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Bitter taste receptors influence glucose homeostasis.

Dotson CD, Zhang L, Xu H, Shin YK, Vigues S, Ott SH, Elson AE, Choi HJ, Shaw H, Egan JM, Mitchell BD, Li X, Steinle NI, Munger SD - PLoS ONE (2008)

Bottom Line: These receptors are also expressed in subsets of cells within the mammalian gastrointestinal tract, where they mediate nutrient assimilation and endocrine responses.For example, sweeteners stimulate taste receptors on the surface of gut enteroendocrine L cells to elicit an increase in intracellular Ca(2+) and secretion of the incretin hormone glucagon-like peptide-1 (GLP-1), an important modulator of insulin biosynthesis and secretion.We also found that one SNP within this haplotype disrupts normal responses of a single receptor, TAS2R9, to its cognate ligands ofloxacin, procainamide and pirenzapine.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA.

ABSTRACT
TAS1R- and TAS2R-type taste receptors are expressed in the gustatory system, where they detect sweet- and bitter-tasting stimuli, respectively. These receptors are also expressed in subsets of cells within the mammalian gastrointestinal tract, where they mediate nutrient assimilation and endocrine responses. For example, sweeteners stimulate taste receptors on the surface of gut enteroendocrine L cells to elicit an increase in intracellular Ca(2+) and secretion of the incretin hormone glucagon-like peptide-1 (GLP-1), an important modulator of insulin biosynthesis and secretion. Because of the importance of taste receptors in the regulation of food intake and the alimentary responses to chemostimuli, we hypothesized that differences in taste receptor efficacy may impact glucose homeostasis. To address this issue, we initiated a candidate gene study within the Amish Family Diabetes Study and assessed the association of taste receptor variants with indicators of glucose dysregulation, including a diagnosis of type 2 diabetes mellitus and high levels of blood glucose and insulin during an oral glucose tolerance test. We report that a TAS2R haplotype is associated with altered glucose and insulin homeostasis. We also found that one SNP within this haplotype disrupts normal responses of a single receptor, TAS2R9, to its cognate ligands ofloxacin, procainamide and pirenzapine. Together, these findings suggest that a functionally compromised TAS2R receptor negatively impacts glucose homeostasis, providing an important link between alimentary chemosensation and metabolic disease.

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TAS2R9 in enteroendocrine cells.(A) PCR amplicons for TAS2R9 or TAS1R3 from NCI-H716 and human cecum cDNA. The size of the TAS1R3 amplicon (434 bp) indicates no genomic DNA contamination (the genomic product would be 693 bp). TAS2R7 was not amplified from either cDNA pool. (B) GLP-1 secretion from NCI H716 cells in response to ofloxacin stimulation, normalized to the buffer only control, in the absence (black) or presence (red) of an α-gustducin siRNA. The specificity of the siRNA probe for α-gustducin in these cells was previously reported [15]. Repeated measures ANOVA showed significant effects of concentration (P<1×10−9), siRNA treatment (P = 1.4×10−5) and siRNA treatment X concentration (P = 9×10−5). Posthoc t-tests: * P<0.05; ** P<0.001. (C) Levels of α-gustducin message in NCI H716 cells measured by quantitative real-time PCR in the absence (black) or presence (red) of the α-gustducin siRNA and normalized for α-gustducin levels in the absence of stimulus and siRNA. Error bars: standard error.
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pone-0003974-g003: TAS2R9 in enteroendocrine cells.(A) PCR amplicons for TAS2R9 or TAS1R3 from NCI-H716 and human cecum cDNA. The size of the TAS1R3 amplicon (434 bp) indicates no genomic DNA contamination (the genomic product would be 693 bp). TAS2R7 was not amplified from either cDNA pool. (B) GLP-1 secretion from NCI H716 cells in response to ofloxacin stimulation, normalized to the buffer only control, in the absence (black) or presence (red) of an α-gustducin siRNA. The specificity of the siRNA probe for α-gustducin in these cells was previously reported [15]. Repeated measures ANOVA showed significant effects of concentration (P<1×10−9), siRNA treatment (P = 1.4×10−5) and siRNA treatment X concentration (P = 9×10−5). Posthoc t-tests: * P<0.05; ** P<0.001. (C) Levels of α-gustducin message in NCI H716 cells measured by quantitative real-time PCR in the absence (black) or presence (red) of the α-gustducin siRNA and normalized for α-gustducin levels in the absence of stimulus and siRNA. Error bars: standard error.

