Skip Navigation

European Journal of Heart Failure 2008 10(1):30-38; doi:10.1016/j.ejheart.2007.11.005
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Fliegner, D.
Right arrow Articles by Regitz-Zagrosek, V.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fliegner, D.
Right arrow Articles by Regitz-Zagrosek, V.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© 2008 European Society of Cardiology

Up-regulation of PPAR{gamma} in myocardial infarction

Daniela Fliegnera, Dirk Westermannb, Alexander Riadb, Carola Schuberta, Eva Bechera, Jens Fielitza, Carsten Tschöpeb and Vera Regitz-Zagroseka,c,*

a Cardiovascular Disease in Women, Charité, Center for Cardiovascular Research (CCR), Charité, University of Medicine Berlin Germany
b Department of Cardiology and Pneumology, University Hospital Benjamin Franklin, Free University of Berlin Germany
c German Heart Institute Berlin (DHZB) Germany

* Corresponding author. CCR — Center for Cardiovascular Research, Hessische Str. 3-4, 10115 Berlin, Germany. Tel.: +4930 450 525 172; fax: +4930 450 525 972. E-mail address: vera.regitz-zagrosek{at}charite.de (V. Regitz-Zagrosek)


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
Background: Peroxisome proliferator activated receptors (PPARs) are key regulators for cardiac energy metabolism after myocardial injury. We hypothesized, that PPARs are regulated in myocardial infarction (MI) and their activity is modulated by angiotensin receptor blockers (ARBs).

Methods: Following induction of MI, male rats were treated with placebo or the ARB irbesartan for three weeks. PPAR{alpha}, β/{delta} and {gamma} protein expression and gene expression of PPAR target genes and glucose transporters were measured. PPAR{gamma}-protein expression was analyzed by immunofluorescence.

Results: MI decreased LVP and dp/dtmax and increased LVEDP, this effect was counteracted by irbesartan. PPAR{alpha} and PPARβ/{delta} protein expression was not altered in MI and was not affected by irbesartan. PPAR{gamma} protein content was increased in the infarcted area and localized to cardiac myocytes and fibroblasts. In parallel, expression of CTGF was increased 10-fold in the infarcted zone. PPAR target genes (CD36, MCAD, ACO and GLUT4) were significantly decreased in infarcted tissue, and this was unaffected by irbesartan. However, CD36 and ACO in the non-infarcted areas were up-regulated by irbesartan.

Conclusion: Endogenous up-regulation of PPAR{gamma} in MI is insufficient to counteract the decrease in metabolic genes, but parallels an increase in the profibrotic mediator CTGF. Irbesartan increases fatty acid oxidating enzymes after MI independent of PPAR{gamma} regulation.

Key Words: Myocardial infarction • PPARs • Myocardial metabolism • Angiotensin receptor blockers (ARBs) • Fibrosis

Received July 5, 2007; Revised October 1, 2007; Accepted November 13, 2007


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 
Energy homeostasis in the human heart and in post-ischaemic remodelling depends on the balance between fatty acid oxidation (FAO) and glucose utilization and is controlled by PPARs [1]. PPARs belong to the nuclear hormone receptor superfamily of ligand-activated transcription factors, like retinoid, thyroid and steroid receptors. The members of the PPAR-family, PPAR{alpha}, PPARβ/{delta} and PPAR{gamma} play an important role in the regulation of lipid and glucose metabolism [2,3]. PPAR{alpha} is highly expressed in tissues with an elevated capacity for fatty acid oxidation (FAO), like liver, heart, brown fat and kidneys. PPARβ/{delta} is almost ubiquitously expressed and regulates FAO transcriptionally. PPAR{gamma} which is enriched in adipose tissue, controls lipid storage, adipocyte formation and metabolism [4,5]. PPAR{gamma} is also expressed in extra-adipose tissues including the vascular wall, the skeletal muscle and the heart. The molecular mechanism by which PPAR{gamma} regulates myocardial metabolism remains poorly understood.

