Selective downregulation of the high molecular weight form of adiponectin in hyperinsulinemia and in type 2 diabetes: differential regulation from nondiabetic subjects

Short-term induced hyperinsulinaemia and dexamethasone challenge do not affect circulating total adiponectin concentrations in insulin-sensitive ponies

BACKGROUND

Hypoadiponectinaemia is a risk factor for endocrinopathic laminitis, but the directionality and nature of its association with insulin dysregulation is unclear.

OBJECTIVES

To investigate the effects of short-term induced hyperinsulinaemia and dexamethasone challenge on circulating [total adiponectin] and whole blood expression of adiponectin (AdipoR1 and AdipoR2), insulin, and insulin-like growth factor 1 (IGF-1) receptors in insulin-sensitive ponies.

STUDY DESIGN

In vivo experiment.

METHODS

Six never-laminitic, insulin-sensitive, native-breed UK ponies first underwent a dexamethasone challenge (0.08 mg/kg i.v.) with blood samples collected every 15 min over 3 h. After a 14-day washout period, hyperinsulinaemia was induced for 9 h via a euglycaemic-hyperinsulinaemic clamp (EHC), with blood samples collected every 30 min. Serum [insulin], plasma [total adiponectin], and plasma [IGF-1] were measured using validated assays and receptor gene expression was assessed via quantitative polymerase chain reaction (qPCR). Finally, whole blood was incubated with 10-1000 ng/mL dexamethasone for 3 h at 37°C to investigate its direct effects on gene expression.

RESULTS

There were no adverse effects observed during either protocol. Dexamethasone challenge did not alter circulating [insulin] or [total adiponectin] at any time-point, but significantly upregulated AdipoR1 and IGF-1R expression at 150 and 180 min. Ex vivo incubation of whole blood with dexamethasone did not alter expression of the genes examined. There was no change in [total adiponectin] or expression of the genes examined associated with EHC-induced hyperinsulinemia.

MAIN LIMITATIONS

This was a small sample size that included only native-breed ponies; total adiponectin was measured rather than high-molecular-weight adiponectin.

CONCLUSIONS

Short-term induced hyperinsulinaemia and dexamethasone challenge did not affect circulating [total adiponectin] in insulin-sensitive ponies. However, dexamethasone administration was associated with upregulation of two receptors linked to adiponectin signalling, suggesting that a physiological response occurred possibly to counteract dexamethasone-associated changes in tissue insulin sensitivity.

Adiponectin protects against myocardial ischemia-reperfusion injury: a systematic review and meta-analysis of preclinical animal studies

BACKGROUND

Myocardial ischemia-reperfusion injury (MIRI) is widespread in the treatment of ischemic heart disease, and its treatment options are currently limited. Adiponectin (APN) is an adipocytokine with cardioprotective properties; however, the mechanisms of APN in MIRI are unclear. Therefore, based on preclinical (animal model) evidence, the cardioprotective effects of APN and the underlying mechanisms were explored.

METHODS

The literature was searched for the protective effect of APN on MIRI in six databases until 16 November 2023, and data were extracted according to selection criteria. The outcomes were the size of the myocardial necrosis area and hemodynamics. Markers of oxidation, apoptosis, and inflammation were secondary outcome indicators. The quality evaluation was performed using the animal study evaluation scale recommended by the Systematic Review Center for Laboratory animal Experimentation statement. Stata/MP 14.0 software was used for the summary analysis.

RESULTS

In total, 20 papers with 426 animals were included in this study. The pooled analysis revealed that APN significantly reduced myocardial infarct size [weighted mean difference (WMD) = 16.67 (95% confidence interval (CI) = 13.18 to 20.16, P < 0.001)] and improved hemodynamics compared to the MIRI group [Left ventricular end-diastolic pressure: WMD = 5.96 (95% CI = 4.23 to 7.70, P < 0.001); + dP/dtmax: WMD = 1393.59 (95% CI = 972.57 to 1814.60, P < 0.001); -dP/dtmax: WMD = 850.06 (95% CI = 541.22 to 1158.90, P < 0.001); Left ventricular ejection fraction: WMD = 9.96 (95% CI = 7.29 to 12.63, P < 0.001)]. Apoptosis indicators [caspase-3: standardized mean difference (SMD) = 3.86 (95% CI = 2.97 to 4.76, P < 0.001); TUNEL-positive cells: WMD = 13.10 (95% CI = 8.15 to 18.05, P < 0.001)], inflammatory factor levels [TNF-α: SMD = 4.23 (95% CI = 2.48 to 5.98, P < 0.001)], oxidative stress indicators [Superoxide production: SMD = 4.53 (95% CI = 2.39 to 6.67, P < 0.001)], and lactate dehydrogenase levels [SMD = 2.82 (95% CI = 1.60 to 4.04, P < 0.001)] were significantly reduced. However, the superoxide dismutase content was significantly increased [SMD = 1.91 (95% CI = 1.17 to 2.65, P < 0.001)].

CONCLUSION

APN protects against MIRI via anti-inflammatory, antiapoptotic, and antioxidant effects, and this effect is achieved by activating different signaling pathways.

Adiponectin-mediated regulation of the adiponectin cascade in cardiovascular disease: Updates

The endocrine function of white adipose tissue is characterized by the synthesis of one its main hormones: adiponectin. Although the biological role of adiponectin has not been fully defined, clinical and experimental observations have shown that low plasma concentrations of adiponectin participate in the prevalence of insulin resistance and cardiovascular diseases, mainly in obese patients. Adiponectin also exerts its effects on the heart and blood vessels, thereby influencing their physiology. Studying the effects of adiponectin presents some complexities, primarily due to potential cross-interactions and interference with other pathways, such as the AdipoR1/R2 pathways. Under optimal conditions, the activation of the adiponectin cascade may involve signals such as AMPK and PPARα. Interestingly, these pathways may trigger similar responses, such as fatty acid oxidation. Understanding the downstream effectors of these pathways is crucial to comprehend the extent to which adiponectin signaling impacts metabolism. In this review, the aim is to explore the current mechanisms that regulate the adiponectin pathways. Additionally, updates on the major downstream factors involved in adiponectin signaling are provided, specifically in relation to metabolic syndrome and atherosclerosis.

Efficient production of recombinant human adiponectin in egg white using genome edited chickens

The prevalence of obesity-related metabolic diseases caused by insulin resistance is rapidly increasing worldwide. Adiponectin (ADPN), a hormone derived from adipose tissue, is a potential therapeutic agent for insulin resistance. Chickens are considered efficient bioreactors for recombinant protein production because they secrete large amounts of high-concentration proteins from the oviduct. Additionally, chickens express high levels of high-molecular-weight (HMW) ADPN, which is considered the active form in the body. Therefore, in this study, a gene-targeted chicken model was produced in which the gene encoding human ADPN was inserted into Ovalbumin (OVA) using the CRISPR/Cas9 system, and the characteristics of the resulting recombinant ADPN protein were evaluated. As a result, human ADPN was expressed in G₁ hen oviducts and egg whites of OVA ADPN knock-in (KI) chickens. The concentration of ADPN in egg white ranged from 1.47 to 4.59 mg/mL, of which HMW ADPN accounted for ∼29% (0.24-1.49 mg/mL). Importantly, egg white-derived ADPN promoted expression of genes related to fatty acid oxidation and activated the 5'-AMP-activated protein kinase (AMPK) signaling pathway in muscle cells. In summary, the OVA gene-targeted chicken bioreactor proved to be an advantageous model for production of human ADPN, and the resulting protein was of sufficient quantity and efficacy for industrial use.

