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

Protective roles of adiponectin and molecular signatures of HNF4α and PPARα as downstream targets of adiponectin in pancreatic β cells

The disease progression of the metabolic syndrome is associated with prolonged hyperlipidemia and insulin resistance, eventually giving rise to impaired insulin secretion, often concomitant with hypoadiponectinemia. As an adipose tissue derived hormone, adiponectin is beneficial for insulin secretion and β cell health and differentiation. However, the down-stream pathway of adiponectin in the pancreatic islets has not been studied extensively. Here, along with the overall reduction of endocrine pancreatic function in islets from adiponectin KO mice, we examine PPARα and HNF4α as additional down-regulated transcription factors during a prolonged metabolic challenge. To elucidate the function of β cell-specific PPARα and HNF4α expression, we developed doxycycline inducible pancreatic β cell-specific PPARα (β-PPARα) and HNF4α (β-HNF4α) overexpression mice. β-PPARα mice exhibited improved protection from lipotoxicity, but elevated β-oxidative damage in the islets, and also displayed lowered phospholipid levels and impaired glucose-stimulated insulin secretion. β-HNF4α mice showed a more severe phenotype when compared to β-PPARα mice, characterized by lower body weight, small islet mass and impaired insulin secretion. RNA-sequencing of the islets of these models highlights overlapping yet unique roles of β-PPARα and β-HNF4α. Given that β-HNF4α potently induces PPARα expression, we define a novel adiponectin-HNF4α-PPARα cascade. We further analyzed downstream genes consistently regulated by this axis. Among them, the islet amyloid polypeptide (IAPP) gene is an important target and accumulates in adiponectin KO mice. We propose a new mechanism of IAPP aggregation in type 2 diabetes through reduced adiponectin action.

Adiponectin: A Promising Target for the Treatment of Diabetes and Its Complications

Diabetes mellitus, a chronic metabolic disorder characterized by hyperglycemia, presents a formidable global health challenge with its associated complications. Adiponectin, an adipocyte-derived hormone, has emerged as a significant player in glucose metabolism and insulin sensitivity. Beyond its metabolic effects, adiponectin exerts anti-inflammatory, anti-oxidative, and vasoprotective properties, making it an appealing therapeutic target for mitigating diabetic complications. The molecular mechanisms by which adiponectin impacts critical pathways implicated in diabetic nephropathy, retinopathy, neuropathy, and cardiovascular problems are thoroughly examined in this study. In addition, we explore possible treatment options for increasing adiponectin levels or improving its downstream signaling. The multifaceted protective roles of adiponectin in diabetic complications suggest its potential as a novel therapeutic avenue. However, further translational studies and clinical trials are warranted to fully harness the therapeutic potential of adiponectin in the management of diabetic complications. This review highlights adiponectin as a promising target for the treatment of diverse diabetic complications and encourages continued research in this pivotal area of diabetes therapeutics.

The Interplay of Adipokines and Pancreatic Beta Cells in Metabolic Regulation and Diabetes

The interplay between adipokines and pancreatic beta cells, often referred to as the adipo-insular axis, plays a crucial role in regulating metabolic homeostasis. Adipokines are signaling molecules secreted by adipocytes that have profound effects on several physiological processes. Adipokines such as adiponectin, leptin, resistin, and visfatin influence the function of pancreatic beta cells. The reciprocal communication between adipocytes and beta cells is remarkable. Insulin secreted by beta cells affects adipose tissue metabolism, influencing lipid storage and lipolysis. Conversely, adipokines released from adipocytes can influence beta cell function and survival. Chronic obesity and insulin resistance can lead to the release of excess fatty acids and inflammatory molecules from the adipose tissue, contributing to beta cell dysfunction and apoptosis, which are key factors in developing type 2 diabetes. Understanding the complex interplay of the adipo-insular axis provides insights into the mechanisms underlying metabolic regulation and pathogenesis of metabolic disorders. By elucidating the molecular mediators involved in this interaction, new therapeutic targets and strategies may emerge to reduce the risk and progression of diseases, such as type 2 diabetes and its associated complications. This review summarizes the interactions between adipokines and pancreatic beta cells, and their roles in the pathogenesis of diabetes and metabolic diseases.

Chemerin as an Inducer of β Cell Proliferation Mediates Mitochondrial Homeostasis and Promotes β Cell Mass Expansion

Loss of the β cell population is a crucial feature of type 2 diabetes. Restoring the β cell mass by stimulating β cell proliferation and preventing its apoptosis was proposed as a therapeutic approach to treating diabetes. Therefore, researchers have been increasingly interested in identifying exogenous factors that can stimulate β cell proliferation in situ and in vitro. Adipokine chemerin, which is secreted from adipose tissue and the liver, has been identified as a chemokine that plays a critical role in the regulation of metabolism. In this study, we demonstrate that chemerin as a circulating adipokine promotes β cell proliferation in vivo and in vitro. Chemerin serum levels and the expression of the main receptors within islets are highly regulated under a variety of challenging conditions, including obesity and type 2 diabetes. As compared to their littermates, mice overexpressing chemerin had a larger islet area and increased β cell mass with both a normal and high-fat diet. Moreover, in chemerin-overexpressed mice, we observed improved mitochondrial homeostasis and increased insulin synthesis. In summary, our findings confirm the potential role of chemerin as an inducer of β cell proliferation, and they provide novel insights into the helpful strategy to expand β cell population.

Pancreatic Islets as a Target of Adipokines

Rising rates of obesity are intricately tied to the type 2 diabetes epidemic. The adipose tissues can play a central role in protection against or triggering metabolic diseases through the secretion of adipokines. Many adipokines may improve peripheral insulin sensitivity through a variety of mechanisms, thereby indirectly reducing the strain on beta cells and thus improving their viability and functionality. Such effects will not be the focus of this article. Rather, we will focus on adipocyte-secreted molecules that have a direct effect on pancreatic islets. By their nature, adipokines represent potential druggable targets that can reach the islets and improve beta-cell function or preserve beta cells in the face of metabolic stress. © 2022 American Physiological Society. Compr Physiol 12:1-27, 2022.

