Cellular and Molecular Mechanisms of Fat Taste Perception

A new perspective on obesity: perception of fat taste and its relationship with obesity

BACKGROUND

Obesity, which results from a long-term positive energy balance, is affected by many factors, especially nutrition. The sensory properties of foods are associated with increased food intake through hedonic appetite. Taste perception, a component of flavor, is also responsible for increased consumption, through reward and hedonic mechanisms. Foods with high fat and energy content are among the foods that create the reward perception. The perception of fat taste, the primary taste that has recently entered the literature, may also be associated with increased food consumption and body weight. Therefore, in this review, the relationship between fat taste and obesity is examined, using the latest literature.

RESULTS

Different hypotheses have been proposed regarding the mechanism of the relationship between fat-taste perception and obesity, such as hedonic appetite, microbiota, decreased taste perception, and increased taste threshold level. In addition, some studies examining this relationship reported significant associations between the level of fat-taste perception and obesity, whereas others did not find a significant difference.

CONCLUSION

Considering the prevalence and contribution to obesity of Western-style nutrition, characterized by high amounts of fat and sugar consumption, elucidating this relationship may be an essential solution for preventing and treating obesity.

Chronic social defeat stress broadly inhibits gene expression in the peripheral taste system and alters taste responses in mice

Human studies have linked stress exposure to unhealthy eating behavior. However, the mechanisms that drive stress-associated changes in eating behavior remain incompletely understood. The sense of taste plays important roles in food preference and intake. In this study, we use a chronic social defeat stress (CSDS) model in mice to address whether chronic stress impacts taste sensation and gene expression in taste buds and the gut. Our results showed that CSDS significantly elevated circulating levels of corticosterone and acylated ghrelin while lowering levels of leptin, suggesting a change in metabolic hormones that promotes food consumption. Stressed mice substantially increased their intake of food and water 3-5 days after the stress onset and gradually gained more body weight than that of controls. Moreover, CSDS significantly decreased the expression of multiple taste receptors and signaling molecules in taste buds and reduced mRNA levels of several taste progenitor/stem cell markers and regulators. Stressed mice showed significantly reduced sensitivity and response to umami and sweet taste compounds in behavioral tests. In the small intestine, the mRNA levels of Gnat3 and Tas1r2 were elevated in CSDS mice. The increased Gnat3 was mostly localized in a type of Gnat3+ and CD45+ immune cells, suggesting changes of immune cell distribution in the gut of stressed mice. Together, our study revealed broad effects of CSDS on the peripheral taste system and the gut, which may contribute to stress-associated changes in eating behavior.

Long-term regulation of fat sensing in rainbow trout (Oncorhynchus mykiss) fed a vegetable diet from the first feeding: focus on free fatty acid receptors and their signalling

Taste plays a fundamental role in an animal’s ability to detect nutrients and transmits key dietary information to the brain, which is crucial for its growth and survival. Providing alternative terrestrial ingredients early in feeding influences the growth of rainbow trout (RT, Oncorhynchus mykiss). Thus, the present study aimed to assess the influence, via long-term feeding (from the first feeding to 8 months), of alternative plant ingredients (V diet for vegetable diet v. C diet for a control diet) in RT on the mechanism of fat sensing at the gustatory level. After the feeding trial, we studied the pathways of the fat-sensing mechanism in tongue tissue and the integrated response in the brain. To this end, we analysed the expression pattern of free fatty acid receptors (ffar) 1 and 2, markers of calcium-signalling pathways (phospholipase Cβ, Orai, Stim or Serca), the serotonin level (a key neurotransmitter in taste buds) and the expression pattern of appetite-regulating neuropeptides in the hypothalamus (central area of appetite regulation). The results revealed that the V diet modified the expression pattern of ffar1 and paralogs of ffar2 genes in tongue tissue, along with differential regulation of calcium-signalling pathways and a defect in serotonin level and brain turnover, without influencing neuropeptide expression. This study is the first to support that changes in feeding behaviour of RT fed a V diet could be due to the difference in nutrient sensing and a decrease in hedonic sensation. We revealed that RT have similar fat-detection mechanisms as mammals.

[Genetic variants in CD36: emerging role in oral fat perception and food preferences]

Introduction

CD36 is a receptor involved in physiologic, metabolic and pathologic processes. Due to its affinity for long-chain fatty acids, it has been postulated as a taste receptor of fatty taste. In this review, the emerging genetic evidence linking CD36 to oral fat perception is analyzed. A systematic literature search was conducted in PubMed, published articles from 2000 to 2022 were considered. Multiple studies have shown an association of some genetic variants in CD36 with fat foods preferences and it has been suggested that these variants can modify oral fat perception thresholds however the evidence is still heterogeneous; this can be explained by the genetic diversity of populations, the nutritional status and participant's characteristics, as well as other methodological aspects. Other factors involved in oral fat perception were and identified and discussed including the interaction with other flavors, hormones, and epigenetic factors. The conclusion is that the evidence supporting the role of CD36 as a dietary lipid receptor, the role of its genetic variants in fat acids oral perception thresholds and food preferences is intermediate level and more investigations are necessary in other populations with large number of participants as well as considering the interaction between different hormones and the expression of CD36.

