Simvastatin inhibits stem cell proliferation in human leiomyoma via TGF-beta 3 and Wnt/beta-Catenin pathways

Uterine leiomyoma (UL) is the most common gynaecologic tumour, affecting an estimated 70 to 80% of women. Leiomyomas develop from the transformation of myometrial stem cells into leiomyoma stem (or tumour-initiating) cells. These cells undergo self-renewal and differentiation to mature cells, both are necessary for the maintenance of tumour stem cell niche and tumour growth, respectively. Wnt/beta-catenin and TGF-beta/SMAD pathways, both overactive in UL, promote stem cell self-renewal, crosstalk between stem and mature cells, cellular proliferation, extracellular matrix (ECM) accumulation and drive overall UL growth. Recent evidence suggests that simvastatin, an antihyperlipidemic drug, may have anti-leiomyoma properties. Herein, we investigated the effects of simvastatin on UL stem cells. We isolated leiomyoma stem cells by flow cytometry using DyeCycle Violet staining and Stro-1/CD44 surface markers. We found that simvastatin inhibits proliferation and induces apoptosis in UL stem cells. In addition, it also suppressed the expression of the sternness markers Nanog, Oct4 and Sox2. Simvastatin significantly decreased the production of the key ECM proteins, collagen 1 and fibronectin. Finally, it inhibited genes and/or proteins expression of TGF-beta 1, 2 and 3, SMAD2, SMAD4, Wnt4, beta-Catenin, LRP6, AXIN2 and Cyclin D1 in UL stem cells, all are key drivers of the TGF-beta 3/SMAD2 and Wnt4/beta-Catenin pathways. Thus, we have identified a novel stem cell-targeting anti-leiomyoma simvastatin effect. Further studies are needed to replicate these findings in vivo.