Spermatogenesis‐related change in the synthesis of the creatine kinase B‐type and M‐type isoforms in human spermatozoa

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Abstract
We have demonstrated earlier that the per sperm creatine‐N‐phosphotransferase (CK) activity was increased in oligospermic vs. normospermic men. The increased sperm CK activity is related to higher concentrations of cellular CK, which may indicate a defect of cytoplasmic extrusion during spermatogenesis. In the present work, we examined whether in spermatozoa, similar to muscle, there is a change in the synthesis of B‐CK and M‐CK isoforms during cellular differentation. In 109 normospermic and 50 oligospermic specimens (sperm concentrations 60.6 ± 3.7 vs. 8.8 ± 1.3 million sperm/ml; all values expressed as mean ± SEM), the relative concentrations of the M‐CK isoform (M‐CK / M‐CK+B‐CK) were 27.2% ± 2.1% vs. 6.7% ± 0.9% (P < 0.001). The per sperm CK activities showed comparable differences (0.21 ± 0.02 vs. 0.89 ± 0.1 CK IU/100 million sperm; P < 0.001) in the two groups, and there was a close correlation between per sperm CK activities and M‐CK concentrations (R = 0.69, P < 0.001, N = 159). This indicates that the loss of cytoplasm and the commencement of M‐CK isoform synthesis are related events during the last phase of spermatogenesis, also that the incidence of spermatozoa with incomplete cellular maturation is higher in oligospermic specimens. In characterizing the M‐CK, we found that sperm (unlike muscle tissue) lack the MB hybrid of CK dimers. However, in the presence of muscle M‐CK, the muscle‐sperm MB‐CK hybrid has formed. Thus in sperm and muscle the M‐CK isoforms are structurally different, whereas the B‐CKs are apparently homologous. We suggest that the relative concentrations of sperm M‐CK isoform is a biochemical marker of cellular differentiation that may also predict the functional intetrity, such as fertilization potential, of spermatozoa.