Fat and carbohydrate preferences in mice: the contribution of α-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.

Taste Preference for Fatty Acids Is Mediated by GPR40 and GPR120

“…GPR40 may couple to a G-protein ␣ subunit from the G␣q or G␣i family (Briscoe et al, 2003;Itoh et al, 2003). GPR120 and GPR40 are unlikely to couple to gustducin because ␣-gustducin knock-out mice have a normal response to soybean oil (Sclafani et al, 2007b). Trpm5, a key signaling molecule for sweet, bitter and umami tastes plays a role in the transduction of fat taste signals since Trpm5 KO mice showed no preference for soybean oil emulsions (supplemental Fig.…”

The opioid system majorly contributes to preference for fat emulsions but not sucrose solutions in mice

“…24−26) Mice lacking these proteins show a lower preference for sucrose compared to wild-type mice. 25,27,28) However, even in mice lacking these proteins, the preference for fat does not differ much from wild-type animals. 27) In addition, we have reported that fat metabolism inhibitors suppress the palatability of fat, while a fat or carbohydrate metabolism inhibitor does not affect the palatability of sucrose.…”

“…25,27,28) However, even in mice lacking these proteins, the preference for fat does not differ much from wild-type animals. 27) In addition, we have reported that fat metabolism inhibitors suppress the palatability of fat, while a fat or carbohydrate metabolism inhibitor does not affect the palatability of sucrose. 29,30) These observations suggest that the mechanisms for the palatability of sucrose and fat differ.…”

The role of dopamine in the pursuit of nutritional value

“…Mice engineered to lack the other components of the taste transduction pathway including the G-protein, α-gustducin, or calcium homeostasis modulator 1 (CALHM1), show initial insensitivity to sweet taste but develop a preference with experience reflecting the action of a post-ingestive reinforcing mechanism [70,71].…”