The role of Ca2+, calmodulin, and protein phosphatases on motility and hyperactivation of noncapacitated, capacitating, and detergent-permeabilized reactivated human sperm was examined. In noncapacitated sperm, W7 inhibited percent motility (%MOT), curvilinear velocity (VCL), amplitude of lateral head displacement (ALH), and percent hyperactivation (%HYP) in an extracellular Ca2+ concentration-dependent manner (p < .05). However, in capacitating sperm, inhibition of motility by W7 was independent of external Ca2+. Treatment of reactivated sperm with a synthetic calmodulin inhibitor peptide decreased VCL and ALH in a Ca(2+)-dependent manner (p < .05). Ca2+ exhibited a dramatic influence on motility within a narrow concentration range (0.7 to 1.0 microM) in reactivated sperm. A calmodulin-dependent protein phosphatase (PP2B) was identified by activity assay, immunoblotting, and dephosphorylation of endogenous phosphoproteins. The sperm enzyme, unlike bovine brain PP2B, was inhibited by 1 microM okadaic acid (OA) in the presence of Mn2+, suggesting that the sperm enzyme is unique. In reactivated sperm, inhibition of endogenous PP2B-like activity with anti-PP2B antibodies altered ALH, whereas OA altered both VCL and ALH and also inhibited a subset of Ca(2+)-dependent dephosphorylations of cAMP-dependent phosphoproteins in capacitating sperm. These results suggest (1) an important role for calmodulin and PP2B in Ca(2+)-regulated motility parameters, particularly ALH, and (2) that modulation of human sperm motility, including hyperactivation by cAMP-dependent phosphorylation, requires calmodulin-dependent as well as other protein dephosphorylations.
The presence of antiidiotypic antibodies (ab-2) to sperm was investigated in the sera of fertile, infertile, and virgin women using sperm-specific anti-FA-1 monoclonal antibody Fab'. ab-2 were detected in 71% (17 /24) of sera from fertile women and in none (0/12) of the sera from virgin females by the enzymelinked immunosorbent assay, Western blot procedure, and immunoprecipitation procedure. Sera from infertile women that had antisperm antibodies showed a minimal presence of ab-2, with only three sera (13%, 3/23) demonstrating the presence of low levels of ab-2. The ab-2 present in fertile women were capable of neutralizing the fertilization-inhibitory activity of anti-FA-1 antibody in a concentration-dependent manner in a human sperm penetration assay (SPA) of zona-free hamster oocytes. ab-2 were also capable of inhibiting the binding of antisperm antibodies to the sperm surface as determined by the immunobead binding technique. This is the first report demonstrating the presence of ab-2 in the sera of fertile women that are capable of neutralizing antisperm antibodies present in sera of infertile women. These findings suggest that the inability to detect antisperm antibody activity in the sera of fertile women may be due to higher levels of ab-2 present in these sera than levels found in sera of infertile women, although both groups may be producing antisperm antibody response after sexual exposure to sperm. (J. Clin. Invest. 1993. 92:2331-2338
The presence and role of c-myc protein was investigated in mature sperm cells of the human, mouse, and rabbit. The monoclonal antibodies against c-myc protein (c-myc) reacted with the acrosomal region of the sperm of these mammalian species in the indirect immunofluorescence technique. The c-myc monoclonal antibody (MCA) recognized c-myc protein of 62 and 64 kDa on Western blots of lithium diiodosalicylate-solubilized sperm preparations of these species. The c-myc MCA showed a dose-dependent inhibition of human sperm penetration of zona-free hamster eggs, inhibition of murine in vitro fertilization, and reduced in vivo fertilization in rabbits. There was no effect of the antibody on percent sperm motility, though the antibody significantly affected various motility characteristics such as mean and maximum amplitude of lateral head displacement and curvilinear velocity involved in hyperactivation phenomenon of human sperm cells. These results suggest that c-myc or c-myc-like protein is present in mature sperm cells and may have a role in sperm cell function especially in capacitation and/or acrosome reaction.
Based upon findings that the scatter factor/hepatocyte growth factor (SF/HGF) has strong mitogenic and motogenic properties, and that the sperm cell acquires its fertilizing capacity and motility in the distal parts of mammalian epididymis, the present study was conducted to investigate the role of SF/HGF in initiation of sperm cell motility. This was investigated by determining the expression of SF/HGF in various regions of the murine male genital tract by scatter and cell tracking assays using MDCK epithelial cells, Western blot procedure, and the immunohistochemical procedure using paraffin sections of various regions of the male genital tract. The findings from all these assays indicate that SF/HGF is differentially expressed in various parts of the male genital tract with slight or no expression in the testes, caput epididymis, and vas deferens, and with the highest expression in cauda and corpus (distal) epididymis followed by expression in the corpus (proximal) epididymis. This region-specific SF/HGF expression pattern coincides with the pattern of acquiring the fertilizing capacity and motility by the sperm cell during its transit through the male genital tract. However, wherever SF/HGF was expressed in the male genital tract, its molecular weight was slightly higher (Mr, 82 kD), compared to the SF/HGF expressed in various other somatic tissues (Mr, 78 kD), indicating that the genital tract SF/HGF may be a different molecular species that shares some immunoreactive epitopes with the somatic cell SF/HGF. Incubation of immotile sperm from caput epididymis with the purified human placental SF/HGF of 78 kD initiated motility in 5-15% of sperm population. These results strongly suggest that the SF/HGF-like activity is expressed in the male genital tract in a region-specific manner, and this activity may have a role in initiation of sperm motility acquired during its transit through the epididymis in mammals.
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