UCP2-dependent redox sensing in POMC neurons regulates feeding

Synergism Between Hypothalamic Astrocytes and Neurons in Metabolic Control

Astrocytes are no longer considered as passive support cells. In the hypothalamus, these glial cells actively participate in the control of appetite, energy expenditure, and the processes leading to obesity and its secondary complications. Here we briefly review studies supporting this conclusion and the advances made in understanding the underlying mechanisms.

Regulation of hypothalamic reactive oxygen species and feeding behavior by phosphorylation of the beta 2 thyroid hormone receptor isoform

Unlike other thyroid hormone receptors (THRs), the beta 2 isoform (THRB2) has a restricted expression pattern and is uniquely and abundantly phosphorylated at a conserved serine residue S101 (S102 in humans). Using tagged and or phosphorylation-defective (S101A) THRB2 mutant mice, we show that THRB2 is present in a large subset of POMC neurons and mitigates ROS accumulation during ROS-triggering events, such as fasting/refeeding or high fat diet (HFD). Excessive ROS accumulation in mutant POMC neurons was accompanied by a skewed production of orexigenic/anorexigenic hormones, resulting in elevated food intake. The prolonged exposure to pathogenic hypothalamic ROS levels during HFD feeding lead to a significant loss of POMC neurons in mutant versus wild-type (WT) mice. In cultured cells, the presence of WT THRB2 isoform, but not other THRs, or THRB2S101A, reduced ROS accumulation upon exogenous induction of oxidative stress by tert-butyl hydroperoxide. The protective function of phospho-THRB2 (pTHRB2) did not require thyroid hormone (TH), suggesting a TH-independent role of the THRB2 isoform, and phospho-S101 in particular, in regulating oxidative stress. We propose that pTHRB2 has a fundamental role in neuronal protection against ROS cellular damage, and mitigates hypothalamic pathological changes found in diet-induced obesity.

Microglia in Central Control of Metabolism

Beyond their role as brain immune cells, microglia act as metabolic sensors in response to changes in nutrient availability, thus playing a role in energy homeostasis. This review highlights the evidence and challenges of studying the role of microglia in metabolism regulation.

Electrophysiological Comparison of Definitive Pro-opiomelanocortin Neurons in the Arcuate Nucleus and the Retrochiasmatic Area of Male and Female Mice

Pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus (ARC) are considered a major site of leptin action. Due to increasing evidence that POMC neurons are highly heterogeneous and indications that the conventional molecular tools to study their functions have important limitations, a reassessment of leptin's effects on definitive POMC neurons is needed. POMC neurons are also expressed in the retrochiasmatic area (RCA), where their function is poorly understood. Furthermore, the response of POMC neurons to leptin in females is largely unknown. Therefore, the present study aimed to determine the differences in leptin responsiveness of POMC neurons in the ARC and the RCA using a mouse model allowing adult-inducible fluorescent labeling. We performed whole-cell patch clamp electrophysiology on 154 POMC neurons from male and female mice. We confirmed and extended the model by which leptin depolarizes POMC neurons, in both the ARC and the RCA. Furthermore, we characterized the electrophysiological properties of an underappreciated subpopulation representing ∼10% of hypothalamic POMC neurons that are inhibited by leptin. We also provide evidence that sex does not appear to be a major determinant of basal properties and leptin responsiveness of POMC neurons, but that females are overall less responsive to leptin compared to males.

Recent progress on action and regulation of anorexigenic adipokine leptin

Organismal energy balance is controlled by inter-tissue communication mediated by the nervous system and hormones, the disruption of which causes metabolic syndrome exemplified by diabetes and obesity. Fat-storing adipose tissue, especially those located in subcutaneous white adipose tissue, secretes leptin in a proportion of fat mass, inhibiting the accumulation of organismal fat by suppressing appetite and promoting energy expenditure. With a prevalence of obesity that exhibits hyperleptinemia, most of the investigation on leptin has been focused on how it works and how it does not, which is expected to be a clue for treating obesity. In contrast, how it is synthesized, transported, and excreted, all of which are relevant to the homeostasis of blood leptin concentration, are not much understood. Of note, acute leptin reduction after hyperleptinemia in the context of obesity exhibited a beneficial effect on obesity and insulin sensitivity, indicating that manipulation of circulating leptin level may provide a therapeutic strategy. Technological advances such as "omics" analysis combined with sophisticated gene-engineered mice studies in the past decade enabled a deeper understanding of leptin's action in more detail. Here, we summarize the updated understanding of the action as well as regulation of leptin and point out the emerging direction of research on leptin.

Exerkines and redox homeostasis

Exercise physiology has gained increasing interest due to its wide effects to promote health. Recent years have seen a growth in this research field also due to the finding of several circulating factors that mediate the effects of exercise. These factors, termed exerkines, are metabolites, growth factors, and cytokines secreted by main metabolic organs during exercise to regulate exercise systemic and tissue-specific effects. The metabolic effects of exerkines have been broadly explored and entail a promising target to modulate beneficial effects of exercise in health and disease. However, exerkines also have broad effects to modulate redox signaling and homeostasis in several cellular processes to improve stress response. Since redox biology is central to exercise physiology, this review summarizes current evidence for the cross-talk between redox biology and exerkines actions. The role of exerkines in redox biology entails a response to oxidative stress-induced pathological cues to improve health outcomes and to modulate exercise adaptations that integrate redox signaling.