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European Journal of Heart Failure 2006 8(2):154-161; doi:10.1016/j.ejheart.2005.06.002
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© 2006 European Society of Cardiology

Activation of peroxisome proliferator-activated receptor-{alpha} and -{gamma} in auricular tissue from heart failure patients

Dulcenombre Gómez-Garrea,*, Marta Herraíza, Ma Luisa González-Rubioa, Rosa Bernala, Paloma Aragoncillob, Amparo Carbonellc, Juan José Rufilanchasc and Arturo Fernández-Cruza

a Vascular Biology and Atherosclerosis Research Laboratory, Área de Prevención Cardiovascular y Rehabilitación Cardíaca, Instituto Cardiovascular Spain
b Department of Pathology, Hospital Clínico San Carlos-UCM Spain
c Heart Failure and Transplant Unit, Cardiology Department Hospital 12 de Octubre-UCM, Madrid, Spain

* Corresponding author. Laboratorio de Biología vascular y Arteriosclerosis (Medicina Nuclear-sótano norte), Hospital Clínico San Carlos, C/Martín Lagos s/n, 28040-Madrid, Spain. Tel.: +34 91 330 3000x7364. E-mail address: mgomezg.hcsc{at}salud.madrid.org


   Abstract
Top
 Abstract
1. Methods
 2. Results
 3. Discussion
 Acknowledgments
 References
 
Objective: Peroxisome proliferator-activated receptors (PPARs), key transcriptional regulators of lipid and energy metabolism in cardiomyocytes, have recently been proposed to modulate cardiovascular pathophysiological responses in experimental models. However, there is little information about the functional activity of PPARs in human heart failure.

Aims: To investigate PPAR-{alpha} and -{gamma} expression and activity, and the association with ET-1 production and fibrosis, in cardiac biopsies from patients with end-stage heart failure due to ischemic cardiomyopathy (ICM) in comparison and from non-failing donor hearts. All samples were obtained during cardiac transplantation.

Methods and results: Morphological analysis (by Masson trichrome and image analysis) did not detect fibrosis in the left atrium from non-failing donors (NFLA) or from ICM patients (FLA). However, left ventricles from failing hearts (FLV) contained a greater number of fibrotic areas (NFLA: 3.21±1.15, FLA: 1.63±0.83, FLV: 14.5±3.45%; n=9, P<0.05). By RT-PCR, preproET-1 expression was similar in the non-failing and failing atrium but was significantly higher in the ventricles from failing hearts (NFLA: 1.00±0.06, FLA: 1.08±0.11, FLV: 1.74±0.19; n=9, P<0.05). PPAR-{alpha} and PPAP-{gamma} mRNA (by RT-PCR) and protein (by Western blot) levels were higher in the ventricles from failing hearts compared with the atrium from failing and non-failing hearts. Electrophoretic mobility shift assays showed that PPAR-{alpha} and PPAP-{gamma} were not activated in the ventricles (NFLA: 1.00±0.11, FLA: 1.89±0.24, FLV: 0.95±0.07; n=9, P<0.05).

Conclusions: These data suggest that PPAR-{alpha} and PPAP-{gamma} are selectively activated in the atria from ICM patients and might be functionally important in the maintenance of atrial morphology.

Key Words: Heart failure • Atrium • Endothelin-1 • Cardiac remodelling • Nuclear receptors

Received November 12, 2004; Accepted June 6, 2005

Left ventricular hypertrophy (LVH), characterized by hypertrophy, loss of myocytes and increased interstitial fibrosis, is now recognized as an important aspect of cardiovascular disease progression and is related to the onset of morbidity and mortality in heart failure (HF) patients. LVH is therefore emerging as a therapeutic target in HF of all aetiologies [reviewed in [1]].

