Transforming growth factor beta-1 in acute myocardial infarction in rats

Protective effect of Pueraria lobata leaves on doxorubicin-induced myocardial infarction in experimental Wistar rats

The present study intended to explore the preventive effects of Pueraria lobata leaves against doxorubicin (DOX)-induced myocardial infarction (MI) in Wistar rats. The rats were separated into four groups, with each group containing six rats. Group I control rats; group II received DOX-alone in six equivalent injections for 2 weeks; group III received DOX as abovementioned with P. lobata oral administration for 2 weeks; group IV received P. lobata alone for 2 weeks. At the end of the experiment, postcervical dislocation and MI induced by DOX were determined on the basis of the variations in the animal body and heart weight and further instabilities in cardiac marker enzymes aspartate transaminase, lactate dehydrogenase, creatine kinase, creatine kinase-myoglobin binding, and cardiac troponin I in the serum. At the same time, for group III animals, which were exposed to P. lobata, all the above-denoted marker levels were maintained. Levels of some crucial heart-binding proteins like heart fatty acid binding protein, monocyte chemoattractant protein-1, and transforming growth factor beta were elevated in DOX-alone treated rats. Additionally, group III animals treated with P. lobata showed some preventive downregulated expressions of these binding proteins. Histopathological observations also revealed the preventive effect of P. lobata. Ultimately proteins tangled in the phosphoinositide 3-kinase/protein kinase B pathway were studied by Western blot. P. lobata treatment downregulated the inflammatory markers. The findings suggest that P. lobata exhibits cardioprotective effect on MI.

Role of echocardiography on early diagnosis of atrial remodelling and fibrosis in elite athletes

There is emerging data indicating that long-standing vigorous exercise may be associated with atrial structural remodelling. This remodelling process is may be the cause of the increasing frequency of atrial arrythmias in athletes. Early diagnosis of atrial remodelling by atrial imaging could have a role in management of atrial arrythmias in elite athletes. In this study we aimed to diagnose early phases of atrial remodelling in elite athletes. Two groups of athletes including professional weight lifters (n = 33), professional marathoners (n = 32) and sedentary participants (n = 30) were enrolled. We also studied patients who received cardiotoxic chemotherapy (n = 10) for comparison. Serum TGF-beta level as a marker of fibrosis was measured. Both left atrial (LA) 3D volume and strain values were analysed. There was a positive correlation between serum TGF-beta levels and LA volumes and negative correlation between TGF-beta levels and strain values. TGF-beta levels were higher among chemotherapy and weight lifter groups, compared to control and marathoner groups [mean 0.57 ± 0.3 and 0.55 ± 0.2 vs. 0.45 ± 0.2 and 0.47 ± 0.2, respectively, p = 0.005]. LA volumes were higher among chemotherapy and weight lifter groups [median 33 (26-38) and 31 (23-36) respectively, p = 0.005], and strain values were lower in these two groups [mean 20.3 ± 2.5 and 24.6 ± 4.5, respectively, p < 0.005] compared to control and marathoner groups. Total exercise volume was higher in weight lifter group compared to marathoners [13,780 (2496-36,400) vs. 4732 (780-44928), respectively, p = 0.001]. There wasn't any difference between any group regarding left ventricular systolic and diastolic functions. Vigorous exercise causes atrial remodelling and fibrosis in elite athletes. Strength exercise carries higher risk for atrial fibrosis than endurance exercise. Burden of exercise is correlated with the severity of cardiac fibrosis. Echocardiographic evaluation of the left atrium and TGF-beta levels may help to detect subclinical cardiac remodelling and fibrosis.

Complex Relationship Between Cardiac Fibroblasts and Cardiomyocytes in Health and Disease

Cardiac fibroblasts are the primary cell type responsible for deposition of extracellular matrix in the heart, providing support to the contracting myocardium and contributing to a myriad of physiological signaling processes. Despite the importance of fibrosis in processes of wound healing, excessive fibroblast proliferation and activation can lead to pathological remodeling, driving heart failure and the onset of arrhythmias. Our understanding of the mechanisms driving the cardiac fibroblast activation and proliferation is expanding, and evidence for their direct and indirect effects on cardiac myocyte function is accumulating. In this review, we focus on the importance of the fibroblast-to-myofibroblast transition and the cross talk of cardiac fibroblasts with cardiac myocytes. We also consider the current use of models used to explore these questions.

The role of 5-HT7 receptors on isoproterenol-induced myocardial infarction in rats with high-fat diet exacerbated coronary endothelial dysfunction

The presence of 5-HT7r's in both human and rat cardiovascular and immune tissues and their contribution to inflammatory conditions prompted us to hypothesize that these receptors contribute in acute myocardial infarction (MI) with underlying chronic endothelial dysfunction. We investigated the role of 5-HT7 receptors on heart tissue that damaged by isoproterenol (ISO)-induced MI in rats with high-fat diet (HFD). In vitro and in vivo effects of 5-HT7r agonist (LP44) and antagonist (SB269970) have been investigated on the H9C2 cell line and rats, respectively. For in vivo analyses, rats were fed with HFD for 8 weeks and after this period ISO-induced MI model has been applied to rat. To investigate the role of 5-HT7r's, two different doses of LP44 and SB269970 were evaluated and compared with standard hypolipidemic agent, atorvastatin. In vitro studies showed that LP44 has protective and proliferative effects on rat cardiomyocytes. Also in in vivo studies stimulating 5-HT7r's by LP44 improved blood lipid profile (decreased total cholesterol, low-density lipoprotein-C, and triglyceride, increased high-density lipoprotein), decreased cardiac damage markers (creatine kinase and troponin-I), and corrected inflammatory status (tumor necrosis factor-α, interleukin-6). Our results showed significant improvement in LP44 administered rats in terms of histopathologic analyses. In damaged tissues, 5-HT7 mRNA expression increased and agonist administration decreased this elevation significantly. We determined for the first time that 5-HT7r's are overexpressed in ISO-induced MI of rats with underlying HFD-induced endothelial dysfunction. Restoration of this overexpression by LP44, a 5-HT7r agonist, ameliorated heart tissue in physiopathologic, enzymatic, and molecular level, showing the cardiac role of these receptors and suggesting them as future potential therapeutic targets.

Zebrafish heart regeneration: Factors that stimulate cardiomyocyte proliferation

Myocardial infarctions (MI) remain a leading cause of global morbidity and mortality, and a reason for this is the inability of adult, mammalian cardiomyocytes to divide post-MI. Recent studies demonstrate a limited population of cardiomyocytes retain their proliferative capacity and understanding how endogenous cardiomyocytes can be stimulated to re-enter the cell cycle is a focus of current research. In this review we discuss the history of zebrafish cardiac regeneration and highlight how different models reveal the molecular pathways important in driving cardiomyocyte proliferation after injury. Understanding the molecules that regulate cell cycle re-entry can provide insights into promoting cardiac repair in humans.

Mechanisms of cardiac collagen deposition in experimental models and human disease

The inappropriate deposition of extracellular matrix within the heart (termed cardiac fibrosis) is associated with nearly all types of heart disease, including ischemic, hypertensive, diabetic, and valvular. This alteration in the composition of the myocardium can physically limit cardiomyocyte contractility and relaxation, impede electrical conductivity, and hamper regional nutrient diffusion. Fibrosis can be grossly divided into 2 types, namely reparative (where collagen deposition replaces damaged myocardium) and reactive (where typically diffuse collagen deposition occurs without myocardial damage). Despite the widespread association of fibrosis with heart disease and general understanding of its negative impact on heart physiology, it is still not clear when collagen deposition becomes pathologic and translates into disease symptoms. In this review, we have summarized the current knowledge of cardiac fibrosis in human patients and experimental animal models, discussing the mechanisms that have been deduced from the latter in relation to the former. Because assessment of the extent of fibrosis is paramount both as a research tool to further understanding and as a clinical tool to assess patients, we have also summarized the current state of noninvasive/minimally invasive detection systems for cardiac fibrosis. Albeit not exhaustive, our aim is to provide an overview of the current understanding of cardiac fibrosis, both clinically and experimentally.

Cardioprotective effects of nanoceria in a murine model of cardiac remodeling

Isoproterenol (ISO), a synthetic β₁ adrenergic agonist is a well-known agent to be associated with severe cardiotoxicity manifested as marked myocardial necrosis and fibrosis. Oxidative stress plays a crucial role in mediating ISO induced cardiotoxicity. In present study, we have investigated the possible protective effect of nanoceria (NC) in ISO induced cardiac injury. We have given long duration exposure (a total of 10 days) of low dose ISO (20 mg/kg/day) to investigate the protective effects of NC in chronic cardiac injury model. ISO (20 mg/kg/day for 10 days) produced cardiac injury as evident by increased plasma LDH and CK-MB, AST, ALT, cardiac hypertrophy, severe myocardial fibrosis (MF) and significantly higher levels of cytokines, IL-6, TGF-β and TNF-α. Interestingly, the treatment with NC (0.2 and 2 mg/kg) abrogated cardiotoxicity symptoms and provided protection from ISO induced cardiac injury. The results from present study demonstrated strong evidences of cardioprotective effects of NC as shown by reduction in the levels of LDH (p < 0.05 at 2 mg/kg) and CK-MB (p < 0.05 at 2 mg/kg). In addition, NC reduced oxidative stress parameters MDA (p < 0.05 at 2 mg/kg) and enhanced GSH levels which is physiological antioxidant (p < 0.01 at both doses). Further, NC exhibited promising anti-inflammatory activity and curbed the levels of cytokines (p < 0.05 at 0.2 mg/kg and p < 0.001 for IL-1β and p < 0.001 at both doses for IL-6). In addition, NC also reduced the levels of pro-fibrotic cytokine, TGF-β (p < 0.05 at 2 mg/kg) and helped in reduction of collagen deposition in heart thereby, preventing the myocardial remodeling. Our results strongly suggested that NC might be of potential use as a cardioprotective agent.

