Probes for POMC

Pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus represent key regulators of metabolic homeostasis. Electrophysiological and single-cell sequencing experiments have revealed a remarkable degree of heterogeneity of these neurons. However, the exact molecular basis and functional consequences of this heterogeneity have not yet been addressed. Here, we have developed new mouse models in which intersectional Cre/Dre-dependent recombination allowed for successful labeling, translational profiling and functional characterization of distinct POMC neurons expressing the leptin receptor (Lepr) and glucagon like peptide 1 receptor (Glp1r). Our experiments reveal that POMCLepr+ and POMCGlp1r+ neurons represent largely nonoverlapping subpopulations with distinct basic electrophysiological properties. They exhibit a specific anatomical distribution within the arcuate nucleus and differentially express receptors for energy-state communicating hormones and neurotransmitters. Finally, we identify a differential ability of these subpopulations to suppress feeding. Collectively, we reveal a notably distinct functional microarchitecture of critical metabolism-regulatory neurons.

The arcuate nucleus (ArcN) is an integrative hub for the regulation of energy balance, reproduction, and arterial pressure (AP), all of which are influenced by Angiotensin II (AngII); however, the cellular mechanisms and downstream neurocircuitry are unclear. Here we show that ArcN AngII increases AP in female rats via two phases, both of which are mediated via activation of AngII type 1 receptors (AT1aR): initial vasopressin-induced vasoconstriction, followed by slowly developing increases in sympathetic nerve activity (SNA) and heart rate (HR). In male rats, ArcN AngII evoked a similarly slow increase in SNA, but the initial pressor response was variable. In females, the effects of ArcN AngII varied during the estrus cycle, with significant increases in SNA, HR, and AP occurring during diestrus and estrus, but only increased AP during proestrus. Pregnancy markedly increased the expression of AT1aR in the ArcN with parallel substantial AngII-induced increases in SNA and MAP. In both sexes, the sympathoexcitation relied on suppression of tonic ArcN sympathoinhibitory Neuropeptide Y inputs, and activation of pro-opiomelanocortin (POMC) projections, to the paraventricular nucleus (PVN). Few or no NPY or POMC neurons expressed the AT1aR, suggesting that AngII increases AP and SNA at least in part indirectly via local interneurons, which express tyrosine hydroxylase (TH) and VGat (i.e. GABAergic). ArcN TH neurons release GABA locally, and central AT1aR and TH neurons mediate stress responses; therefore, we propose that TH AT1aR neurons are well situated to locally coordinate the regulation of multiple modalities within the ArcN in response to stress.SIGNIFICANCEThe arcuate nucleus (ArcN) is an integrative hub for the regulation of energy balance, reproduction, and arterial pressure (AP), all of which are influenced by Angiotensin II (AngII). Here we show that ArcN AngII activates AT1aR to increase AP in male and female rats by slowly increasing sympathetic nerve activity. In females, ArcN AngII also evoked an initial pressor response mediated by vasopressin-induced vasoconstriction. Pregnant and estrus females responded more than males, in association with higher ArcN AT1aR expression. AT1aR were identified in ArcN interneurons that express tyrosine hydroxylase (TH) and GABA. Since brain AT1aR and TH mediate stress responses, ArcN AT1aR TH neurons are well situated to locally coordinate autonomic, hormonal, and behavioral responses to stress.

Autophagy represents a key regulator of aging and metabolism in sensing energy deprivation. We find that fasting in mice activates autophagy in the liver paralleled by activation of hypothalamic AgRP neurons. Optogenetic and chemogenetic activation of AgRP neurons induces autophagy, alters phosphorylation of autophagy regulators, and promotes ketogenesis. AgRP neuron-dependent induction of liver autophagy relies on NPY release in the paraventricular nucleus of the hypothalamus (PVH) via presynaptic inhibition of NPY1R-expressing neurons to activate PVHCRH neurons. Conversely, inhibiting AgRP neurons during energy deprivation abrogates induction of hepatic autophagy and rewiring of metabolism. AgRP neuron activation increases circulating corticosterone concentrations, and reduction of hepatic glucocorticoid receptor expression attenuates AgRP neuron-dependent activation of hepatic autophagy. Collectively, our study reveals a fundamental regulatory principle of liver autophagy in control of metabolic adaptation during nutrient deprivation.

Insulin acts on neurons and glial cells to regulate systemic glucose metabolism and feeding. However, the mechanisms of insulin access in discrete brain regions are incompletely defined. Here we show that insulin receptors in tanycytes, but not in brain endothelial cells, are required to regulate insulin access to the hypothalamic arcuate nucleus. Mice lacking insulin receptors in tanycytes (IR∆Tan mice) exhibit systemic insulin resistance, while displaying normal food intake and energy expenditure. Tanycytic insulin receptors are also necessary for the orexigenic effects of ghrelin, but not for the anorexic effects of leptin. IR∆Tan mice exhibit increased agouti-related peptide (AgRP) neuronal activity, while displaying blunted AgRP neuronal adaptations to feeding-related stimuli. Lastly, a highly palatable food decreases tanycytic and arcuate nucleus insulin signalling to levels comparable to those seen in IR∆Tan mice. These changes are rooted in modifications of cellular stress responses and of mitochondrial protein quality control in tanycytes. Conclusively, we reveal a critical role of tanycyte insulin receptors in gating feeding-state-dependent regulation of AgRP neurons and systemic insulin sensitivity, and show that insulin resistance in tanycytes contributes to the pleiotropic manifestations of obesity-associated insulin resistance.