GROUP VIA PHOSPHOLIPASE A2 AND SPERM WITH IMPAIRED MOTILITY/REDUCED FERTILITY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Group VIA Phospholipase A2 (iPLA2B) is the first recognized cytosolic Ca2+-independent PLA2 and has been proposed to participate in arachidonic acid (20:4) incorporation into glycerophosphocholine lipids, cell proliferation, exocytosis, apoptosis, and other processes. To study iPLA2B functions, we disrupted its gene by homologous recombination to generate mice that do not express iPLA2B. Heterozygous iPLA2B+/- breeding pairs yield a Mendelian 1:2:1 ratio of iPLA2B+/+, iPLA2B+/-, and iPLA2B-/- pups and a 1:1 male:female gender distribution of iPLA2B-/- pups. Several tissues of wild-type mice express iPLA2B mRNA, immunoreactive protein, and activity, and testes express the highest levels. Testes or other tissues of iPLA2B-/- mice express no iPLA2B mRNA or protein, but iPLA2B-/- testes are not deficient in 20:4-containing glycerophosphocholine lipids, indicating that iPLA2B does not play an obligatory role in formation of such lipids in that tissue. Spermatozoa from iPLA2B/- mice have reduced motility and impaired ability to fertilize mouse oocytes in vitro and in vivo, and inhibiting iPLA2B with a bromoenol lactone suicide substrate reduces motility of wild-type spermatozoa in a time- and concentration-dependent manner. Mating iPLA2B-/- male mice with iPLA2B+/+, iPLA2B+/-, or iPLA2B-/- female mice yields only about 7% of the number of pups produced by mating pairs with an iPLA2B+/+ or iPLA2B+/- male, but iPLA2B-/- female mice have nearly normal fertility. These findings indicate that iPLA2B plays an important functional role in spermatozoa, suggest a target for developing male contraceptive drugs, and complement reports that disruption of the Group IVA PLA2 (cPLA2B) gene impairs female reproductive ability.