One-day high-fat diet induces inflammation in the nodose ganglion and hypothalamus of mice

A high-fat diet (HFD) induces inflammation in systemic organs including the hypothalamus, resulting in obesity and diabetes. The vagus nerve connects the visceral organs and central nervous system, and the gastric-derived orexigenic peptide ghrelin transmits its starvation signals to the hypothalamus via the vagal afferent nerve. Here we investigated the inflammatory response in vagal afferent neurons and the hypothalamus in mice following one day of HFD feeding. This treatment increased the number of macrophages/microglia in the nodose ganglion and hypothalamus. Furthermore, one-day HFD induced expression of Toll-like receptor 4 in the goblet cells of the colon and upregulated mRNA expressions of the proinflammatory biomarkers Emr1, Iba1, Il6, and Tnfα in the nodose ganglion and hypothalamus. Both subcutaneous administration of ghrelin and celiac vagotomy reduced HFD-induced inflammation in these tissues. HFD intake triggered inflammatory responses in the gut, nodose ganglion, and subsequently in the hypothalamus within 24 h. These findings suggest that the vagal afferent nerve may transfer gut-derived inflammatory signals to the hypothalamus via the nodose ganglion, and that ghrelin may protect against HFD-induced inflammation.

Diet-induced obesity causes peripheral and central ghrelin resistance by promoting inflammation

Ghrelin, a stomach-derived orexigenic peptide, transmits starvation signals to the hypothalamus via the vagus afferent nerve. Peripheral administration of ghrelin does not induce food intake in high fat diet (HFD)-induced obese mice. We investigated whether this ghrelin resistance was caused by dysfunction of the vagus afferent pathway. Administration (s.c.) of ghrelin did not induce food intake, suppression of oxygen consumption, electrical activity of the vagal afferent nerve, phosphorylation of ERK2 and AMP-activated protein kinase alpha in the nodose ganglion, or Fos expression in hypothalamic arcuate nucleus of mice fed a HFD for 12 weeks. Administration of anti-ghrelin IgG did not induce suppression of food intake in HFD-fed mice. Expression levels of ghrelin receptor mRNA in the nodose ganglion and hypothalamus of HFD-fed mice were reduced. Inflammatory responses, including upregulation of macrophage/microglia markers and inflammatory cytokines, occurred in the nodose ganglion and hypothalamus of HFD-fed mice. A HFD blunted ghrelin signaling in the nodose ganglion via a mechanism involving in situ activation of inflammation. These results indicate that ghrelin resistance in the obese state may be caused by dysregulation of ghrelin signaling via the vagal afferent.

Central Regulation of Branched-Chain Amino Acids Is Mediated by AgRP Neurons

Circulating branched-chain amino acids (BCAAs) are elevated in obesity and diabetes, and recent studies support a causal role for BCAAs in insulin resistance and defective glycemic control. The physiological mechanisms underlying BCAA regulation are poorly understood. Here we show that insulin signaling in the mediobasal hypothalamus (MBH) of rats is mandatory for lowering plasma BCAAs, most probably by inducing hepatic BCAA catabolism. Insulin receptor deletion only in agouti-related protein (AgRP)-expressing neurons (AgRP neurons) in the MBH impaired hepatic BCAA breakdown and suppression of plasma BCAAs during hyperinsulinemic clamps in mice. In support of this, chemogenetic stimulation of AgRP neurons in the absence of food significantly raised plasma BCAAs and impaired hepatic BCAA degradation. A prolonged fasting or ghrelin treatment recapitulated designer receptors exclusively activated by designer drugs-induced activation of AgRP neurons and increased plasma BCAAs. Acute stimulation of vagal motor neurons in the dorsal motor nucleus was sufficient to decrease plasma BCAAs. Notably, elevated plasma BCAAs were associated with impaired glucose homeostasis. These findings suggest a critical role of insulin signaling in AgRP neurons for BCAA regulation and raise the possibility that this control may be mediated primarily via vagal outflow. Furthermore, our results provide an opportunity to closely examine the potential mechanistic link between central nervous system-driven BCAA control and glucose homeostasis.

