Taste preference for fatty acids is mediated by GPR40 and GPR120

Abstract

The oral perception of fat has traditionally been considered to rely mainly on texture and olfaction, but recent findings suggest that taste may also play a role in the detection of long chain fatty acids. The two G-protein coupled receptors GPR40 (Ffar1) and GPR120 are activated by medium and long chain fatty acids. Here we show that GPR120 and GPR40 are expressed in the taste buds, mainly in type II and type I cells, respectively. Compared with wild-type mice, male and female GPR120 knock-out and GPR40 knock-out mice show a diminished preference for linoleic acid and oleic acid, and diminished taste nerve responses to several fatty acids. These results show that GPR40 and GPR120 mediate the taste of fatty acids.

Figure 1.

A, Photomicrographs of frozen sections of circumvallate papilla from transgenic mice expressing eGFP under the control of the Trpm5 promoter stained (red) with GPR120 (top) or GPR40 antibodies (bottom). The staining obtained with the GPR120 antibody is mostly colocalized with Trpm5 promoter-driven eGFP fluorescence. The GPR40 antibody stained mainly cells that do not express eGFP. With this antibody, staining is most intense in the taste pore (arrow). B, Microphotograph of a frozen section of foliate papilla from a wild-type mouse stained with a GPR40 antibody. Staining is most intense in the taste pore (arrow). The dotted line shows the boundary of the taste bud. C, Photomicrographs of frozen sections of circumvallate papilla from wild-type mice double-stained with GPR40 antibody (red) and GLAST (top, green) or SNAP25 (bottom, green) antibodies; Most GPR40-expressing cells also express GLAST and there is little coexpression of SNAP25 and GPR40. D, Photomicrographs of frozen sections of circumvallate papillae from wild-type (1, 4), GPR40 KO (2, 3) and GPR120 KO (5, 6) mice stained with GPR40 (1, 2), GPR120 (4, 5), or α-gustducin (3, 6) specific antibodies. The GPR120 and GPR40 proteins are not detected in the CV of GPR120 KO and GPR40 KO mice, respectively. Sections from GPR120 KO or GPR40 KO mice stained with α-gustducin antibody show that the knock-out mice have normal taste buds and type II cells, and that the expression of α-gustducin is not affected by the absence of GPR120 or GPR40.

Figure 2.

Mean preference ratios for tastants consumed during 48 h two-bottle preference tests comparing KO (open circles) and control mice (black squares). The mice were given two bottles, one with tastant and one with vehicle alone for 24 h then the bottles were swapped to eliminate position preferences and presented for an extra 24 h. The vehicle was 0.3% xanthan gum to mimic the viscosity of the fatty suspensions. The ratios of tastant to total liquid consumed over 48 h were measured and compared between groups. The GPR40 KO mice showed a diminished preference for linoleic acid and oleic acid. The GPR120 KO mice showed a diminished preference for linoleic acid. The dashed line indicates the indifference line. Asterisks indicate a significant difference in preference (*p < 0.05) when all concentrations are analyzed together; **p < 0.001. n = 10–15; error bars are SEM.

Figure 3.

Mean number of licks per trial during short access tests comparing linoleic acid (100 or 350 mm, open bars) and xanthan gum (gray bars). GPR40 KO, GPR120 KO and wild-type mice were tested. The mice were water and food restricted 23.5 h before the testing session, and then tested for 30 min in 5 s trials with one concentration of tastant and vehicle presented alternatively. The mean number of licks per 5 s trial was recorded. ⁺p = 0.027, *p < 0.025, **p < 0.01. Error bars are SEM.

Figure 4.

CT and GL integrated whole nerve responses of control (black squares) and GPR120 KO or GPR40 KO (open circles) mice to lingual application of tastants. All responses were normalized to the response to 100 mm NH₄Cl. GPR120 KO mice show diminished responses in both nerves to several fatty acids, whereas only the response of the GL nerve is affected in the GPR40 KO mice. The response to lauric acid is diminished in the GPR40 KO, but not in the GPR120 KO mice. There is no effect of mineral oil. Asterisks indicate a significant difference between KO and control, across all concentrations (*p < 0.05 and **p < 0.01, respectively). For each group and each nerve, n = 6–9. Error bars are SEM.

Figure 5.

A, B, Integrated whole nerve responses from the GL (A) and CT (B) nerves. Denatonium benzoate was tested in the absence (KO, red circles; control, black squares) or presence (KO, inverted blue triangle; control, green triangle) of a mix of 55 μm linoleic acid and 33 μm oleic acid. KO groups are GPR120 KO (left) and GPR40 KO (right). There is no difference in responses to denatonium between KO and control mice. The fatty acid mix reduces the nerve response to denatonium, but this effect is GPR120 and GPR40 independent. Error bars are SEM.

Figure 6.

CT and GL integrated whole nerve responses of control (black squares) and GPR120 KO or GPR40 KO (open circles) mice to lingual application of tastants. All responses were normalized to the response to 100 mm NH₄Cl. There is no significant difference between KO and control in the nerve responses to NaCl, HCl, monopotassium glutamate (MPG), and sucrose. Error bars are SEM.