Prostaglandin F2 alpha induces cardiac myocyte hypertrophy in vitro and cardiac growth in vivo

Prostanoids in Cardiac and Vascular Remodeling

Prostanoids are biologically active lipids generated from arachidonic acid by the action of the COX (cyclooxygenase) isozymes. NSAIDs, which reduce the biosynthesis of prostanoids by inhibiting COX activity, are effective anti-inflammatory, antipyretic, and analgesic drugs. However, their use is limited by cardiovascular adverse effects, including myocardial infarction, stroke, hypertension, and heart failure. While it is well established that NSAIDs increase the risk of atherothrombotic events and hypertension by suppressing vasoprotective prostanoids, less is known about the link between NSAIDs and heart failure risk. Current evidence indicates that NSAIDs may increase the risk for heart failure by promoting adverse myocardial and vascular remodeling. Indeed, prostanoids play an important role in modulating structural and functional changes occurring in the myocardium and in the vasculature in response to physiological and pathological stimuli. This review will summarize current knowledge of the role of the different prostanoids in myocardial and vascular remodeling and explore how maladaptive remodeling can be counteracted by targeting specific prostanoids.

Droplet Digital PCR Is a Novel Screening Method Identifying Potential Cardiac G-Protein-Coupled Receptors as Candidate Pharmacological Targets in a Rat Model of Pressure-Overload-Induced Cardiac Dysfunction

The identification of novel drug targets is needed to improve the outcomes of heart failure (HF). G-protein-coupled receptors (GPCRs) represent the largest family of targets for already approved drugs, thus providing an opportunity for drug repurposing. Here, we aimed (i) to investigate the differential expressions of 288 cardiac GPCRs via droplet digital PCR (ddPCR) and bulk RNA sequencing (RNAseq) in a rat model of left ventricular pressure-overload; (ii) to compare RNAseq findings with those of ddPCR; and (iii) to screen and test for novel, translatable GPCR drug targets in HF. Male Wistar rats subjected to transverse aortic constriction (TAC, n = 5) showed significant systolic dysfunction vs. sham operated animals (SHAM, n = 5) via echocardiography. In TAC vs. SHAM hearts, RNAseq identified 69, and ddPCR identified 27 significantly differentially expressed GPCR mRNAs, 8 of which were identified using both methods, thus showing a correlation between the two methods. Of these, Prostaglandin-F2α-receptor (Ptgfr) was further investigated and localized on cardiomyocytes and fibroblasts in murine hearts via RNA-Scope. Antagonizing Ptgfr via AL-8810 reverted angiotensin-II-induced cardiomyocyte hypertrophy in vitro. In conclusion, using ddPCR as a novel screening method, we were able to identify GPCR targets in HF. We also show that the antagonism of Ptgfr could be a novel target in HF by alleviating cardiomyocyte hypertrophy.

Early Protective Role of Inflammation in Cardiac Remodeling and Heart Failure: Focus on TNFα and Resident Macrophages

Cardiac hypertrophy, initiated by a variety of physiological or pathological stimuli (hemodynamic or hormonal stimulation or infarction), is a critical early adaptive compensatory response of the heart. The structural basis of the progression from compensated hypertrophy to pathological hypertrophy and heart failure is still largely unknown. In most cases, early activation of an inflammatory program reflects a reparative or protective response to other primary injurious processes. Later on, regardless of the underlying etiology, heart failure is always associated with both local and systemic activation of inflammatory signaling cascades. Cardiac macrophages are nodal regulators of inflammation. Resident macrophages mostly attenuate cardiac injury by secreting cytoprotective factors (cytokines, chemokines, and growth factors), scavenging damaged cells or mitochondrial debris, and regulating cardiac conduction, angiogenesis, lymphangiogenesis, and fibrosis. In contrast, excessive recruitment of monocyte-derived inflammatory macrophages largely contributes to the transition to heart failure. The current review examines the ambivalent role of inflammation (mainly TNFα-related) and cardiac macrophages (Mφ) in pathophysiologies from non-infarction origin, focusing on the protective signaling processes. Our objective is to illustrate how harnessing this knowledge could pave the way for innovative therapeutics in patients with heart failure.

Stretch modulation of cardiac contractility: importance of myocyte calcium during the slow force response

The mechanical response of the heart to myocardial stretch has been understood since the work of muscle physiologists more than 100 years ago, whereby an increase in ventricular chamber filling during diastole increases the subsequent force of contraction. The stretch-induced increase in contraction is biphasic. There is an abrupt increase in the force that coincides with the stretch (the rapid response), which is then followed by a slower response that develops over several minutes (the slow force response, or SFR). The SFR is associated with a progressive increase in the magnitude of the Ca²⁺ transient, the event that initiates myocyte cross-bridge cycling and force development. However, the mechanisms underlying the stretch-dependent increase in the Ca²⁺ transient are still debated. This review outlines recent literature on the SFR and summarizes the different stretch-activated Ca²⁺ entry pathways. The SFR might result from a combination of several different cellular mechanisms initiated in response to activation of different cellular stretch sensors.

