B-type natriuretic peptide exerts broad functional opposition to transforming growth factor-beta in primary human cardiac fibroblasts: fibrosis, myofibroblast conversion, proliferation, and inflammation

Dynamic expression profiles of MMPs/TIMPs and collagen deposition in mechanically unloaded rat heart: implications for left ventricular assist device support-induced cardiac alterations

Left ventricular assist devices (LVADs) ameliorate heart failure by reducing preload and afterload. However, extracellular matrix (ECM) deposition after application of LVADs is not clearly defined. The purpose of the present study was to investigate ECM remodeling after mechanical unloading in a rat heart transplant model. Sixty male Lewis rats were subjected to abdominal heterotopic heart transplantation, and the transplanted hearts were pressure- and volume-unloaded. The age- and weight- matched male Lewis rats who had undergone open thoracic surgeries were used as the control. Left ventricle ECM accumulation and the expression/activity of matrix metalloproteinases (MMPs) and tissue inhibitor of matrix metalloproteinases (TIMPs) were measured on the third, seventh, and fourteenth days after transplantation/sham surgery. Compared with the control group, myocardial ECM deposition significantly increased on the seventh and fourteenth days after heart transplantation (P < 0.05) and peaked on the 14th day. The gelatinase activity as well as mRNA expression of MMP-2 and MMP-9 significantly increased after transplantation (P < 0.05). Both mRNA and protein levels of TIMP-1 and TIMP-2 significantly increased compared with those of the control group. Mechanical unloading may lead to adverse remodeling of the ECM of the left ventricle. The underlying mechanism may due to the imbalance of the MMP/TIMP system, especially the remarkable upregulation of TIMPs in the pressure and volume unloaded heart.

Modest elevation in BNP in asymptomatic hypertensive patients reflects sub-clinical cardiac remodeling, inflammation and extracellular matrix changes

In asymptomatic subjects B-type natriuretic peptide (BNP) is associated with adverse cardiovascular outcomes even at levels well below contemporary thresholds used for the diagnosis of heart failure. The mechanisms behind these observations are unclear. We examined the hypothesis that in an asymptomatic hypertensive population BNP would be associated with sub-clinical evidence of cardiac remodeling, inflammation and extracellular matrix (ECM) alterations. We performed transthoracic echocardiography and sampled coronary sinus (CS) and peripheral serum from patients with low (n = 14) and high BNP (n = 27). Peripheral BNP was closely associated with CS levels (r = 0.92, p<0.001). CS BNP correlated significantly with CS levels of markers of collagen type I and III turnover including: PINP (r = 0.44, p = 0.008), CITP (r = 0.35, p = 0.03) and PIIINP (r = 0.35, p = 0.001), and with CS levels of inflammatory cytokines including: TNF-α (r = 0.49, p = 0.002), IL-6 (r = 0.35, p = 0.04), and IL-8 (r = 0.54, p<0.001). The high BNP group had greater CS expression of fibro-inflammatory biomarkers including: CITP (3.8±0.7 versus 5.1±1.9, p = 0.007), TNF-α (3.2±0.5 versus 3.7±1.1, p = 003), IL-6 (1.9±1.3 versus 3.4±2.7, p = 0.02) and hsCRP (1.2±1.1 versus 2.4±1.1, p = 0.04), and greater left ventricular mass index (97±20 versus 118±26 g/m², p = 0.03) and left atrial volume index (18±2 versus 21±4, p = 0.008). Our data provide insight into the mechanisms behind the observed negative prognostic impact of modest elevations in BNP and suggest that in an asymptomatic hypertensive cohort a peripheral BNP measurement may be a useful marker of an early, sub-clinical pathological process characterized by cardiac remodeling, inflammation and ECM alterations.

Molecular analysis of the TGF-beta controlled gene expression program in chicken embryo dermal myofibroblasts

The myofibroblast is a mesenchymal cell characterized by synthesis of the extracellular matrix, plus contractile and secretory activities. Myofibroblasts participate in physiological tissue repair, but can also cause devastating fibrosis. They are present in the tumor stroma of carcinomas and contribute to tumor growth and spreading. As myofibroblasts derive from various cell types and appear in a variety of tissues, there is marked variability in their phenotype. As regulatory mechanisms of wound healing are likely conserved among vertebrates, detailed knowledge of these mechanisms in more distant species will help to distinguish general from specific phenomena. To provide this as yet missing comparison, we analyzed the impact of the chemical inhibition of TGF-beta signaling on gene expression in chicken embryo dermal myofibroblasts. We revealed genes previously reported in mammalian systems (e.g. SPON2, ASPN, COMP, LUM, HAS2, IL6, CXCL12, VEGFA) as well as novel TGF-beta dependent genes, among them PGF, VEGFC, PTN, FAM180A, FIBIN, ZIC1, ADCY2, RET, HHIP and DNER. Inhibition of TGF-beta signaling also induced multiple genes, including NPR3, AGTR2, MTUS1, SOD3 and NOV. We also analyzed the effects of long term inhibition, and found that it is not able to induce myofibroblast dedifferentiation.

Cardiac intercellular communication: are myocytes and fibroblasts fair-weather friends?

The cardiac fibroblast (CF) has historically been thought of as a quiescent cell of the heart, passively maintaining the extracellular environment for the cardiomyocytes (CM), the functional cardiac cell type. The increasingly appreciated role of the CF, however, extends well beyond matrix production, governing many aspects of cardiac function including cardiac electrophysiology and contractility. Importantly, its contributions to cardiac pathophysiology and pathologic remodeling have created a shift in the field's focus from the CM to the CF as a therapeutic target in the treatment of cardiac diseases. In response to cardiac injury, the CF undergoes a pathologic phenotypic transition into a myofibroblast, characterized by contractile smooth muscle proteins and upregulation of collagens, matrix proteins, and adhesion molecules. Further, the myofibroblast upregulates expression and secretion of a variety of pro-inflammatory, profibrotic mediators, including cytokines, chemokines, and growth factors. These mediators act in both an autocrine fashion to further activate CFs, as well as in a paracrine manner on both CMs and circulating inflammatory cells to induce myocyte dysfunction and chronic inflammation, respectively. Together, cell-specific cytokine-induced effects exacerbate pathologic remodeling and progression to HF. A better understanding of this dynamic intercellular communication will lead to novel targets for the attenuation of cardiac remodeling. Current strategies aimed at targeting cytokines have been largely unsuccessful in clinical trials, lending insights into ways that such intercellular cross talk can be more effectively attenuated. This review will summarize the current knowledge regarding CF functions in the heart and will discuss the regulation and signaling behind CF-mediated cytokine production and function. We will then highlight clinical trials that have exploited cytokine cross talk in the treatment of heart failure and provide novel strategies currently under investigation that may more effectively target pathologic CF-CM communication for the treatment of cardiac disease. This review explores novel mechanisms to directly attenuate heart failure progression through inhibition of signaling downstream of pro-inflammatory cytokines that are elevated after cardiac injury.

Cardiac fibroblasts, fibrosis and extracellular matrix remodeling in heart disease

Fibroblasts comprise the largest cell population in the myocardium. In heart disease, the number of fibroblasts is increased either by replication of the resident myocardial fibroblasts, migration and transformation of circulating bone marrow cells, or by transformation of endothelial/epithelial cells into fibroblasts and myofibroblasts. The primary function of fibroblasts is to produce structural proteins that comprise the extracellular matrix (ECM). This can be a constructive process; however, hyperactivity of cardiac fibroblasts can result in excess production and deposition of ECM proteins in the myocardium, known as fibrosis, with adverse effects on cardiac structure and function. In addition to being the primary source of ECM proteins, fibroblasts produce a number of cytokines, peptides, and enzymes among which matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitor of metalloproteinases (TIMPs), directly impact the ECM turnover and homeostasis. Function of fibroblasts can also in turn be regulated by MMPs and TIMPs. In this review article, we will focus on the function of cardiac fibroblasts in the context of ECM formation, homeostasis and remodeling in the heart. We will discuss the origins and multiple roles of cardiac fibroblasts in myocardial remodeling in different types of heart disease in patients and in animal models. We will further provide an overview of what we have learned from experimental animal models and genetically modified mice with altered expression of ECM regulatory proteins, MMPs and TIMPs.

