Adipose Tissue Of Obese Mice Research Articles

Aerobic Training Reduces Immune Cell Recruitment and Cytokine Levels in Adipose Tissue in Obese Mice

Obesity is associated with an energy imbalance that results from excessive energy intake, low diet quality and a sedentary lifestyle. In this regard, the increased consumption of a high‐refined carbohydrate diet (HC) is strongly related to higher adiposity and low‐grade inflammation. Aerobic training is a well‐known non‐pharmacological intervention to treat obesity and metabolic disturbances. However, the mechanisms through which aerobic training ameliorates the low‐grade inflammation induced by the HC diet need to be further investigated. Herein, our hypothesis was that aerobic training would decrease the recruitment of leukocytes in the adipose tissue thereby reducing the levels of cytokines and improving metabolism in mice fed the HC diet. Male Balb/c were assigned to the following groups: control non‐trained (C‐NT), control trained (C‐T), HC‐NT and HC‐T. Mice were submitted to moderate‐intensity training sessions that consisted of running 60 min/day for 8 weeks. The intravital microscopy technique was performed in vivo in anesthetized mice to visualize the microvasculature of the adipose tissue. The HC diet induced obesity and increased the influx of immune cells into the adipose tissue. In contrast, HC‐T mice presented a lower adiposity and adipocyte area. Furthermore, HC‐T mice showed an increased resting energy expenditure, a decreased recruitment of immune cells in the adipose tissue, reduced cytokine levels, and ameliorated hyperglycemia and fatty liver deposition relative to HC‐NT mice. Collectively, our data enhance the understanding about the anti‐inflammatory effect of aerobic training and shed light on the adipose tissue‐mediated mechanisms by which training promotes a healthier metabolic profile.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Obesity-Induced Methylation of Osteopontin Contributes to Adipogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells.

Obesity is a major risk factor for many chronic diseases, including diabetes, fatty livers, and cancer. Expansion of the adipose mass has been shown to be related to adipogenic differentiation of adipose-derived mesenchymal stem cells (ASCs). However, the underlying mechanism of this effect has yet to be elucidated. We found that osteopontin (OPN) is downregulated in ASCs and adipose tissues of obese mice and overweight human beings because of methylation on its promoter, indicating that OPN may affect the development of obesity. Silencing of OPN in wild-type ASCs promotes adipogenic differentiation, while reexpression of OPN reduced adipogenic differentiation in OPN−/− ASCs. The role of extracellular OPN in ASC differentiation was further demonstrated by supplementation and neutralization of OPN. Additionally, OPN suppresses adipogenic differentiation in ASCs through the C/EBP pathways. Consistent with these in vitro results, by intravenous injection of OPN-expressing adenovirus to the mice, we found OPN can delay the development of obesity and improve insulin sensitivity. Therefore, our study demonstrates an important role of OPN in regulating the development of obesity, indicating OPN might be a novel target to attenuate obesity and its complications.

Inflammation and ER stress differentially regulate STAMP2 expression and localization in adipocytes

BackgroundChronic ER stress and dysfunction is a hallmark of obesity and a critical contributor to metaflammation, abnormal hormone action and altered substrate metabolism in metabolic tissues, such as liver and adipocytes. Lack of STAMP2 in lean mice induces inflammation and insulin resistance on a regular diet, and it is dysregulated in the adipose tissue of obese mice and humans. We hypothesized that the regulation of STAMP2 is disrupted by ER stress. Methods3T3-L1 and MEF adipocytes were treated with ER stress inducers thapsigargin and tunicamycin, and inflammation inducer TNFα. The treatments effect on STAMP2 expression and enzymatic function was assessed. In addition, 3T3-L1 adipocytes and HEK cells were utilized for Stamp2 promoter activity investigation performed with luciferase and ChIP assays. ResultsER stress significantly reduced both STAMP2 mRNA and protein expression in cultured adipocytes whereas TNFα had the opposite effect. Concomitant with loss of STAMP2 expression during ER stress, intracellular localization of STAMP2 was altered and total iron reductase activity was reduced. Stamp2 promoter analysis by reporter assays and chromatin immunoprecipitation, showed that induction of ER stress disrupts C/EBPα-mediated STAMP2 expression. ConclusionThese data suggest a clear link between ER stress and quantitative and functional STAMP2-deficiency.

