Communication between myocytes and fibroblasts in cardiac remodeling in angiotensin chimeric mice

Of Mouse and Man: Cross-Species Characterization of Hypertensive Cardiac Remodeling

Hypertension is a major public health concern and poses a significant risk for sudden cardiac death (SCD). However, the characterisation of human tissues tends to be macroscopic, with little appreciation for the quantification of the pathological remodelling responsible for the advancement of the disease. While the components of hypertensive remodelling are well established, the timeline and comparative quantification of pathological changes in hypertension have not been shown before. Here, we sought to identify the phasing of cardiac remodelling with hypertension using post-mortem tissue from SCD patients with early and advanced hypertensive heart disease (HHD). In order to study and quantify the progression of phenotypic changes, human specimens were contrasted to a well-described angiotensin-II-mediated hypertensive mouse model. While cardiomyocyte hypertrophy is an early adaptive response in the mouse that stabilises in established hypertension and declines as the disease progresses, this finding did not translate to the human setting. In contrast, optimising fibrosis quantification methods and applying them to each setting identified perivascular fibrosis as the prevailing possible cause for overall disease progression. Indeed, assessing myocardial inflammation highlights CD45+ inflammatory cell infiltration that precedes fibrosis and is an early-phase event in response to elevated arterial pressures that may underscore perivascular remodelling. Along with aetiology insight, we highlight cross-species comparison for quantification of cardiac remodelling in human hypertension. As such, this platform could assist with the development of therapies specific to the disease phase rather than targeting global components of hypertension, such as blood pressure lowering.

Left Ventricular Remodeling in Degenerative Aortic Valve Stenosis

Aortic stenosis was once considered a pure isolated valve obstacle challenging left ventricle driving force of contraction and flow generation. Left ventricular (LV) adaptation was merely interpreted as a uniform hypertrophic response to increased afterload. However, in these last 2 decades cardiac imaging research and some histopathology correlation studies brought insight towards the complex interaction between the vasculature, the valve and the myocardium. Verily, LV remodeling in this setting is a complex multidetermined process that goes further beyond myocardial hypertrophy. Ultrastructural changes involving both diffuse and replacement fibrosis of the myocardium take part and might explain the transition of clinical phenotypes with distinct prognosis, from compensated hypertrophy to LV maladaptive dysfunction and heart failure. Presently, the combined appropriate use of echocardiography and cardiac magnetic resonance may better assess the global LV afterload, hypertrophy and geometric remodeling, global and regional LV function, beyond ejection fraction, and structural changes that include the fibrotic burden of the myocardium. As a whole these may not only better stratify individual risk of disease progression but also identify patients benefiting from earlier valve intervention. In this paper, we review the maladaptive response of the LV to chronic pressure overload, describing the different signaling pathways and mechanisms that underly both hypertrophy and remodeling. Histomorphology changes in this setting are described and we try to make sense of the use of new imaging tools for LV characterization.

Innate immune response in the pathogenesis of heart failure in survivors of myocardial infarction

Among the different cardiovascular disease complications, atherosclerosis-induced myocardial infarction (MI) is the major contributor of heart failure (HF) and loss of life. This review presents short- and long-term features of post-MI in human hearts and animal models. It is known that the heart does not regenerate, and thus loss of cardiac cells after an MI event is permanent. In survivors of a heart attack, multiple neurohumoral adjustments as well as simultaneous remodeling in both infarcted and noninfarcted regions of the heart help sustain pump function post-MI. In the early phase, migration of inflammatory cells to the infarcted area helps repair and remove the cell debris, while apoptosis results in the elimination of damaged cardiomyocytes, and there is an increase in the antioxidant response to protect the survived myocardium against oxidative stress (OS) injury. However, in the late phase, it appears that there is a relative increase in OS and activation of the innate inflammatory response in cardiomyocytes without any obvious inflammatory cells. In this late stage in survivors of MI, a progressive slow activation of these processes leads to apoptosis, fibrosis, cardiac dysfunction, and HF. Thus, this second phase of an increase in OS, innate inflammatory response, and apoptosis results in wall thinning, dilatation, and consequently HF. It is important to note that this inflammatory response appears to be innate to cardiomyocytes. Blunting of this innate immune cardiomyocyte response may offer new hope for the management of HF.

Blunting of estrogen modulation of cardiac cellular chymase/RAS activity and function in SHR

The relatively low efficacy of ACE-inhibitors in the treatment of heart failure in women after estrogen loss may be due to their inability to reach the intracellular sites at which angiotensin (Ang) II is generated and/or the existence of cell-specific mechanisms in which ACE is not the essential processing pathway for Ang II formation. We compared the metabolic pathway for Ang II formation in freshly isolated myocytes (CMs) and non-myocytes (NCMs) in cardiac membranes extracted from hearts of gonadal-intact and ovariectomized (OVX) adult WKY and SHR rats. Plasma Ang II levels were higher in WKY vs. SHR (strain effect: WKY: 62 ± 6 pg/ml vs. SHR: 42 ± 9 pg/ml; p < 0.01), independent of OVX. The enzymatic activities of chymase, ACE, and ACE2 were higher in NCMs versus CMs, irrespective of whether assays were performed in cardiac membranes from WKY or SHR or in the presence or absence of OVX. E2 depletion increased chymase activity, but not ACE activity, in both CMs and NCMs. Moreover, cardiac myocyte chymase activity associated with diastolic function in WKYs and cardiac structure in SHRs while no relevant functional and structural relationships between the classic enzymatic pathway of Ang II formation by ACE or the counter-regulatory Ang-(1-7) forming path from Ang II via ACE2 were apparent. The significance of these novel findings is that targeted cell-specific chymase rather than ACE inhibition may have a greater benefit in the management of HF in women after menopause.

The impact of arteriovenous fistulae on the myocardium: the impact of creation and ligation in the transplant era

Cardiac hypertrophy is a relatively common complication seen in patients with advanced chronic kidney disease (CKD) and end-stage renal disease (ESRD). Moreover, cardiac hypertrophy is even more frequently seen in patients with ESRD who have an arteriovenous (AV) access. There has been substantial evidence pertaining to the effects of AV access creation on the heart structure and function. Similarly, there is increasing evidence on the effects of AV access closure, flow reduction, transplantation, and immunosuppressive medication on both endpoints. In this review, we present the evidence available in the literature on these topics and open the dialog for further research in this interesting field.