Circadian locomotor output cycles kaput accelerates atherosclerotic plaque formation by upregulating plasminogen activator inhibitor-1 expression

To explore the association between clock circadian regulator circadian locomotor output cycles kaput gene (CLOCK) and the forming of atherosclerotic plaques and its underlying mechanisms, mouse aortic endothelial cells (MAECs) and atherosclerosis (AS) mouse model were recruited for our study. The apoE gene knockout mouse was used as the model of AS and we accelerated the formation of unstable plaques through the combination of carotid artery ligation and high-fat (HF) diet administration (0.2% cholesterol, 20% fat). The mRNA and protein expressions of CLOCK in peripheral blood monouclear cells of acute coronary syndrome (ACS) patients or mouse AS model were detected by qPCR, western blot analysis and immunohistochemical staining. The number of adherent cells and atherosclerotic plaques was counted to assess the effects of CLOCK on the progression of ACS, and adherence-associated genes, such as vascular cell adhesion molecule (VCAM)-1, C-C motif chemokine ligand 2 (CCL-2), and CCL-5. The results showed that CLOCK expression was significantly increased in both ACS patients and AS mouse model. The levels of CLOCK, leukemia inhibitory factor (LIF), intercellular adhesion molecule 1 (ICAM-1), perilipin 2 (ADFP), nuclear factor kappa B (NF-κB), and plasminogen activator inhibitor-1 (PAI-1), as well as the number of atherosclerotic plaques were elevated in the AS mouse model, as compared with the control group. Chromatin immunoprecipitation assay showed that CLOCK bound directly to the promoter of PAI-1 gene and CLOCK could positively regulate the expressions of LIF, ICAM-1, ADFP, NF-κB, and PAI-1. Reduction of CLOCK expression would decrease the expressions of VCAM-1, CCL-2, and CCL-5, and the number of adherent cells and atherosclerotic plaques, but these effects were neutralized when PAI-1 was simultaneously overexpressed in either mouse model or MAECs. Our results demonstrate that CLOCK overexpression triggers the formation of atherosclerotic plaques by directly upregulating PAI-1 expression.

MK5 haplodeficiency attenuates hypertrophy and preserves diastolic function during remodeling induced by chronic pressure overload in the mouse heart

MAPK-activated protein kinase-5 (MK5) is a protein serine/threonine kinase that is activated by p38 MAPK and the atypical MAPKs ERK3 and ERK4. The physiological function(s) of MK5 remains unknown. Here, we examined the effect of MK5 haplodeficiency on cardiac function and myocardial remodeling. At 12 wk of age, MK5 haplodeficient mice (MK5^+/-) were smaller than age-matched wild-type littermates (MK5^+/+), with similar diastolic function but reduced systolic function. Transverse aortic constriction (TAC) was used to induce chronic pressure overload in 12-wk-old male MK5^+/- and MK5^+/+ mice. Two weeks post-TAC, heart weight-to-tibia length ratios were similarly increased in MK5^+/- and MK5^+/+ hearts, as was the abundance of B-type natriuretic peptide and β-myosin heavy chain mRNA. Left ventricular ejection fraction was reduced in both MK5^+/+ and MK5^+/- mice, whereas regional peak systolic tissue velocities were reduced and isovolumetric relaxation time was prolonged in MK5^+/+ hearts but not in MK5^+/- hearts. The TAC-induced increase in collagen type 1-α₁ mRNA observed in MK5^+/+ hearts was markedly attenuated in MK5^+/- hearts. Eight weeks post-TAC, systolic function was equally impaired in MK5^+/+ and MK5^+/- mice. In contrast, the increase in E wave deceleration rate and progression of hypertrophy observed in TAC MK5^+/+ mice were attenuated in TAC MK5^+/- mice. MK5 immunoreactivity was detected in adult fibroblasts but not in myocytes. MK5^+/+, MK5^+/-, and MK5^-/- fibroblasts all expressed α-smooth muscle actin in culture. Hence, reduced MK5 expression in cardiac fibroblasts was associated with the attenuation of both hypertrophy and development of a restrictive filling pattern during myocardial remodeling in response to chronic pressure overload.NEW & NOTEWORTHY MAPK-activated protein kinase-5 (MK5)/p38-regulated/activated protein kinase is a protein serine/threonine kinase activated by p38 MAPK and/or the atypical MAPKs ERK3 and ERK4. MK5 immunoreactivity was detected in adult ventricular fibroblasts but not in myocytes. MK5 haplodeficiency attenuated the progression of hypertrophy, reduced collagen type 1 mRNA, and protected diastolic function in response to chronic pressure overload.

Histopathological lesions in encephalon and heart of mice infected with Toxoplasma gondii increase after Lycopodium clavatum 200dH treatment

In many cases, symptoms of toxoplasmosis are mistaken for the ones of other infectious diseases. Clinical signs are rare in immunocompetent people. However, when they arise, in the acute phase of infection, several organs are affected due to the rapid spread of tachyzoites through the bloodstream. In the present study, the reduction of tachyzoites in peripheral blood of mice of G72 (infected 72h after treatment) and G48 (infected 48h after treatment and treated three more times), when compared with IC (infected and non-treated), suggests protective effect exerted by Lycopodium clavatum. If on the one hand L. clavatum brought benefits, reducing parasitemia, on the other hand, the parasitism became exacerbated. Histopathological analysis demonstrated focal, multifocal and diffuse inflammatory infiltrates, ranging from absent, discreet, moderate to intense, in heart and encephalon of mice of NIC (non-infected and non-treated), IC, G48 and G72 groups, respectively. In the perivascular region and meninges, the injuries were enlarged. The presence of tachyzoites was demonstrated through immunohistochemical (IHC) assay in myocardium. Toxoplasma gondii induced increase of collagen fibers in myocardium of mice of G72 and G48 groups, compared with IC (p<0.05) and NIC (p<0.001). The presence of inflammatory infiltrates, as well as the progressive fibrosis, caused myocardial remodeling in animals treated with L. clavatum. Counterstaining with H&E suggests TGF-β expression by mononuclear cells in the inflammatory infiltrate. Based on our results, we can conclude that the adopted regimen and potency exerted a protective effect, reducing parasitemia. However, it intensified the histopathological lesions in encephalon and heart of mice infected with T. gondii.

p63RhoGEF regulates auto- and paracrine signaling in cardiac fibroblasts

Cardiac remodeling, a hallmark of heart disease, is associated with intense auto- and paracrine signaling leading to cardiac fibrosis. We hypothesized that the specific mediator of Gq/11-dependent RhoA activation p63RhoGEF, which is expressed in cardiac fibroblasts, plays a role in the underlying processes. We could show that p63RhoGEF is up-regulated in mouse hearts subjected to transverse aortic constriction (TAC). In an engineered heart muscle model (EHM), p63RhoGEF expression in cardiac fibroblasts increased resting and twitch tensions, and the dominant negative p63ΔN decreased both. In an engineered connective tissue model (ECT), p63RhoGEF increased tissue stiffness and its knockdown as well as p63ΔN reduced stiffness. In 2D cultures of neonatal rat cardiac fibroblasts, p63RhoGEF regulated the angiotensin II (Ang II)-dependent RhoA activation, the activation of the serum response factor, and the expression and secretion of the connective tissue growth factor (CTGF). All these processes were inhibited by the knockdown of p63RhoGEF or by p63ΔN likely based on their negative influence on the actin cytoskeleton. Moreover, we show that p63RhoGEF also regulates CTGF in engineered tissues and correlates with it in the TAC model. Finally, confocal studies revealed a closely related localization of p63RhoGEF and CTGF in the trans-Golgi network.

Pathophysiology of Myocardial Infarction

Myocardial infarction is defined as sudden ischemic death of myocardial tissue. In the clinical context, myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function. Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium. Mitochondrial alterations are prominently involved in apoptosis and necrosis of cardiomyocytes in the infarcted heart. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells. Clearance of dead cells and matrix debris by infiltrating phagocytes activates anti-inflammatory pathways leading to suppression of cytokine and chemokine signaling. Activation of the renin-angiotensin-aldosterone system and release of transforming growth factor-β induce conversion of fibroblasts into myofibroblasts, promoting deposition of extracellular matrix proteins. Infarct healing is intertwined with geometric remodeling of the chamber, characterized by dilation, hypertrophy of viable segments, and progressive dysfunction. This review manuscript describes the molecular signals and cellular effectors implicated in injury, repair, and remodeling of the infarcted heart, the mechanistic basis of the most common complications associated with myocardial infarction, and the pathophysiologic effects of established treatment strategies. Moreover, we discuss the implications of pathophysiological insights in design and implementation of new promising therapeutic approaches for patients with myocardial infarction.