Cardiac thromboxane A2 receptor activation does not directly induce cardiomyocyte hypertrophy but does cause cell death that is prevented with gentamicin and 2-APB

Background

We have previously shown that the thromboxane (TXA2) receptor agonist, U46619, can directly induce ventricular arrhythmias that were associated with increases in intracellular calcium in cardiomyocytes. Since TXA2 is an inflammatory mediator and induces direct calcium changes in cardiomyocytes, we hypothesized that TXA2 released during ischemia or inflammation could also cause cardiac remodeling.

Methods

U46619 (0.1-10 μM) was applied to isolated adult mouse ventricular primary cardiomyocytes, mouse ventricular cardiac muscle strips, and cultured HL-1 cardiomyocytes and markers of hypertrophy and cell death were measured.

Results

We found that TXA2 receptors were expressed in ventricular cardiomyocytes and were functional via calcium imaging. U46619 treatment for 24 h did not increase expression of pathological hypertrophy genes (atrial natriuretic peptide, β-myosin heavy chain, skeletal muscle α-actin) and it did not increase protein synthesis. There was also no increase in cardiomyocyte size after 48 h treatment with U46619 as measured by flow cytometry. However, U46619 (0.1-10 μM) caused a concentration-dependent increase in cardiomyocyte death (trypan blue, MTT assays, visual cell counts and TUNEL stain) after 24 h. Treatment of cells with the TXA2 receptor antagonist SQ29548 and inhibitors of the IP3 pathway, gentamicin and 2-APB, eliminated the increase in cell death induced by U46619.

Conclusions

Our data suggests that TXA2 does not induce cardiac hypertrophy, but does induce cell death that is mediated in part by IP3 signaling pathways. These findings may provide important therapeutic targets for inflammatory-induced cardiac apoptosis that can lead to heart failure.

Fatty acids and cardiac disease: fuel carrying a message

From the viewpoint of the prevention of cardiovascular disease (CVD) burden, there has been a continuous interest in the detrimental effects of the Western-type high-fat diet for more than half a century. More recently, this general view has been subject to change as epidemiological studies showed that replacing fat by carbohydrate may even be worse and that various polyunsaturated fatty acids (FA) have beneficial rather than detrimental effects on CVD outcome. At the same time, advances in lipid biology have provided insight into the mechanisms by which the different lipid components of the Western diet affect the cardiovascular system. In fact, this still is a rapidly growing field of research and in recent years novel FA derivatives and FA receptors have been discovered. This includes fish-oil derived FA-derivatives with anti-inflammatory properties, the so-called resolvins, and various G-protein-coupled receptors that recognize FA as ligands. In the present review, we will extensively discuss the role of FA and their metabolites on cardiac disease, with special emphasis on the role of the different saturated and polyunsaturated FA and their respective metabolites in cellular signal transduction and the possible implications for the development of cardiac hypertrophy and cardiac failure.

N-acetyl-4-aminophenol and musculoskeletal adaptations to resistance exercise training

N-acetyl-4-aminophenol (ACET) may impair musculoskeletal adaptations to progressive resistance exercise training (PRT) by inhibiting exercise-induced muscle protein synthesis and bone formation. To test the hypothesis that ACET would diminish training-induced increases in fat-free mass (FFM) and osteogenesis, untrained men (n = 26) aged ≥50 years participated in 16 weeks of high-intensity PRT and bone-loading exercises and were randomly assigned to take ACET (1,000 mg/day) or placebo (PLAC) 2 h before each exercise session. Total body FFM was measured by DXA at baseline and week 16. Serum bone-specific alkaline phosphatase (BAP) and C-terminal crosslinks of type-I collagen (CTX) were measured at baseline and week 16. Vastus lateralis muscle biopsies were performed at baseline and weeks 3 and 16 for prostanoid, anabolic, and catabolic gene expression by RT-PCR. In exercise-compliant men (ACET, n = 10; PLAC, n = 7), the increase in FFM was not different between groups (p = 0.91). The changes in serum BAP and CTX were not different between groups (p > 0.7). There were no significant changes in any of the target genes at week 3. After 16 weeks of PRT, the mRNA expressions of the anabolic marker p70S6K (p = 0.003) and catabolic marker muscle-atrophy F-box (MAFbx) (p = 0.03) were significantly reduced as compared to baseline in ACET. The mRNA expression of the prostanoids were unchanged (all p ≥ 0.40) in both groups. The administration of ACET (1,000 mg) prior to each exercise session did not impair PRT-induced increases in FFM or significantly alter bone formation markers in middle aged and older men.

