Understanding the effect of Vitamin D treatment on human uterine leiomyoma growth using in vitro and in vivo models

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Uterine leiomyomas affect 70 % of women of reproductive age, disturbing life quality of many of them due to its associated symptoms. Despite its high prevalence and the large amount of management options, there is no effective treatment for leiomyoma size reduction minimally invasive and without side effects. Although uterine leiomyoma pathogenesis is not fully understood, the relationship between Vitamin D deficiency and human uterine leiomyoma risk along with its antiproliferative effects on cancer, pointed to Vitamin D as a possible therapeutic option for uterine leiomyomas. In this regard, Vitamin D action have been widely studied in cancer cells, demonstrating that its anti-tumor effects imply mechanisms that are associated with G0/G1 cellular phase arrest, Wnt/β-Catenin pathway inhibition, and apoptosis induction. In uterine leiomyomas, although Vitamin D action have been evaluated in vitro using uterine leiomyoma cells lines, and in vivo using Eker rats or its derived cells, an in-depth study of the molecular mechanisms through which Vitamin D could act on human uterine leiomyoma primary cells (HULP) and tissues is still pending. Considering this, the main objective of our study was to evaluate the effect of Vitamin D treatment on HULP cells and tissues through molecular mechanisms involved in leiomyoma development, to test its potential as therapeutic option, considering the high inter-patient variability and resembling the physiological conditions of uterine leiomyomas. Our results revealed that an increased cell proliferation rate along with a deregulation of Wnt/β-Catenin pathway in leiomyoma tissue compared to adjacent myometrium could be a key piece in the development and growth of uterine leiomyoma, while apoptosis appears not to contribute. The in vitro study showed that Vitamin D exerts an antiproliferative action on HULP cells through cell growth arrest and Wnt/β-catenin pathway inhibition, but not through apoptosis regulation, suggesting Vitamin D as an effective therapy to stabilize leiomyoma size and prevent its growth. Subsequently, we aimed to corroborate the antiproliferative effects of Vitamin D in a xenograft mouse model. The in vivo study demonstrated that short-term Vitamin D treatment was able to maintain human leiomyoma xenografts size, while a prolonged treatment with Vitamin D significantly reduced leiomyoma size via the decrease of cell proliferation, the inhibition of extracellular matrix production throughout TGFβ signaling pathway, and the increase of apoptosis. We concluded that short-term Vitamin D treatment could be an effective therapy to prevent leiomyoma growth an stabilize its size, while Vitamin D treatment for an extended period could effectively reduce leiomyoma size without associated side effects. In summary, Vitamin D is an anti-proliferative, anti-fibrotic, and pro-apoptotic factor that may be useful as a safe, nonsurgical therapeutic treatment to reduce uterine leiomyoma size in women.
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