Time-Series Change of Serum Soluble T-Cadherin Concentrations and Its Association with Creatine Kinase-MB Levels in ST-Segment Elevation Myocardial Infarction

AIMS

T-cadherin (T-cad) is a specific binding partner of adiponectin (APN), adipocyte-specific secretory protein. APN exhibits organ protection via the T-cad-dependent accumulation onto several tissues such as the aorta, heart, and muscle. Recently, for the first time, we showed that three forms (130, 100, and 30 kDa) of soluble T-cad existed in human serum and correlated with several clinical parameters in patients with type 2 diabetes. Nevertheless, the significance of soluble T-cad has not been elucidated in the acute stage of cardiovascular diseases. We herein examined soluble T-cad concentrations and investigated their clinical significance in patients with emergency hospital admission due to ST-segment elevation myocardial infarction (STEMI).

METHODS

This observational study enrolled 47 patients with STEMI who were treated via primary percutaneous coronary intervention (PCI). Soluble T-cad and APN concentrations were measured by using an enzyme-linked immunosorbent assay. This study is registered with the University Hospital Medical Information Network (Number: UMIN 000014418).

RESULTS

Serum concentrations of soluble 130 and 100 kDa T-cad rapidly and significantly decreased after hospitalization and reached the bottom at 72 h after admission (p＜0.001 and p＜0.001, respectively). The patients with high soluble T-cad and low APN concentrations on admission showed a significantly higher area under the curve of serum creatine kinase-MB (p＜0.01).

CONCLUSION

Serum soluble T-cad concentration changed dramatically in patients with STEMI, and the high T-cad and low APN concentrations on admission were associated with the myocardial infarction size. Further study is needed to investigate the usefulness of categorizing patients with STEMI by serum T-cad and APN for the prediction of severe prognoses.

A Potential Interplay between HDLs and Adiponectin in Promoting Endothelial Dysfunction in Obesity

Obesity is an epidemic public health problem that has progressively worsened in recent decades and is associated with low-grade chronic inflammation (LGCI) in metabolic tissues and an increased risk of several diseases. In particular, LGCI alters metabolism and increases cardiovascular risk by impairing endothelial function and altering the functions of adiponectin and high-density lipoproteins (HDLs). Adiponectin is an adipokine involved in regulating energy metabolism and body composition. Serum adiponectin levels are reduced in obese individuals and negatively correlate with chronic sub-clinical inflammatory markers. HDLs are a heterogeneous and complex class of lipoproteins that can be dysfunctional in obesity. Adiponectin and HDLs are strictly interdependent, and the maintenance of their interplay is essential for vascular function. Since such a complex network of interactions is still overlooked in clinical settings, this review aims to highlight the mechanisms involved in the impairment of the HDLs/adiponectin axis in obese patients to predict the risk of cardiovascular diseases and activate preventive countermeasures. Here, we provide a narrative review of the role of LGCI in altering HDLs, adiponectin and endothelial functions in obesity to encourage new studies about their synergic effects on cardiovascular health and disease.

Effects of Short Term Adiponectin Receptor Agonism on Cardiac Function and Energetics in Diabetic db/db Mice

Objective

Impaired cardiac efficiency is a hallmark of diabetic cardiomyopathy in models of type 2 diabetes. Adiponectin receptor 1 (AdipoR1) deficiency impairs cardiac efficiency in non-diabetic mice, suggesting that hypoadiponectinemia in type 2 diabetes may contribute to impaired cardiac efficiency due to compromised AdipoR1 signaling. Thus, we investigated whether targeting cardiac adiponectin receptors may improve cardiac function and energetics, and attenuate diabetic cardiomyopathy in type 2 diabetic mice.

Methods

A non-selective adiponectin receptor agonist, AdipoRon, and vehicle were injected intraperitoneally into Eight-week-old db/db or C57BLKS/J mice for 10 days. Cardiac morphology and function were evaluated by echocardiography and working heart perfusions.

Results

Based on echocardiography, AdipoRon treatment did not alter ejection fraction, left ventricular diameters or left ventricular wall thickness in db/db mice compared to vehicle-treated mice. In isolated working hearts, an impairment in cardiac output and efficiency in db/db mice was not improved by AdipoRon. Mitochondrial respiratory capacity, respiration in the presence of oligomycin, and 4-hydroxynonenal levels were similar among all groups. However, AdipoRon induced a marked shift in the substrate oxidation pattern in db/db mice towards increased reliance on glucose utilization. In parallel, the diabetes-associated increase in serum triglyceride levels in vehicle-treated db/db mice was blunted by AdipoRon treatment, while an increase in myocardial triglycerides in vehicle-treated db/db mice was not altered by AdipoRon treatment.

Conclusion

AdipoRon treatment shifts myocardial substrate preference towards increased glucose utilization, likely by decreasing fatty acid delivery to the heart, but was not sufficient to improve cardiac output and efficiency in db/db mice.

Vascular endothelial adiponectin signaling across the life span

Cardiovascular disease risk increases with age regardless of sex. Some of this risk is attributable to alterations in natural hormones throughout the life span. The quintessential example of this being the dramatic increase in cardiovascular disease following the transition to menopause. Plasma levels of adiponectin, a "cardioprotective" adipokine released primarily by adipose tissue and regulated by hormones, also fluctuate throughout one's life. Plasma adiponectin levels increase with age in both men and women, with higher levels in both pre- and postmenopausal women compared with men. Younger cohorts seem to confer cardioprotective benefits from increased adiponectin levels yet elevated levels in the elderly and those with existing heart disease are associated with poor cardiovascular outcomes. Here, we review the most recent data regarding adiponectin signaling in the vasculature, highlight the differences observed between the sexes, and shed light on the apparent paradox regarding increased cardiovascular disease risk despite rising plasma adiponectin levels over time.

Adiponectin: a pleiotropic hormone with multifaceted roles

Adipose tissue mostly composed of different types of fat is one of the largest endocrine organs in the body playing multiple intricate roles including but not limited to energy storage, metabolic homeostasis, generation of heat, participation in immune functions and secretion of a number of biologically active factors known as adipokines. The most abundant of them is adiponectin. This adipocite-derived hormone exerts pleiotropic actions and exhibits insulin-sensitizing, antidiabetic, anti-obesogenic, anti-inflammatory, antiatherogenic, cardio- and neuroprotective properties. Contrariwise to its protective effects against various pathological events in different cell types, adiponectin may have links to several systemic diseases and malignances. Reduction in adiponectin levels has an implication in COVID-19-associated respiratory failure, which is attributed mainly to a phenomenon called 'adiponectin paradox'. Ample evidence about multiple functions of adiponectin in the body was obtained from animal, mostly rodent studies. Our succinct review is entirely about multifaceted roles of adiponectin and mechanisms of its action in different physiological and pathological states.

Stimulation of exosome biogenesis by adiponectin, a circulating factor secreted from adipocytes

Adiponectin is an adipocyte-derived circulating factor that protects various organs and tissues. Such a pleiotropic action mechanism has not yet been fully explained. Clinically important multimer adiponectin existing in serum bound to cells expressing T-cadherin, a glycosylphosphatidylinositol-anchored cadherin, but not to the cells expressing other known receptors, AdipoRs or calreticulin. Adiponectin bound to the cell-surface, accumulated inside of multivesicular bodies through T-cadherin, and increased exosome biogenesis and secretion from the cells. Such increased exosome production accompanied the reduction of cellular ceramides in endothelial cells and mouse aorta, and enhanced skeletal muscle regeneration. Significantly lower plasma exosome levels were found in mice genetically deficient in either adiponectin or T-cadherin. Therapeutic effects of mesenchymal stem cells (MSCs) for a pressure overload-induced heart failure in mice required the presence of adiponectin in plasma, T-cadherin expression and exosome biogenesis in MSCs themselves, accompanying an increase of plasma exosomes. Essentially all organs seem to have MSCs and/or their related somatic stem cells expressing T-cadherin. Our recent studies suggested the importance of exosome-stimulation by multimer adiponectin in its well-known pleiotropic organ protections.

