Kerry McInnes

Prenatal Dexamethasone Programs Expression of Genes in Liver and Adipose Tissue and Increased Hepatic Lipid Accumulation But Not Obesity on a High-Fat Diet

The association between low birth weight and cardiovascular disease is amplified by the development of obesity. We explored the effects of postnatal high-fat (HF) feeding in dexamethasone (Dex)-programmed rats, in which prenatal glucocorticoid overexposure is associated with reduced birth weight and adult glucose intolerance. Male Wistar rats exposed to Dex or vehicle (Veh) during the last week of gestation were weaned onto HF or control diets for 6 months. Dex-exposed animals were of lower birth weight and showed catch-up growth by 7 wk. There were no differences in obesity or hyperinsulinaemia between Dex-HF and Veh-HF animals. However, Dex-HF animals had increased hepatic triglyceride content compared with Veh-HF animals. mRNA transcript profiles in adipose tissue revealed depot-specific changes in the expression of genes involved in fatty acid esterification and triglyceride synthesis and storage with prenatal Dex exposure. Thus, antenatal glucocorticoid overexposure in rats does not confer increased sensitivity to HF diet-induced obesity, but increases susceptibility to fatty liver. This may be due to depot-specific-programmed alterations in fat metabolism in adipose tissue.

Deletion of the Androgen Receptor in Adipose Tissue in Male Mice Elevates Retinol Binding Protein 4 and Reveals Independent Effects on Visceral Fat Mass and on Glucose Homeostasis

Testosterone deficiency is epidemic in obese ageing males with type 2 diabetes, but the direction of causality remains unclear. Testosterone-deficient males and global androgen receptor (AR) knockout mice are insulin resistant with increased fat, but it is unclear whether AR signaling in adipose tissue mediates body fat redistribution and alters glucose homoeostasis. To investigate this, mice with selective knockdown of AR in adipocytes (fARKO) were generated. Male fARKO mice on normal diet had reduced perigonadal fat but were hyperinsulinemic and by age 12 months, were insulin deficient in the absence of obesity. On high-fat diet, fARKO mice had impaired compensatory insulin secretion and hyperglycemia, with increased susceptibility to visceral obesity. Adipokine screening in fARKO mice revealed a selective increase in plasma and intra-adipose retinol binding protein 4 (RBP4) that preceded obesity. AR activation in murine 3T3 adipocytes downregulated RBP4 mRNA. We conclude that AR signaling in adipocytes not only protects against high-fat diet–induced visceral obesity but also regulates insulin action and glucose homeostasis, independently of adiposity. Androgen deficiency in adipocytes in mice resembles human type 2 diabetes, with early insulin resistance and evolving insulin deficiency.

Regulation of LKB1 expression by sex hormones in adipocytes

Objective:In the adipose tissue, activation of AMP-activated protein kinase (AMPK) by phosphorylation favours local fatty acid oxidation and inhibition of lipogenesis. We have previously shown that the potent androgen dihydrotestosterone (DHT) can inhibit phosphorylation of AMPK in adipose tissue and 3T3-L1 adipocytes in a dose-dependent manner. This negative effect of DHT was reversed by oestrogen treatment. The purpose of this current study was to determine the underlying mechanisms whereby androgens and oestrogens can regulate AMPK phosphorylation in adipocytes, and whether this mechanism is receptor dependent.Results:Phosphorylation of AMPK was assessed by western blot in cells treated for 24 h with testosterone or DHT (1–1000 nM). Testosterone and DHT significantly inhibited basal phosphorylation of AMPK. Addition of the androgen receptor antagonist Flutamide (1 μM) to the media reversed the negative effect of testosterone and DHT by returning AMPK phosphorylation levels to those of basal. To further dissect the mechanism underlying AMPK inhibition by testosterone or DHT, we examined the mRNA expression of the upstream activator of AMPK, namely LKB1. Testosterone and DHT treatment of murine 3T3-L1 or human SGBS adipocytes for 24 h significantly decreased the mRNA expression of LKB1. In contrast, 17β-estradiol treatment increased LKB1 mRNA, an effect mediated by oestrogen receptor alpha.Conclusion:We conclude that regulation of AMPK phosphorylation by androgens and oestrogens is receptor-dependent, and demonstrate for the first time that LKB1 is regulated by sex hormones in adipocytes.

