Detection of Neurotrophin‐4 (NT‐4) in Ejaculated Bull Spermatozoa and its Effect on Spermatozoa Mitochondrial Activity
2013
Wang, C‐Q | Zhang, J | Sun, Y‐F | Wang, D | Li, C‐J | Li, W‐H | Lu, C | Liu, Z. | Wu, H | Hou, X‐F | Chen, C. | Zhou, X
Recently, we demonstrated that two members of neurotrophins, nerve growth factor and brain‐derived neurotrophic factor, and two types of receptor, tyrosine kinase A (TrkA) and tyrosine kinase (TrkB), exist in ejaculated bull spermatozoa, and play a crucial role in the normal function of spermatozoa. Neurotrophin‐4 (NT‐4) is another neurotrophic factor that signals predominantly through the TrkB receptor tyrosine kinase, and no reports of detection of NT‐4 in spermatozoa have been published. In the present study, the presence of NT‐4 in mature bull spermatozoa was investigated using RT‐PCR, immunofluorescence and Western blotting. The result shows that there was no RT‐PCR evidence for NT‐4 transcripts in bovine spermatozoa. However, the NT‐4 protein was present in bovine spermatozoa, and the NT‐4 immunoreactivity was localized to the equatorial segment and midpiece of bovine spermatozoa. In addition, effects of NT‐4 on function of spermatozoa were studied. Significant increased mitochondria activity of mature bovine spermatozoa was observed in response to 300 or 500 ng/ml exogenous NT‐4 (p < 0.05), in comparison with the control, while addition of inhibitors (40 ng/ml k252α) specific for tyrosine protein kinase significantly blocked the increase of mitochondria activity. However, NT‐4 had no effects on the viability or acrosome reaction of spermatozoa (p > 0.05). Consequently, this study provided evidence that NT‐4 protein was presented in the mature bull spermatozoa and can influence the mitochondrial activity of bovine spermatozoa through TrkB tyrosine kinase–dependent pathways.
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