Tissue-specific dysregulation of hexose-6-phosphate dehydrogenase and glucose-6-phosphate transporter production in db/db mice as a model of type 2 diabetes

Abstract

Aims/hypothesis Tissue-specific amplification of glucocorticoid action through 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) affects the development of the metabolic syndrome. Hexose-6-phosphate dehydrogenase (H6PDH) mediates intracellular NADPH availability for 11β-HSD1 and depends on the glucose-6-phosphate transporter (G6PT). Little is known about the tissue-specific alterations of H6PDH and G6PT and their contributions to local glucocorticoid action in db/db mice. Methods We characterised the role of H6PDH and G6PT in pre-receptor metabolism of glucocorticoids by examining the production of the hepatic 11β-HSD1-H6PDH–G6PT system in db/db mice. Results We observed that increased production of hepatic H6PDH in db/db mice was paralleled by upregulation of hepatic G6PT production and responded to elevated circulating levels of corticosterone. Treatment of db/db mice with the glucocorticoid antagonist RU486 markedly reduced production of both H6PDH and 11β-HSD1 and improved hyperglycaemia and insulin resistance. The reduction of H6PDH and 11β-HSD1 production by RU486 was accompanied by RU486-induced suppression of hepatic G6pt (also known as Slc37a4) mRNA. Incubation of mouse primary hepatocytes with corticosterone enhanced G6PT and H6PDH production with corresponding activation of 11β-HSD1 and PEPCK: effects that were blocked by RU486. Knockdown of H6pd by small interfering RNA showed effects comparable with those of RU486 for attenuating the corticosterone-induced H6PDH production and 11β-HSD1 reductase activity in these intact cells. Addition of the G6PT inhibitor chlorogenic acid to primary hepatocytes suppressed H6PDH production. Conclusions/interpretation These findings suggest that increased hepatic H6PDH and G6PT production contribute to 11β-HSD1 upregulation of local glucocorticoid action that may be related to the development of type 2 diabetes.

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

“…Reduction of C/EBP may thus provide an additional mechanism to adipose 11␤-HSD1 knockdown, which is linked to the improvement of GCinduced adipolysis. Additionally, CORT induced the expression of adipose PEPCK mRNA, a key regulatory enzyme of fatty acid reesterification for adipose fatty acid release that is activated by GCs (49). In contrast, 11␤-HSD1 shRNA blocked GC-mediated induction of epididymal fat PEPCK, although it maintained subcutaneous fat PEPCK expression in GC-treated mice.…”

“…3 H]11-DHC as tracer to microsomes in KRB solution at 37°C for 1-2 h, as in our previous study (49). Adipose corticosterone concentrations were measured by methanol extraction using a corticosterone ELISA kit (Abcam), as in our previous report (48).…”

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

“…The adipose microsomal pellet was obtained, and H6PDH enzyme activity was carried out by spectrophotometric measurement of NADPH production in the presence of G-6-P and NADP using absorbance at 340 nm per our previous reports (47,15). Protein (100 g) from adipose microsomes was incubated with 0.5-5 mM G-6-P, 1-5 mM NADP, and 100 mM glycine buffer solution at 22°C for 0 -10 min.…”

“…Transgenic ␣P2-H6PDH mice and their nontransgenic littermates were given a standard laboratory chow diet with water ad libitum, and body weights and food intake were recorded weekly. Glucose tolerance (GTTs) and insulin tolerance (ITTs) tests were performed as previously described (29,47). For the GTT, 1 g/kg glucose was used in mice after a 12-h fast.…”

“…Targeted deletion or mutation of H6PDH results in a switch in the set point of 11␤-HSD1 inactivating cortisol to cortisone and demonstrates the physiological relevance of 11␤-HSD1 for H6PDH (6,14). We recently reported that tissue-specific elevation of 11␤-HSD1 in liver, visceral, and subcutaneous fat is associated with H6PDH expression in obese db/db diabetic mice (47). In human subcutaneous adipose cells, H6PDH mRNA level is elevated during the differentiation of adipocytes with stimulation of cortisol production by 11␤-HSD1 (5).…”