Age Associated Changes in Transcription of Adiponectin, AdipoR1 and AdipoR2 Genes in Pancreas of Rats

Objective

Adiponectin has a crucial role in the function, proliferation and viability of β-cell via action of two receptors: AdipoR1 and AdipoR2. Nevertheless, age related change of Adiponectin system genes in pancreas is unclear or controversial. This study sought to investigate the effects of aging process on serum Adiponectin levels, Adiponectin and its receptor expression in the rat pancreas.

Materials and Methods

In this experimental study, insulin resistance markers including serum insulin and glucose concentrations, homeostatic model assessment of insulin resistance (HOMA-IR), oral glucose tolerance test (OGTT), glucose induced insulin secretion (GIIS), serum Adiponectin levels, pancreatic expression of Adiponectin and its receptors were studied in male Sprague-Dawley rats at the age of 2, 5, 10, 18, 52 and 72 weeks of age.

Results

We found that aging triggered signs of insulin resistance characteristics in rats at 72 age weeks including marked insulin reduction, hyperglycemia and increased HOMA-IR. Circulating Adiponectin as well as pancreatic expression of Adiponectin and AdipoR1 was gradually decreased with age, while the opposite expression pattern of AdipoR2 was observed in the old rats.

Conclusion

Because Adiponectin and Adiponectin signaling have crucial role in β-cell function and viability, we concluded that reduction of Adiponectin signaling may be involved in aging induced β-cell dysfunction. As a result, manipulation of Adiponectin signaling may be a beneficial approach for improvement of β-cell function in the old people.

Adipokines as key players in β cell function and failure

The growing prevalence of obesity and its related metabolic diseases, mainly Type 2 diabetes (T2D), has increased the interest in adipose tissue (AT) and its role as a principal metabolic orchestrator. Two decades of research have now shown that ATs act as an endocrine organ, secreting soluble factors termed adipocytokines or adipokines. These adipokines play crucial roles in whole-body metabolism with different mechanisms of action largely dependent on the tissue or cell type they are acting on. The pancreatic β cell, a key regulator of glucose metabolism due to its ability to produce and secrete insulin, has been identified as a target for several adipokines. This review will focus on how adipokines affect pancreatic β cell function and their impact on pancreatic β cell survival in disease contexts such as diabetes. Initially, the "classic" adipokines will be discussed, followed by novel secreted adipocyte-specific factors that show therapeutic promise in regulating the adipose-pancreatic β cell axis.

Levels of nitric oxide metabolites, adiponectin and endothelin are associated with SNPs of the adiponectin and endothelin genes

Adiponectin, endothelin and nitric oxide (NO) are major regulators of vascular function. An imbalance of vasoactive factors contributes to the onset and progression of atherosclerosis. Various single nucleotide polymorphisms (SNPs) are considered to be risk factors for coronary heart disease. However, the molecular mechanisms of their associations with the components of endothelial dysfunction are poorly understood. In the present study, rs17366743, rs17300539, rs266729, rs182052 and rs2241766 SNPs of the adiponectin (ADIPOQ) gene and rs2070699, rs1800542 and rs1800543 SNPs of the endothelin-1 (EDN1) gene were genotyped in 477 patients with coronary heart disease who were subjected to coronary angiography, in order to determine the presence or absence of coronary atherosclerosis. The serum levels of adiponectin, endothelin and stable metabolites of NO, (nitrate and nitrite NOx), were assayed and their associations with the SNP genotypes and coronary lesions were calculated. The results indicated that rs17366743 of the ADIPOQ gene and rs2070699 and rs1800543 of the EDN1 gene were associated with the levels of NOx in women, which in turn was associated with cardiovascular mortality. In men, rs182052 and rs266729 of the ADIPOQ gene were associated with adiponectin levels, whereas rs17366743 of the ADIPOQ gene was associated with endothelin levels. Additionally, these SNPs were indirectly associated with the prevalence of coronary lesions in men. Therefore, the tested SNPs can be considered potential risk factors that lead to imbalance of vasoactive mediators in a gender-specific manner and contribute to the development of clinical manifestations of atherosclerosis.

Changes in Visceral and Subcutaneous Fat in Youth With Type 2 Diabetes in the TODAY Study

OBJECTIVE

In the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study, metformin plus rosiglitazone (M + R) maintained glycemic control better than metformin alone (M) or metformin plus lifestyle (M + L) in youth with type 2 diabetes (T2D). We hypothesized that changes in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) would explain the differential treatment effects on glycemia.

RESEARCH DESIGN AND METHODS

In 626 youth ages 11-17 years with T2D duration <2 years, VAT and SAT were estimated by DXA at baseline and at 6 and 24 months. Changes from baseline were analyzed in linear mixed models.

RESULTS

Baseline mean age was 13.9 years, 66.4% were female, 72.2% were Hispanic/non-Hispanic black, and 20.3% were non-Hispanic white (NHW). Mean BMI was 33.7 kg/m². VAT increased more in M + R (13.1%) than M + L (3.9%, P = 0.0006) or M (6.5%, P = 0.0146). SAT also increased more in M + R (13.3%) than in M + L (5.4%, P < 0.0001) or M (6.4%, P = 0.0005), indicating no significant fat redistribution in M + R. In NHWs, VAT increased more in M + R than M (P = 0.0192) and M + L (P = 0.0482) but did not explain the race-ethnicity differences in treatment effects on glycemic control among treatment groups. VAT and SAT increases correlated with higher HbA_1c, lower insulin sensitivity, and lower oral disposition index (all P < 0.05), but associations did not differ by treatment group.

CONCLUSIONS

In contrast to the existing reports in adults with T2D, in TODAY, M + R resulted in the most VAT accumulation compared with M + L or M. Differential effects on depot-specific indirect measures of adiposity are unrelated to treatment effects in sustaining glycemic control. Additional studies are needed to understand the clinical markers of metabolic risk profile in youth with T2D on rosiglitazone.

