Calcium is involved in formation of high molecular weight adiponectin

20 Years with SGBS cells - a versatile in vitro model of human adipocyte biology

20 years ago, we described a human cell strain derived from subcutaneous adipose tissue of an infant supposed to have Simpson-Golabi-Behmel Syndrome (SGBS), thus called “SGBS cells”. Since then, these cells have emerged as the most commonly used cell model for human adipogenesis and human adipocyte biology. Although these adipocyte derived stem cells have not been genetically manipulated for transformation or immortalization, SGBS cells retain their capacity to proliferate and to differentiate into adipocytes for more than 50 population doublings, providing an almost unlimited source of human adipocyte progenitor cells. Original data obtained with SGBS cells led to more than 200 peer reviewed publications comprising investigations on adipogenesis and browning, insulin sensitivity, inflammatory response, adipokine production, as well as co-culture models and cell-cell communication. In this article, we provide an update on the characterization of SGBS cells, present basic methods for their application and summarize results of a systematic literature search on original data obtained with this cell strain.

Potential Roles of Adiponectin Isoforms in Human Obesity with Delayed Wound Healing

Adiponectin is an adipokine with anti-insulin resistance and anti-inflammatory functions. It exists in serum predominantly in three multimeric complexes: the trimer, hexamer, and high-molecular-weight forms. Although recent studies indicate that adiponectin promotes wound healing in rodents, its role in the wound healing process in humans is unknown. This study investigated the expression levels of adiponectin in adipose tissue and serum of women who experienced either normal or delayed wound healing after abdominal plastic surgery. We found that obese women with delayed healing had slightly lower total adiponectin levels in their adipose tissue compared with women with normal healing rates. Among the different isoforms of adiponectin, levels of the trimer forms were significantly reduced in adipose tissue, but not the serum, of obese women with delayed healing compared to women who healed normally. This study provides clinical evidence for a potential role of low-molecular-weight oligomers of adiponectin in the wound healing process as well as implications for an autocrine and/or paracrine mechanism of adiponectin action in adipose tissues.

Ca2+ entry via TRPC1 is essential for cellular differentiation and modulates secretion via the SNARE complex

Properties of adipocytes, including differentiation and adipokine secretion, are crucial factors in obesity-associated metabolic syndrome. Here, we provide evidence that Ca²⁺ influx in primary adipocytes, especially upon Ca²⁺ store depletion, plays an important role in adipocyte differentiation, functionality and subsequently metabolic regulation. The endogenous Ca²⁺ entry channel in both subcutaneous and visceral adipocytes was found to be dependent on TRPC1–STIM1, and blocking Ca²⁺ entry with SKF96365 or using TRPC1^−/− knockdown adipocytes inhibited adipocyte differentiation. Additionally, TRPC1^−/− mice have decreased organ weight, but increased adipose deposition and reduced serum adiponectin and leptin concentrations, without affecting total adipokine expression. Mechanistically, TRPC1-mediated Ca²⁺ entry regulated SNARE complex formation, and agonist-mediated secretion of adipokine-loaded vesicles was inhibited in TRPC1^−/− adipose. These results suggest an unequivocal role of TRPC1 in adipocyte differentiation and adiponectin secretion, and that loss of TRPC1 disturbs metabolic homeostasis.

This article has an associated First Person interview with the first author of the paper.

Summary: TRPC1 modulates Ca²⁺ entry, which is essential in adipocyte differentiation and adiponectin secretion, through facilitating SNARE complex formation, thereby maintaining metabolic homeostasis.