Pistachio Consumption Prevents and Improves Lipid Dysmetabolism by Reducing the Lipid Metabolizing Gene Expression in Diet-Induced Obese Mice.

Pistachios contain beneficial substances such as unsaturated fatty acids, phytosterols, and polyphenols. In the present study, we investigated if pistachio consumption is able to prevent or to revert hyperglycemia, dyslipidemia, hepatic steatosis, and adipose tissue morphological alterations caused by high fat diet (HFD) in the mouse. Moreover, the impact of pistachio intake on the mRNA expression of peroxisome proliferator-activated receptor γ (PPAR-γ), fatty acid transport proteins (FAT-P), fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD1), and sterol regulatory element-binding transcription factor-1c (SREBP-1c) in liver and adipose tissue was also analyzed. No change in body weight, food intake, and hyperglycemia was observed between mice consuming pistachios (HFD-P) and HFD mice. Pistachio intake was able to prevent but not to reverse HFD-induced hypertriglyceridemia. Cholesterol plasma levels, steatosis grading, body fat mass, and adipocyte size were significantly lower in HFD-P group compared to HFD in both prevention and reversal protocol. Pistachio-diet was able to prevent HFD-induced overexpression of PPAR-γ, FAS, and SCD1 in the liver and SREBP-1c, PPAR-γ, and FAT-P in adipose tissue. Similarly, HFD-P significantly ameliorated the expression levels of FAT-P and SCD1 in the liver and SREBP-1c, FAS, and SCD1 in adipose tissue of obese mice. The present study shows that pistachio consumption is able to prevent and to ameliorate obesity-related dysfunctions by positively modulating the expression of genes linked to lipid metabolism.

Alogliptin improves endothelial function by promoting autophagy in perivascular adipose tissue of obese mice through a GLP-1-dependent mechanism

ObjectivePerivascular adipose tissue (PVAT) regulates vascular function in a paracrine manner and the vasodilatory effect of PVAT on vessels is completely abolished in obesity. In addition, autophagy is required for maintaining biological function of PVAT and has been shown to be inhibited in obesity. The aim of this study was to explore whether alogliptin improves endothelial function by promoting autophagy in PVAT in obese mice. MethodsC57BL/6 mice were maintained on high fat diet with or without alogliptin intervention for 3 months. Vasorelaxation function of thoracic aorta with or without PVAT was determined. Autophagy related protein level of p62 and LC3B, along with phosphorylated mTOR (p-mTOR) were evaluated. In addition, the effects of alogliptin on autophagy were also investigated in cultured adipocytes. ResultsThe presence of PVAT significantly impaired endothelium-dependent vasodilation in obese mice and alogliptin intervention corrected this defect. Autophagy in PVAT was decreased in obese mice and alogliptin intervention activated autophagy. Activating autophagy in PVAT improved endothelium-dependent vasodilation while blocking it in PVAT impaired vasodilation function. Further, addition of glucagon-like peptide-1 (GLP-1) but not alogliptin alone activated autophagy. Moreover, GLP-1 and alogliptin co-treatment did not show additive effect on activating autophagy. ConclusionsThese results revealed that promoting autophagy in PVAT improved endothelial function in response to alogliptin intervention. Additionally, the beneficial effect of alogliptin intervention on PVAT was GLP-1 dependent.

Aerobic training reduces immune cell recruitment and cytokine levels in adipose tissue in obese mice

Obesity is associated with an energy imbalance that results from excessive energy intake, low diet quality, and a sedentary lifestyle. The increased consumption of a high-refined carbohydrate (HC) diet is strongly related to higher adiposity and low-grade inflammation. Aerobic training is a well-known nonpharmacological intervention to treat obesity and metabolic disturbances. However, the mechanisms through which aerobic training ameliorates the low-grade inflammation induced by an HC diet should be further investigated. Our hypothesis herein was that aerobic training would decrease the recruitment of leukocytes in adipose tissue, thereby reducing the levels of cytokines and improving metabolism in mice fed an HC diet. Male Balb/c mice were assigned to the following groups: control diet/nontrained (C-NT), control diet/trained (C-T), high-refined carbohydrate diet/nontrained (HC-NT), and high-refined carbohydrate diet/trained (HC-T). Mice were submitted to moderate-intensity training sessions that consisted of running 60 min per day for 8 weeks. An intravital microscopy technique was performed in vivo in anesthetized mice to visualize the microvasculature of the adipose tissue. The HC diet induced obesity and increased the influx of immune cells into the adipose tissue. In contrast, HC-T mice presented a lower adiposity and adipocyte area. Furthermore, relative to HC-NT mice, HC-T mice showed increased resting energy expenditure, decreased recruitment of immune cells in the adipose tissue, reduced cytokine levels, and ameliorated hyperglycemia and fatty liver deposition. Collectively, our data enhance understanding about the anti-inflammatory effect of aerobic training and shed light on the adipose tissue-mediated mechanisms by which training promotes a healthier metabolic profile.