The autophagy protein Becn1 improves insulin sensitivity by promoting adiponectin secretion via exocyst binding

Autophagy dysregulation is implicated in metabolic diseases, including type 2 diabetes. However, the mechanism by which the autophagy machinery regulates metabolism is largely unknown. Autophagy is generally considered a degradation process via lysosomes. Here, we unveil a metabolically important non-cell-autonomous, non-degradative mechanism regulated by the essential autophagy protein Becn1 in adipose tissue. Upon high-fat diet challenge, autophagy-hyperactive Becn1F121A mice show systemically improved insulin sensitivity and enhanced activation of AMP-activated protein kinase (AMPK), a central regulator of energy homeostasis, via a non-cell-autonomous mechanism mediated by adiponectin, an adipose-derived metabolic hormone. Adipose-specific Becn1F121A expression is sufficient to activate AMPK in non-adipose tissues and improve systemic insulin sensitivity by increasing adiponectin secretion. Further, Becn1 enhances adiponectin secretion by interacting with components of the exocyst complex via the coiled-coil domain. Together, our study demonstrates that Becn1 improves insulin sensitivity by facilitating adiponectin secretion through binding the exocyst in adipose tissue.

Adiponectin Synthesis, Secretion and Extravasation from Circulation to Interstitial Space

Adiponectin, an adipokine that circulates as multiple multimeric complexes at high levels in serum, has antidiabetic, anti-inflammatory, antiatherogenic, and cardioprotective properties. Understanding the mechanisms regulating adiponectin's physiological effects is likely to provide critical insight into the development of adiponectin-based therapeutics to treat various metabolic-related diseases. In this review, we summarize our current understanding on adiponectin action in its various target tissues and in cellular models. We also focus on recent advances in two particular regulatory aspects; namely, the regulation of adiponectin gene expression, multimerization, and secretion, as well as extravasation of circulating adiponectin to the interstitial space and its degradation. Finally, we discuss some potential therapeutic approaches using adiponectin as a target and the current challenges facing adiponectin-based therapeutic interventions.

Adiponectin Stimulates Exosome Release to Enhance Mesenchymal Stem-Cell-Driven Therapy of Heart Failure in Mice

Mesenchymal stem/stromal cells (MSCs) are cultured adult stem cells that originally reside in virtually all tissues, and the gain of MSCs by transplantation has become the leading form of cell therapy in various diseases. However, there is limited knowledge on the alteration of its efficacy by factors in recipients. Here, we report that the cardioprotective properties of intravenously injected MSCs in a mouse model of pressure-overload heart failure largely depend on circulating adiponectin, an adipocyte-secreted factor. The injected MSCs exert their function through exosomes, extracellular vesicles of endosome origin. Adiponectin stimulated exosome biogenesis and secretion through binding to T-cadherin, a unique glycosylphosphatidylinositol-anchored cadherin, on MSCs. A pharmacological or adenovirus-mediated genetic increase in plasma adiponectin enhanced the therapeutic efficacy of MSCs. Our findings provide novel insights into the importance of adiponectin in mesenchymal-progenitor-mediated organ protections.

Protein Modifications Critical for Myonectin/Erythroferrone Secretion and Oligomer Assembly

Myonectin/erythroferrone (also known as CTRP15) is a secreted hormone with metabolic function and a role in stress erythropoiesis. Despite its importance in physiologic processes, biochemical characterization of the protein is lacking. Here, we show that multiple protein modifications are critical for myonectin secretion and multimerization. Abolishing N-linked glycosylation by tunicamycin, glucosamine supplementation, or glutamine substitutions of all four potential Asn glycosylation sites blocked myonectin secretion. Mass spectrometry confirmed that Asn-229 and Asn-281 were glycosylated, and substituting both Asn sites with Gln prevented myonectin secretion. Although Asn-319 is not identified as glycosylated, Gln substitution caused protein misfolding and retention in the endoplasmic reticulum. Of the four conserved cysteines, Cys-273 and Cys-278 were required for proper protein folding; Ala substitution of either site inhibited protein secretion. In contrast, Ala substitutions of Cys-142, Cys-194, or both markedly enhanced protein secretion, suggesting endoplasmic reticulum retention that facilitates myonectin oligomer assembly. Secreted myonectin consists of trimers, hexamers, and high-molecular weight (HMW) oligomers. The formation of higher-order structures via intermolecular disulfide bonds depended on Cys-142 and Cys-194; while the C142A mutant formed almost exclusively trimers, the C194A mutant was impaired in HMW oligomer formation. Most Pro residues within the short collagen domain of myonectin were also hydroxylated, a modification that stabilized the collagen triple helix. Inhibiting Pro hydroxylation or deleting the collagen domain markedly reduced the rate of protein secretion. Together, our results reveal key determinants that are important for myonectin folding, secretion, and multimeric assembly and provide a basis for future structure-function studies.

Interorgan communication by exosomes, adipose tissue, and adiponectin in metabolic syndrome

Adipose tissue plays important roles in regulating whole-body energy metabolism through its storage function in white adipocytes and its dissipating function in brown and beige adipocytes. Adipose tissue also produces a variety of secreted factors called adipocytokines, including leptin and adiponectin. Furthermore, recent studies have suggested the important roles of extracellular vesicles of endosomal origin termed exosomes, which are secreted from adipocytes and other cells in adipose tissue and influence whole-body glucose and lipid metabolism. Adiponectin is known to be a pleiotropic organ-protective protein that is exclusively produced by adipocytes and decreased in obesity. Adiponectin accumulates in tissues such as heart, muscle, and vascular endothelium through binding with T-cadherin, a glycosylphosphatidylinositol-anchored (GPI-anchored) cadherin. Recently, adiponectin was found to enhance exosome biogenesis and secretion, leading to a decrease in cellular ceramides, excess of which is known to cause insulin resistance and cardiovascular disease phenotypes. These findings support the hypothesis that adipose tissue metabolism systemically regulates exosome production and whole-body metabolism through exosomes. This review focuses on intra-adipose and interorgan communication by exosomes, adiponectin-stimulated exosome production, and their dysregulation in metabolic diseases.

Mapping and engineering the interaction between adiponectin and T-cadherin

Adiponectin is a highly abundant protein hormone secreted by adipose tissue. It elicits diverse biological responses, including anti-diabetic, anti-inflammatory, anti-tumor, and anti-atherosclerotic effects. Adiponectin consists of a globular domain and a collagen-like domain, and it occurs in three major oligomeric forms that self-assemble: trimers, hexamers, and high-molecular-weight oligomers. Adiponectin has been reported to bind to two seven-transmembrane domain receptors, AdipoR1 and AdipoR2, as well as to the protein T-cadherin, which is highly expressed in the cardiovascular system and binds only the high-molecular-weight form of adiponectin. The molecular mechanisms underlying this specificity remain unclear. Here we used a combination of X-ray crystallography and protein engineering to define the details of adiponectin's interaction with T-cadherin. We found that T-cadherin binds to the globular domain of adiponectin, relying on structural stabilization of this domain by bound metal ions. Moreover, we show that the adiponectin globular domain can be engineered to enhance its binding affinity for T-cadherin. These results help to define the molecular basis for the interaction between adiponectin and T-cadherin, and our engineered globular domain variants may be useful tools for further investigating adiponectin's functions.

Effects of Adiponectin on T2DM and Glucose Homeostasis: A Mendelian Randomization Study

PURPOSE

The associations of adiponectin with type 2 diabetes mellitus (T2DM), glucose homeostasis (including β-cell function index (HOMA-β), insulin resistance (HOMA-IR), fasting insulin (FI) and fasting glucose (FG)) have reported in epidemiological studies. However, the previous observational studies are prone to biases, such as reverse causation and residual confounding factors. Herein, a Mendelian Randomization (MR) study was conducted to determine whether causal effects exist among them.

