Differentially regulated expression of neurokinin B (NKB)/NK3 receptor system in uterine leiomyomata.

STUDY QUESTION

Are the vasoactive peptide neurokinin B (NKB) and its preferred NK3 receptor (NK3R) differentially expressed in leiomyomas compared with normal myometrium?

SUMMARY ANSWER

In leiomyomas, NKB is up-regulated and delocalized, while its preferred NK3R is also differentially regulated.

WHAT IS KNOWN ALREADY

The expression of NKB/NK3R in the central nervous system is essential for proper function of the human reproductive axis. Additionally, this system is also widely expressed throughout the female genital tract. Leiomyomas impair fertility and are a major source of abnormal uterine bleeding. The aberrant synthesis of local factors can contribute to the pathological symptoms observed in women with leiomyomata. NKB could be one of these factors, since a vasoactive role of this peptide at a peripheral level has been observed in different systems and species, including humans. NK3R is strongly regulated by estrogens and its activation leads to nuclear translocation affecting chromatin structure and gene expression.

STUDY DESIGN, SIZE, DURATION: Samples were obtained between 2006 and 2012 from 28 women of reproductive age at different stages of the menstrual cycle by hysterectomy. Leiomyomas and matched macroscopically normal myometrium from each woman were analysed in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS: RT-PCR, quantitative real time, immunohistochemistry and in situ hybridization were used to investigate the pattern of expression of NKB/NK3R in tissue samples.

MAIN RESULTS AND THE ROLE OF CHANCE

Expression of the gene encoding NKB (TAC3) was up-regulated 20-fold in leiomyomas, compared with matched myometrium (P = 0.0008). In tumour tissue, not only connective cells, but also myometrial, endothelial and vascular smooth muscle cells express TAC3 mRNA. Immunoreactivity to NKB was preferentially located in the smooth muscle cell nuclei from normal myometrium in the secretory phase, unlike matched leiomyoma, which showed a predominant cytoplasmic expression pattern. In the normal myometrium, TACR3 mRNA showed variable expression throughout the menstrual phases, with samples showing strong, reduced or no amplification. In leiomyoma, TACR3 was significantly up-regulated compared with matched myometrium (P = 0.0349).

LIMITATIONS, REASONS FOR CAUTION: This study is descriptive and although we observed clear differential regulation of the NKB/NK3R system at mRNA and immunohistochemical staining levels in leiomyoma, future functional studies are needed to determine the precise role of NKB in the myometrium in normal and pathological conditions. In addition, further analysis (e.g. in cell culture models) will be required to determine the role of NKB in the nucleus of normal smooth muscle cells, whether nuclear translocation is mediated by NK3R and the consequences of the cytoplasmic expression of NKB in tumour cells.

WIDER IMPLICATIONS OF THE FINDINGS

The NKB/NK3R system dysregulation observed in leiomyoma may contribute to the pathological symptoms observed in women with leiomyomata.