Altered R-spondin 1/CART neurocircuit in the hypothalamus contributes to hyperphagia in diabetes

Nogo-B deficiency suppresses white adipogenesis by regulating β-catenin signaling

AIMS

Obesity is a global epidemic around the world. Reticulon-4B (Nogo-B) is an endoplasmic reticulum-resident protein. Our previous work demonstrated that Nogo-B deficiency inhibited obesity and decreased the size of white adipocytes. However, the underlying molecular mechanism of Nogo-B in white adipogenesis remains poorly understood. This study aims to explore the effect of Nogo-B in white adipogenesis, as well as its underlying molecular mechanisms.

MAIN METHODS AND FINDINGS

The study adopted mouse embryonic fibroblasts (MEFs) and 3T3-L1 preadipocytes to induce white adipogenesis and investigate the effect of Nogo-B on adipogenesis using qRT-PCR, Western blotting, immunofluorescence, lipid quantification, and Oil Red O staining. During white adipogenesis, Nogo-B expression was increased accompanied by upregulation of adipogenic markers. In contrast, Nogo-B deficiency inhibited white adipocyte markers expression and lipid accumulation. Furthermore, the mechanism study showed that Nogo-B deficiency decreased the destruction complex [AXIN1-APC-glycogen synthase kinase 3β (GSK3β)] levels through activating protein kinase B 2 (AKT2), resulting in β-catenin translocating into the nucleus and inhibiting the expression of adipogenic markers. Moreover, Nogo-B deficiency promoted the expression of brown/beige adipocytes markers while improving mitochondrial thermogenesis by activating β-catenin pathway. In addition, Nogo-B deficiency reduced the levels of inflammatory molecules during white adipogenic differentiation.

SIGNIFICANCE

This study revealed that Nogo-B deficiency inhibited white adipogenesis through AKT2/GSK3β/β-catenin pathway. Meanwhile, Nogo-B deficiency increased the expression of brown/beige adipocyte markers and promoted mitochondrial thermogenesis. In addition, Nogo-B deficiency reduced inflammatory cytokine levels caused by adipogenesis. Collectively, blocking Nogo-B expression may be a potential strategy to suppress white adipogenesis.

Mechanism of Jujube (Ziziphus jujuba Mill.) Fruit in the Appetite Regulation Based on Network Pharmacology and Molecular Docking Method

Objective

To investigate the mechanism of jujube (Ziziphus jujuba Mill.) in appetite regulation based on network pharmacology.

Methods

The active components and action targets of jujube were retrieved through the TCMSP and TCMID databases. GeneCards, DisGeNet, Therapeutic Target Database, and OMIM were used to screen the related targets for appetite, appetite suppression, and appetite regulation, and the intersection target of the two was selected. A protein-protein interaction (PPI) network was constructed. Important protein nodes and subnets were predicted based on the cytoHubba plug-in, and the hub gene was screened. Additionally, GO and KEGG pathway analyses were performed to obtain potential biological processes and signaling pathways of key targets. And the active ingredient-target-action pathway diagram was constructed.

Results

A total of 16 active components were screened from jujube, including 131 action targets related to appetite and appetite regulation. Three key targets (MAOA, MMP2, and HSPB1) were screened out by MCODE analysis. KEGG enrichment analysis was mainly enriched in neuroactive ligand-receptor interaction, serotonin-containing synapse, gap junction, cAMP signaling pathway, and dopaminergic synapse. Molecular docking results showed that the components coclaurine, (−)-catenin, (+)-stepholidine, berberine, cianidanol, coclaurine, and moupinamide in jujube had strong binding activity to the main targets (ESR1, ADRA2C, and MMP2).

Conclusion

Based on network pharmacology, the appetite modulating effects of jujube on multiple components, targets, and channels were explored, and the main active components of jujube were predicted to act on multiple signaling pathways to regulate appetite. The molecular docking results showed that the components in jujube had strong binding activity to the main targets, which provided new ideas and methods to further investigate the mechanisms of appetite regulation by jujube.

Congenital Anomalies Programmed by Maternal Diabetes and Obesity on Offspring of Rats

Embryo-fetal exposure to maternal disorders during intrauterine life programs long-term consequences for the health and illness of offspring. In this study, we evaluated whether mild diabetic rats that were given high-fat/high-sugar (HF/HS) diet presented maternal and fetal changes at term pregnancy. Female rats received citrate buffer (non-diabetic-ND) or streptozotocin (diabetic-D) after birth. According to the oral glucose tolerance test (OGTT), the experimental groups (n = 11 animals/group) were composed of non-diabetic and diabetic receiving standard diet (S) or HF/HS diet. High-fat/high-sugar diet (30% kcal of lard) in chow and water containing 5% sucrose and given 1 month before mating and during pregnancy. During and at the end of pregnancy, obesity and diabetes features were determined. After laparotomy, blood samples, periovarian fat, and uterine content were collected. The diabetic rats presented a higher glycemia and percentage of embryonic losses when compared with the NDS group. Rats DHF/HS presented increased obesogenic index, caloric intake, and periovarian fat weight and reduced gravid uterus weight in relation to the other groups. Besides, this association might lead to the inflammatory process, confirmed by leukocytosis. Obese rats (NDHF/HS and DHF/HS) showed higher triglyceride levels and their offspring with lower fetal weight and ossification sites, indicating intrauterine growth restriction. This finding may contribute to vascular alterations related to long-term hypertensive disorders in adult offspring. The fetuses from diabetic dams showed higher percentages of skeletal abnormalities, and DHF/HS dams still had a higher rate of anomalous fetuses. Thus, maternal diabetes and/or obesity induces maternal metabolic disorders that contribute to affect fetal development and growth.

