Involvement of μ-Calpain in Human Sperm Capacitation for Fertilization

Authors

  • TOMOMI AOYAMA,

  • YASUHIKO OZAKI,

  • KAORU SUZUMORI,

  • YASUHIKO OZAKI,

  • MITOSHI KUNIMATSU,

  • MAKOTO SASAKI,

  • KOJI AOKI,

  • TOYOHIRO TADA


Address reprint requests to Yasuhiko Ozaki, Department of Obstetrics and Gynecology, Nagoya City University Medical School, Mizuho-ku, Nagoya 467-8601, Japan

E-mail: yozaki@med.nagoya-cu.ac.jp

Abstract

PROBLEM: The distribution and physiological role of calpains in human sperm were investigated.
METHOD OF STUDY: Semen collected manually from healthy donors was liquefied then centrifuged by percoll gradient centrifugation. After exposure to different concentrations of Ca2+ ionophore A23187, the samples were used for immunostaining sodium dodecyl sulfate polyacrylamide gel electrophoresis, and western blot analysis. It was speculated from the results of the study using calpain-specific inhibitors that calpain contributes to the sperm motility and acrosome reaction.
RESULTS: With the anti-pro μ-calpain antibody, sperm were immunostained, whereas all were negative for anti-pro m-calpain antibody binding. Stained sperm were classified into four types according to the staining pattern: acrosome type, equatorial segment type, whole head type, and neck and tail segments type. Western blot analysis of sperm homogenate revealed a single 80-kDa band using the anti-pro μ-calpain antibody, its dose-dependent reduction with Ca2+ ionophore A23187 suggesting activation by this treatment. In the presence of membrane permeable calpain inhibitors, sperm motility and acrosome reaction were significantly suppressed.
CONCLUSION: These results indicate that μ-calpain may play pivotal roles in the process of fertilization of human sperm.

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