The proposed research aims to examine the molecular basis for differences in individual taste preferences and sensitivities. Bitter taste is thought to be the most complex of the five basic taste qualities, as it is modulated by ~25 different receptors. The genes that encode these receptors (TAS2Rs) vary among individuals, such that some people are very sensitive to certain bitter compounds, while others cannot taste them at all. Although other factors can affect the sense of taste, genetics plays an essential role. For example, a polymorphism in TAS2R16 changes a single amino acid in the receptor, such that it is unresponsive to bitter stimuli. Variants of the TAS2R38 gene are best-documented example. Individuals expressing the amino acid combination proline- alanine-valine (PAV) find compounds with a thiourea moiety, such as 6-n-propylthiouracil (PROP), to be extremely bitter at low concentrations, whereas individuals with the alanine-valine-isoleucine (AVI) combination require high concentrations to detect PROP or may not be able to taste it at all. The greatest variability is seen with individuals who have one allele that encodes PAV and one allele that encodes AVI (PAV/AVI). Not only do these individuals have a wider range of tasting ability, but cross-sectional studies reveal that they become less sensitive to PROP with age. Additionally, PAV/AVI adults do not transcribe from both alleles evenly. Uneven expression may explain the broad range of phenotypes seen in individuals heterozygous for TAS2R38, and differential expression of TAS2Rs in general may explain the range of bitter sensitivities in individuals with similar genotypes. We will determine PROP thresholds and liking and intensity ratings of bitter tastants and vegetables and measure levels of TAS2R mRNA by quantitative PCR in human taste buds donated on the same day as testing. We hypothesize that increased TAS2R mRNA in taste cells predicts increased bitterness sensitivity (Aim 1). We will look at TAS2R38 in particular for epigenetic changes that affect gene expression. Bisulfite sequencing will be used to monitor differences in methylation of the gene body and the upstream region of TAS2R38 DNA isolated from saliva and taste tissue. We hypothesize that epigenetic changes on the DNA differ on each allele and correlate with mRNA levels present in taste tissue and with PROP sensitivity (Aim 2). The proposed studies will provide valuable insight into the molecular basis for variations in taste perception and sensitivity among individuals with the same genotype and may provide a better understanding of bitter taste that will aid in modifying vegetable consumption in the general population. The proposed methods could be expanded in the future to include studies in children to understand age-related changes in taste sensitivity and preferences. In addition, the tools developed in the proposed studies will be useful for understanding other aspects of the taste system, including the other four basic taste qualities and expression of taste receptors in nontaste tissue such as pancreas and testis.

Public Health Relevance

Understanding the molecular mechanisms that regulate taste receptor expression will provide insights into individual differences in taste preference and sensitivity. It will also lay the groundwork for answering questions about the roles of taste receptors in non-taste tissues, such as lung, brain, pancreas and testis, and may aid in discovering new ways to manipulate taste preferences to promote consumption of healthy foods.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Postdoctoral Individual National Research Service Award (F32)
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Communication Disorders Review Committee (CDRC)
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Sklare, Dan
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Monell Chemical Senses Center
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Mennella, Julie A; Finkbeiner, Susana; Lipchock, Sarah V et al. (2014) Preferences for salty and sweet tastes are elevated and related to each other during childhood. PLoS One 9:e92201
Lipchock, Sarah V; Mennella, Julie A; Spielman, Andrew I et al. (2013) Human bitter perception correlates with bitter receptor messenger RNA expression in taste cells. Am J Clin Nutr 98:1136-43
Lipchock, Sarah V; Reed, Danielle R; Mennella, Julie A (2012) Relationship between bitter-taste receptor genotype and solid medication formulation usage among young children: a retrospective analysis. Clin Ther 34:728-33