Once activated by a ligand, PPARs recruit transcriptional co-activators, which are necessary to initiate target gene transcription. The target genes are mainly involved in the energy homeostasis and include genes from the β-oxidation, the free fatty acid translocase (CD36), the carnitine-palmitate transporter (CPT-1), the medium chain acetyl dehydrogenase (MCAD), the acetyl-CoA-oxidase (ACO) and the carbohydrate oxidative pathways like the insulin-insensitive (GLUT1) and the insulin-sensitive (GLUT4) glucose transporters. These genes were first established as target genes of PPAR{alpha} and β/{delta}, but recently it was shown that CD36, ACO and GLUT1 are also PPAR{gamma} target genes [6,7]. PPAR{gamma} is mainly involved in fat cell differentiation and lipid storage, but is also involved in the regulation of glucose homeostasis and cardiac energy metabolism [4,7,8]. In addition, PPARs have been implicated as regulators of inflammatory processes and tissue repair. PPAR{alpha} and PPAR{gamma} have been shown to prevent or attenuate cardiac fibrosis in anoxia/reoxygenation and pressure-overloaded hearts [9-11].

It has also been shown, that the connective tissue growth factor (CTGF) promotes fibroblast proliferation and extracellular matrix production in connective tissues. A large increase in CTGF has been observed in wound repair, fibrotic disorders and myocardial infarction (MI) [12]. CTGF is also involved in remodelling of the viable myocardium in the chronic stage after MI, when fibrosis is ongoing [13].

There is evidence that PPARs have a critical role in the development of myocardial dysfunction in hypertrophy or ischaemia [14]. PPARs are down- or up-regulated in a variety of cardiac diseases [2,7]. Based on the observed regulation in myocardial hypertrophy, we hypothesized that PPARs might also be regulated after myocardial infarction [15]. PPARs can be activated by endogenous secreted ligands like free fatty acids or prostaglandins. A number of exogenous activators are also available, including angiotensin receptor blockers (ARBs) [8,16]. ARBs have different protective effects in the ischaemic heart [17,18]. Recently it has been shown that ARBs induce the activity of PPAR{gamma} [16]. Therefore, we speculate that treatment with an ARB might increase the expression of PPAR target genes. Consequently we investigated which PPAR isoform is regulated in MI and analyzed the effect of placebo or irbesartan treatment on PPAR target genes.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 5. Conclusion
 References
 
2.1. Animal experiments
The experiments were performed in male Sprague Dawley rats weighing 300-330 g (Charles River, Germany). The animals were allowed free access to water and standard chow under a 12 h light/dark cycle. Animal housing and experiments were approved by the committee for the protection of experimental animals at the Charité, Universitätsmedizin Berlin, and performed in accordance with the recommendations of the Society for Laboratory Animal Science (GV-SOLAS) and the Federation of European Laboratory Animal Science Association (FELASA).

Myocardial infarction (MI) was induced by permanent ligation of the left descending coronary artery (LAD) as described by Tschöpe et al. [19]. Six animals per group (sham or MI) were treated with either placebo or irbesartan for three weeks starting the day after MI. The dosage of the medication was 50 mg/kg and was administered orally by gavage.

2.2. Haemodynamic measurements
Three weeks after surgery the rats were again anaesthetized (sodium pentobarbital 60 mg/kg; i.p.), intubated, and artificially ventilated. A 2F Millar-tip catheter (Millar Instruments Inc.; Houston, Texas, USA) was positioned in the left ventricle (LV) via the right carotid artery for measurement of systolic and diastolic cardiac function [20].

On completion of the haemodynamic measurements, animals were sacrificed. Tissue samples were obtained from the left ventricular wall (sham), the infarcted area and from the non-infarcted left ventricular myocardium. All tissues were then rapidly frozen in liquid nitrogen and stored at –80 °C prior to analysis.

2.3. Quantitative real time (RT)-PCR-analysis
Total RNA from rat myocardial tissue was extracted by standard methods [21] and reverse transcribed after complete DNA digestion, as previously described [22]. For the measurement of PPAR target genes, a RT-PCR procedure was performed in duplicate with the Taqman instrument (ABI 7000). The primer sequences are shown in the supplemental data (Table1). The mRNA content of each target gene was normalized to the stably expressed gene 18S (ribosomal RNA).