N-terminal pro-brain natriuretic peptide levels and aortic diameters

BACKGROUND

Women with X-chromosome monosomy or Turner syndrome (TS) are at increased risk for aortic dilation and dissection. To better understand the pathology and develop tools to monitor the risk of aortic disease, we investigated N-terminal pro-brain natriuretic peptide (BNP) (NT-proBNP) levels in women with TS and healthy female controls.

METHODS

We evaluated NT-proBNP levels in women with karyotype-proven TS and healthy female volunteers in relation to ascending aortic diameter and descending aortic diameter measured by cardiovascular magnetic resonance imaging.

RESULTS

The NT-proBNP levels were strongly and positively correlated with ascending aortic diameter and descending aortic diameter in both cohorts. The TS group (n = 114, age 37.4 ± 12 yr) had greater body surface area-indexed aortic diameters and higher NT-proBNP levels than the control group (n = 27, age 46.4 ± 11 years): 88.3 ± 62.7 versus 53.5 ± 35 pg/mL, P = .0003. Within the TS group, NT-proBNP levels were higher in those with dilated ascending aorta (n = 42, 112.4 ± 75.7 pg/mL) compared with those with normal aortic dimensions (n = 72, 74.2 ± 49 pg/mL, P = .0014). Abnormally high NT-pro BNP levels were seen in 3 of 4 TS women who presented with previously undetected aortic aneurysm and/or dissection.

CONCLUSIONS

The NT-proBNP levels are positively associated with aortic diameters in women with and without TS, suggesting a role for BNP in arterial wall homeostasis. Further study is necessary to determine whether NT-proBNP measurement may be used to monitor aortic diameter and/or detect aortic pathology in individuals at risk for aortic disease.

Plasma BNP, a useful marker of fluid overload in hospitalized hemodialysis patients

Hospitalization for intercurrent illness frequently disrupts the nutritional status of hemodialysis (HD) patients and jeopardizes the dry weight prescription. We report in this study the evolution of brain natriuretic peptide (BNP), blood pressure and body weight in hospitalized patients and the relationship between BNP plasma level and nutritional and inflammation parameters. We have studied 42 patients requiring hospitalization (F/M: 18/24; 72.5 ± 12.5 years old; 19/42 with diabetes). The plasma BNP levels at baseline, during hospitalization (BNP-Hosp), and in the recovery phase were compared. Predialysis and postdialysis blood pressure and postdialysis body weight were recorded and compared. BNP-Hosp increased significantly when compared with BNP levels at baseline, from 421 ± 647.2 pg/mL to 1584 ± 1584.4 pg/mL (P < 0.0001). Brain natriuretic peptide decreased from 1223 ± 1342.1 pg/mL during hospitalization to 616 ± 892.1 pg/mL after discharge (P = 0.005). The BNP-Hosp was positively correlated with C-reactive protein (P = 0.003) and negatively correlated with serum prealbumin (P = 0.0001) and albumin (P = 0.0001). The postdialysis body weight prescription decreased from 71.0 ± 15.7 kg at baseline to 70.5 ± 15.4 kg during hospitalization and to 67.8 ± 14.4 kg 4 months after discharge (P = 0.0032). Our study displays clearly the significant changes of plasma BNP levels occurring during intercurrent events. Fluid overload triggered by inflammation-associated catabolism and the lag time for dry weight adjustment is the cause of this finding. Hence, plasma BNP level may be used as a marker of fluid overload in patients with intercurrent events and may allow efficient dry weight adjustment. We cannot rule out an effect of inflammation on BNP synthesis.

Mechanical stretch up-regulates the B-type natriuretic peptide system in human cardiac fibroblasts: a possible defense against transforming growth factor-β mediated fibrosis

Background

Mechanical overload of the heart is associated with excessive deposition of extracellular matrix proteins and the development of cardiac fibrosis. This can result in reduced ventricular compliance, diastolic dysfunction, and heart failure. Extracellular matrix synthesis is regulated primarily by cardiac fibroblasts, more specifically, the active myofibroblast. The influence of mechanical stretch on human cardiac fibroblasts’ response to pro-fibrotic stimuli, such as transforming growth factor beta (TGFβ), is unknown as is the impact of stretch on B-type natriuretic peptide (BNP) and natriuretic peptide receptor A (NPRA) expression. BNP, acting via NPRA, has been shown to play a role in modulation of cardiac fibrosis.

Methods and results

The effect of cyclical mechanical stretch on TGFβ induction of myofibroblast differentiation in primary human cardiac fibroblasts and whether differences in response to stretch were associated with changes in the natriuretic peptide system were investigated. Cyclical mechanical stretch attenuated the effectiveness of TGFβ in inducing myofibroblast differentiation. This finding was associated with a novel observation that mechanical stretch can increase BNP and NPRA expression in human cardiac fibroblasts, which could have important implications in modulating myocardial fibrosis. Exogenous BNP treatment further reduced the potency of TGFβ on mechanically stretched fibroblasts.

Conclusion

We postulate that stretch induced up-regulation of the natriuretic peptide system may contribute to the observed reduction in myofibroblast differentiation.

[Recent advances in natriuretic peptide family genes and cardiovascular diseases]

Natriuretic peptide family consists of several hormones produced by cardiomyocyte, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). They possess similar gene structures and protective effects of cardiovascular physiology, such as anti-hypertrophy, anti-fibrosis, myocardial relaxation and blood pressure regulation. The corresponding natriuretic peptide receptor A, B and C mediate multiple effects of natriuretic peptides to maintain cardiovascular homeostasis. Specially, natriuretic peptide receptor-A preferentially binds ANP and BNP, while natriuretic peptide receptor-B is more selective for C-type natriuretic peptides. Natriuretic peptide receptor-C(NPR-C), binding all kinds of natriuretic peptides, clears natriuretic peptides from the circulation through receptor-mediated internalization and degradation. BNP levels were reported to be a good predictor of left ventricular dysfunction and decompensated heart failure from a clinical standpoint. BNP infusion is an effective treatment for acute heart failure. Investigations on natriuretic peptides' single nucleotide polymorphisms and biological function suggested that they could be associated with several cardiovascular diseases, such as atrial fibrillation, cardiomyopathy, heart failure and so on. Transgenic mice with natriuretic peptides and their receptors gene deletion display myocardial hypertrophy and fibrosis, which are associated with the development of hypertension, cardiomyopathy and heart failure. Certain stimuli triggering cardiac hypertrophy and ischemic injuries may be involved in regulating gene expression of natriuretic peptides and their receptors. Therefore, advances in understanding of natriuretic peptide family genes and their regulatory mechanisms will lead to greater insight into the pathogenesis of cardiovascular diseases and blaze a new trail in clinical treatment.