Genetic Preference for Sweet Taste in Mothers Associates with Mother-Child Preference and Intake

Taste perception is a well-documented driving force in food selection, with variations in, e.g., taste receptor encoding and glucose transporter genes conferring differences in taste sensitivity and food intake. We explored the impact of maternal innate driving forces on sweet taste preference and intake and assessed whether their children differed in their intake of sweet foods or traits related to sweet intake. A total of 133 single nucleotide polymorphisms (SNPs) in genes reported to associate with eating preferences were sequenced from saliva-DNA from 187 mother-and-child pairs. Preference and intake of sweet-, bitter-, sour-, and umami-tasting foods were estimated from questionnaires. A total of 32 SNP variants associated with a preference for sweet taste or intake at a p-value < 0.05 in additive, dominant major, or dominant minor allele models, with two passing corrections for multiple testing (q < 0.05). These were rs7513755 in the TAS1R2 gene and rs34162196 in the OR10G3 gene. Having the T allele of rs34162196 was associated with higher sweet intake in mothers and their children, along with a higher BMI in mothers. Having the G allele of rs7513755 was associated with a higher preference for sweets in the mothers. The rs34162196 might be a candidate for a genetic score for sweet intake to complement self-reported intakes.

Oral Microbiota-Host Interaction Mediated by Taste Receptors

Taste receptors, originally identified in taste buds, function as the periphery receptors for taste stimuli and play an important role in food choice. Cohort studies have revealed that single nucleotide polymorphisms of taste receptors such as T1R1, T1R2, T2R38 are associated with susceptibility to oral diseases like dental caries. Recent studies have demonstrated the wide expression of taste receptors in various tissues, including intestinal epithelia, respiratory tract, and gingiva, with an emerging role of participating in the interaction between mucosa surface and microorganisms via monitoring a wide range of metabolites. On the one hand, individuals with different oral microbiomes exhibited varied taste sensitivity, suggesting a potential impact of the oral microbiota composition on taste receptor function. On the other hand, animal studies and in vitro studies have uncovered that a variety of oral cells expressing taste receptors such as gingival solitary chemosensory cells, gingival epithelial cells (GECs), and gingival fibroblasts can detect bacterial signals through bitter taste receptors to trigger host innate immune responses, thus regulating oral microbial homeostasis. This review focuses on how taste receptors, particularly bitter and sweet taste receptors, mediate the oral microbiota-host interaction as well as impact the occurrence and development of oral diseases. Further studies delineating the role of taste receptors in mediating oral microbiota-host interaction will advance our knowledge in oral ecological homeostasis establishment, providing a novel paradigm and treatment target for the better management of dental infectious diseases.

Tongue Leptin Decreases Oro-Sensory Perception of Dietary Fatty Acids

Leptin, an anorectic hormone, regulates food intake, energy expenditure and body weight. We assessed the implication of tongue leptin in the modulation of oro-sensory detection of dietary fatty acids in mice. The RT-PCR analysis showed that mRNA encoding leptin and leptin receptor (Ob-Rb) was expressed in mice taste bud cells (TBC). Confocal microscopic studies showed that the lipid sensor CD36 was co-expressed with leptin in mice TBC. Silencing of leptin or Ob-Rb mRNA in tongue papillae upregulated preference for a long-chain fatty acid (LCFA), i.e., linoleic acid (LA), in a two-bottle paradigm in mice. Furthermore, tongue leptin application decreased the preference for the LCFA. These results suggest that tongue leptin exerts an inhibitory action on fatty acid preference. In isolated mice TBC, leptin decreased LCFA-induced increases in free intracellular calcium concentrations, [Ca²⁺]i. Leptin and LCFA induced the phosphorylation of ERK1/2 and STAT-3 and there were no additive or opposite effects of the two agents on the degree of phosphorylation. However, leptin, but not the LCFA, induced phosphoinositide-3-kinase (PI-3-K)-dependent Akt phosphorylation in TBC. Furthermore, leptin induced hyperpolarization, whereas LCFA induced depolarization in TBC. Our study demonstrates that tongue leptin exerts an inhibitory action on oro-sensory detection of a dietary fatty acid by interfering with Ca²⁺ signaling and membrane potential in mice TBC.