Several neurohormonal factors, including endothelin-1 (ET-1), have been reported to be involved in the process of cardiac remodelling [2]. ET-1 is a potent vasoconstrictor peptide, synthesized and secreted by different cell types, including cardiac myocytes and fibroblasts [3-5]. ET-1 has been shown to induce cardiomyocyte growth in vitro [6] and to promote collagen synthesis by cardiac fibroblasts [7]. Moreover, ET-1 plasma levels are elevated in patients with chronic heart failure [8] and previous studies have linked endothelins with myocardial fibrosis, despite their hemodynamic effects [9].

Peroxisome proliferator-activated receptors (PPARs) are a family of ligand-activated transcription factors that play an important role in the control of lipid metabolism and adipocyte differentiation [10]. However, they have recently been identified as modulators of vascular biology. In vivo, in an experimental model of pressure overload induced by abdominal aortic banding in rats, the administration of fenofibrate (a PPAR-P activator) reduced collagen type I and II mRNA expression as well as interstitial and perivascular cardiac fibrosis [11] and the administration of thiazolidinediones (PPAR-{gamma} activators) inhibited cardiac hypertrophy [12]. These effects were associated with an inhibitory modulation of cardiac ET-1 production. In vitro, it has been reported that ET-1 production by endothelial cells and cardiomyocytes can be inhibited by PPAR-P and PPAR-{gamma} activators through a direct interaction on the preproET-1 promoter [13,14].

However, despite the suggested pathophysiological role of the cardiac PPAR system in the modulation of fibrotic and hypertrophic responses in experimental models, information about its functional activity in human heart failure is lacking. The present study was therefore designed to investigate the presence and/or alterations of PPAR-P and -{gamma}, and their association with fibrosis and ET-1 production, in the left auricular and ventricular tissue from patients with end-stage heart failure due to ischemic cardiomyopathy (ICM). We hypothesized that the activity of PPAR-P and/or PPAR-{gamma} might modulate cardiac fibrosis by an effect on ET-1 expression.


   1. Methods
Top
 Abstract
 1. Methods
2. Results
 3. Discussion
 Acknowledgments
 References
 
We investigated myocardial biopsies (left atrium and ventricle) collected from 9 patients who consecutively underwent orthotopic heart transplantation at Hospital 12 de Octubre, Madrid, due to ICM and end-stage heart failure. The study protocol complies with the principles of the Helsinki Declaration. The study was approved by the hospital ethics committee and all patients gave written informed consent to participate in the study. Cardiac specimens (left atrium) were also obtained from the corresponding non-failing donors. Following the published guidelines from the United Network for Organ Sharing (UNOS) [15], cardiac donor selection criteria were: age <55 years, no history of chest trauma or heart disease, no prolonged hypotension or hypoxemia, mean arterial pressure >60 mmHg, central venous pressure 8-12 mmHg, dopamine <10 µg/Kg/min or dobutamine <10 µg/Kg/min, normal echocardiogram and ECG, and negative HBsAg, HCV and HIV serologies. All biopsies were taken during cardiac transplantation.

1.1. Histopathological studies
For light microscopy, paraffin-embedded cardiac sections (4 µm thick) were prepared and stained with hematoxylin-eosin and Masson's trichrome. From each sample, the amount of fibrosis was assessed using computerised software (LeicaQwin software, Leica Corporation, St Galen, Switzerland) [16]. Areas of fibrosis, which appeared blue with Masson-trichrome stain, were calculated by software. The nontissue spaces, areas overlying the endocardium or perivascular fibrosis of the selected field (if present) were subtracted to provide the corrected total myocardial tissue area in the field. The ratio of the area of fibrotic tissue to the total myocardial tissue provided a measure of the percentage of fibrosis. A pathologist unaware of the patient group to which the specimen belonged performed the biopsy studies.

