Acylation-stimulating protein precursor proteins in adipose tissue in human obesity

A randomized diet-induced weight-loss intervention reduces plasma complement C3: Possible implication for endothelial dysfunction

OBJECTIVE

Complement C3 and other components of the alternative pathway are higher in individuals with obesity. Moreover, C3 has been identified as a risk factor for cardiovascular disease. This study investigated whether, and how, a weight-loss intervention reduced plasma C3, activated C3 (C3a), and factor D and explored potential biological effects of such a reduction.

METHODS

The study measured plasma C3, C3a, and factor D by ELISA and measured visceral adipose tissue, subcutaneous adipose tissue, and intrahepatic lipid by magnetic resonance imaging in lean men (n = 25) and men with abdominal obesity (n = 52). The men with obesity were randomized to habitual diet or an 8-week dietary weight-loss intervention.

RESULTS

The intervention significantly reduced C3 (-0.15 g/L [95% CI: -0.23 to -0.07]), but not C3a or factor D. The C3 reduction was mainly explained by reduction in visceral adipose tissue but not subcutaneous adipose tissue or intrahepatic lipid. This reduction in C3 explained a part of the weight-loss-induced improvement of markers of endothelial dysfunction, particularly the reduction in soluble endothelial selectin and soluble intercellular adhesion molecule.

CONCLUSIONS

Diet-induced weight loss in men with abdominal obesity could be a way to lower plasma C3 and thereby improve endothelial dysfunction. C3 reduction may be part of the mechanism via which diet-induced weight loss could ameliorate the risk of cardiovascular disease in men with abdominal obesity.

Adipsin Serum Concentrations and Adipose Tissue Expression in People with Obesity and Type 2 Diabetes

(1) Adipsin is an adipokine that may link increased fat mass and adipose tissue dysfunction to obesity-related cardiometabolic diseases. Here, we investigated whether adipsin serum concentrations and adipose tissue (AT) adipsin mRNA expression are related to parameters of AT function, obesity and type 2 diabetes (T2D). (2) Methods: A cohort of 637 individuals with a wide range of age and body weight (Age: 18–85 years; BMI: 19–70 kg/m2) with (n = 237) or without (n = 400) T2D was analyzed for serum adipsin concentrations by ELISA and visceral (VAT) and subcutaneous (SAT) adipsin mRNA expression by RT-PCR. (3) Results: Adipsin serum concentrations were significantly higher in patients with T2D compared to normoglycemic individuals. We found significant positive univariate relationships of adipsin serum concentrations with age (r = 0.282, p < 0.001), body weight (r = 0.264, p < 0.001), fasting plasma glucose (r = 0.136, p = 0.006) and leptin serum concentrations (r = 0.362, p < 0.001). Neither VAT nor SAT adipsin mRNA expression correlated with adipsin serum concentrations after adjusting for age, sex and BMI. Independent of T2D status, we found significantly higher adipsin expression in SAT compared to VAT (4) Conclusions: Our data suggest that adipsin serum concentrations are strongly related to obesity and age. However, neither circulating adipsin nor adipsin AT expression reflects parameters of impaired glucose or lipid metabolism in patients with obesity with or without T2D.

An overview of lipodystrophy and the role of the complement system

The complement system is a major component of innate immunity playing essential roles in the destruction of pathogens, the clearance of apoptotic cells and immune complexes, the enhancement of phagocytosis, inflammation, and the modulation of adaptive immune responses. During the last decades, numerous studies have shown that the complement system has key functions in the biology of certain tissues. For example, complement contributes to normal brain and embryonic development and to the homeostasis of lipid metabolism. However, the complement system is subjected to the effective balance between activation-inactivation to maintain complement homeostasis and to prevent self-injury to cells or tissues. When this control is disrupted, serious pathologies eventually develop, such as C3 glomerulopathy, autoimmune conditions and infections. Another heterogeneous group of ultra-rare diseases in which complement abnormalities have been described are the lipodystrophy syndromes. These diseases are characterized by the loss of adipose tissue throughout the entire body or partially. Complement over-activation has been reported in most of the patients with acquired partial lipodystrophy (also called Barraquer-Simons Syndrome) and in some cases of the generalized variety of the disease (Lawrence Syndrome). Even so, the mechanism through which the complement system induces adipose tissue abnormalities remains unclear. This review focuses on describing the link between the complement system and certain forms of lipodystrophy. In addition, we present an overview regarding the clinical presentation, differential diagnosis, classification, and management of patients with lipodystrophy associated with complement abnormalities.

