Leptin and insulin act on POMC neurons to promote the browning of white fat

Pathogenic hypothalamic extracellular matrix promotes metabolic disease

Metabolic diseases such as obesity and type 2 diabetes are marked by insulin resistance1,2. Cells within the arcuate nucleus of the hypothalamus (ARC), which are crucial for regulating metabolism, become insulin resistant during the progression of metabolic disease3-8, but these mechanisms are not fully understood. Here we investigated the role of a specialized chondroitin sulfate proteoglycan extracellular matrix, termed a perineuronal net, which surrounds ARC neurons. In metabolic disease, the perineuronal net of the ARC becomes augmented and remodelled, driving insulin resistance and metabolic dysfunction. Disruption of the perineuronal net in obese mice, either enzymatically or with small molecules, improves insulin access to the brain, reversing neuronal insulin resistance and enhancing metabolic health. Our findings identify ARC extracellular matrix remodelling as a fundamental mechanism driving metabolic diseases.

Hypothalamic SLC7A14 accounts for aging-reduced lipolysis in white adipose tissue of male mice

The central nervous system has been implicated in the age-induced reduction in adipose tissue lipolysis. However, the underlying mechanisms remain unclear. Here, we show the expression of SLC7A14 is reduced in proopiomelanocortin (POMC) neurons of aged mice. Overexpression of SLC7A14 in POMC neurons alleviates the aging-reduced lipolysis, whereas SLC7A14 deletion mimics the age-induced lipolysis impairment. Metabolomics analysis reveals that POMC SLC7A14 increased taurochenodeoxycholic acid (TCDCA) content, which mediates the SLC7A14 knockout- or age-induced WAT lipolysis impairment. Furthermore, SLC7A14-increased TCDCA content is dependent on intestinal apical sodium-dependent bile acid transporter (ASBT), which is regulated by intestinal sympathetic afferent nerves. Finally, SLC7A14 regulates the intestinal sympathetic afferent nerves by inhibiting mTORC1 signaling through inhibiting TSC1 phosphorylation. Collectively, our study suggests the function for central SLC7A14 and an upstream mechanism for the mTORC1 signaling pathway. Moreover, our data provides insights into the brain-gut-adipose tissue crosstalk in age-induced lipolysis impairment.

βAR-mTOR-lipin1 pathway mediates PKA-RIIβ deficiency-induced adipose browning

Background: Enhancing white adipose tissue (WAT) browning combats obesity. The RIIβ subunit of cAMP-dependent protein kinase (PKA) is primarily expressed in the brain and adipose tissue. Deletion of the hypothalamic RIIβ gene centrally induces WAT browning, yet the peripheral mechanisms mediating this process remain unexplored. Methods: This study investigates the mechanisms underlying WAT browning in RIIβ-KO mice. Genetic approaches such as β3-adrenergic receptors (β3ARs) deletion and sympathetic denervation of WAT were utilized. Genome-wide transcriptomic sequencing and bioinformatic analysis were employed to identify potential mediators of WAT browning. siRNA assays were employed to knock down mTOR and lipin1 in vitro, while AAV-shRNAs were used for the same purpose in vivo. Results: We found that WAT browning substantially contributes to the lean and obesity-resistant phenotypes of RIIβ-KO mice. The WAT browning can be dampened by β3ARs deletion or WAT sympathetic denervation. We identified that adipocytic mTOR and lipin1 may act as mediators of the WAT browning. Inhibition of mTOR or lipin1 abrogates WAT browning and hinders the lean phenotype of RIIβ-KO mice. In human subcutaneous white adipocytes and mouse white adipocytes, β3AR stimulation can activate mTOR and causes lipin1 nuclear translocation; knockdown of mTOR and Lipin1 mitigates WAT browning-associated gene expression, impedes mitochondrial activity. Moreover, mTOR knockdown reduces lipin1 level and nuclear translocation, indicating that lipin1 may act downstream of mTOR. Additionally, in vivo knockdown of mTOR and Lipin1 diminished WAT browning and increased adiposity. Conclusions: The β3AR-activated mTOR-lipin1 axis mediates WAT browning, offering new insights into the molecular basis of PKA-regulated WAT browning. These findings provide potential adipose target candidates for the development of drugs to treat obesity.

A roadmap to the molecular human linking multiomics with population traits and diabetes subtypes

In-depth multiomic phenotyping provides molecular insights into complex physiological processes and their pathologies. Here, we report on integrating 18 diverse deep molecular phenotyping (omics-) technologies applied to urine, blood, and saliva samples from 391 participants of the multiethnic diabetes Qatar Metabolomics Study of Diabetes (QMDiab). Using 6,304 quantitative molecular traits with 1,221,345 genetic variants, methylation at 470,837 DNA CpG sites, and gene expression of 57,000 transcripts, we determine (1) within-platform partial correlations, (2) between-platform mutual best correlations, and (3) genome-, epigenome-, transcriptome-, and phenome-wide associations. Combined into a molecular network of > 34,000 statistically significant trait-trait links in biofluids, our study portrays "The Molecular Human". We describe the variances explained by each omics in the phenotypes (age, sex, BMI, and diabetes state), platform complementarity, and the inherent correlation structures of multiomics data. Further, we construct multi-molecular network of diabetes subtypes. Finally, we generated an open-access web interface to "The Molecular Human" ( http://comics.metabolomix.com ), providing interactive data exploration and hypotheses generation possibilities.

Insulin and leptin oscillations license food-entrained browning and metabolic flexibility

Timed feeding drives adipose browning, although the integrative mechanisms for the same remain unclear. Here, we show that twice-a-night (TAN) feeding generates biphasic oscillations of circulating insulin and leptin, representing their entrainment by timed feeding. Insulin and leptin surges lead to marked cellular, functional, and metabolic remodeling of subcutaneous white adipose tissue (sWAT), resulting in increased energy expenditure. Single-cell RNA-sequencing (scRNA-seq) analyses and flow cytometry demonstrate a role for insulin and leptin surges in innate lymphoid type 2 (ILC2) cell recruitment and sWAT browning, since sWAT depot denervation or loss of leptin or insulin receptor signaling or ILC2 recruitment each dampens TAN feeding-induced sWAT remodeling and energy expenditure. Consistently, recreating insulin and leptin oscillations via once-a-day timed co-injections is sufficient to favorably remodel innervated sWAT. Innervation is necessary for sWAT remodeling, since denervation of sWAT, but not brown adipose tissue (BAT), blocks TAN-induced sWAT remodeling and resolution of inflammation. In sum, reorganization of nutrient-sensitive pathways remodels sWAT and drives the metabolic benefits of timed feeding.

Transcriptomic analysis reveals the effects of maternal exposure to bisphenol AF on hypothalamic development in male neonatal mice

Fragmented data suggest that bisphenol AF (BPAF), a chemical widely used in a variety of products, might have potential impacts on the hypothalamus. Here, we employed male neonatal mice following maternal exposure to explore the effects of low-dose BPAF on hypothalamic development by RNA-sequencing. We found that maternal exposure to approximately 50 µg/(kg·day) BPAF from postanal day (PND) 0 to PND 15 altered the hypothalamic transcriptome, primarily involving the pathways and genes associated with extracellular matrix (ECM) and intercellular adhesion, neuroendocrine regulation, and neurological processes. Further RNA analysis confirmed the changes in the expression levels of concerned genes. Importantly, we further revealed that low-dose BPAF posed a stimulatory impact on pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus and induced the browning of inguinal white adipose tissue. All findings indicate that developmental exposure to low-dose BPAF could interfere with hypothalamic development and thereby lead to alterations in the metabolism. Interestingly, 5000 µg/(kg·day) BPAF caused slighter, non-significant or even inverse alterations than the low dose of 50 µg/(kg·day), displaying a dose-independent effect. Further observations suggest that the the dose-independent effects of BPAF might be associated with oxidative stress and inflammatory responses caused by the high dose. Overall, our study highlights a risk of low-dose BPAF to human neuroendocrine regulation and metabolism.

