Regulation of globular adiponectin-induced apoptosis by reactive oxygen/nitrogen species in RAW264 macrophages

Adiponectin Ameliorates Hyperglycemia-Induced Retinal Endothelial Dysfunction, Highlighting Pathways, Regulators, and Networks

Background

The pathophysiology of diabetic retinopathy (DR) is multifaced. A low level of circulating adiponectin (APN) in type 2 diabetes is associated with microvasculature complications, and its role in the evolution of DR is complex.

Aim

This study is designed to explore the potential impact of APN in the pathogenesis of DR, linking the changes in cellular and biological processes with the pathways, networks, and regulators involved in its actions.

Methods

Human microvascular retinal endothelial cells (HMRECs) were exposed to 30mM glucose (HG) and treated with globular adiponectin (30μg/mL) for 24 hours. The cells were evaluated for reactive oxidative stress (ROS) and apoptosis. RT-PCR profile arrays were utilized to evaluate the profile of genes involved in endothelial functions, angiogenesis, extracellular matrix, and adhesion molecules for hyperglycemic HMRECs treated with adiponectin. In addition, the barrier function, leukocyte migration, and angiogenesis were evaluated. The differential expressed genes (DEGs) were outlined, and bioinformatic analysis was applied.

Results

Adiponectin suppresses ROS production and apoptosis in HMRECs under HG conditions. Adiponectin improved migration and barrier functions in hyperglycemic cells. The bioinformatic analysis highlighted that the signaling pathways of integrin, HMGB1, and p38 AMPK, are mainly involved in the actions of APN on HMRECs. APN significantly affects molecular functions, including the adhesion of cells, chemotaxis, migration of WBCs, and angiogenesis. STAT3, NFKB, IKBKB, and mir-8 are the top upstream regulators, which affect the expressions of the genes of the data set, while TNF and TGFB1 are the top regulators.

Conclusion

Adiponectin significantly counteracts hyperglycemia at various cellular and molecular levels, reducing its impact on the pathophysiological progression towards DR in vitro using HMRECs. Adiponectin ameliorates inflammatory response, oxidative stress, and endothelial barrier dysfunction using a causal network of NFBk complex, TNF, and HMGB1 and integrin pathways.

C1q/tumour necrosis factor-related protein-9 aggravates lipopolysaccharide-induced inflammation via promoting NLRP3 inflammasome activation

The NLRP3 inflammasome plays a vital role in inflammation by increasing the maturation of interleukin-1β (IL-1β) and promoting pyroptosis. Given that C1q/tumour necrosis factor-related protein-9 (CTRP9) has been shown to be involved in diverse inflammatory diseases, we sought to assess the underlying impact of CTRP9 on NLRP3 inflammasome activation. In vitro, macrophages isolated from murine peritonea were stimulated with exogenous CTRP9, followed by lipopolysaccharide (LPS) and adenosine 5'-triphosphate (ATP). We demonstrated that CTRP9 markedly augmented the activation of the NLRP3 inflammasome, as shown by increased mature IL-1β secretion, triggering ASC speck formation and promoting pyroptosis. Mechanistically, CTRP9 increased the levels of NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS). Suppressing ROS with N-acetylcysteine (NAC) or interfering with NOX2 by small interfering RNA weakened the promoting effect of CTRP9 on the NLRP3 inflammasome. Furthermore, NLRP3 inflammasome activation, pyroptosis and secretion of mature IL-1β were significantly decreased in macrophages from CTRP9-KO mice compared to those from WT mice with the same treatment. In vivo, we established a sepsis model by intraperitoneal injection of LPS into WT and CTRP9-KO mice. CTRP9 knockout improved the survival rates of the septic mice and attenuated NLRP3 inflammasome-mediated inflammation. In conclusion, our study indicates that CTRP9 aggravates LPS-induced inflammation by promoting NLRP3 inflammasome activation via the NOX2/ROS pathway. CTRP9 could be a promising target for NLRP3 inflammasome-driven inflammatory diseases.