MATERIALS AND AND METHODS

Two-sample MR analyses and multiple sensitivity analyses were performed using the summary data from the ADIPOGen consortium, MAGIC Consortium, and a meta-analysis of GWAS with a considerable sample of T2DM (62,892 cases and 596,424 controls of European ancestry). We got eight valid genetic variants to predict the causal effect among adiponectin and T2DM and glucose homeostasis after excluding the probable invalid or pleiotropic variants.

RESULTS

Adiponectin was not associated with T2DM (odds ratio (OR) = 1.004; 95% confidence interval (CI): 0.740, 1.363) when using MR Egger after removing the invalid SNPs, and the results were consistent when using the other four methods. Similar results existed among adiponectin and HOMA-β, HOMA-IR, FI, FG.

CONCLUSION

Our MR study revealed that adiponectin had no causal effect on T2DM and glucose homeostasis and that the associations among them in observational studies may be due to confounding factors.

Adipokines underlie the early origins of obesity and associated metabolic comorbidities in the offspring of women with pregestational obesity

Maternal pregestational obesity is a well-known risk factor for offspring obesity, metabolic syndrome, cardiovascular disease and type 2 diabetes. The mechanisms by which maternal obesity can induce alterations in fetal and later neonatal metabolism are not fully elucidated due to its complexity and multifactorial causes. Two adipokines, leptin and adiponectin, are involved in fetal and postnatal growth trajectories, and both are altered in women with pregestational obesity. The placenta synthesizes leptin, which goes mainly to the maternal circulation and in lesser amount to the developing fetus. Maternal pregestational obesity and hyperleptinemia are associated with placental dysfunction and changes in nutrient transporters which directly affect fetal growth and development. By the other side, the embryo can produce its own leptin from early in development, which is associated to fetal weight and adiposity. Adiponectin, an insulin-sensitizing adipokine, is downregulated in maternal obesity. High molecular weight (HMW) adiponectin is the most abundant form and with most biological actions. In maternal obesity lower total and HMW adiponectin levels have been described in the mother, paralleled with high levels in the umbilical cord. Several studies have found that cord blood adiponectin levels are related with postnatal growth trajectories, and it has been suggested that low adiponectin levels in women with pregestational obesity enhance placental insulin sensitivity and activation of placental amino acid transport systems, supporting fetal overgrowth. The possible mechanisms by which maternal pregestational obesity, focusing in the actions of leptin and adiponectin, affects the fetal development and postnatal growth trajectories in their offspring are discussed.

The cholecystokinin receptor agonist, CCK-8, induces adiponectin production in rat white adipose tissue

BACKGROUND AND PURPOSE

A cholecystokinin (CCK) system has been identified in white adipose tissue (WAT). Nevertheless, the endocrine actions of CCK on WAT remain unknown. Our goal was to investigate the role of CCK in regulating the production of adiponectin, an adipokine expressed in WAT, which is pivotal in preserving energy homeostasis.

EXPERIMENTAL APPROACH

The effect of the bioactive CCK fragment CCK-8 on adiponectin production was studied both in vivo and in vitro. CCK-8 effects were characterized in rats treated with selective CCK₁ and CCK₂ receptor antagonists as well as in pre-adipocytes carrying the selective silencing of either CCK₁ or CCK₂ receptors. The influence of insulin on CCK-8 responses was also analysed.

KEY RESULTS

In WAT, CCK-8 increased plasma adiponectin levels and the expression of the adiponectin gene (Adipoq). In pre-adipocytes, CCK-8 up-regulated adiponectin production. CCK-8 effects were abolished by L-365,260, a selective CCK₂ receptor antagonist. CCK₂ receptor knockdown also abolished the effects of CCK-8 in pre-adipocytes. Moreover, in vitro CCK-8 effects were blocked by triciribine, a specific inhibitor of protein kinase B (Akt) and by the PPARγ antagonist T0070907. Silencing the expression of the insulin receptor inhibited CCK-8-induced Adipoq expression in pre-adipocytes. Furthermore, insulin potentiated the effect of CCK-8.

CONCLUSION AND IMPLICATIONS

CCK-8 stimulates adiponectin production in WAT by acting on CCK₂ receptors, through a mechanism involving both Akt and PPARγ. Moreover, CCK-8 actions are only observed in the presence of insulin. Our results could have translational value in the design of new insulin-sensitizing therapies.

Adiponectin promotes muscle regeneration through binding to T-cadherin

Skeletal muscle has remarkable regenerative potential and its decline with aging is suggested to be one of the important causes of loss of muscle mass and quality of life in elderly adults. Metabolic abnormalities such as obesity were linked with decline of muscle regeneration. On the other hand, plasma levels of adiponectin are decreased in such metabolic conditions. However, plasma levels of adiponectin have been shown to inversely correlate with muscle mass and strength in elderly people especially with chronic heart failure (CHF). Here we have addressed whether adiponectin has some impact on muscle regeneration after cardiotoxin-induced muscle injury in mice. Muscle regeneration was delayed by angiotensin II infusion, mimicking aging and CHF as reported. Adiponectin overexpression in vivo decreased necrotic region and increased regenerating myofibers. Such enhanced regeneration by excess adiponectin was also observed in adiponectin null mice, but not in T-cadherin null mice. Mechanistically, adiponectin accumulated on plasma membrane of myofibers both in mice and human, and intracellularly colocalized with endosomes positive for a multivesicular bodies/exosomes marker CD63 in regenerating myofibers. Purified high-molecular multimeric adiponectin similarly accumulated intracellularly and colocalized with CD63-positive endosomes and enhanced exosome secretion in differentiating C2C12 myotubes but not in undifferentiated myoblasts. Knockdown of T-cadherin in differentiating C2C12 myotubes attenuated both adiponectin-accumulation and adiponectin-mediated exosome production. Collectively, our studies have firstly demonstrated that adiponectin stimulates muscle regeneration through T-cadherin, where intracellular accumulation and exosome-mediated process of adiponectin may have some roles.

Impact of Exercise on Inflammatory Mediators of Metabolic and Vascular Insulin Resistance in Type 2 Diabetes

The development of obesity is cornerstone in the etiology of metabolic and vascular insulin resistance and consequently exacerbates glycemic control. Exercise is an efficacious first-line therapy for type 2 diabetes that improves insulin action through, in part, reducing hormone mediated inflammation. Together, improving the coordination of skeletal muscle metabolism with vascular delivery of glucose will be required for optimizing type 2 diabetes and cardiovascular disease treatment.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Adipokines affect mammary growth and function in farm animals

The essential role of mammary fat pads in mammary growth and morphogenesis was the first indication that biologically active molecules, secreted from adipocytes or other stromal cells, could regulate endocrine cues for growth and function of the mammary gland. The presence of leptin and adiponectin receptors in mammary tissues suggested that locally produced or circulating adipokines could affect mammary growth and function. Herein, we present the current knowledge on the role of adipokines in mammary cell proliferation and differentiation and in lactogenesis and galactopoiesis in farm animals. We also address the role of milk adipokines in the neonate. Accumulating evidence suggests that adipokines could act as metabolic sensors, regulating mammary growth and function in periods of metabolic adaptations such as late pregnancy and early lactation. Indeed, different experiments reported that adiponectin and leptin expression varies according to physiological stages and nutritional status of the animal. The current review also demonstrates that adipokines, such as leptin and adiponectin, are important regulators of the action of lactogenic hormones in the mammary gland. Findings also suggest important roles for adipokines in growth and intestinal maturation of the neonate.