Regulation of obesity-associated metabolic disturbance by the antipsychotic drug olanzapine: Role of the autophagy-lysosome pathway

Metabolic disturbance is commonly observed in schizophrenia patients, and the metabolic impacts of atypical antipsychotics such as olanzapine (OLA) have received much attention. Drug naive schizophrenia patients display metabolic abnormality to varying degrees, but how this shapes the metabolic responses to chronic OLA exposure is unknown. Using high-fat diet (HFD, 8 weeks) induced obesity, here we explored the metabolic outcome of chronic OLA exposure in conditions of pre-existing metabolic disturbance. OLA treatment (2 mg/kg) for 4 weeks led to markedly reduced body weight and adiposity in obese mice, concomitant with reduced adipose inflammation and hepatic steatosis. No significant change was observed on insulin sensitivity or energy expenditure after OLA exposure. Mechanistically, OLA restored autophagic clearance in the subcutaneous adipose tissue of obese mice, in line with its potentiation of lysosomal function in adipocytes. The metabolic phenotypes induced by OLA were partially reversed by chemical suppression of autolysosome. Together, these data uncover distinct metabolic effects of OLA in obesity involving the regulation of adipose tissue autophagy, and suggest a complicated link between OLA therapy and metabolic disturbance in schizophrenia.

Obesity-Associated miR-199a/214 Cluster Inhibits Adipose Browning via PRDM16-PGC-1α Transcriptional Network.

miRNAs are important regulators of differentiation, development, and function of brown and beige fat cells. In this study, we identify the role of the miR-199a/214 cluster in the regulation of brown and beige adipocyte development and thermogenesis in vitro and in vivo. We show that expression of the miR-199a/214 cluster is dramatically decreased during brown and beige adipocyte differentiation and in response to cold exposure or β-adrenergic receptor activation. The cluster levels are significantly upregulated in the adipose tissues of obese mice and human subjects. Overexpression of the miR-199a/214 cluster suppresses brown adipocyte differentiation and inhibits thermogenic gene expression and mitochondrial respiration, whereas knockdown of the cluster increases thermogenic gene expression and mitochondrial function in beige adipocytes. In addition, inhibition of the miR-199a/214 cluster promotes beiging effects in vivo. We further show that miR-199a/214 suppresses brown adipocyte differentiation and beige fat development by directly targeting PRDM16 and peroxisome PGC-1α, two key transcriptional regulators of adipose browning. Together, these observations reveal that the miR-199a/214 cluster is a key negative regulator of brown and beige fat development and thermogenesis.

MicroRNA-143a-3p modulates preadipocyte proliferation and differentiation by targeting MAPK7.

Adipogenesis plays a key role in increasing fat mass, which is a main characteristic for obesity, and involves preadipocyte proliferation and differentiation. Recently, more and more evidences suggested that microRNAs (miRNAs) is an important member of the regulatory network of adipogenesis. In this study, miR-143a-3p was highly expressed in adipose tissues of obese mice, and was up-regulated at the middle and last stage of 3T3-L1 adipocyte differentiation. Using mouse 3T3-L1 cells line, which is an ideal model in vitro for the study of adipogenesis, we observed that overexpression of miR-143a-3p inhibited the preadipocyte proliferation, and enhanced the preadipocyte differentiation. In contrast, the inhibition of miR-143a-3p expression promoted the preadipocyte proliferation, and inhibited the preadipocyte differentiation. Further analysis suggested that miR-143a-3p mediating preadipocyte differentiation might be involved in fatty acid metabolism. In addition, we found that miR-143-3p and PPARγ, an activator of miR-143a-3p transcription, could regulate each other. Compared with miR-143a-3p, MAPK7 played an opposite role in the proliferation and differentiation of adipocyte. Further analysis indicated that MAPK7 is a target gene of miR-143a-3p in 3T3-L1 cells, and inhibition of MAPK7 recede the effect of miR-143a-3p on preadipocyte proliferation and differentiation. Taken together, these results indicated that as a regulator of PPARγ, miR-143a-3p play an important role in adipogenesis via regulating MAPK7 and fatty acid.

