Fariba Assadi-porter
University of Wisconsin-Madison, Zoology, Department Member
Taste signaling is a complex process that is linked to obesity and its associated metabolic syndromes. The sweet taste is mediated through a heterodimeric G protein coupled receptor (GPRC) in a species-specific manner and at multi-tissue... more
Taste signaling is a complex process that is linked to obesity and its associated metabolic syndromes. The sweet taste is mediated through a heterodimeric G protein coupled receptor (GPRC) in a species-specific manner and at multi-tissue specific levels. The sweet receptor recognizes a large number of ligands with structural and functional diversities to modulate different amplitudes of downstream signaling pathway(s). The human sweet-taste receptor has been extremely difficult to study by biophysical methods due to inadequate methods for producing large homogeneous quantities of the taste-receptor protein and a lack of reliable in vitro assays to precisely measure productive ligand binding modes leading to activity upon their interactions with the receptor protein. We report a multimodal high throughput assays to monitor ligand binding, receptor stability and conformational changes to model the molecular interactions between ligand-receptor. We applied saturation transfer differenc...
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Obesity is a complex disease associated with environmental and genetic factors. 3-Iodothyronamine (T1AM) has revealed great potential as an effective weight loss drug. We used metabolomics and associated transcriptional gene and protein... more
Obesity is a complex disease associated with environmental and genetic factors. 3-Iodothyronamine (T1AM) has revealed great potential as an effective weight loss drug. We used metabolomics and associated transcriptional gene and protein expression analysis to investigate the tissue specific metabolic reprogramming effects of subchronic T1AM treatment at two pharmacological daily doses (10 and 25 mg/kg) on targeted metabolic pathways. Multi-analytical results indicated that T1AM at 25 mg/kg can act as a novel master regulator of both glucose and lipid metabolism in mice through sirtuin-mediated pathways. In liver, we observed an increased gene and protein expression of (a master gene regulator of glucose) and (glucose kinase) and a decreased expression of (a negative regulator of fatty acids oxidation (FAO)), whereas in white adipose tissue only was increased. Metabolomics analysis supported physiological changes at both doses with most increases in FAO, glycolysis indicators and the...
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Polyunsaturated fatty acid (PUFA)-rich diets are thought to provide beneficial effects toward metabolic health in part through their bioactive properties. We hypothesized that increasing PUFA intake in mice would increase peroxisome... more
Polyunsaturated fatty acid (PUFA)-rich diets are thought to provide beneficial effects toward metabolic health in part through their bioactive properties. We hypothesized that increasing PUFA intake in mice would increase peroxisome proliferator activated receptor delta (PPARδ) expression and activity, and we sought to examine the effect of different PUFA-enriched oils on muscle PPARδ expression. One of the oils we tested was cottonseed oil (CSO) which is primarily linoleic acid (53%) and palmitic acid (24%). Mice fed a CSO-enriched diet (50% energy from fat) displayed no change in muscle PPARδ expression; however, in the liver, it was consistently elevated along with its transcriptional coactivator Pgc-1. Male mice were fed chow or CSO-, saturated fat (SFA)-, or linoleic acid (18:2)-enriched diets that were matched for macronutrient content for 4 weeks. There were no differences in food intake, body weight, fasting glucose, glucose tolerance, or energy expenditure between chow- and CSO-fed mice, whereas SFA-fed mice had increased fat mass and 18:2-fed mice were less glucose tolerant. Metabolomic analyses revealed that the livers of CSO-fed mice closely matched those of chow-fed but significantly differed from SFA- and 18:2-enriched groups. Fatty acid composition of the diets and livers revealed an impairment in desaturase activity and the presence of dihydrosterculic acid (DHSA) in the CSO-fed mice. The effect of DHSA on PPARδ and stearoyl-CoA desaturase-1 expression mimicked that of the CSO-fed mice. Taken together, these data suggest that DHSA from CSO may be an effective means to increase PPARδ expression with concomitant suppression of liver stearoyl-CoA desaturase-1 activity.