The role of cardiac fibroblasts in extracellular matrix-mediated signaling during normal and pathological cardiac development

The extracellular matrix is no longer considered a static support structure for cells but a dynamic signaling network with the power to influence cell, tissue, and whole organ physiology. In the myocardium, cardiac fibroblasts are the primary cell type responsible for the synthesis, deposition, and degradation of matrix proteins, and they therefore play a critical role in the development and maintenance of functional heart tissue. This review will summarize the extensive research conducted in vivo and in vitro, demonstrating the influence of both physical and chemical stimuli on cardiac fibroblasts and how these interactions impact both the extracellular matrix and, by extension, cardiomyocytes. This work is of considerable significance, given that cardiovascular diseases are marked by extensive remodeling of the extracellular matrix, which ultimately impairs the functional capacity of the heart. We seek to summarize the unique role of cardiac fibroblasts in normal cardiac development and the most prevalent cardiac pathologies, including congenital heart defects, hypertension, hypertrophy, and the remodeled heart following myocardial infarction. We will conclude by identifying existing holes in the research that, if answered, have the potential to dramatically improve current therapeutic strategies for the repair and regeneration of damaged myocardium via mechanotransductive signaling.

Role of miR-181 family in regulating vascular inflammation and immunity

The microRNA family, miR-181, plays diverse roles in regulating key aspects of cellular growth, development, and activation. Accumulating evidence supports a central role for the miR-181 family in vascular inflammation by controlling critical signaling pathways, such as downstream NF-κB signaling, and targets relevant to endothelial cell activation and immune cell homeostasis. This review examines the current knowledge of the miR-181 family's role in key cell types that critically control cardiovascular inflammation under pathological and physiological stimuli.

Cross talk between cardiac myocytes and fibroblasts: from multiscale investigative approaches to mechanisms and functional consequences

The heart is comprised of a syncytium of cardiac myocytes (CM) and surrounding nonmyocytes, the majority of which are cardiac fibroblasts (CF). CM and CF are highly interspersed in the myocardium with one CM being surrounded by one or more CF. Bidirectional cross talk between CM and CF plays important roles in determining cardiac mechanical and electrical function in both normal and diseased hearts. Genetically engineered animal models and in vitro studies have provided evidence that CM and CF can regulate each other's function. Their cross talk contributes to structural and electrical remodeling in both atria and ventricles and appears to be involved in the pathogenesis of various heart diseases that lead to heart failure and arrhythmia disorders. Mechanisms of CM-CF cross talk, which are not yet fully understood, include release of paracrine factors, direct cell-cell interactions via gap junctions and potentially adherens junctions and nanotubes, and cell interactions with the extracellular matrix. In this article, we provide an overview of the existing multiscale experimental and computational approaches for the investigation of cross talk between CM and CF and review recent progress in our understanding of the functional consequences and underlying mechanisms. Targeting cross talk between CM and CF could potentially be used therapeutically for the modulation of the cardiac remodeling response in the diseased heart and may lead to new strategies for the treatment of heart failure or rhythm disturbances.

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.

The dynamic role of cardiac fibroblasts in development and disease

Cardiac fibroblasts are the most abundant cell in the mammalian heart. While they have been historically overlooked in terms of functional contributions to development and physiology, cardiac fibroblasts are now front and center. They are currently recognized as key protagonists during both normal development and cardiomyopathy disease, and work together with cardiomyocytes through paracrine, structural, and potentially electrical interactions. However, the lack of specific biomarkers and fibroblast heterogeneous nature currently convolutes the study of this dynamic cell lineage; though, efforts to advance marker analysis and lineage mapping technologies are ongoing. These tools will help elucidate the functional significance of fibroblast-cardiomyocyte interactions in vivo and delineate the dynamic nature of normal and pathological cardiac fibroblasts. Since therapeutic promise lies in understanding the interface between developmental biology and the postnatal injury response, future studies to understand the divergent roles played by cardiac fibroblasts both in utero and following cardiac insult are essential.

The role of renin angiotensin system intervention in stage B heart failure

This article outlines the link between the renin angiotensin aldosterone system (RAAS) and various forms of cardiomyopathy, and also reviews the understanding of the effectiveness of RAAS intervention in this phase of ventricular dysfunction. The authors focus their discussion predominantly on patients who have had previous myocardial infarction or those who have left ventricular hypertrophy and also briefly discuss the role of RAAS activation and intervention in patients with alcoholic cardiomyopathy.

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.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.

Angiotensin-(1-7) ameliorates myocardial remodeling and interstitial fibrosis in spontaneous hypertension: role of MMPs/TIMPs

Angiotensin-(1-7) displays antihypertensive and antiproliferative properties although its effect on cardiac remodeling and hypertrophy in hypertension has not been fully elucidated. The present study was designed to examine the effect of chronic angiotensin-(1-7) treatment on myocardial remodeling, cardiac hypertrophy and underlying mechanisms in spontaneous hypertension. Adult male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were treated with or without angiotensin-(1-7) or the angiotensin-(1-7) antagonist A-779 for 24 weeks. Mean arterial pressure, left ventricular geometry, expression of the hypertrophic markers ANP and β-MHC, collagen contents (type I and III), collagenase (MMP-1), matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of MMPs-1 (TIMP-1) were evaluated in WKY and SHR rats with or without treatment. Our data revealed that chronic angiotensin-(1-7) treatment significantly suppressed hypertension, left ventricular hypertrophy, expression of ANP and β-MHC as well as myocardial fibrosis in SHR rats, the effects of which were nullified by the angiotensin-(1-7) receptor antagonist A-779. In addition, angiotensin-(1-7) treatment significantly counteracted hypertension-induced changes in the mRNA expression of MMP-2 and TIMP-1 and collagenase activity, the effects of which were blunted by A-779. In vitro study revealed that angiotensin-(1-7) directly increased the activity of MMP-2 and MMP-9 while decreasing the content of TIMP-1 and TIMP-2. Taken together, our results revealed a protective effect of angiotensin-(1-7) against cardiac hypertrophy and collagen deposition, which may be related to concerted changes in MMPs and TIMPs levels. These data indicated the therapeutic potential of angiotensin-(1-7) in spontaneous hypertension-induced cardiac remodeling.

