Luteinizing Hormone Stimulates Mammalian Target of Rapamycin Signaling in Bovine Luteal Cells via Pathways Independent of AKT and Mitogen-Activated Protein Kinase: Modulation of Glycogen Synthase Kinase 3 and AMP-Activated Protein Kinase

Abstract

LH stimulates the production of cAMP in luteal cells, which leads to the production of progesterone, a hormone critical for the maintenance of pregnancy. The mammalian target of rapamycin (MTOR) signaling cascade has recently been examined in ovarian follicles where it regulates granulosa cell proliferation and differentiation. This study examined the actions of LH on the regulation and possible role of the MTOR signaling pathway in primary cultures of bovine corpus luteum cells. Herein, we demonstrate that activation of the LH receptor stimulates the phosphorylation of the MTOR substrates ribosomal protein S6 kinase 1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1. The actions of LH were mimicked by forskolin and 8-bromo-cAMP. LH did not increase AKT or MAPK1/3 phosphorylation. Studies with pathway-specific inhibitors demonstrated that the MAPK kinase 1 (MAP2K1)/MAPK or phosphatidylinositol 3-kinase/AKT signaling pathways were not required for LH-stimulated MTOR/S6K1 activity. However, LH decreased the activity of glycogen synthase kinase 3Beta (GSK3B) and AMP-activated protein kinase (AMPK). The actions of LH on MTOR/S6K1 were mimicked by agents that modulated GSK3B and AMPK activity. The ability of LH to stimulate progesterone secretion was not prevented by rapamycin, a MTOR inhibitor. In contrast, activation of AMPK inhibited LH-stimulated MTOR/S6K1 signaling and progesterone secretion. In summary, the LH receptor stimulates a unique series of intracellular signals to activate MTOR/S6K1 signaling. Furthermore, LH-directed changes in AMPK and GSK3B phosphorylation appear to exert a greater impact on progesterone synthesis in the corpus luteum than rapamycin-sensitive MTOR-mediated events.

TGFB1 disrupts the angiogenic potential of microvascular endothelial cells of the corpus luteum

“…Bovine collagen type I, Matrigel basement membrane growth factor reduced, Matrigel matrix thin layer multiwell plates and cell culture inserts (transparent PET membrane, 3 and 8 m pore) were purchased from BD Biosciences (Bedford, MA). The HSD3B antibody was a gift from Ian Mason, University of Texas Southwestern Medical Center, Dallax, TX (Hou et al, 2010). Western Lightning ECL was from PerkinElmer Life Sciences (Waltham, MA).…”

Improving Type 2 Diabetes Through a Distinct Adrenergic Signaling Pathway Involving mTORC2 That Mediates Glucose Uptake in Skeletal Muscle

“…There is, however, some evidence that other GPCRs can activate mTORC1 independently of Akt/PI3K, including the Gaq/11-coupled a 1 -adrenoceptors in cardiomyocytes (47), the Gaq/11-coupled prostaglandin F2a receptor, and the Gas-coupled luteinizing hormone receptor in the corpus luteum (48). There has been great attention focused on the regulation and downstream targets of mTORC1 that can be pharmacologically inhibited by rapamycin.…”

The effect of nutrition and metabolic status on the development of follicles, oocytes and embryos in ruminants

“…In cows, AMPK is also found in the corpus luteum. In cultured bovine luteal cells, the activation of AMPK regulated LH-induced progesterone secretion (Hou et al, 2010).…”