Modulation of lipid mediator profile may contribute to amelioration of chronic inflammation in adipose tissue of obese mice by pioglitazone

Thiazolidinediones exert their antidiabetic effect in part by ameliorating chronic inflammation in adipose tissue. However, the precise mechanism of this anti-inflammatory action has remained unclear. We here investigated the effects of the TZD pioglitazone on the lipid mediator profile of adipose tissue in obese diabetic KKAy mice by metabololipidomics analysis based on liquid chromatography and tandem mass spectrometry. Pioglitazone treatment increased the amounts of pro-resolving lipid mediators including lipoxin B4 (LXB4), resolvin E2, and eicosapentaenoic acid as well as reduced those of prostaglandin E2 and 4-hydroxydocosahexaenoic acid in epididymal adipose tissue of KKAy mice. These effects were accompanied by increased expression of genes for the anti-inflammatory proteins arginase 1, interleukin (IL)–13, and IL-10 in this tissue. Pioglitazone also increased LXB4 production in cultured 3T3-L1 adipocytes. Finally, LXB4 increased IL-10 gene expression in adipose tissue explants from KKAy mice. Together, our results suggest that up-regulation of LXB4 may contribute to the anti-inflammatory effect of pioglitazone in obese adipose tissue.

Dietary Intake of Curcumin Improves eIF2 Signaling and Reduces Lipid Levels in the White Adipose Tissue of Obese Mice

White adipose tissue (eWAT) plays a crucial role in preventing metabolic syndrome. We aimed to investigate WAT distribution and gene expression and lipidomic profiles in epididymal WAT (eWAT) in diet-induced obese mice, reflecting a Western-style diet of humans to elucidate the bioactive properties of the dietary antioxidant curcumin in preventing lifestyle-related diseases. For 16 weeks, we fed C57BL/6J mice with a control diet, a high-fat, high-sucrose and high-cholesterol Western diet or Western diet supplemented with 0.1% (w/w) curcumin. Although the dietary intake of curcumin did not affect eWAT weight or plasma lipid levels, it reduced lipid peroxidation markers’ levels in eWAT. Curcumin accumulated in eWAT and changed gene expressions related to eukaryotic translation initiation factor 2 (eIF2) signalling. Curcumin suppressed eIF2α phosphorylation, which is induced by endoplasmic reticulum (ER) stress, macrophage accumulation and nuclear factor-κB (NF-κB) p65 and leptin expression, whereas it’s anti-inflammatory effect was inadequate to decrease TNF-α and IFN-γ levels. Lipidomic and gene expression analysis revealed that curcumin decreased some diacylglycerols (DAGs) and DAG-derived glycerophospholipids levels by suppressing the glycerol-3-phosphate acyltransferase 1 and adipose triglyceride lipase expression, which are associated with lipogenesis and lipolysis, respectively. Presumably, these intertwined effects contribute to metabolic syndrome prevention by dietary modification.

Vernonia cinerea water extract improves insulin resistance in high-fat diet–induced obese mice

Vernonia cinerea (V cinerea) is a plant distributed in grassy areas in Southeast Asia and has several pharmacological effects, including antidiabetic activity. However, the information available regarding the effect of V cinerea on insulin resistance in high-fat diet (HFD)–induced obese mice is not yet determined. We hypothesized that V cinerea water extract (VC) improves insulin sensitivity in HFD-induced obese mice by modulating both phosphatidylinositol-3-kinase (PI3K) and adenosine monophosphate–activated protein kinase (AMPK) pathways in liver, skeletal muscle, and adipose tissue. Obesity was induced in mice from the Institute for Cancer Research by feeding an HFD 188.28 kJ (45 kcal % lard fat) for 12 weeks. During the last 6 weeks of the HFD, obese mice were treated with VC (250 and 500 mg/kg). We found that VC at both doses significantly reduced the hyperglycemia, hyperinsulinemia, hyperleptinemia, and hyperlipidemia. Obese mice treated with VC could increase serum adiponectin but reduce the proinflammatory cytokines, tumor necrosis factor–α, and monocyte chemoattractant protein–1. The extracts decreased triglyceride storage in liver and skeletal muscle of obese mice. The average size of fat cells was smaller in VC-treated groups than that of the HFD group. The protein expressions of PI3K and AMPK pathways in liver, skeletal muscle, and adipose tissue were upregulated (increased phosphorylation of PI3K, protein kinase B, AMPK, and acetyl-CoA carboxylase) by VC treatment. Furthermore, the glucose transporter 4 was increased in muscle and adipose tissue in obese mice treated with VC. These data indicate that VC treatment stimulates phosphorylation of PI3K and AMPK pathways in liver, muscle, and adipose tissue. Stimulating these pathways may improve impaired glucose and lipid homeostasis in an HFD-induced obesity mouse model. Based on these findings, it appears that VC has potential as a functional food or therapeutic agent in management of insulin resistance related diseases, such as type 2 diabetes mellitus.

