Heme is an essential prosthetic group of numerous proteins and a central signaling molecule in many physiologic processes 1,2. The chemical reactivity of heme requires that a network of intracellular chaperone proteins exist to avert the cytotoxic effects of free heme, but the constituents of such trafficking pathways are unknown 3,4. Heme synthesis is completed in mitochondria, with ferrochelatase (FECH) adding iron to protoporphyrin IX. How this vital but Reprints and permissions information is available at http://www.nature.com/reprints.Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Highlights d Calorie restriction (CR) causes hypothermia and elevates Leu-enkephalin d Activation of prodynorphin neurons lowers temperature d Inhibition of kappa opioid receptor (KOR) neurons reduces CR-induced hypothermia d Blocking KOR halts CR-induced hypothermia, promoting weight loss during dieting

BackgroundThe majority of Parkinson’s disease (PD) cases are sporadic and idiopathic suggesting that this neurodegenerative disorder is the result of both environmental and genetic factors. Stress and neuroinflammation are among the factors being investigated for their possible contributions to PD. Experiments in rodents showed that severe chronic stress can reduce the number of dopaminergic neurons in the substantia nigra pars compacta (SNc); the same cells that are lost in PD. These actions are at least in part mediated by increased oxidative stress. Here, we tested the hypothesis that the interleukin-13 receptor alpha 1 (IL-13Rα1), a cytokine receptor whose activation increases the vulnerability of dopaminergic neurons to oxidative damage, participates in the stress-dependent damage of these neurons.MethodsMice were subject to daily sessions of 8 h (acute) stress for 16 weeks (5 days a week), a procedure previously showed to induce loss of dopaminergic neurons in the SNc. The source and the kinetics of interleukin-13 (IL-13), the endogenous ligand of IL-13Rα1, were evaluated 0, 1, 3, 6, and 8 h and at 16 weeks of stress. Identification of IL-13 producing cell-type was performed by immunofluorescent and by in situ hybridization experiments. Markers of oxidative stress, microglia activation, and the number of dopaminergic neurons in IL-13Rα1 knock-out animals (Il13ra1 Y/−) and their wild-type littermates (Il13ra1 Y/+) were evaluated at 16 weeks of stress and at 20 weeks, following a 4 week non-stressed period and compared to non-stressed mice.ResultsIL-13 was expressed in microglial cells within the SN and in a fraction of the tyrosine hydroxylase-positive neurons in the SNc. IL-13 levels were elevated during daily stress and peaked at 6 h. 16 weeks of chronic restraint stress significantly reduced the number of SNc dopaminergic neurons in Il13ra1 Y/+mice. Neuronal loss at 16 weeks was significantly lower in Il13ra1 Y/− mice. However, the loss of dopaminergic neurons measured at 20 weeks, after 4 weeks of non-stress following the 16 weeks of stress, was similar in Il13ra1 Y/+ and Il13ra1 Y/− mice.ConclusionsIL-13, a cytokine previously demonstrated to increase the susceptibility of SNc dopaminergic neurons to oxidative stress, is elevated in the SN by restraint stress. Lack of IL-13Rα1 did not prevent nor halted but delayed neuronal loss in the mouse model of chronic restraint stress. IL-13/IL-13Rα1 may represent a target to reduce the rate of DA neuronal loss that can occur during severe chronic restraint stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-017-0862-1) contains supplementary material, which is available to authorized users.

When food resources are scarce, endothermic animals can lower core body temperature (T b ). This phenomenon is believed to be part of an adaptive mechanism that may have evolved to conserve energy until more food becomes available. Here, we found in the mouse that the insulin-like growth factor 1 receptor (IGF-1R) controls this response in the central nervous system. Pharmacological or genetic inhibition of IGF-1R enhanced the reduction of temperature and of energy expenditure during calorie restriction. Full blockade of IGF-1R affected female and male mice similarly. In contrast, genetic IGF-1R dosage was effective only in females, where it also induced transient and estrusspecific hypothermia in animals fed ad libitum. These effects were regulated in the brain, as only central, not peripheral, pharmacological activation of IGF-1R prevented hypothermia during calorie restriction. Targeted IGF-1R knockout selectively in forebrain neurons revealed that IGF signaling also modulates calorie restriction-dependent T b regulation in regions rostral of the canonical hypothalamic nuclei involved in controlling body temperature. In aggregate, these data identify central IGF-1R as a mediator of the integration of nutrient and temperature homeostasis. They also show that calorie restriction, IGF-1R signaling, and body temperature, three of the main regulators of metabolism, aging, and longevity, are components of the same pathway.IGF-1R | temperature | calorie restriction | energy homeostasis | aging

Calorie restriction (CR) enhances health span (the length of time that an organism remains healthy) and increases longevity across species. In mice, these beneficial effects are partly mediated by the lowering of core body temperature that occurs during CR. Conversely, the favorable effects of CR on health span are mitigated by elevating ambient temperature to thermoneutrality (30°C), a condition in which hypothermia is blunted. In this study, we compared the global metabolic response to CR of mice housed at 22°C (the standard housing temperature) or at 30°C and found that thermoneutrality reverted 39 and 78% of total systemic or hypothalamic metabolic variations caused by CR, respectively. Systemic changes included pathways that control fuel use and energy expenditure during CR. Cognitive computing-assisted analysis of these metabolomics results helped to prioritize potential active metabolites that modulated the hypothermic response to CR. Last, we demonstrated with pharmacological approaches that nitric oxide (NO) produced through the citrulline-NO pathway promotes CR-triggered hypothermia and that leucine enkephalin directly controls core body temperature when exogenously injected into the hypothalamus. Because thermoneutrality counteracts CR-enhanced health span, the multiple metabolites and pathways altered by thermoneutrality may represent targets for mimicking CR-associated effects.