2.4. Western immunoblot analysis
Left ventricular myocardial tissue samples were homogenized in a FastPrep homogenizer (FP120, Qbiogene) containing LysisMatrix particles and a double-detergent lysis buffer. After centrifugation, protein content was measured (BCA protein assay, Pierce). Myocardial proteins were separated by 8% SDS-PAGE and were transferred to nitrocellulose membranes. The blots were incubated with a specific antibody against the amino terminus of PPAR{gamma} (H-100; 1:200 dilution in 3% Blocking Buffer), PPAR{alpha} (H-98; 1:400 dilution in 3% Blocking Buffer), PPARβ/{delta} (H-74;1:400 in 1xTBS-T Buffer), GLUT1 (H-43; 1:200 in 3% Blocking Buffer), GLUT4 (H-61; 1:400 in 3% Blocking Buffer) and GAPDH (1:50,000 in 1xTBS-T buffer). After washing steps, the membranes were incubated with the secondary antibody (all 1:5000, GAPDH 1:100,000) in 5% Blocking Buffer. All antibodies were purchased from Santa Cruz Biotechnology, Inc.; (except for the GAPDH antibody which was from Chemicon). The signal was visualized with ECLTM Western Blotting Detection Reagents (Amersham Biosciences) and Chemiluminescence Bio Max Light Film (Kodak). The protein content was normalized to GAPDH. The results were quantified with AlphaEaseFC (software, version 3.1.2, Alpha Innotech Corporation).

2.5. Immunofluorescence microscopy
Tissue samples were fixed in frozen section medium Neg-50 (Richard Allan Scientific). Cryostat sections were made using a Cryrostat microtome (Jung Frigocut 2800E; Leica). After cutting the samples into 4 {varepsilon}m sections, they were mounted on slides and air dried overnight. For immunohistochemistry the sections were fixed for 10 min in acetone, then washed three times for 10 min in PBS-T buffer (10 mmol/L phosphate buffer: pH 7.4, 140 mmol/L NaCl, 3 mmol/L KCl). After washing, samples were blocked in blocking solution 3% BSA in PBS-T buffer for 1 h. The slides were incubated with the first antibody (Vimentin and PPAR{gamma}-antibody, Santa Cruz) at a dilution of 1:50 in 1% blocking solution overnight in a humidified atmosphere. After several washings with PBS-T buffer, the slides were incubated with the secondary antibodies conjugated to FITC-anti rabbit and Cy3-anti mouse in a dilution of 1:50 in 1% blocking solution for 1 h. The slides were rinsed again several times with PBS-T buffer. Negative controls included sections incubated with secondary antibodies only, omitting primary antibodies. After several washing steps with PBS, the slides were mounted with fluorescence mounting medium (Vectashield). Fluorescence micrographs were taken with a confocal laser scanning microscope (Leica DM FLSA) and analyzed using Leica Confocal Software.

2.6. Statistical methods
Results are expressed as mean+SEM. Data were analyzed using a two-sided analysis of variance (ANOVA) in conjunction with the Student's t-test. The gene/18S and protein/GAPDH ratios were compared to the mean ratio respective sham group being set to 100%. Statistical analyses of the relative amount of the mRNA and the protein expression of target genes were performed with the Mann Whitney U test. Differences were considered significant with a p-value ≤0.05. All analyses were performed using Sigma Plot (release 8.0) and SPSS software for Windows (release 11.5).


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 5. Conclusion
 References
 
3.1. Haemodynamic changes
Left ventricular pressure (LVP) and dp/dtmax were significantly reduced and the left ventricular end-diastolic pressure (LVEDP) and dp/dtmin were significantly increased in the infarcted hearts (Fig. 1). Irbesartan partially restored LVP, decreased LVEDP and dp/dtmin, and increased dp/dtmax (Fig. 1). Heart rate was not different between the groups (data not shown).


Figure 01
View larger version (17K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 1 Cardiac function parameters after surgery and the effects of irbesartan. A-D show the summarized haemodynamic functional parameters, three weeks (3w) post myocardial infarction in the sham-operated and infarcted animals according to placebo or irbesartan treatment. Statistically significant differences between sham-operated and infarct induced rats in each treatment group are indicated by *P<0.05, **P<0.01, ***P<0.001. Statistically significant differences between infarction with irbesartan treatment and infarction with placebo treatment are indicated by §P<0.01. LVP, left ventricular pressure in mmHg; LVEDP, left ventricular end-diastolic pressure in mmHg; (mmHg/s), maximal rate of increase in pressure; dp/dtmin (mmHg/s), maximal rate of decrease in pressure; Data are the mean±SEM.