Sex-dependent reductions in high molecular weight adiponectin during acute hyperinsulinemia are prevented with endurance training in older females

OBJECTIVE

The high molecular weight (HMW) adiponectin isoform is considered the active form of adiponectin and is linked to insulin sensitivity and the reduced risk of developing cardiovascular disease. The purpose of the first study was to determine the effects of age and sex on the plasma HMW adiponectin response to acute hyperinsulinemia, and secondly determine whether either endurance or resistance exercise training could affect this response.

DESIGN AND PARTICIPANTS

Twenty-six healthy males (19-84 years) and twenty-six healthy females (18-76 years) were recruited and matched for BMI to examine the effects of sex and age on the plasma adiponectin response to a 2-hour hyperinsulinemic-euglycemic clamp. To examine the effects of exercise training, a subgroup of young (<35 years) and aged (>55 years) individuals were randomized into a 12-week endurance or resistance training programme and had their adiponectin response to hyperinsulinemia measured before and after training. High molecular weight (HMW) and total adiponectin were measured by ELISA.

RESULTS

In response to hyperinsulinemia, plasma HMW adiponectin decreased in females (-9%, P < .005), but not males. After 12 weeks of endurance training, the response of plasma HMW adiponectin to hyperinsulinemia increased in older females (36%, P < .05) only. Resistance training had no effect on the plasma adiponectin response to hyperinsulinemia. Despite no age or sex differences at baseline, skeletal muscle AdipoR1 increased in response to endurance training (~120%, P < .001) and resistance training (~38%, P < .05), regardless of age or sex.

CONCLUSION

The inhibitory action of hyperinsulinemia on plasma HMW adiponectin occurs in females but not males, irrespective of age. Twelve weeks of endurance training protects older females against the hyperinsulinemic inhibition of plasma HMW adiponectin, which could promote healthy ageing.

Adiponectin/T-cadherin system enhances exosome biogenesis and decreases cellular ceramides by exosomal release

Adiponectin, an adipocyte-derived circulating protein, accumulates in vasculature, heart, and skeletal muscles through interaction with a unique glycosylphosphatidylinositol-anchored cadherin, T-cadherin. Recent studies have demonstrated that such accumulation is essential for adiponectin-mediated cardiovascular protection. Here, we demonstrate that the adiponectin/T-cadherin system enhances exosome biogenesis and secretion, leading to the decrease of cellular ceramides. Adiponectin accumulated inside multivesicular bodies, the site of exosome generation, in cultured cells and in vivo aorta, and also in exosomes in conditioned media and in blood, together with T-cadherin. The systemic level of exosomes in blood was significantly affected by adiponectin or T-cadherin in vivo. Adiponectin increased exosome biogenesis from the cells, dependently on T-cadherin, but not on AdipoR1 or AdipoR2. Such enhancement of exosome release accompanied the reduction of cellular ceramides through ceramide efflux in exosomes. Consistently, the ceramide reduction by adiponectin was found in aortas of WT mice treated with angiotensin II, but not in T-cadherin-knockout mice. Our findings provide insights into adiponectin/T-cadherin-mediated organ protection through exosome biogenesis and secretion.

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.

A study of high-, middle- and low-molecular weight adiponectin in urine as a surrogate marker for early diabetic nephropathy using ultrasensitive immune complex transfer enzyme immunoassay

Background

For the early identification of patients at risk of developing diabetic nephropathy, we have developed an ultrasensitive immune complex transfer enzyme immunoassay to measure adiponectin in urine.

Methods

We developed immune complex transfer enzyme immunoassay for adiponectin and measured urinary adiponectin from 70 healthy subjects, 35 obese non-diabetic subjects and 20 patients with diabetes.

Results

The urinary adiponectin concentrations in patients with diabetes (3.3 ± 10.7 ng/mg creatinine) were significantly higher than those in obese subjects (0.54 ± 0.44; P < 0.01) and healthy subjects (0.46 ± 0.42; P < 0.001). The gel filtration elution profile of urine from healthy subjects showed traces of four immunoreactive peaks (high-, medium-, low-molecular weight and monomer molecules), despite the majority of blood adiponectin being high-molecular weight. However, urinary adiponectin molecules were more frequent in low-molecular weight as the estimate glomerular filtration rate decreased. Furthermore, as blood glucose concentrations rose, middle-molecular weight and high-molecular weight increased in urine. Further, urinary adiponectin concentrations correlated with estimate glomerular filtration rate ( r = −0.61, P < 0.001), but not urinary albumin. In addition, our analysis showed a significantly ( P < 0.001) higher value for urinary adiponectin in the G2 stage of chronic kidney disease classification where urinary albumin is not elevated.

Conclusion

Adiponectin increases in urine as renal function decreases, and urinary adiponectin may be useful as a surrogate marker for diabetic nephropathy risk.

The Adiponectin Paradox for All-Cause and Cardiovascular Mortality

Basic science studies have shown beneficial effects of adiponectin on glucose homeostasis, chronic low-grade inflammation, apoptosis, oxidative stress, and atherosclerotic processes, so this molecule usually has been considered a salutary adipokine. It was therefore quite unexpected that large prospective human studies suggested that adiponectin is simply a marker of glucose homeostasis, with no direct favorable effect on the risk of type 2 diabetes and cardiovascular disease. But even more unforeseen were data addressing the role of adiponectin on the risk of death. In fact, a positive, rather than the expected negative, relationship was reported between adiponectin and mortality rate across many clinical conditions, comprising diabetes. The biology underlying this paradox is unknown. Several explanations have been proposed, including adiponectin resistance and the confounding role of natriuretic peptides. In addition, preliminary genetic evidence speaks in favor of a direct role of adiponectin in increasing the risk of death. However, none of these hypotheses are based on robust data, so further efforts are needed to unravel the elusive role of adiponectin on cardiometabolic health and, most important, its paradoxical association with mortality rate.

Chicken Is a Useful Model to Investigate the Role of Adipokines in Metabolic and Reproductive Diseases

Reproduction is a complex and essential physiological process required by all species to produce a new generation. This process involves strict hormonal regulation, depending on a connection between the hypothalamus-pituitary-gonadal axis and peripheral organs. Metabolic homeostasis influences the reproductive functions, and its alteration leads to disturbances in the reproductive functions of humans as well as animals. For a long time, adipose tissue has been recognised as an endocrine organ but its ability to secrete and release hormones called adipokines is now emerging. Adipokines have been found to play a major role in the regulation of metabolic and reproductive processes at both central and peripheral levels. Leptin was initially the first adipokine that has been described to be the most involved in the metabolism/reproduction interrelation in mammals. In avian species, the role of leptin is still under debate. Recently, three novel adipokines have been discovered: adiponectin (ADIPOQ, ACRP30), visfatin (NAMPT, PBEF), and chemerin (RARRES2, TIG2). However, their mode of action between mammalian and nonmammalian species is different due to the different reproductive and metabolic systems. Herein, we will provide an overview of the structure and function related to metabolic and reproductive mechanisms of the latter three adipokines with emphasis on avian species.