Asprosin contributes to pathogenesis of obesity by adipocyte mitophagy induction to inhibit white adipose browning in mice

BACKGROUND

Asprosin (ASP) is a newly discovered adipokine secreted by white adipose tissue (WAT), which can regulate the homeostasis of glucose and lipid metabolism. However, it is not clear whether it can regulate the browning of WAT and mitophagy during the browning process. Accordingly, this study aims to investigate the effects and possible mechanisms of ASP on the browning of WAT and mitophagy in vivo and in vitro.

METHODS

In in vivo experiments, some mouse models were used including adipose tissue ASP-specific deficiency (ASP-/-), high fat diet (HFD)-induced obesity and white adipose browning; in in vitro experiments, some cell models were also established and used, including ASP-deficient 3T3-L1 preadipocyte (ASP-/-) and CL-316243 (CL, 1 µM)-induced browning. Based on these models, the browning of WAT and mitophagy were evaluated by morphology, functionality and molecular markers.

RESULTS

Our in vivo data show that adipose tissue-specific deletion of ASP contributes to weight loss in mice; supplementation of ASP inhibits the expressions of browning-related proteins including UCP1, PRDM16 and PGC1ɑ during the cold exposure-induced browning, and promotes the expressions of mitophagy-related proteins including PINK1 and Parkin under the conditions of whether normal diet (ND) or HFD. Similarly, our in vitro data also show that the deletion of ASP in 3T3-L1 cells significantly increases the expressions of the browning-related proteins and decreases the expressions of the mitophagy-related proteins.

CONCLUSIONS

These data demonstrate that ASP deletion can facilitate the browning and inhibit mitophagy in WAT. The findings will lay an experimental foundation for the development of new drugs targeting ASP and the clinical treatment of metabolic diseases related to obesity.

Comprehensive expression analysis of hormone-like substances in the subcutaneous adipose tissue of the common bottlenose dolphin Tursiops truncatus

Marine mammals possess a specific subcutaneous fat layer called blubber that not only insulates and stores energy but also secretes bioactive substances. However, our understanding of its role as a secretory organ in cetaceans is incomplete. To exhaustively explore the hormone-like substances produced in dolphin subcutaneous adipose tissue, we performed seasonal blubber biopsies from captive female common bottlenose dolphins (Tursiops truncatus; N = 8, n = 32) and analyzed gene expression via transcriptomics. Analysis of 186 hormone-like substances revealed the expression of 58 substances involved in regulating energy metabolism, tissue growth/differentiation, vascular regulation, immunity, and ion/mineral homeostasis. Adiponectin was the most abundantly expressed gene, followed by angiopoietin protein like 4 and insulin-like growth factor 2. To investigate the endocrine/secretory responses of subcutaneous adipose tissue to the surrounding temperature, we subsequently compared the mean expression levels of the genes during the colder and warmer seasons. In the colder season, molecules associated with appetite suppression, vasodilation, and tissue proliferation were relatively highly expressed. In contrast, warmer seasons enhanced the expression of substances involved in tissue remodeling, immunity, metabolism, and vasoconstriction. These findings suggest that dolphin blubber may function as an active secretory organ involved in the regulation of metabolism, appetite, and tissue reorganization in response to changes in the surrounding environment, providing a basis for elucidating the function of hormone-like substances in group-specific evolved subcutaneous adipose tissue.

Site-Specifically Modified Peptide Inhibitors of Protein Tyrosine Phosphatase 1B and T-Cell Protein Tyrosine Phosphatase with Enhanced Stability and Improved In Vivo Long-Acting Activity

Protein tyrosine phosphatase 1B (PTP1B) and TC-PTP can function in a coordinated manner to regulate diverse biological processes including insulin and leptin signaling, T-cell activation, and tumor antigen presentation, which makes them potential targets for several therapeutic applications. We have previously demonstrated that the lipidated BimBH3 peptide analogues were a new class of promising PTP1B inhibitors with once-weekly antidiabetic potency. Herein, we chemically synthesized two series of BimBH3 analogues via site-specific modification and studied their structure-activity relationship. The screened analogues S2, S6, A2-14, A2-17, A2-20, and A2-21 exhibited an improved PTP1B/TC-PTP dual inhibitory activity and achieved good stability in the plasma of mice and dogs, which indicated long-acting potential. In mouse models of type 2 diabetes mellitus (T2DM), the selected analogues S6, S7, A2-20, and A2-21 with an excellent target activity and plasma stability generated once-weekly therapeutic potency for T2DM at lower dosage (0.5 μmol/kg). In addition, evidence was provided to confirm the cell permeability and targeted enrichment of the BimBH3 analogues. In summary, we report here that site-specific modification and long fatty acid conjugation afforded cell-permeable peptidomimetic analogues of BimBH3 with enhanced stability, in vivo activity, and long-acting pharmacokinetic profile. Our findings could guide the further optimization of BimBH3 analogues and provide a proof-of-concept for PTP1B/TC-PTP targeting as a new therapeutic approach for T2DM, which may facilitate the discovery and development of alternative once-weekly anti-T2DM drug candidates.

AZGP1 in POMC neurons modulates energy homeostasis and metabolism through leptin-mediated STAT3 phosphorylation

Zinc-alpha2-glycoprotein (AZGP1) has been implicated in peripheral metabolism; however, its role in regulating energy metabolism in the brain, particularly in POMC neurons, remains unknown. Here, we show that AZGP1 in POMC neurons plays a crucial role in controlling whole-body metabolism. POMC neuron-specific overexpression of Azgp1 under high-fat diet conditions reduces energy intake, raises energy expenditure, elevates peripheral tissue leptin and insulin sensitivity, alleviates liver steatosis, and promotes adipose tissue browning. Conversely, mice with inducible deletion of Azgp1 in POMC neurons exhibit the opposite metabolic phenotypes, showing increased susceptibility to diet-induced obesity. Notably, an increase in AZGP1 signaling in the hypothalamus elevates STAT3 phosphorylation and increases POMC neuron excitability. Mechanistically, AZGP1 enhances leptin-JAK2-STAT3 signaling by interacting with acylglycerol kinase (AGK) to block its ubiquitination degradation. Collectively, these results suggest that AZGP1 plays a crucial role in regulating energy homeostasis and glucose/lipid metabolism by acting on hypothalamic POMC neurons.

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Physiological Appetite Regulation and Bariatric Surgery

Obesity remains a common metabolic disorder and a threat to health as it is associated with numerous complications. Lifestyle modifications and caloric restriction can achieve limited weight loss. Bariatric surgery is an effective way of achieving substantial weight loss as well as glycemic control secondary to weight-related type 2 diabetes mellitus. It has been suggested that an anorexigenic gut hormone response following bariatric surgery contributes to weight loss. Understanding the changes in gut hormones and their contribution to weight loss physiology can lead to new therapeutic treatments for weight loss. Two distinct types of neurons in the arcuate hypothalamic nuclei control food intake: proopiomelanocortin neurons activated by the anorexigenic (satiety) hormones and neurons activated by the orexigenic peptides that release neuropeptide Y and agouti-related peptide (hunger centre). The arcuate nucleus of the hypothalamus integrates hormonal inputs from the gut and adipose tissue (the anorexigenic hormones cholecystokinin, polypeptide YY, glucagon-like peptide-1, oxyntomodulin, leptin, and others) and orexigeneic peptides (ghrelin). Replicating the endocrine response to bariatric surgery through pharmacological mimicry holds promise for medical treatment. Obesity has genetic and environmental factors. New advances in genetic testing have identified both monogenic and polygenic obesity-related genes. Understanding the function of genes contributing to obesity will increase insights into the biology of obesity. This review includes the physiology of appetite control, the influence of genetics on obesity, and the changes that occur following bariatric surgery. This has the potential to lead to the development of more subtle, individualised, treatments for obesity.

