The endogenous metabolite itaconate has recently emerged as a regulator of macrophage function, but its precise mechanism of action remains poorly understood. Here we show that itaconate is required for the activation of the anti-inflammatory transcription factor Nrf2 (also known as NFE2L2) by lipopolysaccharide in mouse and human macrophages. We find that itaconate directly modifies proteins via alkylation of cysteine residues. Itaconate alkylates cysteine residues 151, 257, 288, 273 and 297 on the protein KEAP1, enabling Nrf2 to increase the expression of downstream genes with anti-oxidant and anti-inflammatory capacities. The activation of Nrf2 is required for the anti-inflammatory action of itaconate. We describe the use of a new cell-permeable itaconate derivative, 4-octyl itaconate, which is protective against lipopolysaccharide-induced lethality in vivo and decreases cytokine production. We show that type I interferons boost the expression of Irg1 (also known as Acod1) and itaconate production. Furthermore, we find that itaconate production limits the type I interferon response, indicating a negative feedback loop that involves interferons and itaconate. Our findings demonstrate that itaconate is a crucial anti-inflammatory metabolite that acts via Nrf2 to limit inflammation and modulate type I interferons.

Hypothalamic AMP-activated protein kinase (AMPK) has been suggested to act as a key sensing mechanism, responding to hormones and nutrients in the regulation of energy homeostasis. However, the precise neuronal populations and cellular mechanisms involved are unclear. The effects of long-term manipulation of hypothalamic AMPK on energy balance are also unknown. To directly address such issues, we generated POMCα2KO and AgRPα2KO mice lacking AMPKα2 in proopiomelanocortin-(POMC-) and agouti-related protein-expressing (AgRP-expressing) neurons, key regulators of energy homeostasis. POMCα2KO mice developed obesity due to reduced energy expenditure and dysregulated food intake but remained sensitive to leptin. In contrast, AgRPα2KO mice developed an age-dependent lean phenotype with increased sensitivity to a melanocortin agonist. Electrophysiological studies in AMPKα2-deficient POMC or AgRP neurons revealed normal leptin or insulin action but absent responses to alterations in extracellular glucose levels, showing that glucose-sensing signaling mechanisms in these neurons are distinct from those pathways utilized by leptin or insulin. Taken together with the divergent phenotypes of POMCα2KO and AgRPα2KO mice, our findings suggest that while AMPK plays a key role in hypothalamic function, it does not act as a general sensor and integrator of energy homeostasis in the mediobasal hypothalamus.

Leptin, the protein encoded by the obese (ob) gene, is secreted from adipose tissue and is thought to act in the central nervous system to regulate food intake and body weight. It has been proposed that leptin acts in the hypothalamus, the main control centre for satiety and energy expenditure. Mutations in leptin or the receptor isoform (Ob-R[L]) present in hypothalamic neurons result in profound obesity and symptoms of non-insulin-dependent diabetes. Here we show that leptin hyperpolarizes glucose-receptive hypothalamic neurons of lean Sprague-Dawley and Zucker rats, but is ineffective on neurons of obese Zucker (fa/fa) rats. This hyperpolarization is due to the activation of a potassium current, and is not easily recovered on removal of leptin, but is reversed by applying the sulphonylurea, tolbutamide. Single-channel recordings demonstrate that leptin activates an ATP-sensitive potassium (K[ATP]) channel. Our data indicate that the K(ATP) channel may function as the molecular end-point of the pathway following leptin activation of the Ob-R(L) receptor in hypothalamic neurons.

Insulin and leptin receptors are present in hypothalamic regions that control energy homeostasis, and these hormones reduce food intake and body weight in lean, but not obese, Zucker rats. Here we demonstrate that insulin, like leptin, hyperpolarizes lean rat hypothalamic glucose-responsive (GR) neurons by opening KATP channels. These findings suggest hypothalamic K ATP channel function is crucial to physiological regulation of food intake and body weight.

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