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NHC Key Laboratory of the Study of Abnormal Gametes and the Reproductive Tract, Anhui Medical University, Hefei, China
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In brief
During pregnancy, uterine kept quiescence along with uterine overdistention before labor. Prolonged stretching induced uterus myometrial hypoxia, increased TREK1 expression, and relaxed the myometrium, which may contribute to uterine quiescence and atony during pregnancy.
Abstract
The mechanisms underlying pre-labor uterine quiescence and uterine atony during overdistention are unclear. TREK1 (a two-pore domain potassium channel) and hypoxia-inducible factor-1α (HIF-1α) are activated by mechanical stretch, and their expression is upregulated by decreased uterine contractility. HIF-1α is a nuclear factor which regulates numerous target proteins, but whether it regulates TREK1 during the uterine stretch to cause uterine quiescence and/or atony is unclear. We investigated uterine contractility at different gestational stages in rats, as well as in non-pregnant uteri, which were induced by prolonged stretching and hypoxia. We also assessed the effects of incubating the uteri with or without echinomycin or l-methionine. Moreover, we analyzed HIF-1α and TREK1 expression levels in each group, as well as at various gestational stages of pregnant human uteri. We found that contractility was significantly decreased in pregnant uteri when compared with non-pregnant uteri, and this decrease was associated with increases in HIF-1α and TREK1 expression levels. HIF-1α and TREK1 expression levels in human uteri increased with the gestational length. Decreased uterine contractility and increased HIF-1α and TREK1 expression levels were also observed in non-pregnant rat uteri under 8 g of stretching tension or hypoxia. Inhibition of hypoxia with echinomycin restored normal uterine contractility, while HIF-1α and TREK1 protein expression remained reduced. TREK1 inhibition with l-methionine also restored uterine contractility under tension or hypoxia. In conclusion, we demonstrated that prolonged stretching induces myometrial hypoxia, increases TREK1 expression, and relaxes the myometrium, which may contribute to uterine quiescence and atony.
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Hypoxia is closely associated with physiological and pathological conditions in the human body, and the myometrium is affected by hypoxic stress during pregnancy and delivery. Autophagy is a catabolic pathway involved in the regulation of apoptosis, proliferation and migration of a variety of cells, which can be activated under hypoxia. However, the mechanism and function of autophagy in uterine smooth muscle cells remained unclear. The aim of this study was to investigate the changes of autophagy in pregnant uterine smooth muscle cells (pUSMCs) under hypoxia and the effect of autophagy on myometrial cells proliferation during pregnancy. In this study, primary uterine smooth muscle cells were isolated from mice in late pregnancy and cultured under normoxic and hypoxic conditions respectively. Western blotting and immunofluorescence were used to detect the expression levels of autophagy-related proteins LC3B, P62, mTOR and p-mTOR under different culture conditions. Cell proliferation was assessed by CCK-8 assay. In addition, 3-Methyladenine (3-MA) was used to inhibit autophagy in hypoxia-treated pUSMCs and MHY1485 was used to activate mTOR. Studies have confirmed that under hypoxic conditions, autophagy is enhanced and cell proliferative viability is reduced in pUSMCs. Autophagy inhibitor 3-MA restored cell proliferation inhibited by hypoxia. Furthermore, hypoxia in pUSMCs led to a downregulation of p-mTOR/mTOR levels. The mTOR activator MHY1485 inhibited autophagy by preventing the binding of autophagosomes to lysosomes and reversed the hypoxia-induced inhibition of cell proliferation. Collectively, our results indicate that hypoxia upregulates autophagy through the mTOR pathway in pUSMCs, thereby inhibiting cell proliferation during pregnancy.
