Loss of hypothalamic-pituitary-adrenal axis improves obese phenotype and restores hypothalamic agouti-related protein mRNA in leptin-deficient ob/ob mice
M. Nishiyama1, S. Nakayama1, M. Okazaki1, M. Tsugita1, T. Taguchi1, S. Makino2, Y. Okada1, M. Tsuda1, Y. Iwasaki1 & Y. Terada1
Purpose: Glucocorticoid excess causes obesity and hyperphagia (e.g. Cushing syndrome), but the molecular mechanism of glucocorticoid-induced hyperphagia is not fully understood. To clarify this point, we investigated here the phenotype of leptin and Corticotropin-releasing hormone (CRH) double knockout mice (DKO).
Methods: Leptin-deficient ob/ob mice were bred with CRH-deficient mice for generation of DKO mice. We examined body weight, food consumption and hypothalamic appetite-related neuropeptide mRNA levels [neuropetide Y (NPY), proopiomelanocortin (POMC) and Agouti-related protein (AgRP)] by quantitative real time PCR, in wild-type littermates (WT), ob/ob and DKO. We also examined the effect of glucocorticoid replacement (corticosterone pellet implantation for 4 weeks) on DKO.
Results: Circulating glucocorticoid levels were markedly high in ob/ob but low in DKO (CORT: WT 4.2±3.5, ob/ob 206.1±48.1, DKO 0.0±0.0 ng/ml). At 9 weeks old, body weight and food intake in DKO were decreased compared with ob/ob, but still increased compared with WT (body weight: WT 25.4±0.3, ob/ob 42.7±1.6, DKO 35.2±0.5 g). The changes of hypothalamic appetite-related neuropeptide levels observed in ob/ob, such as increased in NPY and AgRP mRNA and decreased in POMC mRNA, were attenuated in DKO, especially, hypothalamic AgRP mRNA were dynamically changed (AgRP/GAPDH: WT 100.0±6.7, ob/ob 509.4±33.2, DKO 90.8±8.3). Finally, glucocorticoid replacement on DKO caused to increase food intake and hypothalamic AgRP mRNA (AgRP/GAPDH: WT 100.0±7.8, ob/ob 521.3±59.5, DKO 94.2±8.8, DKO+CORT 243.4±20.0), but there were no alteration in NPY or POMC.
Conclusion: These results suggest that ob/ob mice require glucocorticoid excess and related changes in hypothalamic neuropeptides (NPY, POMC and AgRP) to maintain their body weight and appetite. Because hypothalamic AgRP expressions are quite parallel to circulating glucocorticoid levels in the present study, hypothalamic AgRP is considered as a key molecule in glucocorticoid-induced hyperphagia.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.