Structural commonality of C1q TNF-related proteins and their potential to activate relaxin/insulin-like family peptide receptor 1 signalling pathways in cancer cells

We established the role of the GPCR relaxin/insulin-like family peptide receptor 1 (RXFP1 receptor) as a novel active receptor in human glioblastoma (GB), a fatal brain tumour. We identified C1q/TNF-related protein 8 (CTRP8) as a novel agonist of the RXFP1 receptor. CTRP8 enhanced the motility and matrix invasion of GB, and this involved PKC-mediated up-regulation of cathepsin B, a marker for poor prognosis in GB patients. We conclude that the absence of relaxin isoforms does not preclude the activation of the RXFP1 receptor, as the least known member of the CTRP family, CTRP8, can effectively target and activate RXFP1 receptors.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

RXFP1 is Targeted by Complement C1q Tumor Necrosis Factor-Related Factor 8 in Brain Cancer

The relaxin-like RXFP1 ligand-receptor system has important functions in tumor growth and tissue invasion. Recently, we have identified the secreted protein, CTRP8, a member of the C1q/tumor necrosis factor-related protein (CTRP) family, as a novel ligand of the relaxin receptor, RXFP1, with functions in brain cancer. Here, we review the role of CTRP members in cancers cells with particular emphasis on CTRP8 in glioblastoma.

Characterization of adiponectin concentrations and molecular weight forms in serum, seminal plasma, and ovarian follicular fluid from cattle

Adiponectin (AdipoQ), an adipocyte-derived hormone, is one of the most abundant adipokines in the blood circulation. Adiponectin has various metabolic functions, such as improving insulin sensitivity in humans and rodents. The role of AdipoQ in reproduction is not yet fully understood, but the expression of AdipoQ in reproductive tissues has been observed in various animals and humans, including chicken testis, bovine ovary, and human placenta. The objective of this study was to characterize AdipoQ in the bovine body fluids related to reproduction. Therefore, we evaluated the seminal plasma (SP) from breeding bulls (n = 29) and follicular fluid (FF) from heifers (n = 14), and we also collected blood samples from these animals. In addition, blood samples from other bulls (n = 30) and heifers (n = 14) were assayed for AdipoQ. The concentrations were assessed using a bovine-specific ELISA, and the molecular weight (MW) pattern of the AdipoQ protein was estimated by the Western blot analysis. The SP AdipoQ concentrations were approximately 180-fold lower compared with that in the serum concentrations. Furthermore, the AdipoQ concentrations in the serum and SP were positively correlated. The MW patterns of AdipoQ in the serum and SP were different such that the high MW form of AdipoQ was more abundant in the SP than serum. The AdipoQ concentrations in the serum and SP also increased with age: old bulls (>6 years) had higher AdipoQ concentrations in the serum and SP than bulls aged 24 months or lesser (P < 0.05). In the FF, the AdipoQ concentrations were 1.6-fold lower than those in the corresponding serum samples, and the concentrations in the serum and FF were not correlated (P > 0.1). In the FF, only the middle MW forms of AdipoQ were detectable by Western blotting. The MW pattern in the serum did not differ between the sexes. Our data provide both the AdipoQ concentration and the MW patterns for bovine body fluids related to reproduction.

Assembly of adiponectin oligomers

Adiponectin is among the most studied adipokines, the collection of molecules secreted from adipose tissue. It is also one of the most architecturally complex adipokines with its various oligomeric states that include trimers, hexamers, nonamers (9mers), dodecamers (12mers), and octadecamers (18mers). The importance of adiponectin in metabolic regulation is underscored by its strong positive associations with improvement in insulin action and also decreased risks for developing type 2 diabetes. Understanding the mechanisms involved in maintaining the steady-state concentrations of adiponectin oligomers in circulation is therefore likely to provide important insight into the development of insulin resistance. This review will discuss the current state of knowledge regarding the biochemical composition of adiponectin oligomers, the commonly used techniques to analyze them, and the known post-translational modifications that affect their assembly. Evidence based on in vitro oligomer assembly reactions in support of a "cystine ratchet" model of adiponectin oligomer formation will be considered along with limitations of the evidence. Secretory pathway proteins that have been shown to affect the distribution of adiponectin oligomers will also be discussed along with hypotheses regarding their potential involvement in the cystine ratchet model of adiponectin oligomerization.

