Effect of inhibition of sterol delta 14-reductase on accumulation of meiosis-activating sterol and meiotic resumption in cumulus-enclosed mouse oocytes in vitro.
Two sterols of the cholesterol biosynthetic pathway induce resumption of meiosis in mouse oocytes in vitro. The sterols, termed meiosis-activating sterols (MAS), have been isolated from human follicular fluid (FF-MAS, 4,4-dimethyl-5 alpha-cholest-8,14,24-triene-3 beta-ol) and from bull testicular tissue (T-MAS, 4,4-dimethyl-5 alpha-cholest-8,24-diene-3 beta-ol). FF-MAS is the first intermediate in the cholesterol biosynthesis from lanosterol and is converted to T-MAS by sterol delta 14-reductase. An inhibitor of delta 7-reductase and delta 14 reductase, AY9944-A-7, causes cells with a constitutive cholesterol biosynthesis to accumulate FF-MAS and possibly other intermediates between lanosterol and cholesterol. The aim of the present study was to evaluate whether AY9944-A-7 added to cultures of cumulus-oocyte complexes (COC) from mice resulted in accumulation of MAS and meiotic maturation. AY9944-A-7 stimulated dose dependently (5-25 mumol l-1) COC to resume meiosis when cultured for 22 h in alpha minimal essential medium (alpha-MEM) containing 4 mmol hypoxanthine l-1, a natural inhibitor of meiotic maturation. In contrast, naked oocytes were not induced to resume meiosis by AY9944-A-7. When cumulus cells were separated from their oocytes and co-cultured, AY9944-A-7 did not affect resumption of meiosis, indicating that intact oocyte-cumulus cell connections are important for AY9944-A-7 to exert its effect on meiosis. Cultures of COC with 10 mumol AY9944-A-7 l-1 in the presence of [3H]mevalonic acid, a natural precursor for steroid synthesis, resulted in accumulation of labelled FF-MAS, which had an 11-fold greater amount of radioactivity incorporated per COC compared with the control culture without AY9944-A-7. In contrast, incorporation of radioactivity into the cholesterol fraction was reduced 30-fold in extracts from the same oocytes. The present findings demonstrate for the first time that COC can synthesize cholesterol from mevalonate and accumulate FF-MAS in the presence of AY9944-A-7. Furthermore, AY9944-A-7 stimulated meiotic maturation dose dependently, indicating that FF-MAS, and possibly other sterol intermediates of the cholesterol synthesis pathway, play a central role in stimulating mouse oocytes to resume meiosis. The results also indicate that oocytes may not synthesize steroids from mevalonate.
Leonardsen
L
L
Laboratory of Reproductive Biology, Juliane Marie Center for Children, Women and Reproduction, Rigshospitalet, Blegdamsvej, Denmark.
Strömstedt
M
M
Jacobsen
D
D
Kristensen
K S
KS
Baltsen
M
M
Andersen
C Y
CY
Byskov
A G
AG
D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D002782:Cholestenes / Q000378:metabolism* / Q000494:pharmacology; D002784:Cholesterol / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D007810:Lanosterol / Q000096:biosynthesis; D008540:Meiosis / Q000187:drug effects*; D008798:Mevalonic Acid / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009865:Oocytes / Q000166:cytology* / Q000187:drug effects; D012044:Regression Analysis; D001371:trans-1,4-Bis(2-chlorobenzaminomethyl)cyclohexane Dihydrochloride / Q000494:pharmacology*
D000924:Anticholesteremic Agents; D002782:Cholestenes; D004791:Enzyme Inhibitors; D007810:Lanosterol; D001371:trans-1,4-Bis(2-chlorobenzaminomethyl)cyclohexane Dihydrochloride; C100324:4,4-dimethylcholesta-8,14,24-trienol; D002784:Cholesterol; D008798:Mevalonic Acid