Detection of nerve growth factor (NGF) and its specific receptor (TrkA) in ejaculated bovine sperm, and the effects of NGF on sperm function

The objective was to confirm the presence of nerve growth factor (NGF) and its specific receptor, TrkA, in ejaculated bovine sperm, and to investigate the effects of NGF on specific aspects of bovine sperm function. Both TrkA transcripts and immunoreactivity typical of the translated protein were detected by RT-PCR and western blotting. However, only the NGF protein was detected in bovine sperm using western blotting, and there was no RT-PCR evidence for NGF transcripts in sperm. Using an immunofluorescent technique, NGF-immunoreactivity was localized to the sperm head and tail, whereas that of TrkA was detected in the acrosomal cap, nucleus, and tail regions When sperm were treated with exogenous NGF, both leptin secretion and sperm viability were increased (P < 0.05); moreover, the percentages of late apoptotic and dead sperm were increased (P < 0.05). However, NGF had no effects on insulin secretion, mitochondrial activity, intracellular calcium levels, or the acrosome reaction of sperm (P > 0.05). In conclusion, the presence of TrkA transcript, as well as NGF and TrkA immunoreactivity were confirmed in bovine sperm. Furthermore, exogenous NGF had significant effects on the secretion of leptin, cell viability, and sperm apoptosis. This study provided strong evidence that NGF/TrkA may have roles in regulation of sperm physiology and perhaps male fertility and infertility.