FAM3C in Cancer-Associated Adipocytes Promotes Breast Cancer Cell Survival and Metastasis.

Adipose tissue within the tumor microenvironment (TME) plays a critical role in supporting breast cancer progression. In this study, we identified FAM3 metabolism-regulating signaling molecule C (FAM3C) produced by cancer-associated adipocytes (CAA) as a key regulator of tumor progression. FAM3C overexpression in cultured adipocytes significantly reduced cell death in both adipocytes and cocultured breast cancer cells while suppressing markers of fibrosis. Conversely, FAM3C depletion in CAAs resulted in adipocyte-mesenchymal transition (AMT) and increased fibrosis within the TME. Adipocyte FAM3C expression was driven by TGFß signaling from breast cancer cells and was reduced upon treatment with a TGFß-neutralizing antibody. FAM3C knockdown in CAAs early in tumorigenesis in a genetically engineered mouse model of breast cancer significantly inhibited primary and metastatic tumor growth. Circulating FAM3C levels were elevated in patients with metastatic breast cancer compared with those with nonmetastatic breast cancer. These results suggest that therapeutic inhibition of FAM3C expression levels in CAAs during early tumor development could be a promising approach in the treatment of patients with breast cancer. SIGNIFICANCE: High FAM3C levels in cancer-associated adipocytes contribute to tumor-supportive niches and are tightly associated with metastatic growth, indicating that FAM3C inhibition could be beneficial for treating patients with breast cancer.

High levels of intracellular endotrophin in adipocytes mediate COPII vesicle supplies to autophagosome to impair autophagic flux and contribute to systemic insulin resistance in obesity.

BACKGROUND AND AIMS: Extracellular matrix (ECM) homeostasis plays a crucial role in metabolic plasticity and endocrine function of adipose tissue. High levels of intracellular endotrophin, a cleavage peptide of type VI collagen alpha 3 chain (Col6a3), have been frequently observed in adipocyte in obesity and diabetes. However, how endotrophin intracellularly traffics and influences metabolic homeostasis in adipocyte remains unknown. Therefore, we aimed to investigate the trafficking of endotrophin and its metabolic effects in adipocytes depending on lean or obese condition. METHODS: We used doxycycline-inducible adipocyte-specific endotrophin overexpressed mice for a gain-of-function study and CRISPR-Cas9 system-based Col6a3-deficient mice for a loss-of-function study. Various molecular and biochemical techniques were employed to examine the effects of endotrophin on metabolic parameters. RESULTS: In adipocytes during obesity, the majority of endosomal endotrophin escapes lysosomal degradation and is released into the cytosol to mediate direct interactions between SEC13, a major component of coat protein complex II (COPII) vesicles, and autophagy-related 7 (ATG7), leading to the increased formation of autophagosomes. Autophagosome accumulation disrupts the balance of autophagic flux, resulting in adipocyte death, inflammation, and insulin resistance. These adverse metabolic effects were ameliorated by either suppressing ATG7 with siRNA ex vivo or neutralizing endotrophin with monoclonal antibodies in vivo. CONCLUSIONS: High levels of intracellular endotrophin-mediated autophagic flux impairment in adipocyte contribute to metabolic dysfunction such as apoptosis, inflammation, and insulin resistance in obesity.

Epigenetic regulation of Neuregulin 1 promotes breast cancer progression associated to hyperglycemia.

Hyperglycemia is a risk factor for breast cancer-related morbidity and mortality. Hyperglycemia induces Neuregulin 1 (Nrg1) overexpression in breast cancer, which subsequently promotes tumor progression. However, molecular mechanisms underlying hyperglycemia-induced Nrg1 overexpression remain poorly understood. Here, we show that hyperglycemia causes active histone modifications at the Nrg1 enhancer, forming enhanceosome complexes where recombination signal binding protein for immunoglobulin kappa J region (RBPJ), E1A binding protein p300 (P300), and SET domain containing 1 A (SETD1A) are recruited to upregulate Nrg1 expression. Deletions in RBPJ-binding sites causes hyperglycemia-controlled Nrg1 levels to be downregulated, resulting in decreased tumor growth in vitro and in vivo. Mice with modest-temporary hyperglycemia, induced by low-dose short-exposure streptozotocin, display accelerated tumor growth and lapatinib resistance, whereas combining lapatinib with N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S42 phenylglycine t-butyl ester (DAPT) ameliorates tumor growth under these modest hyperglycemic conditions by inhibiting NOTCH and EGFR superfamilies. NOTCH activity is correlated with NRG1 levels, and high NRG1 levels predicts poor outcomes, particularly in HER2-positive breast cancer patients. Our findings highlight the hyperglycemia-linked epigenetic modulation of NRG1 as a potential therapeutic strategy for treating breast cancer patients with diabetes.