Mentions: Though the mechanism by which this taste receptor-associated haplotype affects glucose and insulin homeostasis remains unclear, these receptors could be involved in the modulation of GLP-1 secretion from gut enteroendocrine L cells [14]. We used reverse transcription-polymerase chain reaction (RT-PCR) to determine if TAS2R9 is expressed in these cells. We amplified both TAS2R9 and TAS1R3 (a subunit of the sweet and umami taste receptors previously reported to be expressed in enteroendocrine L cells [15], [23], [25]) from cDNA obtained from NCI-H716 cells (a human enteroendocrine L cell line; Figure 3A), from human cecum (Figure 3A), and from human tongue (data not shown). We were unable to amplify TAS2R7 from any of these cDNA pools (Figure 3A and data not shown), though we could amplify a product from human genomic DNA (data not shown). The TAS2R9 products were amplified from cDNA and not genomic DNA contaminants: PCR from control samples that were not reverse transcribed gave no TAS2R9 product (data not shown), and oligos that recognize coding sequences in exons 4 and 6 of taste receptor TAS1R3 amplify a product lacking the two intervening introns (Figure 3A). Independent clones of the TAS2R9 product amplified from the NCI-H716 cells had either an A or T at bp 560, indicating that this cell line is heterozygous for this allele. Next, we tested whether a TAS2R9 ligand can promote GLP-1 secretion from enteroendocrine L cells. Stimulation of NCI-H716 cells with ofloxacin elicited a concentration-dependent secretion of GLP-1 from this cell line (Figure 3B). siRNA knockdown of the G protein α-gustducin (Figure 3C), which mediates bitter taste responses in the tongue [34] and which has been implicated in taste receptor-mediated GLP-1 secretion in the gut [15], reduced ofloxacin-stimulated GLP-1 secretion (Figure 3B). Together, these results are consistent with a role of TAS2R9 in the regulation of nutrient-dependent GLP-1 secretion from L cells.


Bitter taste receptors influence glucose homeostasis.

Dotson CD, Zhang L, Xu H, Shin YK, Vigues S, Ott SH, Elson AE, Choi HJ, Shaw H, Egan JM, Mitchell BD, Li X, Steinle NI, Munger SD - PLoS ONE (2008)

TAS2R9 in enteroendocrine cells.(A) PCR amplicons for TAS2R9 or TAS1R3 from NCI-H716 and human cecum cDNA. The size of the TAS1R3 amplicon (434 bp) indicates no genomic DNA contamination (the genomic product would be 693 bp). TAS2R7 was not amplified from either cDNA pool. (B) GLP-1 secretion from NCI H716 cells in response to ofloxacin stimulation, normalized to the buffer only control, in the absence (black) or presence (red) of an α-gustducin siRNA. The specificity of the siRNA probe for α-gustducin in these cells was previously reported [15]. Repeated measures ANOVA showed significant effects of concentration (P<1×10−9), siRNA treatment (P = 1.4×10−5) and siRNA treatment X concentration (P = 9×10−5). Posthoc t-tests: * P<0.05; ** P<0.001. (C) Levels of α-gustducin message in NCI H716 cells measured by quantitative real-time PCR in the absence (black) or presence (red) of the α-gustducin siRNA and normalized for α-gustducin levels in the absence of stimulus and siRNA. Error bars: standard error.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2597743&req=5

