HIF-1α in Myeloid Cells Promotes Adipose Tissue Remodeling Toward Insulin Resistance

Hypoxia-inducible factor-1α-deficient adipose-tissue macrophages produce the heat to mediate lipolysis of white adipose tissue through uncoupling protein-1

BACKGROUND

Uncoupling protein 1 (UCP1) is a proton uncoupler located across the mitochondrial membrane generally involved in thermogenesis of brown adipose tissues. Although UCP1 is known to be strongly expressed in brown adipocytes, recent evidence suggest that white adipocytes can also express UCP1 under certain circumstances such as cold- or β-adrenergic receptor-stimulation, allowing them to acquire brown adipocyte-like features thereby becoming 'beige' adipocytes.

RESULTS

In this study, we report that UCP1 can be expressed in adipose-tissue macrophages (ATM) lacking functional hypoxia-inducible factor-1 (HIF-1) and this does not require cold- nor β-adrenergic receptor activation. By using myeloid-specific Hif-1α knockout (KO) mice, we observed that these mice were protected from diet-induced obesity and exhibited an improved thermogenic tolerance upon cold challenge. ATM isolated from white adipose tissues (WAT) of these mice fed with high fat diet exhibited significantly higher M2-polarization, decreased glycolysis, increased mitochondrial functions and acetyl-CoA levels, along with increased expression of Ucp1, peroxisome proliferator activated receptor-gamma co-activator-1a, and others involved in histone acetylation. Consistent with the increased Ucp1 gene expression, these ATM produced a significant amount of heat mediating lipolysis of co-cultured adipocytes liberating free fatty acid. Treating ATM with acetate, a substrate for acetyl-CoA synthesis was able to boost the heat production in wild-type or Hif-1α-deficient but not UCP1-deficient macrophages, indicating that UCP1 was necessary for the heat production in macrophages. Lastly, we observed a significant inverse correlation between the number of UCP1-expressing ATM in WAT and the body mass index of human individuals.

CONCLUSIONS

UCP1-expressing ATM produce the heat to mediate lipolysis of adipocytes, indicating that this can be a novel strategy to treat and prevent diet-induced obesity.

MDM2 induces pro-inflammatory and glycolytic responses in M1 macrophages by integrating iNOS-nitric oxide and HIF-1α pathways in mice

M1 macrophages induce protective immunity against infection, but also contribute to metabolic and inflammatory diseases. Here we show that the E3 ubiquitin ligase, MDM2, promotes the glycolytic and inflammatory activities of M1 macrophage by increasing the production of IL-1β, MCP-1 and nitric oxide (NO). Mechanistically, MDM2 triggers the ubiquitination and degradation of E3 ligase, SPSB2, to stabilize iNOS and increases production of NO, which s-nitrosylates and activates HIF-1α for triggering the glycolytic and pro-inflammatory programs in M1 macrophages. Myeloid-specific haplodeletion of MDM2 in mice not only blunts LPS-induced endotoxemia and NO production, but also alleviates obesity-induced adipose tissue-resident macrophage inflammation. By contrast, MDM2 haplodeletion induces higher mortality, tissue damage and bacterial burden, and also suppresses M1 macrophage response, in the cecal ligation and puncture-induced sepsis mouse model. Our findings thus identify MDM2 as an activator of glycolytic and inflammatory responses in M1 macrophages by connecting the iNOS-NO and HIF-1α pathways.

Implications of obesity and insulin resistance for the treatment of oestrogen receptor-positive breast cancer

Breast cancer is the most common cancer in women, and incidence rates are rising, it is thought in part, due to increasing levels of obesity. Endocrine therapy (ET) remains the cornerstone of systemic therapy for early and advanced oestrogen receptor-positive (ER + ) breast cancer, but despite treatment advances, it is becoming more evident that obesity and insulin resistance are associated with worse outcomes. Here, we describe the current understanding of the relationship between both obesity and diabetes and the prevalence and outcomes for ER+ breast cancer. We also discuss the mechanisms associated with resistance to ET and the relationship to treatment toxicity.

Metabolic Messengers: itaconate

The metabolite itaconate has emerged as an important immunoregulator with roles in antibacterial defence, inhibition of inflammation and, more recently, as an inhibitory factor in obesity. Itaconate is one of the most upregulated metabolites in inflammatory macrophages. It is produced owing to the disturbance of the tricarboxylic acid cycle and the diversion of aconitate to itaconate via the enzyme aconitate decarboxylase 1. In immunology, initial studies concentrated on the role of itaconate in inflammatory macrophages where it was shown to be inhibitory, but this has expanded as the impact of itaconate on other cell types is starting to emerge. This review focuses on itaconate as a key immunoregulatory metabolite and describes its diverse mechanisms of action and its many impacts on the immune and inflammatory responses and in cancer. We also examine the clinical relevance of this immunometabolite and its therapeutic potential for immune and inflammatory diseases.

Metabolic flux in macrophages in obesity and type-2 diabetes

Recent literature extensively investigates the crucial role of energy metabolism in determining the inflammatory response and polarization status of macrophages. This rapidly expanding area of research highlights the importance of understanding the link between energy metabolism and macrophage function. The metabolic pathways in macrophages are intricate and interdependent, and they can affect the polarization of macrophages. Previous studies suggested that glucose flux through cytosolic glycolysis is necessary to trigger pro-inflammatory phenotypes of macrophages, and fatty acid oxidation is crucial to support anti-inflammatory responses. However, recent studies demonstrated that this understanding is oversimplified and that the metabolic control of macrophage polarization is highly complex and not fully understood yet. How the metabolic flux through different metabolic pathways (glycolysis, glucose oxidation, fatty acid oxidation, ketone oxidation, and amino acid oxidation) is altered by obesity- and type 2 diabetes (T2D)-associated insulin resistance is also not fully defined. This mini-review focuses on the impact of insulin resistance in obesity and T2D on the metabolic flux through the main metabolic pathways in macrophages, which might be linked to changes in their inflammatory responses. We closely evaluated the experimental studies and methodologies used in the published research and highlighted priority research areas for future investigations.

Unraveling the complex roles of macrophages in obese adipose tissue: an overview

Macrophages, a heterogeneous population of innate immune cells, exhibit remarkable plasticity and play pivotal roles in coordinating immune responses and maintaining tissue homeostasis within the context of metabolic diseases. The activation of inflammatory macrophages in obese adipose tissue leads to detrimental effects, inducing insulin resistance through increased inflammation, impaired thermogenesis, and adipose tissue fibrosis. Meanwhile, adipose tissue macrophages also play a beneficial role in maintaining adipose tissue homeostasis by regulating angiogenesis, facilitating the clearance of dead adipocytes, and promoting mitochondrial transfer. Exploring the heterogeneity of macrophages in obese adipose tissue is crucial for unraveling the pathogenesis of obesity and holds significant potential for targeted therapeutic interventions. Recently, the dual effects and some potential regulatory mechanisms of macrophages in adipose tissue have been elucidated using single-cell technology. In this review, we present a comprehensive overview of the intricate activation mechanisms and diverse functions of macrophages in adipose tissue during obesity, as well as explore the potential of drug delivery systems targeting macrophages, aiming to enhance the understanding of current regulatory mechanisms that may be potentially targeted for treating obesity or metabolic diseases.

PDGFRβ + cell HIF2α is dispensable for white adipose tissue metabolic remodeling and hepatic lipid accumulation in obese mice

BACKGROUND

Obesity is associated with extensive white adipose tissue (WAT) expansion and remodeling. Healthy WAT expansion contributes to the maintenance of energy balance in the liver, thereby ameliorating obesity-related hepatic steatosis. Tissue-resident mesenchymal stromal cell populations, including PDGFRβ + perivascular cells, are increasingly recognized pivotal as determinants of the manner in which WAT expands. However, the full array of regulatory factors controlling WAT stromal cell functions remains to be fully elucidated. Hypoxia-inducible factors (HIFs) are critical regulators in WAT stromal cell populations such as adipocyte precursor cells (APCs). It is revealed that HIF1α activation within PDGFRβ + stromal cells results in the suppression of de novo adipogenesis and the promotion of a pro-fibrogenic cellular program in obese animals. However, the role of HIF2α in PDGFRβ + cells remains undetermined in vivo.