Adipose Tissue-Derived Signatures for Obesity and Type 2 Diabetes: Adipokines, Batokines and MicroRNAs

: Obesity is one of the main risk factors for type 2 diabetes mellitus (T2DM). It is closely related to metabolic disturbances in the adipose tissue that primarily functions as a fat reservoir. For this reason, adipose tissue is considered as the primary site for initiation and aggravation of obesity and T2DM. As a key endocrine organ, the adipose tissue communicates with other organs, such as the brain, liver, muscle, and pancreas, for the maintenance of energy homeostasis. Two different types of adipose tissues-the white adipose tissue (WAT) and brown adipose tissue (BAT)-secrete bioactive peptides and proteins, known as "adipokines" and "batokines," respectively. Some of them have beneficial anti-inflammatory effects, while others have harmful inflammatory effects. Recently, "exosomal microRNAs (miRNAs)" were identified as novel adipokines, as adipose tissue-derived exosomal miRNAs can affect other organs. In the present review, we discuss the role of adipose-derived secretory factors-adipokines, batokines, and exosomal miRNA-in obesity and T2DM. It will provide new insights into the pathophysiological mechanisms involved in disturbances of adipose-derived factors and will support the development of adipose-derived factors as potential therapeutic targets for obesity and T2DM.

Examining the Potential of Developing and Implementing Use of Adiponectin-Targeted Therapeutics for Metabolic and Cardiovascular Diseases

Cardiometabolic diseases encompass those affecting the heart and vasculature as well as other metabolic problems, such as insulin resistance, diabetes, and non-alcoholic fatty liver disease. These diseases tend to have common risk factors, one of which is impaired adiponectin action. This may be due to reduced bioavailability of the hormone or resistance to its effects on target tissues. A strong negative correlation between adiponectin levels and cardiometabolic diseases has been well-documented and research shown that adiponectin has cardioprotective, insulin sensitizing and direct beneficial metabolic effects. Thus, therapeutic approaches to enhance adiponectin action are widely considered to be desirable. The complexity of adiponectin structure and function has so far made progress in this area less than ideal. In this article we will review the effects and mechanism of action of adiponectin on cardiometabolic tissues, identify scenarios where enhancing adiponectin action would be of clinical value and finally discuss approaches via which this can be achieved.

The obesogen tributyltin induces features of polycystic ovary syndrome (PCOS): a review

Polycystic ovary syndrome (PCOS) is a heterogeneous syndrome characterized by abnormal reproductive cycles, irregular ovulation, and hyperandrogenism. This complex disorder has its origins both within and outside the hypothalamic-pituitary-ovarian axis. Cardio-metabolic factors, such as obesity and insulin resistance, contribute to the manifestation of the PCOS phenotype. Polycystic ovary syndrome is one of the most common endocrine disorders among women of reproductive age. Growing evidence suggested an association between reproductive and metabolic features of PCOS and exposure to endocrine-disrupting chemicals (EDC), such as bisphenol A. Further, the environmental obesogen tributyltin (TBT) was shown to induce reproductive, metabolic and cardiovascular abnormalities resembling those found in women and animal models of PCOS. However, the causal link between TBT exposure and PCOS development remains unclear. The objective of this review was to summarize the most recent research findings on the potential association between TBT exposure and development of PCOS-like features in animal models and humans.

Microfluidic Chip with Integrated Electrophoretic Immunoassay for Investigating Cell-Cell Interactions

Microfluidics have been used to create "body-on-chip" systems to mimic in vivo cellular interactions with a high level of control. Most such systems rely on optical observation of cells as a readout. In this work we integrated a cell-cell interaction chip with online microchip electrophoresis immunoassay to monitor the effects of the interaction on protein secretion dynamics. The system was used to investigate the effects of adipocytes on insulin secretion. Chips were loaded with 190 000 3T3-L1 adipocytes and a single islet of Langerhans in separate chambers. The chambers were perfused at 300-600 nL/min so that adipocyte secretions flowed over the islets for 3 h. Adipocytes produced 80 μM of nonesterified fatty acids (NEFAs), a factor known to impact insulin secretion, at the islets. After perfusion, islets were challenged with a step change in glucose from 3 to 11 mM while monitoring insulin secretion at 8 s intervals by online immunoassay. Adipocyte treatment augmented insulin secretion by 6-fold compared to controls. The effect was far greater than comparable concentrations of NEFA applied to the islets demonstrating that adipocytes release multiple factors that can strongly potentiate insulin secretion. The experiments reveal that integration of chemical analysis with cell-cell interaction can provide valuable insights into cellular functions.

Adiponectin protects against development of metabolic disturbances in a PCOS mouse model

Adiponectin, together with adipocyte size, is the strongest factor associated with insulin resistance in women with polycystic ovary syndrome (PCOS). This study investigates the causal relationship between adiponectin levels and metabolic and reproductive functions in PCOS. Prepubertal mice overexpressing adiponectin from adipose tissue (APNtg), adiponectin knockouts (APNko), and their wild-type (WT) littermate mice were continuously exposed to placebo or dihydrotestosterone (DHT) to induce PCOS-like traits. As expected, DHT exposure led to reproductive dysfunction, as judged by continuous anestrus, smaller ovaries with a decreased number of corpus luteum, and an increased number of cystic/atretic follicles. A two-way between-groups analysis showed that there was a significant main effect for DHT exposure, but not for genotype, indicating adiponectin does not influence follicle development. Adiponectin had, however, some protective effects on ovarian function. Similar to in many women with PCOS, DHT exposure led to reduced adiponectin levels, larger adipocyte size, and reduced insulin sensitivity in WTs. APNtg mice remained metabolically healthy despite DHT exposure, while APNko-DHT mice were even more insulin resistant than their DHT-exposed littermate WTs. DHT exposure also reduced the mRNA expression of genes involved in metabolic pathways in gonadal adipose tissue of WT and APNko, but this effect of DHT was not observed in APNtg mice. Moreover, APNtg-DHT mice displayed increased pancreatic mRNA levels of insulin receptors, Pdx1 and Igf1R, suggesting adiponectin stimulates beta cell viability/hyperplasia in the context of PCOS. In conclusion, adiponectin improves metabolic health but has only minor effects on reproductive functions in this PCOS-like mouse model.

