Effect of adiponectin on apoptosis: proapoptosis or antiapoptosis?

The mysterious association between adiponectin and endometriosis

Adiponectin is a pleiotropic cytokine predominantly derived from adipose tissue. In addition to its role in regulating energy metabolism, adiponectin may also be related to estrogen-dependent diseases, and many studies have confirmed its involvement in mediating diverse biological processes, including apoptosis, autophagy, inflammation, angiogenesis, and fibrosis, all of which are related to the pathogenesis of endometriosis. Although many researchers have reported low levels of adiponectin in patients with endometriosis and suggested that it may serve as a protective factor against the development of the disease. Therefore, the purpose of this review was to provide an up-to-date summary of the roles of adiponectin and its downstream cytokines and signaling pathways in the aforementioned biological processes. Further systematic studies on the molecular and cellular mechanisms of action of adiponectin may provide novel insights into the pathophysiology of endometriosis as well as potential therapeutic targets.

Protective effects of AdipoRon on the liver of Huoyan goose fed a high-fat diet

Adiponectin can participate in the regulation of glucose and lipid metabolism, energy regulation, immune response, resistance to inflammation, oxidative stress, and apoptosis. Studies in rodents demonstrated that the small molecule compound adiponectin receptor agonist AdipoRon could activate the adiponectin receptor and played the same biological role as adiponectin. To explore the influence and regulation of AdipoRon on lipid metabolism disorder in Huoyan goose liver, in this study, goslings were fed a high-fat diet and then administered different dosages of AdipoRon. Subsequently, goose body weight, liver index, liver histopathological changes, blood glucose, blood and liver lipid, biochemical indexes related to liver function and oxidative stress, and the expression levels of genes related to lipid metabolism, inflammation, apoptosis, and autophagy, adiponectin and its receptors, key molecules of adiponectin involved signal pathway, and transcription factors in the liver, were detected using H&E and Oil red O staining, ELISA, and qRT-PCR methods. The results indicated that AdipoRon could alter the expression of lipid metabolism-related genes, inflammatory factors, apoptosis and autophagy genes, and adiponectin and its receptor genes in liver tissues through signaling pathways such as AMPK and p38 MAPK, as well as the involvement of transcription factors such as PPARα, PPARγ, SIRT1, and FOXO1, reduce the lipid content in blood and liver tissues of geese fed high-fat diets, improve liver antioxidant capacity, regulate apoptosis and autophagy of hepatocytes, and reduce liver inflammatory injury. Our study suggests that AdipoRon has a protective effect on fatty liver injury in goslings fed a high-fat diet.

Adiponectin as Well as Compressive Forces Regulate in vitro β-Catenin Expression on Cementoblasts via Mitogen-Activated Protein Kinase Signaling Activation

We aimed to investigate the molecular effect that adiponectin exerts on cementoblasts especially in the presence of compressive forces. OCCM-30 cells (M. Somerman, NIH, NIDCR, United States) were used. Real-time reverse transcriptase–polymerase chain reaction (RT-PCR) and western blots were employed to verify if the mRNA and protein levels of adiponectin receptors (AdipoRs), mitogen-activated protein kinase (MAPK), and β-catenin signaling were influenced by compressive forces or adiponectin. Moreover, siRNAs targeting P38α, JNK1, ERK1, ERK2, and AdipoRs as well as pharmacological MAPK inhibition were performed. We found that compressive forces increase the expression of AdipoRs. Adiponectin and compression up-regulate P38α,JNK1, ERK1, and ERK2 as well as β-catenin gene expression. Western blots showed that co-stimuli activate the MAPK and β-catenin signaling pathways. MAPK inhibition alters the compression-induced β-catenin activation and the siRNAs targeting AdipoRs, P38α, and JNK1, showing the interaction of single MAPK molecules and β-catenin signaling in response to compression or adiponectin. Silencing by a dominantly negative version of P38α and JNK1 attenuates adiponectin-induced TCF/LEF reporter activation. Together, we found that light compressive forces activate β-catenin and MAPK signaling pathways. Adiponectin regulates β-catenin signaling principally by inactivating the GSK-3β kinase activity. β-Catenin expression was partially inhibited by MAPK blockade, indicating that MAPK plays a crucial role regulating β-catenin during cementogenesis. Moreover, adiponectin modulates GSK-3β and β-catenin mostly through AdipoR1. P38α is a key connector between β-catenin, TCF/LEF transcription, and MAPK signaling pathway.