Local angiotensin II aggravates cardiac remodeling in hypertension

Angiotensin II (ANG II) contributes to hypertension, cardiac hypertrophy, fibrosis, and dysfunction; however, it is difficult to separate the cardiac effect of ANG II from its hemodynamic action in vivo. To overcome the limitations, we used transgenic mice with cardiac-specific expression of a transgene fusion protein that releases ANG II from cardiomyocytes (Tg-ANG II) and treated them with deoxycorticosterone acetate (DOCA)-salt to suppress their systemic renin-angiotensin system. Using this unique model, we tested the hypothesis that cardiac ANG II, acting on the angiotensin type 1 receptor (AT(1)R), increases inflammation, oxidative stress, and apoptosis, accelerating cardiac hypertrophy and fibrosis. Male Tg-ANG II mice and their nontransgenic littermates (n-Tg) were uninephrectomized and divided into the following three groups: 1) vehicle-treated normotensive controls; 2) DOCA-salt; and 3) DOCA-salt + valsartan (AT(1)R blocker).Under basal conditions, systolic blood pressure (SBP) and cardiac phenotypes were similar between strains. In DOCA-salt hypertension, SBP increased similarly in both n-Tg and Tg-ANG II, and cardiac function did not differ between strains; however, Tg-ANG II had 1) greater ventricular hypertrophy as well as interstitial and perivascular fibrosis; 2) a higher number of deoxynucleotidyl-transferase-mediated dUTP nick end labeling-positive cells and infiltrating macrophages; 3) increased protein expression of NADPH oxidase 2 and transforming growth factor-β(1); and 4) downregulation of phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase B (Akt) phosphorylation. Valsartan partially reversed these effects in Tg-ANG II but not in n-Tg. We conclude that, when hemodynamic loading conditions remain unchanged, cardiac ANG II does not alter heart size or cardiac functions. However, in animals with hypertension, cardiac ANG II, acting via AT(1)R, enhances inflammation, oxidative stress, and cell death (most likely via downregulation of PI 3-kinase and Akt), contributing to cardiac hypertrophy and fibrosis.

Tissue renin-angiotensin-aldosterone systems: Targets for pharmacological therapy

The renin-angiotensin-aldosterone system is one of the most important systems in cardiovascular control and in the pathogenesis of cardiovascular diseases. Therefore, it is already a very successful drug target for the therapy of these diseases. However, angiotensins are generated not only in the plasma but also locally in tissues from precursors and substrates either locally expressed or imported from the circulation. In most areas of the brain, only locally generated angiotensins can exert effects on their receptors owing to the blood-brain barrier. Other tissue renin-angiotensin-aldosterone systems are found in cardiovascular organs such as kidney, heart, and vessels and play important roles in the function of these organs and in the deleterious actions of hypertension and diabetes on these tissues. Novel components with mostly opposite actions to the classical renin-angiotensin-aldosterone systems have been described and need functional characterization to evaluate their suitability as novel drug targets.

Disruption of the Ang II type 1 receptor promotes longevity in mice

The renin-angiotensin system plays a role in the etiology of hypertension and the pathophysiology of cardiac and renal diseases in humans. Ang II is the central product of this system and is involved in regulating immune responses, inflammation, cell growth, and proliferation by acting through Ang II type 1 receptors (AT1 and AT2). Here, we show that targeted disruption of the Agtr1a gene that encodes AT1A results in marked prolongation of life span in mice. Agtr1a-/- mice developed less cardiac and vascular injury, and multiple organs from these mice displayed less oxidative damage than wild-type mice. The longevity phenotype was associated with an increased number of mitochondria and upregulation of the prosurvival genes nicotinamide phosphoribosyltransferase (Nampt) and sirtuin 3 (Sirt3) in the kidney. In cultured tubular epithelial cells, Ang II downregulated Sirt3 mRNA, and this effect was inhibited by an AT1 antagonist. These results demonstrate that disruption of AT1 promotes longevity in mice, possibly through the attenuation of oxidative stress and overexpression of prosurvival genes, and suggests that the Ang II/AT1 pathway may be targeted to influence life span in mammals.

Angiotensin(1-7) Blunts Hypertensive Cardiac Remodeling by a Direct Effect on the Heart

Angiotensin-converting enzyme 2 (ACE2) converts the vasopressor angiotensin II (Ang II) into angiotensin (1-7) [Ang(1-7)], a peptide reported to have vasodilatory and cardioprotective properties. Inactivation of the ACE2 gene in mice has been reported by one group to result in an accumulation of Ang II in the heart and an age-related defect in cardiac contractility. A second study confirmed the role of ACE2 as an Ang II clearance enzyme but failed to reproduce the contractility defects previously reported in ACE2-deficient mice. The reasons for these differences are unclear but could include differences in the accumulation of Ang II or the deficiencies in Ang(1-7) in the mouse models used. As a result, the roles of ACE2, Ang II, and Ang(1-7) in the heart remain controversial. Using a novel strategy, we targeted the chronic overproduction of either Ang II or Ang(1-7) in the heart of transgenic mice and tested their effect on age-related contractility and on cardiac remodeling in response to a hypertensive challenge. We demonstrate that a chronic accumulation of Ang II in the heart does not result in cardiac contractility defects, even in older (8-month-old) mice. Likewise, transgenic animals with an 8-fold increase in Ang(1-7) peptide in the heart exhibited no differences in resting blood pressure or cardiac contractility as compared to age-matched controls, but they had significantly less ventricular hypertrophy and fibrosis than their nontransgenic littermates in response to a hypertensive challenge. Analysis of downstream signaling cascades demonstrates that cardiac Ang(1-7) selectively modulates some of the downstream signaling effectors of cardiac remodeling. These results suggest that Ang(1-7) can reduce hypertension-induced cardiac remodeling through a direct effect on the heart and raise the possibility that pathologies associated with ACE2 inactivation are mediated in part by a decrease in production of Ang(1-7).

Gain-of-function mutant of angiotensin II receptor, type 1A, causes hypertension and cardiovascular fibrosis in mice

The role of the renin-angiotensin system has been investigated by overexpression or inactivation of its different genes in animals. However, there is no data concerning the effect of the constitutive activation of any component of the system. A knockin mouse model has been constructed with a gain-of-function mutant of the Ang II receptor, type 1A (AT(1A)), associating a constitutively activating mutation (N111S) with a C-terminal deletion, which impairs receptor internalization and desensitization. In vivo consequences of this mutant receptor expression in homozygous mice recapitulate its in vitro characteristics: the pressor response is more sensitive to Ang II and longer lasting. These mice present with a moderate (~20 mmHg) and stable increase in BP. They also develop early and progressive renal fibrosis and cardiac fibrosis and diastolic dysfunction. However, there was no overt cardiac hypertrophy. The hormonal parameters (low-renin and inappropriately normal aldosterone productions) mimic those of low-renin human hypertension. This new model reveals that a constitutive activation of AT(1A) leads to cardiac and renal fibrosis in spite of a modest effect on BP and will be useful for investigating the role of Ang II in target organs in a model similar to some forms of human hypertension.