Ameliorative effect of panaxynol on the reduction in high-molecular-weight adiponectin secretion from 3T3-L1 adipocytes treated with palmitic acids

Reduced plasma levels of the high-molecular weight (HMW) form of adiponectin, rather than total adiponectin levels, have been shown to be closely associated with various metabolic diseases including insulin resistance, type 2 diabetes, and cardiovascular disease. Therefore, we sought to explore active, naturally occurring compounds that promote the recovery of HMW adiponectin secretion suppressed by palmitic acid in our model. A total of 90 crude drug extracts were screened for the ability to augment HMW adiponectin secretion from 3T3-L1 adipocytes treated with palmitic acid. Panaxynol was isolated from Saposhnikovia divaricata as an active compound with HMW adiponectin promoting properties. Peroxisome proliferator-activated receptor-γ (PPARγ) agonists are reported to increase the secretion of HMW adiponectin, although the effects of panaxynol were found to be independent of PPARγ activation. When the underlying mechanisms were further examined, panaxynol was found to inhibit the palmitic-acid-induced downregulation of forkhead box O1 (FoxO1) protein, and the anti-lipotoxic effects were abolished by a FoxO1 inhibitor. Furthermore, CCAAT/enhancer-binding protein-α (C/EBPα) mRNA levels were also increased by panaxynol. Reactive oxygen species have critical roles in the reduction in HMW adiponection secretion by palmitic acid; however, panaxynol reduced this increase in reactive oxygen species generation, followed by reductions in markers of endoplasmic reticulum stress and inflammation. Taken together, these findings suggest that panaxynol ameliorates the impaired HMW adiponection secretion in adipocytes treated with palmitic acid by restoring FoxO1 expression, owing to inhibition of reactive oxygen species generation, in a PPARγ-independent manner.

Resveratrol Cardioprotection Against Myocardial Ischemia/Reperfusion Injury Involves Upregulation of Adiponectin Levels and Multimerization in Type 2 Diabetic Mice

Downregulation of adiponectin (APN) multimerization is significantly correlated with the aggravation of myocardial ischemia/reperfusion (MI/R) injury in type 2 diabetes mellitus (T2DM). Resveratrol (RSV) upregulates APN multimerization in adipocytes, but whether RSV improves endogenous APN multimerization and thus attenuates MI/R injury in T2DM mice has never been investigated. T2DM mice were treated with 10 mg/kg RSV daily for 3 weeks, followed by 30 minutes of myocardial ischemia and 3 hours or 24 hours of reperfusion. RSV administration alleviated MI/R injury in diabetic mice, as evidenced by reduced infarct size, cardiomyocyte apoptosis, and caspase-3 activity, and improved cardiac function. Moreover, RSV reversed the downregulated APN levels and multimerization both in plasma and adipose tissue, accompanied by increased disulfide bond A oxidoreductase-like protein (DsbA-L) expression in T2DM mice. Conversely, serving as a key downstream molecule of APN in ameliorating MI/R injury, inhibition of AMP-activated protein kinase (AMPK) significantly attenuated the cardioprotective effects of RSV. In conclusion, long-term administration of RSV upregulates adiponectin levels and multimerization in T2DM mice, consequently attenuating MI/R injury partially through APN-AMPK signaling.

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.

High-molecular weight adiponectin/HOMA-IR ratio as a biomarker of metabolic syndrome in urban multiethnic Brazilian subjects

Metabolic syndrome (MetS) has an important epidemiological relevance due to its increasing prevalence and association with type 2 diabetes and cardiovascular disease. Insulin resistance is a core feature of the MetS. HOMA-IR is a robust clinical and epidemiological marker of MetS. Adiponectin is an adipokine with insulin-sensitizing and anti-inflammatory functions; its levels decrease as number of components of MetS increases. High-molecular weight adiponectin (HMWA) is the multimer responsible for the relationship of adiponectin with insulin sensitivity. HOMA-IR and HMWA are suitable candidates for MetS biomarkers. The ratio of adiponectin to HOMA-IR has been validated as a powerful index of MetS and considered a better marker of its presence, than either HOMA-IR or adiponectin alone, in selected homogeneous populations. We compared the strength of association between HMWA, HOMA-IR and HMWA/HOMA-IR ratio with MetS and its key components. Our data have shown that the median (25^th, 75^th percentile) of HMWA/HOMA-IR ratio was lower in subjects with MetS [0.51 (0.33, 1.31)] as compared to those without it [2.19 (1.13, 4.71)]. The correlation coefficient (r) was significantly higher for HMWA/HOMA-IR ratio as compared to HMWA for waist circumference (-0.65; -0.40, respectively); mean blood pressure (-0.27; -0.14, respectively); fasting glucose (-0.38; -0.19, respectively); HDL-cholesterol (0.44; 0.40, respectively); and triglycerides (-0.35; -0.18, respectively). In a multivariable logistic regression analysis, the HMWA/HOMA-IR ratio was a sensitive predictor for MetS, being the only marker that was significantly associated with each and all the individual components of the syndrome. These results expand on previous studies in that we used the active circulating form of adiponectin, i.e. HMWA, and represent a typical Brazilian cohort characterized by intense interethnic admixture. Thus, the HMWA/HOMA-IR ratio is a minimally invasive biomarker for MetS that could be clinically useful in prognosing patient outcome.

WSF-P-1, a novel AMPK activator, promotes adiponectin multimerization in 3T3-L1 adipocytes

Adiponectin, an adipokine with insulin-sensitizing effect, is secreted from adipocytes into circulation as high, medium, and low molecular weight forms (HMW, MMW, and LMW). The HMW adiponectin oligomers possess the most potent insulin-sensitizing activity. WSF-P-1(N-methyl-1,2,3,4,5,6-hexahydro-1,1,5,5-tetramethyl-7H-2,4α-methanonaphthalen-7-amine) is derived from natural sesquiterpene longifolene by chemical modifications. We found that WSF-P-1 activates AMPK in both 3T3-L1 adipocytes and 293T cells in this study. Activation of AMPK by WSF-P-1 promotes the assembly of HMW adiponectin and increases the HMW/total ratio of adiponectin in 3T3-L1 adipocytes. We demonstrated that the Ca²⁺-dependent CaMKK signaling pathway is involved in WSF-P-1-induced AMPK activation and adiponectin multimerization. WSF-P-1 also activates GLUT1-mediated glucose uptake in 3T3-L1 adipocytes, making it a potential drug candidate for the treatment of type 2 diabetes, obesity, and other obesity-related metabolic diseases.

Role of Adipokines in Cardiovascular Disease

Cardiovascular disease (CVD) is the greatest cause of death, accounting for nearly one-third of all deaths worldwide. The increase in obesity rates over 3 decades is widespread and threatens the public health in both developed and developing countries. Obesity, the excessive accumulation of visceral fat, causes the clustering of metabolic disorders, such as type 2 diabetes, dyslipidemia, and hypertension, culminating in the development of CVD. Adipose tissue is not only an energy storage organ, but an active endocrine tissue producing various biologically active proteins known as adipokines. Since leptin, a central regulator of food intake and energy expenditure, was demonstrated to be an adipose-specific adipokine, attention has focused on the identification and characterization of unknown adipokines to clarify the mechanisms underlying obesity-related disorders. Numerous adipokines have been identified in the past 2 decades; most adipokines are upregulated in the obese state. Adipokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, and resistin are pro-inflammatory, and exacerbate various metabolic and cardiovascular diseases. However, a small number of adipokines, including adiponectin, are decreased by obesity, and generally exhibit antiinflammatory properties and protective functions against obesity-related diseases. Collectively, an imbalance in the production of pro- and antiinflammatory adipokines in the obese condition results in multiple complications. In this review, we focus on the pathophysiologic roles of adipokines with cardiovascular protective properties.

Intracellular complement - the complosome - in immune cell regulation

The complement system was defined over a century ago based on its ability to "complement" the antibody-mediated and cell-mediated immune responses against pathogens. Today our understanding of this ancient part of innate immunity has changed substantially and we know now that complement plays an undisputed pivotal role in the regulation of both innate and adaptive immunity. The complement system consists of over 50 blood-circulating, cell-surface expressed and intracellular proteins. It is key in the recognition and elimination of invading pathogens, also in the removal of self-derived danger such as apoptotic cells, and it supports innate immune responses and the initiation of the general inflammatory reactions. The long prevailing classic view of complement was that of a serum-operative danger sensor and first line of defence system, however, recent experimental and clinical evidences have demonstrated that "local" tissue and surprisingly intracellular complement (the complosome) activation impacts on normal cell physiology. This review will focus on novel aspects of intracellular complement activation and its unexpected roles in basic cell processes such as metabolism. We also discuss what the existence of the complosome potentially means for how the host handles intracellular pathogens such as viruses.

