Adiponectin binds C1q and activates the classical pathway of complement

Is the endotoxin-complement cascade the major driver in lipedema?

Lipedema is a poorly understood disorder of adipose tissue characterized by abnormal but symmetrical deposition of subcutaneous white adipose tissue (WAT) in proximal extremities. Here, we propose that the underlying cause for lipedema could be triggered by a selective accumulation of bacterial lipopolysaccharides (LPS; also known as endotoxin) in gluteofemoral WAT. Together with a malfunctioning complement system, this induces low-grade inflammation in the depot and raises its uncontrollable expansion. Correspondingly, more attention should be paid in future research to the endotoxemia prevalent in patients with lipedema. We would like to propose that proper management of endotoxemia can reduce the progression and even improve the state of disease in patients with lipedema.

Complement in Human Brain Health: Potential of Dietary Food in Relation to Neurodegenerative Diseases

The complement pathway is a major component of the innate immune system, which is critical for recognizing and clearing pathogens that rapidly react to defend the body against external pathogens. Many components of this pathway are expressed throughout the brain and play a beneficial role in synaptic pruning in the developing central nervous system (CNS). However, excessive complement-mediated synaptic pruning in the aging or injured brain may play a contributing role in a wide range of neurodegenerative diseases. Complement Component 1q (C1q), an initiating recognition molecule of the classical complement pathway, can interact with a variety of ligands and perform a range of functions in physiological and pathophysiological conditions of the CNS. This review considers the function and immunomodulatory mechanisms of C1q; the emerging role of C1q on synaptic pruning in developing, aging, or pathological CNS; the relevance of C1q; the complement pathway to neurodegenerative diseases; and, finally, it summarizes the foods with beneficial effects in neurodegenerative diseases via C1q and complement pathway and highlights the need for further research to clarify these roles. This paper aims to provide references for the subsequent study of food functions related to C1q, complement, neurodegenerative diseases, and human health.

Transcriptomic profiling of immune-associated molecules in the coelomocytes of lugworm Arenicola marina (Linnaeus, 1758)

Organization and functioning of immune system remain unevenly studied in different taxa of lophotrochozoan animals. We analyzed transcriptomic data on coelomocytes of the lugworm Arenicola marina (Linnaeus, 1758; Annelida, Polychaeta) to gain insights into the molecular mechanisms involved in polychaete immunity. Coelomocytes are specialized motile cells populating coelomic fluid of annelids, responsible for cellular defense reactions and providing humoral immune factors. The transcriptome was enriched with immune-related transcripts by challenging the cells in vitro with lipopolysaccharides of Escherichia coli and Zymosan from Saccharomyces cerevisiae. Our analysis revealed a multifaceted and complex internal defense system of the lugworm. A. marina possesses orthologs of proto-complement-like factors: six thioester-containing proteins, a complement-like receptor, and a MASP-related serine protease (MReM2). A. marina coelomocytes employ pattern-recognition receptors to detect pathogens and regulate immune responses. Among them, there are 18 Toll-like receptors and various putative lectin-like proteins with evolutionary conserved and taxa-specific domains. C-type lectins and a novel family of Gal-binding and CUB domains containing receptors were the most abundant in the transcriptome. The array of pore-forming proteins in the coelomocytes was surprisingly reduced compared to that of other invertebrate species. We characterized a set of conserved proteins metabolizing reactive oxygen species and nitric oxide and expanded the arsenal of potential antimicrobial peptides. Phenoloxidase activity in immune cells of lugworm is mediated only by laccase enzyme. The described repertoire of immune-associated molecules provides valuable candidates for further functional and comparative research on the immunity of annelids.

The CTRP3-AdipoR2 Axis Regulates the Development of Experimental Autoimmune Encephalomyelitis by Suppressing Th17 Cell Differentiation

C1q/TNF-related proteins (CTRP) including CTRP3 are a group of secreted proteins which have a complement C1q-like domain in common, and play versatile roles in lipid metabolism, inflammation, tumor metastasis and bone metabolism. Previously, we showed that the expression of C1qtnf3, encoding CTRP3, is highly augmented in joints of autoimmune arthritis models and CTRP3-deficiency exacerbates collagen-induced arthritis in mice. However, the mechanisms how CTRP3-deficiency exacerbates arthritis still remain to be elucidated. In this study, we showed that CTRP3 was highly expressed in Th17 cell, a key player for the development of autoimmune diseases, and Th17 cell differentiation was augmented in C1qtnf3^–/– mice. Th17 cell differentiation, but not Th1 cell differentiation, was suppressed by CTRP3 and this suppression was abolished by the treatment with a receptor antagonist against AdipoR2, but not AdipoR1, associated with suppression of Rorc and Stat3 expression. Furthermore, AdipoR1 and AdipoR2 agonist, AdipoRon suppressed Th17 cell differentiation via AdipoR2, but not AdipoR1. The development of myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis was enhanced in C1qtnf3^–/– mice associated with increase of Th17 cell population. CTRP3 inhibited MOG-induced IL-17 production from T cells by affecting both T cells and dendritic cells. These results show that CTRP3 is an endogenous regulator of Th17 differentiation, suggesting that the CTRP3-AdipoR2 axis is a good target for the treatment of Th17 cell-mediated diseases.

Adiponectin's globular domain inhibits T cell activation by interacting with LAIR-1

Adiponectin (APN) is the most abundant adipokine in human plasma, and has insulin-sensitizing effect. Recent studies have reported that APN plays both anti- and pro-inflammatory roles under different circumstances. However, there is a lack of convincing evidence that decipher APN's anti-inflammatory role through the known receptors and their downstream signaling pathways. In this study, we evaluated a new molecular mechanism underlying APN's anti-inflammatory roles. Our results revealed that the globular domain of adiponectin (gAdp) interacted with the inhibitory leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1). In vitro experiments showed that gAdp inhibited activation of the T cells via the LAIR-1, through a process that also involved downstream SHP-2. These findings indicate that LAIR-1 is a novel APN receptor, affirming APN's anti-inflammatory effect. In summary, we have identified a novel mechanism of peripheral immunoregulatory processes that provides baseline information for further studies on gAdp's role and its contribution to inflammation.

Multiplex Serum Biomarker Assays Improve Prediction of Renal and Mortality Outcomes in Chronic Kidney Disease

BACKGROUND

We investigated the predictive value of 11 serum biomarkers for renal and mortality end points in people with CKD.

METHODS

Adults with CKD (n=139) were enrolled from outpatient clinics between February 2014 and November 2016. Biomarker quantification was performed using two multiplex arrays on a clinical-grade analyzer. Relationships between biomarkers and renal and mortality end points were investigated by random forests and Cox proportional hazards regression.

RESULTS

The cohort was 56% male. The mean age was 63 years and median (IQR) CKD-EPI eGFR was 33 (24-51) ml/min per BSA. A total of 56 (40%) people developed a composite end point defined as ≥40% decline in eGFR, doubling of serum creatinine, RRT, or death over median (IQR) follow-up of 5.4 (4.7-5.7) years. Prediction of the composite end point was better with random forests trained on serum biomarkers compared with clinical variables (area under the curve of 0.81 versus 0.78). The predictive performance of biomarkers was further enhanced when considered alongside clinical variables (area under the curve of 0.83 versus 0.81 for biomarkers alone). Patients (n=27, 19%) with high soluble TNF receptor-1 (≥3 ng/ml) and neutrophil gelatinase-associated lipocalin (≥156 ng/ml), coupled with low complement 3a des-arginine (<2368 ng/ml), almost universally (96%) developed the composite renal and mortality end point. C-reactive protein (adjusted hazard ratio, 1.4; 95% CI, 1.1 to 1.8), neutrophil gelatinase-associated lipocalin (adjusted hazard ratio, 2.8; 95% CI, 1.3 to 6.1) and complement 3a desarginine (adjusted hazard ratio, 0.6; 95% CI, 0.4 to 0.96) independently predicted time to the composite end point.

