Published online before print February 28, 2008, doi: 10.1161/ATVBAHA.107.156687
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© 2008 American Heart Association, Inc.
Integrated Physiology/Experimental Medicine |
Adiponectin Protects Against Angiotensin II–Induced Cardiac Fibrosis Through Activation of PPAR-
From the Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, Japan.
Correspondence to Norikazu Maeda, MD, Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, 2-2-B5, Yamada-oka, Suita, Osaka 565-0871, Japan. E-mail nmaeda{at}imed2.med.osaka-u.ac.jp
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Abstract |
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Objectives— Adiponectin is recognized as an antidiabetic, antiatherosclerotic, and anti-inflammatory protein derived from adipocytes. However, the role of adiponectin in cardiac fibrosis remains uncertain. We herein explore the effects of adiponectin on cardiac fibrosis induced by angiotensin II (Ang II).
Methods and Results— Wild-type (WT), adiponectin knockout (Adipo-KO), and PPAR-
knockout (PPAR--KO) mice were infused with Ang II at 1.2 mg/kg/d. Severe cardiac fibrosis and left ventricular dysfunction were observed in Ang II–infused Adipo-KO mice compared to WT mice. Adenovirus-mediated adiponectin treatment improved the above phenotypes and the dysregulation of reactive oxygen species (ROS)-related mRNAs in Adipo-KO mice, whereas such amelioration was not observed in PPAR--KO mice despite adiponectin accumulation in heart tissue. In cultured cardiac fibroblasts, adiponectin improved the reduction of AMP-activated protein kinase (AMPK) activity and elevation of extracellular signal–regulated kinase 1/2 (ERK1/2) activity induced by Ang II. Adiponectin significantly enhanced PPAR- activity, whereas the adiponectin-dependent PPAR- activation was diminished by Compound C, an inhibitor of AMPK.
Conclusion— The present study suggests that adiponectin protects against Ang II–induced cardiac fibrosis possibly through AMPK-dependent PPAR- activation.
Adiponectin-deficient mice revealed severe angiotensin II–induced cardiac fibrosis and its phenotype were reversed by adiponectin supplementation. However, adiponectin treatment failed to ameliorate cardiac fibrosis in angiotensin II–infused PPAR--deficient mice. In vivo and in vitro experiments suggested that adiponectin protects against angiotensin II–induced cardiac fibrosis possibly through AMPK-dependent PPAR- activation.
Key Words: adiponectin • angiotensin II • PPAR- • fibrosis • AMPK
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Introduction |
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Obesity is upstream the metabolic syndrome, which is a cluster of type 2 diabetes, hypertension, and dyslipidemia.1 Recent progresses in adipocyte biology have partly clarified molecular mechanism of metabolic syndrome, but its mechanism has not been fully understood.2 We reported previously that adiponectin is abundantly expressed in adipose tissue and is secreted from adipocytes into the circulation. Interestingly, plasma adiponectin levels correlate inversely with body mass index, although adiponectin mRNA is expressed specifically in adipocytes. A number of clinical trials showed that hypoadiponectinemic subjects are liable to type 2 diabetes and myocardial infarction. We and other groups analyzed mice lacking or overexpressing adiponectin and reported that adiponectin exhibits antidiabetic, antiatherosclerotic, and antiinflammatory effects. Thus, adiponectin may be a protective molecule in the development of metabolic syndrome.3
The renin-angiotensin-aldosterone system (RAAS) is often activated in human subjects and animal models with metabolic syndrome as well as heart failure.4 Accumulating evidence has shown that RAAS exists not only in the circulation where it is driven by renal renin, but it is activated locally also in many tissues and cells. In this context, the use of angiotensin-converting-enzyme (ACE) inhibitors or angiotensin-receptor blockers (ARBs) has been recognized as an important element in clinical therapeutic strategy not only for hypertension but also for diabetes, heart failure, and cardiovascular diseases, suggesting that blockade of activated RAAS may be a significant therapeutic target for metabolic syndrome as well as heart failure. Angiotensin II (Ang II) is produced by the enzymatic cascade involved in RAAS and strongly causes cell proliferation and migration, and vascular contraction. Another important effect of Ang II is the induction of intracellular oxidative stress and promotion of tissue fibrosis.5,6 Thus, Ang II may contribute to the pathogenesis of heart failure and metabolic syndrome.