Autophagy is a regulator of TGF-β1-induced fibrogenesis in primary human atrial myofibroblasts

Transforming growth factor-β₁ (TGF-β₁) is an important regulator of fibrogenesis in heart disease. In many other cellular systems, TGF-β₁ may also induce autophagy, but a link between its fibrogenic and autophagic effects is unknown. Thus we tested whether or not TGF-β₁-induced autophagy has a regulatory function on fibrosis in human atrial myofibroblasts (hATMyofbs). Primary hATMyofbs were treated with TGF-β₁ to assess for fibrogenic and autophagic responses. Using immunoblotting, immunofluorescence and transmission electron microscopic analyses, we found that TGF-β₁ promoted collagen type Iα2 and fibronectin synthesis in hATMyofbs and that this was paralleled by an increase in autophagic activation in these cells. Pharmacological inhibition of autophagy by bafilomycin-A1 and 3-methyladenine decreased the fibrotic response in hATMyofb cells. ATG7 knockdown in hATMyofbs and ATG5 knockout (mouse embryonic fibroblast) fibroblasts decreased the fibrotic effect of TGF-β₁ in experimental versus control cells. Furthermore, using a coronary artery ligation model of myocardial infarction in rats, we observed increases in the levels of protein markers of fibrosis, autophagy and Smad2 phosphorylation in whole scar tissue lysates. Immunohistochemistry for LC3β indicated the localization of punctate LC3β with vimentin (a mesenchymal-derived cell marker), ED-A fibronectin and phosphorylated Smad2. These results support the hypothesis that TGF-β₁-induced autophagy is required for the fibrogenic response in hATMyofbs.

Effects of mechanical stimulation induced by compression and medium perfusion on cardiac tissue engineering

Cardiac tissue engineering presents a challenge due to the complexity of the muscle tissue and the need for multiple signals to induce tissue regeneration in vitro. We investigated the effects of compression (1 Hz, 15% strain) combined with fluid shear stress (10(-2) -10(-1) dynes/cm(2) ) provided by medium perfusion on the outcome of cardiac tissue engineering. Neonatal rat cardiac cells were seeded in Arginine-Glycine-Aspartate (RGD)-attached alginate scaffolds, and the constructs were cultivated in a compression bioreactor. A daily, short-term (30 min) compression (i.e., "intermittent compression") for 4 days induced the formation of cardiac tissue with typical striation, while in the continuously compressed constructs (i.e., "continuous compression"), the cells remained spherical. By Western blot, on day 4 the expression of the gap junction protein connexin 43 was significantly greater in the "intermittent compression" constructs and the cardiomyocyte markers (α-actinin and N-cadherin) showed a trend of better preservation compared to the noncompressed constructs. This regime of compression had no effect on the proliferation of nonmyocyte cells, which maintained low expression level of proliferating cell nuclear antigen. Elevated secretion levels of basic fibroblast growth factor and transforming growth factor-β in the daily, intermittently compressed constructs likely attributed to tissue formation. Our study thus establishes the formation of an improved cardiac tissue in vitro, when induced by combined mechanical signals of compression and fluid shear stress provided by perfusion.

MicroRNA dysregulation in diabetic ischemic heart failure patients

Increased morbidity and mortality associated with ischemic heart failure (HF) in type 2 diabetic patients requires a deeper understanding of the underpinning pathogenetic mechanisms. Given the implication of microRNAs (miRNAs) in HF, we investigated their regulation and potential role. miRNA expression profiles were measured in left ventricle biopsies from 10 diabetic HF (D-HF) and 19 nondiabetic HF (ND-HF) patients affected by non-end stage dilated ischemic cardiomyopathy. The HF groups were compared with each other and with 16 matched nondiabetic, non-HF control subjects. A total of 17 miRNAs were modulated in D-HF and/or ND-HF patients when compared with control subjects. miR-216a, strongly increased in both D-HF and ND-HF patients, negatively correlated with left ventricular ejection fraction. Six miRNAs were differently expressed when comparing D-HF and ND-HF patients: miR-34b, miR-34c, miR-199b, miR-210, miR-650, and miR-223. Bioinformatic analysis of their modulated targets showed the enrichment of cardiac dysfunctions and HF categories. Moreover, the hypoxia-inducible factor pathway was activated in the noninfarcted, vital myocardium of D-HF compared with ND-HF patients, indicating a dysregulation of the hypoxia response mechanisms. Accordingly, miR-199a, miR-199b, and miR-210 were modulated by hypoxia and high glucose in cardiomyocytes and endothelial cells cultured in vitro. In conclusion, these findings show a dysregulation of miRNAs in HF, shedding light on the specific disease mechanisms differentiating diabetic patients.

Regulation of the inflammatory response in cardiac repair

Myocardial necrosis triggers an inflammatory reaction that clears the wound from dead cells and matrix debris, while activating reparative pathways necessary for scar formation. A growing body of evidence suggests that accentuation, prolongation, or expansion of the postinfarction inflammatory response results in worse remodeling and dysfunction following myocardial infarction. This review manuscript discusses the cellular effectors and endogenous molecular signals implicated in suppression and containment of the inflammatory response in the infarcted heart. Clearance of apoptotic neutrophils, recruitment of inhibitory monocyte subsets and regulatory T cells, macrophage differentiation and pericyte/endothelial interactions may play an active role in restraining postinfarction inflammation. Multiple molecular signals may be involved in suppressing the inflammatory cascade. Negative regulation of toll-like receptor signaling, downmodulation of cytokine responses, and termination of chemokine signals may be mediated through the concerted action of multiple suppressive pathways that prevent extension of injury and protect from adverse remodeling. Expression of soluble endogenous antagonists, decoy receptors, and posttranslational processing of bioactive molecules may limit cytokine and chemokine actions. Interleukin-10, members of the transforming growth factor-β family, and proresolving lipid mediators (such as lipoxins, resolvins, and protectins) may suppress proinflammatory signaling. In human patients with myocardial infarction, defective suppression, and impaired resolution of inflammation may be important mechanisms in the pathogenesis of remodeling and in progression to heart failure. Understanding of inhibitory and proresolving signals in the infarcted heart and identification of patients with uncontrolled postinfarction inflammation and defective cardiac repair is needed to design novel therapeutic strategies.

Myocardial infarction impairs renal function, induces renal interstitial fibrosis, and increases renal KIM-1 expression: implications for cardiorenal syndrome

Progressive decline in renal function coexists with myocardial infarction (MI); however, little is known about its pathophysiology. This study aimed to systematically identify post-MI renal changes (functional, histological, and molecular) over time in a rat MI model and examine potential mechanisms that may underlie these changes. Rats were randomized into three groups: nonoperated, sham, and MI. Cardiac and renal function was assessed before death at 1, 4, 8, 12, and 16 wk with tissues collected for histological, protein, and gene studies. Tail-cuff blood pressure was lower in MI than sham and nonoperated animals only at 1 wk (P < 0.05). Systolic function was reduced (P < 0.0001) while heart/body weight and left ventricle/body weight were significantly greater in MI animals at all time points. Glomerular filtration rate decreased following MI at 1 and 4 wk (P < 0.05) but not at 8 and 12 wk and then deteriorated further at 16 wk (P = 0.052). Increased IL-6 gene and transforming growth factor (TGF)-β protein expression as well as macrophage infiltration in kidney cortex was detected at 1 wk (P < 0.05). Renal cortical interstitial fibrosis was significantly greater in MI animals from 4 wk, while TGF-β bioactivity (phospho-Smad2) was upregulated at all time points. The degree of fibrosis increased and was maximal at 16 wk. In addition, kidney injury molecule-1-positive staining in the tubules was more prominent in MI animals, maximal at 1 wk. In conclusion, renal impairment occurs early post-MI and is associated with hemodynamic and structural changes in the kidney possibly via activation of the Smad2 signaling pathway.

Association of transforming growth factor-β1 gene polymorphisms with genetic susceptibility to acute myocardial infarction

INTRODUCTION

Transforming growth factor beta 1 (TGF-β1) gene plays an important role in acute myocardial infarction (AMI); however, little is known about the relation of variations within the gene and risk of cardiovascular diseases. In this study, the authors evaluated the influence of TGF-β1 polymorphisms on the onset and progression of AMI in Iranian patients comparing with healthy individuals.

METHODS

Genomic DNA and peripheral blood mononuclear cells of 900 enrolled patients with AMI and 900 control subjects were extracted. The -509 C/T, 868T/C, 913G/C and 11929C/T TGF-β1 polymorphisms were detected. The messenger RNA (mRNA) expression and serum levels of TGF-β1 were analyzed by real-time reverse-transcriptase polymerase chain reaction and ELISA, respectively.

