Endocrine Abstracts

In humans, glucocorticoids (GC) are implicated in the pathogenesis of obesity and insulin resistance. GCs are regulated at the prereceptor level by 11beta-HSDs. 11beta-HSD1 predominately displays oxo-reductase activity (cortisone/11-dehydrocorticosterone to cortisol/ corticosterone), requiring the cofactor NADPH. Recently, studies in humans have shown that the enzyme H6PDH, by generating NAPDH in the endoplasmic reticulum (ER) is crucial for oxo-reductase activity. This study aimed to determine if these enzymes were coexpressed in metabolic tissues in mice. Liver, muscle and adipose tissue were collected from adult male C57BL/6 mice (n=3). Four adipose depots were collected; gonadal, subcutaneous, perirenal and brown adipose tissue (BAT). Real time PCR was used to quantitate expression of 11beta-HSD1 and H6PDH. All tissues expressed 11beta-HSD1, with the highest levels present in liver and perirenal adipose tissue. H6PDH was also expressed in all depots, with a 4 fold higher expression in perirenal depot compared with other depots. Set point of 11beta-HSD1 activity was assessed in cultured preadipocytes (perirenal, subcutaneous, BAT, gonadal), and myocytes. Oxo-reductase activity was predominant in all tissues. Highest levels of oxo-reductase were in perirenal preadipocytes, 65.9 ± 8.6%; then subcutaneous preadipocytes, 60.8 ± 0.9%, BAT had 54 ± 1.16%, myocytes had 52 ± 4.35% and lowest levels were in gonadal preadipocytes, 45 ± 1.5%. Lower levels of dehydrogenase activity were observed, ranging from 8.1 ± 0.98% in perirenal preadipocytes, 8 ± 0.5% in subcutaneous preadipocytes, 8 ± 0.76% in BAT, 10.14 ± 0.34% in myocytes and highest activity was in gonadal preadipocytes, 20 ± 0.05%. All tissues examined, expressed high levels of both genes. Additionally, cultured preadipocytes and myocytes demonstrated predominant 11beta-HSD1 oxo-reductase activity, and correlated with increased expression of H6PDH. This interaction between H6PDH and 11beta-HSD1 in key metabolic tissues such as liver, fat and muscle is likely to play an important role in insulin sensitivity/obesity.