 
3.2. Cardiac protein expression of PPAR{alpha}, PPARβ/{delta} and PPAR{gamma}
In the placebo treated animals, PPAR{alpha} protein expression showed no significant changes in the infarcted zone or in the non-infarcted area in comparison to the sham-operated animals. Treatment with irbesartan did not significantly alter PPAR{alpha} expression in the sham-operated animals, in the infarcted zone or in the non-infarcted area (Fig. 2A). The expression of PPARβ/{delta} in the placebo treated animals was not altered in the zone of infarction or in the non-infarcted area. However, irbesartan treated animals exhibited a significant increase (50%) of PPARβ/{delta} in the area of infarction in comparison to the sham-operated animals. No effect of irbesartan was observed in the sham-operated animals or in the non-infarcted area (Fig. 2B). The PPAR{gamma} protein content showed a significant increase of 70% in the infarcted area in the placebo treated animals, a significant increase was also observed in the irbesartan treated animals (Fig 2C). Irbesartan by itself had no effect on PPAR{gamma} protein expression in the infarcted area, in the non-infarcted area or in the sham operated animals.


Figure 02
View larger version (10K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 2 PPAR protein expression in myocardial tissue. A, B and C show the protein content of all three PPAR isoforms ({alpha}, β/{delta} and {gamma}) in sham, MI and non-infarcted tissue in the placebo and irbesartan treated animals. Protein expression was normalized to GAPDH. Statistically significant differences between sham, infarcted and non-infarcted tissue in the placebo and irbesartan groups and between the irbesartan and placebo treated animals in the same tissue groups are indicated by *P<0.05, **P<0.01. NI=non-infarcted.

 
3.3. Localization of PPAR{gamma}
Since PPAR{gamma} was up-regulated in the infarcted zone, we studied the cellular localization of PPAR{gamma}. Immunofluorescence microscopy of myocardial tissue showed PPAR{gamma} protein expression (green-FITC) in myocytes, but not in fibroblasts in the sham operated hearts (Fig. 3A and C). The expression of vimentin (red-Cy3), a marker for endothelial cells, connective tissue and fibroblasts showed a regular distribution in these hearts (Fig. 3B). No colocalization of vimentin and PPAR{gamma} was observed. The transverse diameter of the myocytes was about 15-20 {varepsilon}m. The infarcted area was characterized by an increase in myocyte diameters up to 20-80 {varepsilon}m with a large amount of variation, and by an increased amount of fibrous tissue (Fig. 3D) as indicated by an increased relative fluorescence intensity for vimentin (Fig. 3E). PPAR{gamma} protein expression in the infarcted area was strikingly increased in myocytes (Fig. 3D/F). PPAR{gamma} protein expression was also found in connective tissue and in fibroblasts (Fig. 3F) in the infarcted area as indicated by the yellow colour, resulting from an overlay of the red and green labels in both cell types.


Figure 03
View larger version (101K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 3 Immunofluorescence revealed PPAR{gamma} and Vimentin in myocardial cryostat sections. Immunocytochemical analysis of PPAR{gamma} (in green) and vimentin (in red) in myocardial tissue. The magnification for all pictures was 20x. A Sham placebo—PPARg/FITC, single layer; B Sham placebo—Vimentin/Cy3, single layer; C Sham placebo—Vimentin/PPAR{gamma}, merge; D Infarct placebo—PPAR{gamma}/FITC, single layer; E Infarct placebo—Vimentin/Cy3, single layer; F Infarct placebo—Vimentin /PPAR{gamma}, merge. Colocalization of PPAR{gamma} and vimentin is indicated by the yellow colour.

 
3.4. Regulation of fatty acid metabolizing enzymes
In placebo treated animals, CD36 was significantly decreased in the infarcted area and was not significantly different from the sham operated animals in the non-infarcted area. Irbesartan induced a significant increase of CD36 mRNA in the non-infarcted area, but induced no changes in the infarcted area or in the sham operated animals (Fig. 4A).