Clinical significance of serum complement factor 3 in patients with type 2 diabetes mellitus

AIMS

Although serum complement factor 3 (C3) is an acute phase reactant mainly synthesized in the liver, several recent studies have shown high C3 gene expression in adipose tissue (AT). However, the relationship between C3 and AT levels has not been fully clarified in type 2 diabetes mellitus (T2DM) patients.

METHODS

A total of 164 T2DM patients (109men and 55 women) participated in this cross-sectional study. A computed tomography scan was performed to measure visceral, subcutaneous, and total AT. The correlation between these factors and C3 levels was examined using Pearson's correlation analysis. A multivariate regression model was used to assess an independent determinant associated with C3 levels after adjusting the explanatory variables (i.e., all ATs [visceral, subcutaneous, and total], and clinical features [sex, age, body mass index, waist circumference, glycated hemoglobin, duration of diabetes, systolic blood pressure, diastolic blood pressure, aspartate aminotransferase levels, alanine aminotransferase levels, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, log(triglyceride levels), estimated glomerular filtration rate, and log(high-sensitivity C-reactive protein levels)]).

RESULTS

Serum C3 levels were correlated with visceral, subcutaneous, and total AT among both men (r=0.505, p<0.001; r=0.545, p<0.001; r=0.617, p<0.001, respectively) and women (r=0.396, p=0.003; r=0.517, p<0.001; r=0.548, p<0.001, respectively). In the multivariate regression model, the association between total AT and C3 levels remained significantly positive (β=0.490, p<0.001).

CONCLUSIONS

Serum C3 levels are associated with visceral, subcutaneous, and total AT in T2DM patients. Furthermore, C3 levels seem to be a marker for overall adiposity rather than regional adiposity.

Complement factors C4 and C3 are down regulated in response to short term overfeeding in healthy young men

Insulin resistance is associated with high circulating level of complement factor C3. Animal studies suggest that improper complement activation mediates high-fat-diet-induced insulin resistance. Individuals born with low birth weight (LBW) are at increased risk of developing insulin resistance. We hypothesized that high-fat overfeeding (HFO) increase circulating C3 and induce complement activation in a birth weight differential manner. Twenty LBW and 26 normal birth weight (NBW) young men were studied using a randomised crossover design. Insulin resistance was measured after a control-diet and after 5-days HFO by a hyperinsulinemic-euglycemic-clamp. Circulating C4, C3, ficolins, mannose-binding-lectin, complement activation products C3bc, terminal complement complex (TCC) and complement activation capacity were determined using turbidimetry and ELISA. HFO induced peripheral insulin resistance in LBW individuals only, while both groups had the same degree of hepatic insulin resistance after HFO. Viewing all individuals circulating levels of C4, C3, C3bc, TCC and complement activation capacity decreased paradoxically along the development of insulin resistance after HFO (P = 0.0015, P < 0.0001, P = 0.01, P < 0.0001, P = 0.0002, P < 0.0001, P = 0.0006). Birth weight did not influence these results. This might reflect a hitherto unrecognized down-regulatory mechanism of the complement system. More human studies are needed to understand the underlying physiology and the potential consequences of these findings.

Plasma complement C3 levels are associated with insulin secretion independently of adiposity measures in non-diabetic individuals

BACKGROUND AND AIMS

To evaluate if complement C3 is associated with insulin secretion, as suggested by recent in vitro studies, independently of confounders including adiposity measures.

METHODS AND RESULTS

1010 nondiabetic subjects were stratified into quartiles according to complement C3 values. Insulin secretion was assessed using indexes derived from oral glucose tolerance test (OGTT) in the whole study group and from intravenous glucose tolerance test (IVGTT) in a subgroup (n = 110). Significant differences between quartiles of C3 were observed in body mass index (BMI), waist, fat mass, blood pressure, total cholesterol, high density lipoprotein (HDL), triglycerides, fasting and 2-h post-load glucose, fasting insulin, C reactive protein (hsCRP), fibrinogen, aspartate aminotransferase (AST), alanine aminotransferase (ALT), complement C4, and insulin sensitivity with C3 quartiles exhibiting graded increases in cardio-metabolic risk factors. Differences in insulin secretion indexes between C3 quartiles remained significant after adjustment for age, gender, BMI, insulin sensitivity, blood pressure, total cholesterol, HDL, triglycerides, hsCRP, fibrinogen, and complement C4 levels (P < 0.0001). A multivariable regression analysis revealed that complement C3 is a contributor of insulin secretion, explaining 2.4% and 1.9% of variation of the Stumvoll index for first-phase and second-phase insulin secretion, respectively, and 2.1% of variation of the InsAUC30/GluAUC30 index, independently of gender, age, BMI, waist, fat mass, blood pressure, total cholesterol, HDL, triglycerides, hsCRP, fibrinogen, AST, ALT.