METHODS

New genetic models were employed in which HIF1α (encoded by the Hif1a gene) and HIF2α (encoded by the Epas1 gene) are selectively inactivated in PDGFRβ + cells in an inducible manner using tamoxifen (TAM). With these models, both in vitro and in vivo functional analysis of PDGFRβ + cells lacking HIF proteins were performed. Additionally, comprehensive metabolic phenotyping in diet-induced mouse models were performed to investigate the roles of PDGFRβ + cell HIF proteins in WAT remodeling, liver energy balance and systemic metabolism.

RESULTS

Unlike HIF1α inactivation, the new findings in this study suggest that inducible ablation of HIF2α in PDGFRβ + cells does not cause apparent effects on WAT expansion induced by obesogenic diet. The adipogenic ability of PDGFRβ + APCs is not significantly altered by genetic HIF2α ablation. Moreover, no difference of key parameters associated with healthy WAT remodeling such as improvements of WAT insulin sensitivity, reduction in metabolic inflammation, as well as changes in liver fat accumulation or systemic glucose metabolism, is detected in PDGFRβ + cell Epas1-deficient mice.

CONCLUSION

The new findings in this study support that, in contrast to HIF1α, PDGFRβ + cell HIF2α appears dispensable for WAT metabolic remodeling and the resulting effects on liver metabolic homeostasis in diet-induced obesity, underscoring the isoform-specific roles of HIFα proteins in the regulation of adipose tissue biology.

Pathogenesis of diabetic complications: Exploring hypoxic niche formation and HIF-1α activation

Hypoxia is a common feature of diabetic tissues, which highly correlates to the progression of diabetes. The formation of hypoxic context is induced by disrupted oxygen homeostasis that is predominantly driven by vascular remodeling in diabetes. While different types of vascular impairments have been reported, the specific features and underlying mechanisms are yet to be fully understood. Under hypoxic condition, cells upregulate hypoxia-inducible factor-1α (HIF-1α), an oxygen sensor that coordinates oxygen concentration and cell metabolism under hypoxic conditions. However, diabetic context exploits this machinery for pathogenic functions. Although HIF-1α protects cells from diabetic insult in multiple tissues, it also jeopardizes cell function in the retina. To gain a deeper understanding of hypoxia in diabetic complications, we focus on the formation of tissue hypoxia and the outcomes of HIF-1α dysregulation under diabetic context. Hopefully, this review can provide a better understanding on hypoxia biology in diabetes.

HIF-1α serves as a co-linker between AD and T2DM

Alzheimer's disease (AD)-related brain deterioration is linked to the type 2 diabetes mellitus (T2DM) features hyperglycemia, hyperinsulinemia, and insulin resistance. Hypoxia as a common risk factor for both AD and T2DM. Hypoxia-inducible factor-1 alpha (HIF-1α) acts as the main regulator of the hypoxia response and may be a key target in the comorbidity of AD and T2DM. HIF-1α expression is closely related to hyperglycemia, insulin resistance, and inflammation. Tissue oxygen consumption disrupts HIF-1α homeostasis, leading to increased reactive oxygen species levels and the inhibition of insulin receptor pathway activity, causing neuroinflammation, insulin resistance, abnormal Aβ deposition, and tau hyperphosphorylation. HIF-1α activation also leads to the deposition of Aβ by promoting the abnormal shearing of amyloid precursor protein and inhibiting the degradation of Aβ, and it promotes tau hyperphosphorylation by activating oxidative stress and the activation of astrocytes, which further exasperates AD. Therefore, we believe that HIF-α has great potential as a target for the treatment of AD. Importantly, the intracellular homeostasis of HIF-1α is a more crucial factor than its expression level.

Sensing the oxygen and temperature in the adipose tissues - who's sensing what?

Adipose tissues, composed of various cell types, including adipocytes, endothelial cells, neurons, and immune cells, are organs that are exposed to dynamic environmental challenges. During diet-induced obesity, white adipose tissues experience hypoxia due to adipocyte hypertrophy and dysfunctional vasculature. Under these conditions, cells in white adipose tissues activate hypoxia-inducible factor (HIF), a transcription factor that activates signaling pathways involved in metabolism, angiogenesis, and survival/apoptosis to adapt to such an environment. Exposure to cold or activation of the β-adrenergic receptor (through catecholamines or chemicals) leads to heat generation, mainly in brown adipose tissues through activating uncoupling protein 1 (UCP1), a proton uncoupler in the inner membrane of the mitochondria. White adipose tissues can undergo a similar process under this condition, a phenomenon known as 'browning' of white adipose tissues or 'beige adipocytes'. While UCP1 expression has largely been confined to adipocytes, HIF can be expressed in many types of cells. To dissect the role of HIF in specific types of cells during diet-induced obesity, researchers have generated tissue-specific knockout (KO) mice targeting HIF pathways, and many studies have commonly revealed that intact HIF-1 signaling in adipocytes and adipose tissue macrophages exacerbates tissue inflammation and insulin resistance. In this review, we highlight some of the key findings obtained from these transgenic mice, including Ucp1 KO mice and other models targeting the HIF pathway in adipocytes, macrophages, or endothelial cells, to decipher their roles in diet-induced obesity.

Insulin resistance and adipose tissue interactions as the cornerstone of metabolic (dysfunction)-associated fatty liver disease pathogenesis

The relationship between metabolic derangements and fatty liver development are undeniable, since more than 75% of patients with type 2 diabetes mellitus present with fatty liver. There is also significant epidemiological association between insulin resistance (IR) and metabolic (dysfunction)-associated fatty liver disease (MAFLD). For little more than 2 years, the nomenclature of fatty liver of non-alcoholic origin has been intended to change to MAFLD by multiple groups. While a myriad of reasons for which MAFLD is thought to be of metabolic origin could be exposed, the bottom line relies on the role of IR as an initiator and perpetuator of this disease. There is a reciprocal role in MAFLD development and IR as well as serum glucose concentrations, where increased circulating glucose and insulin result in increased de novo lipogenesis by sterol regulatory element-binding protein-1c induced lipogenic enzyme stimulation; therefore, increased endogenous production of triglycerides. The same effect is achieved through impaired suppression of adipose tissue (AT) lipolysis in insulin-resistant states, increasing fatty acid influx into the liver. The complementary reciprocal situation occurs when liver steatosis alters hepatokine secretion, modifying fatty acid metabolism as well as IR in a variety of tissues, including skeletal muscle, AT, and the liver. The aim of this review is to discuss the importance of IR and AT interactions in metabolic altered states as perhaps the most important factor in MAFLD pathogenesis.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Adipose tissue macrophages as potential targets for obesity and metabolic diseases

Macrophage infiltration into adipose tissue is a key pathological factor inducing adipose tissue dysfunction and contributing to obesity-induced inflammation and metabolic disorders. In this review, we aim to present the most recent research on macrophage heterogeneity in adipose tissue, with a focus on the molecular targets applied to macrophages as potential therapeutics for metabolic diseases. We begin by discussing the recruitment of macrophages and their roles in adipose tissue. While resident adipose tissue macrophages display an anti-inflammatory phenotype and promote the development of metabolically favorable beige adipose tissue, an increase in pro-inflammatory macrophages in adipose tissue has negative effects on adipose tissue function, including inhibition of adipogenesis, promotion of inflammation, insulin resistance, and fibrosis. Then, we presented the identities of the newly discovered adipose tissue macrophage subtypes (e.g. metabolically activated macrophages, CD9+ macrophages, lipid-associated macrophages, DARC+ macrophages, and MFehi macrophages), the majority of which are located in crown-like structures within adipose tissue during obesity. Finally, we discussed macrophage-targeting strategies to ameliorate obesity-related inflammation and metabolic abnormalities, with a focus on transcriptional factors such as PPARγ, KLF4, NFATc3, and HoxA5, which promote macrophage anti-inflammatory M2 polarization, as well as TLR4/NF-κB-mediated inflammatory pathways that activate pro-inflammatory M1 macrophages. In addition, a number of intracellular metabolic pathways closely associated with glucose metabolism, oxidative stress, nutrient sensing, and circadian clock regulation were examined. Understanding the complexities of macrophage plasticity and functionality may open up new avenues for the development of macrophage-based treatments for obesity and other metabolic diseases.