Role of cardiac overexpression of ANG II in the regulation of cardiac function and remodeling postmyocardial infarction

ANG II has a clear role in development of cardiac hypertrophy, fibrosis, and dysfunction. It has been difficult, however, to determine whether these actions are direct or consequences of its systemic hemodynamic effects in vivo. To overcome this limitation, we used transgenic mice with cardiac-specific expression of a transgene fusion protein that releases ANG II from cardiomyocytes (Tg-ANG II-cardiac) without involvement of the systemic renin-angiotensin system and tested whether increased cardiac ANG II accelerates remodeling and dysfunction postmyocardial infarction (MI), whereas those mice show no evidence of cardiac hypertrophy under the basal condition. Male 12- to 14-wk-old Tg-ANG II-cardiac mice and their wild-type littermates (WT) were subjected to sham-MI or MI by ligating the left anterior descending coronary artery for 8 wk. Cardiac ANG II levels were approximately 10-fold higher in Tg-ANG II-cardiac mice than their WT, whereas ANG II levels in plasma and other tissues did not differ between strains. Systolic blood pressure and heart rate were similar between groups with or without MI. In sham-MI, Tg-ANG II-cardiac mice had increased collagen deposition and decreased capillary density. The differences between strains became more pronounced after MI. Although cardiac function was well preserved in the Tg-ANG II-cardiac mice with sham-MI, cardiac remodeling and dysfunction post-MI were more severe than WT. Our results demonstrate that, independent of systemic hemodynamic effects, cardiac ANG II may act locally in the heart, causing interstitial fibrosis in sham-MI and accelerating deterioration of cardiac dysfunction and remodeling post-MI.

Bone marrow-derived stem cell interactions with adult cardiomyocytes and skeletal myoblasts in vitro

BACKGROUND AND OBJECTIVES

Secreted growth factors and cell-to-cell contact are both required to elicit cellular functions. We tested the hypothesis that bone-marrow-derived growth factors, together with cell-to-cell contact between bone-marrow-derived stem cells and cardiomyocytes or myoblasts, promote the proliferation of cardiomyocytes and myoblasts.

METHODS

Human cardiomyocytes or skeletal myoblasts were cultured for 4 days in the presence of low and high concentrations of bone-marrow-derived mononuclear cell conditioned medium (MNC-CM) or marrow stromal cell conditioned medium (MSC-CM). The concentrations of vascular endothelial growth factor (VEGF), monocyte chemoattractant protein-1 (MCP-1), hepatocyte growth factor (HGF), and insulin-like growth factor-1 in their respective conditioned media were assayed by enzyme-linked immunosorbent assay. Stem cells were mixed with cardiomyocytes or skeletal myoblasts at a 1:1 ratio and cultured for 7 days to assess the proliferation of these cells. In parallel experiments, equal numbers of various cell types were cultured alone.

RESULTS

The concentrations of VEGF, MCP-1, and HGF increased in MNC-CM and MSC-CM. MNC-CM showed no effect on cardiomyocyte proliferation. A low concentration of MSC-CM increased cardiomyocyte proliferation by 60% (P<.05). Low concentrations of MNC-CM or MSC-CM showed a trend toward an increased proliferation of myoblasts. A high concentration of either conditioned medium showed a toxic effect. In contact coculture, the proliferation of cardiomyocytes and MNC showed no synergistic effect; instead, there was some evidence of inhibition. The proliferation of cardiomyocytes and stromal cells showed an additive effect. Myoblasts in contact coculture with MNC or MSC showed no synergistic effect.

CONCLUSION

These in vitro results suggest that paracrine effects may be the mechanism by which stromal cells become beneficial in cardiac therapy. MNC do not induce the proliferation of cardiomyocytes. Stem-cell-secreted growth factors induce the proliferation of myoblasts, which is not influenced by cell-to-cell contact.

Local delivery of angiotensin receptor blocker into the kidney ameliorates progression of experimental glomerulonephritis

Intrarenally synthesized angiotensin II (Ang II) may be involved in the progression of glomerulonephritis, leading to irreversible glomerulosclerosis. There is increasing evidence that systemic angiotensin receptor blocker (ARB) treatment has beneficial effect on the prognosis of progressive glomerulonephritis and diabetic nephropathy. However, the cellular and molecular mechanisms behind this therapeutic effect of ARB remain unclear. In this study, we used a novel strategy of local ARB delivery via type-1 collagen sponge, to treat progressive glomerulonephritis that would result in irreversible glomerulosclerosis in our previously established rat model. At days 9 and 14 after disease induction, mild proteinuria, 20.7+/-4.7 and 10+/-1.3 mg/day, was found. Local ARB treatment reduced proteinuria significantly to 3.19+/-3.2 and 5.25+/-0.95 mg/day (P < 0.01), respectively. Scoring of glomerular matrix expansion and sclerotic index revealed that local ARB treatment significantly ameliorated glomerular pathology. Ang II type 1 receptor mRNA expression was remarkably enhanced in the Ang II group and ARB treatment reversed this effect at 14 days. Local delivery of ARB significantly improved glomerular blood flow levels, compared to the untreated disease control group, from 710+/-18.25 to 859.44+/-22.86 microm/s, respectively. Local delivery of ARB into the kidney affected local RAS and thus improved the renal injury and function in the potentially progressive glomerulosclerosis of rat model.

Reversal of fibrosis: no longer a pipe dream?

The reversal of liver fibrosis is not a new phenomenon. Treatment of the primary disease remains the most effective strategy, but new approaches to promote resolution of fibrosis are being built on the foundations that were provided by research into the basic mechanisms of fibrogenesis. A return to normal hepatic architecture from advanced fibrosis is achievable in some cases, and cirrhosis itself may be partly remediable.

A novel function of angiotensin II in skin wound healing. Induction of fibroblast and keratinocyte migration by angiotensin II via heparin-binding epidermal growth factor (EGF)-like growth factor-mediated EGF receptor transactivation

The role of angiotensin II (Ang II) in the control of systemic blood pressure and volume homeostasis is well known and has been extensively studied. Recently, Ang II was suggested to also have a function in skin wound healing. In the present study, the in vivo function of Ang II in skin wound healing was investigated using Ang II type 1 receptor (AT1R) knock-out mice. Wound healing in these mice was found to be markedly delayed. Keratinocytes and fibroblasts play important roles in wound healing, and thus the effect of Ang II on the migration of these cells was examined. Ang II stimulated keratinocyte and fibroblast migration in a dose-dependent manner. It has been reported that G protein-coupled receptor (GPCR) activation induces epidermal growth factor (EGF) receptor (EGFR) transactivation through the shedding of heparin-binding EGF-like growth factor (HB-EGF). As AT1R is a GPCR, it was hypothesized that Ang II-induced keratinocyte and fibroblast migration is mediated by EGFR transactivation. Ang II induced EGFR phosphorylation, which was inhibited by an AT1R antagonist, HB-EGF neutralizing antibody, and an HB-EGF antagonist in both keratinocytes and in fibroblasts. Moreover, Ang II-induced migration of keratinocytes and fibroblasts was also prevented by these inhibitors. Taken together, these findings clearly demonstrate, for the first time, that Ang II plays an important role in skin wound healing and that it functions by accelerating keratinocyte and fibroblast migration in a process mediated by HB-EGF shedding.