Inhibition of signal transducer and activator of transcription 3 (STAT3) attenuates interleukin-6 (IL-6)-induced collagen synthesis and resultant hypertrophy in rat heart

IL-6 has been shown to play a major role in collagen up-regulation process during cardiac hypertrophy, although the precise mechanism is still not known. In this study we have analyzed the mechanism by which IL-6 modulates cardiac hypertrophy. For the in vitro model, IL-6-treated cultured cardiac fibroblasts were used, whereas the in vivo cardiac hypertrophy model was generated by renal artery ligation in adult male Wistar rats (Rattus norvegicus). During induction of hypertrophy, increased phosphorylation of STAT1, STAT3, MAPK, and ERK proteins was observed both in vitro and in vivo. Treatment of fibroblasts with specific inhibitors for STAT1 (fludarabine, 50 μM), STAT3 (S31-201, 10 μM), p38 MAPK (SB203580, 10 μM), and ERK1/2 (U0126, 10 μM) resulted in down-regulation of IL-6-induced phosphorylation of specific proteins; however, only S31-201 and SB203580 inhibited collagen biosynthesis. In ligated rats in vivo, only STAT3 inhibitors resulted in significant decrease in collagen synthesis and hypertrophy markers such as atrial natriuretic factor and β-myosin heavy chain. In addition, decreased heart weight to body weight ratio and improved cardiac function as measured by echocardiography was evident in animals treated with STAT3 inhibitor or siRNA. Compared with IL-6 neutralization, more pronounced down-regulation of collagen synthesis and regression of hypertrophy was observed with STAT3 inhibition, suggesting that STAT3 is the major downstream signaling molecule and a potential therapeutic target for cardiac hypertrophy.

Integrin expression during reverse remodeling in the myocardium of heart failure patients

BACKGROUND

The main anchoring proteins of myocardial cells with each other and with the extracellular matrix are integrins present in the membranes of myocardial cells. These integrins are important for maintaining the architecture of the myocardial tissue and the mechanotransduction in the heart. Heart failure leads to various alterations in the myocardium, such as changes in morphology, and in expression of mRNAs, miRNAs, and proteins. Left ventricular assist device (LVAD) support in heart failure patients has been described to induce reverse remodeling of the myocardium and thus to (some degree of) reversal of the aforementioned alterations. In this study, we evaluated whether changes in expression of integrins α-1, -3, -5, -6, -7, -10, -11 and β-1, -3, -5 and -6 play a role during reverse remodeling.

METHODS

Three-step immunoperoxidase staining procedures were applied on frozen heart tissue sections to locate the various integrins tested. Integrin mRNA expression was established by standard Q-PCR procedures.

RESULTS

It was shown that mRNA expression of several integrins changes significantly during LVAD support, however without subsequent changes in immunohistochemical detectable quantities. Various integrins showed different locations within the myocardium.

CONCLUSION

LVAD-induced reversed remodeling did not result in significant integrin protein expression, although changes in integrin mRNA expression suggested an adaptation to unloading.

Cellular Interplay between Cardiomyocytes and Nonmyocytes in Cardiac Remodeling

Cardiac hypertrophy entails complex structural remodeling involving rearrangement of muscle fibers, interstitial fibrosis, accumulation of extracellular matrix, and angiogenesis. Many of the processes underlying cardiac remodeling have features in common with chronic inflammatory processes. During these processes, nonmyocytes, such as endothelial cells, fibroblasts, and immune cells, residing in or infiltrating into the myocardial interstitium play active roles. This paper mainly addresses the functional roles of nonmyocytes during cardiac remodeling. In particular, we focus on the communication between cardiomyocytes and nonmyocytes through direct cell-cell interactions and autocrine/paracrine-mediated pathways.

Molecular mechanisms underlying cardiac antihypertrophic and antifibrotic effects of natriuretic peptides

Natriuretic peptides (NPs) exert well-characterized protective effects on the cardiovascular system, such as vasorelaxation, natri- and diuresis, increase of endothelial permeability, and inhibition of renin-angiotensin-aldosterone system. It has been reported that they also possess antihypertrophic and antifibrotic properties and contribute actively to cardiac remodeling. As a consequence, they are involved in several aspects of cardiovascular diseases. Antihypertrophic and antifibrotic actions of NPs appear to be mediated by specific signaling pathways within a more complex cellular network. Elucidation of the molecular mechanisms underlying the effects of NPs on cardiac remodeling represents an important research objective in order to gain more insights on the complex network leading to cardiac hypertrophy, ventricular dysfunction, and transition to heart failure, and in the attempt to develop novel therapeutic agents. The aim of the present article is to review well-characterized molecular mechanisms underlying the antihypertrophic and antifibrotic effects of NPs in the heart that appear to be mainly mediated by guanylyl cyclase type A receptor. In particular, we discuss the calcineurin/NFAT, the sodium exchanger NHE-1, and the TGFβ1/Smad signaling pathways. The role of guanylyl cyclase type B receptor, along with the emerging functional significance of natriuretic peptide receptor type C as mediators of CNP antihypertrophic and antifibrotic actions in the heart are also considered.

Cardiac fibroblasts in cell culture systems: myofibroblasts all along?

The cytoarchitecture of the working myocardium is characterized by densely packed cardiomyocytes that are embedded in a three-dimensional network of numerous fibroblasts. Although the importance of cardiac fibroblasts in maintaining an orderly structured extracellular matrix is well recognized, less is known about their potential paracrine and electrotonic interactions with cardiomyocytes. This is partly the result of the complex intermingling of both cell types in vivo that tends to preclude a direct investigation of heterocellular crosstalk. It is for that reason that most of our present knowledge regarding stromal-parenchymal cell interactions is based on culture systems that permit direct access to either cell type. An often disregarded feature of such studies is that cardiac fibroblasts in standard two-dimensional cell culture have a pronounced tendency to undergo a phenotype switch to myofibroblasts. This cell type typically appears in injured hearts where it contributes importantly to fibrotic remodeling. The present review focuses on recent insights into electrical and paracrine crosstalk between myofibroblasts and cardiomyocytes while acknowledging that a comprehensive understanding of stromal-parenchymal cell interactions will depend on future methodological developments that permit retaining the fibroblast phenotype in cell culture systems and that will, most importantly, allow direct investigations of heterocellular crosstalk in intact tissue.

[Physiology and clinical role of natriuretic peptides]

In the last three decades many members of the natriuretic peptide family was isolated. The function and physiological role of these peptides are pleiotropic. All natriuretic peptides are synthesized from polypeptide precursors. Together with the sympathetic nervous system and other hormones they play key roles, like an endogenous system in the regulation of the body fluid homeostasis and blood pressure. Changes in this balance lead to dysfunction in the endothel and left ventricle, which can cause severe complications. In many cardiovascular diseases natriuretic peptides serve not only as marker for diagnosis and prognosis but they have therapeutic importance. In the last years the potential use of the elevated BNP levels for diagnosis of pre-eclampsia was examined. In our review we discuss the current understanding of molecular biology, biochemistry and clinical relevance of natriuretic peptides.

Modulation of novel cardiorenal and inflammatory biomarkers by intravenous nitroglycerin and nesiritide in acute decompensated heart failure: an exploratory study

BACKGROUND

Modulation of novel cardiorenal and inflammatory markers may provide insight into the disease process and outcomes of patients with acute decompensated heart failure.

METHODS AND RESULTS

In this open-labeled, prospective, randomized study, 89 patients received either nesiritide (NES) or nitroglycerin (NTG) infusion by standard protocol. The serum or plasma concentrations of cystatin-C and inflammatory markers (high-sensitivity C-reactive protein, tumor necrosis factor-α, transforming growth factor-β1, and interleukin-6) were measured in 66 patients with acute decompensated heart failure at baseline and during drug infusion. Mean baseline values for demographics were not significantly different between NTG and NES groups; however, baseline inflammatory markers were elevated on admission. In NES compared with NTG groups, lower cystatin-C (1449 versus 2739 ng/mL, P<0.05) and IL-6 (25 versus 50 pg/mL, P<0.05) were observed. There were no significant differences in concentrations of high-sensitivity C-reactive protein, tumor necrosis factor-α, and transforming growth factor-β1 between groups over time.

CONCLUSIONS

The differential modulation effects of cystatin-C and interleukin-6 but not other inflammatory markers, in response to NES compared with NTG therapy, may provide important implications for vasodilator therapy. Further studies are warranted to confirm these findings.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00842023.

Intramyocardial BNP gene delivery improves cardiac function through distinct context-dependent mechanisms

BACKGROUND

B-type natriuretic peptide (BNP) is an endogenous peptide produced under physiological and pathological conditions mainly by ventricular myocytes. It has natriuretic, diuretic, blood pressure-lowering, and antifibrotic actions that could mediate cardiorenal protection in cardiovascular diseases. In the present study, we used BNP gene transfer to examine functional and structural effects of BNP on left ventricular (LV) remodeling.

