PPARβ/δ activation inhibits angiotensin II-induced collagen type I expression in rat cardiac fibroblasts

Antihypertensive effects of peroxisome proliferator-activated receptor-β/δ activation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors, which is composed of three members encoded by distinct genes: PPARα, PPARβ/δ, and PPARγ. The biological actions of PPARα and PPARγ and their potential as a cardiovascular therapeutic target have been extensively reviewed, whereas the biological actions of PPARβ/δ and its effectiveness as a therapeutic target in the treatment of hypertension remain less investigated. Preclinical studies suggest that pharmacological PPARβ/δ activation induces antihypertensive effects in direct [spontaneously hypertensive rat (SHR), ANG II, and DOCA-salt] and indirect (dyslipemic and gestational) models of hypertension, associated with end-organ damage protection. This review summarizes mechanistic insights into the antihypertensive effects of PPARβ/δ activators, including molecular and functional mechanisms. Pharmacological PPARβ/δ activation induces genomic actions including the increase of regulators of G protein-coupled signaling (RGS), acute nongenomic vasodilator effects, as well as the ability to improve the endothelial dysfunction, reduce vascular inflammation, vasoconstrictor responses, and sympathetic outflow from central nervous system. Evidence from clinical trials is also examined. These preclinical and clinical outcomes of PPARβ/δ ligands may provide a basis for the development of therapies in combating hypertension.

The Functional SNPs in the 5' Regulatory Region of the Porcine PPARD Gene Have Significant Association with Fat Deposition Traits

Peroxisome proliferator-activated receptor delta (PPARD) is a key regulator of lipid metabolism, insulin sensitivity, cell proliferation and differentiation. In this study, we identified two Single Nucleotide Polymorphisms (SNPs, g.1015 A>G and g.1018 T>C) constituting four haplotypes (GT, GC, AC and AT) in the 5’ regulatory region of porcine PPARD gene. Functional analysis of the four haplotypes showed that the transcriptional activity of the PPARD promoter fragment carrying haplotype AC was significantly lower than that of the other haplotypes in 3T3-L1, C2C12 and PK-15 cells, and haplotype AC had the lowest binding capacities to the nuclear extracts. Transcription factor 7-like 2 (TCF7L2) enhanced the transcription activities of promoter fragments of PPARD gene carrying haplotypes GT, GC and AT in C2C12 and 3T3-L1 cells, and increased the protein expression of PPARD gene in C2C12 myoblasts. TCF7L2 differentially bound to the four haplotypes, and the binding capacity of TCF7L2 to haplotype AC was the lowest. There were significant associations between -655A/G and fat deposition traits in three pig populations including the Large White × Meishan F₂ pigs, France and American Large White pigs. Pigs with genotype GG had significantly higher expression of PPARD at both mRNA and protein level than those with genotype AG. These results strongly suggested that the SNPs in 5’ regulatory region of PPARD genes had significant impact on pig fat deposition traits.

Cryptotanshinone attenuates cardiac fibrosis via downregulation of COX-2, NOX-2, and NOX-4

Cryptotanshinone (CTS), a bioactive constituent extracted from a Chinese traditional herb Danshen (Salvia miltiorrhiza), demonstrates multiple protective effects against cardiovascular diseases. The present study was designed to explore the effects of CTS in vitro by cultured adult rat cardiac fibroblasts stimulated with angiotensin II (Ang II) and in vivo by rats with acute myocardial infarction. Our data showed that in cardiac fibroblasts, CTS attenuated Ang II-induced upregulation of fibronectin, connective tissue growth factor, cyclooxygenase-2, and normalized Ang II-induced upregulation of extracellular signal-regulated kinases 1/2 (ERK1/2). Meanwhile, CTS depressed the Ang II-stimulated upregulation of NAD(P)H oxidase 2 and 4 (NOX-2 and NOX-4) and reactive oxygen species production. Similar results were observed in acute myocardial infarction rats with oral administration of CTS, which relieved the pathological changes accompanying myocardial infarction. In conclusion, CTS may exert antifibrotic effects in vitro by inhibiting Ang II-induced extracellular signal-regulated kinases 1/2 phosphorylation and the expression of cyclooxygenase-2, NOX-2, and NOX-4, and also improved the pathological changes and relieved cardiac fibrosis in vivo.