Silencing of RSPO1 mitigates obesity-related renal fibrosis in mice by deactivating Wnt/β-catenin pathway

Obesity, a global epidemic, is one of the critical causes of chronic kidney disease (CKD). R-spondin1 (RSPO1) possessing the potential to activate Wnt/β-catenin pathway was reported to be elevated in circulation of obesity objects. However, the function of RSPO1 and the latent mechanism in obesity-related CKD are still left to be revealed. In the present study, renal RSPO1 expression was increased in mice fed on high-fat diet (HFD) for 12 weeks. Lentivirus-mediated RSPO1 knockdown partly recovered obesity-related metabolic symptoms, while distinctly remitted kidney dysfunction and renal fibrosis in obesity mice. In vitro, recombinant RSPO1 was found to elevate leucine-rich repeat-containing G protein coupled receptor 4 (LGR4) expression, promote Wnt/β-catenin signaling pathway activation, facilitate epithelial-mesenchymal transition (EMT) and increase collagen deposition in HK2 renal tubular cells. Such pro-fibrotic effect of RSPO1 was diminished by LGR4 siRNA in HK2 cells. In summary, we demonstrate that RSPO1/LGR4 axis is involved in obesity-related renal fibrosis at least through activating Wnt/β-catenin signaling pathway, providing a potential therapeutic target for this disease.

Satiety induced by bile acids is mediated via vagal afferent pathways

The aim of this study was to elucidate the role and the pathways used by bile acid receptor TGR5 in transmitting satiety signals. We showed TGR5 colocalized with cholecystokinin type A (CCK-A) receptors in a subpopulation of rat nodose ganglia (NG) neurons. Intra-arterial injection of deoxycholic acid (DCA) dose-dependently increased firing rate in NG while a subthreshold dose of DCA and CCK-8 increased firing rates synergistically. TGR5-specific agonist oleanolic acid induced NG neuronal firing in a dose-dependent manner. However, the same units did not respond to GW4064, a nuclear receptor-specific agonist. Quantity of DCA-activated neurons in the hypothalamus was determined by c-Fos expression. Combining DCA and CCK-8 caused a 4-fold increase in c-Fos activation. In the arcuate nucleus, c-Fos-positive neurons coexpressed cocaine and amphetamine regulated transcript and proopiomelanocortin. DCA-induced c-Fos expression was eliminated following truncal vagotomy or silencing of TGR5 in the NG. Feeding studies showed intravenous injection of 1 μg/kg of DCA reduced food intake by 12% ± 3%, 24% ± 5%, and 32% ± 6% in the first 3 hours, respectively. Silencing of TGR5 or CCK-A receptor in the NG enhanced spontaneous feeding by 18% ± 2% and 13.5% ± 2.4%, respectively. When both TGR5 and CCK-A receptor were silenced, spontaneous feeding was enhanced by 37% ± 4% in the first 3 hours, suggesting that bile acid may have a physiological role in regulating satiety. Working in concert with CCK, bile acid synergistically enhanced satiety signals to reduce spontaneous feeding.

LGR4 is essential for R-spondin1-mediated suppression of food intake via pro-opiomelanocortin

Leucine-rich repeat-containing G-protein coupled receptor 4 (LGR4) suppresses food intake after its activation by binding of its ligands, R-spondins. We investigated the mechanism of food intake suppression by R-spondin1 in a region-specific Lgr4 gene knockout (LGR4 cKO) mouse model, generated by deletion of the Lgr4 gene in arcuate nucleus (ARC) using Lgr4^fx/fx mice combined with infection of an AAV-Cre vector. After R-spondin1 administration, LGR4 cKO mice didn't exhibit a suppressed appetite, compared to that in control mice, which received a vehicle. In ARC of LGR4 cKO mice, Pomc mRNA expression was reduced, leading to suppressed food intake. On the other hand, neurons-specific LGR4 KO mice exhibited no differences in Pomc expression, and no structural differences were observed in the ARC of mutant mice. These results suggest that LGR4 is an essential part of the mechanism, inducing Pomc gene expression with R-spondin1 in ARC neurons in mice, thereby regulating feeding behavior. Abbreviations: LGR4: Leucine-rich repeat-containing G-protein coupled receptor 4; RSPOs: roof plate-specific spondins; ARC: arcuate nucleus; AAV: adeno associated virus; POMC: pro-opiomelanocortin; CART: cocaine and amphetamine-regulated transcript; NPY: neuropeptide Y; AgRP: agouti-related peptide; Axin2: axis inhibition protein 2; Lef1: lymphoid enhancer binding factor 1; ccnd1: cyclin D1.