Emerging therapies for liver fibrosis

Liver fibrosis occurs as a result of a wide range of injurious processes and in its end-stage results in cirrhosis. This gross disruption of liver architecture is associated with impaired hepatic function, portal hypertension and significant resultant morbidity and mortality. Indeed, liver fibrosis and cirrhosis represent a major worldwide healthcare burden. Recent progress in liver transplantation, the management of portal hypertension and the treatment of chronic viral hepatitis have had an important impact. However, these approaches are not without their limitations - in particular, issues regarding organ availability for transplantation - and serve to highlight the urgent requirement to influence pharmacologically the underlying fibrotic process in many patients. Liver fibrosis has been shown to be a bidirectional process and increasing data from laboratory and clinical studies reveal that even advanced fibrosis and cirrhosis are potentially reversible. Exploration of the molecular mechanisms underlying this bi-directionality will lead to char acterisation of the essential attributes of an antifibrotic therapy. In this review, these mechanisms are highlighted and the growing number of emerging antifibrotic agents discussed.

Targeted treatments for cirrhosis

The causes of hepatic scarring (fibrosis) are protean but, unchecked, all result in a common fate--the development of cirrhosis--with gross disruption of the normal liver architecture. Subsequent liver cell dysfunction and portal hypertension give rise to major systemic complications and premature death. Cirrhosis and its sequelae represent a huge, and global, healthcare burden. The success of liver transplantation and the development of efficacious antiviral regimens for hepatitis B and C should not be underestimated, but they also serve to highlight our current inability to manipulate the underlying fibrotic process in many patients with liver disease. Moreover, transplantation as a treatment is limited by organ availability, among other factors. The development of antifibrotic therapies is urgently needed and for this we require a mechanistic and evidence-based approach. Accumulating data from clinical and laboratory studies demonstrate that even advanced fibrosis and cirrhosis are potentially reversible. The hepatic stellate cells have been identified as the pivotal effector cells orchestrating the fibrotic process and, furthermore, reversibility appears to hinge upon their elimination. This review draws on recent scientific advances, and highlights emerging therapeutic interventions in liver fibrosis.

Significance of the transcription factor KLF5 in cardiovascular remodeling

Structural remodeling of the heart and blood vessels is an important pathologic process in the development of many cardiovascular diseases. However, transcriptional regulation of altered gene expression during cardiovascular remodeling is not well understood. We previously isolated KLF5/basic transcription element-binding (BTEB)2, a Krüppel-like factor, as a transcription factor that binds the promoter of the embryonic smooth muscle myosin heavy chain gene (SMemb). KLF5 activates many genes inducible during cardiovascular remodeling, such as platelet-derived growth factor (PDGF)-A/B, Egr-1, plasminogen activator inhibitor-1 (PAI-1), inducible nitric oxide synthase (iNOS), and vascular endothelial growth factor (VEGF) receptors. KLF5 is abundantly expressed in embryonic smooth muscles and is down-regulated with vascular development, but reinduced in proliferative neointimal smooth muscles in response to vascular injury. In KLF5 gene-targeted mice, homozygotes die at an early embryonic stage whereas heterozygotes are apparently normal. However, in response to external stress, arteries of heterozygotes exhibit diminished levels of smooth muscle and adventitial cell activation. Furthermore, angiotensin II-induced cardiac hypertrophy and fibrosis are attenuated in heterozygotes. KLF5 activities are regulated by many transcriptional regulators and nuclear receptors, such as retinoic acid receptor-alpha (RAR alpha), NF-kappaB, PPAR gamma, p300, and SET. Interestingly, RAR alpha agonist suppresses KLF5 and cardiovascular remodeling, whereas RAR alpha antagonist activates KLF5 and induces angiogenesis. These results indicate that KLF5 is an essential transcription factor in cardiovascular remodeling and a potential therapeutic target for cardiovascular disease.

Permanent Genetic Tagging of Podocytes: Fate of Injured Podocytes in a Mouse Model of Glomerular Sclerosis

Injured podocytes lose differentiation markers. Therefore, the true identity of severely injured podocytes remains unverified. A transgenic mouse model equipped with a podocyte-selective injury induction system was established. After induction of podocyte injury, mice rapidly developed glomerulosclerosis, with downregulation of podocyte marker proteins. Proliferating epithelial cells accumulated within Bowman's space, as seen in collapsing glomerulosclerosis. In this study, the fate of injured podocytes was pursued. Utilizing Cre-loxP recombination, the podocyte lineage was genetically labeled with lacZ in an irreversible manner. After podocyte injury, the number of lacZ-labeled cells, which were often negative for synaptopodin, progressively declined, correlating with glomerular damage. Parietal epithelial cells, but not lacZ-labeled podocytes, avidly proliferated. The cells proliferating within Bowman's capsule and, occasionally, on the outer surface of the glomerular basement membrane were lacZ-negative. Thus, when podocytes are severely injured, proliferating parietal epithelial cells migrate onto the visceral site, thereby mimicking proliferating podocytes.

Galpha12/13-mediated production of reactive oxygen species is critical for angiotensin receptor-induced NFAT activation in cardiac fibroblasts

Angiotensin II (Ang II) activates multiple signaling pathways leading to hyperplasia of cardiac fibroblasts. Reactive oxygen species (ROS) produced by Ang II stimulation are assumed to play pivotal roles in this process. Here, we show that ROS mediate Ang II-induced activation of nuclear factor of activated T cells (NFAT) in rat cardiac fibroblasts. Ang II-induced NFAT activation was suppressed by diphenyleneiodonium (an NADPH oxidase inhibitor), dominant negative (DN)-Rac, DN-p47(phox), and an inhibitor of Galpha(12/13) (Galpha(12/13)-specific regulator of G protein signaling domain of p115RhoGEF, p115-regulator of G protein signaling (RGS)). Stimulation of Ang II receptor increased the intracellular ROS level in a Rac- and p47(phox)-dependent manner. Because p115-RGS suppressed Ang II-induced Rac activation, Ang II receptor-coupled Galpha(12/13) mediated NFAT activation through ROS production by Rac activation. Ang II-induced nuclear translocation of the green fluorescent protein (GFP)-tagged amino-terminal region of NFAT4 (GFP-NFAT4) was suppressed by p115-RGS or BAPTA but not by diphenyleneiodonium. The expression of constitutively active (CA)-Galpha(12/13), CA-G translocation alpha(13), or CA-Rac increased the nuclear of GFP-NFAT4. These results suggest that NFAT activity is regulated by both Ca(2+)-dependent and ROS-dependent pathways. Furthermore, activation of c-Jun NH(2)-terminal kinase (JNK) induced by Ang II stimulation is required for NFAT activation because Ang II-induced NFAT activation was inhibited by SP600125, a selective JNK inhibitor. These results indicate that Ang II stimulates the nuclear translocation and activation of NFAT by integrated pathways including the activation of Galpha(12/13), Rac, NADPH oxidase, and JNK and that Galpha(12/13)-mediated ROS production is essential for NFAT transcriptional activation.