Sodium tanshinone IIA sulfonate attenuates the transforming growth factor-β1-induced differentiation of atrial fibroblasts into myofibroblasts in vitro

The differentiation of atrial fibroblasts into myofibroblasts is a critical event in atrial fibrosis. One of the most important factors in atrial fibroblast differentiation is transforming growth factor-β1 (TGF-β1). Accumulating evidence indicates that sodium tanshinone IIA sulfonate (STS) possesses antifibrotic properties. In this study, we therefore investigated whether STS attenuates the TGF-β1‑induced differentiation of atrial fibroblasts. TGF-β1 enhanced collagen production, collagen synthesis and the expression of collagen type I and III, as shown by hydroxyproline assay, collagen synthesis assay and western blot analysis, respectively. In addition, as shown by immunohistochemistry and western blot analysis, TGF-β1 enhanced the expression of α-smooth muscle actin (α-SMA), which is the hallmark of myofibroblast differentiation. These responses were attenuated by treatment with STS. In addition, STS suppressed the TGF-β1‑induced expression of phosphorylated (p)Smad/pSmad3 expression and nuclear translocation. Furthermore, STS suppressed extracellular signal-regulated kinase (ERK) phosphorylation. In conclusion, the current study demonstrates that STS exerts antifibrotic effects by modulating atrial fibroblast differentiation through ERK phosphorylation and the Smad pathway.

The Antifibrosis Effects of Peroxisome Proliferator-Activated Receptor δ on Rat Corneal Wound Healing after Excimer Laser Keratectomy

Corneal stromal fibrosis characterized by myofibroblasts and abnormal extracellular matrix (ECM) is usually the result of inappropriate wound healing. The present study tested the hypothesis that the ligand activation of peroxisome proliferator-activated receptor (PPAR) δ had antifibrosis effects in a rat model of corneal damage. Adult Sprague-Dawley rats underwent bilateral phototherapeutic keratectomy (PTK). The eyes were randomized into four groups: PBS, GW501516 (a selective agonist of PPARδ), GSK3787 (a selective antagonist of PPARδ), or GW501516 combined with GSK3787. The agents were subconjunctivally administered twice a week until sacrifice. The cellular aspects of corneal wound healing were evaluated with in vivo confocal imaging and postmortem histology. A myofibroblast marker (α-smooth muscle actin) and ECM production (fibronectin, collagen type III and collagen type I) were examined by immunohistochemistry and RT-PCR. At the early stages of wound healing, GW501516 inhibited reepithelialization and promoted angiogenesis. During the remodeling phase of wound healing, GW501516 attenuated the activation and proliferation of keratocytes, which could be reversed by GSK3787. GW501516 decreased transdifferentiation from keratocytes into myofibroblasts, ECM synthesis, and corneal haze. These results demonstrate that GW501516 controls corneal fibrosis and suggest that PPARδ may potentially serve as a therapeutic target for treating corneal scars.

The peroxisome proliferator-activated receptor β/δ agonist GW0742 has direct protective effects on right heart hypertrophy

Pulmonary hypertension is a debilitating disease with no cure. We have previously shown that peroxisome proliferator-activated receptor (PPAR) β/δ agonists protect the right heart in hypoxia-driven pulmonary hypertension without affecting vascular remodeling. PPARβ/δ is an important receptor in lipid metabolism, athletic performance, and the sensing of prostacyclin. Treatment of right heart hypertrophy and failure in pulmonary hypertension is an emerging target for future therapy. Here we have investigated the potential of GW0742, a PPARβ agonist, to act directly on the right heart in vivo and what transcriptomic signatures are associated with its actions. Right heart hypertrophy and failure was induced in mice using a pulmonary artery banding (PAB) model. GW0742 was administered throughout the study. Cardiovascular parameters were measured using echocardiography and pressure monitoring. Fibrosis and cellular changes were measured using immunohistochemistry. Transcriptomics were measured using the Illumina MouseRef-8v3 BeadChip array and analyzed using GeneSpring GX (ver. 11.0). PAB resulted in right heart hypertrophy and failure and in increased fibrosis. GW0742 reduced or prevented the effects of PAB on all parameters measured. GW0742 altered a number of genes in the transcriptome, with Angptl4 emerging as the top gene altered (increased) in animals with PAB. In conclusion, the PPARβ/δ agonist GW0742 has direct protective effects on the right heart in vivo. These observations identify PPARβ/δ as a viable therapeutic target to treat pulmonary hypertension that may complement current and future vasodilator drugs.

