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Oxidative Metabolism of Pyruvate Is Required for Meiotic Maturation of Murine Oocytes In Vivo¹

Department of Genetics,⁵ Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106 Colorado Center for Reproductive Medicine,⁶ Englewood, Colorado 80110

ABSTRACT

The requirement for oxidative metabolism of pyruvate during oogenesis in vivo was evaluated by inactivating Pdha1, a gene encoding an enzymatic subunit of pyruvate dehydrogenase complex, in murine oocytes at the beginning of the follicular growth phase. Immunohistochemical analysis revealed that Pdha1^– oocytes have dramatically reduced amounts of pyruvate dehydrogenase enzyme by the secondary follicle stage. Despite this reduction, these oocytes grow to normal size, are ovulated, and can be fertilized. Pdha1^– oocytes are, however, impaired in their ability to support embryonic development, as demonstrated by the failure of fertilized oocytes to develop beyond the one-cell zygote stage in vivo. Immunocytochemical evaluation showed that almost all (98.4%) ovulated Pdha1^– oocytes have not completed meiotic maturation and/or have gross abnormalities of the meiotic spindle and chromatin. Meiotic maturation is even more compromised when these oocytes are matured in vitro in the absence of cumulus cells or in the presence of the gap junction inhibitor 18-alpha glycyrrhetinic acid, indicating that cumulus cells can partially compensate for this enzymatic deficiency through a gap junction-mediated mechanism. Ovulated Pdha1^– oocytes were also shown to have reduced levels of total ATP content and NAD(P)H autofluorescence relative to oocytes without this enzymatic deficiency. These studies demonstrate that oxidative metabolism of pyruvate is essential for proper completion of oogenesis, serving as a vital source of energy during meiotic maturation. At earlier stages of oogenesis this metabolic pathway may not be necessary due to metabolic compensation by the granulosa cells.

embryo, gamete biology, granulosa cells, meiosis, meiotic maturation, mitochondria and metabolism, oocyte development, oogenesis, pyruvate

³Current address: Department of Biology, St. John Fisher College, Rochester, NY 14618.

⁴Current address: School of Molecular Biosciences, Washington State University, Pullman, WA 99164.

¹Supported in part by National Institutes of Health grants K08HD47431-3 (M.T.J.), R01 HD37502-02 (P.A.H.), and R01 ES013527 (P.A.H.).

Correspondence: ²Mark T. Johnson, Colorado Center for Reproductive Medicine, 799 East Hampden Ave., Suite 520, Englewood, CO 80110. FAX: 303 744 0688; e-mail: mtj{at}case.edu