Recently, several clinical reports have shown the increased frequency of left ventricular (LV) dysfunction and structural abnormalities in subjects with metabolic syndrome.7,8 Studies in animal models of metabolic syndrome have also demonstrated the presence of cardiac fibrosis in such animals compared with the control.9,10 However, the molecular mechanism(s) that links fibrosis and metabolic syndrome has not been elucidated.
Based on the above background, we hypothesized the molecular association of adiponectin and Ang II in the pathogenesis of cardiac fibrosis. To test our hypothesis, we investigated the functional role of adiponectin in Ang II–induced cardiac fibrosis by using mice and cultured cardiac fibroblasts.
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Methods |
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Adiponectin knockout (Adipo-KO) mice were generated and backcrossed to C57BL/6J over 6 generations as described previously.11 PPAR-
knockout (PPAR--KO) mice were purchased from the Jackson Laboratory (Bar Harbor, Me). The experimental protocol was approved by the Ethics Review Committee for Animal Experimentation of Osaka University School of Medicine. Details of in vivo and in vitro experiments are fully described in supplemental Methods, available online at http://atvb.ahajournals.org. |
Results |
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Severe Ang II–Induced Cardiac Fibrosis in Adiponectin-Deficient Mice
We treated with Ang II to wild-type (WT) and Adipo-KO mice at various infusion rates (0 to 1.2 mg/kg/d) those were not deviated from previous experiments.12–14 Ang II increased systolic blood pressures (sBP), although there was no significant difference in sBP between WT and Adipo-KO mice at each dose of Ang II (supplemental Figure I-a). The heart weight/body weight (HW/BW) ratio was significantly higher in Adipo-KO mice than WT mice at 1.2 mg/kg/d (supplemental Figure I-b). Supplemental Figure I-c and I-d show ventricle sections stained by hematoxylin and eosin (H&E) and van Gieson modified method, respectively. As shown in supplemental Figure I-d and I-e, there were no apparent changes in these mice under Ang II infusion at 0.3 mg/kg/d, but, at 1.2 mg/kg/d, Ang II induced severe cardiac fibrosis in Adipo-KO mice than WT mice. These data suggest that Adipo-KO mice are vulnerable to Ang II–induced cardiac fibrosis than WT mice.
Expression of Molecules Related to Ang II–Induced Cardiac Fibrosis
We measured mRNA levels relating to cardiac fibrosis. Collagen I and III and transforming growth factor (TGF)-β1 were significantly higher in Adipo-KO mice than in WT mice at Ang II infusion rate of 1.2 mg/kg/d (supplemental Figure II-a to II-c). The mRNA ratio of β-myosin heavy chain (MHC) to -MHC, a marker of cardiac hypertrophy, did not change in both mice at the same dose of Ang II (supplemental Figure II-d). Activation of NADPH oxidase is located upstream of ROS production and is a major player in Ang II–induced fibrosis.5,6 Administration of Ang II at 1.2 mg/kg/d resulted in significantly higher elevations of p22phox and p47phox mRNA levels in Adipo-KO mice relative to those of WT mice (supplemental Figure II-e and II-f). The mRNA levels of catalase and Cu,Zn-superoxide dismutase (Cu,Zn-SOD) tended to be lower in Adipo-KO mice than in WT mice at 1.2 mg/kg/d (supplemental Figure II-g and II-h). Ang II dose-dependently decreased PPAR- mRNA levels in both mice, and interestingly PPAR- mRNA levels in Adipo-KO mice were significantly lower than those of WT mice under Ang II infusion at 1.2 mg/kg/d (supplemental Figure II-i).