Inter-Organ Communication Involved in Brown Adipose Tissue Thermogenesis

Brown and beige adipocytes produce heat from substrates such as fatty acids and glucose. Such heat productions occur in response to various stimuli and are called adaptive non-shivering thermogenesis. This review introduces mechanisms known to regulate brown and beige adipocyte thermogenesis. Leptin and fibroblast growth factor 21 (FGF21) are examples of periphery-derived humoral factors that act on the central nervous system (CNS) and increase brown adipose tissue (BAT) thermogenesis. Additionally, neuronal signals such as those induced by intestinal cholecystokinin and hepatic peroxisome proliferator-activated receptor γ travel through vagal afferent-CNS-sympathetic efferent-BAT pathways and increase BAT thermogenesis. By contrast, some periphery-derived humoral factors (ghrelin, adiponectin, plasminogen activator inhibitor-1, and soluble leptin receptor) act also on CNS but inhibit BAT thermogenesis. Neuronal signals also reduce BAT sympathetic activities and BAT thermogenesis, one such example being signals derived by hepatic glucokinase activation. Beige adipocytes can be induced by myokines (interleukin 6, irisin, and β-aminoisobutyric acid), hepatokines (FGF21), and cardiac-secreted factors (brain natriuretic peptide). Cold temperature and leptin also stimulate beige adipocytes via sympathetic activation. Further investigation on inter-organ communication involving adipocyte thermogenesis may lead to the elucidation of how body temperature is regulated and, moreover, to the development of novel strategies to treat metabolic disorders.

Hibiscus sabdariffa Linn. Extract Increases the mRNA Expression of the Arcuate Nucleus Leptin Receptor and is Predicted in silico as an Anti-obesity Agent

BACKGROUND

Leptin is predominant in regulating body weight by stimulating energy expenditure through its neuronal action in the brain. Moreover, it is projected to adipose tissue and induces adipocyte browning by activating the β3-adrenergic receptor (β3AR). However, the expression of leptin receptor (Lep-R) and β3AR in people with obesity is downregulated.

AIM

We hypothesized that Hibiscus sabdariffa Linn. extract (HSE) would increase hypothalamus arcuate nucleus (ARC) Lep-R and white adipose tissue (WAT) β3AR mRNA expression in DIO rats. This study also analyzed the potency of H. sabdariffa bioactive compounds as activators of Lep-R and β3AR by an in-silico experiment.

METHODS

Twenty-four male Sprague-Dawley rats were divided into four groups: Control (standard food), DIO (high-fat diet), DIO-Hib200 (HFD+HSE 200 mg/kg BW), and DIO-Hib400 (HFD+HSE400 mg/kg BW). HSE was administered orally for five weeks, once a day.

RESULTS

HSE administration significantly (p <0,05) increased the ARC Lep-R expression. The Lee index significantly decreased to the normal range (≤ 310) with p <0,001 for DIO-Hib200 and p <0,01 for DIO-Hib400. Among 39 bioactive compounds, 5-O-caffeoyl shikimic acid exhibited high free binding scores (-8,63) for Lep-R, and myricetin_3_arabinogalactoside had high free binding scores (-9,39) for β3AR. These binding predictions could activate Lep-R and β3AR.

CONCLUSION

This study highlights that HSE could be a potential therapeutic target for obesity by increasing LepR mRNA and leptin sensitivity, enhancing energy expenditure, and reducing obesity.

Leptin and energy balance: exploring Leptin's role in the regulation of energy intake and energy expenditure

Leptin is a tonic appetite-regulating hormone, which is integral for the long-term regulation of energy balance. The current evidence suggests that the typical orexigenic or anorexigenic response of many of these appetite-regulating hormones, most notably ghrelin and cholecystokinin (CCK), require leptin to function whereas glucagon-like peptide-1 (GLP-1) is required for leptin to function, and these responses are altered when leptin injection or gene therapy is administered in combination with these same hormones or respective agonists. The appetite-regulatory pathway is complex, thus peptide tyrosine tyrosine (PYY), brain-derived neurotrophic factor (BDNF), orexin-A (OXA), and amylin also maintain ties to leptin, however these are less well understood. While reviews to date have focused on the existing relationships between leptin and the various neuropeptide modulators of appetite within the central nervous system (CNS) or it's role in thermogenesis, no review paper has synthesised the information regarding the interactions between appetite-regulating hormones and how leptin as a chronic regulator of energy balance can influence the acute appetite-regulatory response. Current evidence suggests that potential relationships exist between leptin and the circulating peripheral appetite hormones ghrelin, GLP-1, CCK, OXA and amylin to exhibit either synergistic or opposing effects on appetite inhibition. Though more research is warranted, leptin appears to be integral in both energy intake and energy expenditure. More specifically, functional leptin receptors appear to play an essential role in these processes.

Betanin from Beetroot (Beta vulgaris L.) Regulates Lipid Metabolism and Promotes Fat Browning in 3T3-L1 Adipocytes

Fat browning, which converts white adipose tissue to brown, has attracted attention as a promising strategy for the treatment of obesity. Betanin (BT) has been reported to have potential anti-obesity activity. 3T3-L1 cells were differentiated for 7 days during BT treatment. The BT concentration range for the study was determined using an MTT assay, and lipid accumulation was evaluated by Oil-Red-O staining. The expression of protein level was analyzed by Western blot. Immunofluorescence images were performed with confocal microscopy to visually show the amount and location of thermogenesis factor uncoupling protein1 (UCP1) and mitochondria. qRT-PCR was performed to evaluate mRNA expression. BT inhibited lipid accumulation and increased the expression of UCP1, peroxisome-proliferator-activated receptor gamma (PPARγ), and PPARγ coactivator-1 alpha (PGC-1α). In addition, the increases in beige adipocyte-specific markers were observed, supporting BT-mediated browning of the fat tissue. The UCP1 was localized in the inner membrane of the mitochondria, and its expression was associated with mitochondrial activation. Consistent with this, the mRNA expression of mitochondrial biogenesis markers increased in 3T3-L1 cells after BT treatment. Immunofluorescence staining also indicated an increased number of mitochondria and UCP1, respectively. Moreover, BT inhibited lipogenesis and enhanced lipolysis and fatty acid oxidation. This mechanism has been suggested to be mediated by an adenosine monophosphate-activated protein kinase (AMPK) pathway. BT induces fat browning and regulates lipid metabolism via the AMPK-mediated pathway in 3T3-L1 cells, suggesting that BT can be a promising candidate for controlling obesity.

Advanced neurobiological tools to interrogate metabolism

Engineered neurobiological tools for the manipulation of cellular activity, such as chemogenetics and optogenetics, have become a cornerstone of modern neuroscience research. These tools are invaluable for the interrogation of the central control of metabolism as they provide a direct means to establish a causal relationship between brain activity and biological processes at the cellular, tissue and organismal levels. The utility of these methods has grown substantially due to advances in cellular-targeting strategies, alongside improvements in the resolution and potency of such tools. Furthermore, the potential to recapitulate endogenous cellular signalling has been enriched by insights into the molecular signatures and activity dynamics of discrete brain cell types. However, each modulatory tool has a specific set of advantages and limitations; therefore, tool selection and suitability are of paramount importance to optimally interrogate the cellular and circuit-based underpinnings of metabolic outcomes within the organism. Here, we describe the key principles and uses of engineered neurobiological tools. We also highlight inspiring applications and outline critical considerations to be made when using these tools within the field of metabolism research. We contend that the appropriate application of these biotechnological advances will enable the delineation of the central circuitry regulating systemic metabolism with unprecedented potential.

Skeletal muscles and gut microbiota-derived metabolites: novel modulators of adipocyte thermogenesis

Obesity occurs when overall energy intake surpasses energy expenditure. White adipose tissue is an energy storage site, whereas brown and beige adipose tissues catabolize stored energy to generate heat, which protects against obesity and obesity-associated metabolic disorders. Metabolites are substrates in metabolic reactions that act as signaling molecules, mediating communication between metabolic sites (i.e., adipose tissue, skeletal muscle, and gut microbiota). Although the effects of metabolites from peripheral organs on adipose tissue have been extensively studied, their role in regulating adipocyte thermogenesis requires further investigation. Skeletal muscles and intestinal microorganisms are important metabolic sites in the body, and their metabolites play an important role in obesity. In this review, we consolidated the latest research on skeletal muscles and gut microbiota-derived metabolites that potentially promote adipocyte thermogenesis. Skeletal muscles can release lactate, kynurenic acid, inosine, and β-aminoisobutyric acid, whereas the gut secretes bile acids, butyrate, succinate, cinnabarinic acid, urolithin A, and asparagine. These metabolites function as signaling molecules by interacting with membrane receptors or controlling intracellular enzyme activity. The mechanisms underlying the reciprocal exchange of metabolites between the adipose tissue and other metabolic organs will be a focal point in future studies on obesity. Furthermore, understanding how metabolites regulate adipocyte thermogenesis will provide a basis for establishing new therapeutic targets for obesity.