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Complex diseases such as polycystic ovary syndrome (PCOS) are associated with intricate pathophysiological, hormonal, and metabolic feedbacks that make their early diagnosis challenging, thus increasing the prevalence risks for obesity,... more
Complex diseases such as polycystic ovary syndrome (PCOS) are associated with intricate pathophysiological, hormonal, and metabolic feedbacks that make their early diagnosis challenging, thus increasing the prevalence risks for obesity, cardiovascular, and fatty liver diseases. To explore the crosstalk between endocrine and lipid metabolic pathways, we administered 3-iodothyronamine (T1AM), a natural analog of thyroid hormone, in a mouse model of PCOS and analyzed plasma and tissue extracts using multidisciplinary omics and biochemical approaches. T1AM administration induces a profound tissue-specific antilipogenic effect in liver and muscle by lowering gene expression of key regulators of lipid metabolism, PTP1B and PLIN2, significantly increasing metabolites (glucogenic, amino acids, carnitine, and citrate) levels, while enhancing protection against oxidative stress. In contrast, T1AM has an opposing effect on the regulation of estrogenic pathways in the ovary by upregulating STAR...
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Brazzein is a small (54 amino acid residue) sweet tasting protein with physical and taste properties superior toother non-carbohydrate sweeteners. In an investigation of sequence-dependent functional properties of the protein, we used NMR... more
Brazzein is a small (54 amino acid residue) sweet tasting protein with physical and taste properties superior toother non-carbohydrate sweeteners. In an investigation of sequence-dependent functional properties of the protein, we used NMR spectroscopy to determine the three-dimensional structures and dynamic properties of two brazzein variants: one with a single-site substitution (D40K),which is three-fold sweeter than wild-type brazzein, and one with a two-residue insertion between residues 18 and 19 (ins18 RI19 ), which is devoid of sweetness. Although the three-dimensional folds of the two variants were very similar to wild-type brazzein, they exhibited local conformational and dynamic differences. The D40K substitution abolished the strong inter-stand H-bond between the side chains of residues Gln46 and Asp40 present in wild-type brazzein and increased the flexibility of the protein especially at the mutation site. This increased flexibility presumably allows this site to intera...
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Typescript. Thesis (Ph. D.)--University of Wisconsin--Madison, 1994. Includes bibliographical references.
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Brazzein is a small, heat-stable, intensely sweet protein consisting of 54 amino acid residues. Based on the wild-type brazzein, 25 brazzein mutants have been produced to identify critical regions important for sweetness. To assess their... more
Brazzein is a small, heat-stable, intensely sweet protein consisting of 54 amino acid residues. Based on the wild-type brazzein, 25 brazzein mutants have been produced to identify critical regions important for sweetness. To assess their sweetness, psychophysical experiments were carried out with 14 human subjects. First, the results suggest that residues 29–33 and 39–43, plus residue 36 between these stretches, as well as the C-terminus are involved in the sweetness of brazzein. Second, charge plays an important role in the interaction between brazzein and the sweet taste receptor.
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How Sweet It Is: Detailed Molecular and Functional ... Studies of Brazzein, a Sweet Protein and Its Analogs ... Fariba Assadi-Porter1,2, Marco Tonelli2, James T. Radek3, Claudia C. Cornilescu4, and John L. Markley1,2 ... 1Department of... more
How Sweet It Is: Detailed Molecular and Functional ... Studies of Brazzein, a Sweet Protein and Its Analogs ... Fariba Assadi-Porter1,2, Marco Tonelli2, James T. Radek3, Claudia C. Cornilescu4, and John L. Markley1,2 ... 1Department of Biochemistry, 2National ...