Adenoviral Overproduction of Adiponectin Ameliorates Ang II–Induced Cardiac Fibrosis in Adiponectin-Deficient Mice, But Not in PPAR--Deficient Mice
Peroxisome proliferator-activated receptor (PPAR) is considered to be located downstream of adiponectin.15 Thus, to examine whether adiponectin operates on cardiac fibrosis through PPAR-, we injected adenovirus-producing adiponectin (Ad-Adipo) to WT, Adipo-KO, and PPAR- knockout (PPAR--KO) mice administered with Ang II at 1.2 mg/kg/d. Ang II infusion increased sBP in these mice, but there were no significant differences in sBP at day 8 (Figure 1A) and day 13 (data not shown) after Ang II infusion between these mice treated with adenovirus producing β-galactosidase (Ad-βgal) or Ad-Adipo. HW/BW ratio was higher in Ad-βgal–treated Adipo-KO mice than in Ad-βgal–treated WT mice (Figure 1B, lane 1 versus 3). Adiponectin supplementation significantly protected against the increase in HW/BW ratio in Adipo-KO mice (Figure 1B, lane 3 versus 4). However, Ad-Adipo–mediated adiponectin overproduction had no effect on HW/BW ratio in PPAR--KO mice (Figure 1B, lane 5 versus 6).
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In WT mice, Ad-Adipo treatment ameliorated histological changes compared with Ad-βgal treatment (Figure 1C, top panels). Supplementation of adiponectin to Adipo-KO mice obviously resulted in histological improvement (Figure 1C, middle panels), whereas adiponectin treatment did not produce histological changes in PPAR--KO mice (Figure 1C, bottom panels). Examination of tissues prepared by staining with van Gieson modified method showed improvement of cardiac fibrosis with adenoviral overproduction of adiponectin in both WT and Adipo-KO mice (Figure 1D, top and middle panels), but not in PPAR--KO mice (Figure 1D, bottom panels). Interstitial fibrosis was more severe in both Ad-βgal–treated Adipo-KO and PPAR--KO mice compared with Ad-βgal–treated WT mice (Figure 1E, lane 1 versus 3 and 5). In WT mice, the adiponectin administration tended to reduce the severity of fibrosis compared to Ad-βgal group (P=0.0836, Figure 1E, lane 1 versus 2). In Adipo-KO mice, adiponectin supplementation markedly reduced cardiac fibrosis (Figure 1E, lane 3 versus 4), whereas such treatment had no antifibrosis effect in PPAR--KO mice (Figure 1E, lane 5 versus 6).
Accumulation of Adiponectin in Ang II–Infused Heart Tissue
We observed the successful elevation of plasma adiponectin levels in mice treated with Ad-Adipo (supplemental Figure III). To investigate whether adiponectin directly acts on cardiac tissues, we performed immunohistochemistry by staining heart sections with antiadiponectin antibody. When WT, Adipo-KO, and PPAR--KO mice were not treated with Ang II, no obvious expression of adiponectin was observed in these mice (Figure 2A, left panels). Interestingly, accumulation of adiponectin protein was noted in Ang II–infused heart tissues of WT and PPAR--KO mice, but not in Adipo-KO mice (Figure 2A, middle panels). Ad-Adipo–mediated plasma adiponectin overexpression resulted in obvious accumulation of adiponectin protein even in heart tissues of Adipo-KO mice under Ang II treatment (Figure 2A, right panels).
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Adiponectin Improves Left Ventricular Contraction in Adiponectin-Deficient Mice, But Not in PPAR--Deficient Mice Under Ang II Infusion
Figure 2B shows representative left ventricular (LV) M-mode echocardiographic recordings, and supplemental Figure IV depicts LV fractional shortening (LVFS). There were no significant differences in LVFS among these mice without Ang II (supplemental Figure IV, lane 1 versus 4 versus 7). Ang II infusion significantly decreased LVFS in WT mice (supplemental Figure IV, lane 1 versus 2), but the degree of Ang II–induced LVFS reduction was more severe in Adipo-KO and PPAR--KO mice than in WT mice, respectively (supplemental Figure IV, lane 4 versus 5, lane 7 versus 8). Supplementation of adiponectin markedly ameliorated the reduced LVFS in Ang II–treated Adipo-KO mice (supplemental Figure IV, lane 5 versus 6), whereas adiponectin overexpression did not rescue the decrease of LVFS in PPAR--KO mice (supplemental Figure IV, lane 8 versus 9).