CONCLUSIONS

Complement C3 concentrations are associated with insulin secretion independently of important determinants of glucose homeostasis such as gender, age, adiposity, subclinical inflammation, and insulin sensitivity.

The complement system in human cardiometabolic disease

The complement system has been implicated in obesity, fatty liver, diabetes and cardiovascular disease (CVD). Complement factors are produced in adipose tissue and appear to be involved in adipose tissue metabolism and local inflammation. Thereby complement links adipose tissue inflammation to systemic metabolic derangements, such as low-grade inflammation, insulin resistance and dyslipidaemia. Furthermore, complement has been implicated in pathophysiological mechanisms of diet- and alcohol induced liver damage, hyperglycaemia, endothelial dysfunction, atherosclerosis and fibrinolysis. In this review, we summarize current evidence on the role of the complement system in several processes of human cardiometabolic disease. C3 is the central component in complement activation, and has most widely been studied in humans. C3 concentrations are associated with insulin resistance, liver dysfunction, risk of the metabolic syndrome, type 2 diabetes and CVD. C3 can be activated by the classical, the lectin and the alternative pathway of complement activation; and downstream activation of C3 activates the terminal pathway. Complement may also be activated via extrinsic proteases of the coagulation, fibrinolysis and the kinin systems. Studies on the different complement activation pathways in human cardiometabolic disease are limited, but available evidence suggests that they may have distinct roles in processes underlying cardiometabolic disease. The lectin pathway appeared beneficial in some studies on type 2 diabetes and CVD, while factors of the classical and the alternative pathway were related to unfavourable cardiometabolic traits. The terminal complement pathway was also implicated in insulin resistance and liver disease, and appears to have a prominent role in acute and advanced CVD. The available human data suggest a complex and potentially causal role for the complement system in human cardiometabolic disease. Further, preferably longitudinal studies are needed to disentangle which aspects of the complement system and complement activation affect the different processes in human cardiometabolic disease.

Downregulation of complement C3 and C3aR expression in subcutaneous adipose tissue in obese women

BACKGROUND

The central component of the complement system, C3, is associated with obesity, metabolic syndrome and cardiovascular disease however the underlying reasons are unknown. In the present study we evaluated gene expression of C3, the cleavage product C3a/C3adesArg and its cognate receptor C3aR in subcutaneous and omental adipose tissue in women.

METHODS

Women (n = 140, 21-69 years, BMI 19.5-79 kg/m2) were evaluated for anthropometric and blood parameters, and adipose tissue gene expression.

RESULTS

Subjects were separated into groups (n = 34-36) according to obesity: normal/overweight (≤30 kg/m2), obese I (≤45 kg/m2), obese II (≤51 kg/m2), and obese III (≤80 kg/m2). Overall, while omental expression remained unchanged, subcutaneous C3 and C3aR gene expression decreased with increasing adiposity (2-way ANOVA, p<0.01), with a concomitant decrease in SC/OM ratio (p<0.001). In subcutaneous adipose, both C3 and C3aR expression correlated with apoB, and apoA1 and inversely with waist circumference and blood pressure, while C3aR also correlated with glucose (p<0.05-0.0001). While omental C3aR expression did not correlate with any factor, omental C3 correlated with waist circumference, glucose and apoB (all p<0.05). Further, while plasma C3a/C3adesArg increased and adiponectin decreased with increasing BMI, both correlated (C3a negatively and adiponectin positively) with subcutaneous C3 and C3aR expression (p<0.05-0.001) or less).

CONCLUSIONS

The obesity-induced down-regulation of complement C3 and C3aR which is specific to subcutaneous adipose tissue, coupled to the strong correlations with multiple anthropometric, plasma and adipokine variables support a potential role for complement in immunometabolism.

Elevated fetal adipsin/acylation-stimulating protein (ASP) in obese pregnancy: novel placental secretion via Hofbauer cells

CONTEXT AND OBJECTIVE

Obesity in pregnancy is associated with increased risks of obesity in the offspring. We investigated the relationship between obesity in pregnancy and circulating maternal and fetal levels of adipose tissue-derived factors adipsin and acylation stimulating protein (ASP) in lean and obese mothers.