AdipoRon promotes diabetic fracture repair through endochondral ossification-based bone repair by enhancing survival and differentiation of chondrocytes

Diabetic bone defects may exhibit impaired endochondral ossification (ECO) leading to delayed bone repair. AdipoRon, a receptor agonist of adiponectin polymers, can ameliorate diabetes and related complications, as well as overcome the disadvantages of the unstable structure of artificial adiponectin polymers. Here, the effects of AdipoRon on the survival and differentiation of chondrocytes in a diabetic environment were explored focusing on related mechanisms in gene and protein levels. In vivo, AdipoRon was applied to diet-induced-obesity (DIO) mice, a model of obesity and type 2 diabetes, with femoral fracture. Sequential histological evaluations and micro-CT were examined for further verification. We found that AdipoRon could ameliorate cell viability, apoptosis, and reactive oxygen species (ROS) production and promote mRNA expression of chondrogenic markers and cartilaginous matrix production of ATDC5 cells in high glucose medium via activating ERK1/2 pathway. Additionally, DIO mice with intragastric AdipoRon administration had more neocartilage and accelerated new bone formation. These data suggest that AdipoRon could stimulate bone regeneration via ECO in diabetes.

Adiponectin, Obesity, and Cancer: Clash of the Bigwigs in Health and Disease

Adiponectin is one of the most important adipocytokines secreted by adipocytes and is called a “guardian angel adipocytokine” owing to its unique biological functions. Adiponectin inversely correlates with body fat mass and visceral adiposity. Identified independently by four different research groups, adiponectin has multiple names; Acrp30, apM1, GBP28, and AdipoQ. Adiponectin mediates its biological functions via three known receptors, AdipoR1, AdipoR2, and T-cadherin, which are distributed throughout the body. Biological functions of adiponectin are multifold ranging from anti-diabetic, anti-atherogenic, anti-inflammatory to anti-cancer. Lower adiponectin levels have been associated with metabolic syndrome, type 2 diabetes, insulin resistance, cardiovascular diseases, and hypertension. A plethora of experimental evidence supports the role of obesity and increased adiposity in multiple cancers including breast, liver, pancreatic, prostrate, ovarian, and colorectal cancers. Obesity mediates its effect on cancer progression via dysregulation of adipocytokines including increased production of oncogenic adipokine leptin along with decreased production of adiponectin. Multiple studies have shown the protective role of adiponectin in obesity-associated diseases and cancer. Adiponectin modulates multiple signaling pathways to exert its physiological and protective functions. Many studies over the years have shown the beneficial effect of adiponectin in cancer regression and put forth various innovative ways to increase adiponectin levels.

High Glucose Concentration Impairs 5-PAHSA Activity by Inhibiting AMP-Activated Protein Kinase Activation and Promoting Nuclear Factor-Kappa-B-Mediated Inflammation

Recently, the endogenous fatty acid palmitic acid-5-hydroxystearic acid (5-PAHSA) was found to increase insulin sensitivity and have anti-inflammatory effects in mice with high-fat diet (HFD)-induced diabetes. However, it is unknown if 5-PAHSA affects glucose and lipid metabolism in db/db mice, which are characterized by extreme hyperglycemia. Here, we aim to determine the effect of continued 5-PAHSA administration on glucose and lipid metabolism in db/db mice. We also used 3T3-L1 cells and HepG2 cells to investigate the mechanism behind this effect. HepG2 cells and 3T3-L1 cells were induced to become models of insulin resistance. The models were used to test the effect of 5-PAHSA on insulin signaling. 5-PAHSA was administered orally to db/db mice for 1 month to assess its effects on glucose and lipid metabolism. We also exposed HepG2 cells to high glucose concentrations to investigate the influence on 5-PAHSA’s effects on hepatic lipid metabolism and inflammation. 5-PAHSA improved glucose uptake and insulin signaling in HepG2 cells and 3T3-L1 cells. However, after 1 month of treatment, 5-PAHSA did not reduce blood glucose levels, but increased inflammation and promoted fatty liver in db/db mice. In HepG2 cells under normal glucose conditions, 5-PAHSA treatment reduced lipogenesis and increased lipid oxidation. Notably, a high glucose concentration in cell media abolished the positive effects of 5-PAHSA treatment. These changes were associated with: decreased phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC); upregulation of sterol-regulatory element-binding protein 1c (SREBP1c), and fatty acid synthase (FAS); and downregulation of carnitine palmitoyltransferase 1 (CPT1). Besides, the anti-inflammatory effect of 5-PAHSA was also impaired by high glucose conditions. Thus, high glucose concentrations impaired 5-PAHSA action by inhibiting the AMPK signaling pathway and promoting nuclear factor-kappa-B (NF-κB) mediated inflammation.

