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Deletion of the alpha-arrestin protein Txnip in mice promotes adiposity and adipogenesis while preserving insulin sensitivity.

Chutkow WA, Birkenfeld AL, Brown JD, Lee HY, Frederick DW, Yoshioka J, Patwari P, Kursawe R, Cushman SW, Plutzky J, Shulman GI, Samuel VT, Lee RT - Diabetes (2010)

Bottom Line: Thioredoxin interacting protein (Txnip), a regulator of cellular oxidative stress, is induced by hyperglycemia and inhibits glucose uptake into fat and muscle, suggesting a role for Txnip in type 2 diabetes pathogenesis.RNA interference gene-silenced preadipocytes and Txnip(-/-) MEFs were markedly adipogenic, whereas Txnip overexpression impaired adipocyte differentiation.As increased adipogenesis and insulin sensitivity suggested aspects of augmented peroxisome proliferator-activated receptor-gamma (PPARgamma) response, we investigated Txnip's regulation of PPARgamma function; manipulation of Txnip expression directly regulated PPARgamma expression and activity.

View Article: PubMed Central - PubMed

Affiliation: Cardiovascular Division, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Cambridge, Massachusetts, USA.

ABSTRACT

Objective: Thioredoxin interacting protein (Txnip), a regulator of cellular oxidative stress, is induced by hyperglycemia and inhibits glucose uptake into fat and muscle, suggesting a role for Txnip in type 2 diabetes pathogenesis. Here, we tested the hypothesis that Txnip- (knockout) mice are protected from insulin resistance induced by a high-fat diet.

Research design and methods: Txnip gene-deleted (knockout) mice and age-matched wild-type littermate control mice were maintained on a standard chow diet or subjected to 4 weeks of high-fat feeding. Mice were assessed for body composition, fat development, energy balance, and insulin responsiveness. Adipogenesis was measured from ex vivo fat preparations, and in mouse embryonic fibroblasts (MEFs) and 3T3-L1 preadipocytes after forced manipulation of Txnip expression.

Results: Txnip knockout mice gained significantly more adipose mass than controls due to a primary increase in both calorie consumption and adipogenesis. Despite increased fat mass, Txnip knockout mice were markedly more insulin sensitive than controls, and augmented glucose transport was identified in both adipose and skeletal muscle. RNA interference gene-silenced preadipocytes and Txnip(-/-) MEFs were markedly adipogenic, whereas Txnip overexpression impaired adipocyte differentiation. As increased adipogenesis and insulin sensitivity suggested aspects of augmented peroxisome proliferator-activated receptor-gamma (PPARgamma) response, we investigated Txnip's regulation of PPARgamma function; manipulation of Txnip expression directly regulated PPARgamma expression and activity.

Conclusions: Txnip deletion promotes adiposity in the face of high-fat caloric excess; however, loss of this alpha-arrestin protein simultaneously enhances insulin responsiveness in fat and skeletal muscle, revealing Txnip as a novel mediator of insulin resistance and a regulator of adipogenesis.

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High-fat feeding preferentially promotes PPARγ target gene expression in Txnip- WAT. A: mRNA transcript expression of PPARγ target genes and PPARγ2 in WAT before and after high-fat feeding. n = 8–12 mice per group for each transcript. AP2, fatty acid binding protein 4; PC, pyruvate carboxylase; PEPCK, phosphoenolpyruvate carboxykinase; ACC-α, acetyl-CoA carboxylase-α; FAS, fatty acid synthase; LPL, lipoprotein lipase. B: Transcript expression levels for non-PPARγ target genes PCG1α and UCP2 after HFD. C and D: Adiponectin, leptin, and GLUT transcript expression levels in WAT after SCD vs. HFD. n = 8–12 mice per group.
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Figure 6: High-fat feeding preferentially promotes PPARγ target gene expression in Txnip- WAT. A: mRNA transcript expression of PPARγ target genes and PPARγ2 in WAT before and after high-fat feeding. n = 8–12 mice per group for each transcript. AP2, fatty acid binding protein 4; PC, pyruvate carboxylase; PEPCK, phosphoenolpyruvate carboxykinase; ACC-α, acetyl-CoA carboxylase-α; FAS, fatty acid synthase; LPL, lipoprotein lipase. B: Transcript expression levels for non-PPARγ target genes PCG1α and UCP2 after HFD. C and D: Adiponectin, leptin, and GLUT transcript expression levels in WAT after SCD vs. HFD. n = 8–12 mice per group.