DESIGN

Paired peripheral and cord blood samples were taken. Paired fat and placenta tissue were taken for explant culture. Media were assayed for secreted adipsin and ASP. Clinical parameters assayed included fasting insulin, glucose, and adipsin.

SETTING

The study was conducted at a university hospital maternity unit.

PATIENTS

Patients included 35 lean [body mass index (BMI) 19-25 kg/m(2), mean age 32 years and 39 obese (BMI) > 30 kg/m(2), mean age 32.49 years] pregnant Caucasian women, delivered by cesarean section at term.

MAIN OUTCOME MEASURE

Identification of placental macrophages [Hofbauer cells (HBCs)], as a source of adipsin and ASP was determined.

RESULTS

HBCs secreted both adipsin and ASP. Cord levels of adipsin (1663.78 ± 52.76 pg/mL) and ASP (354.48 ± 17.17 ng/mL) were significantly elevated in the offspring of obese mothers compared with their lean controls [1354.66 ± 33.87 pg/mL and 302.63 ± 14.98 ng/mL, respectively (P < .05 for both)]. Placentae from obese mothers released significantly more adipsin and ASP than placentae from lean mothers [546.0 ± 44 pg/mL · g vs 284.56 ± 43 pg/mL · g and 5485.75 ± 163.32 ng/mL · g vs 2399.16 ± 181.83 ng/mL · g, respectively (P < .05 for both)]. Circulating fetal adipsin and ASP positively correlated with maternal BMI (r = 0.611, P < .0001, and r = 0.391, P < .05, respectively). Fetal adipsin correlated positively with maternal (r = 0.482, P < .01) and fetal homeostasis model assessment of insulin resistance (r = 0.465, P < .01).

CONCLUSIONS

We demonstrate novel secretion of adipsin and ASP by placental HBCs.

Adipose tissue gene expression of factors related to lipid processing in obesity

Background

Adipose tissue lipid storage and processing capacity can be a key factor for obesity-related metabolic disorders such as insulin resistance and diabetes. Lipid uptake is the first step to adipose tissue lipid storage. The aim of this study was to analyze the gene expression of factors involved in lipid uptake and processing in subcutaneous (SAT) and visceral (VAT) adipose tissue according to body mass index (BMI) and the degree of insulin resistance (IR).

Methods and Principal Findings

VLDL receptor (VLDLR), lipoprotein lipase (LPL), acylation stimulating protein (ASP), LDL receptor-related protein 1 (LRP1) and fatty acid binding protein 4 (FABP4) gene expression was measured in VAT and SAT from 28 morbidly obese patients with Type 2 Diabetes Mellitus (T2DM) or high IR, 10 morbidly obese patients with low IR, 10 obese patients with low IR and 12 lean healthy controls. LPL, FABP4, LRP1 and ASP expression in VAT was higher in lean controls. In SAT, LPL and FABP4 expression were also higher in lean controls. BMI, plasma insulin levels and HOMA-IR correlated negatively with LPL expression in both VAT and SAT as well as with FABP4 expression in VAT. FABP4 gene expression in SAT correlated inversely with BMI and HOMA-IR. However, multiple regression analysis showed that BMI was the main variable contributing to LPL and FABP4 gene expression in both VAT and SAT.

Conclusions

Morbidly obese patients have a lower gene expression of factors related with lipid uptake and processing in comparison with healthy lean persons.

Childhood overweight and asthma symptoms, the role of pro-inflammatory proteins

BACKGROUND

Systemic inflammation is suggested as a mechanism by which overweight might induce asthma. However, few studies have linked childhood overweight, inflammation and asthma.

OBJECTIVE

To study the association between body mass index (BMI), asthma symptoms and pro-inflammatory proteins.

METHODS

High-sensitivity C-reactive protein (hs-CRP), complement factor 3 (C3) and 4 (C4) concentrations, and body weight and height were available for 359 4-year-old children participating in the Prevention and Incidence of Asthma and Mite Allergy birth cohort study. Data on asthma symptoms were obtained by yearly questionnaires. Logistic regression and generalized estimating equations were used to analyse the cross-sectional and prospective associations between BMI, asthma symptoms and pro-inflammatory proteins.

RESULTS

BMI was associated with asthma symptoms {odds ratio [OR] 1.43 [95% confidence interval (CI): 1.08-1.88] per BMI standard deviation scores [SDS]}. The inclusion of hs-CRP, C3 and C4 in the statistical models did not change this association. C3 was cross-sectionally associated with frequent asthma symptoms [OR per interquartile range of C3: 1.97 (95% CI: 1.20-3.24)] and prospectively with asthma symptoms [OR: 1.48 (95%CI: 1.04-2.09)], independent of BMI SDS.