Adiponectin Alters the Expression of Various Genes and ROS in Cardiac Tissues Under Ang II Infusion
In WT mice, adiponectin overexpression significantly reduced Collagen I and III mRNA levels (Figure 3A and 3B, lane 1 versus 2). Supplementation of adiponectin did not change the levels of NADPH oxidase subunits (Figure 3E and 3F, lane 1 versus 2), such as p22phox and p47phox, but significantly increased catalase and Cu,Zn-SOD mRNA levels (Figure 3G and 3H, lane 1 versus 2). Adiponectin overexpression tended to increase PPAR- mRNA levels (Figure 3I, lane 1 versus 2) and significantly increased carnitine palmitoyltransferase 1b (CPT1b) mRNA levels known to be one of PPAR- target genes (supplemental Figure V, lane 1 versus 2). In Adipo-KO mice, adiponectin supplementation markedly reduced Ang II–induced increase in Collagen I and III, and TGF-β1 (Figure 3A to 3C, lane 3 versus 4). The elevated mRNA levels of NADPH oxidase subunits were also improved after adiponectin treatment (Figure 3E and 3F, lane 3 versus 4). Interestingly, adiponectin treatment enhanced catalase and Cu,Zn-SOD mRNA levels and rescued the decrease of PPAR- and CPT1b mRNA levels (Figure 3G to 3I and supplemental Figure V, lane 3 versus 4). However, the above-mentioned adiponectin-induced changes were not observed in PPAR--KO mice (Figure 3A to 3C, 3E to 3H, and supplemental Figure V, lane 5 versus 6). In addition, the catalase, Cu,Zn-SOD, and CPT1b mRNA levels of PPAR--KO mice were apparently lower than those of WT mice (Figure 3G and 3H, and supplemental Figure V, lane 1 versus 5).
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Next, we measured 8-hydroxydeoxyguanosine (8-OHdG) levels in heart tissue, one of ROS indicators (supplemental Figure VI). In Ad-βgal group, 8-OHdG levels of Adipo-KO and PPAR--KO mice were significantly higher than those of WT mice under Ang II infusion (lane 1 versus 3 and 5, respectively). Cardiac 8-OHdG levels tended to decrease in Ad-Adipo–treated WT mice compared to Ad-βgal–treated group (lane 1 versus 2). Adiponectin supplement resulted in a significant reduction of 8-OHdG levels in Adipo-KO mice (lane 3 versus 4), whereas such reduction was not observed in PPAR--KO mice (lane 5 versus 6).
Adiponectin Activates PPAR- in Cardiac Fibroblasts
Cardiac fibroblasts play a critical role in the pathogenesis of cardiac fibrosis. To understand further role of adiponectin-PPAR- axis in cardiac fibrosis, we conducted in vitro experiments by using neonatal rat cardiac fibroblasts. First, we examined the effect of adiponectin and 5-aminoimidazole-4- cardoxamide 1-β-D-ribofuranoside (AICAR), a selective activator of AMPK, on PPAR- activity (Figure 4A). Introduction of PPAR- expression vector significantly increased luciferase activity (lane 2 versus 3) and fenofibric acid (Feno) treatment transactivated PPAR- (lane 3 versus 12). Adiponectin significantly enhanced PPAR- activity in a dose-dependent manner (lane 3 versus 4 to 6), whereas such activation was abolished by Compound C, an inhibitor of AMPK (lane 6 versus 7). Furthermore, AICAR treatment increased dose-dependently PPAR- activity (lane 3 versus 8 to 10). AICAR-dependent PPAR- activity was also extinguished by Compound C (lane 10 versus 11). We also examined CPT1b mRNA level in cardiac fibroblasts (supplemental Figure VII). Feno treatment significantly elevated CPT1b mRNA level (lane 1 versus 2). Such elevation was decreased by Compound C (lane 2 versus 3) and it was rescued by the addition of AICAR (lane 3 versus 4).