METHODS AND RESULTS

Human BNP was overexpressed by using adenovirus-mediated gene delivery in normal rat hearts and in hearts during the remodeling process after infarction and in an experimental model of angiotensin II-mediated hypertension. In healthy hearts, BNP gene delivery into the anterior wall of the LV decreased myocardial fibrosis (P<0.01, n=7 to 8) and increased capillary density (P<0.05, n=7 to 8) associated with a 7.3-fold increase in LV BNP peptide levels. Overexpression of BNP improved LV fractional shortening by 22% (P<0.05, n=6 to 7) and ejection fraction by 19% (P<0.05, n=6 to 7) after infarction. The favorable effect of BNP gene delivery on cardiac function after infarction was associated with normalization of cardiac sarcoplasmic reticulum Ca(2+)-ATPase expression and phospholamban Thr17-phosphorylation. BNP gene delivery also improved fractional shortening and ejection fraction in angiotensin II-mediated hypertension as well as decreased myocardial fibrosis and LV collagen III mRNA levels but had no effect on angiogenesis or Ca(2+)-ATPase expression and phospholamban phosphorylation.

CONCLUSIONS

Local intramyocardial BNP gene delivery improves cardiac function and attenuates adverse postinfarction and angiotensin II-induced remodeling. These results also indicate that myocardial BNP has pleiotropic, context-dependent, favorable actions on cardiac function and suggest that BNP acts locally as a key mechanical load-activated regulator of angiogenesis and fibrosis.

Association between brain natriuretic peptide and distant metastases in advanced non-small cell lung cancer patients

This study aimed to investigate the relationship between clinicopathological factors and plasma brain natriuretic peptide (BNP) levels in non-small cell lung cancer (NSCLC) patients. A total of 133 patients with advanced NSCLC were included in this study. The level of BNP was determined at the time of diagnosis. The BNP plasma concentration was measured using a chemiluminescent enzyme immunoassay kit. The univariate relationship between each independent clinicopathological variable and plasma BNP was examined using the Chi-square test. The survival curves were determined using the Kaplan-Meier method. According to the cut-off value of plasma BNP levels (11.5 and 22.4 pg/ml), plasma BNP negatively correlated with the presence of metastases (Chi-square test, p=0.0374 and p=0.0098, respectively). However, no significant association between patient survival time and plasma BNP levels was found. Reduced plasma BNP levels in advanced NSCLC patients with metastases were noted and the possibility was raised that BNP decreases distant metastases of advanced NSCLC patients.

Therapeutic effects of continuous infusion of brain natriuretic peptides on postmyocardial infarction ventricular remodelling in rats

BACKGROUND

Previous studies have shown protective effects of brain natriuretic peptide (BNP) against the postmyocardial infarction (MI) remodelling process. The transcription factor NF-κB is known to play an important role after MI.

AIMS

To investigate if NF-κB is involved in the protective effects of BNP against adverse post-MI remodelling.

METHODS

Rats were randomly assigned to five groups: sham-operation; MI by coronary ligation; MI treated with chronic BNP infusion; MI treated with enalapril; MI treated with BNP+enalapril. Rats were closely monitored for survival rate analysis. Rats from each group were sacrificed on days 3, 7 and 28 postoperation.

RESULTS

The results showed that chronic continuous BNP infusion achieved similar effects to enalapril therapy, as evidenced by improved survival rate within the 28-day observation period compared with MI group rats; this effect was closely associated with preserved cardiac geometry and performance. The treatment combination did not offer extra benefits in terms of survival rate. Both BNP and enalapril therapy produced higher heart tissue concentrations of cyclic guanosine monophosphate and lower expression levels of inflammatory cytokines, including tumour necrosis factor-α, interleukin-1 and interleukin-6. These benefits were associated with lower phosphorylation levels of NF-κB subunits IκBα, p50 and p65. While enalapril significantly inhibited extracellular matrix remodelling via regulation of the protein expression ratio of matrix metalloproteinase/tissue inhibitor of metalloproteinase and the activity of matrix metalloproteinase, these variables were not affected by BNP, indicating that the two therapies involve different mechanisms.

CONCLUSION

Chronic BNP infusion can provide beneficial effects against adverse post-MI remodelling.

Targeted disruption of guanylyl cyclase-A/natriuretic peptide receptor-A gene provokes renal fibrosis and remodeling in null mutant mice: role of proinflammatory cytokines

Binding of atrial and brain natriuretic peptides to guanylyl cyclase-A/natriuretic peptide receptor-A produces second messenger cGMP, which plays an important role in maintaining renal and cardiovascular homeostasis. Mice carrying a targeted disruption of the Npr1 gene coding for guanylyl cyclase-A/natriuretic peptide receptor-A exhibit changes that are similar to those that occur in untreated human hypertension, including elevated blood pressure, cardiac hypertrophy, and congestive heart failure. The objective of this study was to determine whether disruption of the Npr1 gene in mice provokes kidney fibrosis, remodeling, and derangement. We found that systemic disruption of the Npr1 gene causes increased renal tubular damage characterized by dilation, flattening of epithelium, and expansion of interstitial spaces in Npr1(-/-) (0-copy) mice. Significant increases occurred in the expression levels of TNF-α (4-fold), IL-6 (4.5-fold), and TGF-β1 (2-fold) in 0-copy null mutant mice compared with 2-copy wild-type mice. An increased epithelial-to-mesenchymal transition indicated by increased expression of α-smooth muscle actin, was observed in Npr1(-/-) mouse kidneys. Treatment with captopril and losartan showed a 38 and 46% attenuation in fibrosis and 30 and 42% reduction in α-smooth muscle actin immunoexpression, respectively, in 1-copy and 0-copy mice compared with 2-copy mice. Although bendroflumethiazide treatment did not show any effect. The present results demonstrate that the disruption of Npr1 gene activates proinflammatory cytokines leading to fibrosis, hypertrophic growth, and remodeling of the kidneys of mutant mice.

B-type natriuretic peptide and extracellular matrix protein interactions in human cardiac fibroblasts

Cardiac fibroblasts (CFs) regulate myocardial remodeling by proliferating, differentiating, and secreting extracellular matrix (ECM) proteins. B-type natriuretic peptide (BNP) is anti-fibrotic, inhibits collagen production, augments matrix metalloproteinases, and suppresses CF proliferation. Recently, we demonstrated that the ECM protein fibronectin (FN) augmented production of BNP's second messenger, 3', 5' cyclic guanosine monophosphate (cGMP) in CFs, supporting crosstalk between FN, BNP, and its receptor, natriuretic peptide receptor A (NPR-A). Here, we address the specificity of FN to augment cGMP generation by investigating other matrix proteins, including collagen IV which contains RGD motifs and collagen I and poly-L-lysine, which have no RGD domain. Collagen IV showed increased cGMP generation to BNP similar to FN. Collagen I and poly-L-lysine had no effect. As FN also interacts with integrins, we then examined the effect of integrin receptor antibody blockade on BNP-mediated cGMP production. On FN plates, antibodies blocking RGD-binding domains of several integrin subtypes had little effect, while a non-RGD domain interfering integrin alphavbeta3 antibody augmented cGMP production. Further, on uncoated plates, integrin alphavbeta3 blockade continued to potentiate the BNP/cGMP response. These studies suggest that both RGD containing ECM proteins and integrins may interact with BNP/NPR-A to modulate cGMP generation.

Long-term effects of B-type natriuretic peptide infusion after acute myocardial infarction in a rat model

INTRODUCTION

The effects of exogenous B-type natriuretic peptide (BNP) on postmyocardial infarction (MI) are not known. We tested the hypothesis that in vivo infusion of BNP would improve cardiac function and affect left ventricular (LV) remodeling in an experimental model of MI.