Research Interests: Gene expression, Cell and Molecular Biology, Biological Sciences, Liver, Mice, and 14 moreAnimals, Cluster Analysis, Tandem Mass Spectrometry, Molecular Cell Biology, Amino Acids, Carbohydrate metabolism, Acetylation, Caloric Restriction, Amino Acid Sequence, Proteome, Sirtuin, Mitochondrial Proteins, Molecular Sequence Data, and Medical and Health Sciences
Research Interests: Metabolism, Metabolomics, Magnetic Resonance Spectroscopy, Blood Glucose, Carbon Isotopes, and 14 moreMice, Female, Animals, Plasma, Glycolysis, Clinical Sciences, Spectrum analysis, Aluminum oxide, Lactic Acid, Glucocorticoids, Isotope Labeling, Siloxanes, Pentose Phosphate Pathway, and hydrocortisone
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Objective: 3-Iodothyronamine (T 1 AM), an analog of thyroid hormone, is a recently discovered fast-acting endogenous metabolite. Single high-dose treatments of T 1 AM have produced rapid short-term effects, including a reduction of body... more
Objective: 3-Iodothyronamine (T 1 AM), an analog of thyroid hormone, is a recently discovered fast-acting endogenous metabolite. Single high-dose treatments of T 1 AM have produced rapid short-term effects, including a reduction of body temperature, bradycardia, and hyperglycemia in mice. Design and Methods: The effect of daily low doses of T 1 AM (10 mg/kg) for 8 days on weight loss and metabolism in spontaneously overweight mice was monitored. The experiments were repeated twice (n ¼ 4). Nuclear magnetic resonance (NMR) spectroscopy of plasma and real-time analysis of exhaled 13 CO 2 in breath by cavity ring down spectroscopy (CRDS) were used to detect T 1 AM-induced lipolysis. Results: CRDS detected increased lipolysis in breath shortly after T 1 AM administration that was associated with a significant weight loss but independent of food consumption. NMR spectroscopy revealed alterations in key metabolites in serum: valine, glycine, and 3-hydroxybutyrate, suggesting that the subchronic effects of T 1 AM include both lipolysis and protein breakdown. After discontinuation of T 1 AM treatment, mice regained only 1.8% of the lost weight in the following 2 weeks, indicating lasting effects of T 1 AM on weight maintenance. Conclusions: CRDS in combination with NMR and 13 C-metabolic tracing constitute a powerful method of investigation in obesity studies for identifying in vivo biochemical pathway shifts and unanticipated debilitating side effects.
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3-Iodothyronamide (T1AM) is a naturally produced endogenous hormone like molecule. Only recently it has been discovered in the past decade, the proceeding body of research emerging from its initial discovery has revealed a substantial... more
3-Iodothyronamide (T1AM) is a naturally produced endogenous
hormone like molecule. Only recently it has been discovered in the
past decade, the proceeding body of research emerging from its
initial discovery has revealed a substantial capacity of T1AM as a new
potential hormone that affects numerous physiological processes
and organs. Initially, it was hypothesized to be a byproduct of Thyroid
Hormone (TH) metabolism; however, the current body of evidence
suggests that its production and physiological function appear to be
uncoupled and dramatically divergent from that of TH. This review
summarizes the physiological and biochemical effects of T1AM
reported in the literature along with its proposed mechanisms of
action and production pathways. The physiological effects of T1AM
appear to be dose specific, in some cases exerting opposing effects
in the same biological processes. Uptake, storage, and degree of
effect appear to be tissue specific as well. From the current body
of literature, potential therapeutic applications with T1AM are
quite apparent, ranging from sleep/torpidity induction, conferring
protection against ischemic injury, and anti-obesogenic by inducing
increased metabolic reliance on lipid oxidation. Future research is
needed to understand the specific mechanisms of its dose dependent
and tissue dependent effects, its mechanism of entry into the cell, its
cellular targets, and primary site of production.
hormone like molecule. Only recently it has been discovered in the
past decade, the proceeding body of research emerging from its
initial discovery has revealed a substantial capacity of T1AM as a new
potential hormone that affects numerous physiological processes
and organs. Initially, it was hypothesized to be a byproduct of Thyroid
Hormone (TH) metabolism; however, the current body of evidence
suggests that its production and physiological function appear to be
uncoupled and dramatically divergent from that of TH. This review
summarizes the physiological and biochemical effects of T1AM
reported in the literature along with its proposed mechanisms of
action and production pathways. The physiological effects of T1AM
appear to be dose specific, in some cases exerting opposing effects
in the same biological processes. Uptake, storage, and degree of
effect appear to be tissue specific as well. From the current body
of literature, potential therapeutic applications with T1AM are
quite apparent, ranging from sleep/torpidity induction, conferring
protection against ischemic injury, and anti-obesogenic by inducing
increased metabolic reliance on lipid oxidation. Future research is
needed to understand the specific mechanisms of its dose dependent
and tissue dependent effects, its mechanism of entry into the cell, its
cellular targets, and primary site of production.