Translating the biology of adipokines in atherosclerosis and cardiovascular diseases: Gaps and open questions

AIM

Critically discuss the available data, to identify the current gaps and to provide key concepts that will help clinicians in translating the biology of adipokines in the context of atherosclerosis and cardio-metabolic diseases.

DATA SYNTHESIS

Adipose tissue is nowadays recognized as an active endocrine organ, a function related to the ability to secrete adipokines (such as leptin and adiponectin) and pro-inflammatory cytokines (tumor necrosis factor alpha and resistin). Studies in vitro and in animal models have observed that obesity status presents a chronic low-grade inflammation as the consequence of the immune cells infiltrating the adipose tissue as well as adipocytes. This inflammatory signature is often related to the presence of cardiovascular diseases, including atherosclerosis and thrombosis. These links are less clear in humans, where the role of adipokines as prognostic marker and/or player in cardiovascular diseases is not as clear as that observed in experimental models. Moreover, plasma adipokine levels might reflect a condition of adipokine-resistance in which adipokine redundancy occurs. The investigation of the cardio-metabolic phenotype of carriers of single nucleotide polymorphisms affecting the levels or function of a specific adipokine might help determine their relevance in humans. Thus, the aim of the present review is to critically discuss the available data, identify the current gaps and provide key concepts that will help clinicians translate the biology of adipokines in the context of atherosclerosis and cardio-metabolic diseases.

Adipokines in psoriasis: An important link between skin inflammation and metabolic alterations

Psoriasis is a chronic inflammatory skin disease most common in Europe, North America, and Australia. The etiology and pathomechanisms underlying the evolution and persistence of the skin alterations are increasingly being understood and have led to the development of effective anti-psoriatic therapies. Apart from the skin manifestations, psoriasis is associated with the metabolic syndrome (MetS), known to increase the risk of type 2 diabetes mellitus and cardiovascular disorders. Research of the last years demonstrated a dysregulated adipokine balance as an important link between inflammation, MetS, and consequential disorders. This article describes selected adipokines and their potential role in both metabolic comorbidity and skin inflammation in psoriasis.

Adiponectin signaling and function in insulin target tissues

Obesity-linked type 2 diabetes is one of the paramount causes of morbidity and mortality worldwide, posing a major threat on human health, productivity, and quality of life. Despite great progress made towards a better understanding of the molecular basis of diabetes, the available clinical counter-measures against insulin resistance, a defect that is central to obesity-linked type 2 diabetes, remain inadequate. Adiponectin, an abundant adipocyte-secreted factor with a wide-range of biological activities, improves insulin sensitivity in major insulin target tissues, modulates inflammatory responses, and plays a crucial role in the regulation of energy metabolism. However, adiponectin as a promising therapeutic approach has not been thoroughly explored in the context of pharmacological intervention, and extensive efforts are being devoted to gain mechanistic understanding of adiponectin signaling and its regulation, and reveal therapeutic targets. Here, we discuss tissue- and cell-specific functions of adiponectin, with an emphasis on the regulation of adiponectin signaling pathways, and the potential crosstalk between the adiponectin and other signaling pathways involved in metabolic regulation. Understanding better just why and how adiponectin and its downstream effector molecules work will be essential, together with empirical trials, to guide us to therapies that target the root cause(s) of type 2 diabetes and insulin resistance.

Uncovering Factors Related to Pancreatic Beta-Cell Function

AIM

The incidence of type 2 diabetes has increased rapidly on a global scale. Beta-cell dysfunction contributes to the overall pathogenesis of type 2 diabetes. However, factors contributing to beta-cell function are not clear. The aims of this study were (i) to identify factors related to pancreatic beta-cell function and (ii) to perform mechanistic studies in vitro.

METHODS

Three specific measures of beta-cell function were assessed for 110 participants who completed an oral glucose tolerance test as part of the Metabolic Challenge Study. Anthropometric and biochemical parameters were assessed as potential modulators of beta-cell function. Subsequent in vitro experiments were performed using the BRIN-BD11 pancreatic beta-cell line. Validation of findings were performed in a second human cohort.

RESULTS

Waist-to-hip ratio was the strongest anthropometric modulator of beta-cell function, with beta-coefficients of -0.33 (p = 0.001) and -0.30 (p = 0.002) for beta-cell function/homeostatic model assessment of insulin resistance (HOMA-IR), and disposition index respectively. Additionally, the resistin-to-adiponectin ratio (RA index) emerged as being strongly associated with beta-cell function, with beta-coefficients of -0.24 (p = 0.038) and -0.25 (p = 0.028) for beta-cell function/HOMA-IR, and disposition index respectively. Similar results were obtained using a third measure for beta-cell function. In vitro experiments revealed that the RA index was a potent regulator of acute insulin secretion where a high RA index (20ng ml-1 resistin, 5nmol l-1 g-adiponectin) significantly decreased insulin secretion whereas a low RA index (10ng ml-1 resistin, 10nmol l-1 g-adiponectin) significantly increased insulin secretion. The RA index was successfully validated in a second human cohort with beta-coefficients of -0.40 (p = 0.006) and -0.38 (p = 0.008) for beta-cell function/ HOMA-IR, and disposition index respectively.

CONCLUSIONS

Waist-to-hip ratio and RA index were identified as significant modulators of beta-cell function. The ability of the RA index to modulate insulin secretion was confirmed in mechanistic studies. Future work should identify strategies to alter the RA index.

