Project description:The advent of endothermy more than a hundred million years ago is thought to have been a defining feature of mammalian and avian evolution, achieved through continuous fine-tuned homeostatic regulation of core body temperature and metabolism. However, when challenged by food deprivation or harsh environmental conditions, many mammalian species initiate adaptive energy-conserving survival strategies, including torpor and hibernation, during which their core body temperature decreases far below its homeostatic setpoint. How homeothermic mammals initiate and regulate these extraordinary hypothermic states remains largely unknown. Here, we discover that entry into mouse torpor, a fasting-induced state with greatly decreased metabolic rate and body temperature as low as 20°C, is regulated by a population of neurons in the preoptic area of the hypothalamus. We show that re-stimulation of neurons activated during a previous bout of torpor is sufficient to initiate torpor, even in animals that are not calorically restricted. We localize these torpor-regulating neurons to the anteroventral medial and lateral preoptic area and molecularly identify a population of glutamatergic Adcyap1+ neurons whose activity accurately determines when calorically-restricted animals naturally initiate and exit torpor, and whose inhibition disrupts the natural process of torpor entry, maintenance and arousal. Taken together, we discover a specific hypothalamic neuronal subpopulation in the mouse brain that serves as a core regulator of torpor. This work forms the basis for future explorations of mechanisms and circuitry regulating extreme hypothermic and hypometabolic states, enabling genetic access to monitor, initiate, manipulate and study these ancient adaptations of homeotherm biology.
Project description:Homeotherms maintain a stable internal body temperature despite changing environments. During energy deficiency, some species can cease to defend their body temperature and enter a hypothermic and hypometabolic state known as torpor. Despite recent advances in our understanding of thermoregulation, the precise neurons that coordinate these profound thermoregulatory and metabolic changes remain largely unknown. Here, we demonstrate that estrogen-sensitive neurons in the medial preoptic area (MPA) are key drivers of hypothermia and hypometabolism in mice. We find that selectively activating estrogen-sensitive MPA neurons was sufficient to drive a coordinated depression of metabolic rate and body temperature similar to torpor, as measured by body temperature, physical activity, indirect calorimetry, heart rate, and brain activity. Inducing torpor with a prolonged fast revealed larger and more variable calcium transients from estrogen-sensitive MPA neurons during bouts of hypothermia. Finally, selective ablation of estrogen-sensitive MPA neurons demonstrated that these neurons are required for the full expression of fasting-induced torpor. Together, these findings suggest a role for estrogen-sensitive MPA neurons in directing the thermoregulatory and metabolic responses to energy deficiency.
Project description:GFRAL-expressing neurons actuate aversion and nausea, are targets for obesity treatment and may mediate metformin effects by long-term GDF15-GFRAL agonism. If GFRAL+ neurons acutely regulate glucose and energy homeostasis is however underexplored. Here, we report that cell-specific activation of GFRAL+ neurons using a variety of techniques causes a torpor-like state, including hypothermia, the release of stress hormones, a shift from glucose to lipid oxidation, and impaired insulin sensitivity, glucose tolerance and skeletal muscle glucose uptake but augmented glucose uptake in visceral fat. Metabolomic analysis of blood and transcriptomics of muscle and fat indicate alterations in ketogenesis, insulin signaling, adipose tissue differentiation and mitogenesis, or energy fluxes. Our findings reveal that acute GFRAL+ neuron activation induces endocrine and gluco- and thermoregulatory responses associated with nausea and torpor. While chronic activation of GFRAL signaling promotes weight loss in obesity, these results show that acute activation of GFRAL+ neurons causes hypothermia and hyperglycemia.
Project description:Background: Brain glucose-sensing neurons detect glucose fluctuations and prevent severe hypoglycemia, but mechanisms mediating functions of these glucose-sensing neurons are unclear. Methods: We combined mouse genetics, electrophysiology, neural tracing, optogenetics and Patch-RNA-seq to demonstrate how glucose-sensing neurons in the ventrolateral VMH regulate glucose balance. Results: Here we report that estrogen receptor-α (ERα)-expressing neurons in the ventrolateral subdivision of the ventromedial hypothalamic nucleus (vlVMH) are glucose-sensing neurons to a 5-1-5mM glucose fluctuation, being glucose-inhibited neurons (GI-ERαvlVMH) or glucose-excited neurons (GE-ERαvlVMH). Hypoglycemia activates GI-ERαvlVMH neurons via the anoctamin 4 channel, and inhibits GE-ERαvlVMH neurons through opening the ATP-sensitive potassium channel. Further, we show that GI-ERαvlVMH neurons preferentially project to the medioposterior arcuate nucleus of the hypothalamus (mpARH) and GE-ERαvlVMH neurons preferentially project to the dorsal Raphe nuclei (DRN). Activation of ERαvlVMH-mpARH circuit and inhibition of ERαvlVMH-DRN circuit both increase blood glucose. Conclusions: Our results indicate that ERαvlVMH neurons detect glucose fluctuations and prevent severe hypoglycemia in mice.