Taste Receptors beyond Taste Buds

Abstract

Taste receptors are responsible for detecting their ligands not only in taste receptor cells (TRCs) but also in non-gustatory organs. For several decades, many research groups have accumulated evidence for such “ectopic” expression of taste receptors. More recently, some of the physiologic functions (apart from taste) of these ectopic taste receptors have been identified. Here, we summarize our current understanding of these ectopic taste receptors across multiple organs. With a particular focus on the specialized epithelial cells called tuft cells, which are now considered siblings of type II TRCs, we divide the ectopic expression of taste receptors into two categories: taste receptors in TRC-like cells outside taste buds and taste receptors with surprising ectopic expression in completely different cell types.

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“…Human TAS2Rs are able to form homo-and heterodimers, and they can be categorized into four groups, the three receptor "generalists" with extensive agonist spectra comprising TAS2R10, 14, and 46 (each able to respond to about one third of the bitter substances), a number of narrowly tuned receptor "specialists" (that detect few bitter compounds), and the intermediately tuned receptors representing the majority, as well as two receptors TAS2R16 and 38 which exhibit pronounced selectivity for defined classes of chemicals [87]. In recent years, it has been revealed that these receptors (called ectopic receptors) are also expressed in the respiratory, gastrointestinal, genitourinary, cardiovascular, and central nervous systems [43]. They are involved in a variety of biological processes, including muscle regeneration, broncho-dilation/constriction, inflammation, appetite regulation, energy metabolism, and also defense system and immunological response [88].…”