MC4R in Central and Peripheral Systems

Obesity has emerged as a critical and urgent health burden during the current global pandemic. Among multiple genetic causes, melanocortin receptor-4 (MC4R), involved in food intake and energy metabolism regulation through various signaling pathways, has been reported to be the lead genetic factor in severe and early onset obesity and hyperphagia disorders. Most previous studies have illustrated the roles of MC4R signaling in energy intake versus expenditure in the central system, while some evidence indicates that MC4R is also expressed in peripheral systems, such as the gut and endocrine organs. However, its physiopathological function remains poorly defined. This review aims to depict the central and peripheral roles of MC4R in energy metabolism and endocrine hormone homeostasis, the diversity of phenotypes, biased downstream signaling caused by distinct MC4R mutations, and current drug development targeting the receptor.

A small molecule inhibitor of PTP1B and PTPN2 enhances T cell anti-tumor immunity

The inhibition of protein tyrosine phosphatases 1B (PTP1B) and N2 (PTPN2) has emerged as an exciting approach for bolstering T cell anti-tumor immunity. ABBV-CLS-484 is a PTP1B/PTPN2 inhibitor in clinical trials for solid tumors. Here we have explored the therapeutic potential of a related small-molecule-inhibitor, Compound-182. We demonstrate that Compound-182 is a highly potent and selective active site competitive inhibitor of PTP1B and PTPN2 that enhances T cell recruitment and activation and represses the growth of tumors in mice, without promoting overt immune-related toxicities. The enhanced anti-tumor immunity in immunogenic tumors can be ascribed to the inhibition of PTP1B/PTPN2 in T cells, whereas in cold tumors, Compound-182 elicited direct effects on both tumor cells and T cells. Importantly, treatment with Compound-182 rendered otherwise resistant tumors sensitive to α-PD-1 therapy. Our findings establish the potential for small molecule inhibitors of PTP1B and PTPN2 to enhance anti-tumor immunity and combat cancer.

Neurochemical Basis of Inter-Organ Crosstalk in Health and Obesity: Focus on the Hypothalamus and the Brainstem

Precise neural regulation is required for maintenance of energy homeostasis. Essential to this are the hypothalamic and brainstem nuclei which are located adjacent and supra-adjacent to the circumventricular organs. They comprise multiple distinct neuronal populations which receive inputs not only from other brain regions, but also from circulating signals such as hormones, nutrients, metabolites and postprandial signals. Hence, they are ideally placed to exert a multi-tier control over metabolism. The neuronal sub-populations present in these key metabolically relevant nuclei regulate various facets of energy balance which includes appetite/satiety control, substrate utilization by peripheral organs and glucose homeostasis. In situations of heightened energy demand or excess, they maintain energy homeostasis by restoring the balance between energy intake and expenditure. While research on the metabolic role of the central nervous system has progressed rapidly, the neural circuitry and molecular mechanisms involved in regulating distinct metabolic functions have only gained traction in the last few decades. The focus of this review is to provide an updated summary of the mechanisms by which the various neuronal subpopulations, mainly located in the hypothalamus and the brainstem, regulate key metabolic functions.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

A small molecule inhibitor of PTP1B and PTPN2 enhances T cell anti-tumor immunity

The inhibition of protein tyrosine phosphatases (PTPs), such as PTP1B and PTPN2 that function as intracellular checkpoints, has emerged as an exciting new approach for bolstering T cell anti-tumor immunity to combat cancer. ABBV-CLS-484 is a dual PTP1B and PTPN2 inhibitor currently in clinical trials for solid tumors. Here we have explored the therapeutic potential of targeting PTP1B and PTPN2 with a related small molecule inhibitor, Compound 182. We demonstrate that Compound 182 is a highly potent and selective active site competitive inhibitor of PTP1B and PTPN2 that enhances antigen-induced T cell activation and expansion ex vivo and represses the growth of syngeneic tumors in C57BL/6 mice without promoting overt immune-related toxicities. Compound 182 repressed the growth of immunogenic MC38 colorectal and AT3-OVA mammary tumors as well as immunologically cold AT3 mammary tumors that are largely devoid of T cells. Treatment with Compound 182 increased both the infiltration and activation of T cells, as well as the recruitment of NK cells and B cells that promote anti-tumor immunity. The enhanced anti-tumor immunity in immunogenic AT3-OVA tumors could be ascribed largely to the inhibition of PTP1B/PTPN2 in T cells, whereas in cold AT3 tumors, Compound 182 elicited both direct effects on tumor cells and T cells to facilitate T cell recruitment and thereon activation. Importantly, treatment with Compound 182 rendered otherwise resistant AT3 tumors sensitive to anti-PD1 therapy. Our findings establish the potential for small molecule active site inhibitors of PTP1B and PTPN2 to enhance anti-tumor immunity and combat cancer.

Effects of multi-organ crosstalk on the physiology and pathology of adipose tissue

In previous studies, adipocytes were found to play an important role in regulating whole-body nutrition and energy balance, and are also important in energy metabolism, hormone secretion, and immune regulation. Different adipocytes have different contributions to the body, with white adipocytes primarily storing energy and brown adipocytes producing heat. Recently discovered beige adipocytes, which have characteristics in between white and brown adipocytes, also have the potential to produce heat. Adipocytes interact with other cells in the microenvironment to promote blood vessel growth and immune and neural network interactions. Adipose tissue plays an important role in obesity, metabolic syndrome, and type 2 diabetes. Dysfunction in adipose tissue endocrine and immune regulation can cause and promote the occurrence and development of related diseases. Adipose tissue can also secrete multiple cytokines, which can interact with organs; however, previous studies have not comprehensively summarized the interaction between adipose tissue and other organs. This article reviews the effect of multi-organ crosstalk on the physiology and pathology of adipose tissue, including interactions between the central nervous system, heart, liver, skeletal muscle, and intestines, as well as the mechanisms of adipose tissue in the development of various diseases and its role in disease treatment. It emphasizes the importance of a deeper understanding of these mechanisms for the prevention and treatment of related diseases. Determining these mechanisms has enormous potential for identifying new targets for treating diabetes, metabolic disorders, and cardiovascular diseases.

Daily intranasal insulin at 40IU does not affect food intake and body composition: A placebo-controlled trial in older adults over a 24-week period with 24-weeks of follow-up

Centrally administered insulin stimulates the reward system to reduce appetite in response to food intake in animal studies. In humans, studies have shown conflicting results, with some studies suggesting that intranasal insulin (INI) in relatively high doses may decrease appetite, body fat, and weight in various populations. These hypotheses have not been tested in a large longitudinal placebo-controlled study. Participants in the Memory Advancement with Intranasal Insulin in Type 2 Diabetes (MemAID) trial were enrolled in this study. This study on energy homeostasis enrolled 89 participants who completed baseline and at least 1 intervention visit (42 women; age 65 ± 9 years; 46 INI, 38 with type 2 diabetes) and 76 completed treatment (16 women, age 64 ± 9; 38 INI, 34 with type 2 diabetes). The primary outcome was the INI effect on food intake. Secondary outcomes included the effect of INI on appetite and anthropometric measures, including body weight and body composition. In exploratory analyses, we tested the interaction of treatment with gender, body mass index (BMI), and diagnosis of type 2 diabetes. There was no INI effect on food intake or any of the secondary outcomes. INI also showed no differential effect on primary and secondary outcomes when considering gender, BMI, and type 2 diabetes. INI did not alter appetite or hunger nor cause weight loss when used at 40 I.U. intranasally daily for 24 weeks in older adults with and without type 2 diabetes.