DSCR1 deficiency ameliorates the Aß pathology of Alzheimer's disease by enhancing microglial activity.

Microglial phagocytosis and clearance are important for the removal of amyloid-ß (Aß) plaques in Alzheimer's disease (AD). Chronic exposure of microglia to Aß plaques leads to microglial metabolic dysfunction, and dysregulation of microglia can accelerate the deposition of Aß plaques and cause learning and memory impairment. Thus, regulating microglial Aß clearance is crucial for the development of therapeutics for AD-related dementia. Here, Down syndrome critical region 1 (DSCR1) deficiency ameliorated Aß plaque deposition in the 5xFAD mouse model of AD by altering microglial activity; however, the Aß synthesis pathway was not affected. DSCR1 deficiency improved spatial learning and memory impairment in 5xFAD mice. Furthermore, DSCR1-deficient microglia exhibited accelerated lysosomal degradation of Aß after phagocytosis, and BV2 cells with stable knockdown of DSCR1 demonstrated enhanced lysosomal activity. RNA-sequencing analysis showed that the transcriptional signatures associated with responses to IFN-γ were significantly up-regulated in DSCR1-knockdown BV2 cells treated with Aß. Our data strongly suggest that DSCR1 is a critical mediator of microglial degradation of amyloid plaques and a new potential microglial therapeutic target in AD.

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.

Type VI collagen and its cleavage product, endotrophin, cooperatively regulate the adipogenic and lipolytic capacity of adipocytes.

OBJECTIVE: Obesity-induced adipose tissue remodeling is closely associated with systemic insulin resistance. However, the mechanistic involvement of adipocyte-derived extracellular matrix proteins under pathophysiological conditions remains unclear. Our aim was to investigate the distinctive contributions of each chain of type VI collagens (Col6) and its cleavage protein endotrophin to adipocyte functions and insulin sensitivity. METHODS: Col6 comprises three alpha chains: Col6a1, Col6a2, and Col6a3. We generated Col6a1-, Col6a2-, and Col6a3-deficient 3T3-L1 adipocytes using the CRISPR-Cas9 system as well as a novel Col6a3-deficient (Col6a3KO) mouse model for loss-of-function studies. Adenoviral-endotrophin and adipocyte-specific doxycycline-inducible endotrophin transgenic mice were utilized for the gain-of-function analysis. RESULTS: The holo-Col6 fibrils were found to be required for mature adipocyte differentiation. Only Col6a3-deficient 3T3-L1 adipocytes showed decreased inflammation and basal adipocyte lipolysis and prevented ER-stress-induced insulin resistance. Consistently, Col6a3KO mice showed decreased adipocyte size and fat mass of epididymal adipose tissues due to a defect in adipogenic and lipolytic capacity of adipocytes. Beyond the structural role of Col6a3, overexpression of endotrophin in obese mice further augmented insulin resistance, which was tightly associated with a significant increase in lipolysis, inflammation, and cellular apoptosis in adipose tissues, whereas this showed a limited effect on adipogenesis. CONCLUSIONS: These novel findings corroborate our previous observations suggesting that adipose tissue extracellular matrix regulates adipocyte function and insulin sensitivity in pathophysiological conditions. Mechanistically, holo-Col6 fibrils and their signaling derivative endotrophin govern adipocyte function independently of their role as structural supports via MAPK signaling pathways, and the latter could be an important metabolic effector in obesity-related metabolic diseases.

Deficiency of fibroblast growth factor 21 aggravates obesity-induced atrophic responses in skeletal muscle.

BACKGROUND: Obesity-induced skeletal muscle inflammation is a major contributor of skeletal muscle loss/atrophy and is implicated in metabolic complications such as insulin resistance. Fibroblast growth factor 21 (FGF21) is known to be an important metabolic regulator with anti-inflammatory properties. However, the effect of FGF21 on skeletal muscle atrophy is unclear. In this study, we investigated the effect of FGF21 deficiency on obesity-induced skeletal muscle inflammation and atrophy in mice. RESULTS: The expression of atrophic factors (MuRF1 and Atrogin-1) was upregulated at the mRNA and/or protein levels in the skeletal muscle of FGF21-deficient obese mice compared with wild type obese control mice. This was accompanied by an increase in levels of inflammatory cytokines (TNFα and MCP-1) and a reduction in AMPK phosphorylation. FGF21 treatment markedly suppressed TNFα-mediated inflammatory and atrophic responses in cultured myotubes, and the actions of FGF21 were blunted by the AMPK inhibitor compound C. CONCLUSION: These findings suggest that FGF21 deficiency aggravates obesity-induced inflammation and atrophic responses in the skeletal muscle of obese mice, and FGF21 may protect inflammation-mediated atrophy through the AMPK pathway.