The role of serum magnesium and calcium on the association between adiponectin levels and all-cause mortality in end-stage renal disease patients

BACKGROUND

Adiponectin (ADPN) is the most abundant adipocyte-specific cytokine that plays an important role in energy homeostasis by regulating lipid and glucose metabolism. Studies of the impact of ADPN on clinical outcomes have yielded contradictory results so far. Here, we examined the association of ADPN with serum magnesium (s-Mg) and calcium (s-Ca) levels and explored the possibility whether these two factors could modify the relationship between ADPN and all-cause mortality in patients with end-stage renal disease.

METHODOLOGY/PRINCIPAL FINDINGS

After baseline assessment, 47 hemodialysis and 27 peritoneal dialysis patients were followed- up for a median period of 50 months. S-Mg and s-Ca levels emerged as positive and negative predictors of ADPN levels, respectively. During the follow-up period 18 deaths occurred. There was a significant 4% increased risk for all-cause mortality for each 1-µg/ml increment of ADPN (crude HR, 1.04; 95% CI, 1.01-1.07), even after adjustment for s-Mg and s-Ca levels, dialysis mode, age, albumin and C-reactive protein. Cox analysis stratified by s-Mg levels (below and above the median value of 2.45 mg/dl) and s-Ca levels (below and above the median value of 9.3 mg/dl), revealed ADPN as an independent predictor of total mortality only in the low s-Mg and high s-Ca groups. Furthermore, low s-Mg and high s-Ca levels were independently associated with malnutrition, inflammation, arterial stiffening and risk of death.

CONCLUSIONS/SIGNIFICANCE

The predictive value of ADPN in all-cause mortality in end-stage renal disease patients appears to be critically dependent on s-Mg and s-Ca levels. Conversely, s-Mg and s-Ca may impact on clinical outcomes by directly modifying the ADPN's bioactivity.

Characterization of the weak calcium binding of trimeric globular adiponectin

Adiponectin is secreted from adipose tissue and functions as a protein hormone in regulating glucose metabolism and fatty acid catabolism. Adiponectin plays an important role as a novel risk factor and potential diagnostic and prognostic biomarker in cancer. Crystal structures of globular adiponectin have been resolved with three calcium-binding sites on the top of its central tunnel. However, the calcium-binding property of adiponectin remains elusive. Mouse globular adiponectin was cloned into pET11a and expressed in Escherichia coli. The folding of adiponectin was indicated by the spread of resonances in HSQC spectrum. Luminescence resonance energy transfer was used to obtain the binding constant (K(d)) of Tb(3+) and the inhibitor constant (K(i)) of Ca(2+) for globular adiponectin. The obtained calcium-binding affinity to adiponectin is relatively low (~2 mM), which indicates that the high concentration of adiponectin in circulating system may function as calcium storage bank and buffer the free calcium concentration.

Improvement of vitamin D status via daily intake of fortified yogurt drink either with or without extra calcium ameliorates systemic inflammatory biomarkers, including adipokines, in the subjects with type 2 diabetes

CONTEXT

Systemic inflammation is thought to have a central role in diabetic long-term complications.

OBJECTIVE

The aim of this study was to investigate the effects of vitamin D either with or without extra calcium on certain inflammatory biomarkers in the subjects with type 2 diabetes (T2D).

DESIGN, SETTING, AND PARTICIPANTS

This was a double-blind, randomized, controlled trial conducted over 12 wk in 90 T2D subjects aged 30-60 yr from both sexes.

INTERVENTION

Subjects were randomly allocated to one of three groups to receive two 250-ml bottles a day of plain Persian yogurt drink or doogh (PD, containing 150 mg calcium and no detectable vitamin D(3)/250 ml), vitamin D-fortified doogh (DD, containing 500 IU vitamin D(3) and 150 mg calcium/250 ml), or calcium + vitamin D(3)-fortified doogh (CDD, containing 500 IU vitamin D(3) and 250 mg calcium/250 ml).

