Involvement of mu-calpain in human sperm capacitation for fertilization.
OBJECTIVE
The distribution and physiological role of calpains in human sperm were investigated.


METHODS
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 mu-calpain antibody, sperm were immunostained, whereas all were negative for anti-pro mu-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 mu-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.


CONCLUSIONS
These results indicate that mu-calpain may play pivotal roles in the process of fertilization of human sperm.
Aoyama
T
T
Department of Obstetrics and Gynecology, Nagoya City, University Medical School, Nagoya, Japan.
Ozaki
Y
Y
Aoki
K
K
Kunimatsu
M
M
Tada
T
T
Sasaki
M
M
Suzumori
K
K
D000595:Amino Acid Sequence; D015153:Blotting, Western; D002154:Calpain / Q000032:analysis / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000032:analysis / Q000502:physiology*; D005306:Fertilization; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008969:Molecular Sequence Data; D008970:Molecular Weight; D013075:Sperm Capacitation; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000737:chemistry
D004792:Enzyme Precursors; D002154:Calpain; C098484:mu-calpain proenzyme