1.2. RNA extraction, reverse transcription (RT) and polymerase chain reaction (PCR)
Pieces of cardiac tissue were homogenized and total RNA was obtained by the Trizol® method (Life Technologies, Barcelona, Spain). Isolated RNA was reverse-transcribed and amplified with a commercial kit (Access RT-PCR System®, Promega, Madison, WI) using the corresponding human specific primer: preproET-1 (sense: 5'-CTGTTCCAAGCTTGGGAAAAAGTG-3', antisense: 5'-CCCAGATGAAAGAAGAGACCAAA-3'; 64 °C for annealing, 420 base pair), PPAR-P (sense: 5'-CATCACGGACACGCTTTCACC-3', antisense: 5'-GTTCTTCAAGTAGGCCTCGTAG-3'; 64 °C, 450 base pair), PPAR-{gamma} (sense: 5'-CCATTCTGGCCCACCAAC-3', antisense: 5'-CTGAAACCGACAGTACTG-3'; 59 °C, 479 base pair) and GAPDH (sense: 5'-AATGCATCCTGCACCACCAA-3' antisense: 5'-GTAGCCATATTCATTGTCATA-3'; 54 °C, 516 base pair). The optimum number of amplification cycles used for semi quantitative RT-PCR was chosen on the basis of pilot experiments (25, 28, 30 and 20 cycles, respectively). Then, samples were size-fractioned with 4% acrylamide-bisacrylamide gels. The gels were dried and exposed to X-OMAT UV films (Eastman Kodak, Rochester, NY). Autoradiograms were analyzed using scanning densitometry (Molecular Dynamics, Sunnyvale, CA). The density of each gene was compared after the individual correction by density of GAPDH and expressed as arbitrary densitometric units.

1.3. Western blot
Tissue samples were homogenized and then separated by SDS-PAGE under reducing conditions as previously reported [17]. After electrophoresis, samples were transferred to PVDF membranes (Millipore Corp., Bedford, MA). As a control for even protein loading and transfer, membranes were stained with Ponceau S. Blots were incubated with a goat polyclonal anti-human PPAR-P antibody (1:200; Santa Cruz Biotechnology, Inc.) or a rabbit polyclonal anti-human PPAR-{gamma} (1:1000; Santa Cruz Biotechnology, Inc.), washed and subsequently incubated with horseradish peroxidase-conjugated anti-goat (1:10000, Amersham, Aylesbury, UK) or anti-rabbit IgG (1:2000, Amersham). After washing, the blots were developed with the chemiluminescence method (ECL; Amersham).

1.4. Extraction of nuclear proteins and electrophoretic mobility shift assay
Nuclear extracts from cardiac tissue were obtained and the activity of PPARs was evaluated by electrophoretic mobility shift assay (EMSA). Briefly, frozen heart pieces were pulverized and resuspended in a cold extraction buffer [20 mmol/L Hepes-NaOH, pH 7.6, 20% (v/v) glycerol, 0.35 mol/L NaCl, 5 mmol/L MgCl2, 0.1 mmol/L EDTA, 1 mmol/L dithiothreitol (DTT), 0.5 mmol/L PMSF, 1 µg/ml pepstatin A]. The insoluble materials were precipitated from the homogenate by centrifugation at 12,000 r.p.m. for 90 min at 4 °C. Supernatants were dialyzed overnight against a binding buffer containing 20 mmol/L Hepes-NaOH (pH 7.6), 20% (v/v) glycerol, 0.1 mmol/L NaCl, 5 mmol/L MgCl2, 0.1 mmol/L EDTA, 0.1 mmol/L DTT and 0.5 mmol/L PMSF. Protein concentration of the extracts was quantified by the bicinchoninic acid method (Pierce Biotechnology, Inc., Rockford, IL).