Dual-therapy strategy for modification of adiponectin receptor signaling in aging-associated chronic diseases

Given the paradigm of anti-insulin resistance in therapies for metabolic syndrome, there has been considerable interest in adiponectin (APN), an adipocyte-derived sensitizer of insulin receptor signaling. In contrast to hypoadiponectinemia in metabolic syndrome, evidence suggests that Alzheimer's disease (AD) and other diseases, including chronic heart failure (CHF) and chronic kidney disease (CKD), are characterized by hyperadiponectinemia as well as the APN/obesity paradoxes, indicating that a decrease in APN might also be beneficial for these diseases. Thus, distinct from metabolic syndrome, it is anticipated that APN receptor antagonists rather than agonists might be effective in therapy for some chronic diseases.

The Activity of Adiponectin in Bone

The adipokine adiponectin affects multiple target tissues and plays important roles in glucose metabolism and whole-body energy homeostasis. Circulating adiponectin levels in obese people are lower than in non-obese, and increased serum adiponectin is associated with weight loss. Numerous clinical studies have established that fat mass is positively related to bone mass, a relationship that is maintained by communication between the two tissues through hormones and cytokines. Since adiponectin levels inversely correspond to fat mass, its bone effects and its potential contribution to the relationship between fat and bone have been investigated. In clinical observational studies, adiponectin was found to be negatively associated with bone mineral density, suggesting it might be a negative regulator of bone metabolism. In order to identify the mechanisms that underlie the activity of adiponectin in bone, a large number of laboratory studies in vitro and in animal models of mice over-expressing or deficient of adiponectin have been carried out. Results of these studies are not entirely congruent, partly due to variation among experimental systems and partly due to the complex nature of adiponectin signaling, which involves a combination of multiple direct and indirect mechanisms.

The impact of obesity and adiponectin signaling in patients with renal cell carcinoma: A potential mechanism for the "obesity paradox"

Although obesity increases the risk of renal cell carcinoma (RCC), obese patients with RCC experience longer survival than non-obese patients. However, the mechanism of this "obesity paradox" is unknown. We examined the impact of preoperative BMI, serum total adiponectin (sAd) level, total adiponectin secretion from perinephric adipose tissue, and intratumoral expression of adiponectin receptors on RCC aggressiveness and survival. We also investigated the mechanism underlying enhanced cancer aggressiveness in RCC cells stimulated with exogenous adiponectin. Overweight and obese patients had significantly lower grade cancers than normal patients in all patients and in those without metastasis (p = 0.003 and p = 0.027, respectively). Cancer-specific survival was significantly longer in overweight and obese patients than in normal patients in all patients (p = 0.035). There was a weak inverse correlation between sAd level and BMI in RCC patients (r = -0.344, p = 0.002). Tumor size was slightly correlated with sAd level, and high sAd was significantly associated with poor overall survival rates in patients with non-metastatic RCC (p = 0.035). Adiponectin levels in perinephric adipose tissue and intratumoral AdipoR1/R2 expression were not correlated with RCC aggressiveness or survival. Proliferation significantly increased in 786-O and Caki-2 cells exposed to exogenous adiponectin, whereas cell invasion and migration were unaffected. In addition, exogenous adiponectin significantly inhibited starvation- and metformin-induced apoptosis, and up-regulated p-AMPK and Bcl-xL levels. In summary, low BMI and high adiponectin levels are associated with aggressive cell behaviors and poor survival in surgically-treated RCC patients. The effects of adiponectin on proliferation and apoptosis might underlie the "obesity paradox" of RCC.

Effect of gamma-carboxylase inhibition on serum osteocalcin may be partially protective against developing diabetic cardiomyopathy in type 2 diabetic rats

AIMS

To investigate the possible protective effect of elevated undercarboxylated osteocalcin on diabetic cardiomyopathy mechanisms and risk factors.