CONCLUSIONS

Outpatients with the triad of high soluble TNF receptor-1 and neutrophil gelatinase-associated lipocalin coupled with low complement 3a des-arginine had high adverse event rates over 5-year follow-up. Incorporation of serum biomarkers alongside clinical variables improved prediction of CKD progression and mortality. Our findings require confirmation in larger, more diverse patient cohorts.

Is serum complement C1q related to major depressive disorder?

BACKGROUND

Major depressive disorder (MDD) has a high global incidence. While the pathogenesis of depression remains unknown, accumulating evidence has implicated inflammatory changes.

AIM

The aim of the study is to compare the serum complement C1q levels in patients with MDD and healthy controls.

SETTING AND DESIGN

The design was a case-control study.

MATERIALS AND METHODS

Blood samples were collected from the patients with MDD and healthy controls to assess the serum C1q levels using an immunotransmission turbidimetric method.

STATISTICAL ANALYSIS

Differences in complement C1q levels between patients with MDD and the controls, as well as between sexes among patients with MDD and the controls, were assessed using Mann-Whitney U-test. Spearman correlations were obtained between complement C1q levels and age.

RESULTS

In total, 1016 participants (508 MDD and 508 controls) were recruited. Differences in the sex ratio (male/female among controls, 181/327; and MDD, 178/330) and age (controls, 47.0 ± 14.9 years; MDD, 46.5 ± 16.5 years) were not significant. The C1q level in the patients with MDD was significantly higher than that in the healthy controls (P < 0.05). In the MDD group, C1q level correlated significantly with age.

CONCLUSION

Elevation of the serum complement C1q levels in MDD may support the use of C1q as a potential biomarker for diagnosing depression, but further research is needed.

Complement and human T cell metabolism: Location, location, location

The complement system represents one of the evolutionary oldest arms of our immune system and is commonly recognized as a liver-derived and serum-active system critical for providing protection against invading pathogens. Recent unexpected findings, however, have defined novel and rather "uncommon" locations and activities of complement. Specifically, the discovery of an intracellularly active complement system-the complosome-and its key role in the regulation of cell metabolic pathways that underly normal human T cell responses have taught us that there is still much to be discovered about this system. Here, we summarize the current knowledge about the emerging functions of the complosome in T cell metabolism. We further place complosome activities among the non-canonical roles of other intracellular innate danger sensing systems and argue that a "location-centric" view of complement evolution could logically justify its close connection with the regulation of basic cell physiology.

C1q/TNF-Related Protein 6 Is a Pattern Recognition Molecule That Recruits Collectin-11 from the Complement System to Ligands

C1q/TNF-related protein (CTRP) 6 is a member of the CTRP protein family associated with the regulation of cellular and endocrine processes. CTRP6 contains collagen and globular structures, resembling the pattern recognition molecules (PRMs) of the classical and lectin complement pathways. We expressed human CTRP6 in Chinese hamster ovary cells and investigated the binding to different putative ligands (acetylated BSA [AcBSA], zymosan, mannan, and LPS from Escherichia coli and Salmonella as well as to the monosaccharides l-fucose, d-mannose, N-acetylglucosamine, N-acetylgalactosamine, and galactose). Furthermore, we investigated the binding of CTRP6 to various Gram-negative bacteria as well as PRMs and enzymes of the lectin complement pathway. We found that CTRP6 bound to AcBSA and to a lesser extent to zymosan. Using EDTA as chelating agent, we observed an increased binding to AcBSA, zymosan and the two strains of LPS. We detected no binding to mannan and BSA. We identified l-fucose as a ligand for CTRP6 and that it bound to certain enteroaggregative Escherichia coli and Pseudomonas aeruginosa isolates, whereas to other bacterial isolates, no binding was observed. CTRP6 did not appear to interact directly with the activating enzymes of the lectin pathway; however, we could show the specific recruitment of collectin-11 and subsequent initiation of the complement cascade through deposition of C4. In conclusion, our results demonstrate the binding of CTRP6 to a variety of microbial and endogenous ligands identifying CTRP6 as a novel human lectin and PRM of importance for complement recognition and innate immunity.

Total adiponectin is associated with incident cardiovascular and renal events in treated hypertensive patients: subanalysis of the ATTEMPT-CVD randomized trial

The predictive value of serum adiponectin for hypertensive cardiovascular outcomes is unknown. This study was performed to investigate the association of adiponectin with incident cardiovascular and renal events (CV events) in hypertensive patients. We performed post-hoc analysis on 1,228 hypertensive patients enrolled in the ATTEMPT-CVD study, a prospective randomized study comparing the effects of two antihypertensive therapies. The participants were divided into quartiles of baseline serum total adiponectin or high molecular weight (HMW) adiponectin. Multivariable Cox proportional hazards analysis was performed to determine the prognostic factors associated with CV events. Kaplan-Meier analysis for CV events by quartiles of baseline total adiponectin showed that patients in the highest total adiponectin quartile (Q4) had more CV events (P = 0.0135). On the other hand, no significant difference was noted regarding the incidence of CV events among patients stratified by HMW adiponectin quartile (P = 0.2551). Even after adjustment for potential confounders, the highest total adiponectin quartile (Q4) remained independently associated with incident CV events in hypertensive patients (HR = 1.949: 95%CI 1.051-3.612; P = 0.0341). These results showed that total adiponectin, but not HMW adiponectin, was independently associated with the incidence of CV events in treated hypertensive patients, thereby highlighting total adiponectin as a valuable predictor for hypertensive cardiovascular outcomes.

Role of Complement and Complement-Related Adipokines in Regulation of Energy Metabolism and Fat Storage

Adipose tissue releases many cytokines and inflammatory factors described as adipokines. In obesity, adipokines released from expanding adipose tissue are implicated in disease progression and metabolic dysfunction. However, mechanisms controlling the progression of adiposity and metabolic complications are not fully understood. It has been suggested that expanding fat mass and sustained release of inflammatory adipokines in adipose tissue lead to hypoxia, oxidative stress, apoptosis, and cellular damage. These changes trigger an immune response involving infiltration of adipose tissue with immune cells, complement activation and generation of factors involved in opsonization and clearance of damaged cells. Abundant evidence now indicates that adipose tissue is an active secretory source of complement and complement-related adipokines that, in addition to their inflammatory role, contribute to the regulation of metabolic function. This article highlights advances in knowledge regarding the role of these adipokines in energy regulation of adipose tissue through modulating lipogenic and lipolytic pathways. Several adipokines will be discussed including adipsin, Factor H, properdin, C3a, Acylation-Stimulating Protein, C1q/TNF-related proteins, and response gene to complement-32 (RGC-32). Interactions between these factors will be described considering their immune-metabolic roles in the adipose tissue microenvironment and their potential contribution to progression of adiposity and metabolic dysfunction. The differential expression and the role of complement factors in gender-related fat partitioning will also be addressed. Identifying lipogenic adipokines and their specific autocrine/paracrine roles may provide means for adipose-tissue-targeted therapeutic interventions that may disrupt the vicious circle of adiposity and disease progression. © 2019 American Physiological Society. Compr Physiol 9:1411-1429, 2019.