Common metabolic features of hypertension and type 2 diabetes

Hypertension and type 2 diabetes frequently coexist, suggesting that the two diseases have common pathophysiological bases. This review describes the pathophysiological mechanisms of how type 2 diabetes is frequently associated with hypertension. Multiple common factors mediate between both diseases. Factors that induce both type 2 diabetes and hypertension include obesity-induced hyperinsulinemia, activation of the sympathetic nervous system, chronic inflammation, and changes in adipokines. Vascular complications resulting from type 2 diabetes and hypertension include endothelial dysfunction, vasodilation/constriction dysfunction of peripheral vessels and increased peripheral vascular resistance, arteriosclerosis, and chronic kidney disease. While many of these vascular complications are caused by hypertension, they also exacerbate the pathology of hypertension. In addition, insulin resistance in the vasculature blunts insulin-induced vasodilation and blood flow to skeletal muscle, which contributes to impaired glucose uptake to skeletal muscle and glucose intolerance. In obese and insulin-resistant patients, increase in the circulating fluid volume forms the major pathophysiology of elevated blood pressure. On the other hand, in non-obese and/or insulin-deficient patients, especially those in the middle- or later stages of diabetes, peripheral vascular resistance is the major pathophysiology of hypertension. The relationship between various factors involved in the pathogenesis of type 2 diabetes and hypertension. It should be noted that all the factors shown in the figure are not necessarily present simultaneously in every patient.

The HIF1α polymorphism rs2301104 is associated with obesity and obesity-related cytokines in Han Chinese population

AIMS

To evaluate the association between genetic polymorphisms of HIF1α and obesity and obesity-related cytokines in the Han Chinese population.

METHODS

The study consisted of 160 subjects with obesity and 166 age- and gender-matched healthy controls. We genotyped three tag single nucleotide polymorphisms (SNPs) of HIF1α by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)-based genotyping technology. Plasma cytokine concentrations were determined on the Luminex platform. The genetic associations were analysed statistically.

RESULTS

Obese subjects had significant obesity-related metabolic abnormalities, including hyperglycaemia, insulin resistance, and abnormalities in blood lipids, liver enzymes, and uric acid levels. SNP analysis of HIF1α revealed that the allele and genotype frequencies of rs2301104 were significantly associated with obesity. Our results suggest that the minor allele C of rs2301104 might be a protective mutation of obesity, and CC/CG genotypes of rs2301104 could be protective genotype of obesity. We also found that subjects with CC/CG genotypes of rs2301104 had significantly lower levels of IL-6, TNF-α, IL-1β, IL-8, and IL-10 than subjects with GG genotypes.

CONCLUSIONS

This is the first study to report an association between HIF1α polymorphisms and obesity and obesity-related cytokines in a Han Chinese population. These results require replication in larger populations but suggest that HIF1α may play an important role in obesity development.

Identification of Adipogenesis Subgroups and Immune Infiltration Characteristics in Diabetic Peripheral Neuropathy

Dysregulation of adipogenesis is related to diabetic peripheral neuropathy (DPN) pathogenesis, which may be mediated by immune infiltration. Nevertheless, the expression patterns of multiple adipogenesis-related genes and the differences of immune infiltration in different lipid metabolism levels remain unknown. GSE95849, a gene expression matrix containing DPN patients and healthy participants, was downloaded from Gene Expression Omnibus (GEO) database. Differentially expressed adipogenesis-related genes (DEARGs) were screened by overlapping the adipogenesis-related genes with differentially expressed genes (DEGs). DPN patients from GSE24290 and GSE148059 were divided into two adipogenesis subgroups according to the expression of DEARGs. The single-sample gene set enrichment analysis (ssGSEA) was used to estimate the abundance of the immune cells between two subgroups. The analysis of immune infiltration suggested that a variety of immune cells and immune processes were elevated in the high expression group of DEARGs. The differentially expressed genes of the two subgroups were mainly enriched in biological processes and signaling pathways related to lipid metabolism. PPARG, FABP4, LIPE, FASN, SCD, DGAT2, PNPLA2, ADIPOQ, LEP, and CEBPA were identified as the hub genes of the two subgroups, whose related transcription factors (TFs) and miRNAs were predicted. An immunohistochemical assay was used to verify the expression of hub genes in DPN nerve tissues. Our comprehensive analysis of adipogenesis subgroups in DPN illustrated that different expression patterns of DEARGs may lead to different immune and inflammatory states. The identification of DEARGs may help to further distinguish the different characteristics of DPN patients and lay the foundation for targeted treatment. Our findings may bring a novel perspective to the diagnosis and treatment of DPN patients.

Hypoxia as a Double-Edged Sword to Combat Obesity and Comorbidities

The global epidemic of obesity is tightly associated with numerous comorbidities, such as type II diabetes, cardiovascular diseases and the metabolic syndrome. Among the key features of obesity, some studies have suggested the abnormal expansion of adipose-tissue-induced local endogenous hypoxic, while other studies indicated endogenous hyperoxia as the opposite trend. Endogenous hypoxic aggravates dysfunction in adipose tissue and stimulates secretion of inflammatory molecules, which contribute to obesity. In contrast, hypoxic exposure combined with training effectively generate exogenous hypoxic to reduce body weight and downregulate metabolic risks. The (patho)physiological effects in adipose tissue are distinct from those of endogenous hypoxic. We critically assess the latest advances on the molecular mediators of endogenous hypoxic that regulate the dysfunction in adipose tissue. Subsequently we propose potential therapeutic targets in adipose tissues and the small molecules that may reverse the detrimental effect of local endogenous hypoxic. More importantly, we discuss alterations of metabolic pathways in adipose tissue and the metabolic benefits brought by hypoxic exercise. In terms of therapeutic intervention, numerous approaches have been developed to treat obesity, nevertheless durability and safety remain the major concern. Thus, a combination of the therapies that suppress endogenous hypoxic with exercise plans that augment exogenous hypoxic may accelerate the development of more effective and durable medications to treat obesity and comorbidities.

Depletion of CD206+ M2-like macrophages induces fibro-adipogenic progenitors activation and muscle regeneration

Muscle regeneration requires the coordination of muscle stem cells, mesenchymal fibro-adipogenic progenitors (FAPs), and macrophages. How macrophages regulate the paracrine secretion of FAPs during the recovery process remains elusive. Herein, we systemically investigated the communication between CD206⁺ M2-like macrophages and FAPs during the recovery process using a transgenic mouse model. Depletion of CD206⁺ M2-like macrophages or deletion of CD206⁺ M2-like macrophages-specific TGF-β1 gene induces myogenesis and muscle regeneration. We show that depletion of CD206⁺ M2-like macrophages activates FAPs and activated FAPs secrete follistatin, a promyogenic factor, thereby boosting the recovery process. Conversely, deletion of the FAP-specific follistatin gene results in impaired muscle stem cell function, enhanced fibrosis, and delayed muscle regeneration. Mechanistically, CD206⁺ M2-like macrophages inhibit the secretion of FAP-derived follistatin via TGF-β signaling. Here we show that CD206⁺ M2-like macrophages constitute a microenvironment for FAPs and may regulate the myogenic potential of muscle stem/satellite cells.

Docosahexaenoic Acid Counteracts the Hypoxic-Induced Inflammatory and Metabolic Alterations in 3T3-L1 Adipocytes

Background: Hypoxia is caused by the excessive expansion of the white adipose tissue (AT) and is associated with obesity-related conditions such as insulin resistance, inflammation, and oxidative stress. Docosahexaenoic acid (DHA) is an omega-3 fatty acid reported to have beneficial health effects. However, the effects of DHA in AT against hypoxia-induced immune-metabolic perturbations in adipocytes exposed to low O₂ tension are not well known. Consequently, this study aimed to evaluate the impact of DHA on markers of inflammation, metabolism, apoptosis, and oxidative stress in 3T3-L1 cell adipocytes exposed to low O₂ tension (1% O₂) induced hypoxia. Methods: The apoptosis and reactive oxygen species (ROS) rates were evaluated. Metabolic parameters such as lactate, FFA, glycerol release, glucose uptake, and ATP content were assessed by a fluorometer. The expression of HIF-1, GLUT1 and the secretion of adipocytokines such as leptin, adiponectin, and pro-inflammatory markers was evaluated. Results: DHA-treated hypoxic cells showed significantly decreased basal free fatty acid release, lactate production, and enhanced glucose consumption. In addition, DHA-treatment of hypoxic cells caused a significant reduction in the apoptosis rate and ROS production with decreased lipid peroxidation. Moreover, DHA-treatment of hypoxic cells caused a decreased secretion of pro-inflammatory markers (IL-6, MCP-1) and leptin and increased adiponectin secretion compared with hypoxic cells. Furthermore, DHA-treatment of hypoxic cells caused significant reductions in the expression of genes related to hypoxia (HIF-1, HIF-2), anaerobic metabolism (GLUT1 and Ldha), ATP production (ANT2), and fat metabolism (FASN and PPARY). Conclusion: This study suggests that DHA can exert potential anti-obesity effects by reducing the secretion of inflammatory adipokines, oxidative stress, lipolysis, and apoptosis.