Association of Adipose Tissue and Adipokines with Development of Obesity-Induced Liver Cancer

Obesity is rapidly dispersing all around the world and is closely associated with a high risk of metabolic diseases such as insulin resistance, dyslipidemia, and nonalcoholic fatty liver disease (NAFLD), leading to carcinogenesis, especially hepatocellular carcinoma (HCC). It results from an imbalance between food intake and energy expenditure, leading to an excessive accumulation of adipose tissue (AT). Adipocytes play a substantial role in the tumor microenvironment through the secretion of several adipokines, affecting cancer progression, metastasis, and chemoresistance via diverse signaling pathways. AT is considered an endocrine organ owing to its ability to secrete adipokines, such as leptin, adiponectin, resistin, and a plethora of inflammatory cytokines, which modulate insulin sensitivity and trigger chronic low-grade inflammation in different organs. Even though the precise mechanisms are still unfolding, it is now established that the dysregulated secretion of adipokines by AT contributes to the development of obesity-related metabolic disorders. This review focuses on several obesity-associated adipokines and their impact on obesity-related metabolic diseases, subsequent metabolic complications, and progression to HCC, as well as their role as potential therapeutic targets. The field is rapidly developing, and further research is still required to fully understand the underlying mechanisms for the metabolic actions of adipokines and their role in obesity-associated HCC.

ER stress contributes to autophagy induction by adiponectin in macrophages: Implication in cell survival and suppression of inflammatory response

Adiponectin, the most abundant adipokine, exhibits various physiological functions. In addition to its critical role in lipid metabolism, recent studies have demonstrated its potent anti-inflammatory and cytoprotective properties. Accumulating evidence suggests that autophagy plays a critical role in various biological responses by adiponectin. However, the underlying mechanisms remain elusive. Herein, we investigated the role of ER stress in adiponectin-induced autophagy and its functional roles in biological responses by adiponectin in macrophages. In this study, globular adiponectin (gAcrp) significantly increased the expression of various ER stress markers in both RAW 264.7 and primary peritoneal macrophages. In addition, inhibition of ER stress by treatment with tauroursodeoxycholic acid (TUDCA) or gene silencing of CHOP prominently suppressed gAcrp-induced autophagy. Treatment with gAcrp also induced significant increase in sestrin2 expression. Interestingly, knockdown of sestrin2 prevented autophagy induction and inhibition of ER stress abrogated sestrin2 induction by gAcrp, collectively implying that ER stress critically contributes to gAcrp-induced autophagy activation via sestrin2 induction. Moreover, pretreatment with TUDCA restored suppression of TNF-α and IL-1β expression and attenuated the enhanced viability of macrophages induced by gAcrp. Taken together, these findings indicate the potential role of ER stress in autophagy activation, modulation of inflammatory responses, and cell survival by gAcrp in macrophages.

CTRP9 induces iNOS expression through JAK2/STAT3 pathway in Raw 264.7 and peritoneal macrophages

The C1q tumor necrosis factor (TNF)-related proteins 9 (CTRP9), an adipocyte-derived cytokine, affects a number of physiological processes, including immune function and inflammation. We investigated whether CTRP9 affects the expression of inflammation-related genes in Raw 264.7 and peritoneal macrophages. The CTRP9-induced expression of iNOS increased in a time- and dose-dependent manner. LPS and CTRP9 promote the expression of iNOS jointly in Raw 264.7 and peritoneal macrophages. CTRP9 induced the phosphorylation of JAK2 and STAT3 in Raw 264.7 and peritoneal macrophages. VX509 (JAK2 inhibitor) reduced the CTRP9-induced iNOS protein production. In addition, the CTRP9-induced phosphorylation of JAK2 and STAT3 was dramatically reduced by VX509. Collectively, these results suggest that JAK2/STAT3 signaling is involved in the CTRP9-induced expression of iNOS.

The anti-proliferative effects of adiponectin on human lung adenocarcinoma A549 cells and oxidative stress involvement

Adiponectin (Acrp30) plays an important role in energy metabolism and inflammation. Recently, in vivo serum Acrp30 levels have been reported to be correlated to risk of developing several types of cancers such as lung cancer, and in vitro studies have demonstrated a role for Acrp30 in the control of cell proliferation and survival. However, the molecular effects of Acrp30 on lung cancer have not yet been clearly defined. In the present study, we investigated the effects of different concentrations of Acrp30 on the A549 human alveolar epithelial cell line, an in vitro model of lung adenocarcinoma. A549 cells were exposed to various concentrations of Acrp30 and successively, proliferation, apoptosis and oxidative stress were evaluated by MTT test, caspase activity assay, flow-cytometry and western blotting analysis. Our results demonstrated that Acrp30 causes, in a time- and dose-dependent manner, a reduction of cell viability and duplication together with an increase in cell apoptosis rate. In addition, we found that Acrp30 induces an increase of lipid peroxidation evaluated by TBARS assay and a concomitant reduction of nitric oxide release, both markers of cellular oxidative stress. Taken together, our data on A549 cells provides new insight into potential involvement of Acrp30 on physio-pathologic mechanisms of lung diseases through interference with proliferation, apoptosis and oxidative status.

