Probes for INS

Adaptation of liver to the postprandial state requires coordinated regulation of protein synthesis and folding aligned with changes in lipid metabolism. Here we demonstrate that sensory food perception is sufficient to elicit early activation of hepatic mTOR signaling, Xbp1 splicing, increased expression of ER-stress genes, and phosphatidylcholine synthesis, which translate into a rapid morphological ER remodeling. These responses overlap with those activated during refeeding, where they are maintained and constantly increased upon nutrient supply. Sensory food perception activates POMC neurons in the hypothalamus, optogenetic activation of POMC neurons activates hepatic mTOR signaling and Xbp1 splicing, whereas lack of MC4R expression attenuates these responses to sensory food perception. Chemogenetic POMC-neuron activation promotes sympathetic nerve activity (SNA) subserving the liver, and norepinephrine evokes the same responses in hepatocytes in vitro and in liver in vivo as observed upon sensory food perception. Collectively, our experiments unravel that sensory food perception coordinately primes postprandial liver ER adaption through a melanocortin-SNA-mTOR-Xbp1s axis.

The lateral hypothalamic area (LHA) lies at the intersection of multiple neural and humoral systems and orchestrates fundamental aspects of behavior. Two neuronal cell types found in the LHA are defined by their expression of hypocretin/orexin (Hcrt/Ox) and melanin-concentrating hormone (MCH) and are both important regulators of arousal, feeding and metabolism. Conflicting evidence suggests that these cell populations have a more complex signaling repertoire than previously appreciated, particularly in regard to their co-expression of other neuropeptides and the machinery for the synthesis and release of GABA and glutamate. Here, we undertook a single cell expression profiling approach to decipher the neurochemical phenotype, and heterogeneity therein, of Hcrt/Ox and MCH neurons. In transgenic mouse lines, we used single cell qPCR to quantify the expression of 48 key genes, which include neuropeptides, fast neurotransmitter components and other key markers, which revealed unexpected neurochemical diversity. We found that single MCH and Hcrt/Ox neurons express transcripts for multiple neuropeptides and markers of both excitatory and inhibitory fast neurotransmission. Virtually all MCH and approximately half of the Hcrt/Ox neurons sampled express both the machinery for glutamate release and GABA synthesis in the absence of a vesicular GABA release pathway. Furthermore, we found that this profile is characteristic of a subpopulation of LHA glutamatergic neurons but contrasts with a broad population of LHA GABAergic neurons. Identifying the neurochemical diversity of Hcrt/Ox and MCH neurons will further our understanding of how these populations modulate postsynaptic excitability through multiple signaling mechanisms and coordinate diverse behavioral outputs.

Significance Statement The lateral hypothalamic area (LHA) is a key regulator of fundamental behavioral states such as arousal, stress and reward, and disruption of neural circuits in this region is associated with disorders of sleep, feeding and motivated behavior. The multifunctional nature of the LHA is attributable to a heterogeneous population of neurons that exhibit significant phenotypic and neurochemical diversity. Here we sought to resolve aspects of this diversity in two well-studied but incompletely understood LHA neuron populations, defined by their expression of neuropeptides hypocretin/orexin (Hcrt/Ox) and melanin-concentrating hormone (MCH). These efforts lay a foundation for understanding, at a molecular and cellular level, how Hcrt/Ox and MCH neurons coordinate behavioral output and thereby give rise to fundamental innate behavioral states.

Molecular and cellular processes in neurons are critical for sensing and responding to energy deficit states, such as during weight-loss. AGRP neurons are a key hypothalamic population that is activated during energy deficit and increases appetite and weight-gain. Cell type-specific transcriptomics can be used to identify pathways that counteract weight-loss, and here we report high-quality gene expression profiles of AGRP neurons from well-fed and food-deprived young adult mice. For comparison, we also analyzed POMC neurons, an intermingled population that suppresses appetite and body weight. We find that AGRP neurons are considerably more sensitive to energy deficit than POMC neurons. Furthermore, we identify cell type-specific pathways involving endoplasmic reticulum-stress, circadian signaling, ion channels, neuropeptides, and receptors. Combined with methods to validate and manipulate these pathways, this resource greatly expands molecular insight into neuronal regulation of body weight, and may be useful for devising therapeutic strategies for obesity and eating disorders.