Evidence for the synthesis, secretion and uptake of prorenin in human amnion (#286)
Very high concentrations of prorenin are found in amniotic fluid1, yet its source is unknown. We have shown that the decidua has the highest levels of prorenin mRNA (REN) in term intrauterine tissues2. In contrast, REN levels in human amnion are very low, but strong immunostaining for prorenin is observed3. We propose that decidual prorenin contributes to the high levels of prorenin in amniotic fluid and that the amnion itself may also synthesise small amounts of prorenin.
To test this hypothesis, human amnion was incubated for 0 or 24 h in media containing vehicle, or 50ng/ml recombinant human (rh)prorenin. Total RNA was extracted using TRIzol and converted to cDNA for quantitative real-time PCR. Prorenin (REN) abundance was calculated relative to Alien RNA using the DDCT method. Prorenin levels in the supernatant and amnion tissue were measured by ELISA (Molecular Innovations).
In vehicle treated amnion incubations, REN mRNA levels were very low. At 0 h (prior to incubation) only 3/11 amnion had detectable levels of REN but significant levels of prorenin protein were found in amnion tissue (1.4 mg/g total protein). After 24 h incubation REN mRNA was found in all samples and was significantly increased (P=0.008) as were prorenin levels in the supernatant (P=0.033). Prorenin levels in amnion tissue however, did not change with incubation time. Exogenous prorenin significantly increased amnion prorenin (2.8 mg/g total protein, P=0.001) but not REN mRNA.
This data suggest that the amnion can produce small amounts of REN and secrete prorenin, possibly into amniotic fluid, when incubated ex vivo for 24h. In addition, we have demonstrated that prorenin levels in amnion tissue extracts are increased after exposure to (rh)Prorenin. Whether this is due to (rh)prorenin being internalised by the amnion cells or binding to receptors on the cell surface has yet to be determined.
- Itskovitz, J., et al. J Clin Endocrinol Metab, 1992. 75(3): p. 906-910.
- Pringle, K.G., et al. J Renin Angiotensin Aldosterone Syst, 2011. 12 (3): p. 304-310.
- Marques, F.Z., et al. Placenta, 2011. 32(3): p. 214-221.