Figure 04
View larger version (15K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 4 Expression of PPAR{gamma} target genes in myocardial tissue. A mRNA expression of CD36; B mRNA expression of CPT1 C mRNA expression of ACO; D mRNA expression of MCAD. The mRNA expression was normalized to 18S. Statistically significant differences between sham, infarcted and non-infarcted tissue in the placebo and irbesartan groups and between irbesartan and placebo treated animals in the same tissue groups are indicated by *P<0.05. NI=non-infarcted.

 
CPT-1 was significantly decreased in the infarcted zone and was not significantly altered in the non-infarcted area. Irbesartan induced no changes in the non-infarcted area or in the infarcted area or in the sham operated group (Fig. 4B). ACO was also significantly reduced in the infarcted area and was not significantly altered in the non-infarcted area. Irbesartan induced a significant increase in ACO in the non-infarcted area and in the sham operated group. A tendency towards up-regulation, which did not reach significance, was observed in the infarcted area (Fig. 4C). MCAD was also significantly decreased in the infarcted area and was not significantly altered in the non-infarcted area. Irbesartan induced no changes in the non-infarcted area or in the infarcted area or in the sham operated group (Fig. 4D).

3.5. Regulation of GLUT4 and GLUT1
In the placebo treated animals the insulin sensitive glucose transporter GLUT4 was significantly decreased by 90% in the infarcted area and was not significantly altered in the non-infarcted area (Fig. 5A). Measurement of the myocyte specific gene {alpha}-myosin heavy chain (Myh6) showed that it was also reduced by about 90% in the infarcted area. Thus the loss of Glut4 was probably due to a loss of myocytes. In the placebo and irbesartan treated animals the glucose transporter GLUT1 showed a 50% increase in the infarcted area, which did not reach statistical significance (Fig. 5B). Irbesartan alone induced no significant changes in the infarcted, non-infarcted area or sham operated animals.


Figure 05
View larger version (12K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 5 Gene regulation of GLUT1 and GLUT4 in myocardial tissue. A Gene expression of GLUT4 in myocardial tissue; B Gene expression of GLUT1 in myocardial tissue. The mRNA expression was normalized to 18S. Statistically significant differences between sham, infarcted and non-infarcted tissue in the placebo and irbesartan groups and between irbesartan and placebo treated animals in the same tissue groups are indicated by *P<0.05. NI=non-infarcted.

 
3.6. Regulation of CTGF
The expression of CTGF was significantly increased (up to 1100%) in the area of infarction in comparison to the sham-operated (100%) group or the non-infarcted area in the placebo and irbesartan treated animals. Treatment with irbesartan induced no changes in CTGF expression in the sham-operated animals, non-infarcted area or in the infarcted area (Fig. 6).


Figure 06
View larger version (11K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 6 Regulation of CTGF. Gene expression of CTGF. The mRNA expression was normalized to 18S. Statistically significant differences between sham, infarcted and non-infarcted tissue in the placebo and irbesartan groups and between irbesartan and placebo treated animals in the same tissue groups are indicated by *P<0.05. NI=non-infarcted.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
5. Conclusion
 References
 
We describe for the first time that PPAR{gamma} protein expression is increased in cardiac myocytes and fibroblasts in the infarcted area in rat hearts three weeks after myocardial infarction. This increase occurred in parallel with an up-regulation of the profibrotic mediator CTGF. In contrast, PPAR{alpha} and PPARβ/{delta} were not altered in myocardial infarction. PPAR target genes regulating fatty acid metabolism and the insulin sensitive glucose transporter GLUT4 were decreased at the mRNA level in the infarcted area.

4.1. Effects of myocardial infarction on PPARs, metabolism and fibrosis
There is a wealth of data on PPAR regulation in myocardial hypertrophy. Regulation of PPAR{alpha} and PPARβ/{delta} in models of aortic stenosis and heart failure has been documented in mice. PPAR{gamma} regulation has also been shown in models of hypertrophy [14]. However, less data are available in myocardial infarction. Our findings on unaltered expression of PPAR{alpha} and PPARβ/{delta} in infarcted and non-infarcted areas in the rat heart are novel. Measurements were performed three weeks after induction of MI in a phase where the acute response is almost past, but remodelling has not yet completely finished. Therefore, these data do not exclude an earlier or later up- or down-regulation of PPAR{alpha} and PPARβ/{delta} at another time point.