Genetic basis of dyslipidemia in disease precipitation of coronary artery disease (CAD) associated type 2 diabetes mellitus (T2DM)

Type 2 diabetes mellitus (T2DM) and its complications are linked to environmental, clinical, and genetic factors. This review analyses the disorders of lipids and their genetics with respect to coronary artery disease (CAD) associated with T2DM. Cell organelles, hepatitis C-virus infection, reactive oxygen species produced in mitochondria, and defective insulin signaling due to the arrest of G1 phase to S phase transition of β-cells have significant roles in the precipitation of the diseases. Adiponectin is anti-inflammatory and anti-atherosclerotic and improves insulin resistance. Low-density lipoprotein (LDL) is atherosclerotic, and LDL-cholesterol in T2DM is associated with high-cardiovascular risk. Further, LDL cholesterol reduction significantly reduces cardiovascular morbidity and mortality. High-density lipoprotein (HDL) is also anti-atherosclerotic due to HDL associated paraoxonase-1 serum enzyme, which prevents LDL oxidative modifications and the development of CAD. Moreover, elevated apolipoprotein B and apolipoprotein A-I (ApoB/ApoA-I) ratio in plasma is also a risk factor for CAD. LDL receptor, adiponectin, and endocannabinoid receptor-1 genes are independently associated with CAD and T2DM. Polymorphism of Apo E2 (epsilon2) is a positive factor to increase the T2DM risk and Apo E4 (epsilon4) is a negative factor to reduce the disease risk. Taq 1B polymorphism of cholesterol ester transfer protein (CETP) gene contributes to the development of atherosclerosis, whereas haplotypes of APOA5, APOC3, APOC4, and APOC5 genes are in the same cluster and are independently associated with high plasma triglyceride level, CAD and T2DM. In conclusion, because various genes, LDLR, CETP, APOA5, Apo E, Apo B, and Apo A-I, are associated with the precipitation of CAD associated with T2DM, a personalized diet-gene intervention therapy may be advocated to reduce the disease precipitation.

Tributyltin differentially promotes development of a phenotypically distinct adipocyte

OBJECTIVE

Environmental endocrine disrupting chemicals (EDCs) are increasingly implicated in the pathogenesis of obesity. Evidence implicates various EDCs as being proadipogenic, including tributyltin (TBT), which activates the peroxisome proliferator activated receptor-γ (PPARγ). However, the conditions required for TBT-induced adipogenesis and its functional consequences are incompletely known.

METHODS

The costimulatory conditions necessary for preadipocyte-to-adipocyte differentiation were compared between TBT and the pharmacological PPARγ agonist troglitazone (Trog) in the 3T3-L1 cell line; basal and insulin-stimulated glucose uptake were assessed using radiolabeled 2-deoxyglucose.

RESULTS

TBT enhanced expression of the adipocyte marker C/EBPα with coexposure to either isobutylmethylxanthine or insulin in the absence of other adipogenic stimuli. Examination of several adipocyte-specific proteins revealed that TBT and Trog differentially affected protein expression despite comparable PPARγ stimulation. In particular, TBT reduced adiponectin expression upon maximal adipogenic stimulation. Under submaximal stimulation, TBT and Trog differentially promoted adipocyte-specific gene expression despite similar lipid accumulation. Moreover, TBT attenuated Trog-induced adipocyte gene expression under conditions of cotreatment. Finally, TBT-induced adipocytes exhibited altered glucose metabolism, with increased basal glucose uptake.

CONCLUSIONS

TBT-induced adipocytes are functionally distinct from those generated by a pharmacological PPARγ agonist, suggesting that obesogen-induced adipogenesis may generate dysfunctional adipocytes with the capacity to deleteriously affect global energy homeostasis.

Adiponectin-mediated antilipotoxic effects in regenerating pancreatic islets

Pathways that stimulate β-cell regeneration remain of great clinical interest, yet effective therapeutic avenues that promote survival or reconstitution of β-cell mass remain elusive. Using a mouse model with inducible β-cell apoptosis followed by adiponectin-mediated regeneration, we aimed to identify key molecules boosting β-cell viability. In the regenerating pancreatic islets, we examined changes within the transcriptome and observed an extensive up-regulation of genes encoding proteins involved in lipid transport and metabolism. The most prominent targets were further confirmed by quantitative PCR and immunofluorescence. Among the upstream regulators predicted by pathway analysis of the transcriptome, we detected enhanced levels of 2 key transcription factors, Hepatocyte Nuclear Factor 4α and Peroxisome Proliferator-Activated Receptorα. Our data suggest that improving pancreatic islet lipid metabolism as an important antilipotoxic phenomenon to boost β-cell regeneration. This is primarily mediated by the adipokine adiponectin that exerts its action on both the beta-cell directly as well as on the adipocyte. Adiponectin induces lipid metabolism gene expression in regenerating islets through Hepatocyte Nuclear Factor 4α and Peroxisome Proliferator-Activated Receptorα. Adiponectin also modulates leptin levels via preserving adipose tissue mass in the insulinopenic state.

Dietary exposure to the endocrine disruptor tolylfluanid promotes global metabolic dysfunction in male mice

Environmental endocrine disruptors are implicated as putative contributors to the burgeoning metabolic disease epidemic. Tolylfluanid (TF) is a commonly detected fungicide in Europe, and previous in vitro and ex vivo work has identified it as a potent endocrine disruptor with the capacity to promote adipocyte differentiation and induce adipocytic insulin resistance, effects likely resulting from activation of glucocorticoid receptor signaling. The present study extends these findings to an in vivo mouse model of dietary TF exposure. After 12 weeks of consumption of a normal chow diet supplemented with 100 parts per million TF, mice exhibited increased body weight gain and an increase in total fat mass, with a specific augmentation in visceral adipose depots. This increased adipose accumulation is proposed to occur through a reduction in lipolytic and fatty acid oxidation gene expression. Dietary TF exposure induced glucose intolerance, insulin resistance, and metabolic inflexibility, while also disrupting diurnal rhythms of energy expenditure and food consumption. Adipose tissue endocrine function was also impaired with a reduction in serum adiponectin levels. Moreover, adipocytes from TF-exposed mice exhibited reduced insulin sensitivity, an effect likely mediated through a specific down-regulation of insulin receptor substrate-1 expression, mirroring effects of ex vivo TF exposure. Finally, gene set enrichment analysis revealed an increase in adipose glucocorticoid receptor signaling with TF treatment. Taken together, these findings identify TF as a novel in vivo endocrine disruptor and obesogen in mice, with dietary exposure leading to alterations in energy homeostasis that recapitulate many features of the metabolic syndrome.