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3-Iodothyronamine (T1AM) is a structural analog of thyroid hormone that has been demonstrated to have potent affects on numerous physiological systems. Most studies on T1AM have explored its effects in healthy functional systems; while... more
3-Iodothyronamine (T1AM) is a structural analog of thyroid hormone that has been demonstrated to have potent affects on numerous physiological systems. Most studies on T1AM have explored its effects in healthy functional systems; while its potential therapeutic uses and safety, and efficacy in pathological conditions are largely unknown. We sought to evaluate the effects of T1AM and its structural analog SG-2 on cancer cell growth and viability. We analyzed the cytotoxicity of these analogs on MCF7 breast cancer cells, HepG2 hepatocellular cancer cells as well as normal control cells using primary human foreskin fibroblasts and mouse preadipocytes control cells. The cytotoxicity of T1AM and SG-2 was determined by cell growth curves, and validated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability assays. Cellular uptake analysis was conducted using confocal microscopy. Real-time (RT)-PCR was conducted to identify gene pathways affected by SG-2 in cancer cells. The IC 50 of T1AM was approximately double the concentration of its analog SG-2 in cancer cells. Cytotoxicity studies on normal cells revealed that IC 50 concentrations of SG-2 in cancer cells had no significant impact on cell viability in these cell types. Cell-imaging experiments demonstrated rapid uptake and localization to the mitochondrial membrane. T1AM and SG-2 are able to reduce cancer cell growth and viability. These findings support the potential for use of these compounds and related analogs for their antiproliferation properties in cancer cells.
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ABSTRACT: Polycystic ovary syndrome (PCOS) is associated with metabolic and endocrine disorders in women of reproductive age. The etiology of PCOS is still unknown. Mice prenatally treated with glucocorticoids exhibit metabolic... more
ABSTRACT: Polycystic ovary syndrome (PCOS) is associated
with metabolic and endocrine disorders in women of reproductive age. The etiology of PCOS is still unknown. Mice
prenatally treated with glucocorticoids exhibit metabolic
disturbances that are similar to those seen in women with PCOS. We used an untargeted nuclear magnetic resonance
(NMR)-based metabolomics approach to understand the
metabolic changes occurring in the plasma and kidney over
time in female glucocorticoid-treated (GC-treated) mice.
There are significant changes in plasma amino acid levels
(valine, tyrosine, and proline) and their intermediates (2-
hydroxybutyrate, 4-aminobutyrate, and taurine), whereas in
kidneys, the TCA cycle metabolism (citrate, fumarate, and succinate) and the pentose phosphate (PP) pathway products
(inosine and uracil) are significantly altered (p < 0.05) from 8 to 16 weeks of age. Levels of NADH, NAD+, NAD+/NADH, and
NADH redox in kidneys indicate increased mitochondrial oxidative stress from 8 to 16 weeks in GC-treated mice. These results indicate that altered metabolic substrates in the plasma and kidneys of treated mice are associated with altered amino acid metabolism, increased cytoplasmic PP, and increased mitochondrial activity, leading to a more oxidized state. This study identifies biomarkers associated with metabolic dysfunction in kidney mitochondria of a prenatal gluococorticoxd-treated mouse model of PCOS that may be used as early predictive biomarkers of oxidative stress in the PCOS metabolic disorder in women.
with metabolic and endocrine disorders in women of reproductive age. The etiology of PCOS is still unknown. Mice
prenatally treated with glucocorticoids exhibit metabolic
disturbances that are similar to those seen in women with PCOS. We used an untargeted nuclear magnetic resonance
(NMR)-based metabolomics approach to understand the
metabolic changes occurring in the plasma and kidney over
time in female glucocorticoid-treated (GC-treated) mice.