Small Molecule Degraders of Protein Tyrosine Phosphatase 1B and T-Cell Protein Tyrosine Phosphatase for Cancer Immunotherapy

Protein tyrosine phosphatase 1B (PTP1B) and T-cell protein tyrosine phosphatase (TC-PTP) play non-redundant negative regulatory roles in T-cell activation, tumor antigen presentation, insulin and leptin signaling, and are potential targets for several therapeutic applications. Here, we report the development of a highly potent and selective small molecule degrader DU-14 for both PTP1B and TC-PTP. DU-14 mediated PTP1B and TC-PTP degradation requires both target protein(s) and VHL E3 ligase engagement and is also ubiquitination- and proteasome-dependent. DU-14 enhances IFN-γ induced JAK1/2-STAT1 pathway activation and promotes MHC-I expression in tumor cells. DU-14 also activates CD8+ T-cells and augments STAT1 and STAT5 phosphorylation. Importantly, DU-14 induces PTP1B and TC-PTP degradation in vivo and suppresses MC38 syngeneic tumor growth. The results indicate that DU-14, as the first PTP1B and TC-PTP dual degrader, merits further development for treating cancer and other indications.

Tgr5-/- mice are protected from ethanol-induced metabolic alterations through enhanced leptin and Fgf21 signaling

BACKGROUND

Alcohol-associated liver disease (ALD) is caused by chronic use of alcohol and ranges from hepatic steatosis to fibrosis and cirrhosis. Bile acids are physiological detergents that also regulate hepatic glucose and lipid homeostasis by binding to several receptors. One such receptor, Takeda G protein-coupled receptor 5 (TGR5), may represent a therapeutic target for ALD. Here, we used a chronic 10-day + binge ethanol-feeding model in mice to study the role of TGR5 in alcohol-induced liver injury.

METHODS

Female C57BL/6J wild-type mice and Tgr5-/- mice were pair-fed Lieber-DeCarli liquid diet with ethanol (5% v/v) or isocaloric control diet for 10 days followed by a gavage of 5% ethanol or isocaloric maltose control, respectively, to represent a binge-drinking episode. Tissues were harvested 9 hours following the binge, and metabolic phenotypes were characterized through examination of liver, adipose, and brain mechanistic pathways.

RESULTS

Tgr5-/- mice were protected from alcohol-induced accumulation of hepatic triglycerides. Interestingly, liver and serum levels of Fgf21 were significantly increased during ethanol feeding in Tgr5-/- mice, as was phosphorylation of Stat3. Parallel to Fgf21 levels, increased leptin gene expression in white adipose tissue and increased leptin receptor in liver were detected in Tgr5-/- mice fed ethanol diet. Adipocyte lipase gene expression was significantly increased in Tgr5-/- mice regardless of diet, whereas adipose browning markers were also increased in ethanol-fed Tgr5-/- mice, indicating potential for enhanced white adipose metabolism. Lastly, hypothalamic mRNA targets of leptin, involved in the regulation of food intake, were significantly increased in Tgr5-/- mice fed ethanol diet.

CONCLUSIONS

Tgr5-/- mice are protected from ethanol-induced liver damage and lipid accumulation. Alterations in lipid uptake and Fgf21 signaling, and enhanced metabolic activity of white adipose tissue, may mediate these effects.

TLR4 in POMC neurons regulates thermogenesis in a sex-dependent manner

The rising prevalence of obesity has become a worldwide health concern. Obesity usually occurs when there is an imbalance between energy intake and energy expenditure. However, energy expenditure consists of several components, including metabolism, physical activity, and thermogenesis. Toll-like receptor 4 (TLR4) is a transmembrane pattern recognition receptor, and it is abundantly expressed in the brain. Here, we showed that pro-opiomelanocortin (POMC)-specific deficiency of TLR4 directly modulates brown adipose tissue thermogenesis and lipid homeostasis in a sex-dependent manner. Deleting TLR4 in POMC neurons is sufficient to increase energy expenditure and thermogenesis resulting in reduced body weight in male mice. POMC neuron is a subpopulation of tyrosine hydroxylase neurons and projects into brown adipose tissue, which regulates the activity of sympathetic nervous system and contributes to thermogenesis in POMC-TLR4-KO male mice. By contrast, deleting TLR4 in POMC neurons decreases energy expenditure and increases body weight in female mice, which affects lipolysis of white adipose tissue (WAT). Mechanistically, TLR4 KO decreases the expression of the adipose triglyceride lipase and lipolytic enzyme hormone-sensitive lipase in WAT in female mice. Furthermore, the function of immune-related signaling pathway in WAT is inhibited because of obesity, which exacerbates the development of obesity reversely. Together, these results demonstrate that TLR4 in POMC neurons regulates thermogenesis and lipid balance in a sex-dependent manner.

Combined effects of intermittent fasting with swimming-based high intensity intermittent exercise training in Wistar rats

High caloric intake and physical inactivity are known precursors to the development of several chronic metabolic diseases. For obesity and sedentarism, High Intensity Intermittent Exercise (HIIE) and Intermittent Fasting (IF) have emerged as individual strategies to attenuate their negative effects by improving metabolism. To study their combined effects, Wistar male rats (n = 74, 60 days old) were divided into four groups: Sedentary Control (C), swimming-based HIIE only (HIIE), Intermittent Fasting only (IF), and swimming-based HIIE associated with Intermittent Fasting (HIIE/IF). Over an eight-week period swimming performance, body composition, weight and feeding behavior were analyzed. The final morphology of white adipose tissue showed a significant reduction in adipocyte size consistent with a higher number of cells per area in exercised animals (vs C and IF, p < 0.05), which also displayed characteristics of browning through UCP-1 levels and CD31 staining. These results suggest that the increased performance in the HIIE/IF group is, in part, by modifications of WAT metabolism through the browning process.

The Complex Interplay between Imbalanced Mitochondrial Dynamics and Metabolic Disorders in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a global burden, with an increasing number of people affected and increasing treatment costs. The advances in research and guidelines improve the management of blood glucose and related diseases, but T2DM and its complications are still a big challenge in clinical practice. T2DM is a metabolic disorder in which insulin signaling is impaired from reaching its effectors. Mitochondria are the "powerhouses" that not only generate the energy as adenosine triphosphate (ATP) using pyruvate supplied from glucose, free fatty acid (FFA), and amino acids (AA) but also regulate multiple cellular processes such as calcium homeostasis, redox balance, and apoptosis. Mitochondrial dysfunction leads to various diseases, including cardiovascular diseases, metabolic disorders, and cancer. The mitochondria are highly dynamic in adjusting their functions according to cellular conditions. The shape, morphology, distribution, and number of mitochondria reflect their function through various processes, collectively known as mitochondrial dynamics, including mitochondrial fusion, fission, biogenesis, transport, and mitophagy. These processes determine the overall mitochondrial health and vitality. More evidence supports the idea that dysregulated mitochondrial dynamics play essential roles in the pathophysiology of insulin resistance, obesity, and T2DM, as well as imbalanced mitochondrial dynamics found in T2DM. This review updates and discusses mitochondrial dynamics and the complex interactions between it and metabolic disorders.

An insight into brown/beige adipose tissue whitening, a metabolic complication of obesity with the multifactorial origin

Brown adipose tissue (BAT), a thermoregulatory organ known to promote energy expenditure, has been extensively studied as a potential avenue to combat obesity. Although BAT is the opposite of white adipose tissue (WAT) which is responsible for energy storage, BAT shares thermogenic capacity with beige adipose tissue that emerges from WAT depots. This is unsurprising as both BAT and beige adipose tissue display a huge difference from WAT in terms of their secretory profile and physiological role. In obesity, the content of BAT and beige adipose tissue declines as these tissues acquire the WAT characteristics via the process called "whitening". This process has been rarely explored for its implication in obesity, whether it contributes to or exacerbates obesity. Emerging research has demonstrated that BAT/beige adipose tissue whitening is a sophisticated metabolic complication of obesity that is linked to multiple factors. The current review provides clarification on the influence of various factors such as diet, age, genetics, thermoneutrality, and chemical exposure on BAT/beige adipose tissue whitening. Moreover, the defects and mechanisms that underpin the whitening are described. Notably, the BAT/beige adipose tissue whitening can be marked by the accumulation of large unilocular lipid droplets, mitochondrial degeneration, and collapsed thermogenic capacity, by the virtue of mitochondrial dysfunction, devascularization, autophagy, and inflammation.

Could Naringenin Participate as a Regulator of Obesity and Satiety?