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Next, we tested the effect of Ang II on PPAR- activity (supplemental Figure VIII). Ang II significantly reduced PPAR- activity (lane 1 versus 2), but such reduction was completely rescued by the inhibition of extracellular-signal-regulated kinase 1/2 (ERK1/2) with PD98059, an inhibitor of ERK1/2 (lane 2 versus 3). Treatment with adiponectin augmented PPAR- activity (lane 1 versus 4), but such increase was neither reduced by Ang II nor altered by PD98059 (lane 4 versus 5 and 6). Similar results were noted; Ang II did not reduce AICAR-mediated PPAR- activation (lane 7 versus 8 and 9).
Activation of AMPK Inhibits Ang II–Mediated Phosphorylation of ERK1/2 in Cardiac Fibroblasts
To understand how AMPK activation modulates Ang II–mediated ERK1/2 signaling, we performed Western blotting. First, adiponectin enhanced phosphorylation of AMPK in a dose-dependent manner (Figure 4B). Second, Ang II phosphorylated ERK1/2 but suppressed phosphorylation of AMPK (Figure 4C, lane 1 versus 2). Furthermore, adiponectin rescued the Ang II–induced reduction of AMPK phosphorylation and partially suppressed ERK1/2 activity under Ang II (Figure 4C, lane 2 versus 3). Third, we measured phosphorylation of AMPK and ERK1/2 by using AICAR to clarify the interaction between AMPK and ERK1/2 under Ang II. As expected, AICAR treatment phosphorylated AMPK (Figure 4D, lane 1 versus 2) and the addition of Compound C reduced such phosphorylation (Figure 4D, lane 2 versus 3). Surprisingly, blockade of Ang II–induced ERK1/2 activity by PD98059 resulted in AMPK activation (Figure 4E, lane 1 versus 2). AICAR-induced AMPK activation partially suppressed Ang II–induced ERK1/2 phosphorylation (Figure 4E, lane 1 versus 3).
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Discussion |
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The major findings of the present study were: (1) Ang II induced severe cardiac fibrosis in adiponectin-deficient mice. (2) Treatment of adiponectin-deficient mice with adiponectin protected against Ang II–induced cardiac fibrosis and ameliorated gene expressions related to ROS, whereas such improvement was not observed in PPAR-
-deficient mice. (3) Adiponectin enhanced PPAR- activity through AMPK pathway in cardiac fibroblasts. (4) AMPK activation partly inhibited Ang II–dependent ERK1/2 signaling, whereas blockade of Ang II–induced ERK1/2 activation resulted in AMPK activation. (5) Adiponectin accumulated in Ang II–injured heart tissue.
A striking finding of the present study was that treatment of Ang II–infused PPAR--KO mice with adiponectin failed to improve cardiac fibrosis, ameliorate the expression levels of ROS-associated genes, and improve LV contraction. As shown in supplemental Figure V, adiponectin might exhibit its potency partly through PPAR- activation in vivo. In consistent with our results, Yamauchi et al have demonstrated that fatty acid oxidation was enhanced in skeletal muscle of adiponectin transgenic mice, suggesting adiponectin-PPAR- pathway.15 However, we cannot conclude that adiponectin shows antioxidative and antifibrotic effects only through PPAR--dependent pathway, because genetic PPAR- deficiency has been shown to be quite proinflammatory.16
Importantly, PPAR- has been reported to correlate with ROS in several tissues.17 Activation of PPAR- inhibited Ang II–induced activation of NADPH oxidase and suppressed ROS production in human endothelial cells.18,19 Furthermore, a PPAR-responsive element (PPRE) has been identified in promoter regions of catalase and Cu,Zn-SOD genes, which are key enzymes that reduce ROS production.20,21 Taken together, PPAR- activation seems to decrease tissue fibrosis, partly through ROS reduction. Some kinds of fatty acids are shown to enhance PPARs activity.22,23 Treatment with fatty acids reduced Ang II–induced elevation of collagen expression in cardiac fibroblasts (data not shown). For in vivo experiments, energy source in heart tissues switched fatty acids to glucose when myocardial tissues are overloaded (eg, pressure overloading, ischemia, etc.). There is a possibility that such metabolic switch may reduce PPAR- activity and enhance cardiac remodeling. It would be worth testing in the future whether the administration of fatty acids improves Ang II cardiac fibrosis in Adipo-KO mice.