Mentions: In vivo expression of WAT adipogenic and lipogenic PPARγ target genes was measured in SCD-fed and HFD-fed mice to determine whether HFD potentiated PPARγ activation in Txnip- mice. AP2, CD36, pyruvate carboxylase, fatty acid synthase, phosphoenolpyruvate carboxykinase, lipoprotein lipase, and acetyl-CoA carboxylase-α are known adipogenic and lipogenic PPARγ target genes (30). After 4 weeks of HFD, these PPARγ targets were uniformly upregulated in Txnip knockout HFD-fed adipose tissue relative to Txnip knockout SCD-fed adipose tissue, and HFD Txnip knockout transcript levels were consistently greater than HFD-fed wild-type expression levels (n = 8–12 per group, P < 0.01, Fig. 6A). PGC1α and UCP2 expressions were measured, as the two genes influence lipid metabolism, adiposity, and energy balance, but are not PPARγ targets (31,32). No significant differences in expression were detected for either gene on SCD or after HFD (Fig. 6B). Although HFD-fed Txnip knockout serum adiponectin levels were lower than wild type, adiponectin transcript levels in Txnip knockout HFD-fed adipose were increased relative to wild-type mice, suggesting regulation of, or a defect in, adiponectin translation, protein stability, and/or secretion (Fig. 6C). Similarly, leptin transcript levels in HFD-fed Txnip knockout and wild-type adipose were equivalent, although Txnip knockout serum leptin levels were lower (Fig. 6C). GLUT mRNA levels for the insulin-regulated (and known PPARγ target) GLUT4 and the constitutively expressed GLUT1 were also determined. GLUT1 expression trended downward for both mice after HFD, but GLUT4 expression was significantly increased in Txnip knockout WAT relative to wild type after high-fat diet. Wild-type GLUT4 levels were reduced by 40% after HFD, whereas Txnip knockout post-HFD levels increased 1.6-fold (P < 0.01, Fig. 6D). Finally, we examined both PPARγ and Txnip expression, as PPARγ expression is influenced by its own activation (33), and Txnip expression is augmented in states of insulin resistance (16). High-fat diet increased PPARγ2 expression in Txnip knockout WAT by 1.7-fold (P < 0.01, Fig. 6A). In wild-type WAT, high-fat feeding increased Txnip expression 1.4-fold (P < 0.01, supplementary Fig. 4B). These data support the concept that Txnip deletion augments adipogenic and lipogenic programs in WAT in vivo after high-fat feeding by preferentially augmenting PPARγ activation. HFD-induced Txnip expression may play a role in suppressing dietary PPARγ activation to impede adipogenesis in the face of positive energy balance, resulting in diet-induced insulin resistance.


Deletion of the alpha-arrestin protein Txnip in mice promotes adiposity and adipogenesis while preserving insulin sensitivity.

Chutkow WA, Birkenfeld AL, Brown JD, Lee HY, Frederick DW, Yoshioka J, Patwari P, Kursawe R, Cushman SW, Plutzky J, Shulman GI, Samuel VT, Lee RT - Diabetes (2010)