The role of PPARδ signaling in the cardiovascular system

Peroxisome proliferator-activated receptors (PPARα, β/δ, and γ), members of the nuclear receptor transcription factor superfamily, play important roles in the regulation of metabolism, inflammation, and cell differentiation. All three PPAR subtypes are expressed in the cardiovascular system with various expression patterns. Among the three PPAR subtypes, PPARδ is the least studied but has arisen as a potential therapeutic target for cardiovascular and many other diseases. It is known that PPARδ is ubiquitously expressed and abundantly expressed in cardiomyocytes. Accumulated evidence illustrates the role of PPARδ in regulating cardiovascular function and determining pathological progression. In this chapter, we will discuss the current knowledge in the role of PPARδ in the cardiovascular system, the mechanistic insights, and the potential therapeutic utilization for treating cardiovascular disease.

Sitagliptin reduces cardiac apoptosis, hypertrophy and fibrosis primarily by insulin-dependent mechanisms in experimental type-II diabetes. Potential roles of GLP-1 isoforms

Background

Myocardial fibrosis is a key process in diabetic cardiomyopathy. However, their underlying mechanisms have not been elucidated, leading to a lack of therapy. The glucagon-like peptide-1 (GLP-1) enhancer, sitagliptin, reduces hyperglycemia but may also trigger direct effects on the heart.

Methods

Goto-Kakizaki (GK) rats developed type-II diabetes and received sitagliptin, an anti-hyperglycemic drug (metformin) or vehicle (n=10, each). After cardiac structure and function assessment, plasma and left ventricles were isolated for biochemical studies. Cultured cardiomyocytes and fibroblasts were used for invitro assays.

Results

Untreated GK rats exhibited hyperglycemia, hyperlipidemia, plasma GLP-1 decrease, and cardiac cell-death, hypertrophy, fibrosis and prolonged deceleration time. Moreover, cardiac pro-apoptotic/necrotic, hypertrophic and fibrotic factors were up-regulated. Importantly, both sitagliptin and metformin lessened all these parameters. In cultured cardiomyocytes and cardiac fibroblasts, high-concentration of palmitate or glucose induced cell-death, hypertrophy and fibrosis. Interestingly, GLP-1 and its insulinotropic-inactive metabolite, GLP-1(9-36), alleviated these responses. In addition, despite a specific GLP-1 receptor was only detected in cardiomyocytes, GLP-1 isoforms attenuated the pro-fibrotic expression in cardiomyocytes and fibroblasts. In addition, GLP-1 receptor signalling may be linked to PPARδ activation, and metformin may also exhibit anti-apoptotic/necrotic and anti-fibrotic direct effects in cardiac cells.

Conclusions

Sitagliptin, via GLP-1 stabilization, promoted cardioprotection in type-II diabetic hearts primarily by limiting hyperglycemia e hyperlipidemia. However, GLP-1 and GLP-1(9-36) promoted survival and anti-hypertrophic/fibrotic effects on cultured cardiac cells, suggesting cell-autonomous cardioprotective actions.

Protease-activated receptor 1 inhibition by SCH79797 attenuates left ventricular remodeling and profibrotic activities of cardiac fibroblasts

PURPOSE

Fibroblast activity promotes adverse left ventricular (LV) remodeling that underlies the development of ischemic cardiomyopathy. Transforming growth factor-β (TGF-β) is a potent stimulus for fibrosis, and the extracellular signal-regulated kinases(ERK) 1/2 pathway also contributes to the fibrotic response. The thrombin receptor, protease-activated receptor 1 (PAR1), has been shown to play an important role in the excessive fibrosis in different tissues. The aim of this study was to investigate the influence of a PAR1 inhibitor, SCH79797, on cardiac fibrosis, tissue stiffness and postinfarction remodeling, and effects of PAR1 inhibition on thrombin-induced TGF-β and (ERK) 1/2 activities in cardiac fibroblasts.