Down Syndrome, Obesity, Alzheimer's Disease, and Cancer: A Brief Review and Hypothesis

Down syndrome (trisomy 21), a complex mix of physical, mental, and biochemical issues, includes an increased risk of Alzheimer’s disease and childhood leukemia, a decreased risk of other tumors, and a high frequency of overweight/obesity. Certain features related to the third copy of chromosome 21 (which carries the APP gene and several anti-angiogenesis genes) create an environment favorable for Alzheimer’s disease and unfavorable for cancer. This environment may be enhanced by two bioactive compounds from fat cells, leptin, and adiponectin. This paper outlines these fat-related disease mechanisms and suggests new avenues of research to reduce disease risk in Down syndrome.

Comparison of Serum Adiponectin in Smoke-induced Pulmonary Emphysema Rats Fed Different Diets

BACKGROUND

Smoking and body mass index (BMI) are the key risk factors for chronic obstructive pulmonary disease (COPD). Adiponectin with both anti-inflammatory and pro-inflammatory properties is a vital modulator of inflammatory processes, which is expressed in epithelial cells in the airway in COPD-emphysema. The aim of this study was to examine the effects of adiponectin on tobacco smoke-induced emphysema in rats, which were fed different diets.

METHODS

Seventy-six adult (6-8 weeks old) male Sprague-Dawley rats (average weight 220 ± 20 g) were exposed to smoke or smoke-free room atmosphere and fed different diets (regular, high-fat, or low-fat diets) for 6 months. The rats were randomly divided into six groups. They are nonsmoke-exposed regular diet (n = 10), nonsmoke-exposed high-fat diet (n = 14), nonsmoke-exposed low-fat diet (n = 14), smoke-exposed regular diet (n = 10), smoke-exposed high-fat diet (n = 14), and smoke-exposed low-fat diet groups (n = 14). A full 2 3 factorial design was used to evaluate the effect of independent variables on smoke exposure and different rearing methods. Serum adiponectin and inflammatory cytokines were measured by the enzyme-linked immunosorbent assay (ELISA).

RESULTS

Serum adiponectin levels in rats fed low-fat and regular diets exposed to smoke exposure were remarkably higher than that of rats exposed to room air while serum adiponectin levels of fat-rich diet rats exposed to tobacco smoke were lower than that of rats exposed to room air. Compared with regular diet or low-fat diet group, serum adiponectin levels in high-fat diet rats exposed to tobacco smoke were lower (t = 6.932, 11.026; all P < 0.001). BMI was inversely correlated with serum adiponectin levels (r = -0.751, P = 0.012). Serum interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and 4-hydroxy 2-nonenal (HNE) levels in rats exposed to low-fat or fat-rich diets were remarkably higher than that of rats exposed to normal diets (IL-6, t = 4.196, 3.480; P < 0.01, P = 0.001; TNF-α, t = 4.286, 3.521; P < 0.01, P = 0.001; 4-HNE, t = 4.298, 4.316; all P < 0.001). In nonhigh-fat diet rats exposed to tobacco smoke, serum adiponectin levels correlated positively with serum IL-6, TNF-α, and 4-HNE, bronchoalveolar lavage cell count, and mean linear intercept. In contrast, in high-fat diet rats, serum adiponectin levels correlated inversely with these parameters.

CONCLUSIONS

In smoke-induced emphysema and fat-rich diet rat model, serum adiponectin level was decreased, and the anti-inflammatory effect was attenuated. By contrast, nonhigh-fat diet elevated serum adiponectin and enhanced the role of pro-inflammatory.

