Objective: Transforming growth factor-beta1 is the prototype of a bimodal regulator of cell growth, which can either inhibit or stimulate the proliferation of smooth muscle cells. Part of transforming growth factor-beta1-mediated stimulation of growth is associated with the increased production of platelet-derived growth factor. The conversion of latent-to-active transforming growth factor-beta provides a pivotal mechanism for the regulation of the biologic activity of transforming growth factor-beta. We investigated the differential expression and production of the active form of transforming growth factor-beta1 in the myometrium and leiomyoma throughout the menstrual cycle. We also studied the mitogenic effects of transforming growth factor-beta1 and platelet derived growth factor on myometrial and leiomyoma cells in culture.
Study design: Myometrium and leiomyoma tissue pairs were obtained from 28 women who underwent hysterectomy. Total RNA from each tissue was extracted, and Northern blot analysis was performed for the detection of TGF-beta1 messenger RNA. Active and total transforming growth factor-beta1 protein was quantified with enzyme-linked immunosorbent assay. Cell proliferation of cultured human myometrial and leiomyoma cells that are treated with TGF-beta1 (0.01-1 ng/mL), anti-transforming growth factor-beta antibody (0.01-10 ng/mL), or platelet-derived growth factor (10 ng/mL) was assessed by the [(3)H]thymidine incorporation method.
Results: Overall, the transforming growth factor-beta1 messenger RNA level in myometrial samples was 1.2-fold higher than in the leiomyoma samples (P <.05). Active transforming growth factor-beta1 protein levels in follicular and luteal phase myometrial and leiomyoma samples were significantly greater than the levels in samples from women with atrophic endometrium (P < 0.05). Transforming growth factor-beta1, at low concentrations (0.01 ng/mL), induced an increase in cell proliferation (2- to 3-fold; P <.05). When cells were treated with anti-transforming growth factor-beta antibody, there was a larger magnitude of increase observed (7- to 20-fold; P <.05). Platelet-derived growth factor (10 ng/mL) consistently increased the rate of cell proliferation both in myometrium and leiomyoma cells (5- to 6-fold; P <.05).
Conclusion: Levels of active transforming growth factor-beta1 that were produced in follicular and luteal phases indicate a stimulatory role for ovarian hormones. The finding that transforming growth factor-beta1, only at low concentrations, stimulates cell proliferation mainly in leiomyoma cells is in agreement with the bimodal and dose-dependent effects of transforming growth factor-beta1 that is observed in smooth muscle cells of other tissues. The persistent and high rate of cell proliferation with platelet-derived growth factor suggests that the growth stimulatory effect of transforming growth factor-beta1 may be mediated through its up-regulatory effect on platelet-derived growth factor.