Chemogenetic stimulation of the parasympathetic nervous system lowers hepatic lipid accumulation and inflammation in a nonalcoholic steatohepatitis mouse model

AIMS

The role of the parasympathetic nervous system (PNS) in the pathogenesis of nonalcoholic steatohepatitis (NASH) is largely unknown. In this study, the effect of PNS modulation on NASH was investigated using chemogenetics.

MAIN METHODS

A streptozotocin (STZ) and high-fat diet (HFD)-induced NASH mouse model was used. To activate or inhibit the PNS, chemogenetic human M3-muscarinic receptor coupled with either Gq or Gi protein-containing viruses was injected into the dorsal motor nucleus of the vagus at week 4 and clozapine N-oxide was administered intraperitoneally for a week from week 11. Three groups (PNS-stimulation, PNS-inhibition, and control) were compared in terms of heart rate variability (HRV), histological lipid droplet area, nonalcoholic fatty liver disease activity score (NAS), the area of F4/80-positive macrophages, and biochemical responses.

KEY FINDINGS

The STZ/HFD-treated mouse model showed typical histological characteristics of NASH. HRV analysis confirmed that PNS-stimulation and PNS-inhibition groups had significantly higher and lower PNS activity, respectively (both P < 0.05). The PNS-stimulation group showed a significantly smaller hepatic lipid droplet area (14.3 % vs. 20.6 %, P = 0.02) and lower NAS (5.2 vs. 6.3, P = 0.047) than the control group. The area of F4/80-positive macrophages was significantly smaller in the PNS-stimulation group than in the control group (4.1 % vs. 5.6 %, P = 0.04). The PNS-stimulation group showed a lower serum aspartate aminotransferase level than the control group (119.0 vs. 356.0 U/L, P = 0.04).

SIGNIFICANCE

In STZ/HFD-treated mice, chemogenetic stimulation of the PNS significantly reduced hepatic fat accumulation and inflammation. The hepatic PNS may play a pivotal role in the pathogenesis of NASH.

Mitochondria-derived peptide SHLP2 regulates energy homeostasis through the activation of hypothalamic neurons

Small humanin-like peptide 2 (SHLP2) is a mitochondrial-derived peptide implicated in several biological processes such as aging and oxidative stress. However, its functional role in the regulation of energy homeostasis remains unclear, and its corresponding receptor is not identified. Hereby, we demonstrate that both systemic and intracerebroventricular (ICV) administrations of SHLP2 protected the male mice from high-fat diet (HFD)-induced obesity and improved insulin sensitivity. In addition, the activation of pro-opiomelanocortin (POMC) neurons by SHLP2 in the arcuate nucleus of the hypothalamus (ARC) is involved in the suppression of food intake and the promotion of thermogenesis. Through high-throughput structural complementation screening, we discovered that SHLP2 binds to and activates chemokine receptor 7 (CXCR7). Taken together, our study not only reveals the therapeutic potential of SHLP2 in metabolic disorders but also provides important mechanistic insights into how it exerts its effects on energy homeostasis.

Antagonistic interaction between central glucagon-like Peptide-1 and oxytocin on diet-induced obesity mice

