples of myometrium were obtained with ethical approval and informed consent, and cells prepared as 54P previously described (Hatthachote & Gillespie, 1999). Myometrial cells were exposed to forskolin (5 fiM) in the presence of 10 % fetal calf serum for 24,48 and 72 h. Results are expressed as means ± S.E.M.…”