METHODS

MI was induced by coronary ligation in rats and confirmed by echocardiography. 19 rats were randomized to 1 of 3 groups: sham (n = 7), MI + saline (n = 5), MI + BNP (400 ng.kg(-1).minute(-1)) (n = 7). Infusions were delivered for 7 days via venous catheters tunneled to an infusion pump. Rats were followed for 8 weeks. Echocardiography, hemodynamics, histology, and in vivo and ex vivo pressure-volume relationships were examined.

RESULTS

LV systolic pressure, LV dP/dtmax, and infarct size improved with BNP treatment versus control MI group (132 +/- 4 vs.110 +/- 2 mm Hg, 8097 +/- 317 vs. 5816 +/- 378 mm Hg/s, 19.3% +/- 1.6% vs. 23.3% +/- 1.9%, respectively; all P < 0.05). Ex vivo end-diastolic pressure-volume relationship demonstrated reduced diastolic dysfunction after BNP therapy (P < 0.05 vs. control MI). Serum BNP levels confirmed delivery of BNP.

CONCLUSIONS

We demonstrate beneficial effects on LV function and decreased LV remodeling with BNP infusion in an experimental model of acute MI.

Clinical implications of defective B-type natriuretic peptide

Our understanding of the natriuretic peptide system continues to evolve rapidly. B-type natriuretic peptide (BNP), originally thought to be a simple volume-regulating hormone that is produced in response to cardiac stretch, has been shown to also play important roles in modulating bronchodilation, endothelial function, and cardiac remodeling. Recent data demonstrate that elevated levels of BNP in patients with heart failure do not represent a simple ratcheting up of normal production in response to increased stimulus. Instead, we now know that chronic stimulation of BNP synthesis induces a reversion to fetal gene expression, resulting in production of high molecular weight forms of BNP that are functionally deficient. Standard point-of-care BNP assays are immunoassays that will detect any molecule containing the target epitopes. Consequently, these assays cannot distinguish between defective, high molecular weight forms of BNP and normal, physiologically active BNP. In 2 separate evaluations, mass spectroscopy detected little, if any, normal BNP in patients with heart failure, despite the appearance of high circulating levels of immunoreactive BNP (iBNP) using commercial assays. Therefore, these commercial assays should be considered to be only an indication of myocardial stress. They do not measure physiologic BNP activity. This accounts for the "BNP paradox," namely, that administration of exogenous recombinant human BNP (rhBNP, nesiritide) has substantial clinical and hemodynamic impact in the presence of high levels of circulating iBNP using commercial assays. In addition to its short-term hemodynamic impact, rhBNP may have other important effects in this setting, and further investigation is warranted.

Stromal cell biology--a way to understand the evolution of cardiovascular diseases

Stromal cells, composed of fibroblasts, microvascular endothelial cells, immune cells and inflammatory cells, are critical determinants of the mechanical properties and function of the heart and vasculature, and the mechanisms whereby these types of cells are activated are important to understand the progression of cardiovascular diseases. Emerging studies have suggested that the activation of autocrine and paracrine signaling pathways by stromal cell-derived growth factors, cytokines and bioactive molecules contributes to disease progression. Disruption of the stromal network will result in alterations in the geometry and function in these organs. Interventions targeting the stromal cells (eg, myofibroblasts, microvascular endothelial cells, inflammatory cells) by pharmacological agents or direct gene delivery/small interfering RNA would be potential novel therapeutic strategies to prevent/attenuate the progression of cardiovascular disorders.

Natriuretic peptides and the genomics of left-ventricular hypertrophy

Left-ventricular hypertrophy (LVH) is one of the strongest independent predictors of cardiovascular morbidity and mortality in the general population. Although hypertension and obesity are well-established, independent risk factors for the development of LVH, they explain less than 25% to 50% of the variance of left ventricular mass (LVM) in humans. A substantial body of evidence suggests that there is a genetic basis to the observed inter-individual variability in the susceptibility to the development of LVH. Given the continuous relationship between LVM and cardiovascular morbidity and mortality, elucidating the genetic determinants of inter-individual differences in the susceptibility to LVH is of considerable public health importance. It promises the opportunity to identify high-risk individuals for targeted intervention and may identify novel therapeutic targets for improved prevention and treatment strategies.

Regulation of transforming growth factor-beta-dependent cyclooxygenase-2 expression in fibroblasts

Abnormal transforming growth factor-beta (TGF-beta) signaling is a critical contributor to the pathogenesis of various human diseases ranging from tissue fibrosis to tumor formation. Excessive TGF-beta signaling stimulates fibrotic responses. Recent research has focused in the main on the antiproliferative effects of TGF-beta in fibroblasts, and it is presently understood that TGF-beta-stimulated cyclooxygenase-2 (COX-2) induction in fibroblasts is essential for antifibroproliferative effects of TGF-beta. Both TGF-beta and COX-2 have been implicated in tumor growth, invasion, and metastasis, and therefore tumor-associated fibroblasts are a recent topic of interest. Here we report the identification of positive and negative regulatory factors of COX-2 expression induced by TGF-beta as determined using proteomic approaches. We show that TGF-beta coordinately up-regulates three factors, heterogeneous nuclear ribonucleoprotein A/B (HNRPAB), nucleotide diphosphate kinase A (NDPK A), and nucleotide diphosphate kinase A (NDPK B). Functional pathway analysis showed that HNRPAB augments mRNA and protein levels of COX-2 and subsequent prostaglandin E(2) (PGE(2)) production by suppressing degradation of COX-2 mRNA. In contrast, NDPK A and NDPK B attenuated mRNA and protein levels of COX-2 by affecting TGF-beta-Smad2/3/4 signaling at the receptor level. Collectively, we report on a new regulatory pathway of TGF-beta in controlling expression of COX-2 in fibroblasts, which advances our understanding of pathophysiological mechanisms of TGF-beta.

Brain natriuretic peptide in pulmonary arterial hypertension: biomarker and potential therapeutic agent

B-type natriuretic peptide (BNP) is a member of the natriuretic peptide family, a group of widely distributed, but evolutionarily conserved, polypeptide mediators that exert myriad cardiovascular effects. BNP is a potent vasodilator with mitogenic, hypertrophic and pro-inflammatory properties that is upregulated in pulmonary hypertensive diseases. Circulating levels of BNP correlate with mean pulmonary arterial pressure (mPAP) and pulmonary vascular resistance (PVR) in patients with pulmonary arterial hypertension (PAH). Elevated plasma BNP levels are associated with increased mortality in patients with PAH and a fall in BNP levels after therapy is associated with improved survival. These findings have important clinical implications in that a noninvasive blood test may be used to identify PAH patients at high-risk of decompensation and to guide pulmonary vasodilator therapy. BNP also has several biologic effects that could be beneficial to patients with PAH. However, lack of a convenient method for achieving sustained increases in circulating BNP levels has impeded the development of BNP as a therapy for treating pulmonary hypertension. New technologies that allow transdermal or oral administration of the natriuretic peptides have the potential to greatly accelerate research into therapeutic use of BNP for cor pulmonale and pulmonary vascular diseases. This review will examine the basic science and clinical research that has led to our understanding of the role of BNP in cardiovascular physiology, its use as a biomarker of right ventricular function and its therapeutic potential for managing patients with pulmonary vascular disease.

Lamina-associated polypeptide 2alpha loss impairs heart function and stress response in mice

RATIONALE

Lamina-associated polypeptide (LAP)2alpha is a mammalian chromatin-binding protein that interacts with a fraction of A-type lamins in the nuclear interior. Because mutations in lamins and LAP2alpha lead to cardiac disorders in humans, we hypothesized that these factors may play important roles in heart development and adult tissue homeostasis.

OBJECTIVE

We asked whether the presence of LAP2alpha was required for normal cardiac function.