Glucagon-like peptide-1 (GLP-1), whose agonists are widely prescribed, is a peptide proven effective in reducing obesity. Similarly, oxytocin (OXT) is a peptide known to increase satiety and help reduce body weight. In the present study, we aimed to examine the metabolic effects of co-administration of GLP-1 and OXT in diet-induced obesity (DIO) mice to elucidate their functions and interactions in the central nervous system. To this end, 40 DIO mice were subjected to stereotaxic surgery for the installation of an osmotic minipump and intracerebroventricular administration of GLP-1, OXT, or both. Initially, it was anticipated that co-administration of these anorexigenic peptides would be as effective as, if not more than, either GLP-1 or OXT alone in providing metabolic benefits to the obese mice. Interestingly, co-administration of OXT and GLP-1 offset the reductions in body weight and food intake promoted by either peptide alone. Co-administration also negated the decrease in fat and increase in lean mass produced by either peptide alone. Moreover, co-administration showed an equivalent calorimetric benefit as either peptide alone. Therefore, these results suggest antagonistic, rather than synergistic or additive, effects of centrally administered GLP-1 and OXT that attenuate the metabolic benefits of either peptide.

Erratum to: Stomach clusterin as a gut-derived feeding regulator

[Erratum to: BMB Reports 2024; 57(3): 149-154, PMID: 37817436, PMCID: PMC10979347] The BMB Reports would like to correct in BMB Rep. 57(3):149-154, titled "Stomach clusterin as a gut-derived feeding regulator". This research was supported by the Creative-Pioneering Researchers Program through Seoul National University. Since grant name and number are incorrect, this information has now been corrected as follows: This work was supported by the National Research Foundation of Korea funded by the Korean government (2020R1A2C3004843, 2022M3E5E8017213 to M-S.K., 2020R1C1C10 08033 to O.K.) and by Creative-Pioneering Researchers Program through Seoul National University (to O.K.). The authors apologize for any inconvenience or confusion that may be caused by this error. The ACKNOWLEDGEMENTS of Original PDF version have been corrected.

Stomach clusterin as a gut-derived feeding regulator

The stomach has emerged as a crucial endocrine organ in the regulation of feeding since the discovery of ghrelin. Gut-derived hormones, such as ghrelin and cholecystokinin, can act through the vagus nerve. We previously reported the satiety effect of hypothalamic clusterin, but the impact of peripheral clusterin remains unknown. In this study, we administered clusterin intraperitoneally to mice and observed its ability to suppress fasting-driven food intake. Interestingly, we found its synergism with cholecystokinin and antagonism with ghrelin. These effects were accompanied by increased c-fos immunoreactivity in nucleus tractus solitarius, area postrema, and hypothalamic paraventricular nucleus. Notably, truncal vagotomy abolished this response. The stomach expressed clusterin at high levels among the organs, and gastric clusterin was detected in specific enteroendocrine cells and the submucosal plexus. Gastric clusterin expression decreased after fasting but recovered after 2 hours of refeeding. Furthermore, we confirmed that stomachspecific overexpression of clusterin reduced food intake after overnight fasting. These results suggest that gastric clusterin may function as a gut-derived peptide involved in the regulation of feeding through the gut-brain axis. [BMB Reports 2024; 57(3): 149-154].

Activation of ChAT+ neuron in dorsal motor vagus (DMV) increases blood glucose through the regulation of hepatic gene expression in mice

The brain and peripheral organs communicate through hormones and neural connections. Proper communication is required to maintain normal whole-body energy homeostasis. In addition to endocrine system, from the perspective of neural connections for metabolic homeostasis, the role of the sympathetic nervous system has been extensively studied, but understanding of the parasympathetic nervous system is limited. The liver plays a central role in glucose and lipid metabolism. This study aimed to clarify the innervation of parasympathetic nervous system in the liver and its functional roles in metabolic homeostasis. The liver-specific parasympathetic nervous system innervation (PNS) was shown by tissue clearing, immunofluorescence and transgenic mice at the three-dimensional histological level. The parasympathetic efferent signals were manipulated using a chemogenetic technique and the activation of ChAT+ parasympathetic neurons in dorsal motor vagus (DMV) results in the increased blood glucose through the elevated hepatic gluconeogenic and lipogenic gene expression in the liver. Thus, our study showed the evidence of ChAT+ parasympathetic neurons in the liver and its role for hepatic parasympathetic nervous signaling in glucose homeostasis through the regulation of hepatic gene expression.