Commercial double-stranded oligonucleotide containing a PPAR-P, PPAR-β and PPAR-{gamma} response element (PPRE) (5'-CAAAACTAGGTCAAAGGTCA-3') was end-labelled by incubation with T4 polynucleotide kinase (Promega) in a reaction containing 10 µCi of [{gamma}-32P]ATP (3000 Ci/mmol; Amersham). 20 µg of nuclear proteins were equilibrated for 10 min in a binding buffer containing [1% glycerol, 0.2 mmol/L MgCl2, 0.1 mmol/L EDTA, 0.1 mmol/L DTT, 10 mmol/L NaCl, 2 mmol/L Tris-HCl, pH 7.5, and 10 µg/ml poly (dI-dC)]. Labelled probe (0.035 pmol) was added to the reaction and incubated for 20 min at room temperature. DNA-protein complexes were separated by electrophoresis on a 4% polyacrylamide gel in Tris/borate/EDTA buffer. The gel was dried and exposed to X-OMAT UV films (Eastman Kodak Company) at –80 °C. Autoradiograms were quantified by scanning densitometry (Molecular Dynamics). Competition assays were performed by adding 100-fold molar excess of unlabeled wild-type oligonucleotide.

For supershift assays, 1 µg anti-PPAR-P (Santa Cruz Biotechnology Inc) or anti-PPAR-{gamma} (Santa Cruz Biotechnology Inc) antibody was added and incubated for 1 hour.

1.5. Statistical analysis
Results are expressed as mean±SEM. Comparisons between groups were performed using the Mann-Whitney nonparametric statistic test. Differences were considered significant if the P value was less than 0.05.


   2. Results
Top
 Abstract
 1. Methods
 2. Results
3. Discussion
 Acknowledgments
 References
 
We studied cardiac biopsies from 9 heart failure patients who underwent orthotopic heart transplantation. All patients were diagnosed with ICM and had New York Heart Association (NYHA) functional classification III to IV. Basic clinical characteristics of the studied patients are shown in Table 1.


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  		Table 1 Basic clinical characteristics of end-stage heart failure (CHF) patients

 
The group of non-failing donors consisted of 7 men and 2 women, with a mean age of 25±4 years (range 11 to 38 years). Five donors (55.6%) died due to cerebral haemorrhage and four (44.4%) due to head trauma. All donors were selected following the UNOS recommendations [15].

2.1. Amount of fibrosis
The atrium from non-failing and failing hearts showed narrowed and well aligned myocytes, surrounded with little interstitial tissue (Fig. 1A, B). However, the ventricles from the failing hearts of ICM patients contained a large number of fibrotic areas that were stained green with Masson's trichrome (Fig. 1C).


Figure 1
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  		Fig. 1 Representative tissue cross-sections of left atrium from non-failing donors (A) and left atrium (B) and left ventricle (C) from failing hearts due to ischemic cardiomyopathy. Arrows show interstitial deposition of collagen. (Magnification x10). (D) Morphometric quantification of fibrosis content. Data represent mean±SEM, n=9. *P<0.05 with respect to atrial tissue. Abbreviations: NF: non-failing, F: failing, LA: left atrium, LV: left ventricle.

 
The amount of fibrosis, evaluated by image analysis, did not differ between the non-failing and failing hearts. In contrast, the amount of fibrosis was significantly increased in the left ventricles from ICM patients, compared with the atria from donors and patients (Fig. 1D).

2.2. Pre-proET-1 expression
Semiquantitative RT-PCR showed that levels of preproET-1 expression were similar in the left atria from non-failing and from failing hearts. By contrast, a significant increase in preproET-1 mRNA was observed in the left ventricles from failing hearts (Fig. 2).


Figure 2
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  		Fig. 2 Expression of preproET-1 mRNA in left atrium from non-failing hearts and left atrium and left ventricle from failing hearts due to ischemic cardiomyopathy. Autoradiography showing preproET-1 mRNA expression of two representative subjects from each group. Densitometric analysis of preproET-1 bands from all groups studied. Results are expressed as fold-increase compared with non-failing donors. Individual bar values are mean±SEM of each group, n=9 per group. *P<0.05 with respect to non-failing atrium. Abbreviations: LA: left atrium, LV: left ventricle, AU: arbitrary units.

