Thematic review series: Adipocyte Biology. Adipocyte stress: the endoplasmic reticulum and metabolic disease

Differential scales of protein quality control

Proteins are notorious for their unpleasant behavior-continually at risk of misfolding, collecting damage, aggregating, and causing toxicity and disease. To counter these challenges, cells have evolved elaborate chaperone and quality control networks that can resolve damage at the level of the protein, organelle, cell, or tissue. On the smallest scale, the integrity of individual proteins is monitored during their synthesis. On a larger scale, cells use compartmentalized defenses and networks of communication, capable sometimes of signaling between cells, to respond to changes in the proteome's health. Together, these layered defenses help protect cells from damaged proteins.

Paraoxonases and chemokine (C-C motif) ligand-2 in noncommunicable diseases

Oxidative stress and inflammation underpin most diseases; their mechanisms are inextricably linked. Chronic inflammation is associated with oxidation, anti-inflammatory cascades are linked to decreased oxidation, increased oxidative stress triggers inflammation, and redox balance inhibits the inflammatory cellular response. Whether or not oxidative stress and inflammation represent the cause or consequence of cellular pathology, they contribute significantly to the pathogenesis of noncommunicable diseases (NCD). The incidence of obesity and other related metabolic disturbances are increasing, as are age-related diseases due to a progressively aging population. Relationships between oxidative stress, inflammatory signaling, and metabolism are, in the broad sense of energy transformation, being increasingly recognized as part of the problem in NCD. In this chapter, we summarize the pathologic consequences of an imbalance between circulating and cellular paraoxonases, the system for scavenging excessive reactive oxygen species and circulating chemokines. They act as inducers of migration and infiltration of immune cells in target tissues as well as in the pathogenesis of disease that perturbs normal metabolic function. This disruption involves pathways controlling lipid and glucose homeostasis as well as metabolically driven chronic inflammatory states that encompass several response pathways. Dysfunction in the endoplasmic reticulum and/or mitochondria represents an important feature of chronic disease linked to oxidation and inflammation seen as self-reinforcing in NCD. Therefore, correct management requires a thorough understanding of these relationships and precise interpretation of laboratory test results.

Adipose tissue and liver metabolic responses to different levels of dietary carbohydrates in gilthead sea bream (Sparus aurata)

This study analyzes the effects of replacing dietary lipids by carbohydrates and carbohydrates by fiber on gilthead sea bream growth, as well as lipid and glucose metabolism in adipose tissue and liver over the course of a 15-week feeding trial. Six different diets were formulated and fish were classified into two experimental groups sharing one diet. In the first group (LS), fish were fed four diets where lipids were reduced (23%-17%) by increasing carbohydrates (12%-28%) and, the second group (SF) consisted on three diets where the amount of carbohydrates (28%-11%) was exchanged at expenses of fiber (1%-18%). Differences in growth were not observed; nevertheless, the hepatosomatic index was positively related to dietary starch levels, apparently not due to enhanced hepatic lipogenesis, partly supported by unchanged G6PDH expression. In the LS group, lipogenic activity of adipose tissue was stimulated with low-lipid/high-carbohydrate diets by up-regulating G6PDH expression and a tendency to increase FAS, and promoted carbohydrate utilization versus fatty acid oxidation by modulating the transcription factors LXRα, PPARα and PPARβ expression. In the SF group, PPARs and LXRα increased parallel to fiber levels in adipose tissue. Furthermore, an adaptation of hepatic GK to dietary starch inclusion was observed in both groups; however, the lack of effects on G6Pase expression indicated that gluconeogenesis was not nutritionally regulated under the conditions examined. Overall, metabolic adaptations directed to an efficient use of dietary carbohydrates are present in gilthead sea bream, supporting the possibility of increasing carbohydrate or fiber content in diets for aquaculture sustainability.

Atherothrombotic risk in obesity

A link between obesity and coronary artery disease development has been repeatedly proposed, possibly in part due to the development of a proinflammatory and prothrombotic state in obese subjects. Adipocytes secrete numerous hormones and cytokines (adipokines) which influence gene expression and cell functions in endothelial cells, arterial smooth muscle cells, and monocytes/macrophages favouring the development of an atherosclerotic vulnerable plaque. Moreover, the release of such biologically active molecules also promotes endothelial function impairment, disturbs the haemostatic and fibrinolytic systems, and produces alterations in platelet function affecting the initiation, progression, and stabilization of thrombus formation upon atherosclerotic plaque rupture. In this review we will discuss the pathophysiological mechanisms by which obesity contributes to increase atherothrombosis paying special attention to its effects over thrombosis.

Evolving concepts in the pathogenesis of NASH: beyond steatosis and inflammation

Non-alcoholic steatohepatitis (NASH) is characterised by hepatic steatosis and inflammation and, in some patients, progressive fibrosis leading to cirrhosis. An understanding of the pathogenesis of NASH is still evolving but current evidence suggests multiple metabolic factors critically disrupt homeostasis and induce an inflammatory cascade and ensuing fibrosis. The mechanisms underlying these changes and the complex inter-cellular interactions that mediate fibrogenesis are yet to be fully elucidated. Lipotoxicity, in the setting of excess free fatty acids, obesity, and insulin resistance, appears to be the central driver of cellular injury via oxidative stress. Hepatocyte apoptosis and/or senescence contribute to activation of the inflammasome via a variety of intra- and inter-cellular signalling mechanisms leading to fibrosis. Current evidence suggests that periportal components, including the ductular reaction and expansion of the hepatic progenitor cell compartment, may be involved and that the Th17 response may mediate disease progression. This review aims to provide an overview of the pathogenesis of NASH and summarises the evidence pertaining to key mechanisms implicated in the transition from steatosis and inflammation to fibrosis. Currently there are limited treatments for NASH although an increasing understanding of its pathogenesis will likely improve the development and use of interventions in the future.

Hypoxia and adipocyte physiology: implications for adipose tissue dysfunction in obesity

Hypoxia develops in white adipose tissue in obese mice, resulting in changes in adipocyte function that may underpin the dysregulation that leads to obesity-associated disorders. Whether hypoxia occurs in adipose tissue in human obesity is unclear, with recent studies contradicting earlier reports that this was the case. Adipocytes, both murine and human, exhibit extensive functional changes in culture in response to hypoxia, which alters the expression of up to 1,300 genes. These include genes encoding key adipokines such as leptin, interleukin (IL)-6, vascular endothelial growth factor (VEGF), and matrix metalloproteinase-2 (MMP-2), which are upregulated, and adiponectin, which is downregulated. Hypoxia also inhibits the expression of genes linked to oxidative metabolism while stimulating the expression of genes associated with glycolysis. Glucose uptake and lactate release by adipocytes are both stimulated by hypoxia, and insulin sensitivity falls. Preadipocytes and macrophages in adipose tissue also respond to hypoxia. The hypoxia-signaling pathway may provide a new target for the treatment of obesity-associated disorders.

Activating transcription factor 4 regulates adipocyte differentiation via altering the coordinate expression of CCATT/enhancer binding protein β and peroxisome proliferator-activated receptor γ

Adipose tissue is crucial for energy homeostasis and is a topic interest with respect to investigating the regulation of adipose tissue formation for the ever-increasing health concerns of obesity and type 2 diabetes. Adipocyte differentiation is tightly regulated by the characteristic sequential expression change of adipocyte genes, including members of the CCATT/enhancer binding protein (C/EBP) family of transcription factors, peroxisome proliferator-activated receptor γ and tribbles homolog 3. In the present study, we demonstrate that C/EBPβ and peroxisome proliferator-activated receptor γ (but not tribbles homolog 3) are targeted for activation by activating transcription factor 4 (ATF4), a member of cAMP response element-binding/activator transcription factor family. Importantly, overexpression of ATF4 in 3T3-L1 cells enhanced adipogenesis, whereas small-interfering ATF4 blocked conversion of preadipocytes to adipocytes. These findings were accomplished by altering the coordinate expression of adipogenic transcription factors. Taken together, our results suggest that ATF4 is a positive regulator of adipocyte differentiation. This notion is also supported by the results of the present study showing that the expression of ATF4 is induced during adipocyte differentiation. Thus, ATF4 could be an important regulator of energy homeostasis.

