Activin A and Follistatin in Menstrual Blood: Low Concentrations in Women With Dysfunctional Uterine Bleeding

Activin and inhibin signaling: From regulation of physiology to involvement in the pathology of the female reproductive system

Activins and inhibins - comprising activin A, B, AB, C and E, and inhibin A and B isoforms - belong to the transforming growth factor beta (TGFβ) superfamily. They regulate several biological processes, including cellular proliferation, differentiation and invasiveness, to enhance the formation and functioning of many human tissues and organs. In this review, we have discussed the role of activin and inhibin signaling in the physiological and female-specific pathological events that occur in the female reproductive system. The up-to-date evidence indicates that these cytokines regulate germ cell development, follicular development, ovulation, uterine receptivity, decidualization and placentation through the activation of several signaling pathways; and that their dysregulated expression is involved in the pathogenesis and pathophysiology of the numerous diseases, including pregnancy complications, that disturb reproduction. Hence, some of the isoforms have been suggested as potential biomarkers and therapeutic targets for the management of some of these diseases. Tackling the research directions highlighted in this review will enhance a detailed comprehension and the clinical utility of these cytokines.

Apoptosis modulation by activin A and follistatin in human endometrial stromal cells

Activin A is a growth factor that stimulates decidualization and is abundantly expressed in endometrial proliferative disorders. Nevertheless, whether it directly affects endometrial cell survival is still unknown. This study investigated the effects of activin A on total death and apoptosis rates and on tumor necrosis factor (TNF) release by human endometrial stromal cells (HESC). We performed a controlled prospective in vitro study using primary HESC cultures obtained from healthy reproductive age women (n = 11). Cells were treated with medium alone (control) or activin A (25 ng/mL) or activin A (25 ng/mL) and its antagonist follistatin (250 ng/mL). Apoptosis and total cell death were measured by flow cytometry, while TNF concentrations in culture media were quantified by ELISA. Activin A decreased the percentage of apoptotic/dead cells from 31% to 22% (p < 0.05, paired t-test) and reduced TNF levels in culture medium by 14%, but there was no linear correlation between TNF release and apoptotic rates. Both effects of activin A were reversed by follistatin. These findings indicate that activin A promotes HESC survival, possibly by a TNF-independent pathway. This mechanism may be critical to the actions of activin A upon stromal cell growth and differentiation in physiology and disease.

Role of activins in embryo implantation and diagnosis of ectopic pregnancy: a review

Embryo implantation is a major prerequisite for the successful establishment of pregnancy. Ectopic implantation outside the intrauterine cavity and the development of ectopic pregnancy (EP) is a major cause of maternal morbidity and occasionally mortality during the first trimester. EP may be induced by failure of tubal transport and/or increased tubal receptivity. Activins, their type II receptors and follistatin have been localised in the human endometrial and tubal epithelium and they are major regulators of endometrial and tubal physiology during the menstrual cycle. Pathological expression of activins and their binding protein, follistatin, was observed in tissue and serum samples collected from EP. Several studies with different designs investigated the diagnostic value of a single measurement of serum activin-A in the differentiation between normal intrauterine and failing early pregnancy and the results are controversial. Nevertheless, the diagnostic value of activins in EP, including the other activin isoforms (activin-B and -AB) and follistatin, merits further research. This review appraises the data to date researching the role of activins in the establishment of normal pregnancy and, pathogenesis and diagnosis of tubal EP.

Identification of local angiogenic and inflammatory markers in the menstrual blood of women with endometriosis

The aim of this study was to evaluate the presence of myeloperoxidase (MPO), N-acetyl-β-D-glucosaminidase (NAG), tumor necrosis factor alpha (TNF-α) and vascular endothelial growth factor (VEGF) in peripheral and menstrual blood in women with (n=10) and without (n=7) endometriosis. NAG and MPO activities were evaluated by enzymatic methods, whereas TNF-α and VEGF by immunoassay. No significant differences were found for these markers, neither in menstrual nor in peripheral blood between groups. Menstrual blood NAG (P=0.039) and MPO (P=0.0117) activities in the endometriosis group were significantly higher than in peripheral blood. NAG and MPO presented positive linear correlation in peripheral (P=0.07; r=0.641) and menstrual blood (P=0.01; r=0.603). These findings point to the existence of an increased local inflammatory activity in women with endometriosis.

Activin A stimulates interleukin 8 and vascular endothelial growth factor release from cultured human endometrial stromal cells: possible implications for the pathogenesis of endometriosis

BACKGROUND

Activin A is an endometrial secretory product involved in inflammation and angiogenesis. The present study aimed to evaluate the effect of activin A and its antagonist follistatin on interleukin (IL)-6, IL-8, and vascular endothelial growth factor (VEGF) expression and release from cultured human endometrial stromal cells (HESCs) from women with and without endometriosis.

METHODS

The HESCs were collected from women with endometriosis (n = 6) and controls (n = 6). Primary cultures were treated with activin A at different doses or activin A plus follistatin. The IL-6, IL-8, and VEGF messenger RNA expression was evaluated by real-time polymerase chain reaction and protein release was evaluated by enzyme-linked immunosorbent assay.

