Activation of selective human sperm functions by EGF and TGF-β3 is mediated by an ERK-depended mechanism
G. Band1, N. Etkovitz2, H. Breitbart2 & Z. Naor1
Introduction: The signaling involved in ligand-stimulated spermatozoa is not yet clarified. Moreover, the main question in sperm biology is the identification of the sperm ligands. Analysis of the role of MAPK in mammalian sperm physiology is a prerequisite for assigning a role for MAPK in mammalian sperm functions. The unique opportunity to study ERK1/2 in human spermatozoa, which are differentiated cells lacking active transcriptional machinery, will enable to correlate it to differentiated responses such as: capacitation, motility, acrosome reaction and fertilization. We examined the effect of EGF and TGF-β3, as potential sperm ligands upon ERK1/2 activation and the role of ERK1/2 in forward and hyperactivated motility, capacitation and acrosome reaction.
Methods: Human semen was obtained from healthy donors with normal sperm concentration, motility and morphology according to WHO guidelines (WHO, 2010), or from males attending the Male Infertility Unit, Sheba medical center, Tel-Hashomer hospital, Israel.
Results: We have shown that ERK1/2 is activated during EGF and TGF-β3 activation of sperm after 515 min of incubation. Both ligands elevated total motility after 15 min of incubation and this stimulatory effect was abolished by adding, U0126 a selective inhibitor of MEK1/2. EGF also induced hyperactivated motility after 180 min, while TGF-β3 did not seem to induce hyperactivation. Both ligands elevated the percentage of acrosome reacted sperm cells after capacitation in both healthy donors, and OTA patients. This effect was also abolished after adding U0126, a selective inhibitor of MEK1/2. Regarding capacitation, we have identified several proteins that were phosphorylated on tyrosine residues during capacitation, the effect was markedly reduced in the presence of the MEK1/2 inhibitor.
Conclusions: We conclude that EGF and TGF-β3 activation of selective sperm functions are mediated by an ERK-depended mechanism.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.