The interaction of coronary tone and cardiac fibrosis

Regulation of coronary vascular tone is critical for proper perfusion and function of the myocardium. Many disease processes result in compromised regulation of coronary vascular tone and impaired myocardial perfusion. A common result of coronary vascular dysfunction is the development of areas of replacement fibrosis within the myocardium and surrounding the vasculature. Both intravascular processes, such as coronary atherosclerosis and endothelial dysfunction, and extravascular processes, including compromised myocardial metabolism, hormone excesses, and altered local signaling, may result in coronary vascular dysregulation. Coronary occlusion events, in turn, lead to myocardial damage and the activation of inflammatory cells and fibroblasts. The role of fibroblasts in regulating myocardial fibrosis and the contribution of myofibroblasts, cells that have limited contractile potential while retaining many of the extracellular matrix regulating processes of the fibroblast, may also contribute to the development of myocardial disease. In this review we examine the recent literature on myocardial fibrosis and myofibroblast activity, highlighting the effects of several classes of cardiovascular agents on the remodeling process.

Molecular Mechanism of Apoptosis Induced by Mechanical Forces

In all biological systems, a balance between cell proliferation/growth and death is required for normal development as well as for adaptation to a changing environment. To affect their fate, it is essential for cells to integrate signals from the environment. Recently, it has been recognized that physical forces such as stretch, strain, and tension play a critical role in regulating this process. Despite intensive investigation, the pathways by which mechanical signals are converted to biochemical responses is yet to be completely understood. In this review, we will examine our current understanding of how mechanical forces induce apoptosis in a variety of biological systems. Rather than being a degenerative event, physical forces act through specific receptor-like molecules such as integrins, focal adhesion proteins, and the cytoskeleton. These molecules in turn activate a limited number of protein kinase pathways (p38 MAPK and JNK/SAPK), which amplify the signal and activate enzymes (caspases) that promote apoptosis. Physical forces concurrently activate other signaling pathways such as PIK-3 and Erk 1/2 MAPK, which modulate the apoptotic response. The cell phenotype and the character of the physical stimuli determine which pathways are activated and, consequently, allow for variability in response to a specific stimulus in different cell types.

Protein Kinase Cα Negatively Regulates Systolic and Diastolic Function in Pathological Hypertrophy

The protein kinase C (PKC) family is implicated in cardiac hypertrophy, contractile failure, and beta-adrenergic receptor (betaAR) dysfunction. Herein, we describe the effects of gain- and loss-of-PKCalpha function using transgenic expression of conventional PKC isoform translocation modifiers. In contrast to previously studied PKC isoforms, activation of PKCalpha failed to induce cardiac hypertrophy, but instead caused betaAR insensitivity and ventricular dysfunction. PKCalpha inhibition had opposite effects. Because PKCalpha is upregulated in human and experimental cardiac hypertrophy and failure, its effects were also assessed in the context of the Galphaq overexpression model (in which PKCalpha is transcriptionally upregulated). Normalization (inhibition) of PKCalpha activity in Galpha(q) hearts improved systolic and diastolic function, whereas further activation of PKCalpha caused a lethal restrictive cardiomyopathy with marked interstitial fibrosis. These results define pathological roles for PKCalpha as a negative regulator of ventricular systolic and diastolic function.

Induction of left ventricular remodeling and dysfunction in the recipient heart after donor heart myocardial infarction: new insights into the pathologic role of tumor necrosis factor-alpha from a novel heterotopic transplant-coronary ligation rat model

OBJECTIVES

The present study investigated the effects of tumor necrosis factor (TNF)-alpha and angiotensin II (ANG II) on cardiac remodeling and dysfunction at the early stage of acute myocardial infarction (MI) by using a novel heterotopic cardiac transplantation-coronary ligation model.

BACKGROUND

A recent clinical study has demonstrated a possible role of monocytosis in the development of left ventricular (LV) remodeling in patients with acute MI reperfusion.

METHODS

We performed isogenic heterotopic cardiac transplantation and simultaneous coronary ligation to produce MI in the donor heart and to evaluate the hearts of both donors and recipients in Lewis rats.

RESULTS

A significant decrease in LV fractional shortening and positive rate of rise in LV pressure and a significant increase in LV end-diastolic dimension/body weight and LV end-diastolic pressure were observed in the recipient hearts in the ligation group on day 7. TNF-alpha was significantly elevated not only in the plasma but also in the recipient hearts in the ligation group. In contrast, ANG II was significantly increased only in the infarct region of the donor hearts, but not in the plasma. Furthermore, the recipients' transient LV remodeling and dysfunction were completely abolished by the intravenous administration of a TNF-alpha antagonist. CONCLUSIONS; We developed a novel cardiac transplantation-coronary ligation model capable of inducing MI in the absence of downstream hemodynamic effects and allowing differential quantification of indexes of cardiac remodeling in vivo, including the local and remote effects of ANG II and TNF-alpha on cardiac remodeling.

Structural pathways and prevention of heart failure and sudden death

We review the macroscopic and microscopic anatomy of myocardial disease associated with heart failure (HF) and sudden cardiac death (SCD) and focus on the prevention of SCD in light of its structural pathways. Compared to patients without SCD, patients with SCD exhibit 5- to 6-fold increases in the risks of ventricular arrhythmias and SCD. Epidemiologically, left ventricular hypertrophy by ECG or echocardiography acts as a potent dose-dependent SCD predictor. Dyslipidemia, a coronary disease risk factor, independently predicts echocardiographic hypertrophy. In adult SCD autopsy studies, increases in heart weight and severe coronary disease are constant findings, whereas rates of acute coronary thrombi vary remarkably. The microscopic myocardial anatomy of SCD is incompletely defined but may include prevalent changes of advanced myocardial disease, including cardiomyocyte hypertrophy, cardiomyocyte apoptosis, fibroblast hyperplasia, diffuse and focal matrix protein accumulation, and recruitment of inflammatory cells. Hypertrophied cardiomyocytes express "fetospecific" genetic programs that can account for acquired long QT physiology with risk for polymorphic ventricular arrhythmias. Structural heart disease associated with HF and high SCD risk is causally related to an up-regulation of the adrenergic renin-angiotensin-aldosterone pathway. In outcome trials, suppression of this pathway with combinations of beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin-II receptor blockers, and mineralocorticoid receptor blockers have achieved substantial total mortality and SCD reductions. Contrarily, trials with ion channel-active agents that are not known to reduce structural heart disease have failed to reduce these risks. Device therapy effectively prevents SCD, but whether biventricular pacing-induced remodeling decreases left ventricular mass remains uncertain.

