Leiomyoma growth mediated by disruptions in injury response and angiogenesis

Abstract

Thrombospondin 1 (TSP1) is an extracellular matrix component that interacts with proteoglycans, integrins, fibrinogen, and fibronectin. It is involved in cell proliferation, apoptosis, angiogenesis inhibition, and activates latent transforming growth factor beta 1. TSP1 is secreted in response to injury, and high expression is restricted to sites of tissue remodeling or injury. Given dependence of leiomyoma formation on both TGF-beta mediated aberrant injury response and angiogenesis, we investigated the role of TSP1 expression in human leiomyoma surgical specimens and in immortalized leiomyoma and patient-matched myometrial cultures. Laboratory study. Surgical specimens and immortalized leiomyoma and patient-matched myometrial cell lines were analyzed using qRT-PCR and western blot analysis. In untreated leiomyoma surgical specimens, there was a 30.2% decrease in TSP-1 mRNA expression when compared to patient matched myometrium. Conversely, TSP-1 protein was nearly undetectable in myometrial tissue, while TSP1 protein expression in leiomyoma surgical specimens remained elevated. We demonstrated a similar pattern in immortalized cell lines. In order to determine if we could alter TSP1 expression in leiomyoma cells to patterns comparable to myometrial cells, we treated leiomyoma cells with the retinoic acid metabolic blocking agent liarozole at concentrations ranging from 10−9M to 10−6M. Compared to untreated leiomyoma cells, leiomyoma cells treated with liarozole demonstrated an additional 35% decrease in TSP1 mRNA expression. Leiomyoma surgical specimens had decreased TSP1 gene expression but much greater TSP1 protein expression compared to patient matched myometrium, a pattern mirrored by in vitro cultures. Treatment with liarozole decreased mRNA expression further. Inhibition of TSP1 expression could disrupt both the fibrotic process and angiogenesis, resulting in potential improvement of leiomyoma bulk symptoms.