Protein Kinase A and 59 AMP-Activated Protein Kinase Signaling Pathways Exert Opposite Effects on Induction of Autophagy in Luteal Cells

Authors

Emilia Przygrodzka, University of Nebraska Medical CenterFollow
Corrine F. Monaco, University of Nebraska Medical Center
Michele R. Plewes, University of Nebraska Medical Center, Veterans Affairs Nebraska Western Iowa Health Care SystemFollow
Guojuan Li, University of Nebraska Medical Center
Jennifer R. Wood, University of Nebraska-LincolnFollow
Andrea Cupp, University of Nebraska - LincolnFollow
John S. Davis, University of Nebraska Medical Center, Veterans Affairs Nebraska Western Iowa Health Care SystemFollow

Date of this Version

11-8-2021

Citation

Przygrodzka E, Monaco CF, Plewes MR, Li G, Wood JR, Cupp AS and Davis JS (2021) Protein Kinase A and 5′ AMP-Activated Protein Kinase Signaling Pathways Exert Opposite Effects on Induction of Autophagy in Luteal Cells. Front. Cell Dev. Biol. 9:723563. doi: 10.3389/fcell.2021.723563

Comments

Open access

Abstract

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. In vivo 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. In vitro, 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/Ca²⁺/AMPK activates key signaling pathways involved in luteal cell autophagy.