Obesity is a serious health problem worldwide, since it is associated with multiple metabolic disorders and complications such as cardiovascular disease, type 2 diabetes, fatty liver disease and overall metabolic dysfunction. Dysregulation of the hunger-satiety pathway, which includes alterations of central and peripheral signaling, explains some forms of obesity by favoring hyperphagia and weight gain. The present work comprehensively summarizes the mechanisms by which naringenin (NAR), a predominant flavanone in citrus fruits, could modulate the main pathways associated with the development of obesity and some of its comorbidities, such as oxidative stress (OS), inflammation, insulin resistance (IR) and dyslipidemia, as well as the role of NAR in modulating the secretion of enterohormones of the satiety pathway and its possible antiobesogenic effect. The results of multiple in vitro and in vivo studies have shown that NAR has various potentially modulatory biological effects against obesity by countering IR, inflammation, OS, macrophage infiltration, dyslipidemia, hepatic steatosis, and adipose deposition. Likewise, NAR is capable of modulating peptides or peripheral hormones directly associated with the hunger-satiety pathway, such as ghrelin, cholecystokinin, insulin, adiponectin and leptin. The evidence supports the use of NAR as a promising alternative to prevent overweight and obesity.

The role of oestrogen in determining sexual dimorphism in energy balance

Energy balance is determined by caloric intake and the rate at which energy is expended, with the latter comprising resting energy expenditure, physical activity and adaptive thermogenesis. The regulation of both energy intake and expenditure exhibits clear sexual dimorphism, with young women being relatively protected against weight gain and the development of cardiometabolic diseases. Preclinical studies have indicated that females are more sensitive to the satiety effects of leptin and insulin compared to males. Furthermore, females have greater thermogenic activity than males, whereas resting energy expenditure is generally higher in males than females. In addition to this, in post-menopausal women, the decline in sex steroid concentration, particularly in oestrogen, is associated with a shift in the distribution of adipose tissue and overall increased propensity to gain weight. Oestrogens are known to regulate energy balance and weight homeostasis via effects on both food intake and energy expenditure. Indeed, 17β-oestradiol treatment increases melanocortin signalling in the hypothalamus to cause satiety. Furthermore, oestrogenic action at the ventromedial hypothalamus has been linked with increased energy expenditure in female mice. We propose that oestrogen action on energy balance is multi-faceted and is fundamental to determining sexual dimorphism in weight control. Furthermore, evidence suggests that the decline in oestrogen levels leads to increased risk of weight gain and development of cardiometabolic disease in women across the menopausal transition.

Emerging role of hypothalamus in the metabolic regulation in the offspring of maternal obesity

Maternal obesity has a significant impact on the metabolism of offspring both in childhood and adulthood. The metabolic regulation of offspring is influenced by the intrauterine metabolic programming induced by maternal obesity. Nevertheless, the precise mechanisms remain unclear. The hypothalamus is the primary target of metabolic programming and the principal regulatory center of energy metabolism. Accumulating evidence has indicated the crucial role of hypothalamic regulation in the metabolism of offspring exposed to maternal obesity. This article reviews the development of hypothalamus, the role of the hypothalamic regulations in energy homeostasis, possible mechanisms underlying the developmental programming of energy metabolism in offspring, and the potential therapeutic approaches for preventing metabolic diseases later in life. Lastly, we discuss the challenges and future directions of hypothalamic regulation in the metabolism of children born to obese mothers.

Hypothalamic Grb10 enhances leptin signalling and promotes weight loss

Leptin acts on hypothalamic neurons expressing agouti-related protein (AgRP) or pro-opiomelanocortin (POMC) to suppress appetite and increase energy expenditure, but the intracellular mechanisms that modulate central leptin signalling are not fully understood. Here we show that growth factor receptor-bound protein 10 (Grb10), an adaptor protein that binds to the insulin receptor and negatively regulates its signalling pathway, can interact with the leptin receptor and enhance leptin signalling. Ablation of Grb10 in AgRP neurons promotes weight gain, while overexpression of Grb10 in AgRP neurons reduces body weight in male and female mice. In parallel, deletion or overexpression of Grb10 in POMC neurons exacerbates or attenuates diet-induced obesity, respectively. Consistent with its role in leptin signalling, Grb10 in AgRP and POMC neurons enhances the anorexic and weight-reducing actions of leptin. Grb10 also exaggerates the inhibitory effects of leptin on AgRP neurons via ATP-sensitive potassium channel-mediated currents while facilitating the excitatory drive of leptin on POMC neurons through transient receptor potential channels. Our study identifies Grb10 as a potent leptin sensitizer that contributes to the maintenance of energy homeostasis by enhancing the response of AgRP and POMC neurons to leptin.

Hypothalamic Hnscr regulates glucose balance by mediating central inflammation and insulin signal

OBJECTIVES

Hypothalamic dysfunction leads to glucose metabolic imbalance; however, the mechanisms still need clarification. Our current study was to explore the role of hypothalamic Hnscr in glucose metabolism.

MATERIALS AND METHODS

Using Hnscr knockout or htNSC-specific Hnscr overexpression mice, we evaluated the effects of Hnscr on glucose metabolism through GTTs, ITTs, serum indicator measurements, etc. Immunofluorescence staining and Western blotting were performed to test inflammation levels and insulin signalling in hypothalamus. Conditioned medium intervene were used to investigate the effects of htNSCs on neuronal cell line. We also detected the glucose metabolism of mice with htNSCs implantation.

RESULTS

Hnscr expression decreased in the hypothalamus after high-fat diet feed. Hnscr-null mice displayed aggravated systematic insulin resistance, while mice with htNSC-specific Hnscr overexpression had the opposite phenotype. Notably, Hnscr-null mice had increased NF-κB signal in htNSCs, along with enhanced inflammation and damaged insulin signal in neurons located in arcuate nucleus of hypothalamus. The secretions, including sEVs, of Hnscr-deficient htNSCs mediated the detrimental effects on the CNS cell line. Locally implantation with Hnscr-depleted htNSCs disrupted glucose homeostasis.

CONCLUSIONS

This study demonstrated that decreased Hnscr in htNSCs led to systematic glucose imbalance through activating NF-κB signal and dampening insulin signal in hypothalamic neurons.

The sympathetic nervous system in the 21st century: Neuroimmune interactions in metabolic homeostasis and obesity

The sympathetic nervous system maintains metabolic homeostasis by orchestrating the activity of organs such as the pancreas, liver, and white and brown adipose tissues. From the first renderings by Thomas Willis to contemporary techniques for visualization, tracing, and functional probing of axonal arborizations within organs, our understanding of the sympathetic nervous system has started to grow beyond classical models. In the present review, we outline the evolution of these findings and provide updated neuroanatomical maps of sympathetic innervation. We offer an autonomic framework for the neuroendocrine loop of leptin action, and we discuss the role of immune cells in regulating sympathetic terminals and metabolism. We highlight potential anti-obesity therapeutic approaches that emerge from the modern appreciation of SNS as a neural network vis a vis the historical fear of sympathomimetic pharmacology, while shifting focus from post- to pre-synaptic targeting. Finally, we critically appraise the field and where it needs to go.

Trends in Gliosis in Obesity, and the Role of Antioxidants as a Therapeutic Alternative

Obesity remains a global health problem. Chronic low-grade inflammation in this pathology has been related to comorbidities such as cognitive alterations that, in the long term, can lead to neurodegenerative diseases. Neuroinflammation or gliosis in patients with obesity and type 2 diabetes mellitus has been related to the effect of adipokines, high lipid levels and glucose, which increase the production of free radicals. Cerebral gliosis can be a risk factor for developing neurodegenerative diseases, and antioxidants could be an alternative for the prevention and treatment of neural comorbidities in obese patients.

AIM

Identify the immunological and oxidative stress mechanisms that produce gliosis in patients with obesity and propose antioxidants as an alternative to reducing neuroinflammation.

METHOD

Advanced searches were performed in scientific databases: PubMed, ProQuest, EBSCO, and the Science Citation index for research on the physiopathology of gliosis in obese patients and for the possible role of antioxidants in its management.

CONCLUSION

Patients with obesity can develop neuroinflammation, conditioned by various adipokines, excess lipids and glucose, which results in an increase in free radicals that must be neutralized with antioxidants to reduce gliosis and the risk of long-term neurodegeneration.

