Przygrodzka Emilia, Monaco Corrine F, Plewes Michele R, Li Guojuan, Wood Jennifer R, Cupp Andrea S, Davis John S
Department of Obstetrics and Gynecology, Olson Center for Women's Health, University of Nebraska Medical Center, Omaha, NE, United States.
Department of Cellular and Integrative Physiology, University of Nebraska Medical Center, Omaha, NE, United States.
Front Cell Dev Biol. 2021 Nov 8;9:723563. doi: 10.3389/fcell.2021.723563. eCollection 2021.
In the absence of pregnancy the ovarian corpus luteum undergoes regression, a process characterized by decreased production of progesterone and structural luteolysis involving apoptosis. Autophagy has been observed in the corpus luteum during luteal regression. Autophagy is a self-degradative process important for balancing sources of cellular energy at critical times in development and in response to nutrient stress, but it can also lead to apoptosis. Mechanistic target of rapamycin (MTOR) and 5' AMP-activated protein kinase (AMPK), key players in autophagy, are known to inhibit or activate autophagy, respectively. Here, we analyzed the signaling pathways regulating the initiation of autophagy in bovine luteal cells. studies showed increased activating phosphorylation of AMPKα (Thr172) and elevated content of LC3B, a known marker of autophagy, in luteal tissue during PGF2α-induced luteolysis. , AMPK activators 1) stimulated phosphorylation of regulatory associated protein of MTOR (RPTOR) leading to decreased activity of MTOR, 2) increased phosphorylation of Unc-51-Like Kinase 1 (ULK1) and Beclin 1 (BECN1), at sites specific for AMPK and required for autophagy initiation, 3) increased levels of LC3B, and 4) enhanced colocalization of autophagosomes with lysosomes indicating elevated autophagy. In contrast, LH/PKA signaling in luteal cells 1) reduced activation of AMPKα and phosphorylation of RPTOR, 2) elevated MTOR activity, 3) stimulated phosphorylation of ULK1 at site required for ULK1 inactivation, and 4) inhibited autophagosome formation as reflected by reduced content of LC3B-II. Pretreatment with AICAR, a pharmacological activator of AMPK, inhibited LH-mediated effects on RPTOR, ULK1 and BECN1. Our results indicate that luteotrophic signaling via LH/PKA/MTOR inhibits, while luteolytic signaling via PGF2α/Ca/AMPK activates key signaling pathways involved in luteal cell autophagy.
在未怀孕的情况下，卵巢黄体发生退化，这一过程的特征是孕酮分泌减少以及涉及细胞凋亡的结构性黄体溶解。在黄体退化过程中，黄体中已观察到自噬现象。自噬是一种自我降解过程，在发育的关键时期以及应对营养应激时，对于平衡细胞能量来源非常重要，但它也可能导致细胞凋亡。雷帕霉素机制靶点（MTOR）和5'单磷酸腺苷激活蛋白激酶（AMPK）是自噬的关键参与者，已知它们分别抑制或激活自噬。在此，我们分析了调节牛黄体细胞自噬起始的信号通路。研究表明，在PGF2α诱导的黄体溶解过程中，黄体组织中AMPKα（Thr172）的激活磷酸化增加，以及自噬的已知标志物LC3B的含量升高。此外，AMPK激活剂1）刺激雷帕霉素机制靶点调节相关蛋白（RPTOR）的磷酸化，导致MTOR活性降低；2）增加Unc-51样激酶1（ULK1）和Beclin 1（BECN1）在特定于AMPK且自噬起始所需位点的磷酸化；3）提高LC3B的水平；4）增强自噬体与溶酶体的共定位，表明自噬增强。相反，黄体细胞中的LH/PKA信号传导1）降低AMPKα的激活和RPTOR的磷酸化；2）提高MTOR活性；3）刺激ULK1在ULK1失活所需位点的磷酸化；4）抑制自噬体形成，这通过LC3B-II含量降低得以体现。用AMPK的药理学激活剂AICAR预处理可抑制LH对RPTOR、ULK1和BECN1的介导作用。我们的结果表明，通过LH/PKA/MTOR的黄体营养信号传导起抑制作用，而通过PGF2α/Ca/AMPK的黄体溶解信号传导激活了参与黄体细胞自噬的关键信号通路。