RESULTS

The frequency of "T" allele in -509 C/T, "C" allele in 868T/C, "C" allele in 913G/C and "T" allele in 11929C/T polymorphisms were significantly higher in the patients than control subjects (P < 0.001). There were significant differences in circulating levels of TGF-β1 in the patients than in control subjects (P < 0.001). These concentrations are associated with its gene polymorphism. The mRNA expression levels of TGF-β1 were significantly higher in the patient serums compared with controls (P < 0.001).

CONCLUSIONS

Our results confirmed the association between the TGF-β1 polymorphisms and risk of AMI, which suggest that genetic polymorphisms in TGF-β1 might be helpful for determining susceptibility to AMI in Iranian patients. There are also significant relationship between serum TGF-β1 and occurrence of AMI. In addition, susceptibility to AMI might be related to TGF-β1 gene expression, which affects its serum levels.

Targeting fibrosis for the treatment of heart failure: a role for transforming growth factor-β

Chronic heart failure (CHF) is a growing health problem in developed nations. The pathological accumulation of extracellular matrix is a key contributor to CHF in both diabetic and nondiabetic states, resulting in progressive stiffening of the ventricular walls and loss of contractility. Proinflammatory disease processes, including inflammatory cytokine activation, contribute to accumulation of extracellular matrix in the heart. Transforming growth factor-β is a key profibrotic cytokine mediating fibrosis. Current therapeutic strategies do not directly target the profibrotic inflammatory processes occurring in the heart and hence there is a clear unmet clinical need to develop new therapeutic agents targeting fibrosis. Accordingly, strategies that inhibit proinflammatory cytokine activation and pathological accumulation of extracellular matrix (ECM) provide a potential therapeutic target for prevention of heart failure. This review focuses on the therapeutic targeting of TGF-β in the prevention of pathological fibrosis in the heart.

Intramyocardial fibroblast myocyte communication

Cardiac fibroblasts are emerging as key components of normal cardiac function, as well as the response to stressors and injury. These most numerous cells of the heart interact with myocytes via paracrine mechanisms, alterations in extracellular matrix homeostasis, and direct cell-cell interactions. It is possible that they are a contributor to the inability of adult myocytes to proliferate and may influence cardiac progenitor biology. Furthering our understanding of how cardiac fibroblasts and myocytes interact may provide an avenue to novel treatments for heart failure prevention. This review discusses the most recent concepts in cardiac fibroblast-myocyte communication and areas of potential future research.

The inflammatory response and cardiac repair after myocardial infarction

One of the most important therapeutic targets of current cardiology practice is to determine optimal strategies for the minimization of myocardial necrosis and optimization of cardiac repair following an acute myocardial infarction. Myocardial necrosis after acute myocardial infarction induces complement activation and free radical generation, triggering a cytokine cascade initiated by tumor necrosis factor-alpha (TNF-α) release. When reperfusion of the infarcted area is initiated, intense inflammation follows. Chemokines, cytokines and the complement system play an important role in recruiting neutrophils in the ischemic and reperfused myocardium. Cytokines promote adhesive interactions between leukocytes and endothelial cells, resulting in transmigration of inflammatory cells into the site of injury. The recruited neutrophils have potent cytotoxic effects through the release of proteolytic enzymes, and they interact with adhesion molecules on cardiomyocytes. In spite of the potential injury, reperfusion enhances cardiac repair; this may be related to the inflammatory response. Monocyte chemoattractant protein (MCP)-1 is upregulated in reperfused myocardium and can induce monocyte recruitment in the infarcted area. Monocyte subsets play a role in phagocytosis of dead cardiomyocytes and in granulation tissue formation. In addition, the transforming growth factor (TGF)-β plays a crucial role in cardiac repair by suppressing inflammation. Resolution of inflammatory infiltration, containment of inflammation and the reparative response affecting the infarcted area are essential for optimal infarct healing. Here, we review the current literature on the inflammatory response and cardiac repair after myocardial infarction.

Thrombospondins in the heart: potential functions in cardiac remodeling

Cardiac remodeling after myocardial injury involves inflammation, angiogenesis, left ventricular hypertrophy and matrix remodeling. Thrombospondins (TSPs) belong to the group of matricellular proteins, which are non-structural extracellular matrix proteins that modulate cell-matrix interactions and cell function in injured tissues or tumors. They interact with different matrix and membrane-bound proteins due to their diverse functional domains. That the expression of TSPs strongly increases during cardiac stress or injury indicates an important role for them during cardiac remodeling. Recently, the protective properties of TSP expression against heart failure have been acknowledged. The current review will focus on the biological role of TSPs in the ischemic and hypertensive heart, and will describe the functional consequences of TSP polymorphisms in cardiac disease.

Pharmacological activation of soluble guanylate cyclase protects the heart against ischemic injury

BACKGROUND

The role of the nitric oxide/cGMP/cGMP-dependent protein kinase G pathway in myocardial protection and preconditioning has been the object of intensive investigations. The novel soluble guanylate cyclase activator cinaciguat has been reported to elevate intracellular [cGMP] and activate the nitric oxide/cGMP/cGMP-dependent protein kinase G pathway in vivo. We investigated the effects of cinaciguat on myocardial infarction induced by isoproterenol in rats.

METHODS AND RESULTS

Rats were treated orally twice a day for 4 days with vehicle or cinaciguat (10 mg/kg). Isoproterenol (85 mg/kg) was injected subcutaneously 2 days after the first treatment at an interval of 24 hours for 2 days to produce myocardial infarction. After 17 hours, histopathological observations and left ventricular pressure-volume analysis to assess cardiac function with a Millar microtip pressure-volume conductance catheter were performed, and levels of biochemicals of the heart tissues were measured. Gene expression analysis was performed by quantitative real-time polymerase chain reaction. Isolated canine coronary arterial rings exposed to peroxynitrite were investigated for vasomotor function, and immunohistochemistry was performed for cGMP and nitrotyrosine. The present results show that cinaciguat treatment improves histopathological lesions, improves cardiac performance, improves impaired cardiac relaxation, reduces oxidative stress, ameliorates intracellular enzyme release, and decreases cyclooxygenase 2, transforming growth factor-beta, and beta-actin mRNA expression in experimentally induced myocardial infarction in rats. In vitro exposure of coronary arteries to peroxynitrite resulted in an impairment of endothelium-dependent vasorelaxation, increased nitro-oxidative stress, and reduced intracellular cGMP levels, which were all improved by cinaciguat. A cardioprotective effect of postischemic cinaciguat treatment was shown in a canine model of global ischemia/reperfusion.

CONCLUSIONS

Pharmacological soluble guanylate cyclase activation could be a novel approach for the prevention and treatment of ischemic heart disease.

Role of TGF-beta on cardiac structural and electrical remodeling

The type β transforming growth factors (TGF-βs) are involved in a number of human diseases, including heart failure and myocardial arrhythmias. In fact, during the last 20 years numerous studies have demonstrated that TGF-β affects the architecture of the heart under both normal and pathological conditions. Moreover, TGF-β signaling is currently under investigation, with the aim of discovering potential therapeutic roles in human disease. In contrast, only few studies have investigated whether TGF-β affects electrophysiological properties of the heart. This fact is surprising since electrical remodeling represents an important substrate for cardiac disease. This review discusses the potential role of TGF-β on cardiac excitation-contraction (EC) coupling, action potentials, and ion channels. We also discuss the effects of TGF-β on cardiac development and disease from structural and electrophysiological points of view.

Oxidative stress mediates cardiac fibrosis by enhancing transforming growth factor-beta1 in hypertensive rats

Cardiac fibrosis represented as perivascular/interstial fibrosis occurs in patients with hypertension. Oxidative stress has been demonstrated to contribute to such structural remodeling. The underlying mechanisms, however, remain to be elucidated. Herein, we tested the hypothesis that oxidative stress mediates cardiac fibrogenesis by stimulating transforming growth factor (TGF)-beta1 expression, which in turn triggers a series of fibrogenic responses. Sprague-Dawley rats were treated with angiotensin (Ang)II (9 microg/h s) for 4 weeks with/without co-treatment of combined antioxidants, apocynin, and tempol (120 mg/kg/day each, oral). Untreated rats served as controls. Appearance of cardiac oxidative stress and its potential effect on the expression of TGF-beta1, population of myofibroblasts, collagen synthesis/degradation, and fibrosis in hearts were examined. Chronic AngII infusion elevated systemic blood pressure (210 +/- 5 mmHg). Extensive perivascular and interstitial fibrosis was found in both ventricles, which were co-localized with oxidative stress represented as upregulated NADPH oxidase (gp91(phox) subunit) expression. Co-treatment with antioxidants led to: (1) markedly decreased cardiac gp91(phox); (2) significantly attenuated gene expression of TGF-beta1, type-I collagen, and tissue inhibitors of matrix metalloproteinase (TIMP)-I/II in the heart; (3) largely reduced population of myofibroblasts at sites of fibrosis; (4) significantly reduced cardiac collagen volume; (5) and partially suppressed blood pressure (190 +/- 4 mmHg). Thus, cardiac oxidative stress promotes the development of cardiac fibrosis by upregulating TGF-beta1 expression, which subsequently enhances cardiac collagen synthesis and suppresses collagen degradation in hypertensive rats.