METHODS AND RESULTS

To study the molecular mechanisms of the disease, we analyzed heart structure and function in complete and conditional Lap2alpha(-/-) mice as well as Lap2alpha(-/-)/Mdx mutants. Unlike conditional deletion of LAP2alpha in late embryonic striated muscle, its complete knockout caused systolic dysfunction in young mice, accompanied by sporadic fibrosis in old animals, as well as deregulation of major cardiac transcription factors GATA4 and myocyte enhancer factor 2c. Activation of compensatory pathways, including downregulation of beta-adrenergic receptor signaling, resulted in reduced responsiveness of the myocardium to chronic beta-adrenergic stimulation and stalled the progression of LAP2alpha-deficient hearts from hypertrophy toward cardiac failure. Dystrophin deficiency in an Mdx background resulted in a transient rescue of the Lap2alpha(-/-) phenotype.

CONCLUSIONS

Our data suggest a novel role of LAP2alpha in the maintenance of cardiac function under normal and stress conditions.

Natriuretic peptides and cardiovascular damage in the metabolic syndrome: molecular mechanisms and clinical implications

Natriuretic peptides are endogenous antagonists of vasoconstrictor and salt- and water-retaining systems in the body's defence against blood pressure elevation and plasma volume expansion, through direct vasodilator, diuretic and natriuretic properties. In addition, natriuretic peptides may play a role in the modulation of the molecular mechanisms involved in metabolic regulation and cardiovascular remodelling. The metabolic syndrome is characterized by visceral obesity, hyperlipidaemia, vascular inflammation and hypertension, which are linked by peripheral insulin resistance. Increased visceral adiposity may contribute to the reduction in the circulating levels of natriuretic peptides. The dysregulation of neurohormonal systems, including the renin-angiotensin and the natriuretic peptide systems, may in turn contribute to the development of insulin resistance in dysmetabolic patients. In obese subjects with the metabolic syndrome, reduced levels of natriuretic peptides may be involved in the development of hypertension, vascular inflammation and cardio vascular remodelling, and this may predispose to the development of cardiovascular disease. The present review summarizes the regulation and function of the natriuretic peptide system in obese patients with the metabolic syndrome and the involvement of altered bioactive levels of natriuretic peptides in the pathophysiology of cardiovascular disease in patients with metabolic abnormalities.

Cyclic GMP kinase and RhoA Ser188 phosphorylation integrate pro- and antifibrotic signals in blood vessels

Vascular fibrosis is a major complication of hypertension and atherosclerosis, yet it is largely untreatable. Natriuretic peptides (NPs) repress fibrogenic activation of vascular smooth muscle cells (VSMCs), but the intracellular mechanism mediating this effect remains undetermined. Here we show that inhibition of RhoA through phosphorylation at Ser188, the site targeted by the NP effector cyclic GMP (cGMP)-dependent protein kinase I (cGK I), is critical to fully exert antifibrotic potential. cGK I(+/-) mouse blood vessels exhibited an attenuated P-RhoA level and concurrently increased RhoA/ROCK signaling. Importantly, cGK I insufficiency caused dynamic recruitment of ROCK into the fibrogenic programs, thereby eliciting exaggerated vascular hypertrophy and fibrosis. Transgenic expression of cGK I-unphosphorylatable RhoA(A188) in VSMCs augmented ROCK activity, vascular hypertrophy, and fibrosis more prominently than did that of wild-type RhoA, consistent with the notion that RhoA(A188) escapes the intrinsic inhibition by cGK I. Additionally, VSMCs expressing RhoA(A188) became refractory to the antifibrotic effects of NPs. Our results identify cGK I-mediated Ser188 phosphorylation of RhoA as a converging node for pro- and antifibrotic signals and may explain how diminished cGMP signaling, commonly associated with vascular malfunction, predisposes individuals to vascular fibrosis.

B-type natriuretic peptide attenuates cardiac hypertrophy via the transforming growth factor-ß1/smad7 pathway in vivo and in vitro

1. Previously, we showed that long-term treatment of rats after myocardial infarction (MI) with B-type natriuretic peptide (BNP) prevented ventricular remodelling. However, it is unclear whether long-term BNP treatment affects cardiac hypertrophy and, if so, its mechanism of action. In the present study, we investigated the effects of long-term BNP treatment on cardiac hypertrophy and the molecular mechanisms involved. 2. Cardiac hypertrophy was established in rats by ligation of the left anterior descending coronary artery. After treatment with BNP (5 or 15 microg/kg per day) for 8 weeks, indices of cardiac hypertrophy were determined. In separate in vitro experiments, cardiomyocyte hypertrophy was induced by treatment of cardiomyocytes with 10(-6) mol/L angiotensin (Ang) II for 48 h and cell surface area and [(3)H] incorporation were measured. Transforming growth factor (TGF)-beta1 and smad7 mRNA and protein expression in vivo and in vitro were detected using reverse transcription-polymerase chain reaction and western blotting. 3. Long-term BNP treatment dose-dependently attenuated cardiac hypertrophy and improved cardiac function in rats after MI. Furthermore, BNP attenuated the upregulation of TGF-beta1 and downregulation of smad7 mRNA and protein expression. The in vitro experiments further proved that BNP inhibited cardiac hypertrophy and changes in the TGF-beta1/smad7 pathway, which were completely blocked by the cyclic GMP-dependent protein kinase (PKG) inhibitor, KT5823 (cells were treated with 10(-6) mol/L KT5823 for 48 h). 4. The results of the present study demonstrate that long-term treatment of rats with BNP dose-dependently attenuates cardiac hypertrophy and that this is associated with downregulation of TGF-beta1 and upregulation of smad7 via PKG signalling. Long-term BNP treatment may be a new therapeutic strategy to prevent cardiac hypertrophy and progression to heart failure.

The PDE1A-PKCalpha signaling pathway is involved in the upregulation of alpha-smooth muscle actin by TGF-beta1 in adventitial fibroblasts

BACKGROUND

Increasing evidence has suggested that differentiation of adventitial fibroblasts (AFs) to myofibroblasts plays an important role in arterial remodeling. The molecular mechanisms by which myofibroblast formation is regulated still remain largely unknown. This study aimed to evaluate the role of cyclic nucleotide phosphodiesterase 1A (PDE1A) in the formation of adventitial myofibroblasts induced by transforming growth factor (TGF)-beta(1).

METHODS AND RESULTS

AFs were cultured by the explant method. Western blot and immunocytochemistry were applied for alpha-smooth muscle actin (SMA) or protein kinase C (PKC) alpha protein analysis. Results showed that TGF-beta(1) upregulated PDE1A protein expression in rat aortic AFs and pharmacological inhibition of PDE1A blocked TGF-beta(1)-induced alpha-SMA expression, a marker of myofibroblast formation, suggesting that the upregulation of PDE1A may mediate TGF-beta(1)-induced AF transformation. Moreover, calphostin C (a PKC inhibitor) inhibited TGF-beta(1)-induced alpha-SMA expression, whereas phorbol-12-myristate-13-acetate (a PKC activator) induced it. Finally, the upregulation of PKCalpha expression by TGF-beta(1) was also inhibited by PDE1A inhibition.

CONCLUSIONS

Taken together, our data suggest that TGFbeta(1) induces alpha-SMA expression and myofibroblast formation via a PDE1A-PKCalpha-dependent mechanism. Our study thus unveils a novel signaling mechanism underlying TGF-beta(1)-induced adventitial myofibroblast formation.

Atrial natriuretic peptide suppresses endothelin gene expression and proliferation in cardiac fibroblasts through a GATA4-dependent mechanism

AIMS

Atrial natriuretic peptide (ANP) is a hormone that has both antihypertrophic and antifibrotic properties in the heart. We hypothesized that myocyte-derived ANP inhibits endothelin (ET) gene expression in fibroblasts.