Biasing the prostaglandin F2α receptor responses toward EGFR-dependent transactivation of MAPK

The G protein-coupled prostaglandin F2α (PGF2α) receptor [F prostanoid (FP) receptor] has been implicated in many physiological events including cardiovascular, respiratory, immune, reproductive, and endocrine responses. Binding of PGF2α to FP receptor elicits inositol production and protein kinase C-dependent MAPK activation through Gα(q) coupling. Here we report that AL-8810, previously characterized as an orthosteric antagonist of PGF2α-dependent, Gα(q)-mediated signaling, potently activates ERK1/2 in a protein kinase C-independent manner. Rather, AL-8810 promoted ERK1/2 activation via an epidermal growth factor receptor transactivation mechanism in both human embryonic kidney 293 cells and in the MG-63 osteoblast-like cells, which express endogenous FP receptors. Neither AL-8810- nor PGF2α-mediated stimulation of FP receptor promoted association with β-arrestins, suggesting that MAPK activation induced by these ligands is independent of β-arrestin's signaling scaffold functions. Interestingly, the spatiotemporal activation of ERK1/2 promoted by AL-8810 and PGF2α showed almost completely opposite responses in the nucleus and the cytosol. Finally, using [(3)H]thymidine incorporation, we noted differential regulation of PGF2α- and AL-8810-induced cell proliferation in MG-63 cells. This study reveals, for the first time, the signaling biased nature of FP receptor orthosteric ligands toward MAPK signaling. Our findings on the specific patterns of ERK1/2 activation promoted by FP receptor ligands may help dissect the distinct roles of MAPK in FP receptor-dependent physiological responses.

The Prostaglandin F Synthase Activity of the Human Aldose Reductase AKR1B1 Brings New Lenses to Look at Pathologic Conditions

Prostaglandins are important regulators of female reproductive functions to which aldose reductases exhibiting hydroxysteroid dehydrogenase activity also contribute. Our work on the regulation of reproductive function by prostaglandins (PGs), lead us to the discovery that AKR1B5 and later AKR1B1were highly efficient and physiologically relevant PGF synthases. PGE2 and PGF2α are the main prostanoids produced in the human endometrium and proper balance in their relative production is important for normal menstruation and optimal fertility. Recent evidence suggests that PGE2/EP2 and PGF2α/FP may constitute a functional dyad with physiological relevance comparable to the prostacyclin-thromboxane dyad in the vascular system. We have recently reported that AKR1B1 was expressed and modulated in association with PGF2α production in response to IL-1β in the human endometrium. In the present study, we show that the human AKR1B1 (gene ID: 231) also known as ALDR1 or ALR2 is a functional PGF2α synthase in different models of living cells and tissues. Using human endometrial cells, prostate, and vascular smooth muscle cells, cardiomyocytes and endothelial cells we demonstrate that IL-1β is able to up regulate COX-2 and AKR1B1 proteins as well as PGF2α production under normal glucose concentrations. We show that the promoter activity of AKR1B1 gene is increased by IL-1β particularly around the multiple stress response region containing two putative antioxidant response elements adjacent to TonE and AP1. We also show that AKR1B1 is able to regulate PGE2 production through PGF2α acting on its FP receptor and that aldose reductase inhibitors like alrestatin, Statil (ponalrestat), and EBPC exhibit distinct and characteristic inhibition of PGF2α production in different cell models. The PGF synthase activity of AKR1B1 represents a new and important target to regulate ischemic and inflammatory responses associated with several human pathologies.

Aging-shifted prostaglandin profile in endothelium as a factor in cardiovascular disorders

Age-associated endothelium dysfunction is a major risk factor for the development of cardiovascular diseases. Endothelium-synthesized prostaglandins and thromboxane are local hormones, which mediate vasodilation and vasoconstriction and critically maintain vascular homeostasis. Accumulating evidence indicates that the age-related changes in endothelial eicosanoids contribute to decline in endothelium function and are associated with pathological dysfunction. In this review we summarize currently available information on aging-shifted prostaglandin profiles in endothelium and how these shifts are associated with cardiovascular disorders, providing one molecular mechanism of age-associated endothelium dysfunction and cardiovascular diseases.

The contribution of prostaglandins versus prostacyclin in ventricular remodeling during heart failure

Although the role of Cox-2 in the heart's response to physiologic stress remains controversial (i.e. expression in myocytes versus other resident myocardial cells) the ever expanding role of prostanoids in multiple models of heart failure cannot be denied. Due to the fact that prostanoids are metabolized rather quickly (half life of seconds to minutes) it is believed these signaling mediators act in a paracrine fashion at the site of production. Evidence to date is quite convincing that these bioactive lipid derivatives are involved in physiologic homeostatic regulation as well as beneficial and maladaptive ventricular remodeling in heart failure. Thus, this review will assess the direct contribution of each PG on remodeling in the left ventricle (e.g. hypertrophy, functional effects, and fibrosis).