Fibroblast growth factor 21 deficiency aggravates obesity-induced hypothalamic inflammation and impairs thermogenic response.

OBJECTIVE AND DESIGN: Hypothalamic inflammation is closely associated with metabolic dysregulation. Fibroblast growth factor 21 (FGF21) is known to be an important metabolic regulator with anti-inflammatory properties. In this study, we investigated the effects of FGF21 deficiency on obesity-induced hypothalamic inflammation and thermogenic responses. MATERIALS AND METHODS: FGF21-deficient mice and/or wild-type (WT) mice were fed a high-fat diet (HFD) for 12 weeks. RESULTS: FGF21-deficient mice fed an HFD showed increased levels of inflammatory cytokines compared with WT obese control, and this was accompanied by upregulation of gliosis markers in the hypothalamus. Expression of heat-shock protein 72, a marker of neuronal damage, was increased in the FGF21-deficient obese mice, and the expression of hypothalamic neuronal markers involved in anti-thermogenic or thermogenic responses was altered. Moreover, the protein level of uncoupling protein 1 and other thermogenic genes were markedly reduced in the brown adipose tissue of the FGF21-deficient obese mice. CONCLUSIONS: These findings suggest that FGF21 deficiency aggravates obesity-induced hypothalamic inflammation and neuronal injury, leading to alterations in hypothalamic neural circuits accompanied by a reduction of the thermogenic response.

The involvement of 4-1BB/4-1BBL signaling in glial cell-mediated hypothalamic inflammation in obesity.

Obesity-induced inflammation occurs not only in peripheral tissues but also in areas of the central nervous system. Glial cells such as astrocytes and microglia play crucial roles in obesity-related hypothalamic inflammation, leading to the derangement of energy metabolism and neurodegenerative pathologies. Here, we show that the interaction of 4-1BB/4-1BBL between lipid-laden astrocytes/microglia promotes hypothalamic inflammation in obesity. Stimulation of 4-1BB, a member of the TNF receptor superfamily, and/or its ligand 4-1BBL on astrocytes and/or microglia with a specific agonist resulted in activation of the inflammatory signaling pathway and enhanced production of inflammatory mediators. Contact coculture of lipid-laden astrocytes and microglia increased the production of inflammatory mediators, and blockade of the 4-1BB/4-1BBL interaction reduced the inflammatory response. Moreover, deficiency of 4-1BB reduced hypothalamic inflammation in obese mice fed an high-fat diet. These findings suggest that 4-1BBL/4-1BB signaling enhances the glial cell-mediated inflammatory cross talk and participates in obesity-induced hypothalamic inflammation.

Quercetin Reduces Tumor Necrosis Factor Alpha-Induced Muscle Atrophy by Upregulation of Heme Oxygenase-1.

The inflammatory cytokine tumor necrosis factor α (TNFα), upregulated in the obese condition, promotes protein degradation and is implicated in obesity-related skeletal muscle atrophy and age-related sarcopenia. Quercetin, a flavonoid, elicits antioxidative and anti-inflammatory activities. In this study, we investigated the effect of quercetin on TNFα-induced skeletal muscle atrophy as well as its potential mechanism of action. In this study, we observed that quercetin suppressed expression of TNFα-induced atrophic factors such as MAFbx/atrogin-1 and MuRF1 in myotubes, and it enhanced heme oxygenase-1 (HO-1) protein level accompanied by increased nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) in myotubes. The HO-1 inhibitor ZnPP suppressed the inhibitory actions of quercetin on TNFα-induced atrophic responses and degradation of IκB-α in myotubes. Moreover, quercetin supplementation to high-fat diet-fed obese mice inhibited obesity-induced atrophic responses in skeletal muscle, accompanied by upregulation of HO-1 and inactivation of nuclear factor-kappa B (NF-κB), and the quercetin actions were attenuated in Nrf2-deficient mice. These findings suggest that quercetin protects against TNFα-induced muscle atrophy under obese conditions through Nrf2-mediated HO-1 induction accompanied by inactivation of NF-κB. Quercetin may be used as a dietary supplement to protect against obesity-induced skeletal muscle atrophy.