METHODS AND RESULTS

We have investigated the mechanism(s) involved in the antiproliferative effect of ANP on cardiac fibroblasts in a cell culture model. We found that cardiac myocytes inhibited DNA synthesis in co-cultured cardiac fibroblasts as did treatment with the ET-1 antagonist BQ610. The effect of co-culture was reversed by antibody directed against ANP or the ANP receptor antagonist HS-142-1. ANP inhibited the expression of the ET-1 gene and ET-1 gene promoter activity in cultured fibroblasts. The site of the inhibition was localized to a GATA-binding site positioned between -132 and -135 upstream from the transcription start site. GATA4 expression was demonstrated in cardiac fibroblasts, GATA4 bound the ET-1 promoter both in vitro and in vivo, and siRNA-mediated knockdown of GATA4 inhibited ET-1 expression. ET-1 treatment resulted in increased levels of phospho-serine(105) GATA4 in cardiac fibroblasts and this induction was partially suppressed by co-treatment with ANP.

CONCLUSION

Collectively, these findings suggest that locally produced ET-1 serves as an autocrine stimulator of fibroblast proliferation, that ANP produced in neighbouring myocytes serves as a paracrine inhibitor of this proliferation, and that the latter effect operates through a reduction in GATA4 phosphorylation and coincident reduction in GATA4-dependent transcriptional activity.

Changes in regulatory microRNA expression in myocardium of heart failure patients on left ventricular assist device support

BACKGROUND

Left ventricular assist device support in heart failure patients leads to changes in mRNA and protein expression in the myocardium.

METHODS

MicroRNA's are important regulators of various cellular processes, so changes in their expression were tested by Q-PCR methods.

RESULTS

LVAD support (independently of the duration) leads to a decrease of the expression of miR-1, miR-133a and miR-133b in DCM patients but to an increase in expression in IHD patients. The expression of miR's pre- and post-LVAD in heart failure patients was low compared to the level of miR's in control myocardial tissue.

CONCLUSIONS

Alterations in miRs expression might also be important during repair processes in IHD patients.

Prolonged effects of B-type natriuretic peptide infusion on cardiac remodeling after sustained myocardial injury

B-type natriuretic peptide (BNP) is an established first-line therapy for acute decompensated heart failure (HF), but its efficacy in preventing left ventricular (LV) remodeling after myocardial injury is unknown. The goal of this study was to evaluate the effects of BNP therapy on remodeling after ischemic injury in an awake canine model. Dogs were chronically instrumented for hemodynamics. Ischemia was created by daily coronary embolization (Embo; 3.1 x 10(4) beads/day) for 3 wk; 60 min after the first embolization, BNP (100 ng x kg(-1) x min(-1); n = 6) or saline (control; n = 6) was continuously infused via a left atrial catheter for 3 wk. Hemodynamics and echocardiography were performed in an awake state at baseline, 3 wk after Embo + BNP infusion, and 4 wk after stopping Embo + BNP infusion. End-systolic elastance (E(es)) and LV change in pressure over time (dP/dt) were preserved throughout Embo + BNP therapy versus control therapy (E(es): 3.76 +/- 1.01 vs. 1.41 +/- 0.16 mmHg/ml; LV dP/dt: 2,417 +/- 96 vs. 2,068 +/- 95 mmHg/s; both P < 0.05 vs. control). LV end-diastolic dimension was significantly smaller in BNP-treated dogs compared with control dogs (4.29 +/- 0.10 vs. 4.77 +/- 0.17 cm), and ejection fraction was maintained in treated dogs vs. control dogs (53 +/- 1% vs. 46 +/- 2%) (both P < 0.05 vs. control). Cyclooxygenase (COX)-2 expression in terminal LV tissue was significantly reduced after BNP therapy. Treatment with continuous infusion of BNP preserved LV geometry, improved systolic function, and prevented the progression of systolic HF after persistent ischemic injury.

Cardiac fibroblasts: at the heart of myocardial remodeling

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

Low-dose nesiritide in human anterior myocardial infarction suppresses aldosterone and preserves ventricular function and structure: a proof of concept study

BACKGROUND

B-type natriuretic peptide (BNP, nesiritide) has anti-fibrotic, anti-hypertrophic, anti-inflammatory, vasodilating, lusitropic and aldosterone-inhibiting properties but conventional doses of BNP cause hypotension, limiting its use in heart failure.

OBJECTIVE

To determine whether infusion of low-dose BNP within 24 h of successful reperfusion for anterior acute myocardial infarction (AMI) would prevent adverse left ventricular (LV) remodelling and suppress aldosterone.

METHODS

A translational proof-of-concept study was carried out to determine tolerability and biological activity of intravenous BNP at 0.003 and 0.006 microg/kg/min, without bolus started within 24 h of successful reperfusion for anterior AMI. 24 patients with first anterior wall ST elevation AMI and successful revascularisation were randomly assigned to receive 0.003 (n = 12) or 0.006 (n = 12) microg/kg/min of IV BNP for 72 h in addition to standard care during hospitalisation for anterior AMI.

RESULTS

Baseline characteristics, drugs and peak cardiac biomarkers for myocardial damage were similar between both groups. Infusion of BNP at 0.006 microg/kg/min resulted in greater biological activity than infusion at 0.003 microg/kg/min as measured by higher mean (SEM) plasma cGMP levels (8.6 (1) vs 5.5 (1) pmol/ml, p<0.05) and suppression of plasma aldosterone (8.0 (2) to 4.6 (1) ng/dl, p<0.05), which was not seen in the 0.003 microg/kg/min group. LV ejection fraction (LVEF) improved significantly from baseline to 1 month (40 (4)% to 54 (5)%, p<0.05) in the 0.006 group but not in the 0.003 group. Infusion of BNP at 0.006 microg/kg/min was associated with a decrease of LV end-systolic volume index (61 (9) to 43 (8) ml/m(2), p<0.05) at 1 month, which was not seen in the 0.003 group. No drug-related serious adverse events occurred in either group.

CONCLUSIONS

72 h infusion of low BNP at the time of anterior AMI is well tolerated and biologically active. Patients treated with low-dose BNP had improved LVEF and smaller LV end-systolic volume at 1 month.

Function and dysfunction of mammalian membrane guanylyl cyclase receptors: lessons from genetic mouse models and implications for human diseases

Besides soluble guanylyl cyclase (GC), the receptor for NO, there are seven plasma membrane forms of guanylyl cyclase (GC) receptors, enzymes that synthesize the second-messenger cyclic GMP (cGMP). All membrane GCs (GC-A to GC-G) share a basic topology, which consists of an extracellular ligand binding domain, a short transmembrane region, and an intracellular domain that contains the catalytic (GC) region. Although the presence of the extracellular domain suggests that all these enzymes function as receptors, specific ligands have been identified for only four of them (GC-A through GC-D). GC-A mediates the endocrine effects of atrial and B-type natriuretic peptides regulating arterial blood pressure and volume homeostasis and also local antihypertrophic and antifibrotic actions in the heart. GC-B, the specific receptor for C-type natriuretic peptide, has a critical role in endochondral ossification. GC-C mediates the effects of guanylin and uroguanylin on intestinal electrolyte and water transport and epithelial cell growth and differentiation. GC-E and GC-F are colocalized within the same photoreceptor cells of the retina and have an important role in phototransduction. Finally, GC-D and GC-G appear to be pseudogenes in the human. In rodents, GC-D is exclusively expressed in the olfactory neuroepithelium, with chemosensory functions. GC-G is the last member of the membrane GC form to be identified. No other mammalian transmembrane GCs are predicted on the basis of gene sequence repositories. In contrast to the other orphan receptor GCs, GC-G has a broad tissue distribution in rodents, including the lung, intestine, kidney, skeletal muscle, and sperm, raising the possibility that there is another yet to be discovered family of cGMP-generating ligands. This chapter reviews the structure and functions of membrane GCs, with special focus on the insights gained to date from genetically modified mice and the role of alterations of these ligand/receptor systems in human diseases.