Thirty years of the heart as an endocrine organ: physiological role and clinical utility of cardiac natriuretic hormones

Thirty years ago, De Bold et al. ( 20 ) reported that atrial extracts contain some biologically active peptides, which promote a rapid and massive diuresis and natriuresis when injected in rats. It is now clear that the heart also exerts an endocrine function and in this way plays a key role in the regulation of cardiovascular and renal systems. The aim of this review is to discuss some recent insights and still-debated findings regarding the cardiac natriuretic hormones (CNHs) produced and secreted by cardiomyocytes (i.e., atrial natriuretic peptide and B-type natriuretic peptide). The functional status of the CNH system depends not only on the production/secretion of CNHs by cardiomyocytes but also on both the peripheral activation of circulating inactive precursor of natriuretic hormones and the transduction of the hormone signal by specific receptors. In this review, we will discuss the data supporting the hypothesis that the production and secretion of CNHs is the result of a complex integration among mechanical, chemical, hemodynamic, humoral, ischemic, and inflammatory inputs. The cross talk among endocrine function, adipose tissue, and sex steroid hormones will be discussed more in detail, considering the clinically relevant relationships linking together cardiovascular risk, sex, and body fat development and distribution. Finally, we will review the pathophysiological role and the clinical relevance of both peripheral maturation of the precursor of B-type natriuretic peptides and hormone signal transduction .

Prostanoid signaling: dual role for prostaglandin E2 in neurotoxicity

The prostanoids, a naturally occurring subclass of eicosanoids, are lipid mediators generated through oxidative pathways from arachidonic acid. These cyclooxygenase metabolites, consisting of the prostaglandins (PG), prostacyclin and tromboxane, are released in response to a variety of physiological and pathological stimuli in almost all organs, including the brain. They are produced by various cell types and act upon targeted cells via specific G protein-coupled receptors. The existence of multiple receptors, cross-reactivity and coupling to different signal transduction pathways for each prostanoid, collectively establish their diverse effects. Notably, these effects can occur in functionally opposing directions within the same cell or organ. Prostaglandin E(2) (PGE(2)) is the most versatile prostanoid because of its receptors, E Prostanoid (EP) receptor subtypes 1 through 4, its biological heterogeneity and its differential expression on neuronal and glial cells throughout the central nervous system. Since PGE(2) plays an important role in processes associated with various neurological diseases, this review focuses on its dual neuroprotective and neurotoxic role in EP receptor subtype signaling pathways in different models of brain injury.

Prostaglandin F2α stimulates PI3K/ERK/mTOR signaling and skeletal myotube hypertrophy

Cyclooxygenase (COX) enzymes mediate the synthesis of proinflammatory prostaglandin (PG) species from cellular arachidonic acid. COX/PGs have been implicated in skeletal muscle growth/regeneration; however, the mechanisms by which PGs influence skeletal muscle adaptation are poorly understood. The present study aimed to investigate PGF(2α) signaling and its role in skeletal myotube hypertrophy. PGF(2α) or the FP receptor agonist fluprostenol increased C2C12 myotube diameter. This effect was abolished by the FP receptor antagonist AL8810 and mammalian target of rapamycin (mTOR) inhibition. PGF(2α) stimulated time- and dose-dependent increases in the phosphorylation of extracellular receptor kinase (ERK)1/2 (Thr202/Tyr204), p70S6 kinase (p70S6K) (Thr389 and Thr421/Ser424), and eukaryotic initiation factor 4G (eIF4G) (Ser1108) without influencing Akt (Ser473). Pretreatment with the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 and the ERK inhibitor PD98059 blocked F prostanoid receptor signaling responses, whereas rapamycin blocked heightened p70S6K/eIF4G phosphorylation without influencing ERK1/2 phosphorylation. These data suggest that activation of the F prostanoid receptor is coupled to C2C12 myotube growth and intracellular signaling via a PI3K/ERK/mTOR-dependent pathway.

PG F(2α) Receptor: A Promising Therapeutic Target for Cardiovascular Disease

Prostaglandins (PGs), a group of key lipid mediators, are involved in numerous physiological and pathological processes including inflammation and cardiovascular homeostasis. Each PG acts on its specific and distinct cell surface G protein-coupled receptors (GPCRs) or peroxisome proliferator-activated receptors (PPARs). Prostaglandin F(2α) receptor (FP) is required for female reproductive function such as luteolysis and parturition. It has recently been implicated in blood pressure regulation, atherosclerosis and other inflammation-related disorders. The emerging role of FP in cardiovascular diseases is highlighted and potential therapeutic translation is discussed in the current review.