Quercetin Upregulates Uncoupling Protein 1 in White/Brown Adipose Tissues through Sympathetic Stimulation.

BACKGROUND: Uncoupling protein 1 (UCP1) plays an important role in increasing energy expenditure; thus, it is being considered as a new target for preventing obesity and metabolic complications. In this study, we investigated the effect of quercetin, a naturally occurring flavonoid, on UCP1 expression in white/brown adipose tissues (WAT/BAT). METHODS: Mice were fed a high-fat diet (HFD) supplemented with or without dietary quercetin for 9 weeks, and 3T3-L1 adipocytes were treated with quercetin. Expression of UCP1 and other thermogenic genes/proteins was measured by real-time polymerase chain reaction and/or Western blotting. RESULTS: Dietary quercetin supplementation increased the level of UCP1 in both WAT and/or BAT of HFD-fed obese mice, which was accompanied by upregulated mRNA levels of thermogenesis-related genes. Quercetin supplementation enhanced the plasma norepinephrine level and tended to upregulate ß-adrenergic receptor mRNA level in the WAT of HFD-fed obese mice, accompanied by AMP-activated protein kinase (AMPK) activation. Moreover, quercetin enhanced UCP1 expression in 3T3-L1 adipocytes, and this was blunted by treatment with a peroxisome proliferator-activated receptor gamma (PPARγ) antagonist. CONCLUSION: These findings suggest that quercetin upregulates UCP1, implying increased WAT browning and BAT activity, via activation of the AMPK/PPARγ pathway through sympathetic stimulation. Quercetin may be useful for preventing obesity and metabolic complications.

Quercetin Protects Obesity-Induced Hypothalamic Inflammation by Reducing Microglia-Mediated Inflammatory Responses via HO-1 Induction.

Obesity-induced hypothalamic inflammation is characterized by activation of microglia, which are resident macrophages of the central nervous system, and is implicated in the derangement of energy homeostasis, metabolic complications, and neurodegenerative diseases. Quercetin, a naturally occurring flavonoid, is known to protect against oxidative stress and inflammation-related metabolic complications. Here, we demonstrate that quercetin reduces obesity-induced hypothalamic inflammation by inhibiting microglia-mediated inflammatory responses, and the beneficial action of quercetin is associated with heme oxygenase (HO-1) induction. Quercetin markedly reduced the production of inflammatory mediators (monocyte chemoattractant protein (MCP)-1, interleukin (IL-6), IL-1ß, nitric oxide) by microglia stimulated with saturated fatty acid palmitate and/or lipid-laden microglia-conditioned medium. Quercetin also upregulated the expression of HO-1 in palmitate-treated lipid-laden microglia, and the actions of quercetin against microglia activation accompanied by IκBα degradation were abolished by a HO-1 inhibitor. Moreover, quercetin supplementation reduced the levels of inflammatory cytokines and microglia activation markers in the hypothalamus of high fat diet (HFD)-fed obese mice, which was accompanied by upregulation of HO-1. These findings indicate that quercetin suppresses microglia-mediated inflammatory responses via the induction of HO-1, and hence protects against obesity-induced hypothalamic inflammation.

Suksdorfin Promotes Adipocyte Differentiation and Improves Abnormalities in Glucose Metabolism via PPARγ Activation.

Although the Apiaceae herb family has been traditionally used for the management of type 2 diabetes, its molecular mechanism has not been clarified. Coumarin derivatives, which are abundant in plants of the Apiaceae family, were evaluated for their effects on adipogenesis. We found that suksdorfin significantly promoted adipocyte differentiation and enhanced production of adiponectin, an anti-diabetic adipokine. We also demonstrated that suksdorfin activates peroxisome proliferator-activated receptor gamma (PPARγ), a master regulator of adipogenesis. Furthermore, we showed metabolic disorders in obese diabetic KK-Ay mice were attenuated by suksdorfin feeding. Suksdorfin intake induced adipocyte miniaturization and increased expression levels of PPARγ target genes related to adipocyte differentiation. These results indicated that suksdorfin induces adipogenesis in white adipose tissue (WAT) via the activation of PPARγ, leading to improvement of obesity-induced metabolic disorders. Therefore, suksdorfin-mediated amelioration of WAT dysfunctions might be responsible for the anti-diabetic effects of traditional herbal medicine therapy with Apiaceae.