The immune system and cardiac repair

Myocardial infarction is the most common cause of cardiac injury and results in acute loss of a large number of myocardial cells. Because the heart has negligible regenerative capacity, cardiomyocyte death triggers a reparative response that ultimately results in formation of a scar and is associated with dilative remodeling of the ventricle. Cardiac injury activates innate immune mechanisms initiating an inflammatory reaction. Toll-like receptor-mediated pathways, the complement cascade and reactive oxygen generation induce nuclear factor (NF)-kappaB activation and upregulate chemokine and cytokine synthesis in the infarcted heart. Chemokines stimulate the chemotactic recruitment of inflammatory leukocytes into the infarct, while cytokines promote adhesive interactions between leukocytes and endothelial cells, resulting in transmigration of inflammatory cells into the site of injury. Monocyte subsets play distinct roles in phagocytosis of dead cardiomyocytes and in granulation tissue formation through the release of growth factors. Clearance of dead cells and matrix debris may be essential for resolution of inflammation and transition into the reparative phase. Transforming growth factor (TGF)-beta plays a crucial role in cardiac repair by suppressing inflammation while promoting myofibroblast phenotypic modulation and extracellular matrix deposition. Myofibroblast proliferation and angiogenesis result in formation of highly vascularized granulation tissue. As the healing infarct matures, fibroblasts become apoptotic and a collagen-based matrix is formed, while many infarct neovessels acquire a muscular coat and uncoated vessels regress. Timely resolution of the inflammatory infiltrate and spatial containment of the inflammatory and reparative response into the infarcted area are essential for optimal infarct healing. Targeting inflammatory pathways following infarction may reduce cardiomyocyte injury and attenuate adverse remodeling. In addition, understanding the role of the immune system in cardiac repair is necessary in order to design optimal strategies for cardiac regeneration.

Multiple forms of TGF-beta: distinct promoters and differential expression

There are now five known distinct isoforms of TGF-beta with 64-82% identity. Of these, only TGF-beta 1, 2 and 3 thus far have been demonstrated to be expressed in mammalian tissues; TGF-beta 4 has been described only in chicken and TGF-beta 5 only in frog. Although the biological activities of these five isoforms of TGF-beta are indistinguishable in most in vitro assays their sites of synthesis and localization in vivo are often distinct. Expression of the various isoforms is differentially controlled both in vivo, as in development, and in vitro after treatment of cells with steroids, such as oestrogen or tamoxifen, or with retinoids. To investigate the basis of these observations we have cloned and characterized the promoters for the human TGF-beta 1, 2 and 3 genes. Significant differences have been found: whereas the TGF-beta 1 promoter has no TATAA box and is regulated principally by AP-1 sites, both the TGF-beta 2 and 3 promoters have TATAA boxes as well as AP-2 sites and cAMP-responsive elements. Accordingly, TGF-beta 1 gene expression is induced strongly by phorbol esters whereas that of TGF-beta 2 and 3 is induced by forskolin, an activator of adenylate cyclase. Expression of TGF-beta 2 and 3 is often coordinately regulated in vivo in a pattern distinct from that of TGF-beta 1.

Cardiac natriuretic peptides after myocardial infarction: relationship with infarct size, left ventricular function and remodelling assessed by 99mTc-sestamibi gated-single photon emission tomography

: The aim of the study was to investigate the potential relationship between A-type (atrial) and B-type (brain) natriuretic peptides (ANP, BNP) and infarct size (IS), left ventricular (LV) function and remodelling as assessed by 99m technetium-hexakis-2-methoxy-isobutyl-isonitrile (99mTc-sestamibi) gated-single photon emission tomography (G-SPET).

: Plasma concentrations of ANP and BNP in peripheral blood were measured in 54 patients with coronary artery disease (CAD) and previous myocardial infarction (MI). Of these, 25 subjects had a recent (<2 weeks) and 29 subjects an old (>6 months) MI. IS, left ventricular ejection fraction (LVEF) and end diastolic (EDV), end systolic (ESV) and stroke volume (SV) were quantitatively calculated from at-rest G-SPET.

: In either univariate or multivariate regression analysis that included IS and the other G-SPET derived parameters as co-variables, both BNP and ANP showed a significant association with IS (BNP p<0.002; ANP p<0.01). No significant relationship was found between the two peptides and LVEF, EDV or ESV values. BNP, but not ANP concentrations, were significantly higher in patients with antero-septal vs. infero-lateral (p=0.01) and recent vs. old MI (p=0.003). In these two subgroups, univariate and multivariate analyses confirmed the correlation between BNP and IS, whereas ANP demonstrated a relationship with IS only in subjects with recent MI. CAD extent had no influence on BNP and ANP levels.

: The present study showed a positive correlation between BNP and the perfusion defect measured by 99mTc-sestamibi G-SPET in patients with previous MI. Consequently, BNP may reflect the functional significance of myocardial damage and may be considered of prognostic value. ANP was also related to scintigraphic defects in the early phase after MI, but not in the chronic phase, confirming that ANP is a less sensitive marker of LV remodelling, depending also on atrial load conditions and dilatation. These preliminary data based on a small group of subjects need to be confirmed by prospective longitudinal studies involving larger populations.

Clin Chem Lab Med 2007;45:226–31.

Transforming growth factor-β1 decreases cardiac muscle L-type Ca2+ current and charge movement by acting on the Cav1.2 mRNA

Transforming growth factors-β (TGF-βs) are essential to the structural remodeling seen in cardiac disease and development; however, little is known about potential electrophysiological effects. We hypothesized that chronic exposure (6–48 h) of primary cultured neonatal rat cardiomyocytes to the type 1 TGF-β (TGF-β1, 5 ng/ml) may affect voltage-dependent Ca2+ channels. Thus we investigated T- ( ICaT) and L-type ( ICaL) Ca2+ currents, as well as dihydropyridine-sensitive charge movement using the whole cell patch-clamp technique and quantified CaV1.2 mRNA levels by real-time PCR assay. In ventricular myocytes, TGF-β1 did not exert significant electrophysiological effects. However, in atrial myocytes, TGF-β1 reduced both ICaL and charge movement (55% at 24–48 h) without significantly altering ICaT, cell membrane capacitance, or channel kinetics (voltage dependence of activation and inactivation, as well as the activation and inactivation rates). Reductions of ICaL and charge movement were explained by concomitant effects on the maximal values of L-channels conductance ( Gmax) and charge movement (Qmax). Thus TGF-β1 selectively reduces the number of functional L-channels on the surface of the plasma membrane in atrial but not ventricular myocytes. The TGF-β1-induced ICaL reduction was unaffected by supplementing intracellular recording solutions with okadaic acid (2 μM) or cAMP (100 μM), two compounds that promote L-channel phosphorylation. This suggests that the decreased number of functional L-channels cannot be explained by a possible regulation in the L-channels phosphorylation state. Instead, we found that TGF-β1 decreases the expression levels of atrial CaV1.2 mRNA (70%). Thus TGF-β1 downregulates atrial L-channel expression and may be therefore contributing to the in vivo cardiac electrical remodeling.

The mechanistic basis of infarct healing

Myocardial infarction triggers an inflammatory cascade that results in healing and replacement of the damaged tissue with scar. Cardiomyocyte necrosis triggers innate immune mechanisms eliciting Toll-like receptor- mediated responses, activating the complement cascade and generating reactive oxygen species. Subsequent activation of NF-kappaB is a critical element in the regulation of cytokine, chemokine, and adhesion molecule expression in the ischemic myocardium. Chemokine induction mediates leukocyte recruitment in the myocardium. Pleiotropic proinflammatory cytokines, such as TNF-alpha, IL-1, and IL-6, are also upregulated in the infarct and exert a wide range of effects on a variety of cell types. Timely repression of proinflammatory gene synthesis is crucial for optimal healing; IL-10 and TGF-beta-mediated pathways may be important for suppression of chemokine and cytokine expression and for resolution of the leukocytic infiltrate. In addition, TGF-beta may be critically involved in inducing myofibroblast differentiation and activation, promoting extracellular matrix protein deposition in the infarcted area. The composition of the extracellular matrix plays an important role in regulating cell behavior. Both structural and matricellular proteins modulate cell signaling through interactions with specific surface receptors. The molecular and cellular changes associated with infarct healing directly influence ventricular remodeling and affect prognosis in patients with myocardial infarction.