Derivatives of the lectin complement pathway in Lophotrochozoa

A plethora of non-overlapping immune molecular mechanisms in metazoans is the most puzzling issue in comparative immunobiology. No valid evolutionary retrospective on these mechanisms has been developed. In this study, we aimed to reveal the origin and evolution of the immune complement-like system in Lophotrochozoa. For this, we analyzed publicly available transcriptomes of prebilaterian and lophotrochozoan species, mapping lineage-specific molecular events on the phylogenetic tree. We found that there were no orthologs of mannose-binding lectin (MBL) and ficolins (FCN) in Lophotrochozoa but C1q-like proteins (C1qL), bearing both a collagen domain and a globular C1q domain, were omnipresent in them. This suggests that among all complement-like activators the C1qL-specific domain architecture was an evolutionarily first. Two novel protostomian MASP-Related Molecules, MReM1 and MReM2, might hypothetically compensate for the loss of a prebilaterian MASP-orthologous gene and act in complex with C1qL and C1qDC as a "proto-activator" of an ancient "proto-complement". We proposed a new model of the complement evolution predicting that numerous lineage-specific complement-like systems should have evolved from a stem "antique" molecular complex. First evolved in the common ancestor of coelomic animals, the "antique" humoral complex consisted of a TEP molecule, the common ancestor of TEP-associated proteases (C2/Bf/Сf/Lf), the common ancestor of MASP-like proteases (MASP/C1r/C1s, MReM1/MReM2) and multimeric recognition proteins (C1q-, MBL- and FCN-homologs). Further evolutionary specialization and expansion of the complex was independent and lineage-specific, examples being the mammalian complement system and the Apogastropoda complement-like complex. The latter includes an impressive array of multimeric recognition proteins, the variable immunoglobulin and lectin domain containing molecules (VIgL), homologous to C1q, MBL, FCN and other lectins. Four novel polymorphic subfamilies of VIgLs were found to be expressed in Apogastropoda: C1q-related proteins (QREP), zona pellucida-related proteins (ZREP), Scavenger Receptor Cys-Rich-related proteins (SREP) and HPA-lectin related proteins (HREP). The transcriptional response of fibrinogen-related proteins of VIgL family (LlFREP), LlQREP and LlSREP to infestation of common periwinkle, Littorina littorea, with digenean parasite Himasthla elongata correlates with that of LlMReM1, supporting the model suggested in this study.

The role of adipokines in systemic sclerosis: a missing link?

Systemic sclerosis is a multiorgan autoimmune disease characterized by vasculopathy and tissue fibrosis of unknown etiology. Recently, adipokines (cell signaling proteins secreted by adipose tissue) have attracted much attention as a cytokine family contributing to the various pathological processes of systemic sclerosis. Adipokines, such as leptin, adiponectin, resistin, adipsin, visfatin or chemerin are a heterogenic group of molecules. Adiponectin exhibits anti-fibrotic features and affects inflammatory reactions. Leptin promotes fibrosis and inflammation. Resistin was linked to vascular involvement in systemic sclerosis. Visfatin was associated with regression of skin lesions in late-stage systemic sclerosis. Chemerin appears as a marker of increased risk of impaired renal function and development of skin sclerosis in the early stage of systemic sclerosis. Vaspin was indicated to have a protective role in digital ulcers development. Novel adipokines-adipsin, apelin, omentin and CTRP-3-are emerging as molecules potentially involved in SSc pathogenesis. Serum adipokine levels may be used as predictive and diagnostic factors in systemic sclerosis. However, further investigations are required to establish firm correlations between distinct adipokines and systemic sclerosis.

Dietary fatty acid source has little effect on the development of the immune system in the pyloric caeca of Atlantic salmon fry

The quality and relative amounts of dietary lipids may affect the health and growth of cultured Atlantic salmon. So far, little is known about their effects on the performance of the fish immune system during early life stages and, in particular their importance in the transition from endogenous nutrition (yolk) in the alevin stage to exogenous nutrition in the later fry stage. We investigated the immunomodulatory effects of fish oil, vegetable oil and phospholipid-rich oil in feeds for farmed Atlantic salmon using a transcriptomic approach. The experiment allowed a fine-scale monitoring of gene expression profiles in two tissues, the pyloric caeca of the intestine and the liver, in a 94 days-long first feeding experiment. The analysis of transcriptional profiles revealed that first feeding induced a strong immunomodulation in the pyloric caeca after 48 days of feeding, lasting up to day 94 and possibly beyond. On the other hand, the differential effect of the three dietary regimes was negligible. We interpret this upregulation, undetectable in liver, as a potentiation of the immune system upon the first contact of the digestive system with exogenous feed. This process involved a complex network of gene products involved in both cellular and humoral immunity. We identified the classical pathway of the complement system, acting at the crossroads between innate and adaptive immunity, as a key process modulated in response to the switch from endogenous to exogenous nutrition.

Adipocytokine correlations with thyroid function and autoimmunity in euthyroid sardinians

OBJECTIVE

Cytokines release by adipocytes could interact with TSH secretion. We evaluated the relationship between adipocytokines and TSH. We further tested for association of cytokines and thyroid autoimmunity.

METHODS

We conducted a cross-sectional study in a community-based sample including 5385 individuals (2964 female) with TSH within the reference range. Subjects who reported taking thyroid medications or drugs that alter thyroid function were excluded. TSH, FT4, adiponectin, leptin, antibody against thyroperoxidase and against thyroglobulin were measured. Linear and logistic regression models were used to test for association.

RESULTS

Females had higher adiponectin and leptin level and increased frequency of thyroid antibodies. In multiple regression analysis TSH was directly associated with leptin (β = 0.003, p = 0.001) and the presence of circulating antibody against thyroperoxidase (β = 0.315, p < 0.001), but negatively associated with age (β = -0.012, p < 0.001) and FT4 (β = -0.359, p < 0.001). Adiponectin, the presence of antibody against thyroglobulin and smoking habit were not associated with TSH levels (p = 0.223, p = 0.174 and p = 0.788, respectively). Logistic regression analysis revealed that higher adiponectin levels were associated with thyroid autoimmunity.

CONCLUSIONS

Leptin is positively associated with TSH levels in euthyroid individuals, suggesting an effect of the adipokine on TSH secretion. Our results support the hypothesis that the leptin and pituitary-thyroid axis might interact in the context of energy homeostasis. The effect of adiponectin on thyroid autoimmunity will require more studies.

Adiponectin and Its Isoforms in Pathophysiology

Adiponectin circulates in blood in multiple isoforms. High molecular weight (HMW) adiponectin is thought to be most biologically active and promotes glucose uptake, insulin sensitivity, and fatty acid oxidation. In obesity, adiponectin isoform formation is disrupted, leading to an inverse association between metabolic disease and HMW and total adiponectin. Adiponectin isoforms also function as acute-phase reactants influencing inflammation in acute and chronic disease. Interestingly, adiponectin and mortality have a U-shaped association. Unfortunately, data concerning adiponectin and its pathophysiologic function conflict. This is predominantly due to difficulties in adequate measurement of adiponectin isoforms and lack of a gold standard. In this review we provide a general overview of the formation and function of adiponectin and its isoforms under physiologic conditions. We highlight the ways adiponectin isoform formation is disrupted in obesity and its ensuing pathologic conditions. Furthermore, we will elaborate on the role of adiponectin isoforms as inflammatory proteins with respect to cardiac and kidney disease and discuss the association of adiponectin with mortality. Finally, we will provide a historical perspective on the measurement of adiponectin isoforms, current limitations, and future challenges.

Synthetic peptides designed to modulate adiponectin assembly improve obesity-related metabolic disorders

BACKGROUND AND PURPOSE

Adiponectin, an adipokine possessing profound insulin-sensitizing and anti-inflammatory properties, is a potent biotherapeutic agent . The trimeric adiponectin subunit assembles into hexameric and functionally important higher molecular weight (HMW) forms, controlled by the endoplasmic reticulum protein 44 (ERp44). Obesity-induced ER stress decreases the HMW form in serum, contributing to the development of insulin resistance and Type 2 diabetes. In this study, a panel of synthetic peptides, designed to target ERp44-adiponectin interactions, were tested for their effects on circulating levels of HMW adiponectin.

EXPERIMENTAL APPROACH

Peptides derived from the ERp44 binding region of adiponectin and immunoglobulin IgM were synthesized with or without a cell-penetrating sequence. Cultures of 3T3-L1 adipocytes were incubated with the peptides for assessing the assembly and secretion of HMW adiponectin. Mice given standard chow or a high-fat diet were treated acutely or chronically, with the peptides to investigate the therapeutic effects on insulin sensitivity and energy metabolism.

