Insights into nerve growth factor-β role in bovine reproduction - Review

Nerve growth factor-β (NGF), initially recognized as a neurotrophin involved in regulating neuronal survival and differentiation, was also later revealed as a ubiquitous seminal plasma protein in mammals. In South American camelids, NGF was initially named ovulation-inducing factor and a dose-dependent luteotropic effect was also reported in llamas. Although NGF was present in the seminal plasma of bulls, the first studies only indicated a potential role on regulation of sperm physiology. The breakthrough discovery of NGF ability to induce ovulation in camelids led to a series of studies investigating the potential functions of NGF within the female reproductive system. In the bovine, a potential luteotropic effect of NGF was perceived as potential tool to overcome the current issues with early embryonic losses attributed at least in part to luteal insufficiency and failed maternal recognition of pregnancy. The aims of this review are to discuss recent advancements in the understanding of the biological roles of NGF in the bovine species. The insights of recent studies with NGF administered in cattle include enhancement of steroidogenesis, luteal formation, and function through increased release of LH, and downstream effect of increased expression of interferon-stimulated genes. In addition, a positive association with sire conception rates; the determination that is produced in the ampulla and vesicular glands of bulls and that is secreted into the sperm-rich fraction of the ejaculate; and the absence of improved post-thaw sperm motility, viability, acrosome integrity, or chromatin stability in ejaculated or epididymal derived sperm supplemented with purified NGF is also discussed.