 
2.3. Expression of PPAR-P and PPAR-{gamma} in human cardiac biopsies
The presence of both PPAR-P and PPAR-{gamma} mRNA and proteins was observed in the human cardiac specimens by RT-PCR and Western blot, respectively. We were not able to find any significant difference in PPAR-P gene expression between non-failing atrium and failing atrium and ventricles, although it tended to be higher in the failing heart biopsies (NFLA: 1.00±0.04, FLA: 1.23±0.11, FLV: 1.37±0.13; n=9, P=NS). PPAR-{gamma} mRNA expression was significantly increased in failing ventricles in comparison with atrial tissues (NFLA: 1.00±0.10, FLA: 1.08±0.08, FLV: 1.26±0.12; n=9, P=0.05).

Similar results were obtained when we investigated PPAR-P and PPAR-{gamma} protein production. Fig. 3 shows representative examples of Western blot bands from cardiac biopsies from non-failing donors and failing patients. Densitometric analysis of the bands demonstrated an increment in both PPAR-P and PPAR-{gamma} proteins in the left ventricles from patients compared with atrial tissue from non-failing and from patients that showed similar levels of both PPAR-P and PPAR-{gamma} proteins (Fig. 3).


Figure 3
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  		Fig. 3 PPAR-P and {gamma} protein expression in the left atrium and left ventricle from non-failing donors and failing hearts due to ischemic cardiomyopathy. Upper. Autoradiography showing PPAR-P (A) and PPAR-{gamma} (B) protein production of two representative subjects from each group. Lower. Densitometric analysis of PPAR-P and PPAR-{gamma} bands from all groups studied. Results are expressed as fold-increase compared with non-failing donors. Individual bar values are mean±SEM of each group, n=9 subjects per group. *P<0.05 with respect to non-failing atrium. Abbreviations: LA: left atrium, LV: left ventricle, AU: arbitrary units.

 
2.4. Studies of PPAR activation in cardiac biopsies
An EMSA was performed to determine whether the detected PPAR-P and PPAR-{gamma} proteins were potentially functional. The DNA response element for both PPAR-P and PPAR-{gamma} (PPRE) was used as labelled probe. As shown in Fig. 4, left atrium from failing hearts produced an almost 2-fold increase in PPRE binding activity compared with that of non-failing donors. This increment was not observed in left ventricles from failing hearts. The specificity of the assay was proved since the presence of a 100-fold excess of unlabeled PPRE or the lack of nuclear proteins in the experiment inhibited the binding signal (Fig. 4C).


Figure 4
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  		Fig. 4 PPAR activity in left atrium and left ventricle from non-failing donors and failing hearts due to ischemic cardiomyopathy. (A) Representative electrophoretic mobility shift assay showing two different subjects from each group. Nuclear extracts from cardiac tissue were incubated with 32P-labelled oligonucleotide probes containing a PPAR-P, -β and -{gamma} response element (PPRE). The position of the PPRE complex and the free probe are indicated with arrows. (B) Densitometric analysis of the results expressed as arbitrary units of mean±SEM of 9 subjects per group. *P<0.05 with respect to non-failing donors, #P<0.05 with respect to failing left atrium. (C) Specificity of the assay was demonstrated with a 100-fold excess of unlabeled oligonucleotide containing PPRE (cold PPRE) or the lack of nuclear proteins (negative). (D) Identification of PPAR subclass in left atrium and left ventricle from failing hearts. The cellular extracts of left atrium and left ventricles were incubated with antibodies against PPAR-P or -{gamma}. A supershifted band with decreased intensity was observed with both antibodies. Abbreviations: LA: left atrium, LV: left ventricle.

 
To further characterize the protein binding to the PPAR motif, protein extracts from failing atrium and ventricles were preincubated with specific antibodies. Incubation of the extracts with an anti-PPAR-P or an anti-PPAR-{gamma} antibody yielded a supershifted band with a slight reduction in the intensity of the bands. These results suggest that both PPAR-P and PPAR-{gamma} activity are increased in left atrium from failing hearts in comparison with non-failing donors.


