Role of glucocorticoids in mediating effects of fasting and diabetes on hypothalamic gene expression.

BACKGROUND: Fasting and diabetes are characterized by elevated glucocorticoids and reduced insulin, leptin, elevated hypothalamic AGRP and NPY mRNA, and reduced hypothalamic POMC mRNA. Although leptin replacement can reverse changes in hypothalamic gene expression associated with fasting and diabetes, leptin also normalizes corticosterone; therefore the extent to which the elevated corticosterone contributes to the regulation of hypothalamic gene expression in fasting and diabetes remains unclear. To address if elevated corticosterone is necessary for hypothalamic responses to fasting and diabetes, we assessed the effects of adrenalectomy on hypothalamic gene expression in 48-hour-fasted or diabetic mice. To assess if elevated corticosterone is sufficient for the hypothalamic responses to fasting and diabetes, we assessed the effect of corticosterone pellets implanted for 48 hours on hypothalamic gene expression. RESULTS: Fasting and streptozotocin-induced diabetes elevated plasma glucocorticoid levels and reduced serum insulin and leptin levels. Adrenalectomy prevented the rise in plasma glucocorticoids associated with fasting and diabetes, but not the associated reductions in insulin or leptin. Adrenalectomy blocked the effects of fasting and diabetes on hypothalamic AGRP, NPY, and POMC expression. Conversely, corticosterone implants induced both AGRP and POMC mRNA (with a non-significant trend toward induction of NPY mRNA), accompanied by elevated insulin and leptin (with no change in food intake or body weight). CONCLUSION: These data suggest that elevated plasma corticosterone mediate some effects of fasting and diabetes on hypothalamic gene expression. Specifically, elevated plasma corticosterone is necessary for the induction of NPY mRNA with fasting and diabetes; since corticosterone implants only produced a non-significant trend in NPY mRNA, it remains uncertain if a rise in corticosterone may be sufficient to induce NPY mRNA. A rise in corticosterone is necessary to reduce hypothalamic POMC mRNA with fasting and diabetes, but not sufficient for the reduction of hypothalamic POMC mRNA. Finally, elevated plasma corticosterone is both necessary and sufficient for the induction of hypothalamic AGRP mRNA with fasting and diabetes.

Adrenalectomy stimulates hypothalamic proopiomelanocortin expression but does not correct diet-induced obesity.

BACKGROUND: Elevated glucocorticoid production and reduced hypothalamic POMC mRNA can cause obese phenotypes. Conversely, adrenalectomy can reverse obese phenotypes caused by the absence of leptin, a model in which glucocorticoid production is elevated. Adrenalectomy also increases hypothalamic POMC mRNA in leptin-deficient mice. However most forms of human obesity do not appear to entail elevated plasma glucocorticoids. It is therefore not clear if reducing glucocorticoid production would be useful to treat these forms of obesity. We hypothesized that adrenalectomy would increase hypothalamic POMC mRNA and reverse obese phenotypes in obesity due to a high-fat diet as it does in obesity due to leptin deficiency. RESULTS: Retired breeder male mice were placed on a high-fat diet or a low-fat diet for two weeks, then adrenalectomized or sham-adrenalectomized. The high-fat diet increased body weight, adiposity, and plasma leptin, led to impaired glucose tolerance, and slightly stimulated hypothalamic proopiomelanocortin (POMC) expression. Adrenalectomy of mice on the high-fat diet significantly reduced plasma corticosterone and strikingly increased both pituitary and hypothalamic POMC mRNA, but failed to reduce body weight, adiposity or leptin, although slight improvements in glucose tolerance and metabolic rate were observed. CONCLUSION: These data suggest that neither reduction of plasma glucocorticoid levels nor elevation of hypothalamic POMC expression is effective to significantly reverse diet-induced obesity.