METHODS

In all, 32 male rats were divided into four groups: control, diabetic, diabetic warfarin and normal warfarin-treated groups. Isolated heart functions were assessed; fasting serum insulin, glucose and glycosylated haemoglobin, homeostasis model assessment insulin resistance and lipid profile were investigated. Serum undercarboxylated osteocalcin and adiponectin were also measured. In cardiac tissue, malondialdehyde content, acyl-CoA dehydrogenase gene expression, Bax/Bcl2 ratio, sarcoendoplasmic reticulum calcium ATPase and osteocalcin receptor (G protein-coupled receptor family C group 6 member A) genes expression were investigated.

RESULTS

Prophylactic elevation of undercarboxylated osteocalcin was accompanied by improved insulin sensitivity and lipid profile, increased serum adiponectin, upregulated myocardial osteocalcin receptor with preserved left ventricular function, decreased cardiac malondialdehyde content, acyl-CoA dehydrogenase and Bax/Bcl2 ratio.

CONCLUSION

Undercarboxylated osteocalcin was suggested to have protective effects against diabetic cardiomyopathy, possibly through direct action on upregulated G protein-coupled receptor family C group 6 member A and indirectly via adiponectin. These effects may be mediated through antagonizing oxidative stress and apoptosis.

A live-cell, high-content imaging survey of 206 endogenous factors across five stress conditions reveals context-dependent survival effects in mouse primary beta cells

AIMS/HYPOTHESIS

Beta cell death is a hallmark of diabetes. It is not known whether specific cellular stresses associated with type 1 or type 2 diabetes require specific factors to protect pancreatic beta cells. No systematic comparison of endogenous soluble factors in the context of multiple pro-apoptotic conditions has been published.

METHODS

Primary mouse islet cells were cultured in conditions mimicking five type 1 or type 2 diabetes-related stresses: basal 5 mmol/l glucose, cytokine cocktail (25 ng/ml TNF-α, 10 ng/ml IL-1β, 10 ng/ml IFN-γ), 1 μmol/l thapsigargin, 1.5 mmol/l palmitate and 20 mmol/l glucose (all in the absence of serum). We surveyed the effects of a library of 206 endogenous factors (selected based on islet expression of their receptors) on islet cell survival through multi-parameter, live-cell imaging.

RESULTS

Our survey pointed to survival factors exhibiting generalised protective effects across conditions meant to model different types of diabetes and stages of the diseases. For example, our survey and follow-up experiments suggested that OLFM1 is a novel protective factor for mouse and human beta cells across multiple conditions. Most strikingly, we also found specific protective survival factors for each model stress condition. For example, semaphorin4A (SEMA4A) was toxic to islet cells in the serum-free baseline and serum-free 20 mmol/l glucose conditions, but protective in the context of lipotoxicity. Rank product testing supported the consistency of our observations.

CONCLUSIONS/INTERPRETATION

Collectively, our survey reveals previously unidentified islet cell survival factors and suggest their potential utility in individualised medicine.

Cinnabar-induced subchronic renal injury is associated with increased apoptosis in rats

The aim of this study was to explore the role of apoptosis in cinnabar-induced renal injury in rats. To test this role, rats were dosed orally with cinnabar (1 g/kg/day) for 8 weeks or 12 weeks, and the control rats were treated with 5% carboxymethylcellulose solution. Levels of urinary mercury (UHg), renal mercury (RHg), serum creatinine (SCr), and urine kidney injury molecule 1 (KIM-1) were assessed, and renal pathology was analyzed. Apoptotic cells were identified and the apoptotic index was calculated. A rat antibody array was used to analyze expression of cytokines associated with apoptosis. Results from these analyses showed that UHg, RHg, and urine KIM-1, but not SCr, levels were significantly increased in cinnabar-treated rats. Renal pathological changes in cinnabar-treated rats included vacuolization of tubular cells, formation of protein casts, infiltration of inflammatory cells, and increase in the number of apoptotic tubular cells. In comparison to the control group, expression of FasL, Fas, TNF-α, TRAIL, activin A, and adiponectin was upregulated in the cinnabar-treated group. Collectively, our results suggest that prolonged use of cinnabar results in kidney damage due to accumulation of mercury and that the underlying mechanism involves apoptosis of tubular cells via a death receptor-mediated pathway.

