Activin βA-subunit and activin receptors in human myometrium at term and during labour

Activin and follistatin in female reproduction

Activin and follistatin were initially identified in the follicular fluid based on their effects on pituitary FSH secretion in the mid-1980s. It is now evident that activin, follistatin and activin receptors are widely expressed in many tissues where they function as autocrine/paracrine regulators of a variety of physiological processes including reproduction. The major function of follistatin is to bind to activin with high affinity and block activin binding to its receptors. Total activin A and follistatin are also found in the maternal circulation throughout pregnancy. Activin A levels are increased in abnormal pregnancies such as pre-eclampsia, fetal growth restriction and gestational hypertension. The placenta, vascular endothelial cells and activated peripheral mononuclear cells (PBMC) may all contribute to the raised levels of activin A in pre-eclampsia with unaltered follistatin in pre-eclamptic placenta, PBMCs or vascular endothelial cells suggesting the availability of 'free' activin A that could be biologically active in these cells.

Human endometrium and decidua express follistatin-related gene (FLRG) mRNA and peptide

Activin-A is expressed by human endometrium, and the actions are counteracted by follistatin, its binding protein. We evaluated the endometrial mRNA and peptide expression of follistatin-related gene (FLRG), a protein that binds activin-A, preventing its interaction. By reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, FLRG expression was evaluated in tissues collected at early proliferative (EP; n = 8) and late proliferative (LP; n = 8); early secretory (ES; n = 9) and late secretory (LS; n = 10); and in pregnancy, maternal decidua (MD; n = 12). FLRG mRNA was expressed by all samples, and semi-quantitative analysis showed that FLRG expression was significantly ( P < 0.001) higher in MD. FLRG was strongly immunolocalized in epithelial cells of glands and vessel walls (cytoplasma and nucleus), but only in the stromal cells nucleus. In MD, FLRG immunostaining was found in the nucleus and cytoplasm of vessel endothelium, gland epithelial, and decidualized stromal cells. In conclusion, FLRG is expressed by the human endometrium, and the different cellular localization suggests novel putative functions.