Adiponectin is essential for lipid homeostasis and survival under insulin deficiency and promotes β-cell regeneration

As an adipokine in circulation, adiponectin has been extensively studied for its beneficial metabolic effects. While many important functions have been attributed to adiponectin under high-fat diet conditions, little is known about its essential role under regular chow. Employing a mouse model with inducible, acute β-cell ablation, we uncovered an essential role of adiponectin under insulinopenic conditions to maintain minimal lipid homeostasis. When insulin levels are marginal, adiponectin is critical for insulin signaling, endocytosis, and lipid uptake in subcutaneous white adipose tissue. In the absence of both insulin and adiponectin, severe lipoatrophy and hyperlipidemia lead to lethality. In contrast, elevated adiponectin levels improve systemic lipid metabolism in the near absence of insulin. Moreover, adiponectin is sufficient to mitigate local lipotoxicity in pancreatic islets, and it promotes reconstitution of β-cell mass, eventually reinstating glycemic control. We uncovered an essential new role for adiponectin, with major implications for type 1 diabetes.

DOI:http://dx.doi.org/10.7554/eLife.03851.001

Fat tissue is essential for health. Fat cells store energy and release it when it is needed; they also release hormones that are important for the health of our heart and for regulating our metabolism. One of these hormones, adiponectin, helps cells to remove fat molecules from the bloodstream. This allows the body to maintain appropriate cholesterol levels and prevents fatty build-ups from blocking blood vessels, which is associated with heart disease. Adiponectin also helps cells respond to insulin, a hormone that regulates blood sugar levels, and thus helps to prevent diabetes.

Despite this hormone's important roles in health, mice that lack adiponectin can thrive under normal conditions. Adiponectin becomes essential, however, when blood sugar or fat levels are considerably altered. For example, when mice without adiponectin are fed a high fat-content diet, they become insulin-resistant. Moreover, certain diabetes drugs that boost insulin sensitivity only work if adiponectin is present in the body.

Adiponectin helps to keep the β-cells that produce insulin alive. In patients with diabetes, β-cells slowly die, and this leads to a poor insulin response and an imbalance in the amount of fats and sugars in the cells. This is toxic to the β-cells; and as more β-cells die, less insulin is produced to control sugar levels, and the condition worsens. Adiponectin appears to protect the β-cells against this vicious cycle, but the details of how it does so are unclear.

Ye et al. used a mouse model in which β-cells were destroyed to see what adiponectin does when insulin is in short supply. When insulin levels were extremely low, adiponectin was found to help one type of fat tissue absorb fat molecules from the bloodstream, which reduced blood cholesterol levels. It also protects fat cells from being destroyed when insulin levels are low. Ye et al. also found that mice that lack both insulin and adiponectin lose excessive amounts of fat tissue and develop high blood cholesterol levels, which lead to death.

Increasing adiponectin levels in insulin-deficient mice, however, improves their blood cholesterol levels and protects β-cells from being destroyed. This allows the β-cells to begin regenerating. As the β-cells regenerate, the insulin-deficient mice developed better control over their blood sugar.

Many people with type-1 diabetes (which is caused by their own immune system destroying their β-cells) currently rely on insulin injections and restricted diets to manage their condition. Ye et al.'s findings might lead to new strategies to restore β-cell production and blood sugar control; as such these findings will have important implications for the management of type-1 diabetes.

DOI:http://dx.doi.org/10.7554/eLife.03851.002

The Effect of Leptin and Adiponectin on KiSS-1 and KissR mRNA Expression in Rat Islets of Langerhans and CRI-D2 Cell Line

BACKGROUND

Leptin and adiponectin are the two key metabolic hormones secreted from adipocytes to control food intake and energy expenditure. The action of both hormones in regulation of Gonadotropin Releasing Hormone (GnRH) secretion from the hypothalamus is mediated through Kisspeptins. Kisspeptins are products of KiSS-1 gene. Leptin and adiponectin are modulators of KiSS-1 expression in the hypothalamus. These peptides have also important roles in pancreatic β-cells to control insulin synthesis and secretion and their receptors are detected in Langerhans islets. We hypothesized that leptin and adiponectin might alter KiSS-1 and Kiss Receptor mRNA expression in the islets.

OBJECTIVES

The aim of this study is to investigate any modulatory effect that leptin and adiponectin may have on the expression of Kiss-1 and KiSSR gene in Langerhans islets.

MATERIALS AND METHODS

We isolated the islets from adult male rats by collagenase and cultured CRI-D2 cell lines to investigate the effect of leptin and adiponectin. Then, we incubated them with different concentrations of leptin and adiponectin for 24 hours. After that, RNA was extracted from the islets and CRI-D2 cells and transcripted to cDNA. KiSS-1 and KissR expression levels were evaluated by real time PCR.

RESULTS

In islet and CRI-D2 cells, leptin increased the KiSS-1 mRNA expression significantly, but adiponectin decreased it was expected.

CONCLUSIONS

These findings indicated the possibility that KiSS-1 mRNA expression is a mediator of leptin and adiponectin function in the islets.

Adipose tissue and its role in organ crosstalk

The discovery of adipokines has revealed adipose tissue as a central node in the interorgan crosstalk network, which mediates the regulation of multiple organs and tissues. Adipose tissue is a true endocrine organ that produces and secretes a wide range of mediators regulating adipose tissue function in an auto-/paracrine manner and important distant targets, such as the liver, skeletal muscle, the pancreas and the cardiovascular system. In metabolic disorders such as obesity, enlargement of adipocytes leads to adipose tissue dysfunction and a shift in the secretory profile with an increased release of pro-inflammatory adipokines. Adipose tissue dysfunction has a central role in the development of insulin resistance, type 2 diabetes, and cardiovascular diseases. Besides the well-acknowledged role of adipokines in metabolic diseases, and the increasing number of adipokines being discovered in the last years, the mechanisms underlying the release of many adipokines from adipose tissue remain largely unknown. To combat metabolic diseases, it is crucial to better understand how adipokines can modulate adipose tissue growth and function. Therefore, we will focus on adipokines with a prominent role in auto-/paracrine crosstalk within the adipose tissue such as RBP4, HO-1, WISP2, SFRPs and chemerin. To depict the endocrine crosstalk between adipose tissue with skeletal muscle, the cardiovascular system and the pancreas, we will report the main findings regarding the direct effects of adiponectin, leptin, DPP4 and visfatin on skeletal muscle insulin resistance, cardiovascular function and β-cell growth and function.

