Extra-Oral Taste Receptors—Function, Disease, and Perspectives

Abstract

Taste perception is crucial for the critical evaluation of food constituents in human and other vertebrates. The five basic taste qualities salty, sour, sweet, umami (in humans mainly the taste of L-glutamic acid) and bitter provide important information on the energy content, the concentration of electrolytes and the presence of potentially harmful components in food items. Detection of the various taste stimuli is facilitated by specialized receptor proteins that are expressed in taste buds distributed on the tongue and the oral cavity. Whereas, salty and sour receptors represent ion channels, the receptors for sweet, umami and bitter belong to the G protein-coupled receptor superfamily. In particular, the G protein-coupled taste receptors have been located in a growing number of tissues outside the oral cavity, where they mediate important processes. This article will provide a brief introduction into the human taste perception, the corresponding receptive molecules and their signal transduction. Then, we will focus on taste receptors in the gastrointestinal tract, which participate in a variety of processes including the regulation of metabolic functions, hunger/satiety regulation as well as in digestion and pathogen defense reactions. These important non-gustatory functions suggest that complex selective forces have contributed to shape taste receptors during evolution.

The Complex Journey of the Calcium Regulation Downstream of TAS2R Activation

“…Interestingly, it has been proposed that bitter taste receptors have appeared in the evolutionary process with primary roles different from the taste perception, such as nutrient sensing in the gut [ 3 ]. The hypothesis would be in accord with the more recent observations of the extra-oral localization of these receptors where they may be mediators of a wide chemosensory system [ 17 , 18 ]. Outside the oral cavity, TAS2Rs have been reported in the gastrointestinal tract, the brain, the heart, the immune cells, and the genitourinary and respiratory systems in which they exert different roles ( Figure 1 ).…”

Bitter taste receptors in the reproductive system: Function and therapeutic implications

“…A plethora of studies have highlighted the expression of bitter taste receptors and their downstream signaling components in numerous cells and tissues beyond the tongue. These include vital systems such as the respiratory and gastrointestinal tracts, the urinary system, the brain, the immune system, and even within tumors (Avau & Depoortere, 2016; Behrens & Lang, 2022; Bloxham et al, 2020; Carey et al, 2016; Harmon et al, 2021; Jeruzal‐Swiatecka et al, 2020; Lu et al, 2017; Tuzim & Korolczuk, 2021; Zehentner et al, 2021).…”

“…Despite a plethora of comprehensive reviews elucidating the extraoral functions of TAS2Rs (Avau & Depoortere, 2016; Behrens & Lang, 2022; Bloxham et al, 2020; Carey et al, 2016; Harmon et al, 2021; Jeruzal‐Swiatecka et al, 2020; Lu et al, 2017; Shaik et al, 2016; Tuzim & Korolczuk, 2021; Zehentner et al, 2021), their role within the reproductive system, which is crucial for understanding and potentially improving reproductive health, has not yet been systematically addressed. This gap in the literature is striking, given the evidence for the presence of TAS2Rs in various components of the female and male reproductive systems, including the ovary, uterus, placenta, cervix, vagina, testis, and spermatozoa.…”

Recent Advances in Bitterness-Sensing Systems

“…Briefly, the bitter taste perception of cellular changes is produced by participating transient receptor potential channels (TRP), phospholipase, and organelles, simultaneously releasing adenosine triphosphate (ATP) and neurotransmitters for neural signal transmission [ 29 , 30 , 31 , 32 ]. Additionally, bitter taste receptors have also been found in cells of the digestive system, respiratory system, brain, and testes [ 33 , 34 , 35 ].…”