OUTCOME MEASURES

The changes in inflammatory markers were evaluated.

RESULTS

Compared to the baseline values, highly sensitive C-reactive protein, IL-1β, IL-6, fibrinogen, and retinol binding protein-4 concentrations significantly decreased in both the DD and CDD groups. Although the decrement in highly sensitive C-reactive protein and fibrinogen was more in CDD compared to DD (-4.0 ± 8.5 vs. -1.3 ± 2.8 mg/liter, and -0.40 ± 0.74 and -0.20 ± 0.52 mg/liter, respectively), the differences were not significant. There was a significant increase in serum adiponectin in both the DD and CDD groups (51.3 ± 65.3 vs. 57.1 ± 33.8 μg/liter; P < 0.05). Mean adiponectin changes in CDD were significantly higher than in PD (P = 0.021).

CONCLUSIONS

Daily intake of vitamin D-fortified doogh improved inflammatory markers in T2D subjects, and extra calcium conferred additional benefit only for the antiinflammatory adipokine, i.e. adiponectin.

Crystal structure of a single-chain trimer of human adiponectin globular domain

Adiponectin is increasingly recognized as a potential therapeutic agent for the treatment of diabetes and other metabolic diseases. It circulates in plasma as homotrimers and higher-order oliogomers of homotrimers. To facilitate the production of active recombinant adiponectin as a therapeutic tool, we designed a single-chain globular domain adiponectin (sc-gAd) in which three monomer sequences are linked together in tandem to form one contiguous polypeptide. Here, we present the crystal structure of human sc-gAd at 2.0Å resolution. The structure reveals a similar trimeric topology to that of mouse gAd protein. Trimer formation is further rigidified by three calcium ions.

Association between Hypoadiponectinemia and Low Serum Concentrations of Calcium and Vitamin D in Women with Polycystic Ovary Syndrome

Objective. To investigate the possible association of calcium and vitamin D deficiency with hypoadiponectinemia in women with PCOS. Subjects and Methods. In this case-control study, 103 PCOS cases and 103 controls included. The concentrations of calcium, 25-OH-vitamin D (25OHD), adiponectin, insulin, glucose, total cholesterol, HDL-cholesterol, triglyceride (TG), and androgens were measured in fasting blood samples. Results. Adiponectin (8.4 ± 2.7 ng/mL versus 13.6 ± 5 ng/mL in control group, P : 0.00), calcium (2 ± 0.1 mmol/L versus 2.55 ± 0.17 mmol/L in controls, P : 0.00), and 25-OH-Vit D (30 ± 2.99 nmol/L versus 43.7 ± 5.2 nmol/L in control group, P : 0.00) levels were decreased in women with PCOS. Subjects with PCOS had higher concentrations of TG (1.4 ± 0.77 mmol/L versus 1.18 ± 0.75 mmol/L in control group, P : 0.019) and dehydroepiandrosterone sulfate (DHEA-S) (10.7 ± 11 mmol/L versus 9.7 ± 10.4, P : 0.02 in control group). There were significant correlations between adiponectin concentrations with calcium (r : 0.78, P : 0.00) and 25OHD levels (r : 0.82, P : 0.00). The association of hypoadiponectinemia and PCOS was not significant considering 25OHD as a confounding factor. Conclusion. The present findings indicate that the association of hypoadiponectinemia with PCOS is dependent on vitamin D. A possible beneficiary effect of vitamin D on the metabolic parameters in PCOS may be suggested.

