G Protein-Coupled Receptors in Human Fat Taste Perception

Abstract

In contrast to carbohydrates and proteins, which are detected by specialized taste receptors in the forms of their respective building blocks, sugars, and L-amino acids, the third macronutrient, lipids, has until now not been associated with gustatory receptors. Instead, the recognition of fat stimuli was believed to rely mostly on textural, olfactory, and postingestive cues. During the recent years, however, research done mainly in rodent models revealed an additional gustatory component for the detection of long-chain fatty acids (LCFAs), the main taste-activating component of lipids. Concomitantly, a number of candidate fat taste receptors were proposed to be involved in rodent's gustatory fatty acid perception. Compared with rodent models, much less is known about human fat taste. In order to investigate the ability of the human gustatory system to respond to fat components, we performed sensory experiments with fatty acids of different chain lengths and derivatives thereof. We found that our panelists discriminated a "fatty" and an irritant "scratchy" taste component, with the "fatty" percept restricted to LCFAs. Using functional calcium-imaging experiments with the human orthologs of mouse candidate fat receptors belonging to the G protein-coupled receptor family, we correlated human sensory data with receptor properties characterized in vitro. We demonstrated that the pharmacological activation profile of human GPR40 and GPR120, 2 LCFA-specific receptors associated with gustatory fat perception in rodents, is inconsistent with the "scratchy" sensation of human subjects and more consistent with the percept described as "fatty." Expression analysis of GPR40 and GPR120 in human gustatory tissues revealed that, while the GPR40 gene is not expressed, GPR120 is detected in gustatory and nongustatory epithelia. On a cellular level, we found GPR120 mRNA and protein in taste buds as well as in the surrounding epithelial cells. We conclude that GPR120 may indeed participate in human gustatory fatty acid perception.

The oral lipid sensor GPR120 is not indispensable for the orosensory detection of dietary lipids in mice

“…GPR120 gene invalidation did not interfere on CD36 and ␣ -gustducin expression levels in taste buds as similar mRNA levels were found in CVP from GPR120 +/+ and GPR120 Ϫ / Ϫ mice. According to data found in different species (16)(17)(18), GPR40 mRNA was undetectable in mouse CVP ( Fig. 1B ).…”

“…found by others in mouse ( 16 ), rat ( 17 ), or human ( 18 ) taste buds. In contrast, GPR120 was systematically detected in murine and human gustatory papillae ( 11,15,18 ) in which it was frequently coexpressed with CD36 ( 11,19 ).…”

“…In contrast, GPR120 was systematically detected in murine and human gustatory papillae ( 11,15,18 ) in which it was frequently coexpressed with CD36 ( 11,19 ). This last observation raises the question of the respective role(s) of these two LCFA receptors in the coding mechanisms eliciting the oro-sensory detection of dietary lipids at the periphery.…”

Heritable differences in chemosensory ability among humans

“…Finally, there is another class of chemicals in foods that is sensed by cells in the mouth, the fat 'taste' receptor(s). The idea of a special taste for fat, called pinguis, is an old concept [83], made new by the discovery of several membranebound proteins that are essential for the recognition and ingestion of fat [84][85][86][87]. Gene knockout studies in mice [88,89] suggest that inactivating mutations in humans are likely to have an effect on human oral fat perception [90].…”

The Use of Electrophoresis for the Study of Saliva Involvement in Ingestive Behavior

“…Five basic tastes are commonly admitted: sweetness, saltiness, bitterness, sourness and umami. In addition, discovery of receptors to free fatty acids on the human tongue [16,17] has prompted suggestions that fat could be a sixth taste.…”