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Steroid hormonal regulation of the autophagic response in the mouse uterus
Autophagy is a major cellular catabolic pathway and is tightly associated with survival and death of cells. The involvement of autophagy during prolonged survival of blastocysts in the uterus is established and it was assumed that ovarian steroid hormones – estrogen (E2) and progesterone (P4) – play important roles in its regulation. The uterus is a major target organ of E2 and P4. To examine if E2 or P4 modulate autophagy in the mouse uterus in vivo, the following three systems were used. 1) Normal pregnancy model (days 1 to 8); 2) delayed implantation model; 3) ovariectomized (OVX) mice model treated with single steroid hormone. Six-week-old virgin ICR mice were used for pregnancy and OXV. OVX mice received P4 (1 mg/0.1 ml) or E2 (100 ng/0.1 ml) after 12 days of rest. Collected uteri were subjected to Western blotting and immunofluorescence staining using anti-LC3B antibody to monitor autophagy. In pregnant mouse uterus, the autophagic response was downregulated after implantation. In OVX model, either E2 or P4 injection downregulated the autophagic response in the uterus within several hours. To confirm whether hormone-induced downregulation is mediated by classical estrogen receptor (ER) and progesterone receptor (PR), receptor antagonists (ICI 182,780 and RU-486) were co-treated. Antagonist-treated uteri showed recovery of autophagic response, suggesting that ER or PR mediates hormonal effects on autophagy. In oder to determine which signaling pathway is involved in autophagic regulation by E2, rapamycin (5 mg/kg), a mTOR inhibitor, and LY294002 (5 mg/kg), a PI3 kinase inhibitor, were used. Rapamycin and LY294002 were injected just before E2 injection to OVX mice. Western blotting was performed by using anti-phospho-mTOR and anti-AKT antibodies. We observed that rapamycin treatment partially antagonized downregulation of autophagic activation by E2, whereas LY294002 treatment did not have any effect. Therefore, downregulation of autophagy by E2 seems to be partially mediated by mTOR pathway. Collectively, this study suggests that ovarian steroid hormones are upstream controllers of autophagic response in the mouse uterus.
