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Nonthyrotoxic prevention of diet-induced insulin resistance by 3,5-diiodo-L-thyronine in rats.

de Lange P, Cioffi F, Senese R, Moreno M, Lombardi A, Silvestri E, De Matteis R, Lionetti L, Mollica MP, Goglia F, Lanni A - Diabetes (2011)

Bottom Line: T2 did so by rapidly stimulating hepatic fatty acid oxidation, decreasing hepatic triglyceride levels, and improving the serum lipid profile, while at the same time sparing skeletal muscle from fat accumulation.At the mechanistic level, 1) transfection studies show that T2 does not act via thyroid hormone receptor β; 2) AMP-activated protein kinase is not involved in triggering the effects of T2; 3) in HFD rats, T2 rapidly increases hepatic nuclear sirtuin 1 (SIRT1) activity; 4) in an in vitro assay, T2 directly activates SIRT1; and 5) the SIRT1 targets peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC-1α) and sterol regulatory element-binding protein (SREBP)-1c are deacetylated with concomitant upregulation of genes involved in mitochondrial biogenesis and downregulation of lipogenic genes, and PPARα/δ-induced genes are upregulated, whereas genes involved in hepatic gluconeogenesis are downregulated.Proteomic analysis of the hepatic protein profile supported these changes.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Scienze della Vita, Seconda Università degli Studi di Napoli, Caserta, Italy.

ABSTRACT

Objective: High-fat diets (HFDs) are known to induce insulin resistance. Previously, we showed that 3,5-diiodothyronine (T2), concomitantly administered to rats on a 4-week HFD, prevented gain in body weight and adipose mass. Here we investigated whether and how T2 prevented HFD-induced insulin resistance.

Research design and methods: We investigated the biochemical targets of T2 related to lipid and glucose homeostasis over time using various techniques, including genomic and proteomic profiling, immunoblotting, transient transfection, and enzyme activity analysis.

Results: Here we show that, in rats, HFD feeding induced insulin resistance (as expected), whereas T2 administration prevented its onset. T2 did so by rapidly stimulating hepatic fatty acid oxidation, decreasing hepatic triglyceride levels, and improving the serum lipid profile, while at the same time sparing skeletal muscle from fat accumulation. At the mechanistic level, 1) transfection studies show that T2 does not act via thyroid hormone receptor β; 2) AMP-activated protein kinase is not involved in triggering the effects of T2; 3) in HFD rats, T2 rapidly increases hepatic nuclear sirtuin 1 (SIRT1) activity; 4) in an in vitro assay, T2 directly activates SIRT1; and 5) the SIRT1 targets peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC-1α) and sterol regulatory element-binding protein (SREBP)-1c are deacetylated with concomitant upregulation of genes involved in mitochondrial biogenesis and downregulation of lipogenic genes, and PPARα/δ-induced genes are upregulated, whereas genes involved in hepatic gluconeogenesis are downregulated. Proteomic analysis of the hepatic protein profile supported these changes.

Conclusions: T2, by activating SIRT1, triggers a cascade of events resulting in improvement of the serum lipid profile, prevention of fat accumulation, and, finally, prevention of diet-induced insulin resistance.

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Related in: MedlinePlus

T2 rapidly prevents hepatic and serum fat accumulation. A: Hepatic fat accumulation (assessed by Sudan black staining) is prevented by T2 administration to rats simultaneously fed an HFD. B: T2 rapidly normalizes levels of nonesterified fatty acids, triglycerides, and cholesterol. Levels were measured at the indicated time points after T2 injection. C: Hepatic mitochondrial fatty acid oxidation (FFA OX) rapidly increases in response to T2 treatment. D: Phosphorylation of AMPK (Thr172) increases only after 4 weeks of T2 treatment, and phosphorylation of Akt (Ser473) does not change in response to T2 treatment. Representative blots are shown. The histograms represent values obtained after 4 weeks of treatment. E: T2 normalizes serum adiponectin levels. F: After 4 weeks, neither HFD nor HFD-T2 treatment alters insulin-induced hepatic Akt (Ser473) phosphorylation with respect to controls (N). Error bars represent SEM. *P < 0.05 vs. untreated controls; **P < 0.05 vs. both untreated controls and HFD-fed groups; ***P < 0.05 vs. HFD-fed group; #P < 0.05 vs. sham-injected animals. B: △, N; ◇, HFD; □, HFD-T2. C–F: □, N; ■, HFD; ▨, HFD-T2; prot, protein. (A high-quality color representation of this figure is available in the online issue.)
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Figure 2: T2 rapidly prevents hepatic and serum fat accumulation. A: Hepatic fat accumulation (assessed by Sudan black staining) is prevented by T2 administration to rats simultaneously fed an HFD. B: T2 rapidly normalizes levels of nonesterified fatty acids, triglycerides, and cholesterol. Levels were measured at the indicated time points after T2 injection. C: Hepatic mitochondrial fatty acid oxidation (FFA OX) rapidly increases in response to T2 treatment. D: Phosphorylation of AMPK (Thr172) increases only after 4 weeks of T2 treatment, and phosphorylation of Akt (Ser473) does not change in response to T2 treatment. Representative blots are shown. The histograms represent values obtained after 4 weeks of treatment. E: T2 normalizes serum adiponectin levels. F: After 4 weeks, neither HFD nor HFD-T2 treatment alters insulin-induced hepatic Akt (Ser473) phosphorylation with respect to controls (N). Error bars represent SEM. *P < 0.05 vs. untreated controls; **P < 0.05 vs. both untreated controls and HFD-fed groups; ***P < 0.05 vs. HFD-fed group; #P < 0.05 vs. sham-injected animals. B: △, N; ◇, HFD; □, HFD-T2. C–F: □, N; ■, HFD; ▨, HFD-T2; prot, protein. (A high-quality color representation of this figure is available in the online issue.)