Insulin regulates the unfolded protein response in human adipose tissue

Endoplasmic reticulum (ER) stress is increased in obesity and is postulated to be a major contributor to many obesity-related pathologies. Little is known about what causes ER stress in obese people. Here, we show that insulin upregulated the unfolded protein response (UPR), an adaptive reaction to ER stress, in vitro in 3T3-L1 adipocytes and in vivo, in subcutaneous (sc) adipose tissue of nondiabetic subjects, where it increased the UPR dose dependently over the entire physiologic insulin range (from ∼ 35 to ∼ 1,450 pmol/L). The insulin-induced UPR was not due to increased glucose uptake/metabolism and oxidative stress. It was associated, however, with increased protein synthesis, with accumulation of ubiquitination associated proteins, and with multiple posttranslational protein modifications (acetylations, methylations, nitrosylations, succinylation, and ubiquitinations), some of which are potential causes for ER stress. These results reveal a new physiologic role of insulin and provide a putative mechanism for the development of ER stress in obesity. They may also have clinical and therapeutic implications, e.g., in diabetic patients treated with high doses of insulin.

The effect of inhibition of endoplasmic reticulum stress on lipolysis in white adipose tissue in a rat model of chronic kidney disease

AIM

Lipolysis in fat tissue plays an important role in the development of metabolic disturbances, a characteristic feature of chronic kidney disease (CKD). In the present study, we tested the hypothesis that the inhibition of endoplasmic reticulum (ER) stress could alleviate lipolysis in white adipose tissue in a rat model of CKD.

METHODS

A rat model of CKD was established by a method of reduced renal mass (RRM). Lipolysis was measured as the release of glycerol in ex vivo fat pads and cultured primary adipocytes. The activity of lipases and markers of ER stress were measured by Western blotting and immunoprecipitation.

RESULTS

Our data showed that lipolysis in visceral white adipose tissue was increased in RRM rats compared with control rats. In addition, increased phosphorylation of hormone-sensitive lipase (HSL) and binding of adipose triglyceride lipase (ATGL) to comparative gene identification-58 (CGI-58) protein were observed in the RRM rats. The phosphorylation of ER stress markers, including IRE1α, PERK, and eukaryotic initiation factor (eIF) 2α, and the expression of ER stress marker 78 kDa glucose-regulated protein (GRP78) were significantly increased in RRM rats. Treatment with an inhibitor of ER stress partially but significantly alleviated lipolysis, and this alleviation was accompanied by reduced binding of ATGL to CGI-58.

CONCLUSION

Our results showed that enhanced lipolysis and ER stress occurred in visceral white adipose tissue in a rat model of CKD. Moreover, inhibition of ER stress significantly alleviated lipolysis. These findings suggest that ER stress is a potential therapeutic target for the metabolic disturbances associated with CKD.

Astaxanthin reduces hepatic endoplasmic reticulum stress and nuclear factor-κB-mediated inflammation in high fructose and high fat diet-fed mice

We recently showed that astaxanthin (ASX), a xanthophyll carotenoid, activates phosphatidylinositol 3-kinase pathway of insulin signaling and improves glucose metabolism in liver of high fructose-fat diet (HFFD)-fed mice. The aim of this study is to investigate whether ASX influences phosphorylation of c-Jun-N-terminal kinase 1 (JNK1), reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, and inflammation in liver of HFFD-fed mice. Adult male Mus musculus mice were fed either with control diet or HFFD for 15 days. After this period, mice in each group were divided into two and administered ASX (2 mg/kg/day, p.o) in 0.3 ml olive oil or 0.3 ml olive oil alone for the next 45 days. At the end of 60 days, liver tissue was excised and examined for lipid accumulation (Oil red O staining), intracellular ROS production, ER stress, and inflammatory markers. Elevated ROS production, lipid accumulation, and increased hepatic expression of ER stress markers such as Ig-binding protein, PKR-like ER kinase, phosphorylated eukaryotic initiation factor 2α, X-box binding protein 1, activating transcription factor 6, and the apoptotic marker caspase 12 were observed in the liver of the HFFD group. ASX significantly reversed these changes. This reduction was accompanied by reduced activation of JNK1 and I kappa B kinase β phosphorylation and nuclear factor-kappa B p65 nuclear translocation in ASX-treated HFFD mice. These findings suggest that alleviation of inflammation and ER stress by ASX could be a mechanism responsible for its beneficial effect in this model. ASX could be a promising treatment strategy for insulin resistant patients.

The role of tauroursodeoxycholic acid on adipogenesis of human adipose-derived stem cells by modulation of ER stress

Obesity has become a serious public health problem in the developed world. Increased mass of adipose tissue in the obese is due to an increase in both the size (hypertrophy) and number (hyperplasia) of adipocytes. The chemical chaperone tauroursodeoxycholic acid (TUDCA) not only decreases endoplasmic reticulum (ER) stress, but also plays a role as a leptin-sensitizing agent for preadipocytes in mice and humans. In this study, we examine whether TUDCA has an effect on adipogenesis from human adipose-derived stem cells (hASCs). Therefore, the effect of TUDCA on ER stress, lipid accumulation, and adipogenic differentiation from hASCs was investigated using histological staining, reverse-transcriptase polymerase chain reaction (RT-PCR), and western blotting in vitro. It was found that TUDCA treatment of hASCs significantly decreases the representative ER stress marker (glucose-regulated protein 78 kDa (GRP78)), adipogenic markers (peroxisome proliferator-activated receptor gamma (PPARγ) and glycerol-3-phosphate dehydrogenase 1 (GPDH)), and lipid accumulation. Furthermore, we confirmed that TUDCA treatment of hASCs significantly decreased in vivo adipogenic tissue formation and ER stress comparing with PBS treatment of hASCs. The results indicate that TUDCA plays a critical role in adipogenesis from hASCs by modulating ER stress and, therefore, has potential pharmacologic and therapeutic applications as an anti-obesity agent.

The influence of EPA and DHA on markers of inflammation in 3T3-L1 cells at different stages of cellular maturation

BACKGROUND

EPA and DHA have been reported to have anti-obesity and anti-inflammatory properties. Recent studies revealed that these positive actions of n-3 PUFA at least partially are connected with their influence on metabolism and secretory functions of the adipose tissue. However, their impact on old adipocytes is still poorly understood. Therefore the aim of the present study was to evaluate the influence of EPA and DHA on markers of inflammation in 3T3-L1 cells at different stages of cellular maturation.

METHODS

Young, mature and old differentiated 3T3-L1 adipocytes were cultured for 48 h in the presence of 100 μM EPA, or 50 μM DHA complexed to albumin, whereas in control conditions only albumin was added to the medium. The Oil Red O staining was used to confirm adipocytes differentiation, and measure triglycerides content in cells. The concentration of adipokines (interleukin 6, adiponectin and leptin) in conditioned media was measured using mouse-specific ELISA kits.

RESULTS

The fat accumulation in 3T3-L1 adipocytes was positively correlated with their age; however, EPA and DHA did not affect lipid accumulation on any stage of maturation. EPA and DHA increased the concentration of secreted adiponectin when compared with control, but only in the case of young adipocytes (58% and 35%, respectively). Moreover, EPA supplementation increased interleukin 6 concentration in conditioned medium, while DHA exerted an opposite effect on all stages of cellular maturation. Furthermore, EPA treatment increased leptin release from young cells, while DHA did not affect the secretion of this adipokine. In mature 3T3-L1 adipocytes both experimental factors decreased synthesis of leptin; however, in old cells no impact of these PUFA was noted.