pone-0003974-g003: TAS2R9 in enteroendocrine cells.(A) PCR amplicons for TAS2R9 or TAS1R3 from NCI-H716 and human cecum cDNA. The size of the TAS1R3 amplicon (434 bp) indicates no genomic DNA contamination (the genomic product would be 693 bp). TAS2R7 was not amplified from either cDNA pool. (B) GLP-1 secretion from NCI H716 cells in response to ofloxacin stimulation, normalized to the buffer only control, in the absence (black) or presence (red) of an α-gustducin siRNA. The specificity of the siRNA probe for α-gustducin in these cells was previously reported [15]. Repeated measures ANOVA showed significant effects of concentration (P<1×10−9), siRNA treatment (P = 1.4×10−5) and siRNA treatment X concentration (P = 9×10−5). Posthoc t-tests: * P<0.05; ** P<0.001. (C) Levels of α-gustducin message in NCI H716 cells measured by quantitative real-time PCR in the absence (black) or presence (red) of the α-gustducin siRNA and normalized for α-gustducin levels in the absence of stimulus and siRNA. Error bars: standard error.
Mentions: Though the mechanism by which this taste receptor-associated haplotype affects glucose and insulin homeostasis remains unclear, these receptors could be involved in the modulation of GLP-1 secretion from gut enteroendocrine L cells [14]. We used reverse transcription-polymerase chain reaction (RT-PCR) to determine if TAS2R9 is expressed in these cells. We amplified both TAS2R9 and TAS1R3 (a subunit of the sweet and umami taste receptors previously reported to be expressed in enteroendocrine L cells [15], [23], [25]) from cDNA obtained from NCI-H716 cells (a human enteroendocrine L cell line; Figure 3A), from human cecum (Figure 3A), and from human tongue (data not shown). We were unable to amplify TAS2R7 from any of these cDNA pools (Figure 3A and data not shown), though we could amplify a product from human genomic DNA (data not shown). The TAS2R9 products were amplified from cDNA and not genomic DNA contaminants: PCR from control samples that were not reverse transcribed gave no TAS2R9 product (data not shown), and oligos that recognize coding sequences in exons 4 and 6 of taste receptor TAS1R3 amplify a product lacking the two intervening introns (Figure 3A). Independent clones of the TAS2R9 product amplified from the NCI-H716 cells had either an A or T at bp 560, indicating that this cell line is heterozygous for this allele. Next, we tested whether a TAS2R9 ligand can promote GLP-1 secretion from enteroendocrine L cells. Stimulation of NCI-H716 cells with ofloxacin elicited a concentration-dependent secretion of GLP-1 from this cell line (Figure 3B). siRNA knockdown of the G protein α-gustducin (Figure 3C), which mediates bitter taste responses in the tongue [34] and which has been implicated in taste receptor-mediated GLP-1 secretion in the gut [15], reduced ofloxacin-stimulated GLP-1 secretion (Figure 3B). Together, these results are consistent with a role of TAS2R9 in the regulation of nutrient-dependent GLP-1 secretion from L cells.

Bottom Line: These receptors are also expressed in subsets of cells within the mammalian gastrointestinal tract, where they mediate nutrient assimilation and endocrine responses.For example, sweeteners stimulate taste receptors on the surface of gut enteroendocrine L cells to elicit an increase in intracellular Ca(2+) and secretion of the incretin hormone glucagon-like peptide-1 (GLP-1), an important modulator of insulin biosynthesis and secretion.We also found that one SNP within this haplotype disrupts normal responses of a single receptor, TAS2R9, to its cognate ligands ofloxacin, procainamide and pirenzapine.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA.

ABSTRACT
TAS1R- and TAS2R-type taste receptors are expressed in the gustatory system, where they detect sweet- and bitter-tasting stimuli, respectively. These receptors are also expressed in subsets of cells within the mammalian gastrointestinal tract, where they mediate nutrient assimilation and endocrine responses. For example, sweeteners stimulate taste receptors on the surface of gut enteroendocrine L cells to elicit an increase in intracellular Ca(2+) and secretion of the incretin hormone glucagon-like peptide-1 (GLP-1), an important modulator of insulin biosynthesis and secretion. Because of the importance of taste receptors in the regulation of food intake and the alimentary responses to chemostimuli, we hypothesized that differences in taste receptor efficacy may impact glucose homeostasis. To address this issue, we initiated a candidate gene study within the Amish Family Diabetes Study and assessed the association of taste receptor variants with indicators of glucose dysregulation, including a diagnosis of type 2 diabetes mellitus and high levels of blood glucose and insulin during an oral glucose tolerance test. We report that a TAS2R haplotype is associated with altered glucose and insulin homeostasis. We also found that one SNP within this haplotype disrupts normal responses of a single receptor, TAS2R9, to its cognate ligands ofloxacin, procainamide and pirenzapine. Together, these findings suggest that a functionally compromised TAS2R receptor negatively impacts glucose homeostasis, providing an important link between alimentary chemosensation and metabolic disease.

Show MeSH
Related in: MedlinePlus