Autophagic Degradation Of Collagen 1A1 By Cortisol In Human Amnion Fibroblasts

Rupture of fetal membranes can initiate parturition at both term and preterm.Collagen is the crucial factor determining the tensile strength of the membranes.Toward the end of gestation,a feed-forward regeneration of cortisol via11β-hydroxysteroid dehydrogenase 1(11β-HSD1)exists in fetal membranes.It remains undetermined whether cortisol regeneration contributes to collagen reduction in fetal membranes thereby contributing to the ruprure of membranes toward the end of gestation.Here we have examined whether cortisol accumulation is a causative factor for collagen reduction in human amnion fibroblasts,the major source of collagens in the membranes.Cortisol had no effect on collagen 1A1(COL1A1)and1A2(COL1A2)mRNA abundance but decreased their protein abundance.The latter effect was affected by neither mRNA transcription inhibitor nor protein translation inhibitor.Mechanistic studies revealed that the reduction in COL1A1 but not COL1A2 protein by cortisol was blocked by lysosome inhibitor chloroquine or siRNA-mediated knock-down of ATG7,an essential protein for autophagy,while the proteasome inhibitors MG132 and bortezomib were ineffective.Further analysis showed that cortisol dose-dependently increased the ratio of LC3II/LC3 I,a marker of lysosome activation,an effect blocked by the glucocorticoid receptor(GR)antagonist RU486 and siRNA-mediated knock-down of GR.Consistently,cortisol decreased COL1A1 and COL1A2 protein abundance in amnion tissue explants,and decreased COL1A1 and COL1A2 protein abundance was observed at parturition in the amnion tissue.Conclusively,cortisol regeneration in fetal membranes may contribute to rupture of fetal membranes at parturition by reducing collagen protein abundance.Lysosome-mediated autophagy accounts for the reduction in COL1A1 by cortisol butthe mechanism underlying the reduction in COL1A2 awaits further investigation.