Hepatic Leptin Signaling Improves Hyperglycemia by Stimulating MAPK Phosphatase-3 Protein Degradation via STAT3

A Novel Selenium-Based Nanozyme (GSH-Se) Ameliorates Colitis in Mice by Modulating the Nrf2/Keap1 and GPx4 Pathways

Combination of selenium (Se) and glutathione peroxidase (GPx) can reduce the dose of Se used while concurrently exploiting their antioxidative performance, which can be used as a potential treatment for ulcerative colitis. Nanozymes possess higher stability, are more economical, and have more multifunctionalities than natural enzymes and thus could be an ideal approach for their combination. Therefore, this study synthesised a nanozyme using glutathione (GSH) and Se-GSH-Se-and evaluated its alleviating effects on colitis in mice induced by dextran sulphate sodium salt (DSS). Three doses of GSH-Se, 6 mM, 12 mM, and 18 mM were supplemented in DSS-induced colitis in mice. Findings showed that GSH-Se supplementation ameliorated colitis by improving the colonic mucosal integrity, reducing inflammatory responses and oxidative stress, and alleviating gut microbiota imbalance in mice with DSS-induced colitis. Moreover, an in vitro experiment was performed to unravel the molecular mechanism by which GSH-Se ameliorated colitis in mice, based on lipopolysaccharide-induced inflammation in mouse colon epithelial cells. The results suggested that the alleviating effects of GSH-Se on mouse colitis was likely mediated by the activation of the Nrf2/Keap1 (nuclear factor E2-related factor 2/Kelch-like ECH-associated protein 1) and GPx4 signalling pathways.

Increased hepatic gluconeogenesis and type 2 diabetes mellitus

Abnormally increased hepatic gluconeogenesis is a significant contributor to hyperglycemia in the fasting state in patients with type 2 diabetes mellitus (T2DM) due to insulin resistance. Metformin, the most prescribed drug for the treatment of T2DM, is believed to exert its effect mainly by reducing hepatic gluconeogenesis. Here, we discuss how increased hepatic gluconeogenesis contributes to T2DM and we review newly revealed mechanisms underlying the attenuation of gluconeogenesis by metformin. In addition, we analyze the recent findings on new determinants involved in the regulation of gluconeogenesis, which might ultimately lead to the identification of novel and targeted treatment strategies for T2DM.

Influence of Maternal Adipokines on Anthropometry, Adiposity, and Neurodevelopmental Outcomes of the Offspring

Pregnancy is distinguished by a multitude of intricate interactions between the mother and the new individual, commencing at implantation and persisting until the maturation and integration of the fetal apparatus and systems. The physiological increase in fat mass during pregnancy and the association of maternal obesity with adverse neonatal outcomes have directed attention to the study of maternal adipokines as participants in fetal development. Interestingly, maternal concentrations of certain adipokines such as adiponectin, leptin, tumor necrosis factor-alpha, and interleukin-6 have been found to be associated with offspring anthropometry and adiposity at birth and at three months of age, even with neurodevelopmental alterations later in life. This is partly explained by the functions of these adipokines in the regulation of maternal metabolism and placental nutrient transport. This review compiles, organizes, and analyzes the most relevant studies on the association between maternal adipokines with anthropometry, adiposity, and neurodevelopmental outcomes of the offspring. Furthermore, it proposes the underlying mechanisms involved in this association.

Short-Term Zinc Supplementation Stimulates Visceral Adipose Catabolism and Inflammation in Mice

BACKGROUND

Zinc (Zn), a fundamental trace element in human biology, exhibits pivotal roles in sustaining vital physiological processes and regulating metabolic homeostasis. Insufficient zinc intake has been linked to deleterious consequences on growth, reproductive functions, metabolic activities, and immune responses in both humans and animals. Oral zinc supplementation is usually performed to meet zinc requirement. Previous studies have shown that long-term supplementation of zinc in mice impaired AKT signaling and induced adipocyte hypertrophy in visceral adipose tissue.

METHODS

The presented study was conducted to investigate the role and mechanism of short-term zinc supplementation on lipids metabolism. Zinc sulfate was supplemented in the drinking water of C57/BL6J male mice at 30 ppm or 90 ppm for one week. Water consumption, food intake, and body weight were analyzed, adipose tissue and serum profile of metabolites were investigated, and the key genes related to lipid metabolism were analyzed.