RESULTS

The designed peptides interfered with ERp44-adiponectin interactions and modulated adiponectin assembly and release from adipocytes. In particular, IgM-derived peptides facilitated the release of endogenous adiponectin (especially the HMW form) from adipose tissue, enhanced its circulating level and the ratio of HMW-to-total-adiponectin in obese mice. Long-term treatment of mice fed with high-fat diet by IgM-derived peptides reduced the circulating lipid levels and improved insulin sensitivity.

CONCLUSIONS AND IMPLICATIONS

Targeting ERp44-adiponectin interactions with short peptides represents an effective strategy to treat of obesity-related metabolic disorders, such as insulin resistance and Type 2 diabetes.

The complement system is dysfunctional in metabolic disease: Evidences in plasma and adipose tissue from obese and insulin resistant subjects

The relationship among chronic low-grade inflammation, insulin resistance and other obesity-associated metabolic disturbances is increasingly recognized. The possible mechanisms that trigger these immunologic alterations remain to be fully understood. The complement system is a crucial element of immune defense system, being important in the activation of innate and adaptative immune response, promoting the clearance of apoptotic and damaged endogenous cells and participating in processes of tissue development, degeneration, and regeneration. Circulating components of the complement system appear to be dysregulated in obesity-associated metabolic disturbances. The activation of the complement system is also evident in adipose tissue from obese subjects, in association with subclinical inflammation and alterations in glucose metabolism. The possible contribution of some components of the complement system in the development of insulin resistance and obesity-associated metabolic disturbances, and the possible role of complement system in adipose tissue physiology is reviewed here. The modulation of the complement system could constitute a potential target in the pathophysiology and therapy of obesity and associated metabolic disease.

Westernization of lifestyle affects quantitative and qualitative changes in adiponectin

Background

Although Japanese–Americans and native Japanese share the same genetic predispositions, they live different lifestyles, resulting in insulin resistance in Japanese–Americans. We investigated whether the quantitative and qualitative changes in adiponectin (APN) due to differences in lifestyle contribute to the development of insulin resistance.

Methods

We evaluated 325 native Japanese in Hiroshima, Japan and 304 Japanese–Americans in Los Angeles, the United States, who were aged between 30 and 70 years and underwent medical examinations between 2009 and 2010. All participants underwent a 75-g oral glucose tolerance test (OGTT) to assess their glucose tolerance. The insulin response to oral glucose load, the Matsuda index, total APN levels, and C1q-APN/total-APN ratios were compared between native Japanese and Japanese–Americans.

Results

Compared with the native Japanese, the Japanese–Americans had significantly lower Matsuda index and higher area under the curve values for serum insulin concentration during OGTT in the normal glucose tolerance (NGT) and impaired glucose tolerance (IGT) groups, but not in the diabetes mellitus (DM) group. Furthermore, the Japanese–Americans had significantly lower total APN levels and higher C1q-APN/total-APN ratios than the native Japanese in the NGT and IGT groups, but not in the DM group.

Conclusions

This study suggested that, in Japanese people, the westernization of their lifestyle might affect quantitative and qualitative changes in APN and induce insulin resistance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-017-0565-z) contains supplementary material, which is available to authorized users.

Upregulation of Early and Downregulation of Terminal Pathway Complement Genes in Subcutaneous Adipose Tissue and Adipocytes in Acquired Obesity

Inflammation is an important mediator of obesity-related complications such as the metabolic syndrome but its causes and mechanisms are unknown. As the complement system is a key mediator of inflammation, we studied whether it is activated in acquired obesity in subcutaneous adipose tissue (AT) and isolated adipocytes. We used a special study design of genetically matched controls of lean and heavy groups, rare monozygotic twin pairs discordant for body mass index (BMI) [n = 26, within-pair difference (Δ) in body mass index, BMI >3 kg/m²] with as much as 18 kg mean Δweight. Additionally, 14 BMI-concordant (BMI <3 kg/m²) served as a reference group. The detailed measurements included body composition (DEXA), fat distribution (MRI), glucose, insulin, adipokines, C3a and SC5b-9 levels, and the expression of complement and insulin signaling pathway-related genes in AT and adipocytes. In both AT and isolated adipocytes, the classical and alternative pathway genes were upregulated, and the terminal pathway genes downregulated in the heavier co-twins of the BMI-discordant pairs. The upregulated genes included C1q, C1s, C2, ficolin-1, factor H, receptors for C3a and C5a (C5aR1), and the iC3b receptor (CR3). While the terminal pathway components C5 and C6 were downregulated, its inhibitor clusterin was upregulated. Complement gene upregulation in AT and adipocytes correlated positively with adiposity and hyperinsulinemia and negatively with the expression of insulin signaling-related genes. Plasma C3a, but not SC5b-9, levels were elevated in the heavier co-twins. There were no differences between the co-twins in BMI-concordant pairs. Obesity is associated with increased expression of the early, but not late, complement pathway components and of key receptors. The twins with acquired obesity have therefore an inflated inflammatory activity in the AT. The results suggest that complement is likely involved in orchestrating clearance of apoptotic debris and inflammation in the AT.

Keeping It All Going-Complement Meets Metabolism

The complement system is an evolutionary old and crucial component of innate immunity, which is key to the detection and removal of invading pathogens. It was initially discovered as a liver-derived sentinel system circulating in serum, the lymph, and interstitial fluids that mediate the opsonization and lytic killing of bacteria, fungi, and viruses and the initiation of the general inflammatory responses. Although work performed specifically in the last five decades identified complement also as a critical instructor of adaptive immunity—indicating that complement’s function is likely broader than initially anticipated—the dominant opinion among researchers and clinicians was that the key complement functions were in principle defined. However, there is now a growing realization that complement activity goes well beyond “classic” immune functions and that this system is also required for normal (neuronal) development and activity and general cell and tissue integrity and homeostasis. Furthermore, the recent discovery that complement activation is not confined to the extracellular space but occurs within cells led to the surprising understanding that complement is involved in the regulation of basic processes of the cell, particularly those of metabolic nature—mostly via novel crosstalks between complement and intracellular sensor, and effector, pathways that had been overlooked because of their spatial separation. These paradigm shifts in the field led to a renaissance in complement research and provide new platforms to now better understand the molecular pathways underlying the wide-reaching effects of complement functions in immunity and beyond. In this review, we will cover the current knowledge about complement’s emerging relationship with the cellular metabolism machinery with a focus on the functional differences between serum-circulating versus intracellularly active complement during normal cell survival and induction of effector functions. We will also discuss how taking a closer look into the evolution of key complement components not only made the functional connection between complement and metabolism rather “predictable” but how it may also give clues for the discovery of additional roles for complement in basic cellular processes.

Regulation and Quality Control of Adiponectin Assembly by Endoplasmic Reticulum Chaperone ERp44

Adiponectin, a collagenous hormone secreted abundantly from adipocytes, possesses potent antidiabetic and anti-inflammatory properties. Mediated by the conserved Cys(39) located in the variable region of the N terminus, the trimeric (low molecular weight (LMW)) adiponectin subunit assembles into different higher order complexes, e.g. hexamers (middle molecular weight (MMW)) and 12-18-mers (high molecular weight (HMW)), the latter being mostly responsible for the insulin-sensitizing activity of adiponectin. The endoplasmic reticulum (ER) chaperone ERp44 retains adiponectin in the early secretory compartment and tightly controls the oxidative state of Cys(39) and the oligomerization of adiponectin. Using cellular and in vitro assays, we show that ERp44 specifically recognizes the LMW and MMW forms but not the HMW form. Our binding assays with short peptide mimetics of adiponectin suggest that ERp44 intercepts and converts the pool of fully oxidized LMW and MMW adiponectin, but not the HMW form, into reduced trimeric precursors. These ERp44-bound precursors in the cis-Golgi may be transported back to the ER and released to enhance the population of adiponectin intermediates with appropriate oxidative state for HMW assembly, thereby underpinning the process of ERp44 quality control.