Absence of 4-1BB reduces obesity-induced atrophic response in skeletal muscle.

Obesity-induced inflammation causes skeletal muscle atrophy accompanied by disruption of oxidative metabolism and is implicated in metabolic complications such as insulin resistance and type 2 diabetes. We previously reported that 4-1BB, a member of the tumor necrosis factor receptor superfamily, participated in obesity-induced skeletal muscle inflammation. Here, we show that the absence of 4-1BB in obese mice fed a high-fat diet led to a decrease in expression of atrophic factors (MuRF1 and Atrogin-1) with suppression of NF-κB activity, and that this was accompanied by increases in mitochondrial oxidative metabolic genes/proteins (e.g., PGC-1α, CPT1ß, etc.) expression and oxidative muscle fibers marker genes/proteins in the skeletal muscle. These findings suggest that 4-1BB-mediated inflammatory signaling could be a potential target for combating obesity-related muscle atrophy and metabolic derangement in skeletal muscle.

Hypothalamic lipid-laden astrocytes induce microglia migration and activation.

Obesity-induced hypothalamic inflammation is closely associated with various metabolic complications and neurodegenerative disorders. Astrocytes, the most abundant glial cells in the central nervous system, play a crucial role in pathological hypothalamic inflammatory processes. Here, we demonstrate that hypothalamic astrocytes accumulate lipid droplets under saturated fatty acid-rich conditions, such as obese environment, and that the lipid-laden astrocytes increase astrogliosis markers and inflammatory cytokines (TNFα, IL-1ß, IL-6, MCP-1) at the transcript and/or protein level. Medium conditioned by the lipid-laden astrocytes stimulate microglial chemotactic activity and upregulate transcripts of the microglia activation marker Iba-1 and inflammatory cytokines. These findings indicate that the lipid-laden astrocytes formed in free fatty acid-rich obese condition may participate in obesity-induced hypothalamic inflammation through promoting microglia migration and activation.

Synthesized enone fatty acids resembling metabolites from gut microbiota suppress macrophage-mediated inflammation in adipocytes.

SCOPE: Recent reports indicate that gut microbiota and their metabolites may regulate host inflammatory conditions, including the chronic inflammation of obese adipose tissues. In this study, we investigated whether specific synthesized fatty acids, identical to the metabolites generated by gut microbiota, act as anti-inflammatory factors in obesity-induced inflammation. METHODS AND RESULTS: We first used lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages to examine the anti-inflammatory effect of fatty acids synthesized to resemble representative polyunsaturated fatty acid metabolites from gut microbiota. Fatty acids containing an enone structure showed the most potent anti-inflammatory activity. Enone fatty acids also displayed anti-inflammatory effects on macrophages cocultured with hypertrophied 3T3-L1 or immortalized primary adipocytes; and macrophages stimulated with 3T3-L1 adipocyte conditioned medium. Consistently, the beneficial outcome was revealed in the case of LPS- and obesity-induced inflammatory cytokine stimulation in ex vivo adipose tissues. Furthermore, these fatty acids recovered the suppression of ß-adrenergic receptor-stimulated uncoupling protein 1 expression and secretion of adiponectin in C3H10T1/2 and 3T3-L1 adipocytes, respectively, under inflammatory conditions, suggesting that enone fatty acids can ameliorate dysfunctions of adipocytes induced by inflammation. CONCLUSION: These findings indicate that synthesized enone fatty acids show potent anti-inflammatory effects, leading to the improvement of inflammation-induced dysfunctions in adipocytes.

The hepatokine FGF21 is crucial for peroxisome proliferator-activated receptor-α agonist-induced amelioration of metabolic disorders in obese mice.

Obesity causes excess fat accumulation in white adipose tissues (WAT) and also in other insulin-responsive organs such as the skeletal muscle, increasing the risk for insulin resistance, which can lead to obesity-related metabolic disorders. Peroxisome proliferator-activated receptor-α (PPARα) is a master regulator of fatty acid oxidation whose activator is known to improve hyperlipidemia. However, the molecular mechanisms underlying PPARα activator-mediated reduction in adiposity and improvement of metabolic disorders are largely unknown. In this study we investigated the effects of PPARα agonist (fenofibrate) on glucose metabolism dysfunction in obese mice. Fenofibrate treatment reduced adiposity and attenuated obesity-induced dysfunctions of glucose metabolism in obese mice fed a high-fat diet. However, fenofibrate treatment did not improve glucose metabolism in lipodystrophic A-Zip/F1 mice, suggesting that adipose tissue is important for the fenofibrate-mediated amelioration of glucose metabolism, although skeletal muscle actions could not be completely excluded. Moreover, we investigated the role of the hepatokine fibroblast growth factor 21 (FGF21), which regulates energy metabolism in adipose tissue. In WAT of WT mice, but not of FGF21-deficient mice, fenofibrate enhanced the expression of genes related to brown adipocyte functions, such as Ucp1, Pgc1a, and Cpt1b Fenofibrate increased energy expenditure and attenuated obesity, whole body insulin resistance, and adipocyte dysfunctions in WAT in high-fat-diet-fed WT mice but not in FGF21-deficient mice. These findings indicate that FGF21 is crucial for the fenofibrate-mediated improvement of whole body glucose metabolism in obese mice via the amelioration of WAT dysfunctions.

