Probes for INS

Activation of Agouti-Related Peptide (AgRP)-expressing neurons promotes feeding and insulin resistance. Here, we examine the contribution of neuropeptide Y (NPY)-dependent signaling to the diverse physiological consequences of activating AgRP neurons. NPY-deficient mice fail to rapidly increase food intake during the first hour of either chemo- or optogenetic activation of AgRP neurons, while the delayed increase in feeding is comparable between control and NPY-deficient mice. Acutely stimulating AgRP neurons fails to induce systemic insulin resistance in NPY-deficient mice, while increased locomotor activity upon AgRP neuron stimulation in the absence of food remains unaffected in these animals. Selective re-expression of NPY in AgRP neurons attenuates the reduced feeding response and reverses the protection from insulin resistance upon optogenetic activation of AgRP neurons in NPY-deficient mice. Collectively, these experiments reveal a pivotal role of NPY-dependent signaling in mediating the rapid feeding inducing effect and the acute glucose regulatory function governed by AgRP neurons

Leptin acts on hypothalamic neurons expressing agouti-related protein (AgRP) or pro-opiomelanocortin (POMC) to suppress appetite and increase energy expenditure, but the intracellular mechanisms that modulate central leptin signalling are not fully understood. Here we show that growth factor receptor-bound protein 10 (Grb10), an adaptor protein that binds to the insulin receptor and negatively regulates its signalling pathway, can interact with the leptin receptor and enhance leptin signalling. Ablation of Grb10 in AgRP neurons promotes weight gain, while overexpression of Grb10 in AgRP neurons reduces body weight in male and female mice. In parallel, deletion or overexpression of Grb10 in POMC neurons exacerbates or attenuates diet-induced obesity, respectively. Consistent with its role in leptin signalling, Grb10 in AgRP and POMC neurons enhances the anorexic and weight-reducing actions of leptin. Grb10 also exaggerates the inhibitory effects of leptin on AgRP neurons via ATP-sensitive potassium channel-mediated currents while facilitating the excitatory drive of leptin on POMC neurons through transient receptor potential channels. Our study identifies Grb10 as a potent leptin sensitizer that contributes to the maintenance of energy homeostasis by enhancing the response of AgRP and POMC neurons to leptin.

Transporters of the SLC25 mitochondrial carrier superfamily bridge cytoplasmic and mitochondrial metabolism by channeling metabolites across mitochondrial membranes and are pivotal for metabolic homeostasis. Despite their physiological relevance as gatekeepers of cellular metabolism, most of the SLC25 family members remain uncharacterized. We undertook a comprehensive tissue distribution analysis of all Slc25 family members across metabolic organs and identified SLC25A47 as a liver-specific mitochondrial carrier.We used a murine loss-of-function model to unravel the role of this transporter in mitochondrial and hepatic homeostasis. We performed extensive metabolic phenotyping and molecular characterization of newly generated Slc25a47hep-/- and Slc25a47-Fgf21hep-/- mice.Slc25a47hep-/- mice displayed a wide variety of metabolic abnormalities, as a result of sustained energy deficiency in the liver originating from impaired mitochondrial respiration in this organ. This mitochondrial phenotype was associated with an activation of the mitochondrial stress response (MSR) in the liver, and the development of fibrosis, which was exacerbated upon feeding a high-fat high-sucrose diet. The MSR induced the secretion of several mitokines, amongst which FGF21 played a preponderant role on systemic physiology. To dissect the FGF21-dependent and -independent physiological changes induced in Slc25a47hep-/- mice, we generated a double Slc25a47-Fgf21hep-/- mouse model and demonstrated that several aspects of the hypermetabolic state were driven by hepatic secretion of FGF21. On the other hand, the metabolic fuel inflexibility observed in Slc25a47hep-/- mice could not be rescued with the genetic removal of Fgf21.Collectively, our data place SLC25A47 at the center of mitochondrial homeostasis, which upon dysfunction triggers robust liver-specific and systemic adaptive stress responses. The prominent role of SLC25A47 in hepatic fibrosis identifies this carrier, or its transported metabolite, as a potential target for therapeutic intervention.SLC25A47 is a liver-specific mitochondrial carrier. Slc25a47hep-/- mice are unable to maintain mitochondrial homeostasis in hepatocytes and show impaired mitochondrial respiration resulting in chronic energy deficiency, mitochondrial stress, and fibrosis in hepatocytes. Hepatic mitochondrial stress is characterized by the secretion of the mitokine FGF21 which drives a strong and systemic hypermetabolic state impacting whole-body physiology.

The brain plays a crucial role in maintaining the bodys energy needs, a process involving the activity of a group of hypothalamic neurons that express the neuropeptidergic marker pro-opiomelanocortin (POMC). POMC neuronal dysfunction can cause obesity and its associated metabolic sequelae. However, this population of neurons is highly diverse at a molecular and functional level, and whether or not such heterogeneity is implicated in disease establishment or progression has yet to be elucidated. Here, using a lineage-tracing approach in combination with histological and electrophysiological tools, we have characterized POMC neuronal cells at a single-cell resolution in control of lean and diet-induced obese (DIO) mice. Thanks to this genetic strategy, we traced with a reporter protein POMC neurons in adult mice, thus studying these neuronal cells independently from the expression of their main marker POMC. Different histological techniques, including immunohistochemistry, fluorescent in-situ hybridization, and RNAscope, have been used to cluster genetically traced POMC neuronal cells based on their expression of the main marker POMC. These different approaches consistently allowed the identification of a previously uncharacterized sub-population that expresses negligible POMC mRNA and protein levels, which we named Ghost-POMC neurons. We also observed that Ghost-POMC neurons are insensitive to acute nutritional cues (fasting and refeeding) relative to classic POMC positive neurons. Intriguingly, DIO mice presented an increased number of Ghost-POMC neurons relative to control animals. Furthermore, we developed an approach that combines whole-cell patch-clamp of traced POMC neurons with the subsequent molecular profiling of the patched cell by single-cell qPCR. Thanks to this approach, we observed that DIO leads to electrical alterations only in a fraction of POMC neurons expressing undetectable levels of POMC mRNA, which is reminiscent of the Ghost population previously identified by histological techniques. Thus, Ghost-POMC neurons might constitute a novel subpopulation of POMC neurons that undergo dysfunction in response to prolonged dietary cues, perhaps contributing to obesity establishment or progression.

Calorie-rich diets induce hyperphagia and promote obesity, although the underlying mechanisms remain poorly defined. We find that short-term high-fat-diet (HFD) feeding of mice activates prepronociceptin (PNOC)-expressing neurons in the arcuate nucleus of the hypothalamus (ARC). PNOCARC neurons represent a previously unrecognized GABAergic population of ARC neurons distinct from well-defined feeding regulatory AgRP or POMC neurons. PNOCARC neurons arborize densely in the ARC and provide inhibitory synaptic input to nearby anorexigenic POMC neurons. Optogenetic activation of PNOCARC neurons in the ARC and their projections to the bed nucleus of the stria terminalis promotes feeding. Selective ablation of these cells promotes the activation of POMC neurons upon HFD exposure, reduces feeding, and protects from obesity, but it does not affect food intake or body weight under normal chow consumption. We characterize PNOCARC neurons as a novel ARC neuron population activated upon palatable food consumption to promote hyperphagia