Fat and carbohydrate preferences in mice: the contribution of alpha-gustducin and Trpm5 taste-signaling proteins

Abstract

Trpm5 and alpha-gustducin are key to the transduction of tastes of sugars, amino acids, and bitter compounds. This study investigated the role of these signaling proteins in the preference for fat, starch, and starch-derived polysaccharides (Polycose), using Trpm5 knockout (Trpm5 KO) and alpha-gustducin knockout (Gust KO) mice. In initial two-bottle tests (24 h/day), Trpm5 KO mice showed no preference for soybean oil emulsions (0.313-2.5%), Polycose solutions (0.5-4%), or starch suspensions (0.5-4%). Gust KO mice displayed an attenuated preference for Polycose, but their preferences for soybean oil and starch were comparable to those of C57BL/6J wild-type (WT) mice. Gust KO mice preferred starch to Polycose, whereas WT mice had the opposite preference. After extensive experience with soybean oil emulsions (Intralipid) and Polycose solutions, the Trpm5 KO mice developed preferences comparable to the WT mice, although their absolute intakes remained suppressed. Similarly, Gust KO mice developed a strong Polycose preference with experience, but they continued to consume less than the WT mice. These results implicate alpha-gustducin and Trpm5 as mediators of polysaccharide taste and Trpm5 in fat taste. The disruption in Polycose, but not starch, preference in Gust KO mice indicates that distinct sensory signaling pathways mediate the response to these carbohydrates. The experience-induced rescue of fat and Polycose preferences in the KO mice likely reflects the action of a postoral-conditioning mechanism, which functions in the absence of alpha-gustducin and Trpm5.

Figure 1

Intake (mean ± SEM) of 0.2% saccharin and 0.2% saccharin + 2% sucrose solutions (top panel) and percent preference for sweetener solutions over water (bottom panel) in Trpm5 KO, Gust KO, and B6 WT mice during two-bottle sweetener vs. water tests. Intakes of water are not shown. Significant (P < 0.05) differences between KO and WT genotypes are indicated by an asterisk (*).

Figure 2

Intake (mean ± SEM) of oils (top panels) and percent preference for oils over vehicle (bottom panels) in Trpm5 KO, Gust KO, and B6 WT mice during oil vs. vehicle two-bottle choice tests. Intakes of the vehicle are not shown. Left panels: Soybean oil intakes in Test 2. Right Panels: Non-nutritive Sefa Soyate oil intakes in Test 3. Significant (P < 0.05) differences between KO and WT genotypes are indicated by an asterisk (*).

Figure 3

Intake (mean ± SEM) of carbohydrates (top panels) and percent preference for carbohydrate over vehicle (bottom panels) in Trpm5 KO, Gust KO, and B6 WT mice during carbohydrate vs. vehicle two-bottle choice tests. Intakes of the vehicle are not shown. Left panels: Polycose solution intakes in Test 4. Right panels: Starch suspension intakes in Test 5. Significant (P < 0.05) differences between KO and WT genotypes are indicated by an asterisk (*).

Figure 4

Intake (mean +SEM) of 2% Polycose vs. 2% starch in Trpm5 KO, Gust KO, and B6 WT mice during two-bottle choice test. Significant (P < 0.05) differences between KO and WT genotypes are indicated by an asterisk (*); significant (P < 0.05) differences between Polycose and starch intake indicated by plus sign (+). Numbers atop bar represent percent Polycose intake.

Figure 5

Intake (mean ± SEM) of Intralipid emulsion (top panels), percent preference for Intralipid over water (middle panels) and Intralipid calories consumed (bottom panels) in Trpm5 KO, Gust KO, and B6 WT mice during two-bottle Intralipid vs. water choice tests. Water intakes are not shown. Significant (P < 0.05) differences between Trpm5 KO and WT genotypes are indicated by an asterisk (*).

Figure 6

Intake (mean ± SEM) of Polycose solutions (top panels), percent preference for Polycose over water (middle panels) and Polycose calories consumed (bottom panels) in Trpm5 KO, Gust KO, and B6 WT mice during two-bottle Polycose vs. water choice tests. Water intakes are not shown. Significant (P < 0.05) differences between KO and WT genotypes are indicated by an asterisk (*).