Imbalance of Amniotic Fluid Activin-A and Follistatin in Intraamniotic Infection, Inflammation, and Preterm Birth

Abstract

Context: Microbial invasion of the amniotic fluid (AF) cavity stimulates an inflammatory response that involves activin-A, a pleiotropic mediator member of the TGFβ superfamily involved in connective tissue remodeling. The role of AF follistatin, a natural inhibitor of activin-A, in inflammation-induced preterm birth (PTB), has yet to be determined.

Objective: The objective of the study was to investigate the relationships between AF activin-A and follistatin in physiological gestation and in pregnancies complicated by PTB and to evaluate a possible role played by the activin-A-follistatin balance in processes leading to PTB and preterm premature rupture of membranes (PPROM).

Study design: The AF levels of total activin-A and follistatin were immunoassayed in 168 women with a normal pregnancy outcome or PTB with and without intraamniotic inflammation or PPROM. The impact of the activin-A-follistatin imbalance on PTB terminal effector pathways (prostaglandins [prostaglandin E2, prostaglandin F2α] and matrix metalloproteinases [MMP-1, MMP-2, MMP-3, and MMP-9]) was investigated in an amniochorion explant system challenged with lipopolysaccharide (LPS) to mimic inflammation.

Results: AF follistatin and the activin-A to follistatin ratio varied with gestational age, both decreasing toward term (P < .001). Activin-A was up-regulated in AF infection (>2-fold elevation in activin-A to follistatin ratio) correlating directly with severity of inflammation (both P < .001). Activin-A increased prostaglandins, MMP-1, and MMP-9 released by amniochorion (P < .05) to LPS-equivalent levels. Follistatin effectively blunted the prostaglandin response to activin-A and LPS and that of MMPs after activin-A but not after LPS challenge.

Conclusion: Activin-A and follistatin are part of the complex inflammatory response of the gestational sac to infection and modulate effector pathways leading to PTB. The activin-A to follistatin ratio may play a role in determining the clinical phenotype of PTB as preterm labor or PPROM.

Figure 1.

GA regulation of AF activin-A (A), follistatin (B), and activin-A to follistatin ratio (C) is shown. Thick black line, linear regression line; thick gray lines, 95% confidence intervals; dotted black lines, 95% prediction intervals. The Spearman correlations coefficients (r) and level of significance are presented on each graph.

Figure 2.

Scatterplots of AF activin-A (A and D), follistatin (B and E), and activin-A to follistatin ratio (C and F) are shown. Cases are grouped by results of AF cultures (AFC; positive or negative) and membrane status (intact or PPROM) (A–C) or by severity of inflammation as reflected by MR score (D and E). The thick horizontal lines represent the group median. Groups marked with different letters are statistically different at P < .05. Data were analyzed using a one-way ANOVA on ranks followed by Dunn's post hoc tests.

Figure 3.

Relationships of AF activin-A with AF WBC count (A) and AF IL-6 (B) among women who had an amniocentesis to rule out infection (n = 129). Relationships of AF follistatin with WBC count (C) and with AF IL-6 (D) are also shown. Thick black line, linear regression line; thick gray lines, 95% confidence intervals; dotted black lines, 95% prediction intervals. The correlations coefficients (r) and level of significance are presented on each graph after correction for gestational age at amniocentesis.

Figure 4.

A, PGE₂ and PGF_2α concentration in explant medium after normalization for total tissue protein. Relative changes in PGE₂ (B) and PGF_2α (C) compared with basal levels (medium alone) at 24 hours of incubation. Full-thickness amniochorion tissues from women undergoing elective cesarean deliveries (n = 5) were challenged with activin-A (ACT), follistatin (FS), LPS (endotoxin), and combinations thereof. Bars marked with different letters are different statistically at P < .05. Data were analyzed using a one-way ANOVA on ranks followed by Dunn's post hoc tests.

Figure 5.

A, Concentration of measured MMPs in explant medium after normalization for total tissue protein. Relative changes in MMP-1 (B), MMP-9 (C), MMP-3 (D), MMP-2 (E), and the chemokine (IL-8) (F) compared with basal levels at 24 hours of incubation. Full-thickness amniochorion tissues from women undergoing elective cesarean deliveries (n = 5) were challenged with activin-A (ACT), follistatin (FS), LPS (endotoxin), and combinations thereof. Bars sharing a common letter are not different statistically (P > .05). Data were analyzed using a one-way ANOVA on ranks followed by Dunn's post hoc tests.