Mentions: A 6-h exposure to the HFD already induced a substantial lipid-droplet accumulation. In contrast, this effect was lacking in the HFD-T2 group at that time point (Fig. 2A) and indeed at time points of up to 4 weeks (maximum treatment period) (Fig. 2A). Importantly, T2 treatment consistently prevented the HFD-dependent increases in serum cholesterol, triglycerides, and nonesterified fatty acids (Fig. 2B). Accordingly, mitochondrial free fatty acid oxidation was already elevated by T2 at the 6-h time point, and this increase persisted throughout the treatment period (Fig. 2C). We did not observe increases in AMPK phosphorylation in the HFD-T2 rats in the investigated time points up to 2 weeks of treatment. Actually, AMPK phosphorylation was lower in the HFD and HFD-T2 rats than in the N controls. Only after 4 weeks of treatment was there a T2-induced increase in AMPK phosphorylation toward N levels (Fig. 2D), and at that time point, plasma adiponectin levels were elevated, too (Fig. 2E). Basal hepatic Akt phosphorylation (Ser473) did not change during feeding on the HFD (Fig. 2D), and it was not inhibited in response to insulin after 4 weeks of HFD treatment (Fig. 2F). T2 had no apparent effect on this result. The plasma ALT level, well documented as a marker of hepatocyte damage, was significantly (P < 0.05) elevated in HFD rats, whereas administration of T2 to HFD rats prevented this increase (actual values: 38 ± 1.3, 47 ± 2.0, and 36 ± 1.0 units/L for N, HFD, and HFD-T2 groups, respectively).


Nonthyrotoxic prevention of diet-induced insulin resistance by 3,5-diiodo-L-thyronine in rats.

de Lange P, Cioffi F, Senese R, Moreno M, Lombardi A, Silvestri E, De Matteis R, Lionetti L, Mollica MP, Goglia F, Lanni A - Diabetes (2011)

T2 rapidly prevents hepatic and serum fat accumulation. A: Hepatic fat accumulation (assessed by Sudan black staining) is prevented by T2 administration to rats simultaneously fed an HFD. B: T2 rapidly normalizes levels of nonesterified fatty acids, triglycerides, and cholesterol. Levels were measured at the indicated time points after T2 injection. C: Hepatic mitochondrial fatty acid oxidation (FFA OX) rapidly increases in response to T2 treatment. D: Phosphorylation of AMPK (Thr172) increases only after 4 weeks of T2 treatment, and phosphorylation of Akt (Ser473) does not change in response to T2 treatment. Representative blots are shown. The histograms represent values obtained after 4 weeks of treatment. E: T2 normalizes serum adiponectin levels. F: After 4 weeks, neither HFD nor HFD-T2 treatment alters insulin-induced hepatic Akt (Ser473) phosphorylation with respect to controls (N). Error bars represent SEM. *P < 0.05 vs. untreated controls; **P < 0.05 vs. both untreated controls and HFD-fed groups; ***P < 0.05 vs. HFD-fed group; #P < 0.05 vs. sham-injected animals. B: △, N; ◇, HFD; □, HFD-T2. C–F: □, N; ■, HFD; ▨, HFD-T2; prot, protein. (A high-quality color representation of this figure is available in the online issue.)
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198093&req=5