Activation of TGF-β1-TAK1-p38 MAPK pathway in spared cardiomyocytes is involved in left ventricular remodeling after myocardial infarction in rats

Transforming growth factor-β1 (TGF-β1) alters myocardial gene expression, resulting in myocyte hypertrophy, through activation of TGF-β-activated kinase (TAK1), a member of the mitogen-activated protein kinase kinase kinase (MAPKKK) family. We hypothesized that the TGF-β1-TAK1-p38 MAPK pathway might be activated during ventricular remodeling after myocardial infarction (MI). One, 3, 7, and 14 days after ligation of the left anterior descending coronary artery, noninfarcted left ventricular tissue samples were obtained. Protein levels as well as mRNA levels of the signaling pathway, TGF-β1, TGF-β-receptors, and TAK1 increased in the noninfarcted myocardium in MI rats compared with sham-operated animals. Phosphorylation of MAPKK 3/6 (MKK3/6) and p38 MAPK, the downstream targets of TAK1, was also increased in the noninfarcted region. Moreover, an in vitro kinase assay revealed that the activated TAK1 in the noninfarcted myocardium was capable of activating recombinant MKK3/6, suggesting a causative role of TAK1 in the remodeling process. The activation of the TGF-β1-TAK1-p38 MAPK pathway paralleled the transcriptional upregulation of cardiac markers for ventricular hypertrophy, β-myosin heavy chain and atrial natriuretic peptide. TAK1 was mainly localized to cardiomyocytes, whereas TGF-β1 receptors were observed in vascular smooth muscle cells and fibroblasts as well as cardiomyocytes. Thus the TGF-β1-TAK1-MKK3/6-p38 MAPK pathway in the cardiomyocytes of noninfarcted spared myocardium is activated after acute MI and may play an important role in ventricular hypertrophy and post-MI remodeling in rats.

Fibroblast migration after myocardial infarction is regulated by transient SPARC expression

Secreted protein, acidic, and rich in cysteine (SPARC) is thought to regulate cell matrix interaction during wound repair. We hypothesized that SPARC might promote migration via integrin-dependent mechanisms. The present study was designed to clarify the contribution of SPARC in the wound healing process after myocardial infarction (MI). Adult mice received a specific alpha(v) integrin inhibitor or vehicle through osmotic mini pumps. Mice of each group were either sham-operated or MI was induced. SPARC expression was investigated 2 days, 7 days, and 1 month after the surgical procedure. For migration assays, a modified Boyden chamber assay was used. A transient increase of SPARC levels was observed, starting at day 2 (2.55+/-0.21), day 7 (3.72+/-0.28), and 1 month (1.9+/-0.16) after MI. After 2 months, SPARC expression dropped back to normal levels compared to sham-operated hearts. Immunofluorescence analysis showed an increase of SPARC in the infarcted area 2 days after MI, a strong increase in the scar area 7 days after MI, and only low levels in the scar area 2 months after MI. Integrin alpha(v) inhibition abolished the up-regulation of SPARC. In vitro migration assays demonstrated that fibronectin-stimulated haptotaxis of fibroblasts was modulated by SPARC. This study provides evidence that SPARC is significantly up-regulated in the infarcted region after MI. This up-regulation is dependent on alpha(v) integrins. As SPARC is found to regulate fibroblast migration, it appears to play an important role in the injured myocardium with regard to healing and scar formation.

A 7.1 kbp beta-myosin heavy chain promoter, efficient for green fluorescent protein expression, probably induces lethality when overexpressing a mutated transforming growth factor-beta type II receptor in transgenic mice

The roles of transforming growth factor-beta (TGFbeta) in heart or skeletal muscle development and physiology are still the subject of controversies. Our aim was to block, in transgenic mice, the TGFbeta signalling pathway by a dominant negative mutant of the TGFbeta type II receptor fused to the enhanced green fluorescent protein (TbetaRII-KR-EGFP) under the control of a 7.1 kbp mouse beta-myosin heavy chain (betaMHC) promoter to investigate the roles of TGFbeta in the heart and slow skeletal muscles. First, we generated two transgenic lines overexpressing EGFP under the control of the 7.1 kbp betaMHC promoter. In embryos, EGFP was detectable as early as 7.5 days post coitum. In embryos, newborns and adults, EGFP was expressed mainly in the cardiac ventricles and in slow skeletal muscles. EGFP expression was intense in the bladder but weak in the intestines. In contrast to the endogenous betaMHC promoter, the activity of the 7.1 kbp betaMHC promoter in the transgene was not repressed after birth and remained high in adult transgenic mice. We obtained two founders with the transgene comprising the TbetaRII-KR-EGFP sequence under the control of the 7.1 kbp betaMHC promoter. These founders were generated at a very low frequency and expressed barely detectable levels of TbetaRII-KR-EGFP mRNA. Our failure to obtain transgenic lines overexpressing the dominant negative receptor suggests that the blocking of the TGFbeta signalling pathway in the heart and slow skeletal muscles could be embryonically lethal. To conclude, the 7.1 kbp betaMHC promoter directs high levels of transgene expression in the cardiac ventricles and in slow skeletal muscles of the mouse. Analysis of the consequences of the blocking of the TGFbeta signalling pathway in the heart will require the use of tissue specific means of conditional gene invalidation.

Connective tissue growth factor and cardiac fibrosis after myocardial infarction

The temporal and spatial expression of transforming growth factor (TGF)-beta(1) and connective tissue growth factor (CTGF) was assessed in the left ventricle of a myocardial infarction (MI) model of injury with and without angiotensin-converting enzyme (ACE) inhibition. Coronary artery ligated rats were killed 1, 3, 7, 28, and 180 days after MI. TGF-beta(1), CTGF, and procollagen alpha1(I) mRNA were localized by in situ hybridization, and TGF-beta(1) and CTGF protein levels by immunohistochemistry. Collagen protein was measured using picrosirius red staining. In a separate group, rats were treated for 6 months with an ACE inhibitor. There were temporal and regional differences in the expression of TGF-beta(1), CTGF, and collagen after MI. Procollagen alpha1(I) mRNA expression increased in the border zone and scar peaking 1 week after MI, whereas collagen protein increased in all areas of the heart over the 180 days. Expression of TGF-beta(1) mRNA and protein showed major increases in the border zone and scar peaking 1 week after MI. The major increases in CTGF mRNA and protein occurred in the viable myocardium at 180 days after MI. Long-term ACE inhibition reduced left ventricular mass and decreased fibrosis in the viable myocardium, but had no effect on cardiac TGF-beta(1) or CTGF. TGF-beta(1) is involved in the initial, acute phase of inflammation and repair after MI, whereas CTGF is involved in the ongoing fibrosis of the heart. The antifibrotic benefits of captopril are not mediated through a reduction in CTGF.

Transforming growth factor-β1 downregulates beating frequency and remodeling of cultured rat adult cardiomyocytes

We have observed increased levels of transforming growth factor-beta1 (TGF-beta1) in human hibernating myocardium (HM). Impaired ventricular function in HM is known to be restored to normal following revascularization implying that myocardial structure in HM is to a certain degree preserved. We have therefore tested whether TGF-beta1 can imitate features of HM by reducing the number and frequency of beating cells (chronotropism) and structural remodeling of cultured adult rat cardiomyocytes (ARC), thus saving substrate, energy, and oxygen. Parameters measured were cell size, protein synthesis, protein degradation, protein content, myofibrillogenesis, and chronotropism. ARC were stimulated for 6 days with sera from patients with coronary heart disease, as this period led to a maximum response of cells. An increase of 90% in cell surface area following such treatment was reduced to a 20% increase of the original size by TGF-beta1. Concomitantly, the rate of protein synthesis dropped from 3.6-fold to 2.4-fold, and myofibrillogenesis was reduced. TGF-beta1 downregulated both the number of contracting cells from 81% to 10% and the frequency from 52 to nine beats per minute. However, TGF-beta1 treatment did not reduce the augmentation of protein content (1.28-fold versus 1.25-fold) indicating that protein degradation was also inhibited. Similar results were obtained with serum from healthy volunteers. The effects of TGF-beta1 were reversible. We conclude that TGF-beta1 constrains protein turnover and beating activity in underperfused myocardium, thus mediating protection by adapting myocytes to shortages in blood supply.

Induction of myocardial connective tissue growth factor in pacing-induced heart failure in pigs

AIMS

Connective tissue growth factor (CTGF) is a secreted, heparin-binding, and extracellular matrix associated protein shown to stimulate many of the cellular events underlying fibrosis. Previous investigations have revealed that myocardial CTGF is substantially induced in ischaemic heart failure, particularly in the ischaemic and peri-ischaemic region. The purpose of the present study was to investigate to what extent myocardial induction of CTGF is a general response to congestive heart failure (CHF) and to what extent CTGF is a decisive effector of fibrosis.

METHODS

Experimental heart failure in pigs was induced by rapid pacing at 220-240 beats min(-1) for 3 weeks (CHF pigs; n = 12).

RESULTS

The CHF pigs exhibited significant left ventricular (LV) dilatation, reduced contractility, and increased cardiac filling pressures. Northern blot analysis demonstrated that myocardial CTGF mRNA levels in CHF pigs were fivefold higher (P < 0.05) than those in control pigs (n = 10). Similar elevations of immunoreactive CTGF (sixfold; P < 0.05) were observed in myocardial tissue samples prepared for Western blot analysis. Immunohistochemical analysis of myocardial tissue sections revealed predominant expression in interstitial and perivascular fibroblasts and endothelial cells. Myocardial procollagen alpha1(I) mRNA levels were also significantly elevated (sixfold; P < 0.05) in CHF pigs compared with controls, whereas myocardial tissue contents of collagen were not statistically different between the groups.