Our findings of an up-regulation of PPAR{gamma} in the infarcted area are somewhat surprising. The up-regulation in myocytes occurs at mRNA and protein levels and it is found in the cytoplasm as well as in the nuclei. Cytoplasmic localization of PPAR{gamma} is in agreement with the behaviour of nuclear transcription receptors that are frequently localized in the cytoplasm and translocate into the nucleus after ligand activation. Similar findings have been shown for PPAR{gamma} in pituitary cells [23]. The increased expression of PPAR{gamma} was not only observed in cardiomyocytes but also in fibrotic tissue and probably also in cardiac fibroblasts, suggesting a functional role of PPAR{gamma} in fibrosis. This is in agreement with earlier observations showing that PPAR{gamma} mediates cellular signalling for growth and migration in cardiac fibroblasts [24]. PPAR{gamma} is supposed to participate in regulation of extracellular matrix protein (ECM) expression in conditions of ischaemia, hypoxia and anoxia [24]. However, our data are the first to suggest regulation of PPAR{gamma} in cardiac fibroblasts in ischaemic hearts. The observed up-regulation of PPAR{gamma} goes in parallel with an up-regulation of connective tissue growth factor (CTGF), which is one of the strongest inducers of fibrosis in isolated cardiac fibroblasts [25].

4.2. Effects of myocardial infarction (MI) on PPAR{gamma} and PPAR target genes
Myocardial infarction leads to an increase in glucose utilization including anaerobic glycolysis. Initially this is understood to be beneficial based on the improved myocardial efficiency with glucose oxidation and reduced free radical production, but later has negative effects since energy supply is limited [1]. In the infarcted zone, myocytes are lost and replaced by fibroblasts as shown by histology and by the loss of the myocyte specific gene Myh6 from the infarcted area. Our data support these findings, indicating a severe loss of all FAO enzymes in the infarct zone, together with a decrease in insulin-dependent and an increase in insulin independent glucose uptake proteins. The decrease in genes of FAO, accompanied by increased PPAR{gamma} expression and unchanged PPAR{alpha} and PPARβ/{delta} expressions seems contradictory at first. However, the role of PPAR{gamma} on FAO is much more pronounced on adipose tissue than in the myocardium or in myocardial cells. The observed up-regulation of PPAR{gamma} may thus represent a compensatory mechanism to improve the energy supply by the activation of FAO which however remained insufficient.

4.3. Effects of irbesartan
In myocardial infarction, irbesartan is known to improve haemodynamics, which is in agreement with our findings [26]. In addition, metabolic effects of ARBs have also been described. AT1R blockade with ARBs has been shown to improve insulin sensitivity in humans and in animal models of insulin resistance [27,28]. Recently, insulin sensitizing effects of ARBs have been reported [6,8,16,29]. ARBs potently enhance PPAR{gamma} activity and lipid accumulation in adipocyte cultures [6].

The up-regulation of CD36 and ACO under treatment with irbesartan, as found in our study, is in agreement with improved fatty acid oxidation and may contribute to better functional recovery. However, the mechanism remains uncertain since PPAR{gamma}, PPAR{alpha} and PPARβ/{delta} expression was unchanged by irbesartan.

4.4. Limitations
A limiting factor was the low number of animals used in the study, which limited the statistical power. Secondly, it was not possible to measure PPAR{gamma} activity together with expression in the present setting.


   5. Conclusion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
References
 
In summary, PPAR{gamma} protein expression is increased three weeks after myocardial infarction in rats. However, in spite of PPAR{gamma} up-regulation, expression of metabolic PPAR target genes, which are necessary for FAO, remain low. In contrast, PPAR{gamma} up-regulation on fibroblasts occurred in parallel with an increase in CTGF, suggesting that the potential link between PPAR{gamma} and fibrotic mechanisms should be investigated further.