Ca2+/calmodulin-dependent kinase II triggers cell membrane injury by inducing complement factor B gene expression in the mouse heart

Myocardial Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition improves cardiac function following myocardial infarction (MI), but the CaMKII-dependent pathways that participate in myocardial stress responses are incompletely understood. To address this issue, we sought to determine the transcriptional consequences of myocardial CaMKII inhibition after MI. We performed gene expression profiling in mouse hearts with cardiomyocyte-delimited transgenic expression of either a CaMKII inhibitory peptide (AC3-I) or a scrambled control peptide (AC3-C) following MI. Of the 8,600 mRNAs examined, 156 were substantially modulated by MI, and nearly half of these showed markedly altered responses to MI with CaMKII inhibition. CaMKII inhibition substantially reduced the MI-triggered upregulation of a constellation of proinflammatory genes. We studied 1 of these proinflammatory genes, complement factor B (Cfb), in detail, because complement proteins secreted by cells other than cardiomyocytes can induce sarcolemmal injury during MI. CFB protein expression in cardiomyocytes was triggered by CaMKII activation of the NF-kappaB pathway during both MI and exposure to bacterial endotoxin. CaMKII inhibition suppressed NF-kappaB activity in vitro and in vivo and reduced Cfb expression and sarcolemmal injury. The Cfb-/- mice were partially protected from the adverse consequences of MI. Our findings demonstrate what we believe is a novel target for CaMKII in myocardial injury and suggest that CaMKII is broadly important for the genetic effects of MI in cardiomyocytes.

Human cardiac fibroblasts express B-type natriuretic peptide: fluvastatin ameliorates its up-regulation by interleukin-1alpha, tumour necrosis factor-alpha and transforming growth factor-beta

B-type natriuretic peptide (BNP) is a cardiac hormone, which plays a major role in body fluid and cardiovascular homeostasis. Produced by cardiac ventricles, its expression is highly regulated by various mediators. Canine cardiac fibroblasts have been identified as a source of BNP. Cardiac fibroblasts are key regulators of myocardial structure and function. We treated cultured human adult cardiac fibroblasts (HACF) with 2000 U/ml tumour necrosis factor-α (TNF-α), 200 U/ml interleukin-1α (IL-1α) or 50 ng/ml transforming growth factor-β (TGF-β) in the presence or absence of 500 nM fluvastatin. N-terminal pro-BNP (Nt-proBNP) concentration was determined by a competitive enzyme immunoassay. RealTime polymerase chain reaction (real-time PCR) was performed to investigate changes in BNP mRNA expression. Nt-proBNP peptide was present in the conditioned media of HACF and incubation with fluvastatin significantly reduced Nt-proBNP peptide levels. Treatment of HACF with TNF-α, IL-1α or TGF-β significantly increased Nt-proBNP levels compared with untreated cells. This effect was completely abolished in the presence of fluvastatin. Real-time PCR analysis confirmed these changes at the level of mRNA expression. Our data suggest that cardiac fibroblasts are a potential source of BNP in the human heart. Pro-inflammatory cytokines, associated with ventricular dysfunction and cardiac fibrosis, seem to be major inducers of BNP production in cardiac fibroblasts. This effect can be reverted by a statin. Based on our data, we speculate that elevated plasma BNP levels might not only reflect increased myocardial stretch but also inflammatory and remodelling processes. A possible benefit of statin-induced reduction in BNP production requires further studies.

Heterogeneous activation of the TGFbeta pathway in glioblastomas identified by gene expression-based classification using TGFbeta-responsive genes

BACKGROUND

TGFbeta has emerged as an attractive target for the therapeutic intervention of glioblastomas. Aberrant TGFbeta overproduction in glioblastoma and other high-grade gliomas has been reported, however, to date, none of these reports has systematically examined the components of TGFbeta signaling to gain a comprehensive view of TGFbeta activation in large cohorts of human glioma patients.

METHODS

TGFbeta activation in mammalian cells leads to a transcriptional program that typically affects 5-10% of the genes in the genome. To systematically examine the status of TGFbeta activation in high-grade glial tumors, we compiled a gene set of transcriptional response to TGFbeta stimulation from tissue culture and in vivo animal studies. These genes were used to examine the status of TGFbeta activation in high-grade gliomas including a large cohort of glioblastomas. Unsupervised and supervised classification analysis was performed in two independent, publicly available glioma microarray datasets.

RESULTS

Unsupervised and supervised classification using the TGFbeta-responsive gene list in two independent glial tumor gene expression data sets revealed various levels of TGFbeta activation in these tumors. Among glioblastomas, one of the most devastating human cancers, two subgroups were identified that showed distinct TGFbeta activation patterns as measured from transcriptional responses. Approximately 62% of glioblastoma samples analyzed showed strong TGFbeta activation, while the rest showed a weak TGFbeta transcriptional response.

CONCLUSION

Our findings suggest heterogeneous TGFbeta activation in glioblastomas, which may cause potential differences in responses to anti-TGFbeta therapies in these two distinct subgroups of glioblastomas patients.

Iron-loaded cardiac myocytes stimulate cardiac myofibroblast DNA synthesis

Cardiac fibrosis in iron overload disorders may arise from activation of the interstitial fibroblast. However, the cardiac myocyte, and not the fibroblast, is the main target for iron deposition. We hypothesized that fibroblasts respond to the presence of iron-loaded myocytes with increased proliferative capacity. Cardiac fibroblasts were either co-cultured with myocytes on porous filters or treated with medium conditioned by growth of myocyte cultures. In both circumstances myocytes suppressed [(3)H]thymidine incorporation by fibroblasts over 24 h, compared to stimulation of quiescent fibroblasts with fresh, unconditioned medium. However, when the myocytes were preloaded with iron, the suppressive effect was lost and DNA synthesis was restored to levels seen in unconditioned medium. This effect was not due to early events in cell cycle entry; activation of Erk at 15 min and expression of c-fos mRNA at 30 min were similar in media from control and iron-loaded myocytes. Early markers of progression of G1, namely cyclin D and phosphoretinoblastoma protein, were not significantly different in fibroblasts treated with either conditioned medium. However, cyclin E expression, a marker of the G1/S transition, was significantly increased by conditioned medium from the iron-loaded cells, compared to control-conditioned medium. We conclude that myocytes can suppress proliferation of fibroblasts by cumulative effects on late G1 events leading to DNA synthesis, and these effects are diminished with myocyte iron accumulation.

Inhibition of p38alpha MAPK disrupts the pathological loop of proinflammatory factor production in the myelodysplastic syndrome bone marrow microenvironment

Myelodysplastic syndromes (MDS) are common causes of ineffective hematopoiesis and cytopenias in the elderly. Various myelosuppressive and proinflammatory cytokines have been implicated in the high rates of apoptosis and hematopoietic suppression seen in MDS. We have previously shown that p38 MAPK is overactivated in MDS hematopoietic progenitors, which led to current clinical studies of the selective p38alpha inhibitor, SCIO-469, in this disease. We now demonstrate that the myelosuppressive cytokines TNFalpha and IL-1beta are secreted by bone marrow (BM) cells in a p38 MAPK-dependent manner. Their secretion is stimulated by paracrine interactions between BM stromal and mononuclear cells and cytokine induction correlates with CD34+ stem cell apoptosis in an inflammation-simulated in vitro bone marrow microenvironment. Treatment with SCIO-469 inhibits TNF secretion in primary MDS bone marrow cells and protects cytogenetically normal progenitors from apoptosis ex vivo. Furthermore, p38 inhibition diminishes the expression of TNFalpha or IL-1beta-induced proinflammatory chemokines in BM stromal cells. These data indicate that p38 inhibition has anti-inflammatory effects on the bone marrow microenvironment that complements its cytoprotective effect on progenitor survival. These findings support clinical investigation of p38alpha as a potential therapeutic target in MDS and other related diseases characterised by inflammatory bone marrow failure.