Chemotactic effect of urokinase-type plasminogen activator on mouse spermatozoa in vitro

Abstract

The aim of this study is to investigate the chemotactic effect of urokinase-type plasminogen activator (uPA) on mouse spermatozoa. Capillary assays were applied to study the chemotactic activity of ascending and descending gradients of uPA. Firstly, the chemotactic effect of an ascending gradient of uPA on mouse spermatozoa was observed by counting the number of spermatozoa that migrated into the capillary after incubation with uPA for 5, 10, 20, and 30 min, respectively, compared with that after incubation with F10. Twenty minutes was a suitable incubation time to obtain a plateau of sperm accumulation. Meanwhile, to confirm the specific effect of uPA on mouse sperm chemotaxis, uPA inhibitor (PAI-1) and anti-uPAR rabbit IgG were added to the test solution containing 20 U/mL uPA, respectively. To exclude the possibility that PAI-1 and anti-uPAR rabbit IgG may affect sperm accumulation nonspecifically, PAI-1 and anti-uPAR rabbit IgG were added to F10, respectively. It was found that the chemotactic effect of uPA was neutralized completely by PAI-1 and anti-uPAR rabbit IgG. PAI-1 and anti-uPAR rabbit IgG had no neutralizing effect on the sperm chemotactic effect. Lastly, the sperm chemotaxis response to a descending gradient of uPA was also observed. Taken together, the results suggest that uPA can induce sperm chemotaxis in vitro by binding to its receptor on the sperm membrane and may act as a chemoattractant in precontacting sperm-egg communication thereby increasing the chance encounter of spermatozoa and eggs.