Aconitate decarboxylase 1 regulates glucose homeostasis and obesity in mice

OBJECTIVE

The intersection between immunology and metabolism contributes to the pathogenesis of obesity-associated metabolic diseases as well as molecular control of inflammatory responses. The metabolite itaconate and the cell-permeable derivatives have robust anti-inflammatory effects; therefore, it is hypothesized that cis-aconitate decarboxylase (Acod1)-produced itaconate has a protective, anti-inflammatory effect during diet-induced obesity and metabolic disease.

METHODS

Wild-type and Acod1-/- mice were subjected to diet-induced obesity. Glucose metabolism was analyzed by glucose tolerance tests, insulin tolerance tests, and indirect calorimetry. Gene expression and transcriptome analysis was performed using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and RNA sequencing.

RESULTS

Wild-type and Acod1-/- mice on high-fat diet had equivalent weight gain, but Acod1-/- mice had impaired glucose metabolism. Insulin tolerance tests and glucose tolerance tests after 12 weeks on high-fat diet revealed significantly higher blood glucose levels in Acod1-/- mice. This was associated with significant enrichment of inflammatory gene sets and a reduction in genes related to adipogenesis and fatty acid metabolism. Analysis of naive Acod1-/- mice showed a significant increase in fat deposition at 3 and 6 months of age and obesity and insulin resistance by 12 months.

CONCLUSIONS

The data show that Acod1 has an important role in the regulation of glucose homeostasis and obesity under normal and high-fat diet conditions.

Circadian clock disruptions link oxidative stress and systemic inflammation to metabolic syndrome in obstructive sleep apnea patients

Objectives: Obstructive sleep apnea (OSA) is an independent risk factor for metabolic syndrome (MetS). Recent studies have indicated that circadian clock genes were dysregulated in OSA. In addition, it is clear that the impairment of circadian clocks drives the progression of MetS. Therefore, we hypothesized that circadian rhythm disruption links OSA with MetS.

Methods: A total of 118 participants, who underwent polysomnography (PSG) and were diagnosed as healthy snorers (control, n = 29) or OSA (n = 89) patients based on the apnea–hypopnea index (AHI), were enrolled in the present study. General information, anthropometric data, blood biochemical indicators, clock gene expressions, and levels of oxidative and inflammatory indicators were collected, determined, and compared in all the participants.

Results: We found that Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1 (Bmal1) and Differentiated embryo chondrocyte 1 (Dec1) were upregulated, while Period 1 (Per1) was reduced in OSA patients. In addition, these changing trends were closely associated with the hypoxia indicator of AHI and have a significant impact on the presence of MetS components, such as hyperglycemia (Dec1 and Per1, p < 0.05 and 0.001, respectively), hypertension (Bmal1 and Dec1, p < 0.001 and 0.01, respectively), hyperlipidemia (Dec1, p < 0.01), and obesity (Dec1, p < 0.05). Notably, expressions of Dec1 correlated with IR and predicted the presence of MetS in OSA patients. Finally, we also observed that Dec1 expression was interrelated with levels of both oxidative indicators and inflammatory biomarkers (IL-6) in OSA.

Conclusion: This study concluded that circadian clock disruptions, especially Dec1, link OSA with MetS in an oxidative and inflammatory-related manner. Circadian clock Dec1 can be used as a specific biomarker (p < 0.001) and therapeutic target in OSA combined with Mets patients.

Macrophage Polarization Mediated by Mitochondrial Dysfunction Induces Adipose Tissue Inflammation in Obesity

Obesity is one of the prominent global health issues, contributing to the growing prevalence of insulin resistance and type 2 diabetes. Chronic inflammation in adipose tissue is considered as a key risk factor for the development of insulin resistance and type 2 diabetes in obese individuals. Macrophages are the most abundant immune cells in adipose tissue and play an important role in adipose tissue inflammation. Mitochondria are critical for regulating macrophage polarization, differentiation, and survival. Changes to mitochondrial metabolism and physiology induced by extracellular signals may underlie the corresponding state of macrophage activation. Macrophage mitochondrial dysfunction is a key mediator of obesity-induced macrophage inflammatory response and subsequent systemic insulin resistance. Mitochondrial dysfunction drives the activation of the NLRP3 inflammasome, which induces the release of IL-1β. IL-1β leads to decreased insulin sensitivity of insulin target cells via paracrine signaling or infiltration into the systemic circulation. In this review, we discuss the new findings on how obesity induces macrophage mitochondrial dysfunction and how mitochondrial dysfunction induces NLRP3 inflammasome activation. We also summarize therapeutic approaches targeting mitochondria for the treatment of diabetes.

MicroRNA-29 Ameliorates Fibro-Inflammation and Insulin Resistance in HIF1α-Deficient Obese Adipose Tissue by Inhibiting Endotrophin Generation

Dysregulation of extracellular matrix proteins in obese adipose tissue (AT) induces systemic insulin resistance. The metabolic roles of type VI collagen and its cleavage peptide endotrophin in obese AT are well established. However, the mechanisms regulating endotrophin generation remain elusive. Herein, we identified that several endotrophin-containing peptides (pre-endotrophins) were generated from the COL6A3 chain in a stepwise manner for the efficient production of mature endotrophin, partly through the action of hypoxia-induced matrix metalloproteinases (MMPs), including MMP2, MMP9, and MMP16. Hypoxia is an upstream regulator of COL6A3 expression and the proteolytic processing that regulates endotrophin generation. Hypoxia-inducible factor 1α (HIF1α) and the hypoxia-associated suppression of microRNA-29 (miR-29) cooperatively control the levels of COL6A3 and MMPs, which are responsible for endotrophin generation in hypoxic ATs. Adipocyte-specific Hif1α knock-out (APN-HIF1αKO) mice fed a chronic high-fat diet exhibited the significant amelioration of both local fibro-inflammation in AT and systemic insulin resistance compared with their control littermates, partly through the inhibition of endotrophin generation. Strikingly, adenovirus-mediated miR-29 overexpression in the ATs of APN-HIF1αKO mice in obesity significantly decreased endotrophin levels, suggesting that miR-29, combined with HIF1α inhibition in AT, could be a promising therapeutic strategy for treating obesity and related metabolic diseases.

Metabolism of tissue macrophages in homeostasis and pathology

Cellular metabolism orchestrates the intricate use of tissue fuels for catabolism and anabolism to generate cellular energy and structural components. The emerging field of immunometabolism highlights the importance of cellular metabolism for the maintenance and activities of immune cells. Macrophages are embryo- or adult bone marrow-derived leukocytes that are key for healthy tissue homeostasis but can also contribute to pathologies such as metabolic syndrome, atherosclerosis, fibrosis or cancer. Macrophage metabolism has largely been studied in vitro. However, different organs contain diverse macrophage populations that specialize in distinct and often tissue-specific functions. This context specificity creates diverging metabolic challenges for tissue macrophage populations to fulfill their homeostatic roles in their particular microenvironment and conditions their response in pathological conditions. Here, we outline current knowledge on the metabolic requirements and adaptations of macrophages located in tissues during homeostasis and selected diseases.