CONCLUSIONS AND CLINICAL RELEVANCE

We showed no evidence for a role of hs-CRP, C3 and C4 in the association between BMI and asthma symptoms. C3 concentrations were associated with (frequent) asthma symptoms, independent of BMI.

Association of adipocyte genes with ASP expression: a microarray analysis of subcutaneous and omental adipose tissue in morbidly obese subjects

Background

Prevalence of obesity is increasing to pandemic proportions. However, obese subjects differ in insulin resistance, adipokine production and co-morbidities. Based on fasting plasma analysis, obese subjects were grouped as Low Acylation Stimulating protein (ASP) and Triglyceride (TG) (LAT) vs High ASP and TG (HAT). Subcutaneous (SC) and omental (OM) adipose tissues (n = 21) were analysed by microarray, and biologic pathways in lipid metabolism and inflammation were specifically examined.

Methods

LAT and HAT groups were matched in age, obesity, insulin, and glucose, and had similar expression of insulin-related genes (InsR, IRS-1). ASP related genes tended to be increased in the HAT group and were correlated (factor B, adipsin, complement C3, p < 0.01 each). Differences between LAT and HAT group were almost exclusively in SC tissue, with little difference in OM tissue. Increased C5L2 (p < 0.01), an ASP receptor, in HAT suggests a compensatory ASP pathway, associated with increased TG storage.

Results

HAT adipose tissue demonstrated increased lipid related genes for storage (CD36, DGAT1, DGAT2, SCD1, FASN, and LPL), lipolysis (HSL, CES1, perilipin), fatty acid binding proteins (FABP1, FABP3) and adipocyte differentiation markers (CEBPα, CEBPβ, PPARγ). By contrast, oxidation related genes were decreased (AMPK, UCP1, CPT1, FABP7). HAT subjects had increased anti-inflammatory genes TGFB1, TIMP1, TIMP3, and TIMP4 while proinflammatory PIG7 and MMP2 were also significantly increased; all genes, p < 0.025.

Conclusion

Taken together, the profile of C5L2 receptor, ASP gene expression and metabolic factors in adipose tissue from morbidly obese HAT subjects suggests a compensatory response associated with the increased plasma ASP and TG.

Complement factor H is expressed in adipose tissue in association with insulin resistance

OBJECTIVE

Activation of the alternative pathway of the complement system, in which factor H (fH; complement fH [CFH]) is a key regulatory component, has been suggested as a link between obesity and metabolic disorders. Our objective was to study the associations between circulating and adipose tissue gene expressions of CFH and complement factor B (fB; CFB) with obesity and insulin resistance.

RESEARCH DESIGN AND METHODS

Circulating fH and fB were determined by enzyme-linked immunosorbent assay in 398 subjects. CFH and CFB gene expressions were evaluated in 76 adipose tissue samples, in isolated adipocytes, and in stromovascular cells (SVC) (n = 13). The effects of weight loss and rosiglitazone were investigated in independent cohorts.

RESULTS

Both circulating fH and fB were associated positively with BMI, waist circumference, triglycerides, and inflammatory parameters and negatively with insulin sensitivity and HDL cholesterol. For the first time, CFH gene expression was detected in human adipose tissue (significantly increased in subcutaneous compared with omental fat). CFH gene expression in omental fat was significantly associated with insulin resistance. In contrast, CFB gene expression was significantly increased in omental fat but also in association with fasting glucose and triglycerides. The SVC fraction was responsible for these differences, although isolated adipocytes also expressed fB and fH at low levels. Both weight loss and rosiglitazone led to significantly decreased circulating fB and fH levels.

CONCLUSIONS

Increased circulating fH and fB concentrations in subjects with altered glucose tolerance could reflect increased SVC-induced activation of the alternative pathway of complement in omental adipose tissue linked to insulin resistance and metabolic disturbances.