Molecular mechanisms underlying PGF2alpha-induced hypertrophy of vascular smooth muscle cells

The present review focuses primarily on the studies we made in recent years to improve the understanding of the molecular mechanisms of PGF2alpha-induced hypertrophy of Vascular Smooth Muscle Cells (VSMC). In this review, we will summarize the recent findings in the context of the PGF2alpha signaling pathway in three parts: PGF2alpha binding to its receptor, transactivation of EGF receptor, two independent signaling transduction pathways increasing the expression of NOX1 gene.

High-speed imaging of developing heart valves reveals interplay of morphogenesis and function

Knowing how mutations disrupt the interplay between atrioventricular valve (AVV) morphogenesis and function is crucial for understanding how congenital valve defects arise. Here, we use high-speed fluorescence microscopy to investigate AVV morphogenesis in zebrafish at cellular resolution. We find that valve leaflets form directly through a process of invagination, rather than first forming endocardial cushions. There are three phases of valve function in embryonic development. First, the atrioventricular canal (AVC) is closed by the mechanical action of the myocardium, rolls together and then relaxes. The growing valve leaflets serve to block the canal during the roll and, depending on the developmental stage, either expand or hang down as a leaflet to block the canal. These steps are disrupted by the subtle morphological changes that result from inhibiting ErbB-, TGFbeta-or Cox2 (Ptgs2)-dependent signaling. Cox2 inhibition affects valve development due to its effect on myocardial cell size and shape, which changes the morphology of the ventricle and alters valve geometry. Thus, different signaling pathways regulate distinct aspects of the behavior of individual cells during valve morphogenesis, thereby influencing specific facets of valve function.

PGF2alpha-associated vascular smooth muscle hypertrophy is ROS dependent and involves the activation of mTOR, p70S6k, and PTEN

Prostaglandin F2alpha (PGF2alpha) increases reactive oxygen species (ROS) and induces vascular smooth muscle cell (VSMC) hypertrophy by largely unknown mechanism(s). To investigate the signaling events governing PGF2alpha-induced VSMC hypertrophy we examined the ability of the PGF2alpha analog, fluprostenol to elicit phosphorylation of Akt, the mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase (p70S6k), glycogen synthase kinase-3beta (GSK-3beta), phosphatase and tensin homolog (PTEN), extracellular signal-regulated kinase 1/2 (ERK1/2) and Jun N-terminal kinase (JNK) in growth arrested A7r5 VSMC. Fluprostenol-induced hypertrophy was associated with increased ROS, mTOR translocation from the nucleus to the cytoplasm, along with Akt, mTOR, GSK-3beta, PTEN and ERK1/2 but not JNK phosphorylation. Whereas inhibition of phosphatidylinositol 3-kinase (PI3K) by LY-294002 blocked fluprostenol-induced changes in total protein content, pre-treatment with rapamycin or with the MEK1/2 inhibitor U0126 did not. Taken together, these findings suggest that fluprostenol-induced changes in A7r5 hypertrophy involve mTOR translocation and occur through PI3K-dependent mechanisms.

Thyroid hormone changes cardiomyocyte shape and geometry via ERK signaling pathway: potential therapeutic implications in reversing cardiac remodeling?

It has previously been shown that thyroid hormone can reverse cardiac remodeling in failing hearts by reducing myocardial wall stress due to the unique changes induced in cardiac myocyte shape. This effect may be of therapeutic relevance. Therefore, the present study has investigated potential signaling mechanisms underlying the thyroid hormone action on cardiac myocyte shape and geometry. Neonatal cardiomyocytes were treated with T(3) while untreated cells served as controls. T(3) administration for 48 h significantly increased the ratio of the major to minor cell axis and changed their shape from an almost circular to an elongated form. Cell area and protein synthesis were increased and T(3) treated cells expressed 51% alpha-MHC and 49% beta-MHC as compared to 100% beta-MHC expression in non-treated cells. This response was accompanied by a 1.9-fold increase in phospho-ERK levels early at 8 min which, within 60 min, returned to the levels of the untreated cells. Phospho-JNK levels were significantly reduced within 60 min after T(3) treatment while no changes in the expression of phospho-Akt and phospho-p38 MAPK were found between the T(3) treated and untreated cells. Administration of PD98059 (an inhibitor of ERK signaling) prevented the thyroid hormone induced changes in cardiomyocyte geometry and shape without a significant reduction in cell area and protein synthesis. In conclusion, T(3) induced changes in cardiomyocyte shape and geometry involve the ERK kinase signaling. This response is independent of the effects of T(3) on cell size and protein synthesis.