Adiponectin inhibits murine pancreatic cancer growth

BACKGROUND

Adiponectin is an adipose tissue-derived secretory hormone whose plasma concentrations are lower in obese individuals. Obesity is a risk factor for the development and growth of pancreatic cancer, and hypoadiponectinemia was suggested to be involved in the growth of Pan02 murine pancreatic cancer cells that were inoculated into the flanks of congenitally obese mice.

AIM

The aim of this study was to clarify the role of adiponectin in the growth of pancreatic cancer cells.

METHODS

We examined the effect of adiponectin on the growth of Pan02 cells using recombinant adiponectin and adiponectin knockout mice.

RESULTS

The in vitro treatment of Pan02 cells with adiponectin inhibited cellular proliferation that was accompanied by increased apoptosis and caspase-3 and caspase-7 activities. Transplantation of Pan02 cells into the pancreas of knockout mice resulted in a larger tumor volume with fewer terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells compared with wild-type mice.

CONCLUSIONS

The results indicate that adiponectin directly suppresses the proliferation of Pan02 cells.

Impact of serum omentin-1 levels on cardiac prognosis in patients with heart failure

Background

Various adipokines are reported to be associated with the development of heart failure (HF) through insulin resistance and chronic inflammation. Omentin-1 is a novel adipokine and is associated with incident coronary artery disease. However, it remains unclear whether serum omentin-1 levels are associated with cardiac prognosis in patients with HF.

Methods

We measured serum omentin-1 levels at admission in 136 consecutive patients with HF, and 20 control subjects without signs of significant heart disease. We prospectively followed patients with HF to endpoints of cardiac death or re-hospitalization for worsening HF.

Results

Serum omentin-1 levels were markedly lower in HF patients with cardiac events compared with to without. The patients who were in New York Heart Association (NYHA) functional class IV showed significantly lower serum omentin-1 levels compared to those in class II and III, whereas serum omentin-1 levels did not correlate with serum brain natriuretic peptide levels (r = 0.217, P = 0.011). We divided the HF patients into three groups based on the tertiles of serum omentin-1 level (low T1, middle T2, and high T3). Multivariate Cox hazard analysis showed that the lowest serum omentin-1 level (T1) was independently associated with cardiac events after adjustment for confounding factors (hazard ratio 5.78, 95% confidence interval 1.20-12.79). We divided the HF patients into two groups according to the median serum omentin-1 levels. Kaplan-Meier analysis revealed that the patients with low serum omentin-1 levels had a higher risk of cardiac events compared with those with high serum omentin-1 levels (log-rank test p < 0.001).

Conclusion

Decreased serum omentin-1 levels were associated with a poor cardiac outcome in patients with HF.

Lactation driven dynamics of adiponectin supply from different fat depots to circulation in cows

Adipose tissue (AT) depots are heterogeneous in terms of morphology and adipocyte metabolism. Adiponectin, one of the most abundant adipokines, is known for its insulin sensitizing effects and its role in glucose and lipid metabolism. Little is known about the presence of adiponectin protein in visceral (vc) and subcutaneous (sc) AT depots. We assessed serum adiponectin and adiponectin protein concentrations and the molecular weight forms in vc (mesenterial, omental, and retroperitoneal) and sc (sternum, tail-head, and withers) AT of primiparous dairy cows during early lactation. Primiparous German Holstein cows (n = 25) were divided into a control (CON) and a conjugated linoleic acid (CLA) group. From day 1 of lactation until slaughter, CLA cows were fed 100 g of a CLA supplement/d (approximately 6% of cis-9, trans-11 and trans-10, cis-12 isomers each), whereas the CON cows received 100 g of a fatty acid mixture/d instead of CLA. Blood samples from all animals were collected from 3 wk before calving until slaughter on day 1 (n = 5, CON cows), 42 (n = 5 each of CON and CLA cows), and 105 (n = 5 each of CON and CLA cows) of lactation when samples from different AT depots were obtained. Adiponectin was measured in serum and tissue by ELISA. In all AT depots adiponectin concentrations were lowest on day 1 than on day 42 and day 105, and circulating adiponectin reached a nadir around parturition. Retroperitoneal AT had the lowest adiponectin concentrations; however, when taking total depot mass into consideration, the portion of circulating adiponectin was higher in vc than sc AT. Serum adiponectin was positively correlated with adiponectin protein concentrations but not with the mRNA abundance in all fat depots. The CLA supplementation did not affect adiponectin concentrations in AT depots. Furthermore, inverse associations between circulating adiponectin and measures of body condition (empty body weight, back fat thickness, and vc AT mass) were observed. In all AT depots at each time, adiponectin was present as high (approximately 300 kDa) and medium (approximately 150 kDa) molecular weight complexes similar to that of the blood serum. These data suggest differential contribution of AT depots to circulating adiponectin.