Interactions between central nervous system and peripheral metabolic organs

According to Descartes, minds and bodies are distinct kinds of "substance", and they cannot have causal interactions. However, in neuroscience, the two-way interaction between the brain and peripheral organs is an emerging field of research. Several lines of evidence highlight the importance of such interactions. For example, the peripheral metabolic systems are overwhelmingly regulated by the mind (brain), and anxiety and depression greatly affect the functioning of these systems. Also, psychological stress can cause a variety of physical symptoms, such as bone loss. Moreover, the gut microbiota appears to play a key role in neuropsychiatric and neurodegenerative diseases. Mechanistically, as the command center of the body, the brain can regulate our internal organs and glands through the autonomic nervous system and neuroendocrine system, although it is generally considered to be outside the realm of voluntary control. The autonomic nervous system itself can be further subdivided into the sympathetic and parasympathetic systems. The sympathetic division functions a bit like the accelerator pedal on a car, and the parasympathetic division functions as the brake. The high center of the autonomic nervous system and the neuroendocrine system is the hypothalamus, which contains several subnuclei that control several basic physiological functions, such as the digestion of food and regulation of body temperature. Also, numerous peripheral signals contribute to the regulation of brain functions. Gastrointestinal (GI) hormones, insulin, and leptin are transported into the brain, where they regulate innate behaviors such as feeding, and they are also involved in emotional and cognitive functions. The brain can recognize peripheral inflammatory cytokines and induce a transient syndrome called sick behavior (SB), characterized by fatigue, reduced physical and social activity, and cognitive impairment. In summary, knowledge of the biological basis of the interactions between the central nervous system and peripheral organs will promote the full understanding of how our body works and the rational treatment of disorders. Thus, we summarize current development in our understanding of five types of central-peripheral interactions, including neural control of adipose tissues, energy expenditure, bone metabolism, feeding involving the brain-gut axis and gut microbiota. These interactions are essential for maintaining vital bodily functions, which result in homeostasis, i.e., a natural balance in the body's systems.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

Ultraviolet Radiation Exposure and its Impacts on Cutaneous Phosphorylation Signaling in Carcinogenesis: Focusing on Protein Tyrosine Phosphatases†

Sunlight exposure is a significant risk factor for UV-induced deteriorating transformations of epidermal homeostasis leading to skin carcinogenesis. The ability of UVB radiation to cause melanoma, as well as basal and squamous cell carcinomas, makes UVB the most harmful among the three known UV ranges. UVB-induced DNA mutations and dysregulation of signaling pathways contribute to skin cancer formation. Among various signaling pathways modulated by UVB, tyrosine phosphorylation signaling which is mediated by the action of protein tyrosine kinases (PTKs) on specific tyrosine residues is highly implicated in photocarcinogenesis. Following UVB irradiation, PTKs get activated and their downstream signaling pathways contribute to photocarcinogenesis by promoting the survival of damaged keratinocytes and increasing cell proliferation. While UVB activates oncogenic signaling pathways, it can also activate tumor suppressive signaling pathways as initial protective mechanisms to maintain epidermal homeostasis. Tyrosine dephosphorylation is one of the protective mechanisms and is mediated by the action of protein tyrosine phosphatases (PTPs). PTP can counteract UVB-mediated PTK activation and downregulate oncogenic signaling pathways. However, PTPs have not been studied extensively in photocarcinogenesis with previous studies regarding their inactivation induced by UVB. This current review will summarize the recent progress in the protective function of PTPs in epidermal photocarcinogenesis.

Obesity: an evolutionary context

People completely lacking body fat (lipodystrophy/lipoatrophy) and those with severe obesity both show profound metabolic and other health issues. Regulating levels of body fat somewhere between these limits would, therefore, appear to be adaptive. Two different models might be contemplated. More traditional is a set point (SP) where the levels are regulated around a fixed level. Alternatively, dual-intervention point (DIP) is a system that tolerates fairly wide variation but is activated when critically high or low levels are breached. The DIP system seems to fit our experience much better than an SP, and models suggest that it is more likely to have evolved. A DIP system may have evolved because of two contrasting selection pressures. At the lower end, we may have been selected to avoid low levels of fat as a buffer against starvation, to avoid disease-induced anorexia, and to support reproduction. At the upper end, we may have been selected to avoid excess storage because of the elevated risks of predation. This upper limit of control seems to have malfunctioned because some of us deposit large fat stores, with important negative health effects. Why has evolution not protected us against this problem? One possibility is that the protective system slowly fell apart due to random mutations after we dramatically reduced the risk of being predated during our evolutionary history. By chance, it fell apart more in some people than others, and these people are now unable to effectively manage their weight in the face of the modern food glut. To understand the evolutionary context of obesity, it is important to separate the adaptive reason for storing some fat (i.e. the lower intervention point), from the nonadaptive reason for storing lots of fat (a broken upper intervention point). The DIP model has several consequences, showing how we understand the obesity problem and what happens when we attempt to treat it.

Angiotensin II Promotes White Adipose Tissue Browning and Lipolysis in Mice

Emerging evidence has revealed that all components of the renin-angiotensin system (RAS) are present in adipose tissue. Angiotensin II (Ang II), the major bioactive component of the RAS, has been recognized as an adipokine involved in regulating energy homeostasis. However, the precise role of Ang II in white adipose tissue (WAT) remodeling remains to be elucidated. In this present study, C57BL/C male mice were continuously infused with different doses of Ang II (1.44 mg/kg/d or 2.5 mg/kg/d) or saline for 2 weeks and treated with or without the Ang II type 1 receptor blocker valsartan. H&E staining and immunohistochemistry were conducted to investigate the white-to-brown fat conversion. The level of serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) was measured. RNA sequencing was employed to explore the differentially expressed genes and their enriched pathways between control and Ang II groups. Our results showed that Ang II substantially resulted in loss of body weight and fat mass. Most importantly, Ang II treatment induced WAT browning in mice, which was partially attenuated by valsartan treatment. Furthermore, Ang II perturbed the serum lipid profiles. Ang II treatment elevated serum levels of TC, TG, LDL-C, and HDL-C in mice. Mechanistically, thermogenesis, cell respiration, and lipid metabolism-associated mRNAs showed significantly increased expression profiling in Ang II-treated WATs compared with control WATs. Moreover, we found that Ang II treatment enhanced AMPK phosphorylation in adipocytes. Therefore, Ang II promotes WAT browning and lipolysis via activating the AMPK signaling pathway.

The PACAP Paradox: Dynamic and Surprisingly Pleiotropic Actions in the Central Regulation of Energy Homeostasis

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP), a pleiotropic neuropeptide, is widely distributed throughout the body. The abundance of PACAP expression in the central and peripheral nervous systems, and years of accompanying experimental evidence, indicates that PACAP plays crucial roles in diverse biological processes ranging from autonomic regulation to neuroprotection. In addition, PACAP is also abundantly expressed in the hypothalamic areas like the ventromedial and arcuate nuclei (VMN and ARC, respectively), as well as other brain regions such as the nucleus accumbens (NAc), bed nucleus of stria terminalis (BNST), and ventral tegmental area (VTA) - suggesting that PACAP is capable of regulating energy homeostasis via both the homeostatic and hedonic energy balance circuitries. The evidence gathered over the years has increased our appreciation for its function in controlling energy balance. Therefore, this review aims to further probe how the pleiotropic actions of PACAP in regulating energy homeostasis is influenced by sex and dynamic changes in energy status. We start with a general overview of energy homeostasis, and then introduce the integral components of the homeostatic and hedonic energy balance circuitries. Next, we discuss sex differences inherent to the regulation of energy homeostasis via these two circuitries, as well as the activational effects of sex steroid hormones that bring about these intrinsic disparities between males and females. Finally, we explore the multifaceted role of PACAP in regulating homeostatic and hedonic feeding through its actions in regions like the NAc, BNST, and in particular the ARC, VMN and VTA that occur in sex- and energy status-dependent ways.