There are significant changes in plasma amino acid levels
(valine, tyrosine, and proline) and their intermediates (2-
hydroxybutyrate, 4-aminobutyrate, and taurine), whereas in
kidneys, the TCA cycle metabolism (citrate, fumarate, and succinate) and the pentose phosphate (PP) pathway products
(inosine and uracil) are significantly altered (p < 0.05) from 8 to 16 weeks of age. Levels of NADH, NAD+, NAD+/NADH, and
NADH redox in kidneys indicate increased mitochondrial oxidative stress from 8 to 16 weeks in GC-treated mice. These results indicate that altered metabolic substrates in the plasma and kidneys of treated mice are associated with altered amino acid metabolism, increased cytoplasmic PP, and increased mitochondrial activity, leading to a more oxidized state. This study identifies biomarkers associated with metabolic dysfunction in kidney mitochondria of a prenatal gluococorticoxd-treated mouse model of PCOS that may be used as early predictive biomarkers of oxidative stress in the PCOS metabolic disorder in women.
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The emergence of obesity as a major public health issue in the United States and other First World countries has increased interest in low-calorie natural sweeteners. The 54-residue protein brazzein, which is isolated from the fruit of... more
The emergence of obesity as a major public health issue in the United States and other First World countries has increased interest in low-calorie natural sweeteners. The 54-residue protein brazzein, which is isolated from the fruit of the African vine Pentadiplandra brazzeana, is attractive for development as a low-calorie sweetener because of its small size, strong sweet taste, high thermostability, and lack of toxicity. 1 Mutagenesis studies on brazzein showed that residues critical for sweetness are distributed throughout the primary sequence and secondary structure of the protein. 2 Both mutagenesis and modeling studies suggest that the termini of brazzein interact with the human sweet taste receptor. Mutations in either terminus generate a product that retains some sweetness, suggesting that the termini may be an important locus of brazzein activity. 2 Brazzein folds with β-α-β 2 topology, forming a three-stranded antiparallel β-sheet against which the α-helix packs obliquely ...
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In sequence-function investigations, approaches are needed for rapidly screening protein variants for possible changes in conformation. Recent NMR methods permit direct detection of hydrogen bonds through measurements of scalar couplings... more
In sequence-function investigations, approaches are needed for rapidly screening protein variants for possible changes in conformation. Recent NMR methods permit direct detection of hydrogen bonds through measurements of scalar couplings that traverse hydrogen bonds (trans-hydrogen bond couplings). We have applied this approach to screen a series of five single site mutants of the sweet protein brazzein with altered sweetness for possible changes in backbone hydrogen bonding with respect to wild-type. Long range, three-dimensional data correlating connectivities among backbone 1HN, 15N, and 13C&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; atoms were collected from the six brazzein proteins labeled uniformly with carbon-13 and nitrogen-15. In wild-type brazzein, this approach identified 17 backbone hydrogen bonds. In the mutants, altered magnitudes of the couplings identified hydrogen bonds that were strengthened or weakened; missing couplings identified hydrogen bonds that were broken, and new couplings indicated the presence of new hydrogen bonds. Within the series of brazzein mutants investigated, a pattern was observed between sweetness and the integrity of particular hydrogen bonds. All three &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;sweet&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; variants exhibited the same pattern of hydrogen bonds, whereas all three &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;non-sweet&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; variants lacked one hydrogen bond at the middle of the alpha-helix, where it is kinked, and one hydrogen bond in the middle of beta-strands II and III, where they are twisted. Two of the non-sweet variants lack the hydrogen bond connecting the N and C termini. These variants showed greater mobility in the N- and C-terminal regions than wild-type brazzein.
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ABSTRACT: Subunit c of the Hf-transporting FIFO ATP synthase (EC 3.6.1.34) is thought to fold across the membrane as a hairpin of two a helices with a conserved Asp/Glu residue, centered in the second membrane-spanning helix, which is... more
ABSTRACT: Subunit c of the Hf-transporting FIFO ATP synthase (EC 3.6.1.34) is thought to fold across the membrane as a hairpin of two a helices with a conserved Asp/Glu residue, centered in the second membrane-spanning helix, which is thought to function in H+ translocation. ...
