Dysregulation of glucocorticoid metabolism in murine obesity: comparable effects of leptin resistance and deficiency

Abstract

In obese humans, metabolism of glucocorticoids by 11 beta-hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) and A-ring reduction (by 5 alpha- and 5 beta-reductases) is dysregulated in a tissue specific manner. These changes have been recapitulated in leptin resistant obese Zucker rats but were not observed in high-fat fed Wistar rats. Recent data from mouse models suggest that such discrepancies may reflect differences in leptin signalling. We therefore compared glucocorticoid metabolism in murine models of leptin deficiency and resistance. Male ob/ob and db/db mice and their respective littermate controls (n=10-12/group) were studied at the age of 12 weeks. Enzyme activities and mRNA expression were quantified in snap-frozen tissues. The patterns of altered pathways of steroid metabolism in obesity were similar in ob/ob and db/db mice. In liver, 5 beta-reductase activity and mRNA were increased and 11 beta-HSD1 decreased in obese mice, whereas 5 alpha-reductase 1 (5 alpha R1) mRNA was not altered. In visceral adipose depots, 5 beta-reductase was not expressed, 11 beta-HSD1 activity was increased and 5 alpha R1 mRNA was not altered in obesity. By contrast, in subcutaneous adipose tissue 11 beta-HSD1 and 5 alpha R1 mRNA were decreased. Systematic differences were not found between ob/ob and db/db murine models of obesity, suggesting that variations in leptin signalling through the short splice variant of the Ob receptor do not contribute to dysregulation of glucocorticoid metabolism.

Figure 1

Glucocorticoid metabolic pathways. A is 11-dehydrocorticosterone; B is corticosterone and HSD is hydroxysteroid dehydrogenase.

Figure 2

Hepatic glucocorticoid metabolism. 11β-HSD1 activity measured as velocity of formation of product following incubation of [³H]₄-corticosterone with hepatic homogenate from (A) Db/? control (open) or db/db mice (light striped); (B) Ob/? control (black) or ob/ob mice (dark striped). 5β-Reductase activity measured as velocity of formation of product following incubation of [³H]₄-corticosterone with hepatic cytosol from (C) Db/? control or db/db mice; (D) Ob/? control or ob/ob mice. Abundance of mRNAs for hepatic enzymes measured by real-time PCR (corrected for 18S as a housekeeping gene and presented as a percentage of respective control group) in (E) Db/? control or db/db mice; (F) Ob/? control mice or ob/ob mice. Data are mean±s.e.m.; n=10–12/group; *P<0·05; **P<0·01.

Figure 3

Glucocorticoid metabolism in adipose tissues. 11β-HSD1 activity measured as velocity of formation of product following incubation of [³H]₄-corticosterone with homogenates of adipose tissues from (A) Db/? control (open) or db/db mice (light striped); (B) Ob/? control (black) or ob/ob mice (dark striped). Abundance of mRNA for 11β-HSD1 in adipose tissue depots measured by real-time PCR (corrected for cyclophilin A as a housekeeping gene and presented as a percentage of respective control group) in (C) Db/? control or db/db mice; (D) Ob/? control or ob/ob mice. Abundance of mRNAs for 5α-R1 in adipose beds measured by real-time PCR (corrected for cyclophilin A as a housekeeping gene and presented as a percentage of respective control group) in (E) Db/? control or db/db mice; (F) Ob/? control or ob/ob mice. Subcut is s.c. adipose, Epi is epididymal, R/P is retro-peritoneal and Mes is mesenteric. Data are mean±s.e.m.; n=6–12/group; *P<0·05; **P<0·01.