Adiponectin attenuates osteolysis in aseptic loosening of total hip replacements

Joint replacements have a longer durability in patients with high serum levels of adiponectin (APN) than in patients with low levels. We aimed to characterize the unknown pathophysiological effects of APN on wear particle-induced inflammation, apoptosis and osteolysis. Immunohistochemistry was performed to detect APN, its receptors and apoptosis in patients with and without aseptic loosening. Additionally, APN knockout mouse studies and pharmacological intervention of APN were performed in an established calvarial mouse model. Osteolysis and inflammation were quantified by histomorphometry and microcomputed tomography, apoptosis by immunohistochemistry and TUNEL assay. In a cell culture model, human monocyte-derived macrophages were incubated with or without metal wear debris particles and partially treated with APN. Expression of APN, AdipoR1 and calreticulin in specimens from patients with aseptic loosening were significantly higher than in patients without aseptic loosening. Administration of APN in mice significantly reduced wear particle-induced inflammation, osteolysis and the number of caspase-3-positive macrophages. The cell culture model showed that APN leads to significantly lower values of TNF-α. These findings support a prominent role of APN in the development of particle-induced osteolysis and APN may be therapeutically useful in patients with aseptic loosening.

Identification of adiponectin receptor agonist utilizing a fluorescence polarization based high throughput assay

Adiponectin, the adipose-derived hormone, plays an important role in the suppression of metabolic disorders that can result in type 2 diabetes, obesity, and atherosclerosis. It has been shown that up-regulation of adiponectin or adiponectin receptor has a number of therapeutic benefits. Given that it is hard to convert the full size adiponectin protein into a viable drug, adiponectin receptor agonists could be designed or identified using high-throughput screening. Here, we report on the development of a two-step screening process to identify adiponectin agonists. First step, we developed a high throughput screening assay based on fluorescence polarization to identify adiponectin ligands. The fluorescence polarization assay reported here could be adapted to screening against larger small molecular compound libraries. A natural product library containing 10,000 compounds was screened and 9 hits were selected for validation. These compounds have been taken for the second-step in vitro tests to confirm their agonistic activity. The most active adiponectin receptor 1 agonists are matairesinol, arctiin, (-)-arctigenin and gramine. The most active adiponectin receptor 2 agonists are parthenolide, taxifoliol, deoxyschizandrin, and syringin. These compounds may be useful drug candidates for hypoadiponectin related diseases.

Adipokine adiponectin is a potential protector to human bronchial epithelial cell for regulating proliferation, wound repair and apoptosis: comparison with leptin and resistin

Epidemiological data indicate an increasing incidence of asthma in the obese individuals recent decades, while very little is known about the possible association between them. Here, we compared the roles of adipocyte-derived factors, including leptin, adiponectin and resistin on proliferation, wound repair and apoptosis in human bronchial epithelial cells (HBECs) which play an important role in the pathogenesis of asthma. The results showed that exogenous globular adiponectin (gAd) promoted proliferation, cell-cycle and wound repair of HBECs. This effect may be relevant to Ca(2+)/calmodulin signal pathway. Besides, gAd inhibited apoptosis induced by ozone and release of lactate dehydrogenase (LDH) of HBECs via regulated adipoR1 and reactive oxygen species. No effects of leptin or resistin on proliferation, wound repair and apoptosis of HBECs were detectable. These data indicate that airway epithelium is the direct target of gAd which plays an important role in protecting HBECs from mechanical or oxidant injuries and may have therapeutic implications in the treatment of asthma.