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Brazzein, originally isolated from the fruit of the African plant Pentadiplandra brazzeana Baillon, is the smallest, most heat-stable and pH-stable member of the set of proteins known to have intrinsic sweetness. These properties make... more
Brazzein, originally isolated from the fruit of the African plant Pentadiplandra brazzeana Baillon, is the smallest, most heat-stable and pH-stable member of the set of proteins known to have intrinsic sweetness. These properties make brazzein an ideal system for investigating the chemical and structural requirements of a sweet-tasting protein. We have used the three-dimensional structure of the protein (J. E. Caldwell et al. (1998) Nat. Struct. Biol. 5, 427-431) as a guide in designing 15 synthetic genes in expression constructs aimed at delineating the sweetness determinants of brazzein. Protein was produced heterologously in Escherichia coli, isolated, and purified as described in the companion paper (Assadi-Porter, F. M., Aceti, D., Cheng, H., and Markley, J. L., this issue). Analysis by one-dimensional (1)H NMR spectroscopy indicated that all but one of these variants had folded properly under the conditions used. A taste panel compared the gustatory properties of solutions of these proteins to those of sucrose and brazzein isolated from fruit. Of the 14 mutations in the des-pGlu1-brazzein background, four exhibited almost no sweetness, six had significantly reduced sweetness, two had taste properties equivalent to des-pGlu1-brazzein (two times as sweet as the major form of brazzein isolated from fruit which contains pGlu1), and two were about twice as sweet as des-pGlu1-brazzein. Overall, the results suggest that two regions of the protein are critical for the sweetness of brazzein: a region that includes the N- and C-termini of the protein, which are located close to one another, and a region that includes the flexible loop around Arg43.
Research Interests: Protein Folding, NMR Spectroscopy, Magnetic Resonance Spectroscopy, Humans, Mutation, and 14 moreEscherichia coli, Fruit, Sucrose, Taste, Protein structure, High Pressure Liquid Chromatography, Solutions, Arginine, Protein Conformation, Amino Acid Substitution Rates, Structure activity Relationship, PLANT PROTEINS, *Hot Temperature, and Biochemistry and cell biology
Brazzein is a 54-amino-acid sweet-tasting protein first isolated from the fruit of Pentadiplandra brazzeana Baillon found in West Africa. Brazzein, as isolated from the fruit, is 500 times sweeter than sucrose on a weight basis (9500... more
Brazzein is a 54-amino-acid sweet-tasting protein first isolated from the fruit of Pentadiplandra brazzeana Baillon found in West Africa. Brazzein, as isolated from the fruit, is 500 times sweeter than sucrose on a weight basis (9500 times sweeter on a per-molecule basis). A minor component of brazzein from fruit, des-pGlu1-brazzein, has 53 amino acid residues and has twice the sweetness of the parent protein. We have designed a gene for des-pGlu1- brazzein that incorporates codons that are optimal for protein production in Escherichia coli. Production of brazzein from the chemically synthesized gene resulted in recombinant protein with sweetness similar to that of brazzein isolated from the original source. The best yields were achieved by producing brazzein as a fusion with staphylococcal nuclease with a designed cyanogen bromide cleavage site. Because of its intense sweetness and stability at high pH and temperature, brazzein is an ideal system for investigating the chemical and structural requirements involved in sweet-taste properties. This efficient protein production system for brazzein will facilitate such investigations.