RESULTS

Short-term zinc supplementation decreased visceral adipose tissue weight and adipocyte size compared to the control group, but no difference was observed in food intake, water consumption, and body weight between the two groups. Further studies revealed that short-term zinc supplementation significantly increased the serum insulin level while decreasing the serum NEFA content. In addition, zinc supplementation increased the expression of Atgl and Hsl in the visceral adipose tissue compared with the control mice. Furthermore, the phosphorylation level of HSL and protein level of PPARg in the epididymal adipose tissue increased by zinc supplementation compared with the control mice. In comparison, the protein level of FASN was down-regulated by short-term zinc supplementation in the epididymal adipose tissue, although the expression of lipogenic genes was not changed. The expression of F4/80 and Tnfa were increased in zinc-supplemented adipose tissue as compared with the control group.

CONCLUSIONS

Our findings suggest that short-term zinc supplementation might reduce fat deposition by enhancing lipolysis in mice. Future studies could focus on the effect of intermittent zinc supplementation on fat reduction in both animal models and humans.

Interleukin-1β Signaling Contributes to Cell Cycle Arrest and Apoptotic Cell Death by Leptin via Modulation of AKT and p38MAPK in Hepatocytes

Leptin, an adipose tissue-derived hormone, has exhibited the potent hepatotoxic effects. However, the underlying molecular mechanisms are not fully understood. In this study, we have elucidated the mechanisms by which leptin exerts cytotoxic effects in hepatocytes, particularly focusing on the role of interleukin-1β (IL-1β) signaling. Leptin significantly induced maturation and secretion of IL-1β in cultured rat hepatocytes. Interestingly, inhibition of IL-1β signaling by pretreatment with an IL-1 receptor antagonist (IL-1Ra) or gene silencing of type I IL-1 receptor (IL-1R1) markedly abrogated leptin-induced cell cycle arrest. The critical role of IL-1β signaling in leptin-induced cell cycle arrest is mediated via upregulation of p16, which acts as an inhibitor of cyclin-dependent kinase. In addition, leptin-induced apoptotic cell death was relieved by inhibition of IL-1β signaling, as determined by annexin V/7-AAD binding assay. Mechanistically, IL-1β signaling contributes to apoptotic cell death and cell cycle arrest by suppressing AKT and activation of p38 mitogen-activated protein kinase (p38MAPK) signaling pathways. Involvement of IL-1β signaling in cytotoxic effect of leptin was further confirmed in vivo using hepatocyte specific IL-1R1 knock out (IL-1R1 KO) mice. Essentially similar results were obtained in vivo, where leptin administration caused the upregulation of apoptotic markers, dephosphorylation of AKT, and p38MAPK activation were observed in wild type mice liver without significant effects in the livers of IL-1R1 KO mice. Taken together, these results demonstrate that IL-1β signaling critically contributes to leptin-induced cell cycle arrest and apoptosis, at least in part, by modulating p38MAPK and AKT signaling pathways.

Quercetin Regulates Lipid Metabolism and Fat Accumulation by Regulating Inflammatory Responses and Glycometabolism Pathways: A Review

Fat synthesis and lipolysis are natural processes in growth and have a close association with health. Fat provides energy, maintains physiological function, and so on, and thus plays a significant role in the body. However, excessive/abnormal fat accumulation leads to obesity and lipid metabolism disorder, which can have a detrimental impact on growth and even harm one's health. Aside from genetic effects, there are a range of factors related to obesity, such as excessive nutrient intake, inflammation, glycometabolism disease, and so on. These factors could serve as potential targets for anti-obesity therapy. Quercetin is a flavonol that has received a lot of attention recently because of its role in anti-obesity. It was thought to have the ability to regulate lipid metabolism and have a positive effect on anti-obesity, but the processes are still unknown. Recent studies have shown the role of quercetin in lipid metabolism might be related to its effects on inflammatory responses and glycometabolism. The references were chosen for this review with no date restrictions applied based on the topics they addressed, and the databases PubMed and Web of Sicence was used to conduct the references research, using the following search terms: "quercetin", "obesity", "inflammation", "glycometabolism", "insulin sensitivity", etc. This review summarizes the potential mechanisms of quercetin in alleviating lipid metabolism through anti-inflammatory and hypoglycemic signaling pathways, and describes the possible signaling pathways in the interaction of inflammation and glycometabolism, with the goal of providing references for future research and application of quercetin in the regulation of lipid metabolism.