Different forms of adiponectin reduce the apoptotic and damaging effect of cigarette smoke extract on human bronchial epithelial cells

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease, in which adiponectin may serve an important role. The present study investigated the role of adiponectin in the apoptotic and damaging effect of cigarette smoke extract (CSE) on human bronchial epithelial cells (16HBECs). An MTT assay showed that CSE significantly inhibited the proliferation of 16HBECs (F=1808.88, P<0.01). The 16HBECs were treated with different concentrations of high molecular weight (HMW) adiponectin and globular domain (gAd) adiponectin and it was observed that HMW and gAd dose-dependently inhibited the expression of tumor necrosis factor (TNF)-α and interleukin (IL)-8, and the generation of 4-hydroxy-nonenal and reactive oxygen species (ROS) in 16HBECs, thereby blocking the upregulating effect of CSE on these factors. However, the inhibitory effect of gAd on TNF-α and IL-8 expression was stronger compared with that of HMW, but the suppressing effect of HMW on ROS production was superior compared with that of gAd. Further testing of apoptosis indicated that CSE and HMW promoted the apoptosis of 16HBECs. However, such effects of HMW declined with an increase in concentration. In contrast, gAd showed an inhibitory effect on apoptosis and inhibited the occurrence of CSE-induced apoptosis in a dose-dependent manner. Therefore, the present study demonstrated that different forms of adiponectin may have different mechanisms of action, suggesting that further exploration of their effects may open a new avenue for the treatment of COPD.

Modulation of Cell Death and Survival by Adipokines in the Liver

Adipokines, hormones predominantly produced from adipose tissue, have been shown to impart dynamic functions in the liver. Emerging evidence has shown that adipokines are also involved in modulating liver cell survival and/or death. Among the various adipokines, adiponectin and leptin directly regulate proliferation of hepatocytes, Kupffer cells, and hepatic stellate cells. Moreover, these adipokines control apoptosis and cell cycle of hepatic cancer cells in a complex manner. Adiponectin possesses both pro- and anti-proliferative properties, whereas leptin appears to play roles as a pro-survival hormone. Recent studies have revealed that regulation of cell death and proliferation is one of the critical factors regulating liver physiology by adipokines. In this review, we summarize the effects of adipokines on apoptosis and survival of liver cells and also demonstrate their implications in regulating various liver functions and decipher the underlying molecular mechanisms.

Globular adiponectin inhibits ethanol-induced reactive oxygen species production through modulation of NADPH oxidase in macrophages: involvement of liver kinase B1/AMP-activated protein kinase pathway

Adiponectin, an adipokine predominantly secreted from adipocytes, has been shown to play protective roles against chronic alcohol consumption. Although excessive reactive oxygen species (ROS) production in macrophages is considered one of the critical events for ethanol-induced damage in various target tissues, the effect of adiponectin on ethanol-induced ROS production is not clearly understood. In the present study, we investigated the effect of globular adiponectin (gAcrp) on ethanol-induced ROS production and the potential mechanisms underlying these effects of gAcrp in macrophages. Here we demonstrated that gAcrp prevented ethanol-induced ROS production in both RAW 264.7 macrophages and primary murine peritoneal macrophages. Globular adiponectin also inhibited ethanol-induced activation of NADPH oxidase. In addition, gAcrp suppressed ethanol-induced increase in the expression of NADPH oxidase subunits, including Nox2 and p22(phox), via modulation of nuclear factor-κB pathway. Furthermore, pretreatment with compound C, a selective inhibitor of AMPK, or knockdown of AMPK by small interfering RNA restored suppression of ethanol-induced ROS production and Nox2 expression by gAcrp. Finally, we found that gAcrp treatment induced phosphorylation of liver kinase B1 (LKB1), an upstream signaling molecule mediating AMPK activation. Knockdown of LKB1 restored gAcrp-suppressed Nox2 expression, suggesting that LKB1/AMPK pathway plays a critical role in the suppression of ethanol-induced ROS production and activation of NADPH oxidase by gAcrp. Taken together, these results demonstrate that globular adiponectin prevents ethanol-induced ROS production, at least in part, via modulation of NADPH oxidase in macrophages. Further, LKB1/AMPK axis plays an important role in the suppression of ethanol-induced NADPH oxidase activation by gAcrp in macrophages.