CONCLUSION

Induction of myocardial CTGF in heart failure is not just a response to ischaemia, but rather a general response to evolving heart failure. Yet, induction of myocardial CTGF was clearly not a sufficient effector of fibrosis.

C-type natriuretic peptide, a novel antifibrotic and antihypertrophic agent, prevents cardiac remodeling after myocardial infarction

OBJECTIVES

We assessed the hypothesis that in vivo administration of C-type natriuretic peptide (CNP) might attenuate cardiac remodeling after myocardial infarction (MI) through its antifibrotic and antihypertrophic action.

BACKGROUND

Recently, we have shown that CNP has more potent antifibrotic and antihypertrophic effects than atrial natriuretic peptide (ANP) in cultured cardiac fibroblasts and cardiomyocytes.

METHODS

Experimental MI was induced by coronary ligation in male Sprague-Dawley rats; CNP at 0.1 mug/kg/min (n = 34) or vehicle (n = 35) was intravenously infused by osmotic mini-pump starting four days after MI. Sham-operated rats (n = 34) served as controls. After two weeks of infusion, the effects of CNP on cardiac remodeling were evaluated by echocardiograpic, hemodynamic, histopathologic, and gene analysis.

RESULTS

C-type natriuretic peptide markedly attenuated the left ventricular (LV) enlargement caused by MI (LV end-diastolic dimension, sham: 6.7 +/- 0.1 mm; MI+vehicle; 8.3 +/- 0.1 mm; MI+CNP: 7.7 +/- 0.1 mm, p < 0.01) without affecting arterial pressure. Moreover, there was a substantial decrease in LV end-diastolic pressure, and increases in dP/dt(max), dP/dt(min), and cardiac output in CNP-treated MI rats compared with vehicle-treated MI rats. Importantly, CNP infusion markedly attenuated an increase in morphometrical collagen volume fraction in the noninfarct region (sham: 3.1 +/- 0.2%; MI+vehicle: 5.7 +/- 0.5%; MI+CNP: 3.9 +/- 0.3%, p < 0.01). In addition, CNP significantly reduced an increase in cross-sectional area of the cardiomyocytes. These effects of CNP were accompanied by suppression of MI-induced increases in collagen I, collagen III, ANP, and beta-myosin heavy chain messenger ribonucleic acid levels in the noninfarct region.

CONCLUSIONS

These data suggest that CNP may be useful as a novel antiremodeling agent.

Simvastatin Regulates Myocardial Cytokine Expression and Improves Ventricular Remodeling in Rats after Acute Myocardial Infarction

PURPOSE

Studies have showed that inflammatory cytokines were involved in the process of left ventricular (LV) remodeling after acute myocardial infarction (AMI), anti-inflammation treatment ameliorated LV remodeling and improved cardiac performance. Hydroxymethylglutary coenzyme A reductase inhibition (statins) could affect the expression of inflammatory cytokines. We hypothesized that statins have beneficial effects on early LV remodeling and cardiac performance in rats with AMI by modulating the production of inflammatory cytokines.

METHODS

Rats with AMI were treated with placebo or simvastatin (gastric gavage) for 4 weeks. The pro-inflammatory cytokines: tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6 and the anti-inflammatory cytokine: IL-10 excreted by cardiac myocytes was examined. Echocardiography, hemodynamics and collagen type I production were measured to evaluate LV remodeling and cardiac function.

RESULTS

The mRNA expression and protein production of TNF-alpha, IL-1beta, IL-6 and IL-10 in AMI group were significantly elevated compared with sham rats. Simvastatin markedly attenuated the production of TNF-alpha, IL-1beta, IL-6 and increased IL-10 levels in the noninfarcted and infarcted regions, reduced collagen deposition in the noninfarcted myocardium and improved left ventricular function. However simvastatin did not alter plasma lipids.

CONCLUSIONS

Simvastatin ameliorates early LV remodeling and improve cardiac function after AMI. Simultaneously, it decreased pro-inflammatory and increased anti-inflammatory cytokines, which suggests, but does not prove, a causal relationship independent of plasma lipid-lowering effects.

Independent regulation of transforming growth factor-beta1 transcription and translation by glucose and platelet-derived growth factor

Proximal tubular renal epithelial cells may contribute to the pathogenesis of renal interstitial fibrosis in diabetes by generation of cytokines such as transforming growth factor (TGF)-beta1. We have previously demonstrated that proximal tubular renal epithelial cell TGF-beta1 synthesis may be modulated by elevated glucose concentration and by cytokines such as platelet-derived growth factor (PDGF). The aim of the current study was to characterize the mechanism by which glucose and PDGF synergistically stimulate the generation of TGF-beta1. Addition of either 25 mmol/L of D-glucose or low-dose PDGF increased TGF-beta1 mRNA expression without stimulation of TGF-beta1 protein synthesis. In contrast sequential stimulation with 25 mmol/L of D-glucose for 48 hours followed by low-dose (25 ng/ml) PDGF led to a significant increase in TGF-beta1 synthesis. Elevated glucose concentration stimulated de novo gene transcription as assessed by stimulation of a TGF-beta1 promoter-luciferase construct. This led to induction of a poorly translated TGF-beta1 transcript determined by polysome analysis. PDGF at low dose did not influence TGF-beta1 transcription, but led to alteration in TGF-beta1 mRNA stability and translation. Without a previous glucose-induced increase in the amount of TGF-beta1 transcript, PDGF did not stimulate significant TGF-beta1 protein synthesis. At a high dose (100 ng/ml) PDGF stimulated TGF-beta1 synthesis independent of glucose concentration. This was associated with increased TGF-beta1 gene transcription and alteration in TGF-beta1 mRNA translational efficiency. In conclusion the data suggests that in diabetic nephropathy, the role of glucose is to lower the threshold at which a stimulus such as PDGF stimulates TGF-beta1 protein synthesis. The data also suggest that independent regulation of TGF-beta1 transcription and translation by glucose and PDGF account for their synergistic effect on TGF-beta1 protein synthesis. We hypothesize that the role of glucose in diabetic nephropathy is to prime the kidney for an injurious response to other stimuli.

Stretch-induced paracrine hypertrophic stimuli increase TGF-beta1 expression in cardiomyocytes

Cardiac hypertrophy refers to the abnormal growth of cardiomyocytes, and is often caused by valvular heart disease and hypertension. It involves the activation of growth, including increased protein synthesis and changes in gene expression. Transforming growth factor-beta1 (TGF-beta1) may play a central role in protecting the heart during the hypertrophic response by helping to restore normal functions of the affected myocardium. We tested the hypothesis that cardiomyocytes respond to stretch-induced paracrine hypertrophic stimuli with increased expression of TGF-beta1. To that purpose, we investigated whether angiotensin II (All), endothelin- I (ET-1) and TGF-beta, secreted by stretched cardiac and vascular cells, are involved in the paracrine mechanisms of stretch-induced changes of TGF-beta1 mRNA expression in stationary (i.e. non-stretched) cardiomyocytes. Our results indicated that TGF-beta1 mRNA expression in stationary cardiomyocytes was increased by AII release from cardiomyocytes that had been stretched for 30-60 min. Furthermore, it is likely that ET-1 and TGF-beta were released by stretched cardiac fibroblasts and endothelial cells to induce TGF-beta1 mRNA expression in stationary cardiomyocytes. Stretched vascular smooth muscle cells did not influence TGF-beta1 mRNA expression in stationary cardiomyocytes. These results indicate that AII, ET-I and TGF-beta, released by cardiac cell types, act as paracrine mediators of TGF-beta1 mRNA expression in cardiomyocytes. Therefore, we conclude that in stretched myocardium the cardiomyocytes, cardiac fibroblasts and endothelial cells take part in intercellular interactions contributing to cardiomyocyte hypertrophy.

TGF-beta1 mediates the hypertrophic cardiomyocyte growth induced by angiotensin II

Angiotensin II (Ang II), a potent hypertrophic stimulus, causes significant increases in TGFb1 gene expression. However, it is not known whether there is a causal relationship between increased levels of TGF-beta1 and cardiac hypertrophy. Echocardiographic analysis revealed that TGF-beta1-deficient mice subjected to chronic subpressor doses of Ang II had no significant change in left ventricular (LV) mass and percent fractional shortening during Ang II treatment. In contrast, Ang II-treated wild-type mice showed a >20% increase in LV mass and impaired cardiac function. Cardiomyocyte cross-sectional area was also markedly increased in Ang II-treated wild-type mice but unchanged in Ang II-treated TGF-beta1-deficient mice. No significant levels of fibrosis, mitotic growth, or cytokine infiltration were detected in Ang II-treated mice. Atrial natriuretic factor expression was approximately 6-fold elevated in Ang II-treated wild-type, but not TGF-beta1-deficient mice. However, the alpha- to beta-myosin heavy chain switch did not occur in Ang II-treated mice, indicating that isoform switching is not obligatorily coupled with hypertrophy or TGF-beta1. The Ang II effect on hypertrophy was shown not to result from stimulation of the endogenous renin-angiotensis system. These results indicate that TGF-beta1 is an important mediator of the hypertrophic growth response of the heart to Ang II.