Attenuation of Cardiac Hypertrophy in Carnitine-Deficient Juvenile Visceral Steatosis (JVS) Mice Achieved by Lowering Dietary Lipid

We examined the development of cardiac hypertrophy in juvenile visceral steatosis (JVS) mice, a model of systemic carnitine deficiency, by varying the amount of lipid in the diet. Cardiac hypertrophy was markedly attenuated by decreasing soy bean oil (SBO) from 5% (w/w) to 1%. Triglyceride contents of the ventricles of JVS mice fed 1% SBO were significantly lower than in JVS mice fed 5% SBO. The addition of medium-chain triglycerides metabolically utilized by JVS mice did not affect the development of cardiac hypertrophy. On the other hand, the mRNA levels of atrial natriuretic peptide and skeletal alpha-actin, which are related to cardiac hypertrophy, were also attenuated by decreasing lipid in the diet. Adenylate energy charge and creatine phosphate in the heart of JVS mice at the early stage of hypertrophy were not significantly different from control mice given the same laboratory chow (4.6% of lipid). Although urinary prostaglandin F(2alpha) levels were found to be increased in JVS mice at 15 days of age when they developed cardiac hypertrophy, administration of aspirin was not efficacious. We, therefore, propose that the proportion of lipid in the diet is important in the development of cardiac hypertrophy in carnitine-deficient JVS mice, and that this is not related to prostaglandin formation.

Inhibitory effects of interferon-γ on myocardial hypertrophy

Prostaglandin F(2alpha) (PGF(2alpha)) plays an important role in pathologic cardiac growth. After testing several immune cytokines, we found that interferon-gamma (IFN-gamma) inhibited responsiveness of adult myocytes to PGF(2alpha). The present study was designed to test the hypothesis that IFN-gamma inhibits cardiac hypertrophy induced by PGF(2alpha). Incubation of cultured adult rat cardiac myocytes with PGF(2alpha) caused cell spreading, which was inhibited by IFN-gamma. The inhibitory effect was not affected by nitric oxide (NO) synthase inhibitors. In addition, administration of fluprostenol, a more selective agonist at the PGF(2alpha) receptor, induced cardiac hypertrophy in rats. Chronic treatment with IFN-gamma inhibited this myocardial growth, and the inhibitory effect of IFN-gamma was not accompanied by an increase in myocardial NO synthase gene expression. Further, abdominal aortic constriction resulted in a substantial increase in heart, ventricular and left ventricular weights to BW ratio that was significantly attenuated by treatment with IFN-gamma. The results demonstrate that IFN-gamma inhibits the in vitro and in vivo effects of PGF(2alpha) on cardiac hypertrophy, and that the mechanism of action is likely independent of NO production. IFN-gamma also attenuated cardiac hypertrophy induced by pressure overload, suggesting that PGF(2alpha) plays a role in the pathogeneses of this severe type of cardiac hypertrophy.

Crystalline and amorphous silica differentially regulate the cyclooxygenase-prostaglandin pathway in pulmonary fibroblasts: implications for pulmonary fibrosis

Inhalation of crystalline (CS) and amorphous silica (AS) results in human pulmonary inflammation. However, silicosis develops only following CS exposure, and the pathogenic mechanisms are poorly understood. This report describes the differential abilities of CS and AS to directly upregulate the early inflammatory mediator COX-2, the recently identified prostaglandin E (PGE) synthase and the downstream mediator PGE2 in primary human lung fibroblasts. Increased cyclooxygenase (COX)-2 gene transcription and protein production were demonstrated by ribonuclease protection assay, Western blot analysis, and immunocytochemistry. In each case the ability of AS to induce COX-2 exceeded that of CS. Similarly, downstream of COX-2, production of the antifibrotic prostaglandin PGE2 was induced in a dose-dependent fashion, but AS was significantly more potent (maximal production: CS = 4,710 pg/ml and AS = 7,651 pg/ml). These increases in COX-2 and PGE2 were preceded by induction of the PGE2 synthase protein, demonstrating the potential role of this novel molecule in silica-mediated inflammation. There was specificity of induction of prostaglandins, as PGF2alpha, but not PGD2, was induced. Using specific COX-2 inhibitors, we showed increased PG production to be dependent on the COX-2 enzyme. Furthermore, stimulation of fibroblasts was particle specific, as silica but not carbon black resulted in fibroblast activation. These results demonstrate that silica can directly stimulate human lung fibroblasts to produce key inflammatory enzymes and prostaglandins. Moreover, they suggest a mechanism to explain the differing fibrogenic potential of CS and AS. The molecules COX-2, PGE synthase, and PGE2 are identified as effectors in silicosis.