Complement 3 deficiency impairs early pregnancy in mice

Human oviductal cells produce complement-3 (C3) and its derivative, iC3b. These molecules are important in immune responses. Our recent study suggested that iC3b also possessed embryotrophic activity and it stimulates the blastulation and hatching rates of in vitro cultured mouse embryos. The objective is to study the impact of C3 deficiency on early pregnancy in vivo using homozygous C3-deficient (C3KO) and wild-type (C3WT) mice. C3 protein was undetectable in the reproductive tissues of C3KO mice. Deficiency in C3 is associated with significantly longer estrous cycle (P = 0.037). No significant difference was found in the ovulation rate, total cell count in blastocysts and implantation rate between the wild-type and the C3KO mice, though C3KO mice tended to have lower values in the latter two parameters. On day 15 of pregnancy, C3KO mice had fewer conceptus (P < 0.001) and higher resorption rate (P < 0.001) than that of C3WT mice. The fetal and placental weights (P < 0.001) were lower in the C3KO mice. The placenta of C3KO mice had smaller spongiotrophoblast (P = 0.001) and labyrinth (P = 0.037). Deficiency in C3 is associated with mild impairment in early pregnancy including longer estrous cycle and higher resorption rates after implantation. The impairment may be related to compromised placental development leading to under-developed fetuses.

The PPARγ ligand rosiglitazone influences triacylglycerol metabolism in non-obese males, without increasing the transcriptional activity of PPARγ in the subcutaneous adipose tissue

PPARγ is obligatory for fat mass generation and is thought to determine the amount of TAG stored per fat cell. We investigated whether ligand availability for PPARγ is rate limiting in fat mass generation and substrate metabolism. Twenty healthy men (20–29 years) were randomly assigned to receive the PPARγ ligand rosiglitazone (RSG) (8 mg/d) (n 10) or a placebo (n 10) during a stay of 7 d in a respiration chamber. Food intake was ad libitum, resulting in positive energy balances of 32·2 MJ (placebo) and 44·7 MJ (RSG). Fat cell size and expression of PPARγ, adipocyte fatty acid-binding protein (aP2), adipsin, adiponectin and fasting-induced adipose factor (FIAF) were determined in subcutaneous abdominal fat biopsies. The total amount of fat stored and the amount of TAG per fat cell were not different between groups. For the entire group, fat cell size was decreased after overeating (P = 0·02). FIAF mRNA levels were decreased after overeating in the RSG group (P = 0·01), with a trend towards a decrease in the placebo group. Unexpectedly, RSG treatment did not influence the expression levels of PPARγ and of the PPARγ responsive genes aP2, adiponectin and adipsin. In addition, RSG resulted in a larger increase in plasma TAG during overeating than placebo treatment. These results suggest that in healthy, non-obese males the PPARγ ligand RSG influences TAG metabolism, independent of its PPARγ transcriptional activity in the subcutaneous adipose tissue.

Metabolic liver disease of obesity and role of adipose tissue in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is an increasingly recognized cause of liver-related morbidity and mortality. It can develop secondary to numerous causes but a great majority of NAFLD cases occur in patients who are obese or present with other components of metabolic syndrome (hypertension, dyslipidemia, diabetes). This is called primary NAFLD and insulin resistance plays a key role in its pathogenesis. Obesity is characterized by expanded adipose tissue, which is under a state of chronic inflammation. This disturbs the normal storage and endocrine functions of adipose tissue. In obesity, the secretome (adipokines, cytokines, free fatty acids and other lipid moieties) of fatty tissue is amplified, which through its autocrine, paracrine actions in fat tissue and systemic effects especially in the liver leads to an altered metabolic state with insulin resistance (IR). IR leads to hyperglycemia and reactive hyperinsulinemia, which stimulates lipid-accumulating processes and impairs hepatic lipid metabolism. IR enhances free fatty acid delivery to liver from the adipose tissue storage due to uninhibited lipolysis. These changes result in hepatic abnormal fat accumulation, which may initiate the hepatic IR and further aggravate the altered metabolic state of whole body. Hepatic steatosis can also be explained by the fact that there is enhanced dietary fat delivery and physical inactivity. IR and NAFLD are also seen in various lipodystrophic states in contrary to popular belief that these problems only occur due to excessive adiposity in obesity. Hence, altered physiology of adipose tissue is central to development of IR, metabolic syndrome and NAFLD.

Intra- and interindividual variation in gene expression in human adipose tissue

Adipose tissue is a highly plastic tissue with an important endocrine and metabolic function. To understand its role in human health and disease, it is necessary to understand the extent of variation and the specific differences within and between different depots and subjects. We employed cDNA microarray analysis to investigate this in human subjects ranging from lean to mildly obese. We observe (1) high similarity between different samples of one adipose depot, (2) only small differences between the subcutaneous and visceral adipose tissue depot and (3) larger differences in gene expression between different individuals (per depot). The major variation within adipose depots can be attributed to differences in the non-adipocyte component of adipose tissue. Using only non-obese subjects, we identified genes that were consistently differentially expressed between subcutaneous and omental adipose tissue, despite the variation in gene expression between these subjects. Using quantitative real time polymerase chain reaction (PCR), fatty acid binding protein 4 (FABP4), vimentin (Vim), four and a half LIMs domains (FHL1), CD36 (all higher in subcutaneous adipose tissue) and Matrix Gla protein (MGP; lower in subcutaneous adipose tissue) were confirmed to be significantly differentially expressed between depots.