Leptin: an entry point for the treatment of peripheral tissue fibrosis and related diseases

Leptin is a small peptide mainly secreted by adipocyte, which acts on the central nervous system of the hypothalamus to regulate the body's energy balance by inhibiting food intake, it also can directly act on specific cells through leptin receptors (for example, ObRa, which exists in the blood-brain barrier or kidneys), thereby affect cell metabolism. Excessive deposition of extracellular matrix (ECM) causes damage to normal tissues or destruction of organ structure, which will eventually lead to tissue or organ fibrosis. The sustainable development of fibrosis can lead to structural damage and functional decline of organs, and even exhaustion, which seriously threatens human health and life. In recent years, studies have found that leptin directly alleviates the fibrosis process of various tissues and organs in mammals. Therefore, we speculate that leptin may become a significant treatment for fibrosis of various tissues and organs in the future. So, the main purpose of this review is to explore the specific mechanism of leptin in the process of fibrosis in multiple tissues and organs, and to provide a theoretical basis for the treatment of various tissues and organs fibrosis and related diseases caused by it, which is of great significance in the future.

Inflammation in obesity, diabetes, and related disorders

Obesity leads to chronic, systemic inflammation and can lead to insulin resistance (IR), β-cell dysfunction, and ultimately type 2 diabetes (T2D). This chronic inflammatory state contributes to long-term complications of diabetes, including non-alcoholic fatty liver disease (NAFLD), retinopathy, cardiovascular disease, and nephropathy, and may underlie the association of type 2 diabetes with other conditions such as Alzheimer's disease, polycystic ovarian syndrome, gout, and rheumatoid arthritis. Here, we review the current understanding of the mechanisms underlying inflammation in obesity, T2D, and related disorders. We discuss how chronic tissue inflammation results in IR, impaired insulin secretion, glucose intolerance, and T2D and review the effect of inflammation on diabetic complications and on the relationship between T2D and other pathologies. In this context, we discuss current therapeutic options for the treatment of metabolic disease, advances in the clinic and the potential of immune-modulatory approaches.

DNA demethylase ALKBH1 promotes adipogenic differentiation via regulation of HIF-1 signaling

DNA 6-adenine methylation (6mA), as a novel adenine modification existing in eukaryotes, shows essential functions in embryogenesis and mitochondrial transcriptions. ALKBH1 is a demethylase of 6mA and plays critical roles in osteogenesis, tumorigenesis, and adaptation to stress. However, the integrated biological functions of ALKBH1 still require further exploration. Here, we demonstrate that knockdown of ALKBH1 inhibits adipogenic differentiation in both human mesenchymal stem cells (hMSCs) and 3T3-L1 preadipocytes, while overexpression of ALKBH1 leads to increased adipogenesis. Using a combination of RNA-seq and N6-mA-DNA-IP-seq analyses, we identify hypoxia-inducible factor-1 (HIF-1) signaling as a crucial downstream target of ALKBH1 activity. Depletion of ALKBH1 leads to hypermethylation of both HIF-1α and its downstream target GYS1. Simultaneous overexpression of HIF-1α and GYS1 restores the adipogenic commitment of ALKBH1-deficient cells. Taken together, our data indicate that ALKBH1 is indispensable for adipogenic differentiation, revealing a novel epigenetic mechanism that regulates adipogenesis.

Astaxanthin, a Marine Carotenoid, Maintains the Tolerance and Integrity of Adipose Tissue and Contributes to Its Healthy Functions

Recently, obesity-induced insulin resistance, type 2 diabetes, and cardiovascular disease have become major social problems. We have previously shown that Astaxanthin (AX), which is a natural antioxidant, significantly ameliorates obesity-induced glucose intolerance and insulin resistance. It is well known that AX is a strong lipophilic antioxidant and has been shown to be beneficial for acute inflammation. However, the actual effects of AX on chronic inflammation in adipose tissue (AT) remain unclear. To observe the effects of AX on AT functions in obese mice, we fed six-week-old male C57BL/6J on high-fat-diet (HFD) supplemented with or without 0.02% of AX for 24 weeks. We determined the effect of AX at 10 and 24 weeks of HFD with or without AX on various parameters including insulin sensitivity, glucose tolerance, inflammation, and mitochondrial function in AT. We found that AX significantly reduced oxidative stress and macrophage infiltration into AT, as well as maintaining healthy AT function. Furthermore, AX prevented pathological AT remodeling probably caused by hypoxia in AT. Collectively, AX treatment exerted anti-inflammatory effects via its antioxidant activity in AT, maintained the vascular structure of AT and preserved the stem cells and progenitor's niche, and enhanced anti-inflammatory hypoxia induction factor-2α-dominant hypoxic response. Through these mechanisms of action, it prevented the pathological remodeling of AT and maintained its integrity.

Ru360 and Mitoxantrone inhibit MCU channel to relieve liver steatosis induced by high-fat diet

BACKGROUND AND PURPOSE

Nonalcoholic fatty liver disease (NAFLD) affects over 25% of the general population and lacks an effective treatment. Recent evidence implicates disrupted mitochondrial calcium homeostasis in the pathogenesis of hepatic steatosis.

EXPERIMENTAL APPROACH

In this study, mitochondrial calcium uniporter (MCU) was inhibited through classical genetic approaches, viral vectors or small molecule inhibitors in vivo to study its role in hepatic steatosis induced by HFD. In vitro, MCU was overexpressed or inhibited to change mitochondrial calcium homeostasis; endoplasmic reticulum-mitochondrial linker was adopted to increase mitochondria-associated membranes (MAM); and MICU1-EF hand mutant was used to decrease the sensitivity of mitochondrial calcium uptake 1 (MICU1) to calcium and block MCU channel.

KEY RESULTS

Here we found that inhibition of liver MCU by AAV virus and classical genetic approaches can alleviate HFD-induced liver steatosis. MCU regulates mitochondrial calcium homeostasis and affects lipid accumulation in liver cells. In addition, a HFD in mice enlarged the MAM. The high calcium environment produced by MAM invalidated the function of MICU1 and led to persistent open of MCU channels. Therefore, it caused mitochondrial calcium overload and liver fat deposition. Inhibition of MAM and MCU alleviated HFD-induced hepatic steatosis. MCU inhibitors (Ru360 and mitoxantrone) can block MCU channels and reduce mitochondrial calcium levels. Intraperitoneal injection of MCU inhibitors (0.01 μM/kg bodyweight) can alleviate HFD-induced hepatic steatosis.

CONCLUSION AND IMPLICATIONS

These findings provide molecular insights into the way HFD disrupts mitochondrial calcium homeostasis and identified MCU as a promising drug target for the treatment of hepatic steatosis.

Metformin reduces macrophage HIF1α-dependent proinflammatory signaling to restore brown adipocyte function in vitro

Therapeutic potential of metformin in obese/diabetic patients has been associated to its ability to combat insulin resistance. However, it remains largely unknown the signaling pathways involved and whether some cell types are particularly relevant for its beneficial effects. M1-activation of macrophages by bacterial lipopolysaccharide (LPS) promotes a paracrine activation of hypoxia-inducible factor-1α (HIF1α) in brown adipocytes which reduces insulin signaling and glucose uptake, as well as β-adrenergic sensitivity. Addition of metformin to M1-polarized macrophages blunted these signs of brown adipocyte dysfunction. At the molecular level, metformin inhibits an inflammatory program executed by HIF1α in macrophages by inducing its degradation through the inhibition of mitochondrial complex I activity, thereby reducing oxygen consumption in a reactive oxygen species (ROS)-independent manner. In obese mice, metformin reduced inflammatory features in brown adipose tissue (BAT) such as macrophage infiltration, proinflammatory signaling and gene expression, and restored the response to cold exposure. In conclusion, the impact of metformin on macrophages by suppressing a HIF1α-dependent proinflammatory program is likely responsible for a secondary beneficial effect on insulin-mediated glucose uptake and β-adrenergic responses in brown adipocytes.

Fate of adipocyte progenitors during adipogenesis in mice fed a high-fat diet

Objective

Expansion of adipose tissue during obesity through the recruitment of newly generated adipocytes (hyperplasia) is metabolically healthy, whereas that through the enlargement of pre-existing adipocytes (hypertrophy) leads to metabolic complications. Accumulating evidence from genetic fate mapping studies suggests that in animal models receiving a high-fat diet (HFD), only adipocyte progenitors (APs) in gonadal white adipose tissue (gWAT) have proliferative potential. However, the proliferative potential and differentiating capacity of APs in the inguinal WAT (iWAT) of male mice remains controversial. The objective of this study was to investigate the proliferative and adipogenic potential of APs in the iWAT of HFD-fed male mice.

