We report the presence of protein kinase C (PKC) in ejaculated human sperm as revealed by enzymatic activity assay and indirect immunohistochemistry. PKC is localized in the equatorial segment and in the principal piece of the tail. Addition of phorbol 12-myristate 13-acetate resulted in increased flagellar motility that was blocked by known PKC inhibitors such as sphingosine, staurosporine, and 1-(5-isoquinoylinylsulfonyl)-2-methylpiperazine. A very good correlation (r = 0.9, P < 0.001) was found between the percentage of PKC-stained sperm cells and motility. We propose that PKC is involved in the regulation of flagellar motility in human sperm.
Retrograde ejaculation is an uncommon cause of male infertility. It should be suspected in any case of azoospermia, and might be congenital, acquired or idiopathic in origin. When pharmacological attempts to restore anterograde ejaculation fail, it is suggested that spermatozoa should be recovered from post-ejaculation urine to be applied in one of the modern techniques of assisted reproduction. The successful recovery of viable spermatozoa from the urine is dependent upon careful regulation of pH and osmolarity of the urine at the time of ejaculation. Careful handling of the retrieved spermatozoa enables isolation of sperm cells with good quality for insemination of ovulated oocytes (in vivo) or retrieved oocytes (in vitro).
We report that activated protein kinase C (PKC) can induce acrosome reaction independently of elevated Ca2+. Addition of 12-O-tetradecanoyl phorbol-13-acetate or the membrane-permeable diacylglycerol analog 1-oleoyl-2-acetylglycerol to ejaculated human sperm resulted in stimulation of acrosomal reaction (2- to 3-fold), provided the sperm underwent capacitation. Induction of acrosome reaction by 12-O-tetradecanoyl phorbol-13-acetate was blocked by the PKC inhibitor staurosporine or by down-regulation of endogenous PKC, but not by removal of extracellular Ca2+. Acrosome reaction was also enhanced by the Ca2+ ionophore ionomycin in a Ca(2+)-dependent, PKC-independent fashion. Immunohistochemical analysis with type-specific PKC antibodies revealed the presence of PKC alpha and PKC beta II in the equatorial segment, whereas PKC beta I and PKC epsilon staining was found in the principal piece of the tail. Acrosome reaction, thus far believed to be induced only by elevated Ca2+, can therefore be triggered by activated PKC in a Ca(2+)-independent fashion. The PKC subtypes potentially involved in acrosome reaction are most likely alpha and beta II, whereas the beta I- and epsilon-subspecies might be involved in regulation of flagellar motility of human sperm.
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