Secretion of adipokines by human adipose tissue in vivo: partitioning between capillary and lymphatic transport

Peptides secreted by adipose tissue (adipokines) may enter blood via capillaries or lymph. The relative importance of these pathways for a given adipokine might influence its biological effects. Because this has not been studied in any species, we measured the concentrations of seven adipokines and eight nonsecreted proteins in afferent peripheral lymph and venous plasma from 12 healthy men. Data for nonsecreted proteins were used to derive indices of microvascular permeability, which in conjunction with the molecular radii of the adipokines were used to estimate the amounts leaving the tissue via capillaries. Transport rates via lymph were estimated from the lymph adipokine concentrations and lymph flow rates and total transport (secretion) as the sum of this and capillary transport. Concentrations of nonsecreted proteins were always lower in lymph than in plasma. With the exception of adiponectin, adipokine concentrations were always higher in lymph (P < 0.01). Leptin and MCP-1 were secreted at the highest rates (means: 43 μg/h or 2.7 nmol/h and 32 μg/h or 2.4 nmol/h, respectively). IL-6 and MCP-1 secretion rates varied greatly between subjects. The proportion of an adipokine transported via lymph was directly related to its molecular radius (r(s) = +0.94, P = 0.025, n = 6), increasing from 14 to 100% as the radius increased from 1.18 (IL-8) to 3.24 nm (TNFα). We conclude that the lymph/capillary partitioning of adipokines is a function of molecular size, which may affect both their regional and systemic effects in vivo. This finding may have implications for the physiology of peptides secreted by other tissues.

Vascular smooth muscle cell-derived adiponectin: a paracrine regulator of contractile phenotype

Adiponectin is a cardioprotective adipokine derived predominantly from visceral fat. We recently demonstrated that exogenous adiponectin induces vascular smooth muscle cell (VSMC) differentiation via repression of mTORC1 and FoxO4. Here we report for the first time that VSMC express and secrete adiponectin, which acts in an autocrine and paracrine manner to regulate VSMC contractile phenotype. Adiponectin was found to be expressed in human coronary artery and mouse aortic VSMC. Importantly, siRNA knock-down of endogenous adiponectin in VSMC significantly reduced the expression of VSMC contractile proteins. Contractile protein deficiency was also observed in primary VSMC isolated from Adiponectin(-/-) mice. This deficiency could be rescued by culturing Adiponectin(-/-) VSMC in conditioned media from wild type (WT) VSMC. Moreover, the paracrine effect of VSMC-derived adiponectin was confirmed as adiponectin neutralizing antibody blocked the rescue. Overexpressed adiponectin also exerted paracrine effects on neighboring untransfected VSMC, which was also blocked by adiponectin neutralizing antibody. Interestingly, adiponectin expression was inducible by the PPARγ agonist rosiglitazone. Our data support an important role for VSMC-derived adiponectin in maintaining VSMC contractile phenotype, contributing to critical cardioprotective functions in the vascular wall. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

Vascular biology of metabolic syndrome

The metabolic syndrome is a constellation of clinical risk factors comprising atherogenic dyslipidemia (low high-density lipoprotein and high triglycerides levels), elevated blood pressure, elevated plasma glucose, a prothrombotic state, and a proinflammatory state accompanied by an increased risk for cardiovascular disease and type 2 diabetes mellitus. The adipose tissue of obese humans contains increased numbers of macrophages, and once activated, these macrophages are responsible for the expression of most of the tissue's tumor necrosis factor (TNF)-α and interleukin (IL)-6. Chronic inflammation associated with visceral obesity induces altered lipoprotein metabolism and insulin resistance in the liver. Adipocytes secrete a variety of hormones, cytokines, growth factors, and other bioactive substances, conceptualized as adipocytokines, including plasminogen activator inhibitor 1 (PAI-1), TNF-α, leptin, and adiponectin. The dysregulation of these adipokines contributes to the pathogenesis of obesity. Adipose tissue-resident macrophages and adipocytes in the adipose tissue combined with the consequences of hyperglycemia, altered lipoproteins, and hyperinsulinemia in the vasculature and within organ microcirculation lead to dysfunctional endothelia and a proinflammatory state. Metabolic syndrome thus represents a combination of synergistic vascular pathologies that lead to an accelerated atherogenic state that compromises the ability of the patient to satisfactorily respond to humoral, cellular, and mechanical stresses.