CONCLUSIONS

In summary, age is an important determinant of fat accumulation in adipocytes and affects adipokines secretion by these cells. Moreover, the impact of investigated fatty acids: EPA and DHA on fat cells varies depending on the stage of maturation, and seems to be stronger in young cells than in mature and old ones. Docosahexaenoic acid exerts an anti-inflammatory action; however, on the basis of the obtained data it was not possible to determine whether eicosapentaenoic acid shows anti- or pro-inflammatory properties.

Ursodeoxycholic acid but not tauroursodeoxycholic acid inhibits proliferation and differentiation of human subcutaneous adipocytes

Stress of endoplasmic reticulum (ERS) is one of the molecular triggers of adipocyte dysfunction and chronic low inflammation accompanying obesity. ERS can be alleviated by chemical chaperones from the family of bile acids (BAs). Thus, two BAs currently used to treat cholestasis, ursodeoxycholic and tauroursodeoxycholic acid (UDCA and TUDCA), could potentially lessen adverse metabolic effects of obesity. Nevertheless, BAs effects on human adipose cells are mostly unknown. They could regulate gene expression through pathways different from their chaperone function, namely through activation of farnesoid X receptor (FXR) and TGR5, G-coupled receptor. Therefore, this study aimed to analyze effects of UDCA and TUDCA on human preadipocytes and differentiated adipocytes derived from paired samples of two distinct subcutaneous adipose tissue depots, abdominal and gluteal. While TUDCA did not alter proliferation of cells from either depot, UDCA exerted strong anti-proliferative effect. In differentiated adipocytes, acute exposition to neither TUDCA nor UDCA was able to reduce effect of ERS stressor tunicamycin. However, exposure of cells to UDCA during whole differentiation process decreased expression of ERS markers. At the same time however, UDCA profoundly inhibited adipogenic conversion of cells. UDCA abolished expression of PPARγ and lipogenic enzymes already in the early phases of adipogenesis. This anti-adipogenic effect of UDCA was not dependent on FXR or TGR5 activation, but could be related to ability of UDCA to sustain the activation of ERK1/2 previously linked with PPARγ inactivation. Finally, neither BAs did lower expression of chemokines inducible by TLR4 pathway, when UDCA enhanced their expression in gluteal adipocytes. Therefore while TUDCA has neutral effect on human preadipocytes and adipocytes, the therapeutic use of UDCA different from treating cholestatic diseases should be considered with caution because UDCA alters functions of human adipose cells.

Programmed cell death-4 deficiency prevents diet-induced obesity, adipose tissue inflammation, and insulin resistance

Programmed cell death-4 (PDCD4), a selective protein translation inhibitor, has shown proinflammatory effect in some inflammatory diseases, but its roles in obesity remain unestablished. This study aims to investigate the effects of PDCD4 on obesity, inflammation, and insulin resistance. Surprisingly, high-fat diet (HFD)-fed PDCD4-deficient (PDCD4(-/-)) mice exhibited an absolutely lean phenotype together with improved insulin sensitivity. Compared with wild-type obese mice, HFD-fed PDCD4(-/-) mice showed higher energy expenditure, lower epididymal fat weight, and reduced macrophage infiltration inflammatory cytokine secretion in white adipose tissue (WAT). Alleviated hepatic steatosis along with decreased plasma levels of triglyceride and cholesterol was also observed in these mice. Importantly, PDCD4 appeared to disturb lipid metabolism via inhibiting the expression of liver X receptor (LXR)-α, a master modulator of lipid homeostasis, which was elevated in HFD-fed PDCD4(-/-) mice accompanied by upregulation of its target genes and relieved endoplasmic reticulum stress in WAT. These data demonstrate that PDCD4 deficiency protects mice against diet-induced obesity, WAT inflammation, and insulin resistance through restoring the expression of LXR-α, thereby proposing PDCD4 as a potential target for treating obesity-associated diseases.

Human insulin resistance is associated with increased plasma levels of 12α-hydroxylated bile acids

Bile acids (BAs) exert pleiotropic metabolic effects, and physicochemical properties of different BAs affect their function. In rodents, insulin regulates BA composition, in part by regulating the BA 12α-hydroxylase CYP8B1. However, it is unclear whether a similar effect occurs in humans. To address this question, we examined the relationship between clamp-measured insulin sensitivity and plasma BA composition in a cohort of 200 healthy subjects and 35 type 2 diabetic (T2D) patients. In healthy subjects, insulin resistance (IR) was associated with increased 12α-hydroxylated BAs (cholic acid, deoxycholic acid, and their conjugated forms). Furthermore, ratios of 12α-hydroxylated/non-12α-hydroxylated BAs were associated with key features of IR, including higher insulin, proinsulin, glucose, glucagon, and triglyceride (TG) levels and lower HDL cholesterol. In T2D patients, BAs were nearly twofold elevated, and more hydrophobic, compared with healthy subjects, although we did not observe disproportionate increases in 12α-hydroxylated BAs. In multivariate analysis of the whole dataset, controlling for sex, age, BMI, and glucose tolerance status, higher 12α-hydroxy/non-12α-hydroxy BA ratios were associated with lower insulin sensitivity and higher plasma TGs. These findings suggest a role for 12α-hydroxylated BAs in metabolic abnormalities in the natural history of T2D and raise the possibility of developing insulin-sensitizing therapeutics based on manipulations of BA composition.

Very low density lipoprotein receptor (VLDLR) expression is a determinant factor in adipose tissue inflammation and adipocyte-macrophage interaction

Obesity is associated with adipose tissue remodeling, characterized by adipocyte hypertrophy and macrophage infiltration. Previously, we have shown that very low density lipoprotein receptor (VLDLR) is virtually absent in preadipocytes but is strongly induced during adipogenesis and actively participates in adipocyte hypertrophy. In this study, we investigated the role of VLDLR in adipose tissue inflammation and adipocyte-macrophage interactions in wild type and VLDLR-deficient mice fed a high fat diet. The results show that VLDLR deficiency reduced high fat diet-induced inflammation and endoplasmic reticulum (ER) stress in adipose tissue in conjunction with reduced macrophage infiltration, especially those expressing pro-inflammatory markers. In adipocyte culture, VLDLR deficiency prevented adipocyte hypertrophy and strongly reduced VLDL-induced ER stress and inflammation. Likewise, cultures of primary peritoneal macrophages show that VLDLR deficiency reduced lipid accumulation and inflammation but did not alter chemotactic response of macrophages to adipocyte signals. Moreover, VLDLR deficiency tempered the synergistic inflammatory interactions between adipocytes and macrophages in a co-culture system. Collectively, these results show that VLDLR contributes to adipose tissue inflammation and mediates VLDL-induced lipid accumulation and induction of inflammation and ER stress in adipocytes and macrophages.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Differential responses of hepatic endoplasmic reticulum stress and inflammation in diet-induced obese rats with high-fat diet rich in lard oil or soybean oil

Scopes

To investigate the effects of high-fat diet enriched with lard oil or soybean oil on liver endoplasmic reticulum (ER) stress and inflammation markers in diet-induced obese (DIO) rats and estimate the influence of following low-fat diet feeding.

Methods and Results

Male SD rats were fed with standard low-fat diet (LF, n = 10) and two isoenergentic high-fat diets enriched with lard (HL, n = 45) or soybean oil (HS, n = 45) respectively for 10 weeks. Then DIO rats from HL and HS were fed either high-fat diet continuously (HL/HL, HS/HS) or switched to low-fat diet (HL/LF, HS/LF) for another 8 weeks. Rats in control group were maintained with low-fat diet. Body fat, serum insulin level, HOMA-IR and ectopic lipid deposition in liver were increased in HL/HL and HS/HS compared to control, but increased to a greater extent in HL/HL compared to HS/HS. Markers of ER stress including PERK and CHOP protein expression and phosphorylation of eIF2α were significantly elevated in HL/HL group while phosphorylation of IRE1α and GRP78 protein expression were suppressed in both HL/HL and HS/HS. Besides, inflammatory signals (OPN, TLR2, TLR4 and TNF-α) expressions significantly increased in HL/HL compared to others. Switching to low-fat diet reduced liver fat deposition, HOMA-IR, mRNA expression of TLR4, TNF-α, PERK in both HL/LF and HS/LF, but only decreased protein expression of OPN, PERK and CHOP in HL/LF group. In addition, HL/LF and HS/LF exhibited decreased phosphorylation of eIF2α and increased phosphorylation of IRE1α and GRP78 protein expression when compared with HL/HL and HS/HS respectively.

Conclusions

Lard oil was more deleterious in insulin resistance and hepatic steatosis via promoting ER stress and inflammation responses in DIO rats, which may be attributed to the enrichment of saturated fatty acid. Low-fat diet was confirmed to be useful in recovering from impaired insulin sensitivity and liver fat deposition in this study.

Vasoactive effects of prostaglandins from the perivascular fat of mesenteric resistance arteries in WKY and SHROB rats

AIMS

We have studied the vasoactive role of prostaglandins derived from perivascular adipose tissue (PVAT) and their effects on endothelial function in healthy rats and rats with metabolic syndrome (SHROB).

MAIN METHODS

Mesenteric resistance arteries (MRA) from SHROB and control rats (WKY) were mounted on wire myographs: a) together with a sphere of naturally occurring perivascular adipose tissue (with-PVAT group), or b) dissecting all the adventitial tissue (without-PVAT group).

KEY FINDINGS

Endothelial function, tested by acetylcholine reactivity of SHROB arteries with PVAT, was significantly lower than that of WKY. With-PVAT arteries, especially the SHROB, showed lower responses than those without PVAT. NO synthase inhibition diminished the acetylcholine responses in every group except the with-PVAT SHROB group. Blockade of cyclooxygenase-2, PGI2-IP, TXA2-TP, or TXA2 synthase increased to different extents the arterial responses in the SHROB with-PVAT group. PVAT from both rat strains revealed cyclooxygenase-2 activity and immunoassay confirmed the release of PGE2, PGI2 and TXA2.

SIGNIFICANCE

Our major finding is that PVAT is a source of vasoactive prostaglandins in WKY and SHROB. We also report that the presence of visceral PVAT causes endothelial dysfunction of resistance arteries in the SHROB. The vascular responses to prostaglandins partly underlie the endothelial dysfunction of SHROB arteries.

A chromatin immunoprecipitation (ChIP) protocol for use in whole human adipose tissue

Chromatin immunoprecipitation (ChIP) has become a central method when studying in vivo protein-DNA interactions, with the major challenge being the hope to capture "authentic" interactions. While ChIP protocols have been optimized for use with specific cell types and tissues including adipose tissue-derived cells, a working ChIP protocol addressing the challenges imposed by fresh whole human adipose tissue has not been described. Utilizing human paired omental and subcutaneous adipose tissue obtained during elective abdominal surgeries, we have carefully identified and optimized individual steps in the ChIP protocol employed directly on fresh tissue fragments. We describe a complete working protocol for using ChIP on whole adipose tissue fragments. Specific steps required adaptation of the ChIP protocol to human whole adipose tissue. In particular, a cross-linking step was performed directly on fresh small tissue fragments. Nuclei were isolated before releasing chromatin, allowing better management of fat content; a sonication protocol to obtain fragmented chromatin was optimized. We also demonstrate the high sensitivity of immunoprecipitated chromatin from adipose tissue to freezing. In conclusion, we describe the development of a ChIP protocol optimized for use in studying whole human adipose tissue, providing solutions for the unique challenges imposed by this tissue. Unraveling protein-DNA interaction in whole human adipose tissue will likely contribute to elucidating molecular pathways contributing to common human diseases such as obesity and type 2 diabetes.

Rutaecarpine analogues reduce lipid accumulation in adipocytes via inhibiting adipogenesis/lipogenesis with AMPK activation and UPR suppression

Obesity is characterized by expansion of adipose tissue, which results from an increase in adipocyte number (adipogenesis) and adipocyte size (lipogenesis). A reversal of these processes has been suggested to be a potential antiobetic therapy. Rutaecarpine (Rut) and its novel analogues (R17 and R18) were identified to exert potent effect in reducing lipid accumulation during adipocyte differentiation in 3T3-L1 adipocytes with little cytotoxicity. All three compounds reduced lipid accumulation in a dose-dependent manner, while R17 and R18 exhibited much more potent inhibitory effects compared to that of Rut. Further studies showed that R17 suppressed both adipogenesis and lipogenesis during all stages of adipocyte differentiation as indicated by the reduced protein and mRNA levels of key regulators of adipogenesis/lipogenesis, including PPARγ, C/EBPα, SREBP-1c, ACC, FAS, and SCD-1. We next examined the effect of R17 on the UPR pathway and the results showed that the UPR markers (PERK, eIF2α, IRE1α, and spliced XBP1 mRNA) were all significantly reduced by R17. Further studies revealed that R17 persistently activated AMPK during differentiation, suggesting that the AMPK may be an upstream mechanism for the effect of R17 on adipogenesis and lipogenesis via the adipogenic/lipogenic markers and the UPR pathway. Finally, studies in fast/refeeding mice demonstrated that R17 administration was able to reduce epididymal fat mass and the levels of plasma TG and FFA in vivo. Our results suggest that rutaecarpine analogues may have therapeutic potential for obesity and related metabolic disorders. The mechanism involves the suppression of adipogenic/lipogenic proteins and the suppression of the UPR pathway possibly via the AMPK.

Protein tyrosine phosphatase 1B and insulin resistance: role of endoplasmic reticulum stress/reactive oxygen species/nuclear factor kappa B axis

Obesity-induced endoplasmic reticulum (ER) stress has been proposed as an important pathway in the development of insulin resistance. Protein-tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin signaling and is tethered to the ER-membrane. The aim of the study was to determine the mechanisms involved in the crosstalk between ER-stress and PTP1B. PTP1B whole body knockout and C57BL/6J mice were subjected to a high-fat or normal chow-diet for 20 weeks. High-fat diet feeding induced body weight gain, increased adiposity, systemic glucose intolerance, and hepatic steatosis were attenuated by PTP1B deletion. High-fat diet- fed PTP1B knockout mice also exhibited improved glucose uptake measured using [(3)H]-2-deoxy-glucose incorporation assay and Akt phosphorylation in the skeletal muscle tissue, compared to their wild-type control mice which received similar diet. High-fat diet-induced upregulation of glucose-regulated protein-78, phosphorylation of eukaryotic initiation factor 2α and c-Jun NH2-terminal kinase-2 were significantly attenuated in the PTP1B knockout mice. Mice lacking PTP1B showed decreased expression of the autophagy related protein p62 and the unfolded protein response adaptor protein NCK1 (non-catalytic region of tyrosine kinase). Treatment of C2C12 myotubes with the ER-stressor tunicamycin resulted in the accumulation of reactive oxygen species (ROS), leading to the activation of protein expression of PTP1B. Furthermore, tunicamycin-induced ROS production activated nuclear translocation of NFκB p65 and was required for ER stress-mediated expression of PTP1B. Our data suggest that PTP1B is induced by ER stress via the activation of the ROS-NFκB axis which is causes unfolded protein response and mediates insulin resistance in the skeletal muscle under obese condition.