Abstract 428: An Unexpected Role for ACC in Lipid Droplet Formation in Macrophages in Response to Acellular Adipocyte Fat

In adipose tissues of obese mice, macrophages accumulate in crown-like structures (CLS) formed around dying adipocytes. The CLS macrophages are thought to clear the dead adipocytes by exophagy, which involves exocytosis of lysosomes and digestion of apoptotic adipocytes. After digesting the plasma membrane and other cytosolic contents of the adipocyte, CLS macrophages come in contact with the large lipid droplet, however, it is unknown how macrophages response to such acellular adipocytes. We hypothesized that the acelular adipocytes in CLSs promote inflammation and metabolically activate the macrophages to promote clearance of the lipid. To mimic the in vivo scenario, we exposed cultured murine bone marrow-derived macrophages to lipid droplets isolated from the adipocytes of high-fat diet-induced obese C57BL/6 mice. In response to adipocyte lipid, macrophages accumulated lipid droplets, which were similar in size and number to lipid droplets of CLS macrophages in vivo . Acellular lipid exposure significantly increased TNF-α gene expression, which was suppressed by the CD36 inhibitor sulfo-N-succinimidyl oleate, supporting CD36-mediated inflammatory response. Moreover, lipid exposure significantly lowered metabolic activity of macrophages and impaired clearance of apoptotic bodies from 3T3-L1 adipocytes. Using specific inhibitors, unexpectedly we found that lipid droplet accumulation in macrophages was independent of CD36 activity or processes involved in exophagy such as exocytosis of lysosomes, extracellular lipase activity, lipolysis and phagocytosis. Interestingly, lipid droplet accumulation was dependent on acetyl-CoA carboxylase (ACC) as determined by use of ACC inhibitors soraphen A and TOFA, and siRNA knock-down of ACC in macrophages. Furthermore, confocal microscopy of whole mount adipose tissue revealed expression of ACC in CLS macrophages. Altogether, using a novel in vitro model we demonstrate that acelular adipocytes suppress metabolic activity, but induce inflammation and de novo lipogenesis-mediated lipid droplet formation in macrophages.

1024 Dissecting the molecular interdependence of skin inflammation and obesity

Psoriasis, a chronic inflammatory skin disease, is often compromised by comorbidities with obesity being the most prevalent. Epidemiological studies clearly associate obesity with psoriasis. The aim of the present study was to investigate how obesity alters skin immune responses. To this end, an obesity model was established by feeding of male C57Bl/6J mice with high-fat diet (HFD, 60% fat). To investigate the effect of obesity on Th17/Th1-mediated skin inflammation, a mouse model of 2,4,6-trinitrochlorobenzene (TNCB) contact hypersensitivity (CHS) was used. Challenging sensitized mice resulted in a significant increase of ear swelling of obese mice with an elevation of IFNg- and IL-17-positive cells in draining lymph nodes (dLN) and an increase of IL-17, IL-21, IL-6, TNF in the serum. Th2 cytokin IL-4 was unchanged (serum) or decreased (dLN) due to HFD. Interestingly, the ear swelling of Th2-mediated CHS against fluorescein isothiocyanate (FITC) was diminished in obese mice. This suggests a selective enhancement of Th17/Th1 and a decrease of Th2 immune responses by obesity. Investigating underlying mechanisms, we found increased expression of IL-12, IFNg, TNF, IL-6, iNOS and CCL2 in the adipose tissue of obese mice. TNF, IL-6, iNOS, CCL2, IL-17, and macrophages were also significantly upregulated in TNCB-CHS skin of obese mice. On the contrary, Foxp3 and TGF-beta were downregulated. Further experiments showed that dermal gamma/delta T cells are the major source of IL-17, elevated due to obesity. Unexpectedly, the depletion of gamma/delta T cells resulted in significant elevation of ear swelling in obese mice in comparison to isotype-treated obese mice. These data demonstrate for the first time functional consequences of regulatory functions of gamma/delta T cells relevant for resolution of skin inflammation and that obesity specifically impairs this regulatory function. Taken together, obesity increases Th17/Th1-mediated psoriasis-like skin inflammation by i) increasing cutaneous macrophage recruitment and activation and by ii) impairing Tregs and regulatory gamma/delta T cells causing dysregulation and exaggeration of the immune response.