The amount of C1q-adiponectin complex is higher in the serum and the complex localizes to perivascular areas of fat tissues and the intimal-medial layer of blood vessels of coronary artery disease patients

Background

The complement component C1q triggers activation of the classical immune pathway and can bind to adiponectin (APN). Recently, some studies have been reported that serum C1q-APN/total APN ratio correlates with atherosclerosis and coronary artery disease (CAD). We assessed the relationships between C1q related variables and the severity of CAD, and investigated the localization of the C1q–APN complex.

Methods

The sample included 153 subjects comprising healthy controls and patients with subclinical or overt CAD. We measured the serum concentrations of C1q, total APN, and high-molecular weight (HMW)-APN, and the amount of C1q–APN complex. We identified the sites of C1q–APN complex deposition in various adipose tissues and blood vessels.

Results

Serum concentrations of C1q and HMW-APN and the C1q/HMW-APN ratio were independently associated with the severity of coronary stenosis. The amount of C1q–APN complex was significantly higher in patients with CAD compared with controls. C1q and APN co-localized in perivascular areas of subcutaneous, visceral, and pericardial fat tissues, and the internal mammary artery of patients with severe CAD.

Conclusions

Serum C1q concentration and the C1q/HMW-APN ratio were independent markers of coronary artery stenosis. The amount of C1q–APN complex was significantly greater in serum from CAD patients. C1q and APN co-localized to perivascular areas in adipose tissue and blood vessels. The association between the increased amount of the C1q–APN complex and CAD should be investigated further.

Impact of serum levels of interleukin-6 and adiponectin on all-cause, liver-related, and liver-unrelated mortality in chronic hepatitis C patients

BACKGROUND AND AIM

Various inflammatory cytokines and adipokines have been implicated in hepatitis C virus (HCV)-mediated liver disease, and interleukin-6 (IL-6) and adiponectin may play key roles. In addition, these factors may be associated with chronic hepatitis C (CHC)-induced extrahepatic manifestations. However, little data are available on the role of these factors on future outcomes of CHC patients. This study aims to evaluate the impact of serum levels of IL-6 and adiponectin on all-cause mortality, liver-related mortality, and liver-unrelated mortality.

METHODS

A long-term follow-up study was conducted, consisting of 325 CHC patients, for which we previously reported positive associations between these factors (Serum levels of IL-6 and adiponectin) and hepatocellular carcinoma (HCC) development.

RESULTS

During the follow-up period (mean, 13.0 year), there were 92 events consisting of 91 deaths (liver related, 72; liver unrelated, 19) and 1 liver transplantation due to liver failure. High IL-6 and adiponectin levels, defined as being higher than each median value at baseline, were associated with significantly higher incidences of not only HCC development but also all-cause mortality. Interestingly, high IL-6 was strongly associated with only liver-related mortality, whereas high-serum adiponectin was associated with not only liver-related, but also liver-unrelated mortality. Multivariate analysis identified high IL-6 as an independent risk factor for liver-related mortality and high adiponectin as an independent risk factor for liver-unrelated mortality.

CONCLUSION

High serum levels of IL-6 and adiponectin were associated with higher all-cause and liver-related mortality in CHC patients. In addition, high adiponectin was associated with liver-unrelated mortality. The measurement of these factors may provide information useful for predicting future outcomes in CHC patients.

Diabetes, oxidative stress and therapeutic strategies

BACKGROUND

Diabetes has emerged as a major threat to health worldwide.

SCOPE OF REVIEW

The exact mechanisms underlying the disease are unknown; however, there is growing evidence that excess generation of reactive oxygen species (ROS), largely due to hyperglycemia, causes oxidative stress in a variety of tissues. Oxidative stress results from either an increase in free radical production, or a decrease in endogenous antioxidant defenses, or both. ROS and reactive nitrogen species (RNS) are products of cellular metabolism and are well recognized for their dual role as both deleterious and beneficial species. In type 2 diabetic patients, oxidative stress is closely associated with chronic inflammation. Multiple signaling pathways contribute to the adverse effects of glucotoxicity on cellular functions. There are many endogenous factors (antioxidants, vitamins, antioxidant enzymes, metal ion chelators) that can serve as endogenous modulators of the production and action of ROS. Clinical trials that investigated the effect of antioxidant vitamins on the progression of diabetic complications gave negative or inconclusive results. This lack of efficacy might also result from the fact that they were administered at a time when irreversible alterations in the redox status are already under way. Another strategy to modulate oxidative stress is to exploit the pleiotropic properties of drugs directed primarily at other targets and thus acting as indirect antioxidants.

MAJOR CONCLUSIONS

It appears important to develop new compounds that target key vascular ROS producing enzymes and mimic endogenous antioxidants.

GENERAL SIGNIFICANCE

This strategy might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated with vascular diseases.

Pharmacological ceramide reduction alleviates alcohol-induced steatosis and hepatomegaly in adiponectin knockout mice

Hepatosteatosis, the ectopic accumulation of lipid in the liver, is one of the earliest clinical signs of alcoholic liver disease (ALD). Alcohol-dependent deregulation of liver ceramide levels as well as inhibition of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPAR-α) activity are thought to contribute to hepatosteatosis development. Adiponectin can regulate lipid handling in the liver and has been shown to reduce ceramide levels and activate AMPK and PPAR-α. However, the mechanisms by which adiponectin prevents alcoholic hepatosteatosis remain incompletely characterized. To address this question, we assessed ALD progression in wild-type (WT) and adiponectin knockout (KO) mice fed an ethanol-containing liquid diet or isocaloric control diet. Adiponectin KO mice relative to WT had increased alcohol-induced hepatosteatosis and hepatomegaly, similar modest increases in serum alanine aminotransferase, and reduced liver TNF. Restoring circulating adiponectin levels using recombinant adiponectin ameliorated alcohol-induced hepatosteatosis and hepatomegaly in adiponectin KO mice. Alcohol-fed WT and adiponectin KO animals had equivalent reductions in AMPK protein and PPAR-α DNA binding activity compared with control-fed animals. No difference in P-AMPK/AMPK ratio was detected, suggesting that alcohol-dependent deregulation of AMPK and PPAR-α in the absence of adiponectin are not primary causes of the observed increase in hepatosteatosis in these animals. By contrast, alcohol treatment increased liver ceramide levels in adiponectin KO but not WT mice. Importantly, pharmacological inhibition of de novo ceramide synthesis in adiponectin KO mice abrogated alcohol-mediated increases in liver ceramides, steatosis, and hepatomegaly. These data suggest that adiponectin reduces alcohol-induced steatosis and hepatomegaly through regulation of liver ceramides, but its absence does not exacerbate alcohol-induced liver damage.

High serum C1q-binding adiponectin levels in male patients with acute coronary syndrome

BACKGROUND

The complement system is part of the immune system in acute coronary syndrome (ACS). Adiponectin has anti-atherogenic and anti-inflammatory properties. Adiponectin and C1q form a protein complex in blood, and serum C1q binding adiponectin (C1q-APN) can be measured. We investigated the comparative evaluation of serum C1q-APN levels in males with ACS, stable angina pectoris (SAP) versus controls.

METHODS

The study subjects were 138 Japanese patients who underwent diagnostic coronary angiography. Blood total adiponectin (Total-APN), C1q-APN and C1q were measured by enzyme-linked immunosorbent assays. Patients were divided into three groups according to the clinical condition: ACS (n = 78), SAP (n = 41) or normal coronary (NC, n = 19) groups.

RESULTS

Serum C1q levels were significantly higher in the ACS group (54.9±1.2 μg/mL) than in the NC group (48.0±2.5 μg/mL). Although serum Total-APN levels were significantly lower in the SAP and ACS groups, compared with the NC group (7.0±0.5, 7.2±0.3, 10.6±2.0 μg/mL, respectively), serum C1q-APN levels were significantly higher in the ACS group than in the NC and SAP groups (112.1±4.1, 66.3±4.4, 65.7±2.9 units/mL, respectively).