METHODS

We used a rat model of myocardial ischemia-reperfusion injury, isolated cardiac fibroblasts, and 3-dimensional (3D) cardiac tissue models fabricated to ascertain the contribution of PAR1 activation on cardiac fibrosis and LV remodeling.

RESULTS

The PAR1 inhibitor attenuated LV dilation and improved LV systolic function of the reperfused myocardium at 28 days. This improvement was associated with a nonsignificant decrease in scar size (%LV) from 23 ± % in the control group (n = 10) to 16% ± 5.5% in the treated group (n = 9; P = .052). In the short term, the PAR1 inhibitor did not rescue infarct size or LV systolic function after 3 days. The PAR1 inhibition abolished thrombin-mediated ERK1/2 phosphorylation, TGF-β and type I procollagen production, matrix metalloproteinase-2/9 activation, myofibroblasts transformation in vitro, and abrogated the remodeling of 3D tissues induced by chronic thrombin treatment.

CONCLUSION

These studies suggest PAR1 inhibition initiated after ischemic injury attenuates adverse LV remodeling through late-stage antifibrotic events.

PPARδ agonist GW501516 inhibits PDGF-stimulated pulmonary arterial smooth muscle cell function related to pathological vascular remodeling

Pulmonary arterial hypertension (PAH) is a severe and progressive disease, a key feature of which is pulmonary vascular remodeling. Growth factors, cytokines, and lipid mediators are involved in this remodeling process. Recent reports suggest that the peroxisome proliferator-activated receptors (PPARs) play important roles in the regulation of cell growth and differentiation as well as tissue wounding and repair. In this study, we examined the role of PPARδ in the regulation of proliferation, migration, collagen synthesis, and chemokine production in human pulmonary arterial smooth muscle cells (HPASMCs). The data showed that PPARδ was the most abundant isoform in HPASMCs. PPARδ was upregulated in HPASMCs treated with PDGF, which is the major mediator in pulmonary vascular remodeling. Activation of PPARδ by GW501516, a specific PPARδ ligand, significantly inhibited PDGF-induced proliferation in HPASMCs. The inhibitory effect of GW501516 on HPASMCs was associated with decreased expression of cyclin D1, cyclin D3, CDK2, and CDK4 as well as increased expression of the cell cycle inhibitory genes G0S2 and P27^kip1. Pretreatment of HPASMCs with GW501516 significantly inhibited PDGF-induced cell migration and collagen synthesis. GW501516 also significantly attenuated TNF-mediated expression of MCP-1. These results suggest that PPARδ may be a potential therapeutic target against the progression of vascular remodeling in PAH.

EGCG inhibits CTGF expression via blocking NF-κB activation in cardiac fibroblast

Connective tissue growth factor (CTGF) has been reported to play an important role in tissue fibrosis and presents a promising therapeutic target for fibrotic diseases. In heart, inappropriate increase in level of CTGF promotes fibroblast proliferation and extracellular matrix (ECM) accumulation, thereby exacerbating cardiac hypertrophy and subsequent failure. Epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea, possesses multiple protective effects on the cardiovascular system including cardiac fibrosis. However, the molecular mechanism by which EGCG exerts its anti-fibrotic effects has not been well investigated. In this study, we found that EGCG could significantly reduce collagen synthesis, fibronectin (FN) expression and cell proliferation in rat cardiac fibroblasts stimulated with angiotensinII (AngII). It also ameliorated cardiac fibrosis in rats submitted to abdominal aortic constriction (AAC). Moreover, EGCG attenuated the excessive expression of CTGF induced by AAC or AngII, and reduced the nuclear translocation of NF-κB p65 subunit and degradation of IκB-α. Subsequently, we demonstrated that in cardiac fibroblasts NF-κB inhibition could suppress AngII-induced CTGF expression. Taken together, these findings provide the first evidence that the effect of EGCG against cardiac fibrosis may be attributed to its inhibition on NF-κB activation and subsequent CTGF overexpression, suggesting the therapeutic potential of EGCG on the prevention of cardiac remodeling in patients with pressure overload hypertrophy.