Increased A-ring Reduction of Glucocorticoids in Obese Zucker Rats: Effects of Insulin Sensitization

OBJECTIVE Obesity is associated with altered glucocorticoid metabolism, which may impact on hypothalamic-pituitary-adrenal axis activity. Here we characterize hepatic 5alpha- and 5beta-reductase in obese rats and their responses to insulin sensitization. RESEARCH METHODS AND PROCEDURES Hepatic A-ring reductase protein and mRNA were assessed in lean and obese Zucker rats after insulin sensitization with metformin or rosiglitazone (n = 7 to 8/group). RESULTS Hepatic 5alpha-reductase 1 and 5beta-reductase mRNA and protein (p < 0.01) were increased in obese rats. Insulin sensitization ameliorated increased 5alpha-reductase 1 mRNA in obese rats (p < 0.01) and partially reversed increased 5beta-reductase activity. DISCUSSION Hepatic clearance of glucocorticoids by 5alpha- and 5beta-reductase is increased in obese Zucker rats, and this increase in clearance is attenuated by insulin sensitization. This increased hepatic clearance may underpin compensatory activation of the hypothalamic-pituitary-adrenal axis in obesity.

Association of 11β-hydroxysteroid dehydrogenase type I expression and activity with estrogen receptor β in adipose tissue from postmenopausal women.

Objective 11&bgr;-Hydroxysteroid dehydrogenase type I (11&bgr;HSD1) regenerates active cortisol from inert cortisone in adipose tissue. Elevated adipose tissue 11&bgr;HSD1 activity is observed in obese humans and rodents, where it is linked to obesity and its metabolic consequences. Menopause is also associated with increased abdominal fat accumulation, suggesting that estrogen is also important in adipose tissue metabolism. The purpose of this current study was to establish whether estrogen signaling through estrogen receptor &agr; (ER-&agr;) and estrogen receptor &bgr; (ER-&bgr;) could influence 11&bgr;HSD1 in premenopausal and postmenopausal adipose tissues. Methods Nineteen premenopausal (aged 26 ± 5 y; body mass index, 23.6 ± 1.6 kg/m2) and 23 postmenopausal (aged 63 ± 4 y; body mass index, 23.4 ± 1.9 kg/m2) healthy women were studied. Subcutaneous adipose tissue biopsies and fasting venous blood samples were taken. Body composition was measured by bioelectrical impedance analysis. Human Simpson-Golabi-Behmel syndrome adipocyte cells were treated with ER-&agr;– and ER-&bgr;–specific agonists for 24 hours. Basic anthropometric data, serum 17&bgr;-estradiol and progesterone concentrations, ER-&agr; and ER-&bgr; messenger RNA (mRNA) levels, and 11&bgr;HSD1 mRNA, protein, and activity levels were assessed. Results ER-&bgr; and 11&bgr;HSD1, but not ER-&agr;, mRNAs were significantly increased in adipose tissue from postmenopausal women compared with premenopausal women. ER-&bgr; had a significant positive correlation with the mRNA level of 11&bgr;HSD1 in adipose tissue from premenopausal and postmenopausal women. This association between ER-&bgr; and 11&bgr;HSD1 was greatest in adipose tissue from postmenopausal women. In human Simpson-Golabi-Behmel syndrome adipocytes, diarylpropiolnitrile, a selective ER-&bgr; agonist, increased 11&bgr;HSD1 mRNA, protein, and activity levels. Conclusions We conclude that, in adipose tissue, ER-&bgr;–mediated estrogen signaling can up-regulate 11&bgr;HSD1 and that this may be of particular importance in postmenopausal women.

Pregnancy in Obese Mice Protects Selectively against Visceral Adiposity and Is Associated with Increased Adipocyte Estrogen Signalling

Maternal obesity is linked with increased adverse pregnancy outcomes for both mother and child. The metabolic impact of excessive fat within the context of pregnancy is not fully understood. We used a mouse model of high fat (HF) feeding to induce maternal obesity to identify adipose tissue-mediated mechanisms driving metabolic dysfunction in pregnant and non-pregnant obese mice. As expected, chronic HF-feeding for 12 weeks preceding pregnancy increased peripheral (subcutaneous) and visceral (mesenteric) fat mass. However, unexpectedly at late gestation (E18.5) HF-fed mice exhibited a remarkable normalization of visceral but not peripheral adiposity, with a 53% reduction in non-pregnant visceral fat mass expressed as a proportion of body weight (P<0.001). In contrast, in control animals, pregnancy had no effect on visceral fat mass proportion. Obesity exaggerated glucose intolerance at mid-pregnancy (E14.5). However by E18.5, there were no differences, in glucose tolerance between obese and control mice. Transcriptomic analysis of visceral fat from HF-fed dams at E18.5 revealed reduced expression of genes involved in de novo lipogenesis (diacylglycerol O-acyltransferase 2 - Dgat2) and inflammation (chemokine C-C motif ligand 2 - Ccl2) and upregulation of estrogen receptor α (ERα) compared to HF non pregnant. Attenuation of adipose inflammation was functionally confirmed by a 45% reduction of CD11b+CD11c+ adipose tissue macrophages (expressed as a proportion of all stromal vascular fraction cells) in HF pregnant compared to HF non pregnant animals (P<0.001). An ERα selective agonist suppressed both de novo lipogenesis and expression of lipogenic genes in adipocytes in vitro. These data show that, in a HF model of maternal obesity, late gestation is associated with amelioration of visceral fat hypertrophy, inflammation and glucose intolerance, and suggest that these effects are mediated in part by elevated visceral adipocyte ERα signaling.