High-fat feeding preferentially promotes PPARγ target gene expression in Txnip- WAT. A: mRNA transcript expression of PPARγ target genes and PPARγ2 in WAT before and after high-fat feeding. n = 8–12 mice per group for each transcript. AP2, fatty acid binding protein 4; PC, pyruvate carboxylase; PEPCK, phosphoenolpyruvate carboxykinase; ACC-α, acetyl-CoA carboxylase-α; FAS, fatty acid synthase; LPL, lipoprotein lipase. B: Transcript expression levels for non-PPARγ target genes PCG1α and UCP2 after HFD. C and D: Adiponectin, leptin, and GLUT transcript expression levels in WAT after SCD vs. HFD. n = 8–12 mice per group.
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Figure 6: High-fat feeding preferentially promotes PPARγ target gene expression in Txnip- WAT. A: mRNA transcript expression of PPARγ target genes and PPARγ2 in WAT before and after high-fat feeding. n = 8–12 mice per group for each transcript. AP2, fatty acid binding protein 4; PC, pyruvate carboxylase; PEPCK, phosphoenolpyruvate carboxykinase; ACC-α, acetyl-CoA carboxylase-α; FAS, fatty acid synthase; LPL, lipoprotein lipase. B: Transcript expression levels for non-PPARγ target genes PCG1α and UCP2 after HFD. C and D: Adiponectin, leptin, and GLUT transcript expression levels in WAT after SCD vs. HFD. n = 8–12 mice per group.
Mentions: In vivo expression of WAT adipogenic and lipogenic PPARγ target genes was measured in SCD-fed and HFD-fed mice to determine whether HFD potentiated PPARγ activation in Txnip- mice. AP2, CD36, pyruvate carboxylase, fatty acid synthase, phosphoenolpyruvate carboxykinase, lipoprotein lipase, and acetyl-CoA carboxylase-α are known adipogenic and lipogenic PPARγ target genes (30). After 4 weeks of HFD, these PPARγ targets were uniformly upregulated in Txnip knockout HFD-fed adipose tissue relative to Txnip knockout SCD-fed adipose tissue, and HFD Txnip knockout transcript levels were consistently greater than HFD-fed wild-type expression levels (n = 8–12 per group, P < 0.01, Fig. 6A). PGC1α and UCP2 expressions were measured, as the two genes influence lipid metabolism, adiposity, and energy balance, but are not PPARγ targets (31,32). No significant differences in expression were detected for either gene on SCD or after HFD (Fig. 6B). Although HFD-fed Txnip knockout serum adiponectin levels were lower than wild type, adiponectin transcript levels in Txnip knockout HFD-fed adipose were increased relative to wild-type mice, suggesting regulation of, or a defect in, adiponectin translation, protein stability, and/or secretion (Fig. 6C). Similarly, leptin transcript levels in HFD-fed Txnip knockout and wild-type adipose were equivalent, although Txnip knockout serum leptin levels were lower (Fig. 6C). GLUT mRNA levels for the insulin-regulated (and known PPARγ target) GLUT4 and the constitutively expressed GLUT1 were also determined. GLUT1 expression trended downward for both mice after HFD, but GLUT4 expression was significantly increased in Txnip knockout WAT relative to wild type after high-fat diet. Wild-type GLUT4 levels were reduced by 40% after HFD, whereas Txnip knockout post-HFD levels increased 1.6-fold (P < 0.01, Fig. 6D). Finally, we examined both PPARγ and Txnip expression, as PPARγ expression is influenced by its own activation (33), and Txnip expression is augmented in states of insulin resistance (16). High-fat diet increased PPARγ2 expression in Txnip knockout WAT by 1.7-fold (P < 0.01, Fig. 6A). In wild-type WAT, high-fat feeding increased Txnip expression 1.4-fold (P < 0.01, supplementary Fig. 4B). These data support the concept that Txnip deletion augments adipogenic and lipogenic programs in WAT in vivo after high-fat feeding by preferentially augmenting PPARγ activation. HFD-induced Txnip expression may play a role in suppressing dietary PPARγ activation to impede adipogenesis in the face of positive energy balance, resulting in diet-induced insulin resistance.

Bottom Line: Thioredoxin interacting protein (Txnip), a regulator of cellular oxidative stress, is induced by hyperglycemia and inhibits glucose uptake into fat and muscle, suggesting a role for Txnip in type 2 diabetes pathogenesis.RNA interference gene-silenced preadipocytes and Txnip(-/-) MEFs were markedly adipogenic, whereas Txnip overexpression impaired adipocyte differentiation.As increased adipogenesis and insulin sensitivity suggested aspects of augmented peroxisome proliferator-activated receptor-gamma (PPARgamma) response, we investigated Txnip's regulation of PPARgamma function; manipulation of Txnip expression directly regulated PPARgamma expression and activity.

View Article: PubMed Central - PubMed

Affiliation: Cardiovascular Division, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Cambridge, Massachusetts, USA.

ABSTRACT

Objective: Thioredoxin interacting protein (Txnip), a regulator of cellular oxidative stress, is induced by hyperglycemia and inhibits glucose uptake into fat and muscle, suggesting a role for Txnip in type 2 diabetes pathogenesis. Here, we tested the hypothesis that Txnip- (knockout) mice are protected from insulin resistance induced by a high-fat diet.

Research design and methods: Txnip gene-deleted (knockout) mice and age-matched wild-type littermate control mice were maintained on a standard chow diet or subjected to 4 weeks of high-fat feeding. Mice were assessed for body composition, fat development, energy balance, and insulin responsiveness. Adipogenesis was measured from ex vivo fat preparations, and in mouse embryonic fibroblasts (MEFs) and 3T3-L1 preadipocytes after forced manipulation of Txnip expression.

Results: Txnip knockout mice gained significantly more adipose mass than controls due to a primary increase in both calorie consumption and adipogenesis. Despite increased fat mass, Txnip knockout mice were markedly more insulin sensitive than controls, and augmented glucose transport was identified in both adipose and skeletal muscle. RNA interference gene-silenced preadipocytes and Txnip(-/-) MEFs were markedly adipogenic, whereas Txnip overexpression impaired adipocyte differentiation. As increased adipogenesis and insulin sensitivity suggested aspects of augmented peroxisome proliferator-activated receptor-gamma (PPARgamma) response, we investigated Txnip's regulation of PPARgamma function; manipulation of Txnip expression directly regulated PPARgamma expression and activity.

Conclusions: Txnip deletion promotes adiposity in the face of high-fat caloric excess; however, loss of this alpha-arrestin protein simultaneously enhances insulin responsiveness in fat and skeletal muscle, revealing Txnip as a novel mediator of insulin resistance and a regulator of adipogenesis.

Show MeSH
Related in: MedlinePlus