Antihypertensive effects of peroxisome proliferator-activated receptor-β activation in spontaneously hypertensive rats

Activation of nuclear hormone receptor peroxisome proliferator-activated receptor β/δ (PPARβ) has been shown to improve insulin resistance and plasma high-density lipoprotein levels, but nothing is known about its effects in genetic hypertension. We studied whether the PPARβ agonist GW0742 might exert antihypertensive effects in spontaneously hypertensive rats (SHRs). The rats were divided into 4 groups, Wistar Kyoto rat-control, Wistar Kyoto rat-treated (GW0742, 5 mg · kg(-1) · day(-1) by oral gavage), SHR-control, and SHR-treated, and followed for 5 weeks. GW0742 induced a progressive reduction in systolic arterial blood pressure and heart rate in SHRs and reduced the mesenteric arterial remodeling, the increased aortic vasoconstriction to angiotensin II, and the endothelial dysfunction characteristic of SHRs. These effects were accompanied by a significant increase in endothelial NO synthase activity attributed to upregulated endothelial NO synthase and downregulated caveolin 1 protein expression. Moreover, GW0742 inhibited vascular superoxide production, downregulated p22(phox) and p47(phox) proteins, decreased both basal and angiotensin II-stimulated NADPH oxidase activity, inhibited extracellular-regulated kinase 1/2 activation, and reduced the expression of the proinflammatory and proatherogenic genes, interleukin 1β, interleukin 6, or intercellular adhesion molecule 1. None of these effects were observed in Wistar Kyoto rats. PPARβ activation, both in vitro and in vivo, increased the expression of the regulators of G protein-coupled signaling proteins RGS4 and RGS5, which negatively modulated the vascular actions of angiotensin II. PPARβ activation exerted antihypertensive effects, restored the vascular structure and function, and reduced the oxidative, proinflammatory, and proatherogenic status of SHRs. We propose PPARβ as a new therapeutic target in hypertension.

PPARs as therapeutic targets in cardiovascular disease

IMPORTANCE OF THE FIELD

The role of peroxisome proliferator-activated receptors PPARα, PPARδ and PPARγ in cardiovascular disease is receiving widespread attention. As ligand-activated nuclear receptors, they play a role in regulation of lipid and glucose metabolism. This feature of the PPARs has been successfully exploited to treat systemic metabolic diseases, like hyperlipidemia and type-2 diabetes. Indirectly, their lipid lowering effect also leads to a reduction of the risk for cardiovascular diseases, primarily atherosclerosis.

AREAS COVERED IN THIS REVIEW

The pleiotropic effects of each of the PPAR isotypes on vascular and cardiac disease are discussed, with special emphasis on the molecular mechanism of action and on preclinical observations. The mechanism underlying the beneficial effect of PPARs is not confined to whole body metabolism, but also includes modulation of other vital processes, such as inflammation and cell fate (proliferation, differentiation, apoptosis).

WHAT THE READER WILL GAIN

A large body of preclinical studies indicates that, in addition to their effect on atherogenesis, PPAR ligands also impact on ischemic heart disease and the development of cardiac failure. It remains to be established to what extent these intriguing observations can be translated into clinical practice.

TAKE HOME MESSAGE

The versatile mechanism of action extends the potential therapeutic profile of the PPARs enormously. Conversely, this versatility makes it harder to attain a specific therapeutic effect, without increasing the risk of undesirable side effects. The future challenge will be to design PPAR-based therapeutic strategies that minimize the detrimental side effects.