View this table:
[in this window]
[in a new window]

  		Table 1 Sequence and sizes of primers

 

   Acknowledgements
 
This work was supported by the Deutsche Forschungsgemeinschaft (GK-II-754) and by EU FP6 grant LSHM-CT-2005-018833, EUGeneHeart. D. Fliegner has received grants from GK-II-754 and parts of their doctoral thesis have been incorporated into this article. We also thank Jenny Thomas for excellent technical assistance.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 5. Conclusion
 References
 

  1. Sambandam N., Lopaschuk G.D., Brownsey R.W., Allard M.F. Energy metabolism in the hypertrophied heart. Heart Fail Rev (2002) 7:161–173.[CrossRef][Medline]
  2. Huss J.M., Kelly D.P. Nuclear receptor signaling and cardiac energetics. Circ Res (2004) 95:568–578.[Abstract/Free Full Text]
  3. Huss J.M., Torra I.P., Staels B., Giguere V., Kelly D.P. Estrogen-related receptor alpha directs peroxisome proliferator-activated receptor alpha signaling in the transcriptional control of energy metabolism in cardiac and skeletal muscle. Mol Cell Biol (2004) 24:9079–9091.[Abstract/Free Full Text]
  4. Lee C.H., Olson P., Evans R.M. Minireview: lipid metabolism, metabolic diseases, and peroxisome proliferator-activated receptors. Endocrinology (2003) 144:2201–2207.[Abstract/Free Full Text]
  5. Barak Y., Nelson M.C., Ong E.S., Jones Y.Z., Ruiz-Lozano P., Chien K.R., et al. PPAR gamma is required for placental, cardiac, and adipose tissue development. Mol Cell (1999) 4:585–595.[CrossRef][Web of Science][Medline]
  6. Schupp M., Clemenz M., Gineste R., Witt H., Janke J., Helleboid S., et al. Molecular characterization of new selective peroxisome proliferator-activated receptor gamma modulators with angiotensin receptor blocking activity. Diabetes (2005) 54:3442–3452.[Abstract/Free Full Text]
  7. Stanley W.C., Recchia F.A., Lopaschuk G.D. Myocardial substrate metabolism in the normal and failing heart. Physiol Rev (2005) 85:1093–1129.[Abstract/Free Full Text]
  8. Picard F., Auwerx J. PPAR(gamma) and glucose homeostasis. Annu Rev Nutr (2002) 22:167–197.[CrossRef][Web of Science][Medline]
  9. Iglarz M., Touyz R.M., Viel E.C., Paradis P., Amiri F., Diep Q.N., et al. Peroxisome proliferator-activated receptor-alpha and receptor-gamma activators prevent cardiac fibrosis in mineralocorticoid-dependent hypertension. Hypertension (2003) 42:737–743.[Abstract/Free Full Text]
  10. Ogata T., Miyauchi T., Irukayama-Tomobe Y., Takanashi M., Goto K., Yamaguchi I. The peroxisome proliferator-activated receptor alpha activator fenofibrate inhibits endothelin-1-induced cardiac fibroblast proliferation. J Cardiovasc Pharmacol (2004) 44(Suppl_1):S279–S282.[CrossRef][Web of Science][Medline]
  11. Chen M.M., Lam A., Abraham J.A., Schreiner G.F., Joly A.H. CTGF expression is induced by TGF-beta in cardiac fibroblasts and cardiac myocytes: a potential role in heart fibrosis. J Mol Cell Cardiol (2000) 32:1805–1819.[CrossRef][Web of Science][Medline]
  12. Igarashi A., Okochi H., Bradham D.M., Grotendorst G.R. Regulation of connective tissue growth factor gene expression in human skin fibroblasts and during wound repair. Mol Biol Cell (1993) 4:637–645.[Abstract]
  13. Dean R.G., Balding L.C., Candido R., Burns W.C., Cao Z., Twigg S.M., et al. Connective tissue growth factor and cardiac fibrosis after myocardial infarction. J Histochem Cytochem (2005) 53:1245–1256.[Abstract/Free Full Text]
  14. Asakawa A., Inui A., Fujimiya M., Sakamaki R., Shinfuku N., Ueta Y., et al. Stomach regulates energy balance via acylated ghrelin and desacyl ghrelin. Gut (2005) 54:18–24.[Abstract/Free Full Text]
  15. Wayman N.S., Ellis B.L., Thiemermann C. Ligands of the peroxisome proliferator-activated receptor-PPAR-a reduce myocardial infarct size. Med Sci Monit (2002) 8:BR243–BR247.[Medline]
