Reduction of hepatic glucocorticoid receptor and hexose-6-phosphate dehydrogenase expression ameliorates diet-induced obesity and insulin resistance in mice - PubMed (original) (raw)

Reduction of hepatic glucocorticoid receptor and hexose-6-phosphate dehydrogenase expression ameliorates diet-induced obesity and insulin resistance in mice

Yanjun Liu et al. J Mol Endocrinol. 2008 Aug.

Abstract

Intracellular glucocorticoid (GC) receptor (GR) function determines tissue sensitivity to GCs and strongly affects the development of type 2 diabetes and obesity. 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) mediates intracellular steroid exposure to mouse liver GR by prereceptor reactivation of GCs and is crucially dependent on hexose-6-phosphate dehydrogenase (H6PDH)-generating NADPH system. Pharmacological inhibition of 11beta-HSD1 improves insulin intolerance and obesity. Here, we evaluated the potential beneficial effects of 11beta-HSD1 inhibitor carbenoxolone (CBX) in diet-induced obese (DIO) and insulin-resistant mice by examining the possible influence of CBX on the expression of GR, 11beta-HSD1, and H6PDH in vivo and in vitro in hepatocytes. Treatment of DIO mice with CBX markedly reduced hepatic GR mRNA levels and reduced weight gain, hyperglycemia, and insulin resistance. The reduction of hepatic GR gene expression was accompanied by CBX-induced inhibition of both 11beta-HSD1 and H6PDH activity and mRNA in the liver. Moreover, CBX treatment also suppressed the expression of both phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase enzyme (G6Pase) mRNA and improved hepatic [1, 2-(3)H] deoxy-d-glucose uptake in DIO mice. In addition, the treatment of primary cultures of hepatocytes with increasing concentrations of CBX led to a dose-dependent downregulation of GR mRNA levels, which correlated with the suppression of both 11beta-HSD1 and H6PDH activity and their gene expression. Addition of CBX to primary hepatocytes also resulted in suppression of both PEPCK and G6Pase mRNA levels. These findings suggest that CBX exerts some of its beneficial effects, at least in part, by inhibiting hepatic GR and H6PDH expression.

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Conflict of interest statement

The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.

Figures

Figure 1

Glucose tolerance test (A) and Insulin tolerance test (B) in DIO mice treated with vehicle (□– –DIO), DIO mice treated with CBX (♦– –DIO+CBX), lean mice treated with vehicle (Δ– – Lean), and lean mice treated with CBX (●—Lean+CBX). Data are mean±

s.e.m.

of 7–8 mice/group. (A) *P<0·001 versus lean control; **P<0·01 versus DIO controls; #P<0·01 versus lean controls. (B) **P<0·01 versus CBX-treated DIO mice or lean controls; ##P<0·01 versus vehicle-treated lean mice; #P<0·05 versus vehicle-treated lean mice.

Figure 2

The effects of CBX on the hepatic 2-[3H]DG uptake (A) and the expression of both PEPCK (B) and G6Pase (C) mRNA in lean and DIO mice. Data are mean±

s.e.m.

of 7–8 mice/group. *P<0·01 versus lean controls; †P<0·001 versus DIO controls; ##P<0·05 versus lean controls; #P<0·01 versus DIO controls; &P<0·05 versus lean controls; **P<0·01 versus DIO controls.

Figure 3

The inhibitory effects of CBX on 11β-HSD1 activity (A) and mRNA expression (B), as well as GR mRNA (C) and protein expression (D) in liver of lean and DIO mice. (A) Enzyme activity expressed as percent of [3H]B to [3H]A. (B) Expression and relative quantification of 11β-HSD1 and GR mRNA levels was determined by semiquantitative RT-PCR and are expressed relative to the amount of 18S rRNA. Data are mean±

s.e.m.

of 6–7 mice/group. *P<0·01 versus lean controls; #P<0·001 versus DIO controls; ¶P<0·05 versus lean controls; **P<0·01 versus DIO controls; †P<0·001 versus lean controls.

Figure 4

Hepatic H6PDH activity (A) and mRNA expression (B) in lean and DIO mice treated with vehicle or CBX. (A) Enzyme activity was measured in liver tissue on the basis of NADPH formation using 2 mM G6P as substrate in the presence of NADP. (B) Expression and relative quantification of mRNA levels was done relative to the amount of 18S rRNA. Data are mean±

s.e.m.

of 5–6 mice/group. *P<0·05 versus lean controls; **P<0·01 versus DIO controls; ##P<0·005 versus DIO control.

Figure 5

Inhibition of GR mRNA expression (A) in response to the suppression of 11β-HSD1 reductase activity (B) and mRNA expression (C) by CBX. Primary hepatocytes were incubated with increased concentrations of CBX for 48 h. (A) 11β-HSD1 reductase activity was expressed as the percentage of [3H]A converted to [3H]B in medium from hepatocytes. (B) The levels of GR and 11β-HSD1 and mRNA expression, determined by quantitative RT-PCR, were expressed relative to the amount of 18S. Values are the mean±

s.e.m.

from three separate culture preparations.*P<0·05 versus controls; **P<0·01 versus control; #P<0·001 versus controls; ##P<0·005 versus controls.

Figure 6

The effects of CBX on PEPCK (A) and G6Pase (B) mRNA in primary cultures of hepatocytes. Expression and relative quantification of mRNA levels was done relative to the amount of 18S rRNA. Values are the mean±

s.e.m.

from three separate culture preparations. *P<0·05 versus controls; **P<0·01 versus controls; #P<0·001 versus controls.

Figure 7

The inhibitory effects of CBX on H6PDH protein expression (A) and mRNA (B) and activity (C) in primary cultures of hepatocytes. (A) Expression and relative quantification of H6PDH protein levels expressed relative to the amount of GAPDH. (B) Expression and relative quantitation of H6PDH mRNA levels expressed relative to the amount of 18S rRNA. (C) Relative H6PDH activity was measured on the basis of NADPH production at 5-min intervals for 25 min. Values are the mean±

s.e.m.

from three separate culture preparations. **P<0·01 versus controls; †P<0·001 versus controls; *P<0·05 versus controls.

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Reduction of hepatic glucocorticoid receptor and hexose-6-phosphate dehydrogenase expression ameliorates diet-induced obesity and insulin resistance in mice - PubMed (original) (raw)