RESULTS

Unstimulated HESC from women with endometriosis secreted more IL-6 and IL-8 than controls. The addition of activin A increased IL-8 and VEGF secretion in HESC from controls and decreased IL-6 and IL-8 secretion in HESC from women with endometriosis. These effects were counteracted by follistatin.

CONCLUSION

Activin A regulates the expression and secretion of IL-8 and VEGF in cultured HESC, and this mechanism appears to be disrupted in eutopic endometrial cells from women affected by endometriosis.

Diagnostic value of serum activin A and follistatin levels in women with peritoneal, ovarian and deep infiltrating endometriosis

BACKGROUND

Activin A is a growth factor, produced by the endometrium, whose actions are modulated by the binding protein follistatin. Both proteins are detectable in the peripheral serum and their concentrations may be increased in women with endometriosis. The present study was designed to evaluate whether serum levels of activin A and follistatin are altered, and therefore have a potential diagnostic value, in women with peritoneal, ovarian and deep infiltrating endometriosis.

METHODS

We performed a multicenter controlled study evaluating simultaneously serum activin A and follistatin concentrations in women with and without endometriosis. Women with endometriosis (n = 139) were subdivided into three groups: peritoneal endometriosis (n = 28); ovarian endometrioma (n = 61) and deep infiltrating endometriosis (n = 50). The control group (n = 75) consisted of healthy women with regular menstrual cycles. Blood samples were collected from a peripheral vein and assayed for activin A and follistatin using commercially available enzyme immunoassay kits.

RESULTS

The ovarian endometrioma group had serum activin A levels significantly higher than healthy controls (0.22 ± 0.01 ng/ml versus 0.17 ± 0.01 ng/ml, P < 0.01). None of the endometriosis groups had serum follistatin levels which were significantly altered compared with healthy controls; however, levels found in the endometrioma group (2.34 ± 0.32 ng/ml) were higher than that in the deep endometriosis group (1.50 ± 0.17 ng/ml, P < 0.05). The area under the receiver operating characteristic curve of activin A was 0.700 (95% confidence interval: 0.605-0.794), while that of follistatin was 0.620 (95% confidence interval: 0.510-0.730) for the diagnosis of ovarian endometrioma. The combination of both markers into a duo marker index did not improve significantly their diagnostic accuracy.

CONCLUSIONS

The present study demonstrated that serum activin A and follistatin are not significantly altered in peritoneal or deep infiltrating endometriosis and have limited diagnostic accuracy in the diagnosis of ovarian endometrioma.

Analysis of the effects of androgens and training on myostatin propeptide and follistatin concentrations in blood and skeletal muscle using highly sensitive immuno PCR

Myostatin propeptide (MYOPRO) and follistatin (FOLLI) are potent myostatin inhibitors. In this study we analysed effects of training and androgens on MYOPRO and FOLLI concentrations in blood and skeletal muscle using Immuno PCR. Young healthy males performed either a 3-month endurance training or a strength training. Blood and biopsy samples were analysed. Training did not significantly affect MYOPRO and FOLLI concentrations in serum and muscle. To investigate whether total skeletal muscle mass may affect circulating MYOPRO and FOLLI levels, blood samples of tetraplegic patients, untrained volunteers and bodybuilders were analysed. MYOPRO was significantly increased exclusively in the bodybuilder group. In orchiectomised rats MYOPRO increased in blood and muscle after treatment with testosterone. In summary our data demonstrate that moderate training does not affect the concentrations of MYOPRO to FOLLI. In contrast androgen treatment results in a significant increase of MYOPRO in skeletal muscle and serum.

A new role for activin in endometrial repair after menses

Abnormal uterine bleeding can severely affect the quality of life for women. After menstruation, the endometrium must adequately repair to limit and stop bleeding. Abnormal uterine bleeding may result from incorrect or inadequate endometrial repair after menstruation. Previous studies have shown an important contribution of activin to skin wound healing, with severely delayed wound repair observed in animals transgenically induced to overexpress activin's natural inhibitor, follistatin. Activin subunits have also been identified within human endometrium; however, their role in endometrial repair is unknown. We assessed the contribution of activin to endometrial repair after menses using a human in vitro cell wounding method and our well-characterized mouse model of endometrial breakdown and repair applied to mice overexpressing follistatin. Endometrial repair after menses is initiated with reepithelialization of the uterine surface. To mimic this repair, we utilized a human endometrial epithelial cell line (ECC-1) and demonstrated significant stimulation of wound closure after activin A administration, and attenuation of this response by addition of follistatin. Immunolocalization of activin subunits, betaA and betaB, in control endometrium from the mouse model demonstrated specific epithelial and stromal localization and some leukocyte staining (betaA) around sites of endometrial repair, suggestive of a role for activin in this process. Follistatin-overexpressing animals had significantly higher circulating follistatin levels than wild-type littermates. There was a significant delay in endometrial repair after breakdown in follistatin transgenic animals compared with control animals. This study demonstrates for the first time a functional role for activin in endometrial repair after menses.