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A potential role for AMP-activated protein kinase in meiotic induction in mouse oocytes
Stephen M Downs1, Emma R Hudson, D Grahame Hardie
1Biology Department, Marquette University, 530 N. 15 Street, Milwaukee, WI 53233, USA. Stephen.Downs@Marquette.edu
Abstract:
Cyclic adenosine monophosphate (cAMP) has been implicated as an important regulator of meiotic maturation in mammalian oocytes. A decrease in cAMP, brought about by the action of cAMP phosphodiesterase (PDE), is thought to initiate germinal vesicle breakdown (GVB) by the inactivation of cAMP-dependent protein kinase. However, the product of PDE activity, 5'-AMP, is a potent activator of an important regulatory enzyme, AMP-activated protein kinase (AMPK). The aim of this study was to evaluate a possible role for AMPK in meiotic induction, using oocytes obtained from eCG-primed, immature mice. Alpha-1 and -2 isoforms of the catalytic subunit of AMPK were detected in both oocytes and cumulus cells. When 5-aminoimidazole-4-carboxamide 1-beta-d-ribofuranoside (AICA riboside), an activator of AMPK, was tested on denuded oocytes (DO) and cumulus cell-enclosed oocytes (CEO) maintained in meiotic arrest by dbcAMP or hypoxanthine, GVB was dose-dependently induced. Meiotic induction by AICA riboside in dbcAMP-supplemented medium was initiated within 3 h in DO and 4 h in CEO and was accompanied by increased AMPK activity in the oocyte. AICA riboside also triggered GVB when meiotic arrest was maintained with hypoxanthine, 8-AHA-cAMP, guanosine, or milrinone, but was ineffective in olomoucine- or roscovitine-arrested oocytes, indicating that it acts upstream of maturation-promoting factor. Adenosine monophosphate dose-dependently stimulated GVB in DO when meiotic arrest was maintained with dbcAMP or hypoxanthine. This effect was not mimicked by other monophosphate or adenosine nucleotides and was not affected by inhibitors of ectophosphatases. Combined treatment with adenosine and deoxycoformycin, an adenosine deaminase inhibitor, stimulated GVB in dbcAMP-arrested CEO, suggesting AMPK activation due to AMP accumulation. It is concluded that phosphodiesterase-generated AMP may serve as a transducer of the meiotic induction process through activation of AMPK.
Insights
AMP-activated protein kinase (AMPK) activation by AMP, a phosphodiesterase product, induces meiotic maturation in mammalian oocytes. This study reveals AMP as a key transducer in oocyte meiotic induction via AMPK signaling.
Area of Science:
- Reproductive Biology
- Cell Signaling
- Molecular Endocrinology
Background:
- Cyclic adenosine monophosphate (cAMP) regulates mammalian oocyte meiotic maturation.
- Decreased cAMP, via phosphodiesterase (PDE) activity, is thought to initiate germinal vesicle breakdown (GVB) by inactivating cAMP-dependent protein kinase.
- The PDE product, 5'-AMP, activates AMP-activated protein kinase (AMPK).
Purpose of the Study:
- To investigate the potential role of AMPK in inducing oocyte meiosis.
- To explore the mechanism by which AMP influences meiotic progression.
Main Methods:
- Detection of AMPK isoforms (alpha-1 and -2) in mouse oocytes and cumulus cells.
- Treatment of oocytes (denuded and cumulus cell-enclosed) with AMPK activator (AICA riboside) or AMP under meiotic arrest conditions (dbcAMP, hypoxanthine, etc.).
- Measurement of AMPK activity and assessment of germinal vesicle breakdown (GVB) as an indicator of meiotic progression.
Main Results:
- AICA riboside dose-dependently induced GVB in oocytes, accompanied by increased oocyte AMPK activity.
- AMP dose-dependently stimulated GVB in oocytes arrested with dbcAMP or hypoxanthine.
- AMPK activation by AICA riboside acts upstream of maturation-promoting factor and is linked to AMP accumulation.
Conclusions:
- AMPK plays a significant role in the induction of mammalian oocyte meiosis.
- Phosphodiesterase-generated AMP acts as a crucial signaling molecule, activating AMPK to drive meiotic progression.
- AMPK activation is a key downstream event in the cAMP-mediated regulation of oocyte maturation.