Acute Vitamin D₃ Supplementation in Severe Obesity: Evaluation of Multimeric Adiponectin

Obesity predisposes to vitamin D deficiency (VDD) and glucose abnormalities. It is currently debated if vitamin D administration may improve glucose homeostasis by interacting with modulators of insulin sensitivity, such as adiponectin and its oligomers. In a 4-week inpatient study on a metabolic rehabilitation program, consisting of individualized caloric restriction and aerobic physical exercise in obese subjects with VDD, we assessed the acute effects of 600,000 IU cholecalciferol given per os VD group, 12 subjects; body mass index (BMI) 42.7 ± 1.3 kg/m²) or placebo per os (PL group, 12 subjects, BMI 39.8 ± 0.9 kg/m²) on high (HWM-A), medium (MMW-A), and low molecular weight adiponectin (LMW-A), as quantified by western immunoblot (WIB) and ELISA. During the 4-week study, dieting promoted a similar magnitude of weight loss in VD and PL groups. Compared to the PL group, cholecalciferol administration increased 25(OH)Vit D levels (p < 0.001) and promoted a significant increase of HMW-A expression analyzed by WIB (p = 0.02). In parallel, a significant decrease of leptin/HMW-A ratio (p < 0.05), a biomarker of metabolic homeostasis, was observed. During the study, changes of MMW-A and LMW-A occurred independently of cholecalciferol administration, and were likely explained by weight loss. At odds with these findings, the ELISA assessment of adiponectin oligomers showed no modifications in the VD group or PL group. Current findings suggest that acute cholecalciferol administration selectively modifies HMW-A and the leptin/HMW-A ratio.

The unique prodomain of T-cadherin plays a key role in adiponectin binding with the essential extracellular cadherin repeats 1 and 2

Adiponectin, an adipocyte-derived circulating protein, accumulates in the heart, vascular endothelium, and skeletal muscles through an interaction with T-cadherin (T-cad), a unique glycosylphosphatidylinositol-anchored cadherin. Recent studies have suggested that this interaction is essential for adiponectin-mediated cardiovascular protection. However, the precise protein-protein interaction between adiponectin and T-cad remains poorly characterized. Using ELISA-based and surface plasmon analyses, we report here that T-cad fused with IgG Fc as a fusion tag by replacing its glycosylphosphatidylinositol-anchor specifically bound both hexameric and larger multimeric adiponectin with a dissociation constant of ∼1.0 nm and without any contribution from other cellular or serum factors. The extracellular T-cad repeats 1 and 2 were critical for the observed adiponectin binding, which is required for classical cadherin-mediated cell-to-cell adhesion. Moreover, the 130-kDa prodomain-bearing T-cad, uniquely expressed on the cell surface among members of the cadherin family and predominantly increased by adiponectin, contributed significantly to adiponectin binding. Inhibition of prodomain-processing by a prohormone convertase inhibitor increased 130-kDa T-cad levels and also enhanced adiponectin binding to endothelial cells both by more preferential cell-surface localization and by higher adiponectin-binding affinity of 130-kDa T-cad relative to 100-kDa T-cad. The preferential cell-surface localization of 130-kDa T-cad relative to 100-kDa T-cad was also observed in normal mice aorta in vivo In conclusion, our study shows that a unique key feature of the T-cad prodomain is its involvement in binding of the T-cad repeats 1 and 2 to adiponectin and also demonstrates that adiponectin positively regulates T-cad abundance.

Associations between inflammation-related biomarkers and depressive symptoms in individuals with recently diagnosed type 1 and type 2 diabetes

Depressive disorders represent a frequent comorbidity of both type 1 (T1D) and type 2 diabetes (T2D). Inflammation-related processes have been implicated in the development of both diabetes and depression. This study aimed to investigate whether biomarkers of subclinical inflammation were associated with depressive symptoms in individuals with recently diagnosed diabetes and if such associations differed by diabetes type. This cross-sectional study was based on 295 individuals with T2D (67% men, mean age 53years) and 139 individuals with T1D (60% men, mean age 36years) of the German Diabetes Study. The main inclusion criterion was a known disease duration of <1year. Depressive symptoms were assessed with the Allgemeine Depressionsskala, Langversion (ADS-L) questionnaire, the German version of the Center for Epidemiological Studies Depression scale (CES-D) questionnaire. Associations between biomarkers of subclinical inflammation and the ADS-L as continuous score were assessed using multiple linear regression models adjusting for age, sex, body mass index, HbA1c, lipids, hypertension, medication and comorbidities. Serum high-sensitivity C-reactive protein (hsCRP) and the ratio of high-molecular-weight (HMW)/total adiponectin were positively associated with ADS-L in T2D (both P<0.01), but not in T1D. In contrast, serum levels of soluble intercellular adhesion molecule (sICAM)-1 were positively associated with ADS-L only in T1D (P=0.035). The latter association was significantly different between both diabetes types (P_interaction=0.036). No associations were observed for interleukin (IL)-6, IL-18 and soluble E-selectin. Only the association between HMW/total adiponectin and ADS-L in T2D remained significant after correction for multiple testing. In conclusion, our study shows that the ratio HMW/total adiponectin is associated with depressive symptoms in individuals with recently diagnosed T2D. It also provides suggestive evidence that further biomarkers of subclinical inflammation and endothelial activation may be associated with depressive symptoms in individuals with recently diagnosed T1D and T2D.

Roles of leptin, adiponectin and resistin in the transcriptional regulation of steroidogenic genes contributing to decreased Leydig cells function in obesity

The increase in obesity rate is a major public health issue associated with increased pathological conditions such as type 2 diabetes or cardiovascular diseases. Obesity also contributes to decreased testosterone levels in men. Indeed, the adipose tissue is an endocrine organ which produces hormones such as leptin, adiponectin and resistin. Obesity results in pathological accumulations of leptin and resistin, whereas adiponectin plasma levels are markedly reduced, all having a negative impact on testosterone synthesis. This review focuses on current knowledge related to transcriptional regulation of Leydig cells' steroidogenesis by leptin, adiponectin and resistin. We show that there are crosstalks between the regulatory mechanisms of these hormones and androgen production which may result in a dramatic negative influence on testosterone plasma levels. Indeed leptin, adiponectin and resistin can impact expression of different steroidogenic genes such as Star, Cyp11a1 or Sf1. Further investigations will be required to better define the implications of adipose derived hormones on regulation of steroidogenic genes expression within Leydig cells under physiological as well as pathological conditions.

Association of Anthropometric and Bioelectrical Impedance Analysis Measures of Adiposity with High Molecular Weight Adiponectin Concentration

Objective

To investigate the relationship between adiposity measures and plasma concentration of high molecular weight (HMW) adiponectin.

Methods

In a Chinese sample (n = 1081), we performed measurements of anthropometry and bioelectrical impedance analysis (BIA). We defined overweight and obesity as a body mass index between 24 and 27.4 kg/m² and ≥ 27.5 kg/m², respectively, and central obesity as a waist circumference ≥ 90 cm in men and ≥ 80 cm in women. Plasma HMW adiponectin concentration was measured by the ELISA method.