TRPC5 deletion in the central amygdala antagonizes high-fat diet-induced obesity by increasing sympathetic innervation

Transient receptor potential channel 5 (TRPC5) is predominantly distributed in the brain, especially in the central amygdala (CeA), which is closely associated with pain and addiction. Although mounting evidence indicates that the CeA is related to energy homeostasis, the possible regulatory effect of TRPC5 in the CeA on metabolism remains unclear. Here, we reported that the expression of TRPC5 in the CeA of mice was increased under a high-fat diet (HFD). Specifically, the deleted TRPC5 protein in the CeA of mice using adeno-associated virus resisted HFD-induced weight gain, accompanied by increased food intake. Furthermore, the energy expenditure of CeA-specific TRPC5 deletion mice (TRPC5 KO) was elevated due to augmented white adipose tissue (WAT) browning and brown adipose tissue (BAT) activity. Mechanistically, deficiency of TRPC5 in the CeA boosted nonshivering thermogenesis under cold stimulation by stimulating sympathetic nerves, as the β3-adrenoceptor (Adrb3) antagonist SR59230A blocked the effect of TRPC5 KO on this process. In summary, TRPC5 deletion in the CeA alleviated the metabolic deterioration of mice fed a HFD, and these phenotypic improvements were correlated with the increased sympathetic distribution and activity of adipose tissue.

Diet-responsive transcriptional regulation of insulin in a single neuron controls systemic metabolism

Metabolic homeostasis is coordinated through a robust network of signaling pathways acting across all tissues. A key part of this network is insulin-like signaling, which is fundamental for surviving glucose stress. Here, we show that Caenorhabditis elegans fed excess dietary glucose reduce insulin-1 (INS-1) expression specifically in the BAG glutamatergic sensory neurons. We demonstrate that INS-1 expression in the BAG neurons is directly controlled by the transcription factor ETS-5, which is also down-regulated by glucose. We further find that INS-1 acts exclusively from the BAG neurons, and not other INS-1-expressing neurons, to systemically inhibit fat storage via the insulin-like receptor DAF-2. Together, these findings reveal an intertissue regulatory pathway where regulation of insulin expression in a specific neuron controls systemic metabolism in response to excess dietary glucose.

Metabolic homeostasis is coordinated through a robust network of signaling pathways acting across all tissues. This study shows that Caenorhabditis elegans nematodes fed excess dietary glucose reduce the expression of insulin-1 specifically in the BAG glutamatergic sensory neurons, and that insulin-1 produced by these neurons systemically inhibits fat storage via the insulin-like receptor DAF-2.

The central nervous system control of energy homeostasis: high fat diet induced hypothalamic microinflammation and obesity

Obesity is believed to arise through the imbalance of energy homeostasis controlled by the central nervous system, where the hypothalamus plays the fundamental role in energy metabolism. In this review, we will provide an overview regarding the functions of POMC neurons and AgRP neurons in acute nucleus of the hypothalamus which mediated the energy metabolism, highlighting their interactions with peripheral organs derived hormones in control of energy homeostasis. Furthermore, the role of high fat diet induced hypothalamic microinflammation in the pathogenesis of obesity will be discussed. We hope this review could help researchers to understand the mechanism of hypothalamus in control of energy metabolism, and design related drugs to block the pathways involving in the impaired metabolism in obese patients.

Intragastric safflower yellow and its main component HSYA improve leptin sensitivity before body weight change in diet-induced obese mice

Our previous studies found that safflower yellow (SY) and its main component hydroxysafflor yellow A (HSYA) could alleviate obesity and improve leptin resistance in high-fat diet (HFD) induced obese mice. Therefore, our present study aimed to investigate whether the above effect of SY/HSYA was a direct effect or follow-up effect of weight loss and whether leptin was essential for the anti-obesity effect of SY/HSYA or not. HFD-induced obese mice were treated with SY or HSYA for 4 weeks, while ob/ob mice were treated with SY for 10 weeks. Body weight, food intake, fat mass, and serum leptin levels were measured. The leptin sensitivity experiment was conducted in HFD-induced obese mice. The expressions of leptin and its signaling-related genes were detected by RT-qPCR and Western blot methods. SY/HSYA treatment had no effect on food intake, energy expenditure, body weight, fat mass, and serum leptin levels in HFD-induced obese mice. However, the leptin sensitivity experiment showed that the food intake decreased by 18.4% in the HFD-SY group and the body weight gain decreased by 104.6% in the HFD-HSYA group, respectively (both P < 0.05). Furthermore, the expressions of leptin and leptin signaling inhibitory regulators were significantly decreased, while the phosphorylation of signal transducer and activator of transcription 3 (p-STAT3) were notably increased in WAT of HFD-induced obese mice, fully differentiated 3T3-L1 adipocytes after SY/HSYA intervention (all P < 0.05). Interestingly, SY treatment was ineffective on body weight, fat mass, and glucose metabolism in leptin-deficient ob/ob mice. SY/HSYA administration could firstly improve peripheral leptin resistance in adipose tissue of HFD-induced obese mice before their body weight was significantly changed, and leptin was essential for the anti-obesity effect of SY.

Rutin promotes white adipose tissue "browning" and brown adipose tissue activation partially through the calmodulin-dependent protein kinase kinase β/AMP-activated protein kinase pathway

Promoting white adipose tissue (WAT) "browning" and brown adipose tissue (BAT) activation could contribute to increasing energy expenditure. We explored the mechanisms by which the natural compound rutin induced adipose tissue differentiation and ameliorated obesity in vivo and in vitro. 3T3-L1 preadipocytes were cultured in adipogenic differentiation media with/out rutin. Male C57BL/6 mice (n = 6) were fed a high-fat diet (HFD) for 12 weeks with/out rutin. In HFD-fed mice, rutin treatment significantly inhibited weight gain, improved the metabolic profile of plasma samples, decreased the weights of epididymal WAT (eWAT), inguina WAT (iWAT), and liver, and adipocyte size. Furthermore, rutin also increased the expression of uncoupling protein 1 (Ucp-1) and other thermogenic markers in the WAT and BAT. In 3T3-L1 cells, rutin effectively reduced the formation of lipid droplets, stimulated the expression of thermogenic markers, and reduced the expression of adipogenic genes. Additionally, rutin markedly upregulated the AMP-activated protein kinase (AMPK) pathway, and these effects were diminished by treatment with the AMPK inhibitor compound C (CC). Pretreatment with the calmodulin-dependent protein kinase kinase β (CaMKKβ) inhibitor STO-609 blocked the induction of thermogenic markers in 3T3-L1 cells by rutin. Our results indicated that rutin increased energy consumption, induced WAT "browning" and BAT activation, and thus was a promising target for the development of new therapeutic approaches to improve adipose tissue energy metabolism.

Preoperative Short-Term High Carbohydrate Diet Provides More High-Quality Transplantable Fat and Improves the Outcome of Fat Grafts in Mice

BACKGROUND

Patients with a low body mass index may have inadequate high-quality adipose tissue for transplantation. The influence of high-energy diets on adipose tissue and graft retention remains unknown.

OBJECTIVES

We explored inguinal fat pad alternation in mice fed on a short-time high-fat diet (HFD) or a high-carbohydrate diet (HCD) preoperatively and the morphological and histological differences after transplantation.

METHODS

Mice were fed HFD (60% kilocalories from fat, 20% from carbohydrate), HCD (9.3% kilocalories from fat, 80.1% from carbohydrate), or normal (12% kilocalories from fat, 67% kilocalories from carbohydrate) diets for 2 or 4 weeks. Histological analyses were carried out following hematoxylin and eosin staining, and CD34 and proliferating cell nuclear antigen immunostaining. The uncoupling protein-1 (UCP-1) expression was determined by western blotting. Fat pads from each group were grafted into the dorsal region of the recipient mice and morphological and histological changes were determined 4, 8, and 12 weeks post-transplantation. Vascular endothelial growth factor α and platelet-derived growth factor α expression were determined using quantitative polymerase chain reaction.

RESULTS

The inguinal fat pad volume increased in the HFD and HCD groups. The presence of multilocular adipocytes in inguinal fat of HCD-fed mice, combined with the increased UCP-1 content, suggested adipocyte browning. HCD grafts showed higher volume retention and reduced oil cyst formation, possibly attributed to better angiogenesis and adipogenesis.

CONCLUSIONS

HCD enlarged adipose tissue and improved grafts survival rates, which may be due to the browning of fat before grafting and enhanced angiogenesis after grafting.