Metformin decreases GnRH- and activin-induced gonadotropin secretion in rat pituitary cells: potential involvement of adenosine 5' monophosphate-activated protein kinase (PRKA).
Metformin is an insulin sensitizer molecule used for the treatment of infertility in women with polycystic ovary syndrome and insulin resistance. It modulates the reproductive axis, affecting the release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). However, metformin's mechanism of action in pituitary gonadotropin-secreting cells remains unclear. Adenosine 5' monophosphate-activated protein kinase (PRKA) is involved in metformin action in various cell types. Here, we investigated the effects of metformin on gonadotropin secretion in response to activin and GnRH in primary rat pituitary cells (PRP), and studied PRKA in rat pituitary. In PRP, metformin (10 mM) reduced LH and follicle-stimulating hormone (FSH) secretion induced by GnRH (10(-8) M, 3 h), FSH secretion, and mRNA FSHbeta subunit expression induced by activin (10(-8) M, 12 or 24 h). The different subunits of PRKA are expressed in pituitary. In particular, PRKAA1 is detected mainly in gonadotrophs and thyrotrophs, is less abundant in lactotrophs and somatotrophs, and is undetectable in corticotrophs. In PRP, metformin increased phosphorylation of both PRKA and acetyl-CoA carboxylase. Metformin decreased activin-induced SMAD2 phosphorylation and GnRH-induced mitogen-activated protein kinase (MAPK) 3/1 (ERK1/2) phosphorylation. The PRKA inhibitor compound C abolished the effects of metformin on gonadotropin release induced by GnRH and on FSH secretion and Fshb mRNA induced by activin. The adenovirus-mediated production of dominant negative PRKA abolished the effects of metformin on the FSHbeta subunit mRNA and SMAD2 phosphorylation induced by activin and on the MAPK3/1 phosphorylation induced by GnRH. Thus, in rat pituitary cells, metformin decreases gonadotropin secretion and MAPK3/1 phosphorylation induced by GnRH and FSH release, FSHbeta subunit expression, and SMAD2 phosphorylation induced by activin through PRKA activation.
Tosca
Lucie
L
UMR85, Unité de Physiologie de la Reproduction et des Comportements, Institut National de la Recherche Agronomique, Nouzilly, France.
Froment
Pascal
P
Rame
Christelle
C
McNeilly
J R
JR
McNeilly
A S
AS
Maillard
Virginie
V
Dupont
Joelle
J
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D028341:Activins / Q000494:pharmacology*; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D015536:Down-Regulation; D004789:Enzyme Activation; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006062:Gonadotropins / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism; D008687:Metformin / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction
D006062:Gonadotropins; D007527:Isoenzymes; D011720:Pyrazoles; D011743:Pyrimidines; D028341:Activins; C516138:dorsomorphin; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D008687:Metformin; D017868:Cyclic AMP-Dependent Protein Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase