Rev1 deficiency induces replication stress to cause metabolic dysfunction differently in males and females

DNA damage responses compete for cellular resources with metabolic pathways, but little is known about the metabolic consequences of impaired DNA replication, a process called replication stress. Here we characterized the metabolic consequences of DNA replication stress at endogenous DNA lesions by using mice with a disruption of Rev1, a translesion DNA polymerase specialized in the mutagenic replication of damaged DNA. Male and female Rev1 knockout (KO) mice were compared with wild-type (WT) mice and followed over time to study the natural course of body weight gain and glucose tolerance. Follow-up measurements were performed in female mice for in-depth metabolic characterization. Body weight and fat mass were only increased in female KO mice versus WT mice, whereas glucose intolerance and a reduction in lean mass were observed in both sexes. Female KO mice showed reduced locomotor activity while male KO mice showed increased activity as compared with their WT littermates. Further characterization of female mice revealed that lipid handling was unaffected by Rev1 deletion. An increased respiratory exchange ratio, combined with elevated plasma lactate levels and increased hepatic gluconeogenesis indicated problems with aerobic oxidation and increased reliance on anaerobic glycolysis. Supplementation with the NAD⁺ precursor nicotinamide riboside to stimulate aerobic respiration failed to restore the metabolic phenotype. In conclusion, replication stress at endogenous DNA lesions induces a complex metabolic phenotype, most likely initiated by muscular metabolic dysfunction and increased dependence on anaerobic glycolysis. Nicotinamide riboside supplementation after the onset of the metabolic impairment did not rescue this phenotype.NEW & NOTEWORTHY An increasing number of DNA lesions interferes with cellular replication leading to metabolic inflexibility. We utilized Rev1 knockout mice as a model for replication stress, and show a sex-dependent metabolic phenotype, with a pronounced reduction of lean mass and glucose tolerance. These data indicate that in obesity, we may end up in an infinite loop where metabolic disturbance promotes the formation of DNA lesions, which in turn interferes with cellular replication causing further metabolic disturbances.

Akkermansia muciniphila Exerts Lipid-Lowering and Immunomodulatory Effects without Affecting Neointima Formation in Hyperlipidemic APOE*3-Leiden.CETP Mice

SCOPE

Akkermansia muciniphila (A. muciniphila) is an intestinal commensal with anti-inflammatory properties both in the intestine and other organs. The aim is to investigate the effects of oral administration of A. muciniphila on lipid metabolism, immunity, and cuff-induced neointima formation in hyperlipidemic APOE*3-Leiden (E3L).CETP mice.

METHODS AND RESULTS

Hyperlipidemic male E3L.CETP mice are daily treated with 2 × 108 CFU A. muciniphila by oral gavage for 4 weeks and the effects are determined on plasma lipid levels, immune parameters, and cuff-induced neointima formation and composition. A. muciniphila administration lowers body weight and plasma total cholesterol and triglycerides levels. A. muciniphila influences the immune cell composition in mesenteric lymph nodes, as evident from an increased total B cell population, while reducing the total T cell and neutrophil populations. Importantly, A. muciniphila reduces the expression of the activation markers MHCII on dendritic cells and CD86 on B cells. A. muciniphila also increases whole blood ex vivo lipopolysaccharide-stimulated IL-10 release. Finally, although treatment with A. muciniphila improves lipid metabolism and immunity, it does not affect neointima formation or composition.

CONCLUSIONS

Four weeks of treatment with A. muciniphila exerts lipid-lowering and immunomodulatory effects, which are insufficient to inhibit neointima formation in hyperlipidemic E3L.CETP mice.

The prebiotic inulin modulates gut microbiota but does not ameliorate atherosclerosis in hypercholesterolemic APOE*3-Leiden.CETP mice

Gut microbiota have been implicated in the development of atherosclerosis and cardiovascular disease. Since the prebiotic inulin is thought to beneficially affect gut microbiota, we aimed to determine the effect of inulin supplementation on atherosclerosis development in APOE*3-Leiden.CETP (E3L.CETP) mice. Female E3L.CETP mice were fed a western-type diet containing 0.1% or 0.5% cholesterol with or without 10% inulin. The effects of inulin were determined on: microbiota composition, cecal short-chain fatty acid (SCFA) levels, plasma lipid levels, atherosclerosis development, hepatic morphology and hepatic inflammation. Inulin with 0.5% dietary cholesterol increased specific bacterial genera and elevated levels of cecal SCFAs, but did not affect plasma cholesterol levels or atherosclerosis development. Surprisingly, inulin resulted in mild hepatic inflammation as shown by increased expression of inflammation markers. However, these effects were not accompanied by increased hepatic macrophage number. Analogously, inulin induced mild steatosis and increased hepatocyte size, but did not affect hepatic triglyceride content. Inulin with 0.1% dietary cholesterol did not affect hepatic morphology, nor hepatic expression of inflammation markers. Overall, inulin did not reduce hypercholesterolemia or atherosclerosis development in E3L.CETP mice despite showing clear prebiotic activity, but resulted in manifestations of hepatic inflammation when combined with a high percentage of dietary cholesterol.

Dietary yeast-derived mannan oligosaccharides have immune-modulatory properties but do not improve high fat diet-induced obesity and glucose intolerance

The indigestible mannan oligosaccharides (MOS) derived from the outer cell wall of yeast Saccharomyces cerevisiae have shown potential to reduce inflammation. Since inflammation is one of the underlying mechanisms involved in the development of obesity-associated metabolic dysfunctions, we aimed to determine the effect of dietary supplementation with MOS on inflammation and metabolic homeostasis in lean and diet-induced obese mice. Male C57BL/6 mice were fed either a low fat diet (LFD) or a high fat diet (HFD) with, respectively, 10% or 45% energy derived from lard fat, with or without 1% MOS for 17 weeks. Body weight and composition were measured throughout the study. After 12 weeks of intervention, whole-body glucose tolerance was assessed and in week 17 immune cell composition was determined in mesenteric white adipose tissue (mWAT) and liver by flow cytometry and RT-qPCR. In LFD-fed mice, MOS supplementation induced a significant increase in the abundance of macrophages and eosinophils in mWAT. A similar trend was observed in hepatic macrophages. Although HFD feeding induced a classical shift from the anti-inflammatory M2-like macrophages towards the pro-inflammatory M1-like macrophages in both mWAT and liver from control mice, MOS supplementation had no effect on this obesity-driven immune response. Finally, MOS supplementation did not improve whole-body glucose homeostasis in both lean and obese mice.Altogether, our data showed that MOS had extra-intestinal immune modulatory properties in mWAT and liver. However these effects were not substantial enough to significantly ameliorate HFD-induced glucose intolerance or inflammation.

Dietary Mannan Oligosaccharides Modulate Gut Microbiota, Increase Fecal Bile Acid Excretion, and Decrease Plasma Cholesterol and Atherosclerosis Development

SCOPE

Mannan oligosaccharides (MOS) have proven effective at improving growth performance, while also reducing hyperlipidemia and inflammation. As atherosclerosis is accelerated both by hyperlipidemia and inflammation, we aim to determine the effect of dietary MOS on atherosclerosis development in hyperlipidemic ApoE*3-Leiden.CETP (E3L.CETP) mice, a well-established model for human-like lipoprotein metabolism.

METHODS AND RESULTS

Female E3L.CETP mice were fed a high-cholesterol diet, with or without 1% MOS for 14 weeks. MOS substantially decreased atherosclerotic lesions up to 54%, as assessed in the valve area of the aortic root. In blood, IL-1RA, monocyte subtypes, lipids, and bile acids (BAs) were not affected by MOS. Gut microbiota composition was determined using 16S rRNA gene sequencing and MOS increased the abundance of cecal Bacteroides ovatus. MOS did not affect fecal excretion of cholesterol, but increased fecal BAs as well as butyrate in cecum as determined by gas chromatography mass spectrometry.

CONCLUSION

MOS decreased the onset of atherosclerosis development via lowering of plasma cholesterol levels. These effects were accompanied by increased cecal butyrate and fecal excretion of BAs, presumably mediated via interactions of MOS with the gut microbiota.

A Restricted Role for FcγR in the Regulation of Adaptive Immunity

By their interaction with IgG immune complexes, FcγR and complement link innate and adaptive immunity, showing functional redundancy. In complement-deficient mice, IgG downstream effector functions are often impaired, as well as adaptive immunity. Based on a variety of model systems using FcγR-knockout mice, it has been concluded that FcγRs are also key regulators of innate and adaptive immunity; however, several of the model systems underpinning these conclusions suffer from flawed experimental design. To address this issue, we generated a novel mouse model deficient for all FcγRs (FcγRI/II/III/IV^-/- mice). These mice displayed normal development and lymphoid and myeloid ontogeny. Although IgG effector pathways were impaired, adaptive immune responses to a variety of challenges, including bacterial infection and IgG immune complexes, were not. Like FcγRIIb-deficient mice, FcγRI/II/III/IV^-/- mice developed higher Ab titers but no autoantibodies. These observations indicate a redundant role for activating FcγRs in the modulation of the adaptive immune response in vivo. We conclude that FcγRs are downstream IgG effector molecules with a restricted role in the ontogeny and maintenance of the immune system, as well as the regulation of adaptive immunity.

The Prebiotic Inulin Aggravates Accelerated Atherosclerosis in Hypercholesterolemic APOE*3-Leiden Mice

The prebiotic inulin has proven effective at lowering inflammation and plasma lipid levels. As atherosclerosis is provoked by both inflammation and hyperlipidemia, we aimed to determine the effect of inulin supplementation on atherosclerosis development in hypercholesterolemic APOE*3-Leiden (E3L) mice. Male E3L mice were fed a high-cholesterol (1%) diet, supplemented with or without 10% inulin for 5 weeks. At week 3, a non-constrictive cuff was placed around the right femoral artery to induce accelerated atherosclerosis. At week 5, vascular pathology was determined by lesion thickness, vascular remodeling, and lesion composition. Throughout the study, plasma lipids were measured and in week 5, blood monocyte subtypes were determined using flow cytometry analysis. In contrast to our hypothesis, inulin exacerbated atherosclerosis development, characterized by increased lesion formation and outward vascular remodeling. The lesions showed increased number of macrophages, smooth muscle cells, and collagen content. No effects on blood monocyte composition were found. Inulin significantly increased plasma total cholesterol levels and total cholesterol exposure. In conclusion, inulin aggravated accelerated atherosclerosis development in hypercholesterolemic E3L mice, accompanied by adverse lesion composition and outward remodeling. This process was not accompanied by differences in blood monocyte composition, suggesting that the aggravated atherosclerosis development was driven by increased plasma cholesterol.

GC-MS Analysis of Short-Chain Fatty Acids in Feces, Cecum Content, and Blood Samples

Short-chain fatty acids, the end products of fermentation of dietary fibers by the gut microbiota, have been shown to exert multiple effects on mammalian metabolism. For the analysis of short-chain fatty acids, gas chromatography-mass spectrometry is a very powerful and reliable method. Here, we describe a fast, reliable, and reproducible method for the separation and quantification of short-chain fatty acids in mouse feces, cecum content, and blood samples (i.e., plasma or serum) using gas chromatography-mass spectrometry. The short-chain fatty acids analyzed include acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, and heptanoic acid.

BMT decreases HFD-induced weight gain associated with decreased preadipocyte number and insulin secretion

Experimental bone marrow transplantation (BMT) in mice is commonly used to assess the role of immune cell-specific genes in various pathophysiological settings. The application of BMT in obesity research is hampered by the significant reduction in high-fat diet (HFD)-induced obesity. We set out to characterize metabolic tissues that may be affected by the BMT procedure and impair the HFD-induced response. Male C57BL/6 mice underwent syngeneic BMT using lethal irradiation. After a recovery period of 8 weeks they were fed a low-fat diet (LFD) or HFD for 16 weeks. HFD-induced obesity was reduced in mice after BMT as compared to HFD-fed control mice, characterized by both a reduced fat (-33%; p<0.01) and lean (-11%; p<0.01) mass, while food intake and energy expenditure were unaffected. As compared to control mice, BMT-treated mice had a reduced mature adipocyte volume (approx. -45%; p<0.05) and reduced numbers of preadipocytes (-38%; p<0.05) and macrophages (-62%; p<0.05) in subcutaneous, gonadal and visceral white adipose tissue. In BMT-treated mice, pancreas weight (-46%; p<0.01) was disproportionally decreased. This was associated with reduced plasma insulin (-68%; p<0.05) and C-peptide (-37%; p<0.01) levels and a delayed glucose clearance in BMT-treated mice on HFD as compared to control mice. In conclusion, the reduction in HFD-induced obesity after BMT in mice is at least partly due to alterations in the adipose tissue cell pool composition as well as to a decreased pancreatic secretion of the anabolic hormone insulin. These effects should be considered when interpreting results of experimental BMT in metabolic studies.

Weight loss induced by very low calorie diet is associated with a more beneficial systemic inflammatory profile than by Roux-en-Y gastric bypass

INTRODUCTION

Weight loss interventions such as Roux-en-Y gastric bypass (RYGB) and very low calorie diets (VLCD) lead to improvement of glucose metabolism in obese individuals with type-2 diabetes. Weight loss can also positively influence the unfavorable inflammatory profile associated with obesity. However, a direct comparison of the effect of VLCD and RYGB on systemic inflammation is lacking.

METHODS

Systemic inflammation was investigated in age- and BMI-matched morbidly obese T2DM women by determining the number and activation- or memory status of peripheral blood leukocytes by flow cytometry, in addition to measuring circulating levels of cytokines and CRP. Systemic inflammation was assessed one month before and three months after RYGB (n=15) or VLCD (n=12). An age matched group of lean women (n=12) was studied as control group.

RESULTS

Three months after the intervention, CRP and leptin levels were reduced whereas adiponectin levels were increased both by RYGB and VLCD. TNF-α levels were increased by RYGB, but reduced by VLCD. IL-2 and IL-6 levels were reduced and IL-4 levels were increased by VLCD but not affected by RYGB. The number of activated peripheral cytotoxic T (CD8+CD25+) and B (CD19+CD38+) cells was significantly higher after RYGB than after VLCD.

CONCLUSION

In conclusion, RYGB and VLCD have differential effects on the activation status of peripheral leukocytes and levels of cytokines in obese women with T2DM, despite comparable weight loss three months after the intervention. VLCD seems to have more favorable effects on the inflammatory profile as compared to RYGB.

BCG lowers plasma cholesterol levels and delays atherosclerotic lesion progression in mice

BACKGROUND AND AIMS

Bacille-Calmette-Guérin (BCG), prepared from attenuated live Mycobacterium bovis, modulates atherosclerosis development as currently explained by immunomodulatory mechanisms. However, whether BCG is pro- or anti-atherogenic remains inconclusive as the effect of BCG on cholesterol metabolism, the main driver of atherosclerosis development, has remained underexposed in previous studies. Therefore, we aimed to elucidate the effect of BCG on cholesterol metabolism in addition to inflammation and atherosclerosis development in APOE*3-Leiden.CETP mice, a well-established model of human-like lipoprotein metabolism.

METHODS

Hyperlipidemic APOE*3-Leiden.CETP mice were fed a Western-type diet containing 0.1% cholesterol and were terminated 6 weeks after a single intravenous injection with BCG (0.75 mg; 5 × 10(6) CFU).

RESULTS

BCG-treated mice exhibited hepatic mycobacterial infection and hepatomegaly. The enlarged liver (+53%, p = 0.001) coincided with severe immune cell infiltration and a higher cholesterol content (+31%, p = 0.03). Moreover, BCG reduced plasma total cholesterol levels (-34%, p = 0.003), which was confined to reduced nonHDL-cholesterol levels (-36%, p = 0.002). This was due to accelerated plasma clearance of cholesterol from intravenously injected [(14)C]cholesteryl oleate-labelled VLDL-like particles (t½ -41%, p = 0.002) as a result of elevated hepatic uptake (+25%, p = 0.05) as well as reduced intestinal cholestanol and plant sterol absorption (up to -37%, p = 0.003). Ultimately, BCG decreased foam cell formation of peritoneal macrophages (-18%, p = 0.02) and delayed atherosclerotic lesion progression in the aortic root of the heart. BCG tended to decrease atherosclerotic lesion area (-59%, p = 0.08) and reduced lesion severity.

CONCLUSIONS

BCG reduces plasma nonHDL-cholesterol levels and delays atherosclerotic lesion formation in hyperlipidemic mice.

Identification of a selective glucocorticoid receptor modulator that prevents both diet-induced obesity and inflammation

BACKGROUND AND PURPOSE

High-fat diet consumption results in obesity and chronic low-grade inflammation in adipose tissue. Whereas glucocorticoid receptor (GR) antagonism reduces diet-induced obesity, GR agonism reduces inflammation, the combination of which would be desired in a strategy to combat the metabolic syndrome. The purpose of this study was to assess the beneficial effects of the selective GR modulator C108297 on both diet-induced weight gain and inflammation in mice and to elucidate underlying mechanisms.

EXPERIMENTAL APPROACH

Ten-week-old C57Bl/6 J mice were fed a high-fat diet for 4 weeks while being treated with the selective GR modulator C108297, a full GR antagonist (RU486/mifepristone) or vehicle.

KEY RESULTS

C108297 and, to a lesser extent, mifepristone reduced body weight gain and fat mass. C108297 decreased food and fructose intake and increased lipolysis in white adipose tissue (WAT) and free fatty acid levels in plasma, resulting in decreased fat cell size and increased fatty acid oxidation. Furthermore, C108297 reduced macrophage infiltration and pro-inflammatory cytokine expression in WAT, as well as in vitro LPS-stimulated TNF-α secretion in macrophage RAW 264.7 cells. However, mifepristone also increased energy expenditure, as measured by fully automatic metabolic cages, and enhanced expression of thermogenic markers in energy-combusting brown adipose tissue (BAT) but did not affect inflammation.

CONCLUSIONS AND IMPLICATIONS

C108297 attenuates obesity by reducing caloric intake and increasing lipolysis and fat oxidation, and in addition attenuates inflammation. These data suggest that selective GR modulation may be a viable strategy for the reduction of diet-induced obesity and inflammation.

FcRγ-chain deficiency reduces the development of diet-induced obesity

OBJECTIVE

Pathogenic immunoglobulins are produced during the development of obesity and contribute to the development of insulin resistance (IR). However, the mechanisms by which these antibodies affect IR are largely unknown. This study investigated whether Fc-receptors contribute to the development of diet-induced obesity and IR by studying FcRγ(-/-) mice that lack the γ-subunit necessary for signaling and cell surface expression of FcγR and FcεRI.

METHODS

FcRγ(-/-) and wild-type (WT) mice were fed a high-fat diet (HFD) to induce obesity. At 4 and 11 weeks, body weight and insulin sensitivity were measured, and adipose tissue (AT) inflammation was determined. Furthermore, intestinal triglyceride (TG) uptake and plasma TG clearance were determined, and gut microbiota composition was analyzed.

RESULTS

FcRγ(-/-) mice gained less weight after 11 weeks of HFD. They had reduced adiposity, adipose tissue inflammation, and IR. Interestingly, FcRγ(-/-) mice had higher lean mass compared to WT mice, which was associated with increased energy expenditure. Intestinal TG absorption was increased whereas plasma TG clearance was not affected in FcRγ(-/-) mice. Gut microbial composition differed significantly and might therefore have added to the observed phenotype.

CONCLUSIONS

FcRγ-chain deficiency reduces the development of diet-induced obesity, as well as associated AT inflammation and IR at 11 weeks of HFD.

Increased PUFA Content and 5-Lipoxygenase Pathway Expression Are Associated with Subcutaneous Adipose Tissue Inflammation in Obese Women with Type 2 Diabetes

Obese women with type 2 diabetes mellitus (T2DM) have more inflammation in their subcutaneous white adipose tissue (sWAT) than age-and-BMI similar obese women with normal glucose tolerance (NGT). We aimed to investigate whether WAT fatty acids and/or oxylipins are associated with the enhanced inflammatory state in WAT of the T2DM women. Fatty acid profiles were measured in both subcutaneous and visceral adipose tissue (vWAT) of 19 obese women with NGT and 16 age-and-BMI similar women with T2DM. Oxylipin levels were measured in sWAT of all women. Arachidonic acid (AA) and docosahexaenoic acid (DHA) percentages were higher in sWAT, but not vWAT of the T2DM women, and AA correlated positively to the gene expression of macrophage marker CD68. We found tendencies for higher oxylipin concentrations of the 5-LOX leukotrienes in sWAT of T2DM women. Gene expression of the 5-LOX leukotriene biosynthesis pathway was significantly higher in sWAT of T2DM women. In conclusion, AA and DHA content were higher in sWAT of T2DM women and AA correlated to the increased inflammatory state in sWAT. Increased AA content was accompanied by an upregulation of the 5-LOX pathway and seems to have led to an increase in the conversion of AA into proinflammatory leukotrienes in sWAT.

The limited storage capacity of gonadal adipose tissue directs the development of metabolic disorders in male C57Bl/6J mice

AIMS/HYPOTHESIS

White adipose tissue (WAT) consists of various depots with different adipocyte functionality and immune cell composition. Knowledge of WAT-depot-specific differences in expandability and immune cell influx during the development of obesity is limited, therefore we aimed to characterise different WAT depots during the development of obesity in mice.

METHODS

Gonadal WAT (gWAT), subcutaneous WAT (sWAT) and mesenteric WAT (mWAT) were isolated from male C57Bl/6J mice with different body weights (approximately 25-60 g) and analysed. Linear and non-linear regression models were used to describe the extent of WAT depot expandability and immune cell composition as a function of body weight.

RESULTS

Whereas mouse sWAT and mWAT continued to expand with body weight, gWAT expanded mainly during the initial phase of body weight gain. The expansion diminished after the mice reached a body weight of around 40 g. From this point on, gWAT crown-like structure formation, liver steatosis and insulin resistance occurred. Mouse WAT depots showed major differences in immune cell composition: gWAT consisted mainly of macrophages, whereas sWAT and mWAT primarily contained lymphocytes.

CONCLUSIONS/INTERPRETATION

Marked inter-depot differences exist in WAT immune cell composition and expandability. The limited storage capacity of gWAT seems to direct the development of metabolic disorders in male C57Bl/6J mice.

Splenic autonomic denervation increases inflammatory status but does not aggravate atherosclerotic lesion development

The brain plays a prominent role in the regulation of inflammation. Immune cells are under control of the so-called cholinergic anti-inflammatory reflex, mainly acting via autonomic innervation of the spleen. Activation of this reflex inhibits the secretion of proinflammatory cytokines and may reduce the development of atherosclerosis. Therefore, the aim of this study was to evaluate the effects of selective parasympathetic (Px) and sympathetic (Sx) denervation of the spleen on inflammatory status and atherosclerotic lesion development. Female APOE*3-Leiden.CETP mice, a well-established model for human-like lipid metabolism and atherosclerosis, were fed a cholesterol-containing Western-type diet for 4 wk after which they were subdivided into three groups receiving either splenic Px, splenic Sx, or sham surgery. The mice were subsequently challenged with the same diet for an additional 15 wk. Selective Px increased leukocyte counts (i.e., dendritic cells, B cells, and T cells) in the spleen and increased gene expression of proinflammatory cytokines in the liver and peritoneal leukocytes compared with Sx and sham surgery. Both Px and Sx increased circulating proinflammatory cytokines IL-1β and IL-6. However, the increased proinflammatory status in denervated mice did not affect atherosclerotic lesion size or lesion composition.

CONCLUSION

Predominantly selective Px of the spleen enhances the inflammatory status, which, however, does not aggravate diet-induced atherosclerotic lesion development.

Salsalate activates brown adipose tissue in mice

Salsalate improves glucose intolerance and dyslipidemia in type 2 diabetes patients, but the mechanism is still unknown. The aim of the current study was to unravel the molecular mechanisms involved in these beneficial metabolic effects of salsalate by treating mice with salsalate during and after development of high-fat diet-induced obesity. We found that salsalate attenuated and reversed high-fat diet-induced weight gain, in particular fat mass accumulation, improved glucose tolerance, and lowered plasma triglyceride levels. Mechanistically, salsalate selectively promoted the uptake of fatty acids from glycerol tri[(3)H]oleate-labeled lipoprotein-like emulsion particles by brown adipose tissue (BAT), decreased the intracellular lipid content in BAT, and increased rectal temperature, all pointing to more active BAT. The treatment of differentiated T37i brown adipocytes with salsalate increased uncoupled respiration. Moreover, salsalate upregulated Ucp1 expression and enhanced glycerol release, a dual effect that was abolished by the inhibition of cAMP-dependent protein kinase (PKA). In conclusion, salsalate activates BAT, presumably by directly activating brown adipocytes via the PKA pathway, suggesting a novel mechanism that may explain its beneficial metabolic effects in type 2 diabetes patients.

Chronic helminth infection and helminth-derived egg antigens promote adipose tissue M2 macrophages and improve insulin sensitivity in obese mice

Chronic low-grade inflammation associated with obesity contributes to insulin resistance and type 2 diabetes. Helminth parasites are the strongest natural inducers of type 2 immune responses, and short-lived infection with rodent nematodes was reported to improve glucose tolerance in obese mice. Here, we investigated the effects of chronic infection (12 weeks) with Schistosoma mansoni, a helminth that infects millions of humans worldwide, on whole-body metabolic homeostasis and white adipose tissue (WAT) immune cell composition in high-fat diet-induced obese C57BL/6 male mice. Our data indicate that chronic helminth infection reduced body weight gain (-62%), fat mass gain (-89%), and adipocyte size; lowered whole-body insulin resistance (-23%) and glucose intolerance (-16%); and improved peripheral glucose uptake (+25%) and WAT insulin sensitivity. Analysis of immune cell composition by flow cytometry and quantitative PCR (qPCR) revealed that S. mansoni promoted strong increases in WAT eosinophils and alternatively activated (M2) macrophages. Importantly, injections with S. mansoni-soluble egg antigens (SEA) recapitulated the beneficial effect of parasite infection on whole-body metabolic homeostasis and induced type 2 immune responses in WAT and liver. Taken together, we provide novel data suggesting that chronic helminth infection and helminth-derived molecules protect against metabolic disorders by promoting a T helper 2 (Th2) response, eosinophilia, and WAT M2 polarization.

Mannose-binding lectin is required for the effective clearance of apoptotic cells by adipose tissue macrophages during obesity

Obesity is accompanied by the presence of chronic low-grade inflammation manifested by infiltration of macrophages into adipose tissue. Mannose-binding lectin (MBL), a soluble mediator of innate immunity, promotes phagocytosis and alters macrophage function. To assess the function of MBL in the development of obesity, we studied wild-type and MBL(-/-) mice rendered obese using a high-fat diet (HFD). Whereas no gross morphological differences were observed in liver, an HFD provoked distinct changes in the adipose tissue morphology of MBL(-/-) mice. In parallel with increased adipocyte size, MBL(-/-) mice displayed an increased influx of macrophages into adipose tissue. Macrophages were polarized toward an alternatively activated phenotype known to modulate apoptotic cell clearance. MBL deficiency also significantly increased the number of apoptotic cells in adipose tissue. Consistent with these observations, recombinant MBL enhanced phagocytic capacity of the stromal vascular fraction isolated from adipose tissue and modulated uptake of apoptotic adipocytes by macrophages. Despite changes in macrophage abundance and polarity, the absence of MBL did not affect systemic insulin resistance. Finally, in humans, lower levels of circulating MBL were accompanied by enhanced macrophage influx in subcutaneous adipose tissue. We propose a novel role for MBL in the recognition and clearance of apoptotic adipocytes during obesity.

Roux-en-Y gastric bypass surgery, but not calorie restriction, reduces plasma branched-chain amino acids in obese women independent of weight loss or the presence of type 2 diabetes

OBJECTIVE

Obesity and type 2 diabetes mellitus (T2DM) have been associated with increased levels of circulating branched-chain amino acids (BCAAs) that may be involved in the pathogenesis of insulin resistance. However, weight loss has not been consistently associated with the reduction of BCAA levels.

RESEARCH DESIGN AND METHODS

We included 30 obese normal glucose-tolerant (NGT) subjects, 32 obese subjects with T2DM, and 12 lean female subjects. Obese subjects underwent either a restrictive procedure (gastric banding [GB], a very low-calorie diet [VLCD]), or a restrictive/bypass procedure (Roux-en-Y gastric bypass [RYGB] surgery). Fasting blood samples were taken for the determination of amine group containing metabolites 4 weeks before, as well as 3 weeks and 3 months after the intervention.

RESULTS

BCAA levels were higher in T2DM subjects, but not in NGT subjects, compared with lean subjects. Principal component (PC) analysis revealed a concise PC consisting of all BCAAs, which showed a correlation with measures of insulin sensitivity and glucose tolerance. Only after the RYGB procedure, and at both 3 weeks and 3 months, were circulating BCAA levels reduced.

CONCLUSIONS

Our data confirm an association between deregulation of BCAA metabolism in plasma and insulin resistance and glucose intolerance. Three weeks after undergoing RYGB surgery, a significant decrease in BCAAs in both NGT as well as T2DM subjects was observed. After 3 months, despite inducing significant weight loss, neither GB nor VLCD induced a reduction in BCAA levels. Our results indicate that the bypass procedure of RYGB surgery, independent of weight loss or the presence of T2DM, reduces BCAA levels in obese subjects.

Downregulation of the acetyl-CoA metabolic network in adipose tissue of obese diabetic individuals and recovery after weight loss

AIMS/HYPOTHESIS

Not all obese individuals develop type 2 diabetes. Why some obese individuals retain normal glucose tolerance (NGT) is not well understood. We hypothesise that the biochemical mechanisms that underlie the function of adipose tissue can help explain the difference between obese individuals with NGT and those with type 2 diabetes.

METHODS

RNA sequencing was used to analyse the transcriptome of samples extracted from visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) of obese women with NGT or type 2 diabetes who were undergoing bariatric surgery. The gene expression data was analysed by bioinformatic visualisation and statistical analyses techniques.

RESULTS

A network-based approach to distinguish obese individuals with NGT from obese individuals with type 2 diabetes identified acetyl-CoA metabolic network downregulation as an important feature in the pathophysiology of type 2 diabetes in obese individuals. In general, genes within two reaction steps of acetyl-CoA were found to be downregulated in the VAT and SAT of individuals with type 2 diabetes. Upon weight loss and amelioration of metabolic abnormalities three months following bariatric surgery, the expression level of these genes recovered to levels seen in individuals with NGT. We report four novel genes associated with type 2 diabetes and recovery upon weight loss: ACAT1 (encoding acetyl-CoA acetyltransferase 1), ACACA (encoding acetyl-CoA carboxylase α), ALDH6A1 (encoding aldehyde dehydrogenase 6 family, member A1) and MTHFD1 (encoding methylenetetrahydrofolate dehydrogenase).

CONCLUSIONS/INTERPRETATION

Downregulation of the acetyl-CoA network in VAT and SAT is an important feature in the pathophysiology of type 2 diabetes in obese individuals. ACAT1, ACACA, ALDH6A1 and MTHFD1 represent novel biomarkers in adipose tissue associated with type 2 diabetes in obese individuals.

Prolonged niacin treatment leads to increased adipose tissue PUFA synthesis and anti-inflammatory lipid and oxylipin plasma profile

Prolonged niacin treatment elicits beneficial effects on the plasma lipid and lipoprotein profile that is associated with a protective CVD risk profile. Acute niacin treatment inhibits nonesterified fatty acid release from adipocytes and stimulates prostaglandin release from skin Langerhans cells, but the acute effects diminish upon prolonged treatment, while the beneficial effects remain. To gain insight in the prolonged effects of niacin on lipid metabolism in adipocytes, we used a mouse model with a human-like lipoprotein metabolism and drug response [female APOE*3-Leiden.CETP (apoE3 Leiden cholesteryl ester transfer protein) mice] treated with and without niacin for 15 weeks. The gene expression profile of gonadal white adipose tissue (gWAT) from niacin-treated mice showed an upregulation of the "biosynthesis of unsaturated fatty acids" pathway, which was corroborated by quantitative PCR and analysis of the FA ratios in gWAT. Also, adipocytes from niacin-treated mice secreted more of the PUFA DHA ex vivo. This resulted in an increased DHA/arachidonic acid (AA) ratio in the adipocyte FA secretion profile and in plasma of niacin-treated mice. Interestingly, the DHA metabolite 19,20-dihydroxy docosapentaenoic acid (19,20-diHDPA) was increased in plasma of niacin-treated mice. Both an increased DHA/AA ratio and increased 19,20-diHDPA are indicative for an anti-inflammatory profile and may indirectly contribute to the atheroprotective lipid and lipoprotein profile associated with prolonged niacin treatment.

Increased systemic and adipose tissue inflammation differentiates obese women with T2DM from obese women with normal glucose tolerance

INTRODUCTION

Obesity is strongly related to type-2 diabetes (T2DM), but there is a subset of obese individuals that remains relatively insulin sensitive and metabolically healthy. This study determined to what extent differences in metabolic health in obese women are associated with differences in adipose tissue and/or systemic inflammation.

METHODS

The subject group consisted of age comparable lean (n=12) and obese women either with T2DM (n=28) or normal glucose tolerance (NGT; n=26). Number of crown like structures (CLS) and adipocyte size were measured in subcutaneous and visceral adipose tissue of the obese women. Circulating cytokine and free fatty acid (FFA) levels, as well as number and activation status of peripheral leukocytes were determined.

RESULTS

Obese T2DM subjects showed higher circulating levels of IL-6, FFA and glycerol as compared to obese NGT subjects. Obese T2DM subjects had higher absolute numbers of peripheral leukocytes which were mainly due to an increase of T helper cells. Activation status of circulating cytotoxic T (CD8+CD25+) and B (CD19+CD38+) cells was significantly increased in obese NGT subjects as compared to lean but was not different between the two obese groups. Subcutaneous adipose tissue of obese T2DM subjects contained more CLS than adipose tissue of obese NGT subjects.

CONCLUSION

Obese T2DM subjects show higher FFA levels and adipose tissue macrophage infiltration in addition to higher levels of circulating IL-6 and numbers of CD4+ T cells than obese NGT subjects. Hence, obese T2DM subjects show a higher extent of inflammation at both the systemic and adipose tissue level.

Long-term niacin treatment induces insulin resistance and adrenergic responsiveness in adipocytes by adaptive downregulation of phosphodiesterase 3B

The lipid-lowering effect of niacin has been attributed to the inhibition of cAMP production in adipocytes, thereby inhibiting intracellular lipolysis and release of nonesterified fatty acids (NEFA) to the circulation. However, long-term niacin treatment leads to a normalization of plasma NEFA levels and induces insulin resistance, for which the underlying mechanisms are poorly understood. The current study addressed the effects of long-term niacin treatment on insulin-mediated inhibition of adipocyte lipolysis and focused on the regulation of cAMP levels. APOE*3-Leiden.CETP transgenic mice treated with niacin for 15 wk were subjected to an insulin tolerance test and showed whole body insulin resistance. Similarly, adipocytes isolated from niacin-treated mice were insulin resistant and, interestingly, exhibited an increased response to cAMP stimulation by 8Br-cAMP, β1- and β2-adrenergic stimulation. Gene expression analysis of the insulin and β-adrenergic pathways in adipose tissue indicated that all genes were downregulated, including the gene encoding the cAMP-degrading enzyme phosphodiesterase 3B (PDE3B). In line with this, we showed that insulin induced a lower PDE3B response in adipocytes isolated from niacin-treated mice. Inhibiting PDE3B with cilostazol increased lipolytic responsiveness to cAMP stimulation in adipocytes. These data show that long-term niacin treatment leads to a downregulation of PDE3B in adipocytes, which could explain part of the observed insulin resistance and the increased responsiveness to cAMP stimulation.

CD36 is important for adipocyte recruitment and affects lipolysis

OBJECTIVE

The scavenger receptor CD36 facilitates the cellular uptake of long-chain fatty acids. As CD36-deficiency attenuates the development of high fat diet (HFD)-induced obesity, the role of CD36-deficiency in preadipocyte recruitment and adipocyte function was set out to characterize.

DESIGN AND METHODS

Fat cell size and number were determined in gonadal, visceral, and subcutaneous adipose tissue of CD36(-/-) and WT mice after 6 weeks on HFD. Basal lipolysis and insulin-inhibited lipolysis were investigated in gonadal adipose tissue.

RESULTS

CD36(-/-) mice showed a reduction in adipocyte size in all fat pads. Gonadal adipose tissue also showed a lower total number of adipocytes because of a lower number of very small adipocytes (diameter <50 μm). This was accompanied by an increased pool of preadipocytes, which suggests that CD36-deficiency reduces the capacity of preadipocytes to become adipocytes. Regarding lipolysis, in adipose tissue from CD36(-/-) mice, cAMP levels were increased and both basal and 8-bromo-cAMP stimulated lipolysis were higher. However, insulin-mediated inhibition of lipolysis was more potent in CD36(-/-) mice.

CONCLUSIONS

These results indicate that during fat depot expansion, CD36-deficiency negatively affects preadipocyte recruitment and that in mature adipocytes, CD36-deficiency is associated with increased basal lipolysis and insulin responsiveness.

Adipocyte-derived lipids modulate CD4+ T-cell function

Adipose tissue contains several immune cells whose number and phenotype vary depending on the adiposity. In the present study, we show that IFN-γ(+) CD4(+) T cells are enriched in human adipose tissue compared with in blood. To gain insight into the underlying mechanisms, we investigated the possibility that human adipocytes modulate CD4(+) T-cell cytokine production and proliferation and show that CD4(+) T cells produced increased levels of IFN-γ when activated in the presence of adipocytes. This effect was mediated by soluble mediators, as shown in transwell and adipocyte-conditioned medium (ACM) transfer experiments. Additionally, ACM induced increased proliferation of CD4(+) T cells upon activation. Intriguingly, the proliferation-enhancing effect resided mainly in the lipid fraction of ACM, as shown upon separation of the protein and lipid fraction. Further separation of these lipids based on polarity revealed that the modulatory effect is confined to fractions containing free fatty acids. All identified fatty acids were able to individually enhance T-cell proliferation. These data indicate that adipocytes can modulate CD4(+) T-cell function through the release of lipids. Remarkably, free fatty acids were the most prominent modulators of T-cell proliferation, possibly leading to an accumulation of these cells in adipose tissue.

Angiotensin II Promotes Leptin Production in Cultured Human Fat Cells by an ERK1/2-dependent Pathway

OBJECTIVE

The fat cell hormone leptin is known to be implicated in the pathogenesis of hypertension and cardiovascular disease. Here we tested whether angiotensin (Ang) II is involved in the control of leptin release from human adipocytes.

RESEARCH METHODS AND PROCEDURES

Leptin secretion was assessed from in vitro differentiated human adipocytes by radioimmunoassay. Western blot experiments were used to test for the signaling pathway activated by Ang II.

RESULTS

Ang II increased leptin secretion into the culture medium in a dose- and time-dependent fashion. At 10(-5) M Ang II, the leptin concentration in the medium was increased at 24 hours by 500+/-222% compared with control cultures (p<0.05). This effect was also seen at the mRNA level. Similar effects were seen after exposure of fat cells to Ang III and Ang IV. Preincubation of fat cells with candesartan, an angiotensin II type 1 receptor antagonist, or the extracellular-signal-regulated kinases 1 and 2 inhibitor UO126 completely abolished the effect of Ang II on leptin production. The peroxisome proliferator-activated receptor-gamma agonist troglitazone modestly attenuated leptin release.

DISCUSSION

In conclusion, Ang II and its metabolites stimulated leptin production in human adipocytes. This effect is mediated through an extracellular-signal-regulated kinases 1 and 2-dependent pathway and includes the angiotensin II type 1 receptor subtype.

Monomeric tartrate resistant acid phosphatase induces insulin sensitive obesity

BACKGROUND

Obesity is associated with macrophage infiltration of adipose tissue, which may link adipose inflammation to insulin resistance. However, the impact of inflammatory cells in the pathophysiology of obesity remains unclear. Tartrate resistant acid phosphatase (TRAP) is an enzyme expressed by subsets of macrophages and osteoclasts that exists either as an enzymatically inactive monomer or as an active, proteolytically processed dimer.

PRINCIPAL FINDINGS

Using mice over expressing TRAP, we show that over-expression of monomeric, but not the dimeric form in adipose tissue leads to early onset spontaneous hyperplastic obesity i.e. many small fat cells. In vitro, recombinant monomeric, but not proteolytically processed TRAP induced proliferation and differentiation of mouse and human adipocyte precursor cells. In humans, monomeric TRAP was highly expressed in the adipose tissue of obese individuals. In both the mouse model and in the obese humans the source of TRAP in adipose tissue was macrophages. In addition, the obese TRAP over expressing mice exhibited signs of a low-grade inflammatory reaction in adipose tissue without evidence of abnormal adipocyte lipolysis, lipogenesis or insulin sensitivity.

CONCLUSION

Monomeric TRAP, most likely secreted from adipose tissue macrophages, induces hyperplastic obesity with normal adipocyte lipid metabolism and insulin sensitivity.

Vascular peptide endothelin-1 links fat accumulation with alterations of visceral adipocyte lipolysis

OBJECTIVE

Visceral obesity increases risk of insulin resistance and type 2 diabetes. This may partly be due to a region-specific resistance to insulin's antilipolytic effect in visceral adipocytes. We investigated whether adipose tissue releases the vascular peptide endothelin-1 (ET-1) and whether ET-1 could account for regional differences in lipolysis.

RESEARCH DESIGN AND METHODS

One group consisted of eleven obese and eleven nonobese subjects in whom ET-1 levels were compared between abdominal subcutaneous and arterialized blood samples. A second group included subjects undergoing anti-obesity surgery. Abdominal subcutaneous and visceral adipose tissues were obtained to study the effect of ET-1 on differentiated adipocytes regarding lipolysis and gene and protein expression.

RESULTS

Adipose tissue had a marked net release of ET-1 in vivo, which was 2.5-fold increased in obesity. In adipocytes treated with ET-1, the antilipolytic effect of insulin was attenuated in visceral but not in subcutaneous adipocytes, which could not be explained by effects of ET-1 on adipocyte differentiation. ET-1 decreased the expression of insulin receptor, insulin receptor substrate-1 and phosphodiesterase-3B and increased the expression of endothelin receptor-B (ET(B)R) in visceral but not in subcutaneous adipocytes. These effects were mediated via ET(B)R with signals through protein kinase C and calmodulin pathways. The effect of ET-1 could be mimicked by knockdown of IRS-1.

CONCLUSIONS

ET-1 is released from human adipose tissue and links fat accumulation to insulin resistance. It selectively counteracts insulin inhibition of visceral adipocyte lipolysis via ET(B)R signaling pathways, which affect multiple steps in insulin signaling.

Mechanism of increased lipolysis in cancer cachexia

Loss of fat mass is a key feature of cancer cachexia and has been attributed to increased adipocyte lipolysis. The mechanism behind this alteration is unknown and was presently investigated. We studied mature s.c. fat cells and differentiated preadipocytes from 26 cancer patients with and without cachexia. Hormone-induced lipolysis and expression of lipolysis-regulating genes were determined together with body composition and in vivo lipolytic activity (fasting plasma glycerol or fatty acids related to body fat). Body fat was reduced by 40% and in vivo lipolytic activity was 2-fold increased in cachexia (P = 0.001). In mature adipocytes, the lipolytic effects of catecholamines and natriuretic peptide were 2- to 3-fold increased in cachexia (P < 0.001). This was completely counteracted by inhibiting the rate-limiting lipolysis enzyme hormone-sensitive lipase (HSL). In cachexia, the expression levels of HSL mRNA and protein were increased by 50% and 100%, respectively (P = 0.005-0.03), which strongly correlated with in vitro lipolytic stimulation (r = 0.7-0.9). The antilipolytic effect of insulin in mature fat cells and the stimulated lipolytic effect in differentiated preadipocytes were unaltered in cachexia. Patients who lost weight due to other factors than cancer cachexia had no change in adipocyte lipolysis. In conclusion, adipocyte lipolysis is increased in cancer cachexia not due to nonepigenic factors or to weight loss per se, but most probably because of enhanced expression and function of adipocyte HSL. The selective inhibition of this enzyme may prevent fat loss in cancer patients.

A common haplotype in the G-protein-coupled receptor gene GPR74 is associated with leanness and increased lipolysis

The G-protein-coupled receptor GPR74 is a novel candidate gene for body weight regulation. In humans, it is predominantly expressed in brain, heart, and adipose tissue. We report a haplotype in the GPR74 gene, ATAG, with allele frequency ~4% in Scandinavian cohorts, which was associated with protection against obesity in two samples selected for obese and lean phenotypes (odds ratio for obesity 0.48 and 0.62; nominal P=.0014 and .014; n=1,013 and 1,423, respectively). In a population-based sample, it was associated with lower waist (P=.02) among 3,937 men and with obesity protection (odds ratio 0.36; P=.036) among those selected for obese or lean phenotypes. The ATAG haplotype was associated with increased adipocyte lipid mobilization (lipolysis) in vivo and in vitro. In human fat cells, GPR74 receptor stimulation and inhibition caused a significant and marked decrease and increase, respectively, of lipolysis, which could be linked to catecholamine stimulation of adipocytes through beta -adrenergic receptors. These findings suggest that a common haplotype in the GPR74 gene protects against obesity, which, at least in part, is caused by a relief of inhibition of lipid mobilization from adipose tissue. The latter involves a cross-talk between GPR74 and beta -adrenoceptor signaling to lipolysis in fat cells.

Comparative studies of the role of hormone-sensitive lipase and adipose triglyceride lipase in human fat cell lipolysis

Hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) regulate adipocyte lipolysis in rodents. The purpose of this study was to compare the roles of these lipases for lipolysis in human adipocytes. Subcutaneous adipose tissue was investigated. HSL and ATGL protein expression were related to lipolysis in isolated mature fat cells. ATGL or HSL were knocked down by RNA interference (RNAi) or selectively inhibited, and effects on lipolysis were studied in differentiated preadipocytes or adipocytes derived from human mesenchymal stem cells (hMSC). Subjects were all women. There were 12 lean controls, 8 lean with polycystic ovary syndrome (PCOS), and 27 otherwise healthy obese subjects. We found that norepinephrine-induced lipolysis was positively correlated with HSL protein levels (P < 0.0001) but not with ATGL protein. Women with PCOS or obesity had significantly decreased norepinephrine-induced lipolysis and HSL protein expression but no change in ATGL protein expression. HSL knock down by RNAi reduced basal and catecholamine-induced lipolysis. Knock down of ATGL decreased basal lipolysis but did not change catecholamine-stimulated lipolysis. Treatment of hMSC with a selective HSL inhibitor during and/or after differentiation in adipocytes reduced basal lipolysis by 50%, but stimulated lipolysis was inhibited completely. In contrast to findings in rodents, ATGL is of less importance than HSL in regulating catecholamine-induced lipolysis and cannot replace HSL when this enzyme is continuously inhibited. However, both lipases regulate basal lipolysis in human adipocytes. ATGL expression, unlike HSL, is not influenced by obesity or PCOS.

Differential lipolytic regulation in human embryonic stem cell-derived adipocytes

OBJECTIVE

Human embryonic stem cells (hESCs) have raised great hopes for future clinical applications. Several groups have succeeded in differentiating hESCs into adipocytes, as determined by morphology, mRNA expression, and protein secretion. However, determination of lipolytic response, the most important characteristic of adipocytes, has not been performed. This work was intended to study adipogenic conversion of hESCs by functional assessment of differentiation.

RESEARCH METHODS AND PROCEDURES

Single undifferentiated colonies were allowed to transform into embryonic bodies. mRNA expression for a set of adipocyte-specific genes and leptin/adiponectin secretion and lipolysis were assessed at different time-points after differentiation.

RESULTS

In contrast to primary human adipocytes, hESC-derived adipocytes showed a very small response to classical beta-adrenergic agonists, although they expressed the major genes in the lipolytic cascade. In contrast, there was a significant lipolytic response to atrial natriuretic peptide.

DISCUSSION

Although hESC-derived adipocytes seem to be morphologically and expressionally similar to mature adipocytes, there are important functional differences that could depend on their early developmental origin. We conclude that, in contrast to mature adipocytes, hESC-derived adipocytes display a differential response to atrial natriuretic peptide and catecholamines.

NF-kappaB is important for TNF-alpha-induced lipolysis in human adipocytes

Tumor necrosis factor-alpha (TNF-alpha) promotes lipolysis in mammal adipocytes via the mitogen-activated protein kinase (MAPK) family, resulting in reduced expression/function of perilipin (PLIN). The role of another pivotal intracellular messenger activated by TNF-alpha, nuclear factor-kappaB (NF-kappaB), has not been recognized. We explored the role of NF-kappaB in TNF-alpha-induced lipolysis of human fat cells. Primary cultures of human adipocytes were incubated in the presence of a cell-permeable peptide that inhibits NF-kappaB signaling (WP). Incubation with WP, but not with a biologically inactive peptide (MP), abolished the nuclear translocation of NF-kappaB and effectively abrogated TNF-alpha-induced lipolysis in a concentration-dependent manner. Western blot analysis demonstrated that although TNF-alpha per se reduced mainly PLIN protein expression, TNF-alpha in the presence of WP resulted in a pronounced combined reduction of both hormone-sensitive lipase (HSL) and PLIN protein. The expression of a set of other lipolytic or adipocyte-specific proteins was not affected. The regulation was presumably at the transcriptional level, because mRNA expression for HSL and PLIN was markedly reduced with TNF-alpha in the presence of NF-kappaB inhibition. This was confirmed in gene reporter assays using human PLIN and HSL promoter constructs. We conclude that in the presence of NF-kappaB inhibition, TNF-alpha-mediated lipolysis is reduced, which suggests that NF-kappaB is essential for retained human fat cell lipolysis.

A role of lipin in human obesity and insulin resistance: relation to adipocyte glucose transport and GLUT4 expression

The mouse lipin gene, Lpin1, is important for adipose tissue development and is a candidate gene for insulin resistance. Here, we investigate the adipose tissue expression levels of the human LPIN1 gene in relation to various clinical variables as well as adipocyte function. LPIN1 gene expression was induced at an early step in human preadipocyte differentiation in parallel with peroxisome proliferator-activated receptor gamma. Lipin mRNA levels were higher in fat cells than in adipose tissue segments but showed no difference between subcutaneous and omental depots. Moreover, LPIN1 expression levels were reduced in obesity, improved following weight reduction in obese subjects, and were downregulated in women with the metabolic syndrome. With respect to adipocyte function, adipose LPIN1 gene expression was strongly associated with both basal and insulin-mediated subcutaneous adipocyte glucose transport as well as mRNA levels of glucose transporter 4 (GLUT4). We show that body fat accumulation is a major regulator of human adipose LPIN1 expression and suggest a role of LPIN1 in human preadipocyte as well as mature adipocyte function.

Albumin inhibits adipogenesis and stimulates cytokine release from human adipocytes

Bovine serum albumin (BSA) is commonly used in adipocyte experiments as a binding protein for fat-soluble substances. Therefore, it is of interest to investigate whether BSA per se is influencing the functioning of human adipocytes in vitro. In the present study, we investigated the potential of BSA to affect the proliferation and differentiation capacity of human preadipocytes. BSA was found to inhibit adipose differentiation in a dose-dependent manner (being significant at concentrations of 2.5 μM), whereas proliferation was not affected. We further investigated the effect of BSA on the secretory function of adipocytes focusing on the release of selected cytokines. Preadipocytes and freshly isolated adipocytes incubated with BSA secreted significantly higher amounts of IL-6, -8, and -10, and TNF-α compared with cells incubated without BSA. The effects on cytokine secretion seemed to reside at the level of gene expression because BSA increased TNF-α and IL-6 mRNA in a dose-dependent manner. The results of the present study indicate that the presence of BSA in the culture medium has considerable effects on adipocyte function in vitro. These effects should be carefully considered for in vitro studies of adipose tissue.

Adipocyte lipases and defect of lipolysis in human obesity

The mobilization of fat stored in adipose tissue is mediated by hormone-sensitive lipase (HSL) and the recently characterized adipose triglyceride lipase (ATGL), yet their relative importance in lipolysis is unknown. We show that a novel potent inhibitor of HSL does not inhibit other lipases. The compound counteracted catecholamine-stimulated lipolysis in mouse adipocytes and had no effect on residual triglyceride hydrolysis and lipolysis in HSL-null mice. In human adipocytes, catecholamine- and natriuretic peptide-induced lipolysis were completely blunted by the HSL inhibitor. When fat cells were not stimulated, glycerol but not fatty acid release was inhibited. HSL and ATGL mRNA levels increased concomitantly during adipocyte differentiation. Abundance of the two transcripts in human adipose tissue was highly correlated in habitual dietary conditions and during a hypocaloric diet, suggesting common regulatory mechanisms for the two genes. Comparison of obese and nonobese subjects showed that obesity was associated with a decrease in catecholamine-induced lipolysis and HSL expression in mature fat cells and in differentiated preadipocytes. In conclusion, HSL is the major lipase for catecholamine- and natriuretic peptide-stimulated lipolysis, whereas ATGL mediates the hydrolysis of triglycerides during basal lipolysis. Decreased catecholamine-induced lipolysis and low HSL expression constitute a possibly primary defect in obesity.

Functional studies of mesenchymal stem cells derived from adult human adipose tissue

Recent evidence suggests that cells with the properties of human mesenchymal stem cells (hMSCs) can be derived from adult peripheral tissues, including adipose tissue, muscle and dermis. We isolated hMSCs from the stromal-vascular portion of subcutaneous adipose tissue from seven adult subjects. These cells could be readily differentiated into cells of the chondrocyte, osteocyte and adipocyte lineage demonstrating their multipotency. We studied the functional properties of hMSCs-derived adipocytes and compared them with adipocytes differentiated from hMSCs obtained from bone marrow (BM-hMSC). The two cell types displayed similar lipolytic capacity upon stimulation with catecholamines, including a pronounced antilipolytic effect mediated through alpha2A-adrenoceptors, a typical trait in human but not rodent fat cells. Furthermore, both cell types secreted the fat cell-specific factors leptin and adiponectin in comparable amounts per time unit. The fat tissue-derived hMSCs retained their differentiation capacity up to at least fifteen passages. We conclude that hMSCs derived from adult human adipose tissue can be differentiated into fully functional adipocytes with a similar, if not identical, phenotype as that observed in cells derived from BM-hMSCs. Human adipose-tissue-derived MSCs could therefore constitute an efficient and easily obtainable renewable cellular source for studies of adipocyte biology.

Upstream transcription factor-1 gene polymorphism is associated with increased adipocyte lipolysis

OBJECTIVE

Variations in lipid metabolism between individuals could be due to genetic factors. A transmission of a haplotype of the upstream transcription factor-1 (USF-1) gene containing the minor alleles at the usf1s1 and usfs2 loci is described. We investigated whether these polymorphisms are associated with adipocyte lipolysis.

METHODS AND RESULTS

A total of 196 healthy obese women were investigated for in vitro lipolysis regulation in sc fat cells, which was set in relation to the usf1s1 C-->T and usf1s2 G-->A polymorphisms in the usf1 gene. The two polymorphisms were in complete linkage disequilibrium. The usf1s1/2 T/A allele was associated with increases in the maximum lipolytic action of noradrenaline (P = 0.005), dobutamine (P = 0.008), terbutaline (P = 0.008), CGP12177 (P = 0.015), and forskolin (P = 0.006). In contrast, no significant genotype effect on lipolytic sensitivity (i.e. half-maximum effective concentration) for any of the drugs was demonstrated. Analysis of adipose tissue mRNA expression in 78 women from genes regulating lipolysis at the postadrenoceptor level showed an increased level of protein kinase A subunit R1alpha in the T/A genotype (P = 0.02).

CONCLUSIONS

Polymorphism in the usf1 gene is associated with increased lipolytic effect of catecholamines in fat cells, which is localized at the postadrenoceptor level, possibly, at least, involving protein kinase A.

Angiotensin II Stimulates the Release of Interleukin-6 and Interleukin-8 From Cultured Human Adipocytes by Activation of NF-κB

OBJECTIVE

Several proinflammatory cytokines including IL-6 and IL-8 are produced by human adipocytes, but it is still unclear how this process is regulated. Angiotensin (Ang) II, which is also produced by adipocytes, might play a role as a regulator. In the present study, we investigated the effect of Ang II on the production of IL-6 and IL-8 in in vitro differentiated human adipocytes.

METHODS AND RESULTS

Isolation of preadipocytes and differentiation of these cells into adipocytes, Real-time quantitative reverse-transcriptase polymerase chain reaction, Western-blot, enzyme-linked immunosorbent assay, and electromobility shift assay. Ang II-stimulated IL-6 and IL-8 mRNA expression and protein release in a time- and concentration-dependent way. This action of Ang II was completely blocked by the NF-kappaB-blocker Bay 117082 and the AT1 blocker candesartan, but only partially by the AT2-blocker PD 123 319. Incubation of adipocytes with Ang II resulted in an increased phosphorylation of the p65 subunit of NF-kappaB and an increased translocation of NF-kappaB to the nucleus.

CONCLUSIONS

Ang II stimulates IL-6 and IL-8 production and release from human adipocytes by a NF-kappaB-dependent pathway. This proinflammatory action of Ang II seems to be mediated by the AT1 and less by the AT2 receptor subtype.

Resection of pancreatic cancer normalizes the preoperative increase of tumor necrosis factor alpha gene expression

BACKGROUND

Tumor necrosis factor alpha (TNF-alpha) appears to play a role in the cachexia and diabetes seen in patients with cancers. However, increased TNF-alpha is seen in some, but not all, of the cancer patients.

METHODS

The mRNA transcripts of TNF-alpha and its receptors (TNF-RI and TNF-RII) were quantified in blood cells of pancreatic cancer patients, using competitive quantitative reverse transcriptase-polymerase chain reaction. Plasma TNF-alpha was also quantified in these patients by enzyme-linked immunosorbent assay. Control blood came from healthy subjects.

RESULTS

The TNF-alpha mRNA transcripts (per microgram of total RNA) were increased in pancreatic cancer patients (6.8 +/- 2.1 x 10(6), n = 10), compared to control (1.2 +/- 0.2 x 10(6), n = 9, p < 0.05). After the tumour was removed, the TNF-alpha mRNA transcripts were reduced to a level (2.1 +/- 0.8 x 10(6)) similar to the control. In the cancer patients, no significant changes were found in TNF-RI and TNF-RII gene transcription, compared to the controls.

CONCLUSION

The expression of the TNF-alpha gene is upregulated in patients with pancreatic cancer and normalized after the pancreatic tumor is removed. These results are consistent with the concept that TNF-alpha is involved in metabolic disorders associated with pancreatic cancer.

Increased lipolysis and decreased leptin production by human omental as compared with subcutaneous preadipocytes

Site differences in adipose tissue function may have implications for insulin-resistant conditions. In mature adipose tissue, subcutaneous adipocytes have higher leptin secretion, similar tumor necrosis factor (TNF)-alpha secretion, and lower catecholamine-stimulated lipolysis as compared with omental adipocytes. In this study, lipolysis and leptin and TNF-alpha secretion were compared between human omental and subcutaneous preadipocytes. After 16 days of incubation in a minimal differentiation medium, leptin mRNA and secretion were found to be two to eight times higher in subcutaneous than omental preadipocytes (P < 0.05). On the other hand, norepinephrine-induced lipolysis was about two times higher in the omental than in the subcutaneous preadipocytes, whereas basal lipolysis did not differ between the two regions. TNF-alpha secretion was marginally but significantly higher in the omental than in the subcutaneous preadipocytes. Preadipocyte differentiation was equal in both regions and was augmented to the same extent by different thiazolidinediones (rosiglitazone, pioglitazone, or troglitazone) in the two depots. In the presence of rosiglitazone, leptin secretion remained about three times higher and norepinephrine-induced lipolysis about six times lower in subcutaneous as compared with omental preadipocytes (P < 0.05), whereas TNF-alpha secretion and basal lipolysis were similar in preadipocytes from the two regions. These findings remained unaltered even if rosiglitazone was removed from the medium. However, leptin mRNA showed no regional differences in rosiglitazone-treated cells. Thus, regional differences in adipocyte leptin secretion as well as in norepinephrine-induced lipolysis are marked and present during different stages of preadipocyte differentiation and seem to be determined by intrinsic (i.e., primary) factors.

Mapping of early signaling events in tumor necrosis factor-alpha -mediated lipolysis in human fat cells

Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine with a proposed role in obesity-related insulin resistance. This could be mediated by increased lipolysis in adipose tissue resulting in elevated free fatty acid levels. The early intracellular signals entailed in TNF-alpha-mediated lipolysis are unknown but may involve members of the mitogen-activated protein kinase (MAPK) family. We investigated the possible contribution of MAPK in TNF-alpha-induced lipolysis in human preadipocytes. TNF-alpha activated the three mammalian MAPK, p44/42, JNK, and p38, in a distinct time- and concentration-dependent manner. TNF-alpha also induced a concentration-dependent stimulation of lipolysis with a more than 3-fold increase at the maximal dose. Lipolysis was completely inhibited by blockers specific for p44/42 (PD98059) and JNK (dimetylaminopurine) but was not affected by the p38 blocker SB203580. Use of receptor-specific TNF-alpha mutants showed that activation of MAPK is entirely mediated by the TNFR1 receptor. The results in human preadipocytes differed from those obtained in murine 3T3-L1 adipocytes in which all three MAPK were constitutively active. Thus, studies of intracellular signaling pathways obtained in different cellular contexts should be interpreted with caution. In conclusion, although TNF-alpha activates all three known MAPK in human preadipocytes, only p44/42 and JNK appear to be involved in the regulation of lipolysis.