The cross-talk between leptin and circadian rhythm signaling proteins in physiological processes: a systematic review

BACKGROUND

Today, modern lifestyles and disrupted sleep patterns cause circadian clock rhythm impairments that are associated with altered leptin levels, which subsequently affect a wide range of physiological processes and have significant health burdens on societies. Nevertheless, there has been no systematic review of circadian clock genes and proteins, leptin, and related signaling pathways.

METHODS

Accordingly, we systematically reviewed circadian clock proteins, leptin, and molecular mechanisms between them by searching Pubmed, Scopus, ProQuest, Web of Sciences, and Google Scholar until September 2022. After considering the inclusion and exclusion criteria, 20 animal studies were selected. The risk of bias was assessed in each study.

RESULTS

The results clarified the reciprocal interconnected relationship between circadian clock genes and leptin. Circadian clock genes regulate leptin expression and signaling via different mechanisms, such as CLOCK-BMAL1 heterodimers, which increase the expression of PPARs. PPARs induce the expression of C/EBPα, a key factor in upregulating leptin expression. CLOCK-BMAL1 also induces the expression of Per1 and Rev-erb genes. PER1 activates mTORC1 and mTORC1 enhances the expression of C/EBPα. In addition, REV-ERBs activate the leptin signaling pathway. Also, leptin controls the expression of circadian clock genes by triggering the AMPK and ERK/MAPK signaling pathways, which regulate the activity of PPARs. Moreover, the roles of these molecular mechanisms are elucidated in different physiological processes and organs.

CONCLUSIONS

Crosstalk between circadian clock genes and leptin and their affecting elements should be considered in the selection of new therapeutic targets for related disorders, especially obesity and metabolic impairments.

Acute Endoplasmic Reticulum Stress Suppresses Hepatic Gluconeogenesis by Stimulating MAPK Phosphatase 3 Degradation

Drug-induced liver injury (DILI) is a widespread and harmful disease, and is closely linked to acute endoplasmic reticulum (ER) stress. Previous reports have shown that acute ER stress can suppress hepatic gluconeogenesis and even leads to hypoglycemia. However, the mechanism is still unclear. MAPK phosphatase 3 (MKP-3) is a positive regulator for gluconeogenesis. Thus, this study was conducted to investigate the role of MKP-3 in the suppression of gluconeogenesis by acute ER stress, as well as the regulatory role of acute ER stress on the expression of MKP-3. Results showed that acute ER stress induced by tunicamycin significantly suppressed gluconeogenesis in both hepatocytes and mouse liver, reduced glucose production level in hepatocytes, and decreased fasting blood glucose level in mice. Additionally, the protein level of MKP-3 was reduced by acute ER stress in both hepatocytes and mouse liver. Mkp-3 deficiency eliminated the inhibitory effect of acute ER stress on gluconeogenesis in hepatocytes. Moreover, the reduction effect of acute ER stress on blood glucose level and hepatic glucose 6-phosphatase (G6pc) expression was not observed in the liver-specific Mkp-3 knockout mice. Furthermore, activation of protein kinase R-like ER kinase (PERK) decreased the MKP-3 protein level, while inactivation of PERK abolished the reduction effect of acute ER stress on the MKP-3 protein level in hepatocytes. Taken together, our study suggested that acute ER stress could suppress hepatic gluconeogenesis by stimulating MKP-3 degradation via PERK, at least partially. Thus, MKP-3 might be a therapeutic target for DILI-related hypoglycemia.

Downregulation of hepatic lncRNA Gm19619 improves gluconeogenesis and lipogenesis following vertical sleeve gastrectomy in mice

Long non-coding RNAs (lncRNAs) are emerging important epigenetic regulators in metabolic processes. Whether they contribute to the metabolic effects of vertical sleeve gastrectomy (VSG), one of the most effective treatments for sustainable weight loss and metabolic improvement, is unknown. Herein, we identify a hepatic lncRNA Gm19619, which is strongly repressed by VSG but highly up-regulated by diet-induced obesity and overnight-fasting in mice. Forced transcription of Gm19619 in the mouse liver significantly promotes hepatic gluconeogenesis with the elevated expression of G6pc and Pck1. In contrast, AAV-CasRx mediated knockdown of Gm19619 in high-fat diet-fed mice significantly improves hepatic glucose and lipid metabolism. Mechanistically, Gm19619 is enriched along genomic regions encoding leptin receptor (Lepr) and transcription factor Foxo1, as revealed in chromatin isolation by RNA purification (ChIRP) assay and is confirmed to modulate their transcription in the mouse liver. In conclusion, Gm19619 may enhance gluconeogenesis and lipid accumulation in the liver.