Angiotensin II and canonical transient receptor potential-6 activation stimulate release of a signal transducer and activator of transcription 3-activating factor from mouse podocytes

Previous studies have shown that the transcription factor signal transducer and activator of transcription-3 (STAT3) in podocytes plays an important role in progression of HIV nephropathy and in collapsing forms of glomerulonephritis. Here, we have observed that application of 100 nM angiotensin II (Ang II) to cultured podocytes for 6-24 hours causes a marked increase in the phosphorylation of STAT3 on tyrosine Y705 but has no effect on phosphorylation at serine S727. By contrast, Ang II treatment of short periods (20-60 minutes) caused a small but consistent suppression of tyrosine phosphylation of STAT3. A similar biphasic effect was seen after treatment with the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol (OAG), an agent that causes activation of Ca(2+)-permeable canonical transient receptor potential-6 (TRPC6) channels in podocytes. The stimulatory effects of Ang II on STAT3 phosphorylation were abolished by small-interfering RNA knockdown of TRPC6 and also by inhibitors of the Ca(2+)-dependent downstream enzymes calcineurin and Ca(2+)-calmodulin-dependent protein kinase II. The stimulatory effects of Ang II appear to be mediated by secretion and accumulation of an unknown factor into the surrounding medium, as they are no longer detected when medium is replaced every 2 hours even if Ang II is continuously present. By contrast, the inhibitory effect of Ang II on STAT3 phosphorylation persists with frequent medium changes. Experiments with neutralizing and inhibitory antibodies suggest that the STAT3 stimulatory factor secreted from podocytes is not interleukin-6, but also suggest that this factor exerts its actions through a receptor system that requires glycoprotein 130.

Nutraceutical potential of polyphenolic fractions from Annurca apple (M. pumila Miller cv Annurca)

The capacities of polyphenolic extracts from Annurca apple peel and flesh to inhibit the glucose and cholesterol uptake by HepG2 cells were evaluated, and compared with those of other conventional cultivars, such as Red Delicious (RD), Pink Lady (PL), Fuji (F) and Golden Delicious (GD). RD peels exhibited the best hypoglycaemic effects, while Annurca flesh appeared the most active in reducing cell cholesterol uptake among the cultivars tested. The influence of the apple polyphenolic extracts on the cell proliferation and oxidative stress was also evaluated. Particularly, RD, Annurca and PL peels decreased proliferation by a 62.5%, 48.0% and 37.5%, respectively, probably due to their prooxidant capacity. Conversely, flesh extracts appeared more protective of cells than peels: Annurca and RD, particularly, proved to be able of increasing proliferation by a 32.2% and 11.1%, respectively, probably due to their capacity of reducing cell physiological radical levels of a 33.3% and 19.9%, respectively.

Adiponectin receptor signalling in the brain

Adiponectin is an important adipocyte-derived hormone that regulates metabolism of lipids and glucose, and its receptors (AdipoR1, AdipoR2, T-cadherin) appear to exert actions in peripheral tissues by activating the AMP-activated protein kinase, p38-MAPK, PPARα and NF-kappa B. Adiponectin has been shown to exert a wide range of biological functions that could elicit different effects, depending on the target organ and the biological milieu. There is substantial evidence to suggest that adiponectin receptors are expressed widely in the brain. Their expression has been detected in regions of the mouse hypothalamus, brainstem, cortical neurons and endothelial cells, as well as in whole brain and pituitary extracts. While there is now considerable evidence for the presence of adiponectin and its receptors in the brain, their precise roles in brain diseases still remain unclear. Only a few research studies have looked at this facet of adiponectins in brain disorders. This brief review will describe the evidence for important functions by adiponectin, its structure and known actions, evidence for expression of AdipoRs in the brain, their involvement in brain disorders and the therapeutic potential of agents that could modify AdipoR signalling.