Stop feeding cancer: pro-inflammatory role of visceral adiposity in liver cancer

Liver cancer is the fifth most common cancer in the world with an estimated over half a million new cases diagnosed every year. Due to the difficulty in early diagnosis and lack of treatment options, the prevalence of liver cancer continues to climb with a 5-year survival rate of between 6% and 11%. Coinciding with the rise of liver cancer, the prevalence of obesity has rapidly increased over the past two decades. Evidence from epidemiological studies demonstrates a higher risk of hepatocellular carcinoma (HCC) in obese individuals. Obesity is recognised as a low-grade inflammatory disease, this is of particular relevance as inflammation has been proposed as the seventh hallmark of cancer development with abdominal visceral adiposity considered as an important source of pro-inflammatory stimuli. Emerging evidence points towards the direct role of visceral adipose tissue rather than generalised body fat in carcinogenesis. Cytokines such as IL-6 and TNF-α secreted from visceral adipose tissue have been demonstrated to induce a chronic inflammatory condition predisposing the liver to a protumourigenic milieu. This review focuses on excess visceral adiposity rather than simple obesity; particularly adipokines and their implications for chronic inflammation, lipid accumulation, insulin resistance, Endoplasmic Reticulum (ER) stress and angiogenesis. Evidence of molecular signalling pathways that may give rise to the onset and progression of HCC in this context are depicted. Delineation of the pro-inflammatory role of visceral adiposity in liver cancer and its targeting will provide better rational and therapeutic approaches for HCC prevention and elimination. The concept of a central role for metabolism in cancer is the culmination of an effort that began with one of the 20th century's leading biochemists and Nobel laureate of 1931, Otto Warburg.

Cellular metabolic and autophagic pathways: traffic control by redox signaling

It has been established that the key metabolic pathways of glycolysis and oxidative phosphorylation are intimately related to redox biology through control of cell signaling. Under physiological conditions glucose metabolism is linked to control of the NADH/NAD redox couple, as well as providing the major reductant, NADPH, for thiol-dependent antioxidant defenses. Retrograde signaling from the mitochondrion to the nucleus or cytosol controls cell growth and differentiation. Under pathological conditions mitochondria are targets for reactive oxygen and nitrogen species and are critical in controlling apoptotic cell death. At the interface of these metabolic pathways, the autophagy-lysosomal pathway functions to maintain mitochondrial quality and generally serves an important cytoprotective function. In this review we will discuss the autophagic response to reactive oxygen and nitrogen species that are generated from perturbations of cellular glucose metabolism and bioenergetic function.

Nutritional mismatch in postnatal life of low birth weight rat offspring leads to increased phosphorylation of hepatic eukaryotic initiation factor 2 α in adulthood

OBJECTIVE

Epidemiological studies have established that low birth weight offspring, when faced with a nutritional mismatch in postnatal life, have an increased risk of developing the metabolic syndrome. Our laboratory and others have demonstrated that maternal protein restriction (MPR) leads to high cholesterol and insulin resistance in the offspring due to impaired liver function, though the underlying molecular mechanisms remain elusive. Recent in vitro studies have associated decreased phosphorylation of Akt1 (Serine 473), a marker of insulin sensitivity, with increased phosphorylation of eukaryotic initiation factor (eIF)-2α (Serine 51), a key regulator of protein translation attenuation. The main aim of the study was to determine whether nutritional mismatch in MPR offspring leads to elevated phospho-eIF2α (Ser51) levels in the liver.

MATERIALS/METHODS

To investigate if this occurs long-term in MPR offspring, pregnant Wistar rats were fed a control (20%) protein diet (control) or a low (8%) protein diet during pregnancy and postnatal life (LP1), or during pregnancy and lactation (LP2).

RESULTS

At postnatal day 130, LP2 offspring exhibited increases in hepatic phosphorylation of eIF2α (Ser51) concomitant with decreases in the phosphorylation of Akt1 (Ser473), while LP1 offspring exhibited the converse relationship. Interestingly, in embryonic day 19 livers derived from control or MPR pregnancy, no changes in eIF2α (Ser51) or Ak1 (Ser473) phosphorylation were observed.

CONCLUSION

Collectively, our data provide robust evidence that phosphorylation of eIF2α (Ser51) is inversely correlated with phosphorylated Akt1 (Ser473) in vivo. Moreover, this study demonstrates that this inverse relationship is adversely influenced in these MPR offspring by a mismatch in the postnatal nutritional environment.

Obesity, inflammation and diet

Obesity is a state in which there is an over-accumulation of subcutaneous and/or abdominal adipose tissue. This adipose tissue is no longer considered inert and mainly devoted to storing energy; it is emerging as an active tissue in the regulation of physiological and pathological processes, including immunity and inflammation. Adipose tissue produces and releases a variety of adipokines (leptin, adiponectin, resistin, and visfatin), as well as pro- and anti-inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-4, IL-6, and others). Adipose tissue is also implicated in the development of chronic metabolic diseases such as type 2 diabetes mellitus or cardiovascular disease. Obesity is thus an underlying condition for inflammatory and metabolic diseases. Diet or dietary patterns play critical roles in obesity and other pathophysiological conditions. A healthy diet and some nutrients are generally considered beneficial; however, some dietary nutrients are still considered controversial. In this article, dietary factors that influence inflammation associated with obesity are discussed.

Cryptosporidium parvum induces an endoplasmic stress response in the intestinal adenocarcinoma HCT-8 cell line

Invasion of human intestinal epithelial cells (HCT-8) by Cryptosporidium parvum resulted in a rapid induction of host cell spermidine/spermine N(1)-acetyltransferase 1 (hSSAT-1) mRNA, causing a 4-fold increase in SSAT-1 enzyme activity after 24 h of infection. In contrast, host cell SSAT-2, spermine oxidase, and acetylpolyamine oxidase (hAPAO) remained unchanged during this period. Intracellular polyamine levels of C. parvum-infected human epithelial cells were determined, and it was found that spermidine remained unchanged and putrescine increased by 2.5-fold after 15 h and then decreased after 24 h, whereas spermine decreased by 3.9-fold after 15 h. Concomitant with these changes, N(1)-acetylspermine and N(1)-acetylspermidine both increased by 115- and 24-fold, respectively. Increased SSAT-1 has previously been shown to be involved in the endoplasmic reticulum (ER) stress response leading to apoptosis. Several stress response proteins were increased in HCT-8 cells infected with C. parvum, including calreticulin, a major calcium-binding chaperone in the ER; GRP78/BiP, a prosurvival ER chaperone; and Nrf2, a transcription factor that binds to antioxidant response elements, thus activating them. However, poly(ADP-ribose) polymerase, a protein involved in DNA repair and programmed cell death, was decreased. Cumulatively, these results suggest that the invasion of HCT-8 cells by C. parvum results in an ER stress response by the host cell that culminates in overexpression of host cell SSAT-1 and elevated N(1)-acetylpolyamines, which can be used by a parasite that lacks ornithine decarboxylase.

Differential proinflammatory and oxidative stress response and vulnerability to metabolic syndrome in habitual high-fat young male consumers putatively predisposed by their genetic background

The current nutritional habits and lifestyles of modern societies favor energy overloads and a diminished physical activity, which may produce serious clinical disturbances and excessive weight gain. In order to investigate the mechanisms by which the environmental factors interact with molecular mechanisms in obesity, a pathway analysis was performed to identify genes differentially expressed in subcutaneous abdominal adipose tissue (SCAAT) from obese compared to lean male (21–35 year-old) subjects living in similar obesogenic conditions: habitual high fat dietary intake and moderate physical activity. Genes involved in inflammation (ALCAM, CTSB, C1S, YKL-40, MIF, SAA2), extracellular matrix remodeling (MMP9, PALLD), angiogenesis (EGFL6, leptin) and oxidative stress (AKR1C3, UCHL1, HSPB7 and NQO1) were upregulated; whereas apoptosis, signal transcription (CITED 2 and NR3C1), cell control and cell cycle-related genes were downregulated. Interestingly, the expression of some of these genes (C1S, SAA2, ALCAM, CTSB, YKL-40 and tenomodulin) was found to be associated with some relevant metabolic syndrome features. The obese group showed a general upregulation in the expression of inflammatory, oxidative stress, extracellular remodeling and angiogenic genes compared to lean subjects, suggesting that a given genetic background in an obesogenic environment could underlie the resistance to gaining weight and obesity-associated manifestations.