Recent Advances in the Knowledge of the Mechanisms of Leptin Physiology and Actions in Neurological and Metabolic Pathologies

Excess body weight is frequently associated with low-grade inflammation. Evidence indicates a relationship between obesity and cancer, as well as with other diseases, such as diabetes and non-alcoholic fatty liver disease, in which inflammation and the actions of various adipokines play a role in the pathological mechanisms involved in these disorders. Leptin is mainly produced by adipose tissue in proportion to fat stores, but it is also synthesized in other organs, where leptin receptors are expressed. This hormone performs numerous actions in the brain, mainly related to the control of energy homeostasis. It is also involved in neurogenesis and neuroprotection, and central leptin resistance is related to some neurological disorders, e.g., Parkinson's and Alzheimer's diseases. In peripheral tissues, leptin is implicated in the regulation of metabolism, as well as of bone density and muscle mass. All these actions can be affected by changes in leptin levels and the mechanisms associated with resistance to this hormone. This review will present recent advances in the molecular mechanisms of leptin action and their underlying roles in pathological situations, which may be of interest for revealing new approaches for the treatment of diseases where the actions of this adipokine might be compromised.

Yeast culture supplementation of sow diets regulates the immune performance of their weaned piglets under lipopolysaccharide stress

The aim of this study was to investigate the effect of dietary supplementation of sows with yeast cultures (XPC) during late gestation and lactation on the immune performance of their weaned offspring under lipopolysaccharide (LPS) stress. A total of 40 Landrace × Yorkshire sows (parity 3 to 7) with similar backfat thickness were selected and randomly divided into two treatment groups: a control group (basal diet) and a yeast culture group (basal diet + 2.0 g/kg XPC). The trial was conducted from day 90 of gestation to day 21 of lactation. At the end of the experiment, 12 piglets with similar weights were selected from each group and slaughtered 4 h after intraperitoneal injection with either saline or LPS. The results showed that the concentrations of interleukin-6 (IL-6) in the thymus and tumor necrosis factor-α in the liver increased significantly (P < 0.05) in weaned piglets after LPS injection. Maternal dietary supplementation with XPC significantly reduced the concentration of inflammatory factors in the plasma and thymus of weaned piglets (P < 0.05). LPS injection significantly upregulated the expression of some tissue inflammation-related genes, significantly downregulated the expression of intestinal tight junction-related genes, and significantly elevated the protein expression of liver phospho-nuclear factor kappa B (p-NF-κB), the phospho-inhibitory subunit of NF-κB (p-IκBα), phospho-c-Jun N-terminal kinase (p-JNK), Nuclear factor kappa-B (NF-κB), and the inhibitory subunit of NF-κB (IκBα) in weaned piglets (P < 0.05). Maternal dietary supplementation with XPC significantly downregulated the gene expression of IL-6 and interleukin-10 (IL-10) in the thymus and decreased the protein expression of c-Jun N-terminal kinase (JNK) in the liver of weaned piglets (P < 0.05). In summary, injection of LPS induced an inflammatory response in weaned piglets and destroyed the intestinal barrier. Maternal dietary supplementation of XPC improved the immune performance of weaned piglets by inhibiting inflammatory responses.

Antidiabetic Properties of Chitosan and Its Derivatives

Diabetes mellitus is a chronic metabolic disorder. In addition to taking medication, adjusting the composition of the diet is also considered one of the effective methods to control the levels of blood glucose. Chitosan and its derivatives are natural and versatile biomaterials with health benefits. Chitosan has the potential to alleviate diabetic hyperglycemia by reducing hepatic gluconeogenesis and increasing skeletal muscle glucose uptake and utility. Scientists also focus on the glucose-lowering effect of chitosan oligosaccharide (COS). COS supplementation has the potential to alleviate abnormal glucose metabolism in diabetic rats by inhibiting gluconeogenesis and lipid peroxidation in the liver. Both high and low molecular weight chitosan feeding reduced insulin resistance by inhibiting lipid accumulation in the liver and adipose tissue and ameliorating chronic inflammation in diabetic rats. COS can reduce insulin resistance but has less ability to reduce hepatic lipids in diabetic rats. A clinical trial showed that a 3-month administration of chitosan increased insulin sensitivity and decreased body weight and triglycerides in obese patients. Chitosan and COS are considered Generally Recognized as Safe; however, they are still considered to be of safety concerns. This review highlights recent advances of chitosan and its derivatives in the glucose-lowering/antidiabetic effects and the safety.