Globular adiponectin counteracts VCAM-1-mediated monocyte adhesion via AdipoR1/NF-κB/COX-2 signaling in human aortic endothelial cells

Adiponectin (Ad) is an insulin-sensitizing adipocytokine with anti-inflammatory and vasoprotective properties. Cleavage of native full-length Ad (fAd) by elastases from activated monocytes generates globular Ad (gAd). Increased gAd levels are observed in the proximity of atherosclerotic lesions, but the physiological meaning of this proteolytic Ad fragment in the cardiovascular system is controversial. We compared molecular and biological properties of fAd and gAd in human aortic endothelial cells (HAEC). In control HAEC, both fAd and gAd acutely stimulated nitric oxide (NO) production by AMPK-dependent pathways. With respect to fAd, gAd more efficiently increased activation of NF-κB signaling pathways, resulting in cyclooxygenase-2 (COX-2) overexpression and COX-2-dependent prostacyclin 2 (PGI(2)) release. In contrast with fAd, gAd also increased p38 MAPK phosphorylation and VCAM-1 expression, ultimately enhancing adhesion of monocytes to endothelial cells. In HAEC lacking AdipoR1 (by siRNA), both activation of NF-κB as well as COX-2 overexpression by gAd were abrogated. Conversely, gAd-mediated p38MAPK activation and VCAM-1 expression were unaffected, and monocyte adhesion was greatly enhanced. In HAEC lacking COX-2 (by siRNA), reduced levels of PGI(2) further increased gAd-dependent monocyte adhesion. Our findings suggest that biological activities of fAd and gAd in endothelium do not completely overlap, with gAd possessing both AdipoR1-dependent ability to stimulate COX-2 expression and AdipoR1-independent effects related to expression of VCAM-1 and adhesion of monocytes to endothelium.

Adiponectin and its globular fragment differentially modulate the oxidative burst of primary human phagocytes

Adiponectin (Acrp30) belongs to the family of C1q/tumor necrosis factor α (TNFα)-related proteins. Acrp30 circulates as multimers of high, middle, and low molecular weight. In this study, we detected Acrp30 and its globular fragment (gAcrp30) in synovial fluid from rheumatoid arthritis patients. Intriguingly, the LMW form was more abundant in synovial fluid than in serum from both rheumatoid arthritis patients and healthy subjects. We also investigated the effects of Acrp30 and gAcrp30 on reactive oxygen species (ROS) production via the phagocytic NADPH oxidase. Acrp30 inhibited fMLF-induced ROS production by human phagocytes, whereas gAcrp30 enhanced it. gAcrp30's effect is additive with TNFα, whereas Acrp30 inhibited TNFα-induced priming. gAcrp30 enhanced NOX-2 expression at the plasma membrane, with a concomitant increase in p47(phox) phosphorylation. Selective inhibitors of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1 (ERK1)/2 abrogated p47(phox) phosphorylation by gAcrp30. In contrast, p47(phox) phosphorylation was inhibited by Acrp30 in association with increased AMP-activated protein kinase (AMPK) phosphorylation in phagocytes. These results suggest that human phagocyte ROS production is regulated by different mechanisms selective for Acrp30 versus gAcrp30. An imbalance between gAcrp30 and higher molecular weight isoforms of Acrp30 might contribute to chronic inflammation by regulating NADPH oxidase.

Diacylglycerol kinase alpha regulates globular adiponectin-induced reactive oxygen species

It has previously been reported that the globular form of adiponectin (gAd), mature adipocyte-derived cytokine, induced generation of reactive oxygen species (ROS) and nitric oxide (NO) in the murine macrophage cell line RAW 264. This study investigated whether diacylglycerol kinases (DGKs), enzymes functioning in sub-cellular signalling pathways, had a role on gAd-induced ROS generation in RAW 264 cells. Administration of R59022, a specific inhibitor for DGK, reduced gAd-induced ROS generation and NO release. RAW 264 cell expressed DGKα mRNA. Depression of DGKα mRNA by RNA interference significantly reduced the ROS generation in response to gAd treatment. Interestingly, transfection with the DGKα-specific small interfering RNA attenuated the expression level of Nox1 mRNA in gAd-treated RAW 264 cells. In addition, the DGKα knockdown with siRNA suppressed gAd-induced NO release.

Effect of adiponectin on apoptosis: proapoptosis or antiapoptosis?

Adiponectin is a protein hormone mainly secreted by adipose tissue that regulates energy homeostasis and glucose and lipid metabolism. Compared with other adipose-derived hormones, adiponectin is very abundant in plasma and is proposed to be a convenient biomarker for many diseases. A large number of in vitro and in vivo studies support the beneficial effects of adiponectin on metabolic syndrome, diabetes, and atherosclerosis. However, the protective actions were challenged occasionally by the controversies in its role in inflammation and in the specific functions of its different conformations. Recently, quite a few reports suggested that the antiapoptotic activity of adiponectin might contribute to its therapeutic potential during ischemia/reperfusion injury in vivo, whereas some studies demonstrated that adiponectin induced apoptosis both in vitro and in vivo. Herein, this review attempts to summarize the present consensus and divergence and to provide possible alternative and/or complementary explanations for this apparent paradox.

