Ablation of neurons expressing agouti-related protein, but not melanin concentrating hormone, in leptin-deficient mice restores metabolic functions and fertility

Abstract

Leptin-deficient (Lep ob/ob ) mice are obese, diabetic, and infertile. Ablation of neurons that make agouti-related protein (AgRP) in moderately obese adult Lep ob/ob mice caused severe anorexia. The mice stopped eating for 2 wk and then gradually recovered. Their body weight fell to within a normal range for WT mice, at which point food intake and glucose tolerance were restored to that of WT mice. Remarkably, both male and female Lep ob/ob mice became fertile. Ablation of neurons that express melanin-concentrating hormone (MCH) in adult Lep ob/ob mice had no effect on food intake, body weight, or fertility, but resulted in improved glucose tolerance. We conclude that AgRP-expressing neurons play a critical role in mediating the metabolic syndrome and infertility of Lep ob/ob mice, whereas MCHexpressing neurons have only a minor role.he spontaneous nonsense mutation in the leptin gene that generated Lep ob/ob mice results in obesity, hyperphagia, diabetes, and infertility (1, 2). These phenotypes can be reversed by chronic delivery of recombinant leptin (3, 4). The neural circuitry underlying these phenotypes has been the subject of intense investigation (5-7). Mice lacking leptin have elevated levels of neuropeptide Y (NPY) and melanin-concentrating hormone (MCH) in the hypothalamus (8, 9), and genetic experiments have demonstrated that Lep ob/ob mice lacking either of these peptides have an improved metabolic phenotype (10, 11).Because hypothalamic NPY-expressing neurons send projections to the vicinity of MCH-expressing neurons (12), which have electrophysiological responses to NPY (13), the two neuronal populations may be part of the same circuitry mediating the phenotype of Lep ob/ob mice. NPY-expressing neurons in the arcuate nucleus also express agouti-related protein (AgRP), which exerts the same orexigenic effects as NPY but by a different mechanism (14).We take advantage of the restricted expression of AgRP and MCH to hypothalamic neurons by targeting the human diphtheria toxin (DT) receptor to the genes encoding those neuropeptides, thereby allowing their selective ablation by administration of DT (15). Ablation of AgRP-expressing neurons (AgRP neurons) in adult mice results in severe anorexia and death in ∼6 d (15,16). In this study, we applied this same methodology to MCH-expressing neurons (MCH neurons) and asked whether ablation of either of these neuronal populations in adult Lep ob/ob mice is beneficial (as predicted from the constitutive loss of the neuropeptides) or lethal (as predicted from the loss of AgRP neurons in a WT background). ) gradually stopped feeding and lost 20% of their body weight during the next 6 d and would have succumbed, whereas mice without the Agrp DTR allele maintained their feeding and body weight (Fig. 1). Statistical analyses of our results are reported in the figure legends. Analysis of the brains of DT-treated mice at the end of the experiment revealed a virtual absence of AgRP neurons in Agrp DTR/+ mice, as measured by immunocytochemistry or quantitative PCR for...

PI3Kα inactivation in leptin receptor cells increases leptin sensitivity but disrupts growth and reproduction

“…Deletion of PI3K signaling in LR cells caused lack of responsiveness of AgRP to metabolic cues, potentially leptin, resulting in higher AgRP expression in fed conditions, associated with increased food intake. The AgRP neurons have inhibitory actions on the reproductive axis (51)(52)(53). Therefore, high levels of AgRP may have disrupted the reproductive function of LR Δα mice.…”

Neuroendocrine integration of nutritional signals on reproduction

“…Further supporting the idea that insulin and/or leptin must restrain NPY/AgRP neurons to permit fertility, it was shown that ablating NPY/AgRP-expressing neurons in leptin-deficient (ob/ob) diabetic mice was able to restore their fertility, food intake regulation and glucose tolerance (Wu et al 2012). Additionally, AgRP deficiency alone (vs neuronal ablation) in LepR-null (db/db) mice was also able to rescue their HPG axis function (ShefferBabila et al 2013).…”

AgRP neurons: The foes of reproduction in leptin-deficient obese subjects

“…It is likely that the AgRP neurons and the GnRH neurons are either directly or indirectly connected (24) and that this circuitry dictates the reproductive phenotypes observed in several reports, including the one in PNAS (1). An intriguing question is how hypothalamic circuitry adapts to the lack of AgRP neurons reversing infertility in ob/ob mice in the complete absence of leptin.…”

“…The cellular mechanisms involved in the fine coordination of energy balance and reproduction are largely unknown. In PNAS, Wu et al (1) shed light on a previously unsuspected neuronal population that appears to be fundamental for the coupling of energy deficit with impaired reproduction.…”