Chylomicron accelerates C3 tick-over by regulating the role of factor H, leading to overproduction of acylation stimulating protein

Acylation stimulating protein (ASP) is a fragment of the third component of complement (C3) that is generated in the presence of chylomicron, and plays a role in the synthesis of triacylglycerol by transporting free fatty acids into adipocytes. However, the precise mechanism of ASP generation, especially the role of chylomicron in ASP generation, is unknown. We examined the mechanism through which chylomicron induces ASP generation. Ultracentrifugationally separated chylomicron was incubated with normal human serum (NHS) under various conditions, and the amounts of complement activation products and ASP in the incubation mixture were determined by enzyme-linked immunosorbent assay (ELISA). Upon incubation of NHS with various amounts of chylomicron for 120 min, ASP was generated in a dose-dependent manner. The time course of the production of ASP was similar to the time course of the C3 tick-over phenomenon that occurred by depletion of factor H from the serum. The complement activation induced by chylomicron was different from the usual complement activation that occurs under the regulation of factor H and factor I with respect to the time course and the amount of ASP produced. Our results indicate that chylomicron accelerates C3 tick-over by regulating the role of factor H, leading to the overproduction of ASP.

Adipocyte-derived hormones, cytokines, and mediators

Adipose tissue is responsive to both central and peripheral metabolic signals and is itself capable of secreting a number of proteins. These adipocyte-specific or enriched proteins, termed adipokines, have been shown to have a variety of local, peripheral, and central effects. These secreted proteins, which include tumor necrosis factor (TNF)-alpha, resistin, IL-6, IL-8, acylation-stimulating protein (ASP), angiotensinogen, plasminogen activator inhibitor-1 (PAI-1) ("bad" adipokines) and leptin, adiponectin ("good" adipokines) seem to play important regulatory roles in a variety of complex processes, including fat metabolism, feeding behavior, hemostasis, vascular tone, energy balance, and insulin sensitivity, but none is without controversy regarding its respective mechanism and scope of action. The present review is focused on the effects of free fatty acids and a restricted number of adipokines, which have been implicated in vascular (angiotensinogen, PAI-1) and energy and glucose homeostasis (ASP, TNFalpha, IL-6, resistin, leptin, adiponectin).

Adipocyte-derived hormones, cytokines, and mediators

Adipose tissue is responsive to both central and peripheral metabolic signals and is itself capable of secreting a number of proteins. These adipocyte-specific or enriched proteins, termed adipokines, have been shown to have a variety of local, peripheral, and central effects. These secreted proteins, which include tumor necrosis factor (TNF)-alpha, resistin, IL-6, IL-8, acylation-stimulating protein (ASP), angiotensinogen, plasminogen activator inhibitor-1 (PAI-1) ("bad" adipokines) and leptin, adiponectin ("good" adipokines) seem to play important regulatory roles in a variety of complex processes, including fat metabolism, feeding behavior, hemostasis, vascular tone, energy balance, and insulin sensitivity, but none is without controversy regarding its respective mechanism and scope of action. The present review is focused on the effects of free fatty acids and a restricted number of adipokines, which have been implicated in vascular (angiotensinogen, PAI-1) and energy and glucose homeostasis (ASP, TNFalpha, IL-6, resistin, leptin, adiponectin).

Weight gain in relation to plasma levels of complement factor 3: results from a population-based cohort study

AIMS/HYPOTHESIS

Mice that are deficient for complement factor 3 (C3) have shown resistance to weight gain, despite increased food intake. Cross-sectional studies of humans have reported correlations between C3 and obesity. This longitudinal study explored whether C3 predicts a large weight gain in middle-aged men.

METHODS

Plasma concentrations of C3 and complement factor 4 (C4) were measured in 2,706 non-diabetic healthy men aged between 38 and 50 years, who were re-examined after a mean period of 6.1 years.