The present results support the recent experiments indicating that adiponectin suppressed superoxide production in heart tissue of ischemia-reperfusion model animals and that urinary levels of 8-OHdG were reduced in adiponectin transgenic mice.24,25 However, adiponectin deficiency caused no significant differences in catalase and Cu,Zn-SOD mRNA levels between WT and Adipo-KO mice, whereas superphysiological elevation of plasma adiponectin (4- to 5-fold increase) enhanced catalase and Cu,Zn-SOD mRNA levels both in WT and Adipo-KO mice (Figure 3). This result indicated that expression levels of these antioxidant enzymes were not determined only by adiponectin deficiency and suggested a possibility that some kind of compensatory mechanism occurs by adiponectin deficiency. Further investigations might clarify such discrepancy in the future. On the other hand, the activity of PPAR- was increased by adiponectin within a physiological concentration in cardiac fibroblasts (Figure 4). Thus, the in vivo potency of adiponectin is not always at the same level as in vitro.
Ang II does not only augment ROS formation and increase oxidase activity, but it also upregulates the mRNA and protein expression levels of the majority of NADPH oxidase subunits.5,6 In the present study, Ang II dose-dependently decreased PPAR- mRNA levels (supplemental Figure II), but it was uncertain whether cardiac PPAR- activity was reduced in these mice. Tham et al demonstrated that PPAR- and 
was downregulated in aorta of Ang II–administered apolipoprotein E–deficient mice and suggested that Ang II–induced NF-kappaB activation reduced PPAR- and expressions.26 Furthermore, Suzawa et al showed that NF-kappaB activation resulted in the reduction of PPAR activity by the association of NF-kappaB and PPAR,27 and thus there is a possibility that similar effects may be observed in PPAR- activity. Collectively, Ang II may reduce PPAR- activity via NF-kappaB activation.
Degree of fibrosis was severe in Adipo-KO mice compared to WT mice treated with Ang II at 1.2 mg/kg/d, but no apparent differences were observed in fibrosis under Ang II infusion at 0.3 mg/kg/d (supplemental Figure I-d and I-e). Systemic Ang II infusion elevates blood pressure, causes mechanical stress in cardiac myocytes, and activates various signaling molecules. There is a possibility that we observed no significant differences between WT and Adipo-KO mice treated with Ang II at 0.3 mg/kg/d because these stress-induced signals may complicatedly crosstalk with adiponectin signaling and Ang II receptor signaling each other.
AMPK is considered a key player in the pathogenesis of cardiac hypertrophy, although its mechanism remains elusive. In mouse heart, AMPK is activated during pressure overload-induced hypertrophy.28 Previous reports showed a lower AMPK activation in myocardium of Adipo-KO mice after transverse aortic constriction (TAC) operation, indicating that the lack of stimulatory effect of adiponectin on AMPK accounted for severe TAC-induced cardiac hypertrophy observed in Adipo-KO mice.29,30 In addition, we herein demonstrated that the adiponectin-AMPK-PPAR- pathway might involve in one of pathogenesis for cardiac fibrosis. Consistent with our results, activated AMPK was recently reported to undergo translocation from cytoplasm to nucleus and thus induces the transcription of PPAR- in C2C12 myocytes.31 Supplemental Figure VIII indicates that AMPK activation avoids Ang II–induced reduction of PPAR- activity. Furthermore, Figure 4E suggests that AMPK and ERK1/2 control each other in Ang II–treated cardiac fibroblasts. However, there is a study limitation in present in vitro experiments. The active derivative of AICAR, ZMP, modulates other AMP-sensitive enzymes, such as glycogen phosphorylase and fructose-1,6-bisphosphatase.32 In addition, AICAR can compete with released adenosine for reuptake into cells. Compound C is also considered as an AMPK inhibitor, but its selectivity for AMPK remains uncertain. There is the necessity to confirm the present results by using expression vectors for AMPK and DN-AMPK or siRNA for AMPK in the future.