[Alterations in the protein content and dysfunction of high-density lipoproteins from hyperhomocysteinemic mice]

AIM

The aim of this study was to evaluate the proteic changes in high-density lipoproteins (HDL) induced by methionine-induced hyperhomocysteinemia in mice and its relationship with two of their main antiatherogenic properties.

METHODS AND RESULTS

The oral administration of methionine resulted in an elevation (~8 times) in the plasma concentration of homocysteine. Hyperhomocysteinemia was inversely correlated with the plasma concentration of HDL cholesterol and its main protein component of HDL, apolipoprotein (apo) A-I, respectively. The cholesterol efflux in vivo from macrophages to HDL was decreased in hyperhomocysteinemic mice compared with the control mice. However, the reverse cholesterol transport from macrophages to feces remained unchanged. On the other hand, the ability of HDL from hyperhomocysteinemic mice to prevent the oxidative modification of low-density lipoproteins (LDL) was found decreased and associated with a concomitant reduction in the plasma activity of paraoxonase-1 (PON1) and the plasma concentration of apoA-I, and with a relative reduction in the apoA-IV content (~1.5 times) in the hyperhomocysteinemic HDL, respectively.

CONCLUSION

The decrease in the ability of HDL from hyperhomocysteinemic mice to prevent LDL from oxidation was associated with a decrease in the apoA-I, PON1 and apoA-IV.

Mitochondrial fatty acid oxidation in obesity

SIGNIFICANCE

Current lifestyles with high-energy diets and little exercise are triggering an alarming growth in obesity. Excess of adiposity is leading to severe increases in associated pathologies, such as insulin resistance, type 2 diabetes, atherosclerosis, cancer, arthritis, asthma, and hypertension. This, together with the lack of efficient obesity drugs, is the driving force behind much research.

RECENT ADVANCES

Traditional anti-obesity strategies focused on reducing food intake and increasing physical activity. However, recent results suggest that enhancing cellular energy expenditure may be an attractive alternative therapy.

CRITICAL ISSUES

This review evaluates recent discoveries regarding mitochondrial fatty acid oxidation (FAO) and its potential as a therapy for obesity. We focus on the still controversial beneficial effects of increased FAO in liver and muscle, recent studies on how to potentiate adipose tissue energy expenditure, and the different hypotheses involving FAO and the reactive oxygen species production in the hypothalamic control of food intake.

FUTURE DIRECTIONS

The present review aims to provide an overview of novel anti-obesity strategies that target mitochondrial FAO and that will definitively be of high interest in the future research to fight against obesity-related disorders.

Chronic inflammation role in the obesity-diabetes association: a case-cohort study

BACKGROUND

Chronic inflammation is related to both obesity and diabetes. Our aim was to investigate to what extent this inflammation contributes to the association between obesity and diabetes.

METHODS

Using a case-cohort design, we followed 567 middle-aged individuals who developed diabetes and 554 who did not over 9 years within the ARIC Study. Weighted Cox proportional hazards analyses permitted statistical inference to the entire cohort.

RESULTS

Obese individuals (BMI≥30 kg/m2), compared to those with BMI<25 kg/m2, presented a large increased risk of developing diabetes (HR[obesity]=6.4, 95%CI 4.5-9.2), as did those in the highest (compared to the lowest) quartile of waist circumference (HR[waist]=8.3, 95%CI 5.6-12.3), in analyses adjusted for age, gender, ethnicity, study center, and parental history of diabetes. Notably, further adjustment for adiponectin and inflammation markers halved the magnitude of these associations (HR[obesity]=3.2, 95%CI 2.1-4.7; and HR[waist]=4.2, 95%CI 2.8-6.5). In similar modeling, attenuation obtained by adding fasting insulin, instead of these markers, was only slightly more pronounced HR[obesity]=2.7, 95%CI 1.7-4.1; and HR[waist]=3.6, 95%CI 2.3-5.8).

CONCLUSIONS

The marked decrease in the obesity-diabetes association after taking into account inflammation markers and adipokines indicates their major role in the pathways leading to adult onset of diabetes in obese individuals.

The role of chronic inflammation in obesity-associated cancers

There is a strong relationship between metabolism and immunity, which can become deleterious under conditions of metabolic stress. Obesity, considered a chronic inflammatory disease, is one example of this link. Chronic inflammation is increasingly being recognized as an etiology in several cancers, particularly those of epithelial origin, and therefore a potential link between obesity and cancer. In this review, the connection between the different factors that can lead to the chronic inflammatory state in the obese individual, as well as their effect in tumorigenesis, is addressed. Furthermore, the association between obesity, inflammation, and esophageal, liver, colon, postmenopausal breast, and endometrial cancers is discussed.

ER Stress and β-Cell Pathogenesis of Type 1 and Type 2 Diabetes and Islet Transplantation

Endoplasmic reticulum (ER) stress affects the pathogenesis of diabetes. ER stress plays important roles, both in type 1 and type 2 diabetes, because pancreatic β-cells possess highly developed ER for insulin secretion. This review summarizes the relationship between ER stress and the pathogenesis of type 1 and type 2 diabetes. In addition, the association between islet transplantation and ER stress is discussed.

Antioxidant system response is modified by dietary fat in adipose tissue of metabolic syndrome patients

Metabolic syndrome (MetS) is associated with high oxidative stress, which is caused by an increased expression of NADPH-oxidase and a decreased expression of antioxidant enzymes in the adipose tissue. Our aim was to evaluate whether the quality and quantity of dietary fat can modify that process. A randomized, controlled trial conducted within the LIPGENE study assigned MetS patients to one of four diets for 12 wk each: (i) high-saturated fatty acid (HSFA), (ii) high-monounsaturated fatty acid (HMUFA), (iii) and (iv) two low-fat, high-complex carbohydrate diet supplemented with n-3 polyunsaturated fatty acids (LFHCC n3), or placebo (LFHCC). A fat challenge reflecting the same fatty acid composition as the original diets was conducted post-intervention. The intake of an HSFA meal induced a higher postprandial increase in gp91phox and p67phox mRNA levels than after the intake of HMUFA, LFHCC and LFHCC n-3 meals (all p-values<0.05). The postprandial decrease in CAT, GPXs and TXNRD1 mRNA levels after the HSFA meal intake was higher than after the intake of HMUFA, LFHCC and LFHCC n-3 meals (all p-values<0.05). The intake of an HSFA meal induced a higher postprandial increase in KEAP1 mRNA levels than after the consumption of the HMUFA (P=.007) and LFHCC n-3 (P=.001) meals. Our study demonstrated that monounsaturated fat consumption reduces oxidative stress as compared to saturated fat by inducing higher postprandial antioxidant response in adipose tissue, and thus, replacing SFA for MUFA may be an effective dietary strategy to reduce the oxidative stress in MetS patients and its pathophysiological consequences.