Accelerated Cardiac Hypertrophy and Renal Damage Induced by Angiotensin II in Adrenomedullin Knockout Mice

Adrenomedullin (AM) is a potent vasodilating and natriuretic peptide that is thought to play important roles in cardiovascular function. Whether or not AM is involved in the development of cardiac hypertrophy and renal damage remains controversial. In the present study, using heterozygote knockout mice of the AM gene (AM +/-), we analyzed the physiological and pathological roles of the endogenous AM gene. There were no differences in body size or heart and kidney weight compared with wild-type (AM +/+) mice. However, angiotensin II (Ang II) infusion resulted in more severe cardiac hypertrophy in AM +/- mice. The increases in the heart weight-to-body weight ratio and wall thickness of the left ventricle were more prominent in the AM +/- mice. Renal dysfunction characterized by decreased creatinine clearance (C(cr)) was more severe in AM +/- after Ang II infusion. These results suggest that AM plays critical roles in the defense mechanism against cardiac hypertrophy and renal dysfunction. An improved understanding of these roles may pave the way to a novel pharmacological approach for the prevention of cardiovascular diseases.

Gene expression in fibroblasts and fibrosis: involvement in cardiac hypertrophy

Structural remodeling of the ventricular wall is a key determinant of clinical outcome in heart disease. Such remodeling involves the production and destruction of extracellular matrix proteins, cell proliferation and migration, and apoptotic and necrotic cell death. Cardiac fibroblasts are crucially involved in these processes, producing growth factors and cytokines that act as autocrine and paracrine factors, as well as extracellular matrix proteins and proteinases. Recent studies have shown that the interactions between cardiac fibroblasts and cardiomyocytes are essential for the progression of cardiac remodeling. This review addresses the functional role played by cardiac fibroblasts and the molecular mechanisms that govern their activity during cardiac hypertrophy and remodeling. A particular focus is the recent progress toward our understanding of the transcriptional regulatory mechanisms involved.

Role of the local renin-angiotensin system in cardiac damage: a minireview focussing on transgenic animal models

The local generation of all components of the renin-angiotensin system (RAS) in the heart has been the basis for the postulation of a tissue RAS in this organ. Since angiotensin II is involved in the induction of cardiac hypertrophy and fibrosis the local generation of this peptide may be of highest clinical importance. Several transgenic animal models have been generated to evaluate the functional importance of the cardiac RAS. We have established a new hypertensive mouse model lacking local angiotensinogen expression in the heart. In these animals, cardiac weight and collagen synthesis are increased compared to normotensive control mice but to a lesser extent than in mice with equally enhanced blood pressure but intact cardiac angiotensinogen generation. Thus, we have shown that local synthesis of this protein is involved but not essential in the development of cardiac hypertrophy and fibrosis.

Developing strategies for liver fibrosis treatment

Liver fibrosis represents a major worldwide healthcare burden. Current therapy is limited to removing the causal agent. This approach is successful in some diseases; particularly haemochromatosis and chronic viral hepatitis. However, for many patients treatment is not possible, while other patients present to medical attention at an advanced stage of fibrosis. There is therefore a great need for novel therapies for liver fibrosis. The hepatic stellate cell has been recognised to be responsible for most of the excess extracellular matrix observed in chronic liver fibrosis. The detailed understanding of hepatic stellate cell biology has allowed the rational design of novel antifibrotic therapies. This review describes for the general reader the novel emerging therapies for liver fibrosis.

Krüppel-like zinc-finger transcription factor KLF5/BTEB2 is a target for angiotensin II signaling and an essential regulator of cardiovascular remodeling

We recently isolated a Krüppel-like zinc-finger transcription factor 5 (KLF5; also known as BTEB2 and IKLF), which is markedly induced in activated vascular smooth-muscle cells and fibroblasts. Here we describe our analysis of the in vivo function of KLF5 using heterozygous KLF5-knockout mice (Klf5(+/-)). In response to external stress, Klf5(+/-) mice showed diminished levels of arterial-wall thickening, angiogenesis, cardiac hypertrophy and interstitial fibrosis. Also, angiotensin II induced expression of KLF5, which in turn activated platelet-derived growth factor-A (PDGF-A) and transforming growth factor-beta (TGF-beta) expression. In addition, we determined that KLF5 interacted with the retinoic-acid receptor (RAR), that synthetic RAR ligands modulated KLF5 transcriptional activity, and that in vivo administration of RAR ligands affected stress responses in the cardiovascular system in a KLF5-dependent manner. KLF5 thus seems to be a key element linking external stress and cardiovascular remodeling.

Cell death and mechanoprotection by filamin a in connective tissues after challenge by applied tensile forces

Cells in mechanically challenged environments must cope with high amplitude forces to maintain cell viability and tissue homeostasis. Currently, force-induced cell death and the identity of mechanoprotective factors are not defined. We examined death in cultured periodontal fibroblasts, connective tissue cells that are exposed to heavy applied forces in vivo. Static tensile forces (0.48 piconewtons/microm2 cell area) were applied through magnetite beads coated with collagen or bovine serum albumin. There was a time-dependent increase of the percentage of propidium iodide-permeable cells in force-loaded cultures incubated with collagen but not bovine serum albumin beads, indicating a role for integrins. Cells exhibited reduced mitochondrial membrane potential, increased caspase-3 activation, nuclear condensation, terminal deoxynucleotidyl transferase nick end labeling staining, and detachment from the culture dish. The caspase-3 inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde reduced detachment 3-fold. There was a rapid (<10-s) decrease in plasma membrane potential after force application, which, in filamin A-deficient melanoma cells, contributed to irreversible cell depolarization. In fibroblast cultures, cells with increased permeability to propidium iodide exhibited approximately 2-fold less filamin A content than impermeable cells. Fibroblasts transfected with antisense filamin A constructs or with filamin A constructs without an actin-binding domain exhibited 2-3-fold increased proportions of dead cells relative to controls. We conclude that high amplitude forces delivered through integrins can promote apoptosis in a proportion of cells and that filamin A confers mechanoprotection by preventing membrane depolarization.