Involvement of mTOR in globular adiponectin-induced generation of reactive oxygen species

Globular adiponectin (gAd) induces the generation of reactive oxygen species (ROS) and nitric oxide (NO) in the murine macrophage cell line RAW 264. This study investigated the role of the mammalian target of rapamycin (mTOR) in gAd-induced ROS and NO generation. gAd stimulation induced phosphorylation of mTOR, which peaked at 20 min and dissolved rapidly. Inhibition of phosphatidylinositol 3-kinase activity with wortmannin suppressed gAd-induced phosphorylation of Akt and mTOR. Administration of rapamycin partially reduced gAd-induced generation of intracellular and mitochondrial ROS, but not release of NO. To further confirm the role of mTOR in gAd stimulation, the effect of the activators of AMP-activated protein kinase (AMPK) on gAd-induced mTOR phosphorylation was examined. Pre-treatment with three kinds of AMPK activators, AICAR, 2-deoxy-D-glucose and A-769662, suppressed gAd-induced mTOR phosphorylation. Furthermore, these AMPK activators significantly reduced gAd-evoked intracellular and mitochondrial ROS generation and NO release.

Globular adiponectin-induced RAW 264 apoptosis is regulated by a reactive oxygen species-dependent pathway involving Bcl-2

Globular adiponectin (gAd), a truncated form of adipocyte-derived cytokine, stimulates RAW 264 cells to produce reactive oxygen species (ROS), which trigger an apoptotic cascade. In this study, we investigated the generation of intracellular and mitochondrial ROS in gAd-stimulated RAW 264 cells. Treatment with gAd efficiently induced the generation of intracellular and mitochondrial ROS, as detected by dichlorodihydrofluorescein diacetate and MitoSOX fluorescence, respectively. Furthermore, gAd treatment significantly increased 8-oxoguanine, a specific indicator of oxidative DNA damage. The transfection of RAW 264 cells with iNOS- and gp91(phox)-specific small interfering RNA reduced markedly the generation of intracellular, but not mitochondrial, ROS. Quantitative PCR revealed that the expression ratio of Bcl-2 to Bax was reduced in a time-dependent manner in gAd-treated RAW 264 cells. The overexpression of Bcl-2 markedly inhibited gAd-induced apoptosis in RAW 264 cells and also reduced both the intracellular and the mitochondrial ROS generation induced by gAd treatment. Moreover, the overexpression of Bcl-2 significantly suppressed gAd-induced NO secretion and NOS activity. In addition, the inhibition of NOS activity partially reduced the oxidative DNA damage induced by gAd. Taken together, these results demonstrate that the gAd-induced apoptotic pathway acting via ROS/RNS generation involves Bcl-2.

Involvement of Ca(2+) in globular adiponectin-induced reactive oxygen species

Globular adiponectin (gAd) induces the generation of reactive oxygen species (ROS) and nitric oxide (NO) in the murine macrophage cell line RAW 264. We investigated the role of Ca(2+) in gAd-induced ROS and NO generation. Pretreatment with BAPTA-AM, a selective chelator of intracellular Ca(2+) ([Ca(2+)](i)), partially reduced gAd-induced generation of ROS and NO in gAd-treated RAW 264 cells. The lowest [Ca(2+)](i) occurred 30min after gAd treatment, after which [Ca(2+)](i) increased continually and exceeded the initial level. The mitochondrial Ca(2+) ([Ca(2+)](m)) detected by Rhod-2 fluorescence started to increase at 6h after gAd treatment. Pretreatment with a NAD(P)H oxidase inhibitor, diphenyleneiodonium, prevented the reduction of [Ca(2+)](i) in the early phase after gAd treatment. Calcium depletion by BAPTA-AM had no effect on the gAd-induced [Ca(2+)](m) oscillation. The administration of a specific calmodulin inhibitor, calmidazolium, significantly suppressed gAd-induced ROS and NO generation and NOS activity.