Transgenic overexpression of hexose-6-phosphate dehydrogenase in adipose tissue causes local glucocorticoid amplification and lipolysis in male mice

Abstract

The prereceptor activation of glucocorticoid production in adipose tissue by NADPH-dependent 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) has emerged as a potential mechanism in the pathogenesis of visceral obesity and metabolic syndrome. Hexose-6-phosphate dehydrogenase (H6PDH) is an endoplasmic reticulum lumen-resident enzyme that generates cofactor NADPH and thus mediates 11␤-HSD1 activity. To determine the role of adipose H6PDH in the prereceptor modulation of 11␤-HSD1 and metabolic phenotypes, we generated a transgenic (Tg) mouse model overexpressing H6PDH under the control of the enhancerpromoter region of the adipocyte fatty acid-binding protein (aP2) gene (aP2/H6PDH Tg mice). Transgenic aP2/H6PDH mice exhibited relatively high expression of H6PDH and elevated corticosterone production with induction of 11␤-HSD1 activity in adipose tissue. This increase in corticosterone production in aP2-H6PDH Tg mice resulted in mild abdominal fat accumulation with induction of C/EBP mRNA expression and slight weight gain. Transgenic aP2/H6PDH mice also exhibited fasting hyperglycemia and glucose intolerance with insulin resistance. In addition, the aP2/H6PDH Tg mice have elevated circulating free fatty acid levels with a concomitant increased adipose lipolytic action associated with elevated HSL mRNA and Ser 660 HSL phosphorylation within abdominal fat. These results suggest that increased H6PDH expression specifically in adipose tissue is sufficient to cause intra-adipose glucocorticoid production and adverse metabolic phenotypes. These findings suggest that the aP2/H6PDH Tg mice may provide a favorable model for studying the potential impact of H6PDH in the pathogenesis of human metabolic syndrome.11␤-hydroxysteroid dehydrogenase type 1; transgenic mouse VISCERAL FAT DEPOSITION IS FREQUENTLY ASSOCIATED with metabolic syndrome, including visceral obesity, insulin resistance, hypertension, and dyslipidemia (13,22,39). However, the underlying mechanisms of these metabolic perturbations are poorly understood. Patients with glucocorticoid (GC) excess (Cushing's syndrome) promote visceral fat deposition and develop metabolic syndrome (1, 21). In adipose tissue, GCs promote lipolysis by stimulating two key enzymes, hormonesensitive lipase (HSL) and adipose triglyceride lipase (ATGL), to increase hydrolysis of triacylglycerol and release free fatty acids (FFA) in the circulation that is linked to hyperlipidemia and global insulin resistance (8, 24, 46). However, tissuespecific GC availability is regulated by an intracellular endoplasmic reticulum (ER) lumen-resident enzyme, 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1), that converts inert cortisone (11-dehydrocorticosterone in rodents) to the active glucocorticoid receptor (GR)-ligand cortisol (corticosterone in rodents) and thereby amplifies intracellular GC reproduction, particularly in adipose tissues (7,41,23,33). Increased adipose GC activation by 11␤-HSD1 leads to visceral obesity and features of the metabolic syndrome (29). Prereceptor amplification of GC ...

11β-Hydroxysteroid dehydrogenase type 1 shRNA ameliorates glucocorticoid-induced insulin resistance and lipolysis in mouse abdominal adipose tissue

“…To our knowledge, the alterations of 11␤-HSD1 coupled with H6PDH and their contributions to modulation of lipolysis have not been explored in humans or in in animals after GC challenge. In accord with this concept, adipose 11␤-HSD1 was induced through the availability of local NADPH and caused lipolysis in adipose tissue in H6PDH transgenic mice (48). These data support the possibility that prereceptor induction of adipose 11␤-HSD1 and H6PDH may contribute to GC excessinduced metabolic syndrome.…”

“…At the end of the 3rd wk after Ad-LacZ or Ad-11␤-HSD1shRNA administration, epididymal fat and abdominal subcutaneous fat pads were removed, weighed, and frozen in liquid nitrogen. Blood samples were collected between 0900 and 1000 and then stored at Ϫ80°C until measurement of glucose, insulin, CORT, free fatty acid, and triglycerides using commercially available kits, as described previously (48).…”

“…Adipose corticosterone concentrations were measured by methanol extraction using a corticosterone ELISA kit (Abcam), as in our previous report (48).…”

“…In the ER lumen, H6PDH can metabolize glucose 6-phosphate and NADP to generate NADPH, thus ensuring 11␤-HSD1 activity. Enhanced 11␤-HSD1 and H6PDH expression results in production of excess adipose GCs and produces features of the metabolic syndrome in transgenic mice (28,48). Pharmacological inhibition of 11␤-HSD1 modulates lipid metabolism (3), improves GC-induced hyperglycemia in animals (4), and decreases glycerol concentrations (44).…”

Cortisol in tissue and systemic level as a contributing factor to the development of metabolic syndrome in severely obese patients

“…H6PDH is an endoplasmic reticulum enzyme that generates cofactor NADPH and thus ameliorates NADPHdependent HSD11B1 reductase activity (31,32,33). The significance of H6PDH was demonstrated in a study in which transgenic mice that were overexpressing H6PDH in the adipose tissue exhibited fasting hyperglycaemia, glucose intolerance with IR and elevated circulating free fatty acids (FFA) levels (34). Moreover, hepatic HSD11B1 mRNA levels were positively associated with the WCirc and BMI, suggesting that visceral obesity could induce an increase in the expression of LHSD11B1, which in turn contributes to the appearance of MetS, as is demonstrated in several animal studies (14).…”