Adiponectin and its receptors in preimplantation embryo development

Adiponectin can play an important role in regulating the female reproductive function and embryo development and can affect the embryo at very early stages of pregnancy--during the preimplantation period. Disturbances in the maternal adiponectin system are associated with several diseases, including diabetes type 2, obesity, and some female reproductive disorders. Adiponectin receptors are expressed in oocytes and preimplantation embryos and can be activated by adiponectin produced by maternal adipose tissue or organs of the female reproductive tract. Adiponectin can affect proliferation and survival of cells in preimplantation embryos, and these effects are isoform dependent. Experimental results suggest involvement of various protein kinases, including mitogen-activated protein kinases, in the regulation of these processes by adiponectin. Actions of adiponectin on lipid and glucose metabolism can increase the energy supply to the embryo, and final targets of adiponectin signaling are metabolic enzymes, glucose transporters, and fatty acid transporters. The involvement of several signaling molecules, such as AMPK/PRKA, PI3K, or AKT/PKB, in the regulation of metabolic processes by adiponectin has been demonstrated in preimplantation embryos. In summary, adiponectin produced in an endocrine/paracrine/autocrine manner can significantly influence preimplantation embryo development, uterine receptivity, and embryo implantation.

Globular domain of adiponectin: promising target molecule for detection of atherosclerotic lesions

BACKGROUND

Adiponectin, an adipocyte-specific plasma protein, has been shown to accumulate in injured endothelial cells during development of atherosclerotic lesions. In this study, we investigated the potential of different adiponectin subfractions with special emphasis on globular adiponectin (gAd) to recognize and visualize atherosclerotic lesions.

METHODS

Recombinant mouse gAd and subfractions of full-length adiponectin (ie, trimeric, hexameric, and oligomeric forms) were fluorescence-labeled. Aortas of wild-type and apoprotein E-deficient mice fed a high cholesterol diet were dissected and incubated with the labeled biomarkers. Imaging was performed using confocal laser scanning microscopy.

RESULTS

Confocal laser scanning microscopic images showed that gAd binds more strongly to atherosclerotic plaques than full-length adiponectin subfractions. Further, we showed that gAd accumulates preferentially in endothelial cells and the fibrous cap area of plaques. Here we demonstrate for the first time that gAd recognizes atherosclerotic plaques on aortic sections of apoprotein E-deficient mice.

CONCLUSION

These results suggest that gAd, in addition to its physiological properties, is also suitable as a target molecule for prospective diagnostic strategies in imaging atherosclerotic lesions.

Adiponectin and breast cancer

Adiponectin, an adipose tissue-derived hormone, has been studied intensively for the past decade because of its anti-inflammatory, anti-atherogenic, and anti-diabetic properties. Recent advances suggest that adiponectin also plays an important role in the development and progression of various cancers, especially obesity-related cancers. In this review, the authors focus on the potential role of adiponectin in breast cancer, an obesity- and endocrine-associated tumor. Epidemiological studies have shown that plasma adiponectin level is a risk factor for breast cancer in post-menopausal women. Adiponectin and its receptors are expressed on both breast cancer line cells and tumor tissues. Furthermore, exogenous adiponectin has exhibited therapeutic potential in animal models. Underlying mechanisms include the inhibition of cell proliferation and promotion of apoptosis, the regulation of tumorigenic-related factors, and the suppression of angiogenesis. The signaling pathways linking adiponectin with tumorigenesis might provide potential drug targets for the future. However, more convincing evidence is needed to fully elucidate the exact role of adiponectin in breast cancer, since both its beneficial effects and possible mechanisms remain controversial.

Adiponectin and breast cancer

Adiponectin, an adipose tissue-derived hormone, has been studied intensively for the past decade because of its anti-inflammatory, anti-atherogenic, and anti-diabetic properties. Recent advances suggest that adiponectin also plays an important role in the development and progression of various cancers, especially obesity-related cancers. In this review, the authors focus on the potential role of adiponectin in breast cancer, an obesity- and endocrine-associated tumor. Epidemiological studies have shown that plasma adiponectin level is a risk factor for breast cancer in post-menopausal women. Adiponectin and its receptors are expressed on both breast cancer line cells and tumor tissues. Furthermore, exogenous adiponectin has exhibited therapeutic potential in animal models. Underlying mechanisms include the inhibition of cell proliferation and promotion of apoptosis, the regulation of tumorigenic-related factors, and the suppression of angiogenesis. The signaling pathways linking adiponectin with tumorigenesis might provide potential drug targets for the future. However, more convincing evidence is needed to fully elucidate the exact role of adiponectin in breast cancer, since both its beneficial effects and possible mechanisms remain controversial.