Dilated cardiomyopathy and impaired cardiac hypertrophic response to angiotensin II in mice lacking FGF-2

FGF-2 has been implicated in the cardiac response to hypertrophic stimuli. Angiotensin II (Ang II) contributes to maintain elevated blood pressure in hypertensive individuals and exerts direct trophic effects on cardiac cells. However, the role of FGF-2 in Ang II-induced cardiac hypertrophy has not been established. Therefore, mice deficient in FGF-2 expression were studied using a model of Ang II-dependent hypertension and cardiac hypertrophy. Echocardiographic measurements show the presence of dilated cardiomyopathy in normotensive mice lacking FGF-2. Moreover, hypertensive mice without FGF-2 developed no compensatory cardiac hypertrophy. In wild-type mice, hypertrophy was associated with a stimulation of the c-Jun N-terminal kinase, the extracellular signal regulated kinase, and the p38 kinase pathways. In contrast, mitogen-activated protein kinase (MAPK) activation was markedly attenuated in FGF-2-deficient mice. In vitro, FGF-2 of fibroblast origin was demonstrated to be essential in the paracrine stimulation of MAPK activation in cardiomyocytes. Indeed, fibroblasts lacking FGF-2 expression have a defective capacity for releasing growth factors to induce hypertrophic responses in cardiomyocytes. Therefore, these results identify the cardiac fibroblast population as a primary integrator of hypertrophic stimuli in the heart, and suggest that FGF-2 is a crucial mediator of cardiac hypertrophy via autocrine/paracrine actions on cardiac cells.

Use of a biological peptide pump to study chronic peptide hormone action in transgenic mice. Direct and indirect effects of angiotensin II on the heart

Angiotensin II is a peptide hormone regulator of blood pressure and fluid balance in mammals. Evidence obtained largely in vitro has also suggested that angiotensin II has growth-promoting effects and that it might thereby contribute to such pathological phenomena as cardiac hypertrophy, a major risk factor for cardiovascular mortality. It has been difficult to test for the direct growth-promoting effects of angiotensin II in vivo, however, because of the generalized effects of the peptide on hemodynamics. To overcome this limitation and to test for cardiac-specific functions of angiotensin II, we generated transgenic mice expressing an angiotensin II-producing fusion protein exclusively in cardiac myocytes. Our findings are the first to distinguish between local and systemic effects of angiotensin II on the heart and introduce a novel technique for studying tissue-specific peptide function.

The relevance of tissue angiotensin-converting enzyme: manifestations in mechanistic and endpoint data

Angiotensin-converting enzyme (ACE) is primarily localized (>90%) in various tissues and organs, most notably on the endothelium but also within parenchyma and inflammatory cells. Tissue ACE is now recognized as a key factor in cardiovascular and renal diseases. Endothelial dysfunction, in response to a number of risk factors or injury such as hypertension, diabetes mellitus, hypercholesteremia, and cigarette smoking, disrupts the balance of vasodilation and vasoconstriction, vascular smooth muscle cell growth, the inflammatory and oxidative state of the vessel wall, and is associated with activation of tissue ACE. Pathologic activation of local ACE can have deleterious effects on the heart, vasculature, and the kidneys. The imbalance resulting from increased local formation of angiotensin II and increased bradykinin degradation favors cardiovascular disease. Indeed, ACE inhibitors effectively reduce high blood pressure and exert cardio- and renoprotective actions. Recent evidence suggests that a principal target of ACE inhibitor action is at the tissue sites. Pharmacokinetic properties of various ACE inhibitors indicate that there are differences in their binding characteristics for tissue ACE. Clinical studies comparing the effects of antihypertensives (especially ACE inhibitors) on endothelial function suggest differences. More comparative experimental and clinical studies should address the significance of these drug differences and their impact on clinical events.

Intercellular mechanotransduction: cellular circuits that coordinate tissue responses to mechanical loading

Physical forces play an important role in modulating cell function and shaping tissue structure. Mechanotransduction, the process by which cells transduce physical force-induced signals into biochemical responses, is critical for mediating adaptations to mechanical loading in connective tissues. While much is known about mechanotransduction in cells involving forces delivered through extracellular matrix proteins and integrins, there is limited understanding of how mechanical signals are propagated through the interconnected cellular networks found in tissues and organs. We propose that intercellular mechanotransduction is a critical component for achieving coordinated remodeling responses to force application in connective tissues. We examine here recent evidence on different pathways of intercellular mechanotransduction and suggest a general model for how multicellular structures respond to mechanical loading as an integrated unit.

Integrins and the myocardium

Extracellular matrix provides a structural, chemical, and mechanical substrate that is essential in cardiac development, growth, and responses to pathophysiological signals. Transmembrane receptors termed integrins provide a dynamic interaction of environmental cues and intracellular events. Integrins orchestrate multiple functions in the intact organism including organogenesis, regulation of gene expression, cell proliferation, differentiation, migration, and death. They are expressed in all cellular components of the cardiovascular system, including the vasculature, blood, cardiac myocytes and nonmuscle cardiac cells. The focus of this review will be on the role of integrins in the myocardium. We will provide background on integrin structure and function, discuss how the expression of integrins is critical to the form and function of the developing and postnatal myocardium, and review the known data on integrins as signaling molecules in the heart. Finally, we will offer insights to the future research directions into this important family of extracellular matrix receptors in the myocardium.

Extracellular matrix proteins in cardiac fibroblasts derived from rat hearts with chronic pressure overload: effects of beta-receptor blockade

Left ventricular hypertrophy (LVH) is accompanied by progressive accumulations of extracellular matrix proteins. They are produced predominantly by cardiac fibroblasts that surround the cardiac myocytes. The aim of this study was to emphasize the role of a combined approach using both in vivo and in vitro studies to elucidate the effects of carvedilol on cardiac remodeling. We therefore used an established model of supravalvular aortic banding and cardiac fibroblasts. LVH was induced by banding of the ascending aorta. Male Wistar rats were allocated to four groups: sham-operated, sham+carvedilol, aortic stenosis (AS), and AS+carvedilol. Treatment time was four weeks. Fibroblasts were isolated from the entire left ventricle of sham and AS rats. Carvedilol/metoprolol/prazosin were added (0.1, 1.0 and 10 microM; 24 h). In addition, interferon- gamma was applied for 24 h (10, 100 and 1000 IU). AS rats revealed increased LV weights (+27%) and cardiomyocyte widths as compared to sham-operated rats (1.6-fold, P<0.01). Carvedilol reduced LVH by 20%. This finding was accompanied by a decrease of laminin, fibronectin, collagen I and III in vivo. Collagen I/III and fibronectin were increased in fibroblasts of AS v sham rats (P<0.0001, each). Carvedilol reduced collagen I, III and fibronectin by 40/60/35% (0.1 microM; P<0.001) irrespective of LVH. Carvedilol had no effects on collagen IV and laminin. Carvedilol dose-dependently reduced the proliferation rate by 20% at 0.1 microM(P<0.0001). Metoprolol and prazosin had no effect on the expression of extracellular matrix proteins and on the proliferation of the cells of either origin. Interferon- gamma blunted the proliferation rate of cultured fibroblasts and lead to a significant decrease in extracellular matrix deposits. These results indicate that the effects of carvedilol may be due to the antiproliferative or antioxidative properties of this unselective beta-adrenergic receptor antagonist. These changes of the extracellular matrix represent a new mechanism of carvedilol that may contribute to the observed beneficial effects in congestive heart failure.