Results

Plasma HMW adiponectin concentration was significantly (P < 0.0001) higher in women (n = 677, 2.47 μg/mL) than men (n = 404, 1.58 μg/mL) and correlated with advancing age in men (r = 0.28) and women (r = 0.29). In adjusted analyses, it was lower in the presence of overweight (n = 159, 1.26 μg/mL in men and n = 227, 2.15μg/mL in women) and obesity (n = 60, 1.31 μg/mL and n = 82, 2.10 μg/mL, respectively) than normal weight subjects (n = 185, 2.07μg/mL and n = 368, 2.94 μg/mL, respectively) and in the presence of central obesity (n = 106, 1.28 μg/mL and n = 331, 2.12 μg/mL, respectively) than subjects with a normal waist circumference (n = 298, 1.74 μg/mL and n = 346, 2.74 μg/mL, respectively). In multiple regression analyses stratified for gender, adjusted for confounders and considered separately each of the adiposity measures, all adiposity measures were significantly (r -0.18 to -0.31, P < 0.001) associated with plasma HMW adiponectin concentration. However, in further stratified and adjusted regression analyses considered stepwise all adiposity measures, only waist-to-hip ratio was significantly (P < 0.05) associated with plasma HMW adiponectin concentration in men (r = -0.10) and women (r = -0.15).

Conclusions

Anthropometric measures of obesity, such as waist-to-hip ratio, but not BIA measures, are independently associated with plasma adiponectin concentration.

Longitudinal changes in adiponectin multimer levels in preterm infants

BACKGROUND

Preterm infants have altered adiponectin levels at term-equivalent age and have a higher risk of developing components of the metabolic syndrome in later life than term infants.

AIMS

To investigate the longitudinal changes in adiponectin levels in preterm infants and to compare the levels between term and preterm infants.

STUDY DESIGN

A cohort study.

SUBJECTS

The study subjects were 43 term infants and 42 preterm infants born at ≤ 34-week gestation.

OUTCOME MEASURES

Serum levels of total adiponectin (T-Ad) and high-molecular-weight adiponectin (HMW-Ad) were measured in 42 preterm infants at term-, 6 month-, and 12 month-equivalent ages. Moreover, the levels in 43 term infants investigated previously were reviewed.

RESULTS

In preterm infants, T-Ad and HMW-Ad levels at the 12 month-equivalent age were lower than at the term- and 6 month-equivalent ages (all values p<0.001), which was consistent with previous results in term infants. The difference in ratios of HMW-Ad to T-Ad between term and preterm infants continued at the 6 month-equivalent age but disappeared at the 12 month-equivalent age. Multiple regression analyses revealed that HMW-Ad levels at term-equivalent age were only a significant determinant of the changes in HMW-Ad between the term- and 12 month-equivalent ages in preterm infants (p<0.001).

CONCLUSIONS

The HMW-Ad levels decline till the 12 month-equivalent age in both term and preterm infants. The changes in HMW-Ad level during infancy might be determined at least to a certain degree up to term-equivalent age in preterm infants.

C-reactive protein inhibits high-molecular-weight adiponectin expression in 3T3-L1 adipocytes via PI3K/Akt pathway

Adiponectin, an adipose-specific protein hormone, is secreted from white adipose tissue and involved in glucose and lipid metabolism. It is assembled into low-molecular-weight trimer (LMW), middle-molecular-weight hexameric (MMW) and high-molecular-weight (HMW), among which HMW exhibits higher activity. In this study, we proved that C-reactive protein (CRP), an inflammatory marker, inhibited adiponectin expression, especially HMW in time-and dose-dependent manners. Furthermore, CRP decreased the HMW/total adiponectin ration and reduced adiponectin assembly by increasing ERp44, and decreasing Ero1-α and DsbA-L. CRP activated pAkt, the downstream of PI3K. Inhibition of PI3K or pAkt abolished the effect of CRP. Our study suggested that CRP decreased adiponectin expression and multimerization, while CRP-induced decline in adiponectin might be mediated through the PI3K/Akt pathway.

Stress signaling between organs in metazoa

Many organisms have developed a robust ability to adapt and survive in the face of environmental perturbations that threaten the integrity of their genome, proteome, or metabolome. Studies in multiple model organisms have shown that, in general, when exposed to stress, cells activate a complex prosurvival signaling network that includes immune and DNA damage response genes, chaperones, antioxidant enzymes, structural proteins, metabolic enzymes, and noncoding RNAs. The manner of activation runs the gamut from transcriptional induction of genes to increased stability of transcripts to posttranslational modification of important biosynthetic proteins within the stressed tissue. Superimposed on these largely autonomous effects are nonautonomous responses in which the stressed tissue secretes peptides and other factors that stimulate tissues in different organs to embark on processes that ultimately help the organism as a whole cope with stress. This review focuses on the mechanisms by which tissues in one organ adapt to environmental challenges by regulating stress responses in tissues of different organs.

Improving Adiponectin Levels in Individuals With Diabetes and Obesity: Insights From Look AHEAD

OBJECTIVE

This study investigated whether fitness changes resulting from lifestyle interventions for weight loss may independently contribute to the improvement of low adiponectin levels in obese individuals with diabetes.

RESEARCH DESIGN AND METHODS

Look AHEAD (Action for Health in Diabetes) randomized overweight/obese individuals with type 2 diabetes to intensive lifestyle intervention (ILI) for weight loss or to diabetes support and education (DSE). Total and high-molecular weight adiponectin (adiponectins), weight, and cardiorespiratory fitness (submaximal exercise stress test) were measured in 1,397 participants at baseline and at 1 year, when ILI was most intense. Regression analyses examined the associations of 1-year weight and fitness changes with change in adiponectins.

RESULTS

ILI resulted in greater improvements in weight, fitness, and adiponectins at 1 year compared with DSE (P < 0.0001). Weight loss and improved fitness were each associated with changes in adiponectins in men and women (P < 0.001 for all), after adjusting for baseline adiponectins, demographics, clinical variables, and treatment arm. Weight loss contributed an additional 4-5% to the variance of change in adiponectins than did increased fitness in men; in women, the contributions of improved fitness (1% greater) and of weight loss were similar. When weight and fitness changes were both accounted for, weight loss in men and increased fitness in women retained their strong associations (P < 0.0001) with adiponectin change.

CONCLUSIONS

Improvements in fitness and weight with ILI were favorably but distinctly associated with changes in adiponectin levels in overweight/obese men and women with diabetes. Future studies need to investigate whether sex-specific biological determinants contribute to the observed associations.

Bilirubin Increases Insulin Sensitivity by Regulating Cholesterol Metabolism, Adipokines and PPARγ Levels

Obesity can cause insulin resistance and type 2 diabetes. Moderate elevations in bilirubin levels have anti-diabetic effects. This study is aimed at determining the mechanisms by which bilirubin treatment reduces obesity and insulin resistance in a diet-induced obesity (DIO) mouse model. DIO mice were treated with bilirubin or vehicle for 14 days. Body weights, plasma glucose, and insulin tolerance tests were performed prior to, immediately, and 7 weeks post-treatment. Serum lipid, leptin, adiponectin, insulin, total and direct bilirubin levels were measured. Expression of factors involved in adipose metabolism including sterol regulatory element-binding protein (SREBP-1), insulin receptor (IR), and PPARγ in liver were measured by RT-PCR and Western blot. Compared to controls, bilirubin-treated mice exhibited reductions in body weight, blood glucose levels, total cholesterol (TC), leptin, total and direct bilirubin, and increases in adiponectin and expression of SREBP-1, IR, and PPARγ mRNA. The improved metabolic control achieved by bilirubin-treated mice was persistent: at two months after treatment termination, bilirubin-treated DIO mice remained insulin sensitive with lower leptin and higher adiponectin levels, together with increased PPARγ expression. These results indicate that bilirubin regulates cholesterol metabolism, adipokines and PPARγ levels, which likely contribute to increased insulin sensitivity and glucose tolerance in DIO mice.