   3. Discussion
Top
 Abstract
 1. Methods
 2. Results
 3. Discussion
Acknowledgments
 References
 
Recent studies indicate that PPAR-P and PPAR-{gamma} activators prevent vascular damage induced by hormonal factors such as ET-1 [11,12,18]. Interestingly, PPAR-P and PPAR-{gamma} activation also inhibits production of ET-1 through a direct interaction with AP-1 in endothelial cells and in cardiomyocytes [13,14]. However, these findings on the signalling pathway associated to PPAR activation are based on studies in experimental models and in cultured cells. In the present study, we have shown that this cellular signalling pathway could also occur in humans. We provide evidence that cardiac remodelling occurring in heart failure due to ICM is associated with PPAR activity, whereby inactivation of PPAR-P and PPAR-{gamma} would result in an increase in the expression of ET-1 and the presence of cardiac fibrosis.

PPAR-P is principally detected in tissues with high rates of mitochondrial fatty acid oxidation, such as liver and heart, whereas the expression of PPAR-{gamma} is high in adipose tissue [10]. Recently, PPARs have also been reported to be expressed and functional in vascular cells, such as endothelial cells, vascular smooth muscle cells and monocyte/macrophages, both in normal and pathological conditions [19]. In the normal heart, PPAR-P activates the expression of genes involved in the cellular fatty acid utilization pathway. In the failing heart, which is characterized by a reduced expression of key enzymes of free fatty acid oxidation and an increased utilization of glucose [20], previous studies performed in different models of heart failure and cultured cardiomyocytes have demonstrated that PPAR-P activity is reduced at several stages during hypertrophic growth. In the pressure overload-induced hypertrophied mouse heart and in cardiac myocytes over-expressing PPAR-P, downregulation of PPAR-P gene expression and a deactivation of its regulatory pathway has been reported [20]. However, in pacing-induced heart failure, myocardial levels of PPAR-P were not significantly altered, although the protein expression of RXRP, an obligate cofactor of PPAR-P, was dramatically decreased [21]. The role of PPAR-{gamma} in the heart is unknown, although it is involved in the cardiac antihypertrophic response. In fact, heterozygous PPAR-{gamma}-deficient mice developed more accentuated left ventricular hypertrophy than wild-type counterparts after pressure overload induced by aortic banding [22]. Mehrabi et al has shown that PPAR-{gamma} is highly expressed in left ventricles form healthy donors compared to the aorta and coronary arteries [23]. However, these authors found that left ventricle PPAR-{gamma} mRNA levels were similar in failing hearts from ischemic and dilated cardiomyopathy patients and in controls [24], although they did not investigate PPAR activity. In this study, we have shown that both PPAR-P and PPAP-{gamma} mRNA and protein levels were increased in left ventricles from failing hearts in comparison with left atrium from failing and non-failing hearts, although EMSA studies demonstrated that either PPAR-P or PPAP-{gamma} were not activated in left ventricles from failing hearts. Since we have not investigated healthy left ventricles, we cannot compare our results with these previous papers. However, they seem to confirm that heart failure is associated with a regulation of PPAR system activity, although not necessarily at protein expression level.

As commented above, most studies have associated reduced PPAR activity with alteration in myocardial energy metabolism, characteristic of pathological cardiac hypertrophic growth [20]. Our in vivo data are the first to demonstrate that the atrium from ICM patients, which did not present either fibrosis or increased preproET-1expression, showed an activation of PPAR-P and PPAR-{gamma} compared to the non-failing atrium. By contrast, the ventricles from ICM patients showed decreased PPAR activity coinciding with increased preproET-1 expression and fibrosis. Previous studies have shown that systemic administration of PPAR-P and PPAR-{gamma} agonists prevented cardiac fibrosis and remodelling in different models of hypertension [18,25]. After aortic banding-induced pressure overload in rats, the administration of PPAR-P or PPAR-{gamma} agonists effectively inhibited myocardial fibrosis through suppression of ET-1 gene expression [11,12]. Therefore, it is conceivable that attenuated activity of PPAR-P and/or PPAR-{gamma} and increased expression of ET-1 could be an important pathological mechanism in the development of cardiac fibrosis in the human heart.