Diet-induced obesity has a differential effect on adipose tissue and macrophage inflammatory responses of young and old mice

Obesity and aging are both associated with increased inflammation in adipose tissue. In this study, we investigated effect of diet-induced obesity on inflammatory status in young and old mice. Young (2 months) and old (19 months) C57BL/6 mice were fed a low-fat (10%, LF) or high-fat (60%, HF) diet for 4.5 months. Adipose tissue from old/LF mice expressed higher levels of IL-1β, IL-6, TNFα, and cyclooxygenase-2 mRNA compared with young/LF mice. HF diet upregulated expression of all these inflammatory markers in young mice to the levels seen in the aged. Adipocytes, but not stromal vascular cells, from old/LF mice produced more IL-6, TNFα, and prostaglandin (PG)E2 than those from young/LF mice. HF diet resulted in an increase of all these markers produced by adipocytes in young, but only TNFα in old mice. PGE2 produced by peritoneal macrophages (Mϕ's) was upregulated with aging, and HF diet induced more IL-6, TNFα, and PGE2 production in young but not in old mice. Thus, HF diet/obesity induces an inflammatory state in both visceral fat cells and peritoneal Mϕ's of young mice, but not so in old mice. Together, these results suggest that HF diet-induced obesity may speed up the aging process as characterized by inflammatory status. This study also indicates that animals have a differential response, depending on their ages, to HF diet-induced obesity and inflammation. This age-related difference in response to HF diet should be considered when using inflammation status as a marker in investigating adverse health impacts of HF diet and obesity.

Regulatory coordination between two major intracellular homeostatic systems: heat shock response and autophagy

The eukaryotic cell depends on multitiered homeostatic systems ensuring maintenance of proteostasis, organellar integrity, function and turnover, and overall cellular viability. At the two opposite ends of the homeostatic system spectrum are heat shock response and autophagy. Here, we tested whether there are interactions between these homeostatic systems, one universally operational in all prokaryotic and eukaryotic cells, and the other one (autophagy) is limited to eukaryotes. We found that heat shock response regulates autophagy. The interaction between the two systems was demonstrated by testing the role of HSF-1, the central regulator of heat shock gene expression. Knockdown of HSF-1 increased the LC3 lipidation associated with formation of autophagosomal organelles, whereas depletion of HSF-1 potentiated both starvation- and rapamycin-induced autophagy. HSP70 expression but not expression of its ATPase mutant inhibited starvation or rapamycin-induced autophagy. We also show that exercise induces autophagy in humans. As predicted by our in vitro studies, glutamine supplementation as a conditioning stimulus prior to exercise significantly increased HSP70 protein expression and prevented the expected exercise induction of autophagy. Our data demonstrate for the first time that heat shock response, from the top of its regulatory cascade (HSF-1) down to the execution stages delivered by HSP70, controls autophagy thus connecting and coordinating the two extreme ends of the homeostatic systems in the eukaryotic cell.

Heterogeneity of fibrosis patterns in non-alcoholic fatty liver disease supports the presence of multiple fibrogenic pathways

BACKGROUND

Adult non-alcoholic fatty liver disease (NAFLD) involves lobular necroinflammatory activity and fibrosis is typically centrilobular, whereas paediatric NAFLD has predominantly portal fibrosis. The reasons for these differences are unclear. We aimed to determine (a) how centrilobular and portal fibrosis in children relate to histological parameters; and (b) whether atypical fibrosis patterns exist in adults that are unexplained by current fibrogenesis models.

METHODS

Histological features of paediatric (n = 38) and adult (n = 56) NAFLD were assessed using conventional scoring systems. Keratin-7 immunostaining was used to assess hepatic progenitor cell numbers and the ductular reaction. Centrilobular and portal components of fibrosis were independently scored and fibrosis patterns were classified according to accepted types. Post-treatment (rosiglitazone/gastric banding) biopsies were also examined in adults.

RESULTS

Twenty-six children (68.4%) had portal-predominant fibrosis, although the typical "adult" pattern was seen in 11 (28.9%). Portal fibrosis was associated with a ductular reaction (P = 0.021) and hepatic progenitor cell expansion (P < 0.001), whereas centrilobular fibrosis was associated with lobular inflammation (P = 0.026) and ballooning (P = 0.001). Before intervention, six adults (10.7%) had atypical fibrosis including 3 (5.4%) with a previously unrecognized pattern of very fine, non-zonal sinusoidal fibrosis. Despite improvements in steatosis and inflammation, more patients developed this unusual pattern after intervention with most having had surgery (9 of 10 adults; P < 0.001).

CONCLUSION

Differing associations with portal and centrilobular fibrosis in children and atypical fibrosis patterns in adults suggest that multiple fibrogenic pathways exist in NAFLD. This has implications for therapy and understanding pathogenesis.

Suppression of adipogenesis by pathogenic seipin mutant is associated with inflammatory response

Background

While pathogenic mutations in BSCL2/Seipin cause congenital generalized lipodystrophy, the underlying mechanism is largely unknown. In this study, we investigated whether and how the pathogenic missense A212P mutation of Seipin (Seipin-A212P) inhibits adipogenesis.

Methodology/Results

We analyzed gene expression and lipid accumulation in stable 3T3-L1 cell lines expressing wild type (3T3-WT), non-lipodystrophic mutants N88S (3T3-N88S) and S90L (3T3-S90L), or lipodystrophic mutant A212P Seipin (3T3-A212P). When treated with adipogenic cocktail, 3T3-WT, 3T3-N88S and 3T3-S90L cells exhibited proper differentiation into mature adipocytes, indistinguishable from control 3T3-L1 cells. In contrast, adipogenesis was significantly impaired in 3T3-A212P cells. The defective adipogenesis in 3T3-A212P cells could be partially rescued by either PPARγ agonist or PPARγ overexpression. Gene expression profiling by microarray revealed that inhibition of adipogenesis was associated with activation of inflammatory genes including IL-6 and iNOS. We further demonstrated that Seipin-A212P expression at pre-differentiation stages significantly activated inflammatory responses by using an inducible expression system. The inflammation-associated inhibition of adipogenesis could be rescued by treatment with anti-inflammatory agents.

Conclusions

These results suggest that pathogenic Seipin-A212P inhibits adipogenesis and the inhibition is associated with activation of inflammatory pathways at pre-differentiation stages. Use of anti-inflammatory drugs may be a potential strategy for the treatment of lipodystrophy.

Hypoxia and adipose tissue function and dysfunction in obesity

The rise in the incidence of obesity has led to a major interest in the biology of white adipose tissue. The tissue is a major endocrine and signaling organ, with adipocytes, the characteristic cell type, secreting a multiplicity of protein factors, the adipokines. Increases in the secretion of a number of adipokines occur in obesity, underpinning inflammation in white adipose tissue and the development of obesity-associated diseases. There is substantial evidence, particularly from animal studies, that hypoxia develops in adipose tissue as the tissue mass expands, and the reduction in Po(2) is considered to underlie the inflammatory response. Exposure of white adipocytes to hypoxic conditions in culture induces changes in the expression of >1,000 genes. The secretion of a number of inflammation-related adipokines is upregulated by hypoxia, and there is a switch from oxidative metabolism to anaerobic glycolysis. Glucose utilization is increased in hypoxic adipocytes with corresponding increases in lactate production. Importantly, hypoxia induces insulin resistance in fat cells and leads to the development of adipose tissue fibrosis. Many of the responses of adipocytes to hypoxia are initiated at Po(2) levels above the normal physiological range for adipose tissue. The other cell types within the tissue also respond to hypoxia, with the differentiation of preadipocytes to adipocytes being inhibited and preadipocytes being transformed into leptin-secreting cells. Overall, hypoxia has pervasive effects on the function of adipocytes and appears to be a key factor in adipose tissue dysfunction in obesity.