Inhibition of cyclooxygenase-2 improves cardiac function after myocardial infarction in the mouse

Cyclooxygenase (COX)-2 is expressed in the heart in animal models of ischemic injury. Recent studies have suggested that COX-2 products are involved in inflammatory cell infiltration and fibroblast proliferation in the heart. Using a mouse model, we questioned whether 1) myocardial infarction (MI) in vivo induces COX-2 expression chronically, and 2) COX-2 inhibition reduces collagen content and improves cardiac function in mice with MI. MI was produced by ligation of the left anterior descending coronary artery in mice. Two days later, mice were treated with 3 mg/kg NS-398, a selective COX-2 inhibitor, or vehicle in drinking water for 2 wk. After the treatment period, mice were subjected to two-dimensional M-mode echocardiography to determine cardiac function. Hearts were then analyzed for determination of infarct size, interstitial collagen content, brain natriuretic peptide (BNP) mRNA, myocyte cross-sectional area, and immunohistochemical staining for transforming growth factor (TGF)-β and COX-2. COX-2 protein, detected by immunohistochemistry, was increased in MI versus sham hearts. MI resulted in increased left ventricular systolic and diastolic dimension and decreased ejection fraction, fractional shortening, and cardiac output. NS-398 treatment partly reversed these detrimental changes. Myocyte cross-sectional area, a measure of hypertrophy, was decreased by 30% in the NS-398 versus vehicle group, but there was no effect on BNP mRNA. The interstitial collagen fraction increased from 5.4 ± 0.4% in sham hearts to 10.4 ± 0.9% in MI hearts and was decreased to 7.9 ± 0.6% in NS-398-treated hearts. A second COX-2 inhibitor, rofecoxib (MK-0966), also decreased myocyte cross-sectional area and interstitial collagen fraction. TGF-β, a key regulator of collagen synthesis, was increased in MI hearts. NS-398 treatment reduced TGF-β immunostaining by 40%. NS-398 treatment had no effect on infarct size. These results suggest that COX-2 products contribute to cardiac remodeling and functional deficits after MI. Thus selected inhibition of COX-2 may be a therapeutic target for reducing myocyte damage after MI.

Prostaglandin F2(alpha) stimulates growth of skeletal muscle cells via an NFATC2-dependent pathway

Skeletal muscle growth requires multiple steps to form large multinucleated muscle cells. Molecules that stimulate muscle growth may be therapeutic for muscle loss associated with aging, injury, or disease. However, few factors are known to increase muscle cell size. We demonstrate that prostaglandin F2alpha (PGF2alpha) as well as two analogues augment muscle cell size in vitro. This increased myotube size is not due to PGF2alpha-enhancing cell fusion that initially forms myotubes, but rather to PGF2alpha recruiting the fusion of cells with preexisting multinucleated cells. This growth is mediated through the PGF2alpha receptor (FP receptor). As the FP receptor can increase levels of intracellular calcium, the involvement of the calcium-regulated transcription factor nuclear factor of activated T cells (NFAT) in mediating PGF2alpha-enhanced cell growth was examined. We show that NFAT is activated by PGF2alpha, and the isoform NFATC2 is required for PGF2alpha-induced muscle cell growth and nuclear accretion, demonstrating the first intersection between prostaglandin receptor activation and NFAT signaling. Given this novel role for PGF2alpha in skeletal muscle cell growth, these studies raise caution that extended use of drugs that inhibit PG production, such as nonsteroidal antiinflammatory drugs, may be deleterious for muscle growth.

G-proteins in growth and apoptosis: lessons from the heart

The acute contractile function of the heart is controlled by the effects of released nonepinephrine (NE) on cardiac adrenergic receptors. NE can also act in a more chronic fashion to induce cardiomyocyte growth, characterized by cell enlargement (hypertrophy), increased protein synthesis, alterations in gene expression and addition of sarcomeres. These responses enhance cardiomyocyte contractile function and thus allow the heart to compensate for increased stress. The hypertrophic effects of NE are mediated through Gq-coupled alpha(1)-adrenergic receptors and are mimicked by the actions of other neurohormones (endothelin, prostaglandin F(2alpha) angiotensin II) that also act on Gq-coupled receptors. Activation of phospholipase C by Gq is necessary for these responses, and protein kinase C and MAP kinases have also been implicated. Gq stimulated cardiac hypertrophy is also evident in transgenic mouse models. In contrast, stimulation of G(s)-coupled beta-adrenergic receptors or G(i)-coupled receptors do not directly effect cardiomyocyte hypertrophy. Apoptosis is also induced by G-protein-coupled receptor stimulation in cardiomyocytes. Sustained or excessive activation of either Gq- or Gs-signaling pathways results in apoptotic loss of cardiomyocytes both in vitro and in vivo. Apoptosis is associated with decreased ventricular function in the failing heart. Cardiomyocytes provide an ideal model system for understanding the basis for G-protein mediated hypertrophy and apoptosis, and the mechanisms responsible for the transition from compensatory to deleterious levels of signaling. This information may prove critical for designing interventions that prevent the pathophysiological consequences of heart failure.

