Peroxiredoxin 2 and Peroxidase Enzymatic Activity of Mammalian Spermatozoa
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Peroxiredoxin 2 (PRDX2) is a highly efficient redox protein that neutralizes hydrogen peroxide resulting in protection of cells from oxidative damage and regulation of peroxide-mediated signal transduction events. The oxidized form of PRDX2 is reverted back to the reduced form by the thioredoxin system. In the present study, we investigated the presence of PRDX2 in mouse and boar spermatozoa as well as in mouse spermatids using proteomic techniques and immunocytochemistry. Sperm and spermatid extracts displayed 20 kDa PRDX2 band in Western blotting. PRDX2 occurred as a Triton soluble form in the spermatids and as an insoluble form in mature spermatozoa. Boar seminiferous tubule extracts were immunoprecipitated with PRDX2 antibody and separated by SDS PAGE. Peptide mass fingerprinting by MALDI-TOF and microsequencing by nanospray QqTOF MS/MS revealed the presence of PRDX2 ions in the immunoprecipitated band along with sperm mitochondria associated cysteine rich protein, cellular nucleic acid binding protein and glutathione peroxidase 4. In mouse spermatocytes and spermatids, diffuse labeling of PRDX2 was observed in the cytoplasm and residual bodies. After spermiation PRDX2 localization became confined to the mitochondrial sheath of the sperm tail midpiece. Boar spermatozoa displayed similar PRDX2 localization as in mouse spermatozoa. Boar spermatozoa with disrupted acrosomes expressed PRDX2 in the postacrosomal sheath region. Peroxidase enzyme activity of boar sperm extracts was evaluated by estimating the rate of NADPH oxidation in the presence or absence of a glutathione depletor (diethyl maleate) or a glutathione reductase inhibitor (carmustin). Diethyl maleate partially inhibited peroxidase activity while carmustin showed an insignificant effect. These observations suggest that glutathione and glutathione reductase activity contribute only partially to the total peroxidase activity of the sperm extract. While the specific role of PRDX2 in the total peroxidase activity of sperm extract is still an open question, the present study for the first time shows the presence of PRDX2 in mammalian spermatozoa. Peroxidase activity in sperm extracts is not due to the glutathione system and therefore possibly contributed by PRDX2 and other peroxiredoxins.
Biology of Reproduction 4 February 2009