Aromatase Inhibition Reduces Insulin Sensitivity in Healthy Men

Context: Deficiency of aromatase, the enzyme that catalyzes the conversion of androgens to estrogens, is associated with insulin resistance in humans and mice. Objective: We hypothesized that pharmacological aromatase inhibition results in peripheral insulin resistance in humans. Design: This was a double-blind, randomized, controlled, crossover study. Setting: The study was conducted at a clinical research facility. Participants: Seventeen healthy male volunteers (18–50 y) participated in the study. Intervention: The intervention included oral anastrozole (1 mg daily) and placebo, each for 6 weeks with a 2-week washout period. Main Outcome Measure: Glucose disposal and rates of lipolysis were measured during a stepwise hyperinsulinemic euglycemic clamp. Data are mean (SEM). Results: Anastrozole therapy resulted in significant estradiol suppression (59.9 ± 3.6 vs 102.0 ± 5.7 pmol/L, P = < .001) and a more modest elevation of total T (25.8 ± 1.2 vs 21.4 ± 0.7 nmol/L, P = .003). Glucose infusion rate, during the low-dose insulin infusion, was lower after anastrozole administration (12.16 ± 1.33 vs 14.15 ± 1.55 μmol/kg·min, P = .024). No differences in hepatic glucose production or rate of lipolysis were observed. Conclusion: Aromatase inhibition reduces insulin sensitivity, with respect to peripheral glucose disposal, in healthy men. Local generation and action of estradiol, at the level of skeletal muscle, is likely to be an important determinant of insulin sensitivity.

Increased A-ring reduction of glucocorticoids in obese Zucker rats: effects of insulin sensitization

OBJECTIVE Obesity is associated with altered glucocorticoid metabolism, which may impact on hypothalamic-pituitary-adrenal axis activity. Here we characterize hepatic 5alpha- and 5beta-reductase in obese rats and their responses to insulin sensitization. RESEARCH METHODS AND PROCEDURES Hepatic A-ring reductase protein and mRNA were assessed in lean and obese Zucker rats after insulin sensitization with metformin or rosiglitazone (n = 7 to 8/group). RESULTS Hepatic 5alpha-reductase 1 and 5beta-reductase mRNA and protein (p < 0.01) were increased in obese rats. Insulin sensitization ameliorated increased 5alpha-reductase 1 mRNA in obese rats (p < 0.01) and partially reversed increased 5beta-reductase activity. DISCUSSION Hepatic clearance of glucocorticoids by 5alpha- and 5beta-reductase is increased in obese Zucker rats, and this increase in clearance is attenuated by insulin sensitization. This increased hepatic clearance may underpin compensatory activation of the hypothalamic-pituitary-adrenal axis in obesity.

Increased A-ring reduction of glucocorticoids in obese Zucker rats

OBJECTIVE Obesity is associated with altered glucocorticoid metabolism, which may impact on hypothalamic-pituitary-adrenal axis activity. Here we characterize hepatic 5alpha- and 5beta-reductase in obese rats and their responses to insulin sensitization. RESEARCH METHODS AND PROCEDURES Hepatic A-ring reductase protein and mRNA were assessed in lean and obese Zucker rats after insulin sensitization with metformin or rosiglitazone (n = 7 to 8/group). RESULTS Hepatic 5alpha-reductase 1 and 5beta-reductase mRNA and protein (p < 0.01) were increased in obese rats. Insulin sensitization ameliorated increased 5alpha-reductase 1 mRNA in obese rats (p < 0.01) and partially reversed increased 5beta-reductase activity. DISCUSSION Hepatic clearance of glucocorticoids by 5alpha- and 5beta-reductase is increased in obese Zucker rats, and this increase in clearance is attenuated by insulin sensitization. This increased hepatic clearance may underpin compensatory activation of the hypothalamic-pituitary-adrenal axis in obesity.