Phosphorylation of Beta-3 adrenergic receptor at serine 247 by ERK MAP kinase drives lipolysis in obese adipocytes

ObjectiveThe inappropriate release of free fatty acids from obese adipose tissue stores has detrimental effects on metabolism, but key molecular mechanisms controlling FFA release from adipocytes remain undefined. Although obesity promotes systemic inflammation, we find activation of the inflammation-associated Mitogen Activated Protein kinase ERK occurs specifically in adipose tissues of obese mice, and provide evidence that adipocyte ERK activation may explain exaggerated adipose tissue lipolysis observed in obesity. Methods and ResultsWe provide genetic and pharmacological evidence that inhibition of the MEK/ERK pathway in human adipose tissue, mice, and flies all effectively limit adipocyte lipolysis. In complementary findings, we show that genetic and obesity-mediated activation of ERK enhances lipolysis, whereas adipose tissue specific knock-out of ERK2, the exclusive ERK1/2 protein in adipocytes, dramatically impairs lipolysis in explanted mouse adipose tissue. In addition, acute inhibition of MEK/ERK signaling also decreases lipolysis in adipose tissue and improves insulin sensitivity in obese mice. Mice with decreased rates of adipose tissue lipolysis in vivo caused by either MEK or ATGL pharmacological inhibition were unable to liberate sufficient White Adipose Tissue (WAT) energy stores to fuel thermogenesis from brown fat during a cold temperature challenge. To identify a molecular mechanism controlling these actions, we performed unbiased phosphoproteomic analysis of obese adipose tissue at different time points following acute pharmacological MEK/ERK inhibition. MEK/ERK inhibition decreased levels of adrenergic signaling and caused de-phosphorylation of the β3-adrenergic receptor (β3AR) on serine 247. To define the functional implications of this phosphorylation, we showed that CRISPR/Cas9 engineered cells expressing wild type β3AR exhibited β3AR phosphorylation by ERK2 and enhanced lipolysis, but this was not seen when serine 247 of β3AR was mutated to alanine. ConclusionTaken together, these data suggest that ERK activation in adipocytes and subsequent phosphorylation of the β3AR on S247 are critical regulatory steps in the enhanced adipocyte lipolysis of obesity.

Defining “FGF21 Resistance” during obesity: Controversy, criteria and unresolved questions

The term “FGF21 resistance” was first used to describe increased circulating FGF21 levels concomitant to decreased FGF21 receptor complex expression in white adipose tissue of obese mice. Since this initial report, the term has been associated with a wide range of pathological states, including human obesity, in which circulating FGF21 levels are elevated. However, the notion of “FGF21 resistance” has been controversial partly due to difficulty in delineating the mechanisms underlying the physiological versus pharmacological effects of FGF21. Here, key aspects of the term “FGF21 resistance” are discussed including; the origin and experimental context surrounding the term “FGF21 resistance”, new criteria for evaluating FGF21 sensitivity in vivo and finally, crucial unresolved questions regarding the function of FGF21 during obesity.

Defining "FGF21 Resistance" during obesity: Controversy, criteria and unresolved questions.

The term "FGF21 resistance" was first used to describe increased circulating FGF21 levels concomitant to decreased FGF21 receptor complex expression in white adipose tissue of obese mice. Since this initial report, the term has been associated with a wide range of pathological states, including human obesity, in which circulating FGF21 levels are elevated. However, the notion of "FGF21 resistance" has been controversial partly due to difficulty in delineating the mechanisms underlying the physiological versus pharmacological effects of FGF21. Here, key aspects of the term "FGF21 resistance" are discussed including; the origin and experimental context surrounding the term "FGF21 resistance", new criteria for evaluating FGF21 sensitivity in vivo and finally, crucial unresolved questions regarding the function of FGF21 during obesity.