The molecular mechanisms of the decreased PPAR activity observed in the left ventricles from ICM patients are unknown. In response to falling cardiac output, the heart produces and secretes increased amounts of cytokines and neurohormonal factors [1,2]. Among these factors, tumor necrosis factor P (TNFP) and angiotensin II can be proposed to have a potential role in inhibiting PPAR-P and PPAR-{gamma} activity. TNFP is a proinflammatory cytokine that has been implicated in the pathogenesis of cardiovascular diseases. Several lines of evidence indicate that TNFP is expressed in the failing heart and that circulating TNFP levels are elevated in patients with heart failure [26]. In hepatic stellate cells, it has been recently reported that TNFP inhibits PPAR-{gamma} activity, which has been demonstrated as a critical event in the development of liver fibrosis [27]. In addition, both PPAR-P and PPAR-{gamma} activators inhibit TNFP expression in cardiac myocytes stimulated with lipopolysaccharide [28]. Angiotensin II, the main peptide of the renin-angiotensin system, and another important cardiac hypertrophic factor, has also been associated with a downregulation of PPAR-P and PPAR-{gamma} mRNA and protein expression [29]. Further studies are currently under way in our laboratory testing these potential mechanisms.

One of the major findings of our work is the differential pattern of PPAR activity regulation between the left atrium and the left ventricles of ICM patients. Little is known so far about the molecular pathway leading to ECM production in the atrium. However, in agreement with our results, it has been very recently reported that alterations of atrial ECM components, especially collagen distribution, are distinct to those found previously in the ventricles [30,31]. Since myocardial infarction of the atria is rarely diagnosed, further studies are needed in order to elucidate the contribution of PPAR system to the maintenance of atrial function.

3.1. Study limitations
All patients in our study had ICM. Therefore, the conclusions drawn from this study cannot be applied to other populations. We were not able to compare the data from the left ventricles of patients with those from donors, since only tissue from the left atrium of donors was taken due to the transplantation technique. Because of the small amount of tissue available to us, we were not able to measure any potential mechanism implicated in the PPAR deactivation observed. However, the main aim of our study was to compare the activity of PPAR with the expression on ET-1 and fibrosis, and our data suggest a potential target for prevention and possible reversal of cardiac fibrosis. Finally, a discrepancy between the beneficial effect of PPAR-{gamma} agonists in experimental models and clinical reports has been reported, warning that the PPAR-{gamma} activators, glitazones, may lead to development and/or exacerbate heart failure [32]. Although, it is likely that glitazone side effects such as salt and water retention could precipitate a latent cardiac dysfunction [32,33], differences related to species, doses and timing of treatment should be further investigated.

In summary, we have shown that PPAR-P and PPAP-{gamma} are activated in the left atrium from ICM patients with end-stage heart failure, which did not show significant cardiac fibrosis or ET-1 production in comparison with non-failing left atrium. By contrast, left ventricles from ICM patients showed inhibition of PPAR activation, which coincided with development of cardiac fibrosis and an increase in ET-1 production. These data suggest that PPAR-P and PPAP-{gamma}, selectively upregulated in the left atrium of ICM patients, appear to be functionally associated with the maintenance of atrial morphology and confirm previous studies suggesting the use of selective PPAR-P, PPAP-{gamma} or dual P/{gamma} activators as therapeutic drugs in selected patients.


   Acknowledgments
Top
 Abstract
 1. Methods
 2. Results
 3. Discussion
 Acknowledgments
References
 
This work has been supported partially by grants from Comunidad de Madrid (08.4/0027/2001) and Fondo de Investigación Sanitaria (FIS) (01/3151, 03/0584, 04/0869). MH and ML G-R are fellows from Fundación Fernández-Cruz.


   References
Top
 Abstract
 1. Methods
 2. Results
 3. Discussion
 Acknowledgments
 References
 

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