Figure 2: T2 rapidly prevents hepatic and serum fat accumulation. A: Hepatic fat accumulation (assessed by Sudan black staining) is prevented by T2 administration to rats simultaneously fed an HFD. B: T2 rapidly normalizes levels of nonesterified fatty acids, triglycerides, and cholesterol. Levels were measured at the indicated time points after T2 injection. C: Hepatic mitochondrial fatty acid oxidation (FFA OX) rapidly increases in response to T2 treatment. D: Phosphorylation of AMPK (Thr172) increases only after 4 weeks of T2 treatment, and phosphorylation of Akt (Ser473) does not change in response to T2 treatment. Representative blots are shown. The histograms represent values obtained after 4 weeks of treatment. E: T2 normalizes serum adiponectin levels. F: After 4 weeks, neither HFD nor HFD-T2 treatment alters insulin-induced hepatic Akt (Ser473) phosphorylation with respect to controls (N). Error bars represent SEM. *P < 0.05 vs. untreated controls; **P < 0.05 vs. both untreated controls and HFD-fed groups; ***P < 0.05 vs. HFD-fed group; #P < 0.05 vs. sham-injected animals. B: △, N; ◇, HFD; □, HFD-T2. C–F: □, N; ■, HFD; ▨, HFD-T2; prot, protein. (A high-quality color representation of this figure is available in the online issue.)
Mentions: A 6-h exposure to the HFD already induced a substantial lipid-droplet accumulation. In contrast, this effect was lacking in the HFD-T2 group at that time point (Fig. 2A) and indeed at time points of up to 4 weeks (maximum treatment period) (Fig. 2A). Importantly, T2 treatment consistently prevented the HFD-dependent increases in serum cholesterol, triglycerides, and nonesterified fatty acids (Fig. 2B). Accordingly, mitochondrial free fatty acid oxidation was already elevated by T2 at the 6-h time point, and this increase persisted throughout the treatment period (Fig. 2C). We did not observe increases in AMPK phosphorylation in the HFD-T2 rats in the investigated time points up to 2 weeks of treatment. Actually, AMPK phosphorylation was lower in the HFD and HFD-T2 rats than in the N controls. Only after 4 weeks of treatment was there a T2-induced increase in AMPK phosphorylation toward N levels (Fig. 2D), and at that time point, plasma adiponectin levels were elevated, too (Fig. 2E). Basal hepatic Akt phosphorylation (Ser473) did not change during feeding on the HFD (Fig. 2D), and it was not inhibited in response to insulin after 4 weeks of HFD treatment (Fig. 2F). T2 had no apparent effect on this result. The plasma ALT level, well documented as a marker of hepatocyte damage, was significantly (P < 0.05) elevated in HFD rats, whereas administration of T2 to HFD rats prevented this increase (actual values: 38 ± 1.3, 47 ± 2.0, and 36 ± 1.0 units/L for N, HFD, and HFD-T2 groups, respectively).

Bottom Line: T2 did so by rapidly stimulating hepatic fatty acid oxidation, decreasing hepatic triglyceride levels, and improving the serum lipid profile, while at the same time sparing skeletal muscle from fat accumulation.At the mechanistic level, 1) transfection studies show that T2 does not act via thyroid hormone receptor β; 2) AMP-activated protein kinase is not involved in triggering the effects of T2; 3) in HFD rats, T2 rapidly increases hepatic nuclear sirtuin 1 (SIRT1) activity; 4) in an in vitro assay, T2 directly activates SIRT1; and 5) the SIRT1 targets peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC-1α) and sterol regulatory element-binding protein (SREBP)-1c are deacetylated with concomitant upregulation of genes involved in mitochondrial biogenesis and downregulation of lipogenic genes, and PPARα/δ-induced genes are upregulated, whereas genes involved in hepatic gluconeogenesis are downregulated.Proteomic analysis of the hepatic protein profile supported these changes.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Scienze della Vita, Seconda Università degli Studi di Napoli, Caserta, Italy.

ABSTRACT

Objective: High-fat diets (HFDs) are known to induce insulin resistance. Previously, we showed that 3,5-diiodothyronine (T2), concomitantly administered to rats on a 4-week HFD, prevented gain in body weight and adipose mass. Here we investigated whether and how T2 prevented HFD-induced insulin resistance.

Research design and methods: We investigated the biochemical targets of T2 related to lipid and glucose homeostasis over time using various techniques, including genomic and proteomic profiling, immunoblotting, transient transfection, and enzyme activity analysis.

Results: Here we show that, in rats, HFD feeding induced insulin resistance (as expected), whereas T2 administration prevented its onset. T2 did so by rapidly stimulating hepatic fatty acid oxidation, decreasing hepatic triglyceride levels, and improving the serum lipid profile, while at the same time sparing skeletal muscle from fat accumulation. At the mechanistic level, 1) transfection studies show that T2 does not act via thyroid hormone receptor β; 2) AMP-activated protein kinase is not involved in triggering the effects of T2; 3) in HFD rats, T2 rapidly increases hepatic nuclear sirtuin 1 (SIRT1) activity; 4) in an in vitro assay, T2 directly activates SIRT1; and 5) the SIRT1 targets peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC-1α) and sterol regulatory element-binding protein (SREBP)-1c are deacetylated with concomitant upregulation of genes involved in mitochondrial biogenesis and downregulation of lipogenic genes, and PPARα/δ-induced genes are upregulated, whereas genes involved in hepatic gluconeogenesis are downregulated. Proteomic analysis of the hepatic protein profile supported these changes.

Conclusions: T2, by activating SIRT1, triggers a cascade of events resulting in improvement of the serum lipid profile, prevention of fat accumulation, and, finally, prevention of diet-induced insulin resistance.

Show MeSH
Related in: MedlinePlus