Effects of captopril and omapatrilat on early post-myocardial infarction survival and cardiac hemodynamics in rats: interaction with cardiac cytokine expression

The purpose of this study was to evaluate and compare the effects of simultaneous angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) inhibition by the vasopeptidase inhibitor omapatrilat (10 and 40 mg x kg(-1) x day(-1)) with those of the selective ACE inhibitor captopril (160 mg x kg(-1) x day(-1)) on survival, cardiac hemodynamics, and cytokine mRNA expression in left ventricular (LV) tissues 4 days after myocardial infarction (MI) in rats. The effects of the co-administration of both B1 and B2 kinin receptor antagonists (2.5 mg x kg(-1) x day(-1) each) with and without omapatrilat were also evaluated to assess the role of bradykinin (BK) during this post-MI period. Both omapatrilat and captopril treatments improve early (4 days) post-MI survival when started 4 h post-MI. The use of kinin receptor antagonists had no significant effect on survival in untreated MI rats and omapatrilat-treated MI rats. This improvement in survival with omapatrilat and captopril is accompanied by a reduced LV end-diastolic pressure (LVEDP) and pulmonary congestion. The use of kinin receptor antagonists had little effect on cardiac hemodynamics or morphologic measurements. Acute MI significantly increased the expression of cardiac cytokines (TNF-alpha, TGF-beta1, and IL-10). Captopril significantly attenuated this activation, while omapatrilat had variable effects: sometimes increasing but generally not changing activation depending on the cytokine measured and the dose of omapatrilat used. The co-administration of both kinin receptor antagonists attenuates the increase in expression of cardiac TNF-alpha and TGF-beta1 after omapatrilat treatment. Taken together, these results would suggest that despite very marked differences in the way these drugs modified the expression of cardiac cytokines, both omapatrilat and captopril improved early (4 days) post-MI survival and cardiac function to a similar extent.

Effects of combination of angiotensin-converting enzyme inhibitor and angiotensin receptor antagonist on inflammatory cellular infiltration and myocardial interstitial fibrosis after acute myocardial infarction

OBJECTIVES

The goal of this study was to compare the relative efficacy of an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin receptor blocker (ARB) in suppressing the histopathologic changes that lead to ventricular remodeling after an acute myocardial infarction (AMI).

BACKGROUND

Myocardial interstitial fibrosis in the noninfarcted region is a major histologic landmark resulting in cardiac dysfunction after AMI. However, the relative potency of an ACE inhibitor and ARB on suppressing the histopathologic changes was unclear.

METHODS

Rats with AMI were randomized to fosinopril, valsartan or a combination of the two drugs for two or four weeks. The total, type I and type III collagen and activated fibroblasts and macrophages were quantified by histomorphometry. The expression of transforming growth factor-beta 1 (TGF-beta 1) messenger ribonucleic acid (mRNA) was determined by reverse transcription polymerase chain reaction.

RESULTS

Acute myocardial infarction resulted in significant elevation of total (p < 0.001) and type I (p < 0.001) collagen and a twofold increase in TGF-beta 1 mRNA expression (p < 0.001) in the septum at two and four weeks. Macrophages and activated myofibroblasts infiltrated extensively in the infarct zone. Treatment with valsartan or combination therapy normalized the total and type I collagen (p < 0.001) as well as TGF-beta 1 mRNA level (p < 0.01) in the septum and was associated with the suppression of macrophages and myofibroblasts in the infarct zone (p < 0.01). Fosinopril was less effective than valsartan or combination therapy.

CONCLUSIONS

The use of valsartan, especially combined with fosinopril, was more effective than fosinopril in the suppression of histopathologic changes resulting in cardiac remodeling after AMI. This study has important therapeutic implications in pharmacotherapy of clinical practice.

Time course of collagen and decorin changes in rat cardiac and skeletal muscle post-MI

We examined the temporal relationship between messages (type I and type III mRNAs) for the principal fibrillar procollagens and subsequent collagen accretion, cross-linking, and decorin expression in the left ventricle (LV) postmyocardial infarction (post-MI). We sought to determine 1) what role the proteoglycan decorin plays in extracellular matrix (ECM) remodeling known to take place as a consequence of MI and 2) the extent skeletal muscle ECM is altered early post-MI. Therefore, after surgically induced production of small- to moderate-sized infarcts (approximately 20% of LV mass), extent and time course of ECM remodeling was evaluated in remaining viable LV free wall and in slow- [soleus (SOL)] and fast-twitch [gastrocnemius (GAST)] skeletal muscles. Decorin, collagen, and hydroxylysylpyridinium cross-link concentrations and alpha1(I) (type I) and alpha1(III) (type III) procollagen mRNAs were measured in LVs from noninfarcted controls and at 72 h, 1, 2, 5, and 13 wk post-MI. These same data were collected in SOL and GAST muscles at all time points except 13 wk. Type I procollagen mRNA increased at both 72-h and 1-wk time points in LVs. Type III procollagen mRNA was elevated at 1 wk, returning to baseline by 2 wk post-MI. Collagen concentration was significantly increased by 1 wk, more than doubled by 5 wk, and was elevated 129% by 13 wk in the remaining viable LV. LV decorin expression was unaltered at early time points, but increased 38% at 5 wk post-MI and doubled by 13 wk post-MI. In skeletal muscle, procollagen mRNAs were transiently altered in SOL and GAST muscles without any demonstrable effect on the measured ECM parameters. This study reports, for the first time, the upregulation time course of decorin and its relationship to increased HP cross-linking and accumulation of collagen in viable myocardium post-MI.

Redox-sensitive intermediates mediate angiotensin II-induced p38 MAP kinase activation, AP-1 binding activity, and TGF-beta expression in adult ventricular cardiomyocytes

Cardiac hypertrophy as an adaptation to increased blood pressure leads to an increase in ventricular expression of transforming growth factor Cardiac hypertrophy as an adaptation to increased blood pressure leads to an increase in ventricular expression of transforming growth factor b (TGF-b), probably via the renin-angiotensin system. We studied in vivo to determine whether angiotensin II affects TGF-b expression independent from mechanical effects caused by the concomitant increase in blood pressure and in vitro intracellular signaling involved in angiotensin II-dependent TGF-b1 induction. In vivo, the AT1 receptor antagonist losartan, but not reduction of blood pressure by hydralazine, inhibited the increase in TGF-b1 expression caused by angiotensin II. In vitro, angiotensin II caused an induction of TGF-b1 expression in adult ventricular cardiomyocytes and induced AP-1 binding activity. Transfection with "decoys" directed against the binding site of AP-1 binding proteins inhibited the angiotensin II-dependent TGF-b induction. Angiotensin II induced TGF-b expression in a p38-MAP kinase-dependent way. p38-MAP kinase activation was diminished in presence of the antioxidants or diphenyleneiodium chloride, or by pretreatment with antisense nucleotides directed against phox22 and nox, components of smooth muscle type NAD(P)H oxidase. Thus, our study identifies a previously unrecognized coupling of cardiac AT receptors to a NAD(P)H oxidase complex similar to that expressed in smooth muscle cells and identifies p38-MAP kinase activation as an important downstream target.

Nitric oxide attenuates the expression of transforming growth factor-beta(3) mRNA in rat cardiac fibroblasts via destabilization

Transforming growth factor-beta (TGF-beta) has been implicated in the development of interstitial fibrosis in cardiac hypertrophy. NO has been regarded as a potent inhibitor of cardiac fibroblast growth, albeit the modulation of cellular events associated with interstitial fibrosis remains undefined. In this regard, the regulation of TGF-beta mRNA expression by the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) was examined in neonatal rat cardiac fibroblasts. SNAP treatment for 4 hours decreased TGF-beta(3) mRNA levels, an effect mimicked by 8-bromo-cGMP. TGF-beta(3) mRNA, however, had returned to levels observed in the untreated cells after a 24-hour exposure to SNAP, whereas a decreased expression persisted with 8-bromo-cGMP. In contrast to TGF-beta(3), TGF-beta(1) mRNA levels were modestly increased in response to cGMP-generating molecules. The treatment with actinomycin D for at least 8 hours did not appreciably alter TGF-beta(3) mRNA levels. By contrast, SNAP treatment caused a rapid decrease of TGF-beta(3) mRNA with a half-life of 3.3+/-0.2 hours, thereby supporting a mechanism of destabilization. The pretreatment with SNAP inhibited angiotensin II-stimulated protein synthesis and the concomitant expression of TGF-beta(3) mRNA. These data reveal a disparate pattern of TGF-beta(1) and TGF-beta(3) mRNA regulation by NO and highlight a novel mechanism of destabilization contributing to the decreased expression of TGF-beta(3) mRNA. The modulation of both basal and angiotensin II-stimulated TGF-beta(3) mRNA expression provides a mechanism by which NO may influence the progression of interstitial fibrosis.