Detection of Neurotrophin‐4 (NT‐4) in Ejaculated Bull Spermatozoa and its Effect on Spermatozoa Mitochondrial Activity

Abstract

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.

The potential roles of neurotrophins in male reproduction

“…Both the mRNAs encoding BDNF, NT4 and TRKB and the corresponding proteins have been detected in ejaculated bull sperm. The BDNF protein was found in the head, neck and tail of the sperm cells, whereas NT4 was localized in the equatorial segment and the mid-section of the spermatozoa and TRKB was strongly localized in the acrosome (Li et al 2012, Wang et al 2013.…”

“…Interestingly, BDNF can increase the secretion of insulin and leptin in ejaculated sperm, and treatment with exogenous BDNF for 2 h affects sperm apoptosis and viability. Moreover, both BDNF and NT4 have been shown to regulate mitochondrial activity in sperm (Li et al 2012, Wang et al 2013. A clinical study has shown that the levels of BDNF mRNA in the sperm and BDNF protein in the seminal plasma of a group of oligoasthenozoospermic men were lower than those in a fertile group, indicating that the decreases in the abundance of BDNF and its mRNA transcript may be associated with pathogenesis in some types of male infertility (Zheng et al 2011).…”

“…A clinical study has shown that the levels of BDNF mRNA in the sperm and BDNF protein in the seminal plasma of a group of oligoasthenozoospermic men were lower than those in a fertile group, indicating that the decreases in the abundance of BDNF and its mRNA transcript may be associated with pathogenesis in some types of male infertility (Zheng et al 2011). It is postulated that the BDNF/NT4-TRKB system may promote the survival of testicular cells (Moon et al 2005, Li et al 2012, Wang et al 2013). …”

Possible Involvement of Brain-Derived Neurotrophic Factor in Male Infertility

“…Both the mRNAs encoding BDNF and neurotrophic tyrosine kinase receptor, type 2 (Ntrk2) and the corresponding proteins have been detected in ejaculated bull sperm. The BDNF protein was found in the head, neck, and tail of the sperm cells, whereas Ntrk2 was strongly localized in the acrosome (Li et al, 2012, Wang et al, 2013). Furthermore, BDNF/ Ntrk2 signaling affected sperm viability, mitochondrial activity, and apoptosis (Li et al, 2012).…”

Proteomic applications for studies of bull fertility

“…The truncation containing the mature βNGF was not detected in our study but βNGF contributed to the enrichment of BDNF signaling pathway. BDNF (brain-derived neurotrophic factor) affects sperm mitochondrial activity and apoptosis, as well as sperm viability [113,114]. Enrichment of the calcium signaling pathway, electron transport chain and thermogenesis linked to the seminal plasma profile of LF bulls supports the evidence that sperm membrane from these individuals have lower resistance to cryoinjuries due to premature activation of capacitation and metabolic processes.…”