Research Interests: Protein Folding, West Africa, Magnetic Resonance Spectroscopy, Genetic Engineering, Humans, and 14 moreEscherichia coli, Fruit, Taste, Solubility, Amino Acid Profile, Molecular weight, Codon, Production System, Base Sequence, Recombinant Protein, PLANT PROTEINS, *Hot Temperature, Biochemistry and cell biology, and Isoelectric point
Gprotein-coupled receptors mediate responses to a myriad of ligands, some of which regulate adipocyte differentiation and metabolism. The sweet taste receptors T1R2 and T1R3 are G protein-coupled receptors that function as carbohydrate... more
Gprotein-coupled receptors mediate responses to a myriad of
ligands, some of which regulate adipocyte differentiation and
metabolism. The sweet taste receptors T1R2 and T1R3 are G
protein-coupled receptors that function as carbohydrate sensors
in taste buds, gut, and pancreas. Here we report that sweet
taste receptors T1R2 and T1R3 are expressed throughout adipogenesis
and in adipose tissues. Treatment of mouse and
human precursor cells with artificial sweeteners, saccharin and
acesulfame potassium, enhanced adipogenesis. Saccharin treatment
of 3T3-L1 cells and primary mesenchymal stem cells rapidly
stimulated phosphorylation of Akt and downstream targets
with functions in adipogenesis such as cAMP-response element-
binding protein and FOXO1; however, increased expression
of peroxisome proliferator-activated receptor and
CCAAT/enhancer-binding protein was not observed until relatively
late in differentiation. Saccharin-stimulated Akt phosphorylation
at Thr-308 occurred within 5 min, was phosphatidylinositol
3-kinase-dependent, and occurred in the presence of
high concentrations of insulin and dexamethasone; phosphorylation
of Ser-473 occurred more gradually. Surprisingly, neither
saccharin-stimulated adipogenesis nor Thr-308 phosphorylation
was dependent on expression of T1R2 and/or T1R3,
although Ser-473 phosphorylation was impaired in T1R2/T1R3 double knock-out precursors. In mature adipocytes, artificial
sweetener treatment suppressed lipolysis even in the presence
of forskolin, and lipolytic responses were correlated with phosphorylation
of hormone-sensitive lipase. Suppression of lipolysis
by saccharin in adipocytes was also independent of T1R2 and
T1R3. These results suggest that some artificial sweeteners have
previously uncharacterized metabolic effects on adipocyte differentiation
and metabolism and that effects of artificial sweeteners
on adipose tissue biology may be largely independent of
the classical sweet taste receptors, T1R2 and T1R3.
ligands, some of which regulate adipocyte differentiation and
metabolism. The sweet taste receptors T1R2 and T1R3 are G
protein-coupled receptors that function as carbohydrate sensors
in taste buds, gut, and pancreas. Here we report that sweet
taste receptors T1R2 and T1R3 are expressed throughout adipogenesis
and in adipose tissues. Treatment of mouse and
human precursor cells with artificial sweeteners, saccharin and
acesulfame potassium, enhanced adipogenesis. Saccharin treatment
of 3T3-L1 cells and primary mesenchymal stem cells rapidly
stimulated phosphorylation of Akt and downstream targets
with functions in adipogenesis such as cAMP-response element-
binding protein and FOXO1; however, increased expression
of peroxisome proliferator-activated receptor and
CCAAT/enhancer-binding protein was not observed until relatively
late in differentiation. Saccharin-stimulated Akt phosphorylation
at Thr-308 occurred within 5 min, was phosphatidylinositol
3-kinase-dependent, and occurred in the presence of
high concentrations of insulin and dexamethasone; phosphorylation
of Ser-473 occurred more gradually. Surprisingly, neither
saccharin-stimulated adipogenesis nor Thr-308 phosphorylation
was dependent on expression of T1R2 and/or T1R3,
although Ser-473 phosphorylation was impaired in T1R2/T1R3 double knock-out precursors. In mature adipocytes, artificial
sweetener treatment suppressed lipolysis even in the presence
of forskolin, and lipolytic responses were correlated with phosphorylation
of hormone-sensitive lipase. Suppression of lipolysis
by saccharin in adipocytes was also independent of T1R2 and
T1R3. These results suggest that some artificial sweeteners have
previously uncharacterized metabolic effects on adipocyte differentiation
and metabolism and that effects of artificial sweeteners
on adipose tissue biology may be largely independent of
the classical sweet taste receptors, T1R2 and T1R3.
Research Interests: Signal Transduction, Carbon Isotopes, Escherichia coli, Affinity chromatography, Nmr Structure, and 15 moreNitrogen Isotopes, Phosphodiesterase Inhibitors, Glycerol, Protein expression and purification, Spectrum, Protein Expression, Atomic Structure, Large Scale, Amino Acid Sequence, Recombinant Protein, Recombinant Proteins, Isotope Labeling, Full Length Movies, Transducin, and Biochemistry and cell biology
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Six sweet proteins have been discovered over the last 30 years. The latest discovered is brazzein, isolated from the fruit of Pentadiplandra brazzeana Baillon [2]. Brazzein is a single-chain polypeptide of 54 amino acid residues with four... more
Six sweet proteins have been discovered over the last 30 years. The latest discovered is brazzein, isolated from the fruit of Pentadiplandra brazzeana Baillon [2]. Brazzein is a single-chain polypeptide of 54 amino acid residues with four intramolecular disulfide ...