Role of mitogen-activated protein kinase (MAPK) 14-signalling pathway in bovine spermatozoa exposed to heat stress in vitro

Heat stress has long been recognized as a cause of subfertility in farm animals and the male factor responsibility is considered to be at least 50%. We have recently shown that in vitro pre-incubation of spermatozoa at hyperthermic (41C) condition compromised sperm motility, oocyte penetration and embryo development. Though spermatozoa are transcriptionally and translationally inactive upon leaving the testis, they remain vulnerable for post-translational
modification of proteins which may cause functional damage in response to stress. MAPK14 is the key signaling pathway in heatinduced germ cell apoptosis. We investigated the involvement of the MAPK14 signaling pathway to sperm in response to heat stress by using a specific inhibitor SB203580; taking sperm DNA strand breaks, fertilizing capability and embryo development as endpoints.
Selective pharmacological inhibition of MAPK14 signaling pathway by SB203580 significantly protected sperm motility (45.8% vs. 26.5%; p < 0.01) in comparison with control sperm as evaluated by computer-assisted sperm motility analysis. Moreover, SB203580 significantly prevented DNA strand breaks as detected by terminal deoxynucleotidyl transferase dUTP nick-end labelling (16.9% vs.
23.4%; p < 0.05). However, blocking MAPK14 signaling pathway in spermatozoa during heat stress could not improve fertilization (53.9% vs. 46.1%) and embryo development rates (5.5% vs. 6.9%). In conclusion, for the first time we showed the involvement of MAPK14 signaling pathway in heat-induced ejaculated spermatozoa. Further research will focus on the role of other signaling
pathways in sperm cell damage and subsequent developmental competence.