Mediobasal hypothalamic leucine sensing regulates food intake through activation of a hypothalamus-brainstem circuit

Abstract

In response to nutrient stimuli, the mediobasal hypothalamus (MBH) drives multiple neuroendocrine and behavioral mechanisms to regulate energy balance. While central leucine reduces food intake and body weight, the specific neuroanatomical sites of leucine sensing, downstream neural substrates, and neurochemical effectors involved in this regulation remain largely unknown. Here we demonstrate that MBH leucine engages a neural energy regulatory circuit by stimulating POMC (proopiomelanocortin) neurons of the MBH, oxytocin neurons of the paraventricular hypothalamus, and neurons within the brainstem nucleus of the solitary tract to acutely suppress food intake by reducing meal size. We identify central p70 S6 kinase and Erk1/2 pathways as intracellular effectors required for this response. Activation of endogenous leucine intracellular metabolism produced longer-term reductions in meal number. Our data identify a novel, specific hypothalamus-brainstem circuit that links amino acid availability and nutrient sensing to the control of food intake.

Figure 1.

MBH leucine and KIC injections reduce food intake and body weight in rat and mouse. a–h, Cumulative (Cum.) food intake (a, e), 24 h change in body weight (BW) (b, f), mean meal size (c, g), and cumulative meal number (d, h) in rat (a–d, n = 10–12) and mouse (e–h, n = 8) following an MBH injection of aCSF, leucine, or KIC (injection design 1). Data are means ± SEM. *p < 0.05 versus aCSF; **p < 0.01 versus aCSF; ***p < 0.001 versus aCSF.

Figure 2.

MBH CIC decreases food intake and body weight in mouse. a–d, Food intake (a), meal number (b), meal size (c), and body weight (d) in mouse infused for 8 d with aCSF (n = 8) or CIC (n = 10) in the MBH (injection design 2). Data are means ± SEM. *p < 0.05; **p < 0.01. impl., Implantation.

Figure 3.

Leucine's anorexigenic effect requires direct activation of the melanocortin system. a, Sample traces recorded before and after application of l-leucine from a POMC neuron in current-clamp configuration. b, Immunofluorescence showing colocalization (yellow) of leucine-stimulated c-Fos-positive cells (Cy3, red) and arcuate POMC neurons of POMC-CRE Z/eGFP mice (green), 70 min after MBH leucine administration (injection design 1). c, Quantification of c-Fos-positive cells in different nuclei 70 min after MBH aCSF or leucine injection (injection design 1). d–f, First meal size (d), 12 h food intake (e), and 24 h change in body weight (BW) (f) in mouse (n = 8–12) after MBH coadministration of SHU9119 or aCSF and leucine or aCSF (injection design 3). Data are means ± SEM. *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 4.

Oxytocin receptor antagonist blocks leucine anorexigenic effect. a–d, First meal size (a), food intake (b), meal size (c), and meal number (d) in mouse (n = 9) after coadministration of IVth intracerebroventricular OVT or aCSF and MBH leucine or aCSF (injection design 5). Data are means ± SEM. *p < 0.05; **p < 0.01.

Figure 5.

MBH leucine activates Erk1/2 signaling pathway in MBH, PVN oxytocin, and DVC neurons. a–c, MBH (a), PVN (b), and DVC (c) Erk1/2 Thr202/Tyr204 phosphorylation and CREB Ser133 phosphorylation in mouse 30 min after an MBH injection of aCSF (n = 5) or leucine (n = 5) (injection design 1). d, Immunofluorescence showing colocalization (yellow, right) of oxytocin (Cy2, green, left) and MBH leucine-induced phospho-Thr202/Tyr204 Erk1/2 (Cy3, red, middle) in PVN slices of mice 30 min after MBH leucine administration (injection design 1).

Figure 6.

MBH leucine anorexigenic effect requires MBH Erk1/2 signaling. a–e, First meal size (a), 24 h food intake (b), 24 h change in body weight (BW) (c), MBH Erk1/2 Thr202/Tyr204 phosphorylation (d), and MBH p70 S6 kinase 1 Thr389 phosphorylation (e) in mouse (n = 6–12) after MBH coadministration of U0126 or its vehicle and leucine or aCSF (injection design 7). All data are means ± SEM. *p < 0.05; **p < 0.01.

Figure 7.

Model for MBH leucine's sensing regulation of feeding behavior. Acute increase in MBH leucine levels engages a forebrain/hindbrain neurocircuit to decrease meal size through the activation of MBH POMC neurons, PVN oxytocin neurons, and NTS neurons involved in the regulation of feeding.