Another important finding of the present study was the accumulation of adiponectin in the myocardium (Figure 2A). In the Ad-βgal group, myocardial sections of Ang II–treated WT and PPAR--KO mice were stained with antiadiponectin antibody whereas no such staining was observed in those of Adipo-KO mice. We examined adiponectin mRNA level in heart tissue, but we could not detect adiponectin mRNA expression even in Ad-Adipo group (data not shown). These results suggest that circulating adiponectin accumulated in the injured heart tissues. We also measured cardiac mRNA levels of adiponectin receptors, such as AdipoR1, AdipoR2, and T-cadherin, but no apparent differences of these mRNA levels were observed in WT and Adipo-KO mice (data not shown). Previous studies used the solid-phase binding assay and showed that adiponectin binds specifically to Collagen types I, III, and V.33 The results depicted in supplemental Figure II indicate that Ang II enhances the expression of Collagen I and III in heart tissue. Together, these observations support the hypothesis that circulating adiponectin can potentially accumulate or bind to the injured matrix that abundantly express collagen, but the precise mechanism for adiponectin accumulation in the injured heart tissue remains to be elucidated.
In summary, we herein demonstrated in the present study that adiponectin, Ang II, and PPAR- are closely associated with each other and partly contribute to the pathogenesis of cardiac fibrosis and heart failure, but the precise mechanism has not been fully clarified. Adiponectin enhances PPAR- activity through AMPK, whereas Ang II reduces its activity via ERK1/2. Moreover, AMPK and ERK1/2 control each other in Ang II–treated cardiac fibroblasts. PPAR- activation might result in ROS reduction, and finally protection against cardiac fibrosis and heart failure. In conclusion, adiponectin protects against cardiac fibrosis and dysfunction at least partly through AMPK-dependent PPAR- activation pathway. The present study may provide novel and useful therapeutic strategies against organ fibrosis.
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Acknowledgments |
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We thank Kazunori Kashiwase, Osamu Yamaguchi, and Kinya Otsu for providing the protocol of primary cardiac fibroblast cell culture from neonatal rats, and Fumie Katsube for the excellent technical assistance. We also thank all members of the Adiposcience laboratory, Osaka University for helpful discussions on the project.
Sources of Funding
This work was supported in part by a Grant-in-Aid for Scientific Research (B) no. 19390249 (to T. F.), a Grant-in-Aid for Scientific Research on Priority Areas no. 15081208 (to S. K.), Health and Labor Science Research Grants (to T. F.), The Cell Science Research Foundation (to N. M.), Mitsubishi Pharma Research Foundation (to N. M. and T. F.), Yamanouchi Foundation for Research on Metabolic Disorders (to N. M.), Japan Heart Foundation Grant for Research on Arteriosclerosis Update (to N. M.), Japan Heart Foundation/Novartis Grant for Research Award on Molecular and Cellular Cardiology (to N. M.), Japan Heart Foundation Research Grant (to N. M.), Japan Foundation of Cardiovascular Research (to N. M.), Takeda Science Foundation (to T. F.), Smoking Research Foundation (to T. F.), Takeda Medical Research Foundation (to T. F.), Suzuken Memorial Foundation (to H. N.), and Senri Life Science Foundation (to H. N.).
Disclosures
None.
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Footnotes |
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Original received September 25, 2007; final version accepted February 15, 2008.
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