Tanshinone II-A attenuates cardiac fibrosis and modulates collagen metabolism in rats with renovascular hypertension

The adaptive changes that develop in the pressure-overloaded left ventricular myocardium include cardiac hypertrophy and interstitial fibrosis. The objectives of the present study were to evaluate the effects of Tanshinone II-A, a bioactive diterpene quinone isolated from Danshen, on cardiac fibrosis and collagen metabolism in rats with renovascular hypertension. Male Sprague-Dawley rats were subjected to two-kidney two-clip (2K2C) or sham operation (sham) and treated with Valsartan (Val, 26.7 mg/kg/d), Tanshinone II-A (Tsn, 70, 35 mg/kg/d) or vehicle. Six weeks later, systolic blood pressure (BP), LV weight, collagen abundance, cardiac function parameters, hydroxyproline content and mRNA levels of matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 were evaluated. Both high-dose (Tsn-H, 70 mg/kg/d) and low-dose (Tsn-L, 35 mg/kg/d) of Tsn failed to attenuate 2K2C-induced BP elevation but significantly attenuated the attendant interstitial fibrosis. Val suppressed elevations of BP and left ventricular systolic pressure (LVSP) in 2K2C rats. Val and Tsn-H exerted comparable suppressive effects on the gene expression of MMP-9 and TIMP-1, while Val decreased the MMP-2 mRNA level without affecting the transcript levels of TIMP-2. Both Val and Tsn-H attenuated cardiac dysfunction, while Tsn-L showed slight improvement. These data demonstrate for the first time, that Tsn prevented cardiac fibrosis and improved cardiac function in a rat model of renovascular hypertensive independent of hypotensive effect. Tsn conferred its beneficial effects on the collagen metabolism probably through its regulation of transcript levels of the MMPs/TIMPs balance.

Peroxisome proliferator-activated receptors, metabolic syndrome and cardiovascular disease

Metabolic syndrome (MetS) is a constellation of risk factors including insulin resistance, central obesity, dyslipidemia and hypertension that markedly increase the risk of Type 2 diabetes (T2DM) and cardiovascular disease (CVD). The peroxisome proliferators-activated receptor (PPAR) isotypes, PPARα, PPARδ/ß and PPARγ are ligand-activated nuclear transcription factors, which modulate the expression of an array of genes that play a central role in regulating glucose, lipid and cholesterol metabolism, where imbalance can lead to obesity, T2DM and CVD. They are also drug targets, and currently, PPARα (fibrates) and PPARγ (thiazolodinediones) agonists are in clinical use for treating dyslipidemia and T2DM, respectively. These metabolic characteristics of the PPARs, coupled with their involvement in metabolic diseases, mean extensive efforts are underway worldwide to develop new and efficacious PPAR-based therapies for the treatment of additional maladies associated with the MetS. This article presents an overview of the functional characteristics of three PPAR isotypes, discusses recent advances in our understanding of the diverse biological actions of PPARs, particularly in the vascular system, and summarizes the developmental status of new single, dual, pan (multiple) and partial PPAR agonists for the clinical management of key components of MetS, T2DM and CVD. It also summarizes the clinical outcomes from various clinical trials aimed at evaluating the atheroprotective actions of currently used fibrates and thiazolodinediones.

Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) acts as regulator of metabolism linked to multiple cellular functions

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors. They function as ligand activated transcription factors. They exist in three isoforms, PPARalpha, PPARbeta (formerly PPARdelta), and PPARgamma. For all PPARs lipids are endogenous ligands, linking them directly to metabolism. PPARs form heterodimers with retinoic X receptors, and, upon ligand binding, modulate gene expression of downstream target genes dependent on the presence of co-repressors or co-activators. This results in cell-type specific complex regulations of proliferation, differentiation and cell survival. Specific synthetic agonists for all PPARs are available. PPARalpha and PPARgamma agonists are already in clinical use for the treatment of hyperlipidemia and type 2 diabetes, respectively. More recently, PPARbeta activation came into focus as an interesting novel approach for the treatment of metabolic syndrome and associated cardiovascular diseases. Although the initial notion was that PPARbeta is expressed ubiquitously, more recently extensive investigations have been performed demonstrating high PPARbeta expression in a variety of tissues, e.g. skin, skeletal muscle, adipose tissue, inflammatory cells, heart, and various types of cancer. In addition, in vitro and in vivo studies using specific PPARbeta agonists, tissue-specific over-expression or knockout mouse models have demonstrated a variety of functions of PPARbeta in adipose tissue, muscle, skin, inflammation, and cancer. We will focus here on functions of PPARbeta in adipose tissue, skeletal muscle, heart, angiogenesis and cancer related to modifications in metabolism and the identified underlying molecular mechanisms.