Methods

We generated PDGFRα-GFP-Cre-ER^T2/tdTomato (KI/td) mice and traced PDGFRα-positive APs in male mice fed HFD for 8 weeks. We performed a comprehensive phenotypic analysis, including the histology, immunohistochemistry, flow cytometry, and gene expression analysis, of KI/td mice fed HFD.

Results

Contrary to the findings of others, we found an increased number of newly generated tdTomato⁺ adipocytes in the iWAT of male mice, which was smaller than that observed in the gWAT. We found that in male mice, the iWAT has more proliferating tdTomato⁺ APs than the gWAT. We also found that tdTomato⁺ APs showed a higher expression of Dpp4 and Pi16 than tdTomato⁻ APs, and the expression of these genes was significantly higher in the iWAT than in the gWAT of mice fed HFD for 8 weeks. Collectively, our results reveal that HFD feeding induces the proliferation of tdTomato⁺ APs in the iWAT of male mice.

Conclusion

In male mice, compared with gWAT, iWAT undergoes hyperplasia in response to 8 weeks of HFD feeding through the recruitment of newly generated adipocytes due to an abundance of APs with a high potential for proliferation and differentiation.

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High-fat diet (HFD) increases proliferative APs in iWAT of male mice.

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HFD promotes the recruitment of smaller adipocytes in the iWAT of male mice.

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iWAT expands by recruiting newly-generated adipocytes (hyperplasia) in male mice.

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gWAT expands by enlargement of pre-existing adipocytes (hypertrophy) in male mice.

Chronic tissue inflammation and metabolic disease

In this review, Lee and Olefsky discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes.

Obesity is the most common cause of insulin resistance, and the current obesity epidemic is driving a parallel rise in the incidence of T2DM. It is now widely recognized that chronic, subacute tissue inflammation is a major etiologic component of the pathogenesis of insulin resistance and metabolic dysfunction in obesity. Here, we summarize recent advances in our understanding of immunometabolism. We discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes. Last, we also review current and potential new therapeutic strategies based on immunomodulation.

Insulin/IGF-1 signaling promotes immunosuppression via the STAT3 pathway: impact on the aging process and age-related diseases

BACKGROUND

The insulin/IGF-1 signaling pathway has a major role in the regulation of longevity both in Caenorhabditis elegans and mammalian species, i.e., reduced activity of this pathway extends lifespan, whereas increased activity accelerates the aging process. The insulin/IGF-1 pathway controls protein and energy metabolism as well as the proliferation and differentiation of insulin/IGF-1-responsive cells. Insulin/IGF-1 signaling also regulates the functions of the innate and adaptive immune systems. The purpose of this review was to elucidate whether insulin/IGF-1 signaling is linked to immunosuppressive STAT3 signaling which is known to promote the aging process.

METHODS

Original and review articles encompassing the connections between insulin/IGF-1 and STAT3 signaling were examined from major databases including Pubmed, Scopus, and Google Scholar.

RESULTS

The activation of insulin/IGF-1 receptors stimulates STAT3 signaling through the JAK and AKT-driven signaling pathways. STAT3 signaling is a major activator of immunosuppressive cells which are able to counteract the chronic low-grade inflammation associated with the aging process. However, the activation of STAT3 signaling stimulates a negative feedback response through the induction of SOCS factors which not only inhibit the activity of insulin/IGF-1 receptors but also that of many cytokine receptors. The inhibition of insulin/IGF-1 signaling evokes insulin resistance, a condition known to be increased with aging. STAT3 signaling also triggers the senescence of both non-immune and immune cells, especially through the activation of p53 signaling.

CONCLUSIONS

Given that cellular senescence, inflammaging, and counteracting immune suppression increase with aging, this might explain why excessive insulin/IGF-1 signaling promotes the aging process.

The roles and mechanisms of hypoxia in liver fibrosis

Liver fibrosis occurs in response to any etiology of chronic liver injury. Lack of appropriate clinical intervention will lead to liver cirrhosis or hepatocellular carcinoma (HCC), seriously affecting the quality of life of patients, but the current clinical treatments of liver fibrosis have not been developed yet. Recent studies have shown that hypoxia is a key factor promoting the progression of liver fibrosis. Hypoxia can cause liver fibrosis. Liver fibrosis can, in turn, profoundly further deepen the degree of hypoxia. Therefore, exploring the role of hypoxia in liver fibrosis will help to further understand the process of liver fibrosis, and provide the theoretical basis for its diagnosis and treatment, which is of great significance to avoid further deterioration of liver diseases and protect the life and health of patients. This review highlights the recent advances in cellular and molecular mechanisms of hypoxia in developments of liver fibrosis.

Immunometabolic regulation of adipose tissue resident immune cells

Adipose tissue (AT) performs immunoregulatory functions beyond fat storage. In addition to adipocytes, AT has a diverse spectrum of resident and infiltrating immune cells in health and disease. Immune cells contribute to the homeostatic function of AT by adapting their metabolism in accordance with the microenvironment. However, how the metabolic reprogramming of immune cells affects their inflammatory profile and the subsequent implication for adipocyte function is not completely elucidated. Here, we discuss the available data on metabolic regulatory processes implicated in the control of adipose tissue-resident immune cells and their crosstalk with adipocytes.

Innate Immune Cells in the Adipose Tissue in Health and Metabolic Disease

Metabolic disorders, such as obesity, type 2 diabetes mellitus, and nonalcoholic fatty liver disease, are characterized by chronic low-grade tissue and systemic inflammation. During obesity, the adipose tissue undergoes immunometabolic and functional transformation. Adipose tissue inflammation is driven by innate and adaptive immune cells and instigates insulin resistance. Here, we discuss the role of innate immune cells, that is, macrophages, neutrophils, eosinophils, natural killer cells, innate lymphoid type 2 cells, dendritic cells, and mast cells, in the adipose tissue in the healthy (lean) and diseased (obese) state and describe how their function is shaped by the obesogenic microenvironment, and humoral, paracrine, and cellular interactions. Moreover, we particularly outline the role of hypoxia as a central regulator in adipose tissue inflammation. Finally, we discuss the long-lasting effects of adipose tissue inflammation and its potential reversibility through drugs, caloric restriction, or exercise training.

Exercise retards ongoing adipose tissue fibrosis in diet-induced obese mice

Exercise has been recommended as an important strategy to improve glucose metabolism in obesity. Adipose tissue fibrosis is associated with inflammation and is implicated in glucose metabolism disturbance and insulin resistance in obesity. However, the effect of exercise on the progression of adipose tissue fibrosis is still unknown. The aim of the present study was to investigate whether exercise retarded the progression of adipose tissue fibrosis and ameliorated glucose homeostasis in diet-induced obese mice. To do so, obesity and adipose tissue fibrosis in mice were induced by high-fat diet feeding for 12 weeks and the mice subsequently received high-fat diet and exercise intervention for another 12 weeks. Exercise alleviated high-fat diet-induced glucose intolerance and insulin resistance. Continued high-fat diet feeding exacerbated collagen deposition and further increased fibrosis-related gene expression in adipose tissue. Exercise attenuated or reversed these changes. Additionally, PPARγ, which has been shown to inhibit adipose tissue fibrosis, was observed to be increased following exercise. Moreover, exercise decreased the expression of HIF-1α in adipose fibrosis, and adipose tissue inflammation was inhibited. In conclusion, our data indicate that exercise attenuates and even reverses the progression of adipose tissue fibrosis, providing a plausible mechanism for its beneficial effects on glucose metabolism in obesity.

Hypoxia-inducible factor-2 promotes liver fibrosis in non-alcoholic steatohepatitis liver disease via the NF-κB signalling pathway

Non-alcoholic steatohepatitis (NASH) is one of the most common chronic liver diseases. Chronic hypoxia is related to the pathogenesis of NASH. HIF-2α is the key gene for lipid metabolism, fibrosis, and inflammation in many cells. To identify the molecular mechanism through which hypoxia exposure increases the morbidity of NASH, the expression level of HIF-2α was analysed and was found to be upregulated in human NASH liver. By constructing the NASH model of chronic hypoxia, the mice were housed at an altitude of 4300 m for 4 and 8 weeks, compared to the control groups that were housed at an altitude of 50 m. Histological studies showed that exposure to hypoxia promoted the activation of NF-κB by upregulating the expression of HIF-2α, as well as that of the genes related to inflammation and fibrosis, thereby promoting the development of NASH both in vivo and in vitro. In summary, hypoxia-exposure could upregulate HIF-2α to aggravate tissue fibrosis and inflammation by upregulating inflammation-related genes and fibrosis-related genes metabolites via the activated NF-κB pathway in NASH. Our results suggest that for NASH patients living at high altitudes, drug therapy could focus on treating tissue fibrosis and inflammation, and thus provides a new strategy for NASH treatment.