CONCLUSIONS

Patients with ACS had higher serum C1q-APN levels.

TRIAL REGISTRATION

UMIN000002997.

Cardiometabolic effects of adiponectin

Over the past two decades, adiponectin has been studied in more than eleven thousand publications. A classical adipokine, adiponectin was among the first factors secreted from adipose tissue that were found to promote metabolic function. Circulating levels of adiponectin consistently decline with increasing body mass index. Clinical and basic science studies have identified adiponectin's cardiovascular-protective actions, providing a mechanistic link to the increased incidence of cardiovascular disease in obese individuals. While progress has been made in identifying receptors essential for the metabolic actions of adiponectin (AdipoR1 and AdipoR2), few studies have examined the receptor-mediated signaling pathways in cardiovascular tissues. T-cadherin, a GPI-anchored adiponectin-binding protein, was recently identified as critical for the cardiac-protective and revascularization actions of adiponectin. Adiponectin is abundantly present on the surfaces of vascular and muscle tissues through a direct interaction with T-cadherin. Consistent with this observation, adiponectin is absent from T-cadherin-deficient tissues. Since T-cadherin lacks an intracellular domain, additional studies would further our understanding of this signaling pathway. Here, we review the diverse cardiometabolic actions of adiponectin.

CTRP3 plays an important role in the development of collagen-induced arthritis in mice

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease exhibited most commonly in joints. We found that the expression of C1qtnf3, which encodes C1q/TNF-related protein 3 (CTRP3), was highly increased in two mouse RA models with different etiology. To elucidate the pathogenic roles of CTRP3 in the development of arthritis, we generated C1qtnf3(-/-) mice and examined the development of collagen-induced arthritis in these mice. We found that the incidence and severity score was higher in C1qtnf3(-/-) mice compared with wild-type (WT) mice. Histopathology of the joints was also more severe in C1qtnf3(-/-) mice. The levels of antibodies against type II collagen and pro-inflammatory cytokine mRNAs in C1qtnf3(-/-) mice were higher than WT mice. These observations indicate that CTRP3 plays an important role in the development of autoimmune arthritis, suggesting CTRP3 as a possible medicine to treat RA.

Adiponectin and risk of stroke: prospective study and meta-analysis

BACKGROUND AND PURPOSE

The favorable cardiovascular effects attributed to adiponectin may lower risk of stroke. We investigated this in a prospective study and meta-analysis.

METHODS

A case-cohort study nested within the Potsdam cohort of the European Prospective Investigation into Cancer was performed, with 170 incident cases of ischemic stroke and a randomly selected subcohort of 2155 participants without major cardiovascular disease at baseline. A random-effects dose-response meta-analysis was performed on prospective studies reporting on adiponectin and incident stroke in healthy populations up to April 2013, identified through MEDLINE and EMBASE.

RESULTS

In European Prospective Investigation into Cancer-Potsdam, after adjustment for cardiovascular risk factors, the hazard ratio of ischemic stroke per 5-µg/mL higher total-adiponectin was 1.10 (95% confidence interval, 0.89-1.37). Participants with higher total-adiponectin had higher high-density lipoprotein-cholesterol and lower high-sensitivity C-reactive protein and triglyceride levels, and had less often diabetes mellitus. Additional adjustment for these putative mediators yielded a hazard ratio of 1.31 (95% confidence interval, 1.04-1.64). Nine studies (19,259 participants, 2960 cases), including European Prospective Investigation into Cancer-Potsdam, were meta-analyzed. Pooling relative risks adjusted for cardiovascular risk factors not including putative mediators indicated moderate between-study heterogeneity (I2=52.2%). This was explained by the smallest study, and the pooled relative risk (95% confidence interval) before and after its exclusion was 1.03 (0.98-1.08) and 0.99 (0.96-1.01) per 5 µg/mL, respectively. The pooled relative risk (95% confidence interval) additionally adjusted for potential mediators was 1.08 (1.01-1.15) and 1.05 (1.00-1.11) before and after excluding the same study, respectively.

CONCLUSIONS

Adiponectin is not associated with risk of stroke. If anything, adiponectin relates directly to stroke risk after controlling for risk factors that favorably correlate with adiponectin.

Oligomeric adiponectin forms and their complexes in the blood of healthy donors and patients with type 2 diabetes mellitus

Adiponectin (Adn) is a protein that circulates in the blood in several oligomeric forms, namely low-, medium-, and high-molecular-weight forms. Adn may serve as a risk factor for type 2 diabetes mellitus (T2DM). The aims of this work were (1) to produce monoclonal antibodies (MAbs) specific to different Adn oligomeric forms, (2) to design immunoassays suitable for measuring the Adn forms present in human blood, and (3) to investigate the changes in Adn forms that occur in patients with T2DM. Gel filtration, fluoroimmunoassays, and Western blotting were utilized as major techniques in this study. MAbs recognizing various oligomeric forms of Adn were obtained. Complexes between Adn and complement component C1q and between the low molecular weight form of Adn and albumin were described in human blood. A decrease in the total Adn and Adn-albumin complex levels in the blood of patients with T2DM and no difference in the levels of the Adn-C1q complex in comparison with healthy volunteers were demonstrated. An Adn94-Adn63 fluoroimmunoassay was selected as the technique that most accurately measured the mass ratio of Adn oligomers in blood samples, and an Adn214-Adn27 assay that measured the low-molecular-weight form of Adn only.

Novel roles for complement receptors in T cell regulation and beyond

Complement receptors are expressed on cells of the innate and the adaptive immune system. They play important roles in pathogen and danger sensing as they translate the information gathered by complement fluid phase sensors into cellular responses. Further, they control complement activation on viable and apoptotic host cells, clearance of immune complexes and mediate opsonophagocytosis. More recently, evidence has accumulated that complement receptors form a complex network with other innate receptors systems such as the Toll-like receptors, the Notch signaling system, IgG Fc receptors and C-type lectin receptors contributing to the benefit and burden of innate and adaptive immune responses in autoimmune and allergic diseases as well as in cancer and transplantation. Here, we will discuss recent developments and emerging concepts of complement receptor activation and regulation with a particular focus on the differentiation, maintenance and contraction of effector and regulatory T cells.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors

The activation of the complement cascade, a cornerstone of the innate immune response, produces a number of small (74-77 amino acid) fragments, originally termed anaphylatoxins, that are potent chemoattractants and secretagogues that act on a wide variety of cell types. These fragments, C5a, C4a, and C3a, participate at all levels of the immune response and are also involved in other processes such as neural development and organ regeneration. Their primary function, however, is in inflammation, so they are important targets for the development of antiinflammatory therapies. Only three receptors for complement peptides have been found, but there are no satisfactory antagonists as yet, despite intensive investigation. In humans, there is a single receptor for C3a (C3a receptor), no known receptor for C4a, and two receptors for C5a (C5a₁ receptor and C5a₂ receptor). The most recently characterized receptor, the C5a₂ receptor (previously known as C5L2 or GPR77), has been regarded as a passive binding protein, but signaling activities are now ascribed to it, so we propose that it be formally identified as a receptor and be given a name to reflect this. Here, we describe the complex biology of the complement peptides, introduce a new suggested nomenclature, and review our current knowledge of receptor pharmacology.

Correlation of circulating C1q and C1q-binding adiponectin concentrations with aging in males: a preliminary report

BACKGROUND

Atherosclerosis is an age-related disease. Adiponectin and C1q form a protein complex in human blood, and that serum C1q and C1q-binding adiponectin (C1q-APN) concentrations can be measured. We investigated circulating C1q and C1q-APN levels in Japanese men including elderly men.