Adipocytes under assault: environmental disruption of adipose physiology

The burgeoning obesity epidemic has placed enormous strains on individual and societal health mandating a careful search for pathogenic factors, including the contributions made by endocrine disrupting chemicals (EDCs). In addition to evidence that some exogenous chemicals have the capacity to modulate classical hormonal signaling axes, there is mounting evidence that several EDCs can also disrupt metabolic pathways and alter energy homeostasis. Adipose tissue appears to be a particularly important target of these metabolic disruptions. A diverse array of compounds has been shown to alter adipocyte differentiation, and several EDCs have been shown to modulate adipocyte physiology, including adipocytic insulin action and adipokine secretion. This rapidly emerging evidence demonstrating that environmental contaminants alter adipocyte function emphasizes the potential role that disruption of adipose physiology by EDCs may play in the global epidemic of metabolic disease. Further work is required to better characterize the molecular targets responsible for mediating the effects of EDCs on adipose tissue. Improved understanding of the precise signaling pathways altered by exposure to environmental contaminants will enhance our understanding of which chemicals pose a threat to metabolic health and how those compounds synergize with lifestyle factors to promote obesity and its associated complications. This knowledge may also improve our capacity to predict which synthetic compounds may alter energy homeostasis before they are released into the environment while also providing critical evidentiary support for efforts to restrict the production and use of chemicals that pose the greatest threat to human metabolic health. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

The mechanisms linking adiposopathy to type 2 diabetes

Obesity is defined as excessive accumulation of body fat in proportion to body size. When obesity occurs, the functions of adipose tissue may be deregulated, which is termed as adiposopathy. Adiposopathy is an independent risk factor for many diseases, including diabetes and cardiovascular diseases. In overweight or obese subjects with adiposopathy, hyperlipidemia exerts lipotoxicity in pancreatic islet and liver and induces pancreatic β cell dysfunction and liver insulin resistance, which are the decisive factors causing type 2 diabetes. Moreover, adipokines have been shown to play important roles in the regulation of glucose homeostasis. When adiposopathy occurs, abnormal changes in the serum adipokine profile correlate with the development and progression of pancreatic β cell dysfunction and insulin resistance in peripheral tissue. The current paper briefly discusses the latest findings regarding the effects of adiposopathy-related lipotoxicity and cytokine toxicity on the development of type 2 diabetes.

Islet inflammation: a unifying target for diabetes treatment?

In the past decade, islet inflammation has emerged as a contributor to the loss of functional β cell mass in both type 1 (T1D) and type 2 diabetes (T2D). Evidence supports the idea that overnutrition and insulin resistance result in the production of proinflammatory mediators by β cells. In addition to compromising β cell function and survival, cytokines may recruit macrophages into islets, thus augmenting inflammation. Limited but intriguing data imply a role of adaptive immune response in islet dysfunction in T2D. Clinical trials have validated anti-inflammatory therapies in T2D, whereas immune therapy for T1D remains challenging. Further research is required to improve our understanding of islet inflammatory pathways and to identify more effective therapeutic targets for T1D and T2D.

The effects of Leptin and Adiponectin on Pdx1, Foxm1, and PPARγ Transcription in Rat Islets of Langerhans

BACKGROUND

Leptin and adiponectin are two hormones, which are released from adipocytes in order to control energy expenditure. Both hormones are also involved in glucose homeostasis through control of insulin secretion from pancreatic islets. Since Pdx1, PPARγ, and foxm1 play important roles in islets function, it is essential to understand how these genes are regulated in the islets of Langerhans.

OBJECTIVES

We have designed an experiment to identify the effect of leptin and adiponectin treatment on Pdx1, PPARγ, and foxm1 transcription.

MATERIALS AND METHODS

Islets were isolated from adult male rats by collagenase and incubated with different concentrations of leptin and adiponectin for 24 hours. Next, by means of real time PCR, we evaluated the gene transcription related to a housekeeping gene. The effect of leptin and adiponectin on insulin secretion was evaluated by ELISA.

RESULTS

Leptin decreased PPARγ transcription and insulin secretion, while adiponectin significantly increased Pdx1 and PPARγ transcription and insulin secretion in rat islets. The transcription of foxm1 did not change in the islet cells treated with leptin or adiponectin.

CONCLUSIONS

These findings indicate the possibility that Pdx1 and PPARγ transcription is a mediator of leptin and adiponectin function in control of insulin secretion and glucose homeostasis in pancreatic islets.

Adiponectin, driver or passenger on the road to insulin sensitivity?

Almost 20 years have passed since the first laboratory evidence emerged that an abundant message encoding a protein with homology to the C1q superfamily is highly specifically expressed in adipocytes. At this stage, we refer to this protein as adiponectin. Despite more than 10,000 reports in the literature since its initial description, we seem to have written only the first chapter in the textbook on adiponectin physiology. With every new aspect we learn about adiponectin, a host of new questions arise with respect to the underlying molecular mechanisms. Here, we aim to summarize recent findings in the field and bring the rodent studies that suggest a causal relationship between adiponectin levels in plasma and systemic insulin sensitivity in perspective with the currently available data on the clinical side.

The role of adipokines in β-cell failure of type 2 diabetes

β-Cell failure coupled with insulin resistance is a key factor in the development of type 2 diabetes. Changes in circulating levels of adipokines, factors released from adipose tissue, form a significant link between excessive adiposity in obesity and both aforementioned factors. In this review, we consider the published evidence for the role of individual adipokines on the function, proliferation, death and failure of β-cells, focusing on those reported to have the most significant effects (leptin, adiponectin, tumour necrosis factor α, resistin, visfatin, dipeptidyl peptidase IV and apelin). It is apparent that some adipokines have beneficial effects whereas others have detrimental properties; the overall contribution to β-cell failure of changed concentrations of adipokines in the blood of obese pre-diabetic subjects will be highly dependent on the balance between these effects and the interactions between the adipokines, which act on the β-cell via a number of intersecting intracellular signalling pathways. We emphasise the importance, and comparative dearth, of studies into the combined effects of adipokines on β-cells.