Phorbol ester stimulates cyclooxygenase-2 expression and prostanoid production in cardiac myocytes

Phorbol-12-myristate- 13-acetate (PMA) has been shown to induce hypertrophy of cardiac myocytes. The prostaglandin endoperoxide H synthase isoform 2 (cyclooxygenase-2, COX-2) has been associated with enhanced growth and/or proliferation of several types of cells. Thus we studied whether PMA induces COX-2 and prostanoid products PGE(2) and PGF(2alpha) in neonatal ventricular myocytes and whether endogenous COX-2 products participate in their growth. In addition, we examined whether PMA affects interleukin-1beta (IL-1beta) stimulation of COX-2 and PGE(2) production. PMA (0.1 micromol/l) stimulated growth, as indicated by a 1.6-fold increase in [(3)H]leucine incorporation. PMA increased COX-2 protein levels 2. 8-fold, PGE(2) 3.7-fold, and PGF(2alpha) 2.9-fold. Inhibition of either p38 kinase or protein kinase C (PKC) prevented PMA-stimulated COX-2. Inhibition of COX-2 with either indomethacin or NS-398 had no effect on PMA-stimulated [(3)H]leucine incorporation. Exogenous administration of PGF(2alpha), but not PGE(2), stimulated protein synthesis. Treatment with IL-1beta (5 ng/ml) increased COX-2 protein levels 42-fold, whereas cotreatment with IL-1beta and PMA stimulated COX-2 protein only 32-fold. IL-1beta did not affect control or PMA-stimulated protein synthesis. These findings indicate that: 1) PMA, acting through PKC and p38 kinase, enhances COX-2 expression, but chronic treatment with PMA partially inhibits IL-1beta stimulation of COX-2; and 2) exogenous PGF(2alpha) is involved in neonatal ventricular myocyte growth but endogenous COX-2 products are not.

FP-receptor mediated trophic effects of prostanoids in rat ventricular cardiomyocytes

The aim of this study was to characterize the receptor subtype involved in cardiac effects of prostanoids. For this purpose we determined in neonatal and adult rat cardiomyocytes effects of prostanoids on inositol phosphate (InsP)-formation (assessed as accumulation of total [(3)H]-InsP's in myo-[(3)H]-inositol pre-labelled cells) and on rate of protein synthesis (assessed as [(3)H]-phenylalanine incorporation), and on contractile force in left ventricular strips of the rat heart. For comparison, effects of prostanoids on InsP-formation and contractile force were determined in rat thoracic aorta, a classical TP-receptor containing tissue. Prostanoid increased InsP-formation and rate of protein synthesis in neonatal as well as adult rat cardiomyocytes; the order of potency was in neonatal (PGF(2alpha)>PGD(2)> or =PGE(2)> or =U 46619>PGE(1)) and adult (PGF(2alpha)>PGD(2)> or =PGE(2)>U 46619) rat cardiomyocytes well comparable. Moreover, in electrically driven left ventricular strips PGF(2alpha) caused positive inotropic effects (pD(2) 7.5) whereas U 46619 (up to 1 microM) was uneffective. In contrast, in rat thoracic aorta U 46619 was about 100 times more potent than PGF(2alpha) in increasing InsP-formation and contractile force. The TP-receptor antagonist SQ 29548 only weakly antagonized prostanoid-induced increases in rate of protein synthesis (pK(B) about 6) in rat cardiomyocytes but was very potent (pK(B) about 8-9) in antagonizing prostanoid-induced increases in InsP-formation and contractile force in rat aorta. We conclude that, in cardiomyocytes of neonatal and adult rats, the prostanoid-receptor mediating increases in InsP-formation and rate of protein synthesis is a FP-receptor. Moreover, stimulation of these cardiac FP-receptors can mediate increases in contractile force.

Endogenous cardiac vasoactive factors modulate endothelin production by cardiac fibroblasts in culture

Endothelin, a potent vasoconstrictor, is produced by cardiac fibroblasts in culture and induces hypertrophy in cardiac myoctes. The purpose of this study was to determine whether vasoactive factors endogenous to the heart affect the production of endothelin by cultured cardiac fibroblasts. Vasoactive factors have been shown to play multiple roles in the adaptation of the heart to chronic overload, affecting both vascular tone and cell growth. Both atrial (ANP) and brain (BNP) natriuretic peptides are endogenous cardiac vasodilators and are produced by cultured myocytes in response to stimulation with endothelin. Treatment of cardiac fibroblasts with these peptides decreased endothelin production. Nitroprusside, an activator of guanylyl cyclase, decreased endothelin production indicating the involvement of cGMP in the response. Carbaprostacyclin, a stable derivative of prostacyclin, another endogenous cardiac vasodilator, also decreased endothelin production by fibroblasts. The combination of BNP and carbaprostacyclin was additive in decreasing endothelin production. In contrast, PGF2α and angiotensin II, both endogenous cardiac vasoconstrictors, increased endothelin production and overcame the inhibition induced by BNP and carba-prostacyclin. In summary, endothelin production by cardiac fibroblasts was decreased by the endogenous cardiac vasodilators ANP, BNP, and prostacyclin and increased by the endogenous vasoconstrictors PGF2α and angiotensin II.