The role of adipose tissue M1/M2 macrophages in type 2 diabetes mellitus

Obesity and insulin resistance are closely associated with a state of low-grade inflammation in the body, and adipose tissue macrophages (ATMs) play central roles in this inflammation. ATMs are known to exhibit marked functional heterogeneity. M1 ATMs produce inflammatory cytokines and induce insulin resistance. On the other hand, the majority of ATMs in lean individuals are M2 ATMs, which have anti-inflammatory potential. We found that M1 and M2 ATMs can be clearly distinguished using CD11c and CD206 as markers, and that both the number of the M1 and M2 ATMs and the M1/M2 ratio are correlated with the degree of insulin resistance. M1/M2 polarity in the adipose tissue is influenced not only by the level of secretion of various polarizing adipokines and chemokines, but also by factors in the local microenvironment, such as hypoxia. M1 ATMs acquire their polarity via activation of hypoxia-inducible factor-1α (HIF-1α) by local hypoxia, and absence of HIF-1α in the myeloid cells appears to enhance insulin sensitivity by promoting angiogenesis in adipose tissue. On the other hand, the resident M2 ATMs interact with adipose tissue progenitors to control adiposity. Thus, beyond their role as immunoregulatory cells, the M1/M2 ATMs also regulate the microenvironment in the adipose tissue and control insulin sensitivity. Recently, we have shown that interventions in the gut microbiota may be effective in controlling obesity-induced chronic inflammation. Control of M1/M2 ATM polarity is a potential therapeutic target for the treatment of insulin resistance associated with obesity.

Multiple organs involved in the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) represents the leading cause of chronic liver disease worldwide and the anticipated health burden is huge. There are limited therapeutic approaches for NAFLD now. It’s imperative to get a better understanding of the disease pathogenesis if new treatments are to be discovered. As the hepatic manifestation of metabolic syndrome, this disease involves complex interactions between different organs and regulatory pathways. It’s increasingly clear that brain, gut and adipose tissue all contribute to NAFLD pathogenesis and development, in view of their roles in energy homeostasis. In the present review, we try to summarize currently available data regarding NAFLD pathogenesis and to lay a particular emphasis on the inter-organ crosstalk evidence.

HIF1α activation in dendritic cells under sterile conditions promotes an anti-inflammatory phenotype through accumulation of intracellular lipids

Obesity is among the leading causes of elevated cardiovascular disease mortality and morbidity. Adipose tissue dysfunction, insulin resistance and inflammation are recognized as important risk factors for the development of cardiovascular disorders in obesity. Hypoxia appears to be a key factor in adipose tissue dysfunction affecting not only adipocytes but also immune cell function. Here we examined the effect of hypoxia-induced transcription factor HIF1α activation on classical dendritic cell (cDCs) function during obesity. We found that deletion of Hif1α on cDCs results in enhanced adipose-tissue inflammation and atherosclerotic plaque formation in a mouse model of obesity. This effect is mediated by HIF1α-mediated increased lipid synthesis, accumulation of lipid droplets and alter synthesis of lipid mediators. Our findings demonstrate that HIF1α activation in cDCs is necessary to control vessel wall inflammation.

Stromal cell-derived factor 1 (SDF1) attenuates platelet-derived growth factor-B (PDGF-B)-induced vascular remodeling for adipose tissue expansion in obesity

Platelet-derived growth factor-B (PDGF-B) is a main factor to promote adipose tissue angiogenesis, which is responsible for the tissue expansion in obesity. In this process, PDGF-B induces the dissociation of pericytes from blood vessels; however, its regulatory mechanism remains unclear. In the present study, we found that stromal cell-derived factor 1 (SDF1) plays an essential role in this regulatory mechanism. SDF1 mRNA was increased in epididymal white adipose tissue (eWAT) of obese mice. Ex vivo pharmacological analyses using cultured adipose tissue demonstrated that physiological concentrations (1-100 pg/mL) of SDF1 inhibited the PDGF-B-induced pericyte dissociation from vessels via two cognate SDF1 receptors, CXCR4 and CXCR7. In contrast, higher concentrations (> 1 ng/mL) of SDF1 alone caused the dissociation of pericytes via CXCR4, and this effect disappeared in the cultured tissues from PDGF receptor β (PDGFRβ) knockout mice. To investigate the role of SDF1 in angiogenesis in vivo, the effects of anagliptin, an inhibitor of dipeptidyl peptidase 4 (DPP4) that degrades SDF1, were examined in mice fed a high-fat diet. Anagliptin increased the SDF1 levels in the serum and eWAT. These changes were associated with a reduction of pericyte dissociation and fat accumulation in eWAT. AMD3100, a CXCR4 antagonist, cancelled these anagliptin effects. In flow-cytometry analysis, anagliptin increased and decreased the PDGF-B expression in endothelial cells and macrophages, respectively, whereas anagliptin reduced the PDGFRβ expression in pericytes of eWAT. These results suggest that SDF1 negatively regulates the adipose tissue angiogenesis in obesity by altering the reactivity of pericytes to PDGF-B.

Xanomeline Protects Cortical Cells From Oxygen-Glucose Deprivation via Inhibiting Oxidative Stress and Apoptosis

Xanomeline, a muscarinic acetylcholine receptor agonist, is one of the first compounds that was found to be effective in the treatment of schizophrenics and attenuating behavioral disturbances of patients with Alzheimer's disease (AD). However, its role in ischemia-induced injury due to oxygen and glucose deprivation (OGD) remains unclear. Primary rat neuronal cells were exposed to OGD and treated with xanomeline. The effects of xanomeline on apoptosis, cell viability, lactate dehydrogenase (LDH) levels, and reactive oxygen species (ROS) were determined using an Annexin V Apoptosis Detection Kit, a non-radioactive cell counting kit-8 (CCK-8) assay, colorimetric LDH cytotoxicity assay kit, and a dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay, respectively, and the expressions of Sirtuin 1, haem oxygenase-1 (HO-1), B-cell lymphoma 2 (Bcl-2), poly ADP-ribose polymerase (PARP), and hypoxia-inducible factor α (HIF-1α) as well as the level of phosphorylated kinase B (p-Akt) were determined by Western blotting. Compared with the control, xanomeline pretreatment increased the viability of isolated cortical neurons and decreased the LDH release induced by OGD. Compared with OGD-treated cells, xanomeline inhibited apoptosis, reduced ROS production, attenuated the OGD-induced HIF-1α increase and partially reversed the reduction of HO-1, Sirtuin-1, Bcl-2, PARP, and p-Akt induced by OGD. In conclusion, xanomeline treatment protects cortical neuronal cells possibly through the inhibition of apoptosis after OGD.

Immunometabolism: new insights and lessons from antigen-directed cellular immune responses

Modulation of immune responses by nutrients is an important area of study in cellular biology and clinical sciences in the context of cancer therapies and anti-pathogen-directed immune responses in health and disease. We review metabolic pathways that influence immune cell function and cellular persistence in chronic infections. We also highlight the role of nutrients in altering the tissue microenvironment with lessons from the tumor microenvironment that shapes the quality and quantity of cellular immune responses. Multiple layers of biological networks, including the nature of nutritional supplements, the genetic background, previous exposures, and gut microbiota status have impact on cellular performance and immune competence against molecularly defined targets. We discuss how immune metabolism determines the differentiation pathway of antigen-specific immune cells and how these insights can be explored to devise better strategies to strengthen anti-pathogen-directed immune responses, while curbing unwanted, non-productive inflammation.