FINDINGS

The study subjects were 509 Japanese men including elderly men. Serum levels of total adiponectin (Total-APN), high-molecular weight-adiponectin (HMW-APN), C1q-APN and C1q were measured by enzyme-linked immunosorbent assay. Total-APN, HMW-APN and C1q-APN, but not C1q, correlated significantly and positively with aging (r=0.26, r=0.24, r=0.17, p<0.01, respectively). The HMW-APN/Total-APN ratio correlated significantly and positively with aging (r=0.14, p<0.01). The C1q-APN/Total-APN ratio and C1q-APN/HMW-APN ratio correlated significantly and negatively with aging (r=-0.17, p<0.01, r=-0.12, p=0.01). C1q-APN/C1q correlated significantly and positively with aging (r=0.09, p=0.03). Multiple regression analysis identified age and body mass index as significant determinants of C1q-APN.

CONCLUSIONS

The present study demonstrates that serum HMW-APN, C1q-APN, and Total-APN, but not C1q, correlated positively with aging. These preliminary results could form the basis for future research.

CLINICAL TRIAL REGISTRATION NUMBER

UMIN000004318.

Total and high-molecular-weight adiponectin and risk of coronary heart disease and ischemic stroke in older adults

CONTEXT

Adiponectin is atheroprotective in the laboratory, but prospective studies have shown opposite associations with cardiovascular disease (CVD) in healthy middle-aged populations (protective) and older cohorts (adverse). Whether this relates to different proportions of high-molecular-weight (HMW) adiponectin is unknown.

OBJECTIVE

The aim of the study was to test the hypothesis that total adiponectin is directly associated, but HMW adiponectin is inversely related, with CVD in older adults.

DESIGN, SETTING, AND PARTICIPANTS

We evaluated 3290 participants free of prevalent CVD in a longitudinal cohort study of U.S. adults aged 65 yr and older.

MAIN OUTCOME MEASURES

We measured incident CVD (n = 1291), comprising coronary heart disease and ischemic stroke.

RESULTS

Total and HMW adiponectin were tightly correlated (r = 0.94). Cubic splines adjusted for potential confounders revealed that the associations of total and HMW adiponectin with CVD were U-shaped, with inflection points of 20 and 10 mg/liter, respectively. After controlling for potential confounding, levels of total and HMW adiponectin below these cutpoints tended to be inversely associated with incident CVD, driven by their significant or near-significant relations with coronary heart disease [hazard ratio (HR), 0.85 per sd increase; 95% confidence interval (CI), 0.75-96; and HR, 0.87; 95% CI, 0.75-1.01, respectively]. These associations were abrogated by additional inclusion of putative metabolic intermediates. Above these cutpoints, however, both total and HMW adiponectin were significantly directly associated with CVD after adjustment for confounders and, particularly, mediators (HR, 1.20 per sd increase; 95% CI, 1.06-1.35; and HR, 1.12; 95% CI, 1.02-1.24, respectively).

CONCLUSION

In community-living elders, total and HMW adiponectin showed similar U-shaped relationships with CVD. The inverse relation in the lower range, but not the direct association at the higher end, disappeared after inclusion of putative intermediates, suggesting that high levels may reflect adverse processes separate from adiponectin's beneficial glycometabolic properties.

Binding of adiponectin and C1q in human serum, and clinical significance of the measurement of C1q-adiponectin / total adiponectin ratio

OBJECTIVE

Adiponectin and C1q have similar sequences, exist abundantly in blood, and are produced by adipose tissues. The aim of this study was to examine whether adiponectin and C1q form protein-complex in blood and to know the clinical significance of the C1q-adiponectin (C1q-APN) complex in serum.

METHODS

The direct interaction between adiponectin and C1q was investigated by far western blotting and co-immunoprecipitation. The relationship between serum C1q-APN and various clinical features was analyzed in 329 Japanese men who underwent health check-up, including measurements of visceral (VFA) and subcutaneous fat area (SFA) by computed tomography (Victor-J study).

RESULTS

Adiponectin bound to C1q in vitro and C1q-APN complex existed in human blood. C1q-APN complexes were identified in high- and middle-molecular weight forms of adiponectin in human serum by gel-filtration chromatography. Stepwise multiple regression analysis identified body mass index, VFA and SFA as significant determinants of serum C1q-APN level. Serum C1q-APN/Total-APN ratio correlated positively with cardiovascular risk factor accumulation in subjects with VFA ≥100 cm(2).

CONCLUSIONS

These results indicate that high- and middle-molecular forms of adiponectin partly consist of adiponectin-complex with other proteins including C1q and that the blood C1q-APN/Total-APN ratio may serve as a biomarker of the metabolic syndrome in general male subjects.

Juvenile elastic arteries after 28 years of renal replacement therapy in a patient with complete complement C4 deficiency

BACKGROUND

Complement activation products are present in atherosclerotic plaques. Recently, binding of complement to elastin and collagen in the aortic wall has been demonstrated, suggesting a role of complement in the development aortic stiffness and atherosclerosis. The definitive role of complement in atherosclerosis and arteriosclerosis, however, remains unclear.

CASE PRESENTATION

We here describe a patient with hereditary complete deficiency of complement C4 suffering from Henoch-Schoenlein purpura and on renal replacement therapy for twenty-eight years. The patient had the full range of risk factors for vascular damage such as hypertension, volume overload, hyperphosphatemia and hyperparathyroidism. Despite that, his carotid artery intima media thickness was below the normal range and his pulse wave velocity was normal. In contrast, the patient's coronary and peripheral muscular arteries were heavily calcified.

CONCLUSION

This case supports the hypothesis that complement plays an important role in the development of stiffness of elastic arteries. We speculate that inability to activate complement by the classical or lectin pathways protected the patient from atherosclerosis, arteriosclerosis, stiffening and calcification of the aorta and carotid arteries. Inhibition of complement activation may be a potential target for prophylactic and therapeutic interventions.

Oxidative stress as pathogenesis of cardiovascular risk associated with metabolic syndrome

Metabolic syndrome (MetS) is characterized by accumulation of visceral fat associated with the clustering of metabolic and pathophysiological cardiovascular risk factors: impaired glucose tolerance, dyslipidemia, and hypertension. Although the definition of MetS is different among countries, visceral obesity is an indispensable component of MetS. A growing body of evidence suggests that increased oxidative stress to adipocytes is central to the pathogenesis of cardiovascular disease in MetS. Increased oxidative stress to adipocytes causes dysregulated expression of inflammation-related adipocytokines in MetS, which contributes to obesity-associated vasculopathy and cardiovascular risk primarily through endothelial dysfunction. The purpose of present review is to unravel the mechanistic link between oxidative stress and cardiovascular risk in MetS, focusing on insulin resistance, hypertension, and atherosclerosis. Then, therapeutic opportunities translated from the bench to bedside will be provided to develop novel strategies to cardiovascular risk factors in MetS.

Complement proteins C3 and C4 bind to collagen and elastin in the vascular wall: a potential role in vascular stiffness and atherosclerosis

Circulating inflammatory mediators including complement activation products participate in the pathogenesis of cardiovascular diseases. As such, previous reports demonstrating the presence of complement proteins within atherosclerotic plaque and on the luminal surface would be anticipated. In contrast, we have recently made the unexpected observation that complement proteins also deposit along the external elastic lamina of mouse aortas in the absence of luminal deposition or plaque development. This suggests that complement activation may play a critical role in the pathogenesis of vascular stiffness and atherosclerosis through a mechanism initiated within the adventitia rather than on the endothelial surface. This hypothesis was tested in the current study by ultrastructural identification of the C3- and C4-binding targets within the adventitia of the mouse aorta. The results demonstrate extensive binding of C3 and C4 to both collagen and elastin fibers within the adventitia in both ApoE(-/-) and C57Bl/6J control mice, as well as the presence of C3 and C4 within perivascular adipose tissue. These observations suggest a potential "outside-in" mechanism of vascular stiffness during which perivascular adipose may produce C3 and C4 that bind to collagen and elastin fibers within the adventitia through covalent thiolester bonds, leading to increased vascular stiffness.