Modulation of the IL-33/IL-13 Axis in Obesity by IL-13Rα2.

In obesity, IL-13 overcomes insulin resistance by promoting anti-inflammatory macrophage differentiation in adipose tissue. Endogenous IL-13 levels can be modulated by the IL-13 decoy receptor, IL-13Rα2, which inactivates and depletes the cytokine. In this study, we show that IL-13Rα2 is markedly elevated in adipose tissues of obese mice. Mice deficient in IL-13Rα2 had high expression of IL-13 response markers in adipose tissue, consistent with increased IL-13 activity at baseline. Moreover, exposure to the type 2 cytokine-inducing alarmin, IL-33, enhanced serum and tissue IL-13 concentrations and elevated tissue eosinophils, macrophages, and type 2 innate lymphoid cells. IL-33 also reduced body weight, fat mass, and fasting blood glucose levels. Strikingly, however, the IL-33-induced protection was greater in IL-13Rα2-deficient mice compared with wild-type littermates, and these changes were largely attenuated in mice lacking IL-13. Although IL-33 administration improved the metabolic profile in the context of a high fat diet, it also resulted in diarrhea and perianal irritation, which was enhanced in the IL-13Rα2-deficient mice. Weight loss in this group was associated with reduced food intake, which was likely related to the gastrointestinal effects. These findings outline both potentially advantageous and deleterious effects of a type 2-skewed immune response under conditions of metabolic stress, and identify IL-13Rα2 as a critical checkpoint in adipose tissues that limits the protective effects of the IL-33/IL-13 axis in obesity.

Toll‑like receptor 2 mediates deposition of collagen I in adipose tissue of high fat diet‑induced obese mice.

Obesity is marked by deposition of collagenI in adipose tissue. Toll like receptor(TLR)2 is involved in lipid metabolism, however the association between TLR2 and collagenI remains unclear. The present study was designed to investigate the effect of TLR2 knockout on collagen I in adipose tissue in obese mice. TLR2 knockout and C57BL/6J mice (aged 4weeks) were fed normal chow or a high‑fat‑diet for 16weeks. Compared with adipose tissue from lean controls, that from C57BL/6J mice fed a high‑fat diet had increased levels of collagenI, TIMP1 and TGFβ1 and lower levels of MMP1. However, adipose tissue from TLR2 knockout mice fed a high‑fat diet revealed decreased levels of collagen I, TIMP metallopeptidase inhibitor(TIMP)1, and transforming growth factor(TGF)β1, in addition to increased levels of matrix metallopeptidase(MMP)1. These findings suggest that, in the adipose tissue of obese mice, TLR2 is involved in the metabolism of collagen I and may exhibit a role in the metabolism of MMP1, TIMP1 and TGFβ1.

Raspberry Supplementation Improves Insulin Signaling and Promotes Brown-Like Adipocyte Development in White Adipose Tissue of Obese Mice.

Excessive lipid accumulation in white adipose tissue (WAT) leads to chronic inflammation and metabolic dysfunction. Raspberry (RB) contains high amount of polyphenols and dietary fibers. The objective of the study is to evaluate the effects of RB supplementation on WAT morphology, inflammation, and insulin signaling in high fat diet (HFD)-induced obese mice, and further explore the underlying mechanisms. C57BL/6J mice are fed with a control diet or a HFD supplemented with 0 or 5% freeze dried RB for 12 weeks. RB supplementation decreases WAT hypertrophy induced by HFD and suppresses pro-inflammatory cytokines expression and macrophage infiltration in WAT. Meanwhile, RB addition improves insulin sensitivity of HFD-mice. Additionally, RB supplementation drives the browning of WAT (beige adipogenesis), which is associated with elevated PGC-1α and FNDC5/irisin contents. Consistently, the content of beige adipocyte markers including UCP1, PRDM16, Cytochrome C, Cidea, and Elvol3 is enhanced in HFD-mice, which are correlated with increased AMPK phosphorylation and Sirt1 protein contents. Dietary RB attenuated adipocyte hypertrophy and inflammation of WAT in HFD-mice and improves insulin sensitivity and beige adipogenesis, which is associated with increased FNDC5/irisin content and activation of AMPK/Sirt1 pathway. RB supplementation provides a promising strategy to prevent diet-induced obesity.