Macrophage HIF-1α mediates obesity-related adipose tissue dysfunction via interleukin-1 receptor-associated kinase M

Hypoxia leading to stabilization of hypoxia-inducible factor 1α (HIF-1α) serves as an early upstream initiator for adipose tissue (AT) dysfunction. Monocyte-derived macrophage infiltration in AT contributes to inflammation, fibrosis and obesity-related metabolic dysfunction. It was previously reported that myeloid cell-specific deletion of Hif-1α protected against high-fat diet (HFD)-induced AT dysfunction. Prolyl hydroxylases (PHDs) are key regulators of HIF-1α. We examined the effects of myeloid cell-specific upregulation and stabilization of Hif-1α via deletion of prolyl-hydroxylase 2 (Phd2) and whether interleukin-1 receptor associated kinase-M (Irak-M), a known downstream target of Hif-1α, contributes to Hif-1α-induced AT dysfunction. Our data show that with HFD, Hif-1α and Irak-M expressions were increased in the AT macrophages of Phd2^flox/flox/LysMcre mice compared with LysMcre mice. With HFD, Phd2^flox/flox/LysMcre mice exhibited increased AT inflammation, fibrosis, and systemic insulin resistance compared with control mice. Furthermore, Phd2^flox/flox/LysMcre mice bone marrow-derived macrophages exposed to hypoxia in vitro also had increased expressions of both Hif-1α and Irak-M. In wild-type mice, HFD induced upregulation of both HIF-1a and Irak-M in adipose tissue. Despite equivalent expression of Hif-1α compared with wild-type mice, globally-deficient Irak-M mice fed a HFD exhibited less macrophage infiltration, decreased inflammation and fibrosis and improved glucose tolerance. Global Irak-M deficiency was associated with an alternatively-activated macrophage phenotype in the AT after HFD. Together, these data show for the first time that an Irak-M-dependent mechanism likely mediates obesity-related AT dysfunction in conjunction with Hif-1α upregulation.

Enhanced glycolysis and HIF-1α activation in adipose tissue macrophages sustains local and systemic interleukin-1β production in obesity

During obesity, macrophages infiltrate the visceral adipose tissue and promote inflammation that contributes to type II diabetes. Evidence suggests that the rewiring of cellular metabolism can regulate macrophage function. However, the metabolic programs that characterize adipose tissue macrophages (ATM) in obesity are poorly defined. Here, we demonstrate that ATM from obese mice exhibit metabolic profiles characterized by elevated glycolysis and oxidative phosphorylation, distinct from ATM from lean mice. Increased activation of HIF-1α in ATM of obese visceral adipose tissue resulted in induction of IL-1β and genes in the glycolytic pathway. Using a hypoxia-tracer, we show that HIF-1α nuclear translocation occurred both in hypoxic and non-hypoxic ATM suggesting that both hypoxic and pseudohypoxic stimuli activate HIF-1α and its target genes in ATM during diet-induced obesity. Exposure of macrophages to the saturated fatty acid palmitate increased glycolysis and HIF-1α expression, which culminated in IL-1β induction thereby simulating pseudohypoxia. Using mice with macrophage-specific targeted deletion of HIF-1α, we demonstrate the critical role of HIF-1α-derived from macrophages in regulating ATM accumulation, and local and systemic IL-1β production, but not in modulating systemic metabolic responses. Collectively, our data identify enhanced glycolysis and HIF-1α activation as drivers of low-grade inflammation in obesity.

Obesity, Hypertension, and Cardiac Dysfunction: Novel Roles of Immunometabolism in Macrophage Activation and Inflammation

Obesity and hypertension, which often coexist, are major risk factors for heart failure and are characterized by chronic, low-grade inflammation, which promotes adverse cardiac remodeling. While macrophages play a key role in cardiac remodeling, dysregulation of macrophage polarization between the proinflammatory M1 and anti-inflammatory M2 phenotypes promotes excessive inflammation and cardiac injury. Metabolic shifting between glycolysis and mitochondrial oxidative phosphorylation has been implicated in macrophage polarization. M1 macrophages primarily rely on glycolysis, whereas M2 macrophages rely on the tricarboxylic acid cycle and oxidative phosphorylation; thus, factors that affect macrophage metabolism may disrupt M1/M2 homeostasis and exacerbate inflammation. The mechanisms by which obesity and hypertension may synergistically induce macrophage metabolic dysfunction, particularly during cardiac remodeling, are not fully understood. We propose that obesity and hypertension induce M1 macrophage polarization via mechanisms that directly target macrophage metabolism, including changes in circulating glucose and fatty acid substrates, lipotoxicity, and tissue hypoxia. We discuss canonical and novel proinflammatory roles of macrophages during obesity-hypertension-induced cardiac injury, including diastolic dysfunction and impaired calcium handling. Finally, we discuss the current status of potential therapies to target macrophage metabolism during heart failure, including antidiabetic therapies, anti-inflammatory therapies, and novel immunometabolic agents.

Mechanisms of Macrophage Polarization in Insulin Signaling and Sensitivity

Type-2 diabetes (T2D) is a disease of two etiologies: metabolic and inflammatory. At the cross-section of these etiologies lays the phenomenon of metabolic inflammation. Whilst metabolic inflammation is characterized as systemic, a common starting point is the tissue-resident macrophage, who's successful physiological or aberrant pathological adaptation to its microenvironment determines disease course and severity. This review will highlight the key mechanisms in macrophage polarization, inflammatory and non-inflammatory signaling that dictates the development and progression of insulin resistance and T2D. We first describe the known homeostatic functions of tissue macrophages in insulin secreting and major insulin sensitive tissues. Importantly we highlight the known mechanisms of aberrant macrophage activation in these tissues and the ways in which this leads to impairment of insulin sensitivity/secretion and the development of T2D. We next describe the cellular mechanisms that are known to dictate macrophage polarization. We review recent progress in macrophage bio-energetics, an emerging field of research that places cellular metabolism at the center of immune-effector function. Importantly, following the advent of the metabolically-activated macrophage, we cover the known transcriptional and epigenetic factors that canonically and non-canonically dictate macrophage differentiation and inflammatory polarization. In closing perspectives, we discuss emerging research themes and highlight novel non-inflammatory or non-immune roles that tissue macrophages have in maintaining microenvironmental and systemic homeostasis.

Astaxanthin stimulates mitochondrial biogenesis in insulin resistant muscle via activation of AMPK pathway

BACKGROUND

Skeletal muscle is mainly responsible for insulin-stimulated glucose disposal. Dysfunction in skeletal muscle metabolism especially during obesity contributes to the insulin resistance. Astaxanthin (AX), a natural antioxidant, has been shown to ameliorate hepatic insulin resistance in obese mice. However, its effects in skeletal muscle are poorly understood. The current study aimed to investigate the molecular target of AX in ameliorating skeletal muscle insulin resistance.

METHODS

We fed 6-week-old male C57BL/6J mice with normal chow (NC) or NC supplemented with AX (NC+AX) and high-fat-diet (HFD) or HFD supplemented with AX for 24 weeks. We determined the effect of AX on various parameters including insulin sensitivity, glucose uptake, inflammation, kinase signaling, gene expression, and mitochondrial function in muscle. We also determined energy metabolism in intact C2C12 cells treated with AX using the Seahorse XFe96 Extracellular Flux Analyzer and assessed the effect of AX on mitochondrial oxidative phosphorylation and mitochondrial biogenesis.

RESULTS

AX-treated HFD mice showed improved metabolic status with significant reduction in blood glucose, serum total triglycerides, and cholesterol (p< 0.05). AX-treated HFD mice also showed improved glucose metabolism by enhancing glucose incorporation into peripheral target tissues, such as the skeletal muscle, rather than by suppressing gluconeogenesis in the liver as shown by hyperinsulinemic-euglycemic clamp study. AX activated AMPK in the skeletal muscle of the HFD mice and upregulated the expressions of transcriptional factors and coactivator, thereby inducing mitochondrial remodeling, including increased mitochondrial oxidative phosphorylation component and free fatty acid metabolism. We also assessed the effects of AX on mitochondrial biogenesis in the siRNA-mediated AMPK-depleted C2C12 cells and showed that the effect of AX was lost in the genetically AMPK-depleted C2C12 cells. Collectively, AX treatment (i) significantly ameliorated insulin resistance and glucose intolerance through regulation of AMPK activation in the muscle, (ii) stimulated mitochondrial biogenesis in the muscle, (iii) enhanced exercise tolerance and exercise-induced fatty acid metabolism, and (iv) exerted antiinflammatory effects via its antioxidant activity in adipose tissue.

CONCLUSIONS

We concluded that AX treatment stimulated mitochondrial biogenesis and significantly ameliorated insulin resistance through activation of AMPK pathway in the skeletal muscle.