Adiponectin and polycystic ovary syndrome

INTRODUCTION

Polycystic ovary syndrome (PCOS) has a prevalence of 5-8% in women of reproductive age. Women with PCOS have an increased risk of metabolic syndrome and associated comorbidities. Adiponectin is a circulating protein produced by adipocytes. Circulating levels of adiponectin are inversely related to adipocyte mass. Low levels occur with insulin resistance, type 2 diabetes, metabolic syndrome, and obesity-related cardiovascular disease. This article reviews the literature on the link between adiponectin and PCOS and the potential use of adiponectin as a biomarker for PCOS.

METHOD

Data-based studies on adiponectin and PCOS and adiponectin measurement were identified through the Medline (1950-2009) and ISI Web of Knowledge (1973-2009) databases.

RESULTS

Fifteen studies related to adiponectin and PCOS met inclusion criteria and were included in this review. These studies present evidence that adiponectin is linked to insulin resistance, insulin sensitivity, body mass index (BMI), and adiposity. In women with PCOS, lower levels, as opposed to higher levels, of adiponectin occur in the absence of adiposity.

CONCLUSION

The relationships between adiponectin and insulin resistance and sensitivity, metabolic syndrome, and BMI in women with PCOS suggest that adiponectin potentially could serve as a marker for disease risk and provide opportunity for earlier intervention if knowledge is successfully translated from laboratory to clinical practice. However, further study of the relationship between adiponectin and PCOS is required before there can be direct application to clinical practice.

Disparity in circulating adiponectin multimers between term and preterm infants

AIMS

To study circulating levels and distribution of adiponectin multimers [low molecular weight (LMW)-, medium molecular weight (MMW)- and high molecular weight (HMW)-adiponectin] in preterm and full-term infants.

METHODS

Total serum adiponectin and its multimers were measured in 40 healthy infants at the age of one month and associations with anthropometric parameters [body weight and length, body mass index (BMI)], weight gain and metabolic indices (glucose, insulin) were examined. Twenty of the infants were born preterm (gestational age 33.2+/-1.6 weeks).

RESULTS

LMW-adiponectin level and its fractional ratio to total adiponectin were significantly higher in full-term than in preterm infants (P<0.001 and P<0.01, respectively), whereas, MMW-adiponectin level and its ratio were significantly lower (P=0.03 and P=0.01, respectively). HMW-adiponectin did not differ significantly between full-term and preterm infants and accounted for almost 60% of total adiponectin levels in both groups. HMW-adiponectin, but not MMW adiponectin or LMW adiponectin, correlated significantly with anthropometric measurements, similarly to total adiponectin; in addition, HMW adiponectin correlated significantly with weight gain.

CONCLUSIONS

HMW adiponectin is the most prevalent form in infants. Circulating levels and distribution of MMW- and LMW-adiponectin differ between full-term and preterm infants, but the role of these adiponectin multimers needs to be studied further.

Adipocytokines and the metabolic complications of obesity

CONTEXT

Adipose tissue is increasingly recognized as an active endocrine organ with many secretory products and part of the innate immune system. With obesity, macrophages infiltrate adipose tissue, and numerous adipocytokines are released by both macrophages and adipocytes. Adipocytokines play important roles in the pathogenesis of insulin resistance and associated metabolic complications such as dyslipidemia, hypertension, and premature heart disease.

EVIDENCE ACQUISITION

Published literature was analyzed with the intent of addressing the role of the major adipose secretory proteins in human obesity, insulin resistance, and type 2 diabetes.

EVIDENCE SYNTHESIS

This review analyzes the characteristics of different adipocytokines, including leptin, adiponectin, pro-inflammatory cytokines, resistin, retinol binding protein 4, visfatin, and others, and their roles in the pathogenesis of insulin resistance.

CONCLUSIONS

Inflamed fat in obesity secretes an array of proteins implicated in the impairment of insulin signaling. Further studies are needed to understand the triggers that initiate inflammation in adipose tissue and the role of each adipokine in the pathogenesis of insulin resistance.