Transport-associated pathway responses in ovine fetal membranes to changes in amniotic fluid dynamics

Current evidence suggests that amniotic fluid volume (AFV) is actively regulated by vesicular transport of amniotic fluid outward across the amnion and into the underlying fetal vasculature in the placenta. Our objective was to determine whether gene expression profiles of potential stimulators, inhibitors, and mediators of vesicular transport are altered in response to changes in intramembranous absorption (IMA) rate. Samples of ovine amnion and chorion were obtained from fetal sheep with normal, experimentally reduced or increased AFVs and IMA rates. Amnion and chorion levels of target mRNAs were determined by RT-qPCR. In the amnion, caveolin-1 and flotillin-1 mRNA levels were unchanged during alterations in IMA rate. However, levels of both were significantly higher in amnion than in chorion. Tubulin-α mRNA levels in the amnion but not in chorion were reduced when IMA rate decreased, and amnion levels correlated positively with IMA rate (P < 0.05). Dynamin-2 mRNA levels were not altered by experimental conditions. Vascular endothelial growth factor (VEGF₁₆₄ and VEGF₁₆₄b) mRNA levels increased during both increases and decreases in IMA rate, whereas soluble Flt-1 levels did not change. Neither HIF-1α nor PBEF mRNA levels in the amnion were correlated with VEGF₁₆₄ expression levels and were not related to IMA rate. Collectively, our findings suggest that changes in amnion microtubule expression may be important in the regulation of transcellular vesicular transport of amniotic fluid and thus modulate IMA rate. Further, our results are consistent with the concept that the amnion is the rate-limiting layer for amniotic fluid transport.