Hideo Makimura

Fasting regulates hypothalamic neuropeptide Y, agouti-related peptide, and proopiomelanocortin in diabetic mice independent of changes in leptin or insulin.

Fasting increases hypothalamic neuropeptide Y (NPY) and agouti-related peptide (AGRP) messenger RNA (mRNA) and reduces hypothalamic POMC mRNA, and is also characterized by a reduction in plasma leptin, insulin, and glucose, each of which has been implicated in the regulation of hypothalamic gene expression. To further evaluate the roles of leptin, insulin, and glucose in mediating effects of fasting, we examined hypothalamic gene expression in nondiabetic and streptozotocin (STZ)-induced diabetic mice both under ad lib fed and 48-h fasted conditions. In both diabetic and nondiabetic mice, fasting stimulated hypothalamic NPY and AGRP mRNA and inhibited hypothalamic POMC mRNA and adipose leptin mRNA. However, in diabetic mice fasting had no effect on plasma leptin and insulin while decreasing plasma glucose, whereas in nondiabetic mice fasting decreased plasma leptin, insulin, and glucose. Furthermore, in nondiabetic fasted mice, NPY and AGRP mRNA were higher, and POMC mRNA and plasma glucose were lower, th...

Reducing hypothalamic AGRP by RNA interference increases metabolic rate and decreases body weight without influencing food intake

BackgroundSeveral lines of evidence strongly suggest that agouti-related peptide (AGRP) plays a key role in the regulation of metabolic function but ablation of the AGRP gene has no apparent effect on metabolic function. Since specific pharmacological antagonists of AGRP do not presently exist, we assessed if reduction of hypothalamic AGRP mRNA by RNA interference (RNAI) would influence metabolic function, an outcome suggesting that pharmacological antagonists might constitute useful reagents to treat obesity.ResultsThe RNAI protocol specifically reduced hypothalamic expression of AGRP mRNA by 50% and resulted in reduction of AGRP peptide immunoreactivity. Physiologically, the reduction in AGRP levels was associated with increased metabolic rate and reduced body weight without changes in food intake.ConclusionAGRP can function to increase body weight and reduce metabolic rate without influencing food intake. The present study demonstrates that RNAI protocols can be used to assess physiological function of neuronal genes in vivo.

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

BackgroundFasting 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.ResultsFasting 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).ConclusionThese 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.

Block the FAS, lose the fat.

A small-molecular-weight drug originally developed to treat cancer produces sustained reduction in body weight in obese mice by a novel hypothalamic mechanism. The findings suggest new targets for the development of anti-obesity drugs.

Impaired glucose signaling as a cause of obesity and the metabolic syndrome: The glucoadipostatic hypothesis

Since nutrition-sensitive feedback signals normally act to maintain relatively stable levels of both available and stored nutritional resources, failure in one or more of these feedback signals could plausibly lead to obese phenotypes. The glucostatic hypothesis in its original form posited that glucose serves as a physiological satiety factor (in the sense that post-prandial increases in plasma glucose cause meal termination), but in this form the hypothesis has been difficult to prove, and, especially since the discovery of leptin, the glucostatic hypothesis has largely been abandoned. Nevertheless, reduction of plasma glucose levels or glucose signaling produces a profile of neuroendocrine responses similar to those produced by leptin deficiency. Since leptin is not a physiological satiety factor (because it does not increase before meal termination), yet leptin deficiency causes obesity, we suggest that the glucostatic hypothesis be re-formulated without reference to satiety (i.e., short-term effects on food intake). Instead we argue that like leptin signaling, glucose signaling regulates long-term energy balance, in part by regulating metabolic rate but also by chronically regulating food intake. We further speculate that high-fat diets produce obesity in part because carbohydrates are, per calorie, more effective than lipids to reduce food intake and increase metabolic rate. In support of this glucoadipostatic hypothesis, the 5 present review examines evidence that obesity and the metabolic syndrome may be due to reduction in neuroendocrine sensitivity to glucose leading to increased metabolic efficiency.

The physiological function of the agouti-related peptide gene: the control of weight and metabolic rate

The central melanocortin system plays an important role in the regulation of energy homeostasis both in rodents and humans, and melanocortin receptors appear to be the core of this system. Alpha-melanocyte-stimulating hormone (α-MSH) inhibits feeding through melanocrtin 3 and 4 receptors (MC3-R and MC4-R) as an endogenous agonist. Although mutations in the agouti gene cause an over-expression of agouti peptide which antagonizes effects of α-MSH at MC4-R in the brain and causes obese phenotypes, there was no evidence for the presence of an endogenous antagonist for MC3-R and MC4-R until agouti related protein (AGRP) was identified. AGRP is expressed primarily in the hypothalamic arcuate nucleus and central administration of AGRP stimulates feeding and weight gain, and decreases metabolic rate. Although a complete deletion of the AGRP gene does not produce any significant metabolic phenotypes, reduction in AGRP expression by RNA interference is associated with increased metabolic rate along with reduced weight gain. The currently available data suggest that elevated AGRP mRNA along with reduced proopiomelanocortin (POMC) mRNA is associated with many types of obesity and agents antagonizing the effect of AGRP may be a potential therapeutic target in treating obesity and obesity-associated disorders in which endogenous hypothalamic AGRP is elevated.

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

BackgroundElevated 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.ResultsRetired 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.ConclusionThese data suggest that neither reduction of plasma glucocorticoid levels nor elevation of hypothalamic POMC expression is effective to significantly reverse diet-induced obesity.