  16. Schupp M., Janke J., Clasen R., Unger T., Kintscher U. Angiotensin type 1 receptor blockers induce peroxisome proliferator-activated receptor-gamma activity. Circulation (2004) 109:2054–2057.[Abstract/Free Full Text]
  17. Unger T. Significance of angiotensin type 1 receptor blockade: why are angiotensin II receptor blockers different. Am J Cardiol (1999) 84:9S–15S.[CrossRef][Web of Science][Medline]
  18. Unger T. The ongoing telmisartan alone and in combination with ramipril global endpoint trial program. Am J Cardiol (2003) 91:28G–34G.[Web of Science][Medline]
  19. Tschope C., Koch M., Spillmann F., Heringer-Walther S., Mochmann H.C., et al. Upregulation of the cardiac bradykinin B2 receptors after myocardial infarction. Immunopharmacology (1999) 44:111–117.[CrossRef][Web of Science][Medline]
  20. Tschope C., Walther T., Koniger J., Spillmann F., Westermann D., Escher F., et al. Prevention of cardiac fibrosis and left ventricular dysfunction in diabetic cardiomyopathy in rats by transgenic expression of the human tissue kallikrein gene. Faseb J (2004) 18:828–835.[Abstract/Free Full Text]
  21. Chomczynski P., Sacchi N. Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem (1987) 162:156–159.[Web of Science][Medline]
  22. Schupp M., Kintscher U., Fielitz J., Thomas J., Pregla R., Hetzer R., et al. Cardiac PPARalpha expression in patients with dilated cardiomyopathy. Eur J Heart Fail (2006) 8:290–294.[Abstract/Free Full Text]
  23. Bogazzi F., Russo D., Locci M.T., Chifenti B., Ultimieri F., Raggi F., et al. Peroxisome proliferator-activated receptor (PPAR)gamma is highly expressed in normal human pituitary gland. J Endocrinol Invest (2005) 28:899–904.[Web of Science][Medline]
  24. Makino N., Sugano M., Satoh S., Oyama J., Maeda T. Peroxisome proliferator-activated receptor-gamma ligands attenuate brain natriuretic peptide production and affect remodeling in cardiac fibroblasts in reoxygenation after hypoxia. Cell Biochem Biophys (2006) 44:65–71.[CrossRef][Web of Science][Medline]
  25. Ohnishi H., Oka T., Kusachi S., Nakanishi T., Takeda K., Nakahama M., et al. Increased expression of connective tissue growth factor in the infarct zone of experimentally induced myocardial infarction in rats. J Mol Cell Cardiol (1998) 30:2411–2422.[CrossRef][Web of Science][Medline]
  26. Derosa G., Cicero A.F., Gaddi A., Mugellini A., Ciccarelli L., Fogari R. Effects of doxazosin and irbesartan on blood pressure and metabolic control in patients with type 2 diabetes and hypertension. J Cardiovasc Pharmacol (2005) 45:599–604.[CrossRef][Web of Science][Medline]
  27. Furuhashi M., Ura N., Higashiura K., Murakami H., Tanaka M., Moniwa N., et al. Blockade of the renin-angiotensin system increases adiponectin concentrations in patients with essential hypertension. Hypertension (2003) 42:76–81.[Abstract/Free Full Text]
  28. Henriksen E.J., Jacob S., Kinnick T.R., Teachey M.K., Krekler M. Selective angiotensin II receptor antagonism reduces insulin resistance in obese Zucker rats. Hypertension (2001) 38:884–890.[Abstract/Free Full Text]
  29. Yoshiyama M., Nakamura Y., Omura T., Izumi Y., Matsumoto R., Oda S., et al. Angiotensin converting enzyme inhibitor prevents left ventricular remodelling after myocardial infarction in angiotensin II type 1 receptor knockout mice. Heart (2005) 91:1080–1085.[Abstract/Free Full Text]

Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Fliegner, D.
Right arrow Articles by Regitz-Zagrosek, V.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fliegner, D.
Right arrow Articles by Regitz-Zagrosek, V.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?