Sodium tanshinone IIA sulfonate attenuates angiotensin II-induced collagen type I expression in cardiac fibroblasts in vitro

Cardiac fibrosis occurs after pathological stimuli to the cardiovascular system. One of the most important factors that contribute to cardiac fibrosis is angiotensin II (AngII). Accumulating studies have suggested that reactive oxygen species (ROS) plays an important role in cardiac fibrosis and sodium tanshinone IIA sulfonate (STS) possesses antioxidant action. We therefore examined whether STS depresses Ang II-induced collagen type I expression in cardiac fibroblasts. In this study, Ang II significantly enhanced collagen type I expression and collagen synthesis. Meanwhile, Ang II depressed matrix metalloproteinase-1 (MMP-1) expression and activity. These responses were attenuated by STS. Furthermore, STS depressed the intracellular generation of ROS, NADPH oxidase activity and subunit p47(phox) expression. In addition, N-acetylcysteine the ROS scavenger, depressed effects of Ang II in a manner similar to STS. In conclusion, the current studies demonstrate that anti-fibrotic effects of STS are mediated by interfering with the modulation of ROS.

Sorting out the functional role(s) of peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta) in cell proliferation and cancer

Peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta) has many beneficial physiological functions ranging from enhancing fatty acid catabolism, improving insulin sensitivity, inhibiting inflammation and increasing oxidative myofibers allowing for improved athletic performance. Thus, given the potential for targeting PPARbeta/delta for the prevention and/or treatment of diseases including diabetes, dyslipidemias, metabolic syndrome and cancer, it is critical to clarify the functional role of PPARbeta/delta in cell proliferation and associated disorders such as cancer. However, there is considerable controversy whether PPARbeta/delta stimulates or inhibits cell proliferation. This review summarizes the literature describing the influence of PPARbeta/delta on cell proliferation, with an emphasis toward dissecting the data that give rise to opposing hypotheses. Suggestions are offered to standardize measurements associated with these studies so that interlaboratory comparisons can be accurately assessed.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

Peroxisome proliferator-activated receptor beta stimulation induces rapid cardiac growth and angiogenesis via direct activation of calcineurin

AIMS

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors. PPARbeta agonists were suggested as potential drugs for the treatment of metabolic syndrome, but effects of PPARbeta activation on cardiac growth and vascularization are unknown. Thus, we investigated the consequences of pharmacological PPARbeta activation on the heart and the underlying molecular mechanisms.

METHODS AND RESULTS

Male C57/Bl6 mice were injected with the specific PPARbeta agonists GW0742 or GW501516, or vehicle. Cardiomyocyte size and vascularisation were determined at different time points. Expression differences were investigated by quantitative reverse transcriptase-polymerase chain reaction and western blotting. In addition, the effects of PPARbeta stimulation were compared with hearts of mice undergoing long-term voluntary exercise or pharmacological PPARalpha activation. Five hours after GW0742 injection, we detected an enhanced angiogenesis compared with vehicle-injected controls. After 24 h, the heart-to-body weight ratios were higher in mice injected with either GW0742 or GW501516 vs. controls. The increased heart size was due to cardiomyocyte enlargement. No signs of pathological cardiac hypertrophy (i.e. apoptosis, fibrosis, or deteriorated cardiac function) could be detected. The effects are mediated via calcineurin A (CnA) activation as: (i) CnA was upregulated, (ii) GW0742 administration or co-transfection of PPARbeta significantly stimulated the activity of the CnA promoter, (iii) PPARbeta protein bound directly to the CnA promoter, (iv) the CnA target genes NFATc3, Hif-1alpha, and Cdk 9 were upregulated in response to PPARbeta stimulation, and (v) the inhibition of CnA activity by cyclosporine A abolished the hypertrophic and angiogenic responses to PPARbeta stimulation.

