1. ¹Peking University First Hospital, Institute of Urology of Peking University, Beijing 100034, China
2. ²Reproductive and Genetic Center of Peking University First Hospital, Beijing 100034, China
3. ³Department of Obstetrics and Gynecology, Shanxi Medical University Second Hospital, Taiyuan 030000, China
4. ⁴Reproductive and Genetic Center of National Research Institute for Family Planning, Beijing 100038, China
5. ⁵Department of Genetics, Peking Union Medical College, Beijing 100038, China
6. ⁶WHO Collaborative Center for Research in Human Reproduction, Beijing 100038, China

Correspondence: Xu Ma, Tel: +86-10-62176870; Fax: +86-10-62179059; E-mail:genetic@263.net.cn

^*These two authors contributed equally to this work.

Received 19 March 2006; Revised 19 July 2006; Accepted 10 August 2006; Published online 19 September 2006.

Abstract

Although the role of oxidative stress in maternal aging and infertility has been suggested, the underlying mechanisms are not fully understood. The present study is designed to determine the relationship between mitochondrial function and spindle stability in metaphase II (MII) oocytes under oxidative stress. MII mouse oocytes were treated with H₂O₂ in the presence or absence of permeability transition pores (PTPs) blockers cyclosporin A (CsA). In addition, antioxidant N-acetylcysteine (NAC), F₀/F₁ synthase inhibitor oligomycin A, the mitochondria uncoupler carbonyl cyanide 4-trifluoro-methoxyphenylhydrazone (FCCP) or thapsigargin plus 2.5 mM Ca²⁺ (Th+2.5 mM Ca²⁺) were used in mechanistic studies. Morphologic analyses of oocyte spindles and chromosomes were performed and mitochondrial membrane potential (m), cytoplasmic free calcium concentration ([Ca²⁺]_c) and cytoplasmic ATP content within oocytes were also assayed. In a time- and H₂O₂ dose-dependent manner, disruption of meiotic spindles was found after oocytes were treated with H₂O₂, which was prevented by pre-treatment with NAC. Administration of H₂O₂ led to a dissipation of m, an increase in [Ca²⁺]_c and a decrease in cytoplasmic ATP levels. These detrimental responses of oocytes to H₂O₂ treatment could be blocked by pre-incubation with CsA. Similar to H₂O₂, both oligomycin A and FCCP dissipated m, decreased cytoplasmic ATP contents and disassembled MII oocyte spindles, while high [Ca²⁺]_c alone had no effects on spindle morphology. In conclusion, the decrease in mitochondria-derived ATP during oxidative stress may cause a disassembly of mouse MII oocyte spindles, presumably due to the opening of the mitochondrial PTPs.