Pathological parainflammation and endoplasmic reticulum stress in depression: potential translational targets through the CNS insulin, klotho and PPAR-γ systems

Major depression and bipolar disorder are heterogeneous conditions in which there can be dysregulation of (1) the stress system response, (2) its capacity for counterregulation after danger has passed and (3) the phase in which damaging molecules generated by the stress response are effectively neutralized. The response to stress and depressed mood share common circuitries and mediators, and each sets into motion not only similar affective and cognitive changes, but also similar systemic manifestations. We focus here on two highly interrelated processes, parainflammation and endoplasmic reticulum (ER) stress, each of which can potentially interfere with all phases of a normal stress response in affective illness, including adaptive neuroplastic changes and the ability to generate neural stem cells. Parainflammation is an adaptive response of the innate immune system that occurs in the context of stressors to which we were not exposed during our early evolution, including overfeeding, underactivity, aging, artificial lighting and novel foodstuffs and drugs. We postulate that humans were not exposed through evolution to the current level of acute or chronic social stressors, and hence, that major depressive illness is associated with a parainflammatory state. ER stress refers to a complex program set into motion when the ER is challenged by the production or persistence of more proteins than it can effectively fold. If the ER response is overwhelmed, substantial amounts of calcium are released into the cytoplasm, leading to apoptosis. Parainflammation and ER stress generally occur simultaneously. We discuss three highly interrelated mediators that can effectively decrease parainflammation and ER stress, namely the central insulin, klotho and peroxisome proliferator-activated receptor-γ (PPAR-γ) systems and propose that these systems may represent conceptually novel therapeutic targets for the amelioration of the affective, cognitive and systemic manifestations of major depressive disorder.

Activation of the cellular unfolded protein response by recombinant adeno-associated virus vectors

The unfolded protein response (UPR) is a stress-induced cyto-protective mechanism elicited towards an influx of large amount of proteins in the endoplasmic reticulum (ER). In the present study, we evaluated if AAV manipulates the UPR pathways during its infection. We first examined the role of the three major UPR axes, namely, endoribonuclease inositol-requiring enzyme-1 (IRE1α), activating transcription factor 6 (ATF6) and PKR-like ER kinase (PERK) in AAV infected cells. Total RNA from mock or AAV infected HeLa cells were used to determine the levels of 8 different ER-stress responsive transcripts from these pathways. We observed a significant up-regulation of IRE1α (up to 11 fold) and PERK (up to 8 fold) genes 12–48 hours after infection with self-complementary (sc)AAV2 but less prominent with single-stranded (ss)AAV2 vectors. Further studies demonstrated that scAAV1 and scAAV6 also induce cellular UPR in vitro, with AAV1 vectors activating the PERK pathway (3 fold) while AAV6 vectors induced a significant increase on all the three major UPR pathways [6–16 fold]. These data suggest that the type and strength of UPR activation is dependent on the viral capsid. We then examined if transient inhibition of UPR pathways by RNA interference has an effect on AAV transduction. siRNA mediated silencing of PERK and IRE1α had a modest effect on AAV2 and AAV6 mediated gene expression (∼1.5–2 fold) in vitro. Furthermore, hepatic gene transfer of scAAV2 vectors in vivo, strongly elevated IRE1α and PERK pathways (2 and 3.5 fold, respectively). However, when animals were pre-treated with a pharmacological UPR inhibitor (metformin) during scAAV2 gene transfer, the UPR signalling and its subsequent inflammatory response was attenuated concomitant to a modest 2.8 fold increase in transgene expression. Collectively, these data suggest that AAV vectors activate the cellular UPR pathways and their selective inhibition may be beneficial during AAV mediated gene transfer.

Damned if you do, damned if you don't: the conundrum of adipose tissue vascularization

The plasticity of adipose tissue requires highly regulated changes in accompanying blood vessels. In obesity, adipose tissue angiogenesis plays a complex role to support tissue growth and promote metabolic disease. Emerging research (Sung et al., 2013) indicates that exploiting the mediators of adipose tissue angiogenesis may offer the possibility for therapeutic interventions.

Adipose vascular endothelial growth factor regulates metabolic homeostasis through angiogenesis

Vascular endothelial growth factor A (VEGF) is highly expressed in adipose tissue. Its role, however, has not been fully elucidated. Here, we reveal the metabolic role of adipose-VEGF by studying mice with deletion (VEGF(AdΔ)) or doxycycline-inducible overexpression of a VEGF transgene (VEGF(AdTg)) in the adipose tissue. VEGF(AdΔ) mice have reduced adipose vascular density and show adipose hypoxia, apoptosis, inflammation, and metabolic defects on a high-fat diet. In contrast, induction of VEGF expression in VEGF(AdTg) mice leads to increased adipose vasculature and reduced hypoxia. The latter changes are sufficient to counteract an established compromising effect of high-fat diet on the metabolism, indicating that metabolic misbalance is reversible by adipose vessel density increase. Our data clearly show the essential role of VEGF signaling for adequate adipose function. Besides revealing insights into the molecular mechanisms of obesity-related metabolic diseases, this study points to the therapeutic potential of increased adipose angiogenesis.

4-Phenylbutyric acid reduces endoplasmic reticulum stress, trypsin activation, and acinar cell apoptosis while increasing secretion in rat pancreatic acini

OBJECTIVES

Endoplasmic reticulum (ER) stress leads to misfolded proteins inside the ER and initiates unfolded protein response (UPR). Unfolded protein response components are involved in pancreatic function and activated during pancreatitis. However, the exact role of ER stress in the exocrine pancreas is unclear. The present study examined the effects of 4-phenylbutyric acid (4-PBA), an ER chaperone, on acini and UPR components.

METHODS

Rat acini were stimulated with cholecystokinin (10 pmol/L to 10 nmol/L) with or without preincubation of 4-PBA. The UPR components were analyzed, including chaperone-binding protein, protein kinaselike ER kinase, X-box-binding protein 1, c-Jun NH(2)-terminal kinase, CCAAT/enhancer-binding protein homologous protein, caspase 3, and apoptosis. Effects of 4-PBA were measured on secretion, calcium, and trypsin activation.

RESULTS

4-Phenylbutyric acid led to an increase of secretion, whereas trypsin activation with supraphysiological cholecystokinin was significantly reduced. 4-Phenylbutyric acid prevented chaperone-binding protein up-regulation, diminished protein kinaselike ER kinase, and c-Jun NH2-terminal kinase phosphorylation, prohibited X-box-binding protein 1 splicing and CCAAT/enhancer-binding protein homologous protein expression, caspase 3 activation, and apoptosis caused by supraphysiological cholecystokinin.

CONCLUSION

By incubation with 4-PBA, beneficial in urea cycle deficiency, it was possible to enhance enzyme secretion to suppress trypsin activation, UPR activation, and proapoptotic pathways. The data hint new perspectives for the use of chemical chaperones in pancreatic diseases.

GRP78 plays an essential role in adipogenesis and postnatal growth in mice

To investigate the role of GRP78 in adipogenesis and metabolic homeostasis, we knocked down GRP78 in mouse embryonic fibroblasts and 3T3-L1 preadipocytes induced to undergo differentiation into adipocytes. We also created an adipose Grp78-knockout mouse utilizing the aP2 (fatty acid binding protein 4) promoter-driven Cre-recombinase. Adipogenesis was monitored by molecular markers and histology. Tissues were analyzed by micro-CT and electron microscopy. Glucose homeostasis and cytokine analysis were performed. Our results indicate that GRP78 is essential for adipocyte differentiation in vitro. aP2-cre-mediated GRP78 deletion leads to lipoatrophy with ∼90% reduction in gonadal and subcutaneous white adipose tissue and brown adipose tissue, severe growth retardation, and bone defects. Despite severe abnormality in adipose mass and function, adipose Grp78-knockout mice showed normal plasma triglyceride levels, and plasma glucose and insulin levels were reduced by 40-60% compared to wild-type mice, suggesting enhanced insulin sensitivity. The endoplasmic reticulum is grossly expanded in the residual mutant white adipose tissue. Thus, these studies establish that GRP78 is required for adipocyte differentiation, glucose homeostasis, and balanced secretion of adipokines. Unexpectedly, the phenotypes and metabolic parameters of the mutant mice, which showed early postnatal mortality, are uniquely distinct from previously characterized lipodystrophic mouse models.