Induction of heme oxygenase-1 with dietary quercetin reduces obesity-induced hepatic inflammation through macrophage phenotype switching.

BACKGROUND/OBJECTIVES: Obesity-induced steatohepatitis accompanied by activated hepatic macrophages/Kupffer cells facilitates the progression of hepatic fibrinogenesis and exacerbates metabolic derangements such as insulin resistance. Heme oxyganase-1 (HO-1) modulates tissue macrophage phenotypes and thus is implicated in protection against inflammatory diseases. Here, we show that the flavonoid quercetin reduces obesity-induced hepatic inflammation by inducing HO-1, which promotes hepatic macrophage polarization in favor of the M2 phenotype. MATERIALS/METHODS: Male C57BL/6 mice were fed a regular diet (RD), high-fat diet (HFD), or HFD supplemented with quercetin (HF+Que, 0.5g/kg diet) for nine weeks. Inflammatory cytokines and macrophage markers were measured by ELISA and RT-PCR, respectively. HO-1 protein was measured by Western blotting. RESULTS: Quercetin supplementation decreased levels of inflammatory cytokines (TNFα, IL-6) and increased that of the anti-inflammatory cytokine (IL-10) in the livers of HFD-fed mice. This was accompanied by upregulation of M2 macrophage marker genes (Arg-1, Mrc1) and downregulation of M1 macrophage marker genes (TNFα, NOS2). In co-cultures of lipid-laden hepatocytes and macrophages, treatment with quercetin induced HO-1 in the macrophages, markedly suppressed expression of M1 macrophage marker genes, and reduced release of MCP-1. Moreover, these effects of quercetin were blunted by an HO-1 inhibitor and deficiency of nuclear factor E2-related factor 2 (Nrf2) in macrophages. CONCLUSIONS: Quercetin reduces obesity-induced hepatic inflammation by promoting macrophage phenotype switching. The beneficial effect of quercetin is associated with Nrf2-mediated HO-1 induction. Quercetin may be a useful dietary factor for protecting against obesity-induced steatohepatitis.

The Soy Peptide Phe-Leu-Val Reduces TNFα-Induced Inflammatory Response and Insulin Resistance in Adipocytes.

Obesity-induced adipose inflammation plays a crucial role in the development of obesity-induced metabolic disorders such as insulin resistance and type 2 diabetes. In the presence of obesity, hypertrophic adipocytes release inflammatory mediators, including tumor necrosis factor-alpha (TNFα) and monocyte chemoattractant protein-1 (MCP-1), which enhance the recruitment and activation of macrophages, and in turn augment adipose inflammation. We demonstrate that the soy peptide Phe-Leu-Val (FLV) reduces inflammatory responses and insulin resistance in mature adipocytes. Specifically, the soy peptide FLV inhibits the release of inflammatory cytokines (TNFα, MCP-1, and IL-6) from both TNFα-stimulated adipocytes and cocultured adipocytes/macrophages. This inhibition is mediated by the inactivation of the inflammatory signaling molecules c-Jun N-terminal kinase (JNK) and IκB kinase (IKK), and the downregulation of IκBα in the adipocytes. In addition, soy peptide FLV enhances insulin responsiveness and increases glucose uptake in adipocytes. More importantly, we, for the first time, found that adipocytes express peptide transporter 2 (PepT2) protein, and the beneficial action of the soy peptide FLV was disrupted by the peptide transporter inhibitor GlySar. These findings suggest that soy peptide FLV is transported into adipocytes by PepT2 and then downregulates TNFα-induced inflammatory signaling, thereby increasing insulin responsiveness in the cells. The soy peptide FLV, therefore, has the potential to prevent obesity-induced adipose inflammation and insulin resistance.