Bitter taste receptors: new players in female and male fertility

The mammalian taste perception provides valuable information about the nature and quality of food. Taste transduction involves the interaction of molecules (i.e. tastants) with taste receptor (TASRs) whose expression isn’t limited to the oral cavity; indeed, many studies showed how these receptors can be found also in extraoral location, wherein their function appears less obvious and remains to be understood in most cases. The expression of these receptors outspreads also to brain, respiratory tract, urinary bladder and testis, where some of these receptors are expressed in different stages of spermatogenesis. Moreover, the expression of selected member of different receptor families in ejaculated human sperm has been reported. These findings suggest a possible involvement of TASRs in sperm maturation as well as in sperm chemotactic activation and fertilization. To the best of our knowledge, no data are available regarding the expression of TASRs in the mammalian oocyte nor in the somatic cells of the follicle. Therefore, to investigate the possible role of TASRs in male and female reproductive system, focusing on their impact on human fertility, we analyzed the expression of some members of taste 2 receptors family (TAS2Rs) genes in human germ cells and follicular cells, namely granulosa and cumulus cells. The expression of genes involved in taste receptors signaling cascade was also investigated, both in female and male. Immunofluorescence analysis and western blot of TAS2Rs and related signaling pathways also carried out highlighting the expression of selected TAS2Rs genes in ejaculated sperm and in testis and, for the first time, in somatic cells from human ovarian follicle. An interesting finding of this thesis work is the demonstration of TAS2R14 as the most expressed gene in both granulosa and cumulus cells. These results suggest a key role of this receptor and also for its potential involvement in follicular cells physiology. The possible role of this receptor in reproduction is also supported by a study showed TAS2R14 to be correlated with sperm progressive motility. In order to elaborate an enrichment analysis to summarize functional information about the investigated proteins and to predict possible associations among them, a protein network analysis was performed by MetaCore software. Even if further studies are needed to better understand the precise functional role oftaste receptors in reproduction, this work try to improve our knowledge of the biological role of TAS2Rs for human male and female fertility.