CONCLUSION

Our data suggest PPARbeta pharmacological activation as a novel approach to increase cardiac vascularization and cardiac muscle mass.

PPARδ activity in cardiovascular diseases: A potential pharmacological target

Activation of peroxisome proliferator-activated receptors (PPARs), and particularly of PPARα and PPARγ, using selective agonists, is currently used in the treatment of metabolic diseases such as hypertriglyceridemia and type 2 diabetes mellitus. PPARα and PPARγ anti-inflammatory, antiproliferative and antiangiogenic properties in cardiovascular cells were extensively clarified in a variety of in vitro and in vivo models. In contrast, the role of PPARδ in cardiovascular system is poorly understood. Prostacyclin, the predominant prostanoid released by vascular cells, is a putative endogenous agonist for PPARδ, but only recently PPARδ selective synthetic agonists were found, improving studies about the physiological and pathophysiological roles of PPARδ activation. Recent reports suggest that the PPARδ activation may play a pivotal role to regulate inflammation, apoptosis, and cell proliferation, suggesting that this transcriptional factor could become an interesting pharmacological target to regulate cardiovascular cell apoptosis, proliferation, inflammation, and metabolism.

Direct antiatherosclerotic effects of PPAR agonists

PURPOSE OF REVIEW

Peroxisome proliferator activated receptors (PPARs) are ligand-dependent transcription factors that mediate a range of important metabolic functions by transactivation, transrepression or corepression of various gene targets. PPAR agonists also have direct antiatherosclerotic effects, independent of their metabolic effects on glucose and lipid homeostasis. The purpose of this review is to evaluate the currently available evidence for a direct vasculoprotective effect of PPAR agonists.

RECENT FINDINGS

Current studies have emphasized PPAR-mediated effects on inflammatory and immune responses, oxidative stress, the renin-angiotensin system and modulation of plaque composition. Furthermore, it has become evident that the relative activation of the different PPAR isoforms and the contribution of transactivation of target genes against transrepression of transcription factors need to be considered when assessing the vasculoprotective effects of PPAR agonists.

SUMMARY

It is anticipated that the antiatherosclerotic effects of PPAR agonists observed in experimental studies will translate into reduced cardiovascular events. This promise is yet to be realized in short-to-medium term studies. Given the central role of the PPAR in gene regulation, particularly in metabolic states, it is possible that more targeted modulation of PPAR signalling may hold many rewards for the prevention of atherosclerosis.

Tanshinone IIA protects neonatal rat cardiomyocytes from adriamycin-induced apoptosis

Tanshinone IIA (TSN) is a monomer extracted from the Chinese herb Danshen. In this study, we examined the effect of Tanshinone IIA on adriamycin (ADR)-induced apoptosis in neonatal rat cardiomyocytes and underlying molecular mechanisms. Primary cultured cardiomyocytes were treated with 1 micromol/L of adriamycin for 24 h with or without pretreatment with Tanshinone IIA (0.5-2 micromol/L) for 2 h. 3-(4,5-dimethyl thiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Hoechst staining, and flow cytometry measurement were used to assess cell viability and apoptosis. Fluorescent probes 2',7'-dichlorofluorescein diacetate and dihydroethidium were used to detect the production of reactive oxygen species. Western blotting was used to evaluate the expression of Bcl-2 and Bax proteins. Adriamycin significantly induced apoptosis in cardiomyocytes. Tanshinone IIA (0.5-2 micromol/L) ameliorated apoptosis induced by adriamycin in a dose-dependent manner. Tanshinone IIA (2 micromol/L) markedly attenuated adriamycin-induced reactive oxygen species production. Western blotting revealed that Tanshinone IIA prevented the adriamycin-mediated reduction of the ratio of Bcl-2/Bax. In conclusion, Tanshinone IIA significantly inhibits adriamycin-induced cardiomyocyte apoptosis in a dose-dependent manner, and this effect is at least partly caused by its antioxidant properties.