RESULTS

After adjustments for initial weight, age, height and follow-up time, the odds of incurring large weight gain (75th percentile, > or =3.8 kg) were 1.00 (reference), 0.96 (95% CI:0.7-1.2), 1.1 (CI:0.9-1.5) and 1.4 (CI:1.1-1.8), respectively, among men with C3 levels in the first, second, third and fourth quartiles (p for trend=0.01) respectively. This relationship remained significant after further adjustments for lifestyle factors (physical inactivity, alcohol, smoking), metabolic factors (glucose or homeostasis model assessment values, cholesterol, triglycerides), inflammatory markers (fibrinogen, haptoglobin, ceruloplasmin, orosomucoid, alpha1-antitrypsin) and for C4. C4 was associated with weight gain after adjustments for initial weight, height, follow-up time and lifestyle factors, but not after adjustments for C3.

CONCLUSIONS/INTERPRETATION

C3 is a risk factor for incurring large weight gain in middle-aged men.

Novel roles for acylation stimulating protein/C3adesArg: a review of recent in vitro and in vivo evidence

Recent experimental evidence is shedding more light on the physiological actions of acylation-stimulating protein (ASP)/C3adesArg. The role of ASP in regulating lipid metabolism has primarily focused on its participation in the stimulation of triglyceride synthesis (TGS) and glucose transport. Although there is no doubt that ASP, an adipocyte-produced hormone, plays a key physiological role, accumulating evidence suggests that the effects of ASP go beyond its acute effects on lipid metabolism. In this review, we present novel findings of ASP/C3adesArg effects on preadipocyte differentiation. In 3T3-L1 and 3T3-F442A cells, ASP can substitute for insulin and enhance differentiation as measured by intracellular lipid droplet accumulation, clonal expansion, and increased expression of differentiation markers. Specifically, ASP increased basal TGS by 250% after 9 days differentiation, with similar effects induced by insulin. With ASP treatment, expression of C/EBPdelta was up-regulated early in differentiation (day 2) and decreased thereafter. Expression of PPARgamma and late markers of differentiation, such as adipsin and diacylglycerol acyltransferase-1, were also increased. Effects on clonal expansion were indicated by a twofold increase in [(3)H] thymidine incorporation in 3T3-L1 cells compared to treatment with IBMX + DX alone. Further, the effects of ASP extended beyond adipose tissue to endocrine effects on hormone secretion of insulin (pancreatic cells); cytokines TNFalpha, IL-1beta, and IL-6 (myeloid cells); prolactin, growth hormone, and adrenocorticotropin (pituitary cells). Finally, the potential implication of C5L2, the newly discovered ASP receptor, and its expression profile in various tissues are discussed relative to ASP function.

Evidence for a complex risk profile in obese postmenopausal Turkish women with hypertriglyceridaemia and elevated apolipoprotein B

The aim of the present study was to examine possible pathophysiological relationships among a wide array of proatherogenic risk factors in postmenopausal women. Fasting lipids, apoB (apolipoprotein B), BMI (body mass index) and waist circumference were measured in 178 women (59.4±7.2 years) from the Turkish Adult Risk Factor Study. Fasting levels of complement C3, insulin, SHBG (sex hormone-binding globulin), cortisol, oestradiol, testosterone and DHEA-S (dehydroepiandrosterone sulphate) were also determined. This is the first study to examine the relationships of all these variables with apoB. In the first of two different approaches, three groups of obese women were compared. Group 1 comprised women who were normolipidaemic with normal apoB; group 2, women who were hypertriglyceridaemic, but with normal apoB; and group 3, women who were hypertriglyceridaemic with elevated apoB. Complement C3, fasting insulin and glucose were significantly higher and HDL-C (high-density lipoprotein-cholesterol) and SHBG levels were significantly lower in group 3 than in group 1. In the former group, the testosterone/SHBG ratio tended to be higher, indicating more free testosterone, than in group 1. The mean risk score in group 3 and the odds ratio for coronary disease by logistic regression analysis were significantly higher, 2.56 (confidence intervals, 1.12–5.85; P=0.026), compared with the two other groups combined. In examining the whole group, apoB levels correlated significantly with a wider array of pro-atherogenic risk factors than did LDL-C (low-density lipoprotein-cholesterol), particularly being linked to complement C3 and glucose, as well as the risk score. Complement C3 demonstrated the widest associations and was significantly linked with BMI, waist circumference, insulin, glucose, fibrinogen, triacylglycerols (triglycerides) and apoB and was inversely correlated with HDL-C and SHBG. SHBG was also correlated inversely with a wide spectrum of risk variables. In summary, in Turkish women, apoB was linked with a complex array of proatherogenic risk factors, and hypertriglyceridaemia with elevated apoB was associated with a higher risk of coronary disease.