Expression of Taste Receptor 2 Subtypes in Human Testis and Sperm

Abstract

Taste receptors (TASRs) are expressed not only in the oral cavity but also throughout the body, thus suggesting that they may play different roles in organ systems beyond the tongue. Recent studies showed the expression of several TASRs in mammalian testis and sperm, indicating an involvement of these receptors in male gametogenesis and fertility. This notion is supported by an impaired reproductive phenotype of mouse carrying targeted deletion of taste receptor genes, as well as by a significant correlation between human semen parameters and specific polymorphisms of taste receptor genes. To better understand the biological and thus clinical significance of these receptors for human reproduction, we analyzed the expression of several members of the TAS2Rs family of bitter receptors in human testis and in ejaculated sperm before and after in vitro selection and capacitation. Our results provide evidence for the expression of TAS2R genes, with TAS2R14 being the most expressed bitter receptor subtype in both testis tissue and sperm cells, respectively. In addition, it was observed that in vitro capacitation significantly affects both the expression and the subcellular localization of these receptors in isolated spermatozoa. Interestingly, α-gustducin and α-transducin, two Gα subunits expressed in taste buds on the tongue, are also expressed in human spermatozoa; moreover, a subcellular redistribution of both G protein α-subunits to different sub-compartments of sperm was registered upon in vitro capacitation. Finally, we shed light on the possible downstream transduction pathway initiated upon taste receptor activation in the male reproductive system. Performing ultrasensitive droplets digital PCR assays to quantify RNA copy numbers of a distinct gene, we found a significant correlation between the expression of TAS2Rs and TRPM5 (r = 0.87), the cation channel involved in bitter but also sweet and umami taste transduction in taste buds on the tongue. Even if further studies are needed to clarify the precise functional role of taste receptors for successful reproduction, the presented findings significantly extend our knowledge of the biological role of TAS2Rs for human male fertility.

Clinical Role of Extraoral Bitter Taste Receptors

“…TAS2R14 was indicated as the receptor that mediates the chloroquine-induced effect on [Ca 2+ ] i in human myometrial cells. Most recently, a study on semen cells and testis tissue was conducted by Governini et al [ 38 ]. Sperm was donated by 15 Caucasian males undergoing fertility examination.…”

Longitudinal Expression of Testicular TAS1R3 from Prepuberty to Sexual Maturity in Congjiang Xiang Pigs

“…For example, T1R3 is highly expressed in swine testicular tissues, especially in spermatogenic cells [3]. In mice, T1R3 and its related molecules, T1R1, G αgust , and taste receptor family 2 subunit 5 (T2R5), were primarily detected in developing haploid spermatids [4,5]. These molecules are localized in testicular Leydig cells, epididymal spermatozoa and semen [4][5][6].…”

“…In mice, T1R3 and its related molecules, T1R1, G αgust , and taste receptor family 2 subunit 5 (T2R5), were primarily detected in developing haploid spermatids [4,5]. These molecules are localized in testicular Leydig cells, epididymal spermatozoa and semen [4][5][6]. Interestingly, many initial components of sweet/umami taste signaling cascades, such as PLCβ2, G protein γ13 subunit (Gγ13), and transient receptor potential channel M5 (TRPM5), are also expressed in testicular Leydig cells and late spermatogenic cells [7,8].…”

Odorant and Taste Receptors in Sperm Chemotaxis and Cryopreservation: Roles and Implications in Sperm Capacitation, Motility and Fertility

“…It was reported that OR4C13, MOR23, OR1E2, and OD1 have been localized in testes of human [ 10 ], mouse [ 11 ], dog [ 12 ], and rat [ 13 ] respectively. Similarly, TAS2R3, TAS2R124, and α-gustducin have been localized in testes of human [ 14 ], mouse [ 15 ], and pig [ 16 ]. These ORs and TRs can modulate the motility, fertility, and survivability of sperm, and are even involved in gametogenesis at mitotic and meiotic levels [ 14 ].…”

“…Similarly, TAS2R3, TAS2R124, and α-gustducin have been localized in testes of human [ 14 ], mouse [ 15 ], and pig [ 16 ]. These ORs and TRs can modulate the motility, fertility, and survivability of sperm, and are even involved in gametogenesis at mitotic and meiotic levels [ 14 ]. Egg releases chemicals to attract sperm cell and existence of chemoattractant gradient give cues about interaction of sperm-egg through chemotaxis [ 4 ].…”