Complement and non-complement activating functions of C1q: A prototypical innate immune molecule

C1q is a versatile innate immune molecule that serves as the initiation subcomponent of the classical complement pathway. In addition, it is also a potent pattern recognition molecule, the versatility of which has fuelled its functional flexibility. C1q recognises an array of self, non-self and altered-self ligands. The broad-spectrum ligand-binding potential of C1q is facilitated by the modular organisation of the heterotrimeric globular head region, its ability to change its conformation in a very subtle way, and the manner in which this ancient molecule appears to have evolved to deal with the different types of ligands. Over recent years, molecules that resemble C1q have been put together to form the C1q family. In this review, we briefly summarise complement-dependent and complement-independent functions of C1q, its cognate receptors and key members of the rapidly growing C1q family.

Modulation of lupus phenotype by adiponectin deficiency in autoimmune mouse models

Adiponectin is an adipocyte-derived cytokine with anti-inflammatory properties. Paradoxically, circulating adiponectin levels are increased in a number of inflammatory diseases. Thus, we sought to define the role of adiponectin deficiency in mouse models of autoimmunity. Adiponectin-deficient mice on a C57BL/6 background do not develop an autoimmune phenotype. Autoimmunity was also not observed in adiponectin-deficient mice generated on the permissive MRL background. However, adiponectin deficiency exacerbated the autoimmune phenotype of MRL-lpr mice. Compared with MRL-lpr mice, MRL-lpr.apn(-/-) mice displayed greater lymphadenopathy and splenomegaly, as well as increased anti-nuclear antibody and anti-dsDNA production. In addition, evaluation of the kidney revealed larger glomerular tuft size, crescent formation, increased IgG and C3 deposits, and mesangial expansion in the MRL-lpr.apn(-/-) mice. The effects of adiponectin deficiency on the autoimmune phenotypes were more pronounced in female versus male mice. These data show that, while adiponectin deficiency is not sufficient to confer autoimmunity, adiponectin acts as a negative modulator of the autoimmune phenotype in a murine model of lupus.

Adiponectin reduces C-reactive protein expression and downregulates STAT3 phosphorylation induced by IL-6 in HepG2 cells

By playing a direct proatherogenic role, C-reactive protein (CRP) is a potent independent predictor of future cardiovascular events. CRP is predominately synthesized by hepatocytes when stimulated by interleukin-6 (IL-6). In response to IL-6, the signal transducer and activator of transcription 3 (STAT3) becomes phosphorylated on tyrosine and serine residues. Phosphorylated STAT3 then activates CRP gene transcription. In obesity-related disorders such as diabetes, metabolic syndrome, and cardiovascular diseases, the circulating levels of CRP and adiponectin are inversely correlated, suggesting that these two factors might reciprocally regulate each other. We investigated the possibility that adiponectin inhibits CRP production in HepG(2) cells elicited by IL-6. CRP gene expression was determined using ELISA and semi-quantitative RT-PCR, and the phosphorylation of STAT3 was investigated with western blot. Adiponectin reduced IL-6-induced CRP mRNA levels in HepG(2) cells and CRP protein secretion. Preincubating HepG(2) cells with adiponectin led to a decline in STAT3 phosphorylation on both tyrosine and serine residues. Our results demonstrated that adiponectin suppresses CRP synthesis and secretion from HepG(2) cells and suggested that the suppression may be mediated through inhibition of the STAT3 pathway. The finding provides a novel insight into the molecular linkage between obesity and vascular diseases.

Change in circulating adiponectin in advanced old age: determinants and impact on physical function and mortality. The Cardiovascular Health Study All Stars Study

BACKGROUND

Cross-sectional studies show that adiponectin is higher in older than in younger adults but long-term change in adiponectin, its determinants, and its relationship to functional decline or survival in the elderly population have not been evaluated.

METHODS

We investigated predictors of longitudinal change in adiponectin, and the association of this adipokine or its antecedent change with physical deterioration and all-cause mortality in 988 participants in a population-based study who completed examinations in 1996-1997 and 2005-2006, had serial adiponectin measurements and underwent follow-up through June 2009.

RESULTS

Adiponectin level rose significantly during follow-up, but the increase was smaller in blacks, was associated with declining weight or fasting glucose and, in men, lower albumin, and was affected by medications. Adiponectin was independently associated with greater physical decline, but the relationship for adiponectin change was driven by concomitant weight decrease. Both adiponectin and its change independently predicted mortality, even after adjustment for weight change. The association for adiponectin and mortality was observed in whites but not in blacks and only for levels in the upper range (hazard ratio = 1.85, 95% confidence interval = 1.36-2.52 per SD ≥ 20 mg/L), whereas that for adiponectin change was linear throughout in both racial groups (hazard ratio = 1.30, 95% confidence interval = 1.10-1.52 per SD).

CONCLUSIONS

Adiponectin levels increase over time in long-lived adults and are associated with greater physical disability and mortality. Such increases may occur in response to age-related homeostatic dysregulation. Additional investigation is required to define the underlying mechanisms and whether this represents a marker or causal factor for mortality in this age group.

Regulation of beta-cell viability and gene expression by distinct agonist fragments of adiponectin

Obesity is an established risk factor for type 2 diabetes. Activation of the adiponectin receptors has a clear role in improving insulin resistance although conflicting evidence exists for its effects on pancreatic beta-cells. Previous reports have identified both adiponectin receptors (ADR-1 and ADR-2) in the beta-cell. Recent evidence has suggested that two distinct regions of the adiponectin molecule, the globular domain and a small N-terminal region, have agonist properties. This study investigates the effects of two agonist regions of adiponectin on insulin secretion, gene expression, cell viability and cell signalling in the rat beta-cell line BRIN-BD11, as well as investigating the expression levels of adiponectin receptors (ADRs) in these cells. Cells were treated with globular adiponectin and adiponectin (15-36) +/-leptin to investigate cell viability, expression of key beta-cell genes and ERK1/2 activation. Both globular adiponectin and adiponectin (15-36) caused significant ERK1/2 dependent increases in cell viability. Leptin co-incubation attenuated adiponectin (15-36) but not globular adiponectin induced cell viability. Globular adiponectin, but not adiponectin (15-36), caused a significant 450% increase in PDX-1 expression and a 45% decrease in LPL expression. ADR-1 was expressed at a higher level than ADR-2, and ADR mRNA levels were differentially regulated by non-esterified fatty acids and peroxisome-proliferator-activated receptor agonists. These data provide evidence of roles for two distinct adiponectin agonist domains in the beta-cell and confirm the potentially important role of adiponectin receptor agonism in maintaining beta-cell mass.

Cross-sectional associations between abdominal and thoracic adipose tissue compartments and adiponectin and resistin in the Framingham Heart Study

OBJECTIVE

To test the association of regional fat depots with circulating adiponectin and resistin concentrations and to assess the potential mediating effect of adipokines on associations between abdominal fat depots and cardiometabolic risk factors.

RESEARCH DESIGN AND METHODS

Participants from the Framingham Heart Study offspring cohort (n = 916, 55% women; mean age 59 years) free of cardiovascular disease underwent computed tomography measurement of visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), pericardial fat, and intrathoracic fat volumes and assays of circulating adiponectin and resistin.

RESULTS

VAT, SAT, pericardial fat, and intrathoracic fat were negatively correlated with adiponectin (r = -0.19 to -0.34, P < 0.001 [women]; r = -0.15 to -0.26, P < 0.01 [men] except SAT) and positively correlated with resistin (r = 0.16-0.21, P < 0.001 [women]; r = 0.11-0.14, P < 0.05 [men] except VAT). VAT increased the multivariable model R(2) for adiponectin from 2-4% to 10-13% and for resistin from 3-4% to 3-6%. Adjustment for adipokines did not fully attenuate associations between VAT, SAT, and cardiometabolic risk factors.

CONCLUSIONS

Adiponectin and resistin are correlated with fat depots cross-sectionally, but none of the adipokines can serve as surrogates for the fat depots. Relations between VAT, SAT, and cardiometabolic risk factors were not fully explained by adiponectin or resistin concentrations.