Maintenance of redox state and pancreatic beta-cell function: role of leptin and adiponectin

Whereas oxidative stress is linked to cellular damage, reactive oxygen species (ROS) are also believed to be involved in the propagation of signaling pathways. Studies on the role of ROS in pancreatic beta-cell physiology, in contrast to pathophysiology, have not yet been reported. In this study we investigate the importance of maintaining cellular redox state on pancreatic beta-cell function and viability, and the effects of leptin and adiponectin on this balance. Experiments were conducted on RINm and MIN6 pancreatic beta-cells. Leptin (1-100 ng/ml) and adiponectin (1-100 nM) increased ROS accumulation, as was determined by DCFDA fluorescence. Using specific inhibitors, we found that the increase in ROS levels was mediated by NADPH oxidase (Nox), but not by AMP kinase (AMPK) or phosphatidyl inositol 3 kinase (PI3K). Leptin and adiponectin increased beta-cell number as detected by the XTT method, but did not affect apoptosis, indicating that the increased cell number results from increased proliferation. The adipokines-induced increase in viability is ROS dependent as this effect was abolished by N-acetyl-L-cysteine (NAC) or PEG-catalase. In addition, insulin secretion was found to be regulated by alterations in redox state, but not by adipokines. Finally, the effects of the various treatments on activity and mRNA expression of several antioxidant enzymes were determined. Both leptin and adiponectin reduced mRNA levels of superoxide dismutase (SOD)1. Adiponectin also decreased SOD activity and increased catalase and glutathione peroxidase (GPx) activities in the presence of H2O2. The results of this study show that leptin and adiponectin, by inducing a physiological increase in ROS levels, may be positive regulators of beta-cell mass.

Adiponectin: mechanistic insights and clinical implications

Adiponectin is an adipocyte-derived secretory protein that has been very widely studied over the past 15 years. A multitude of different functions have been attributed to this adipokine. It has been characterised in vitro at the level of tissue culture systems and in vivo through genetic manipulation of rodent models. It is also widely accepted as a biomarker in clinical studies. Originating in adipose tissue, generally positive metabolic effects have been attributed to adiponectin. In this review, we briefly discuss the key characteristics of this interesting but very complex molecule, highlight recent results in the context of its mechanism of action and summarise some of the key epidemiological data that helped establish adiponectin as a robust biomarker for insulin sensitivity, cardiovascular disease and many additional disease phenomena.

Effects of leptin and adiponectin on pancreatic β-cell function

Leptin and adiponectin are hormones secreted from adipocytes that have important roles in metabolism and energy homeostasis. This review evaluates the effects of leptin and adiponectin on β-cell function by analyzing and compiling results from human clinical trials and epidemiologic studies as well as in vitro and in vivo experiments. Leptin has been shown to inhibit ectopic fat accumulation and thereby prevent β-cell dysfunction and protect the β-cell from cytokine- and fatty acid-induced apoptosis. However, leptin suppresses insulin gene expression and secretion as well as glucose transport into the β-cell. Adiponectin stimulates insulin secretion by enhancing exocytosis of insulin granules and upregulating the expression of the insulin gene; however, this effect depends on the prevailing glucose concentration and status of insulin resistance. In addition, adiponectin has antiapoptotic properties in β-cells. Available evidence concerning the role of these adipokines on insulin secretion, insulin gene expression, and apoptosis is not always entirely consistent; and many fundamental questions remain to be answered by future studies.

Adiponectin (15-36) stimulates steroidogenic acute regulatory (StAR) protein expression and cortisol production in human adrenocortical cells: role of AMPK and MAPK kinase pathways

Adiponectin is an abundantly circulating adipokine, orchestrating its effects through two 7-transmembrane receptors (AdipoR1 and AdipoR2). Steroidogenesis is regulated by a variety of neuropeptides and adipokines. Earlier studies have reported adipokine mediated steroid production. A key rate-limiting step in steroidogenesis is cholesterol transportation across the mitochondrial membrane by steroidogenic acute regulatory protein (StAR). Several signalling pathways regulate StAR expression. The actions of adiponectin and its role in human adrenocortical steroid biosynthesis are not fully understood. The aim of this study was to investigate the effects of adiponectin on StAR protein expression, steroidogenic genes, and cortisol production and to dissect the signalling cascades involved in the activation of StAR expression. Using qRT-PCR, Western blot analysis and ELISA, we have demonstrated that stimulation of human adrenocortical H295R cells with adiponectin results in increased cortisol secretion. This effect is accompanied by increased expression of key steroidogenic pathway genes including StAR protein expression via ERK1/2 and AMPK-dependent pathways. This has implications for our understanding of adiponectin receptor activation and peripheral steroidogenesis. Finally, our study aims to emphasise the key role of adipokines in the integration of metabolic activity and energy balance partly via the regulation of adrenal steroid production. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Cytokines in the Progression of Pancreatic β-Cell Dysfunction

The dysfunction of pancreatic β-cell and the reduction in β-cell mass are the decisive events in the progression of type 2 diabetes. There is increasing evidence that cytokines play important roles in the procedure of β-cell failure. Cytokines, such as IL-1β, IFN-γ, TNF-α, leptin, resistin, adiponectin, and visfatin, have been shown to diversely regulate pancreatic β-cell function. Recently, islet-derived cytokine PANcreatic DERived factor (PANDER or FAM3B) has also been demonstrated to be a regulator of islet β-cell function. The change in cytokine profile in islet and plasma is associated with pancreatic β-cell dysfunction and apoptosis. In this paper, we summarize and discuss the recent studies on the effects of certain important cytokines on pancreatic β-cell function. The imbalance in deleterious and protective cytokines plays pivotal roles in the development and progression of pancreatic β-cell dysfunction under insulin-resistant conditions.