Differential Behaviors of Atrial Versus Ventricular Fibroblasts A Potential Role for Platelet-Derived Growth Factor in Atrial-Ventricular Remodeling Differences
TL;DR: Atrial fibroblasts behave differently than ventricular fibro Blasts over a range of in vitro and in vivo paradigms, with atrial Fibroblast showing enhanced reactivity that may explain greater atrial fibrotic responses.
Abstract: Background— In various heart disease paradigms, atria show stronger fibrotic responses than ventricles. The possibility that atrial and ventricular fibroblasts respond differentially to pathological stimuli has not been examined. Methods and Results— We compared various morphological, secretory, and proliferative response indexes of canine atrial versus ventricular fibroblasts. Cultured atrial fibroblasts showed faster cell surface area increases, distinct morphology at confluence, and greater α-smooth muscle actin expression than ventricular fibroblasts. Atrial fibroblast proliferation ([3H]thymidine incorporation) responses were consistently greater for a range of growth factors, including fetal bovine serum, platelet-derived growth factor (PDGF), basic fibroblast growth factor, angiotensin II, endothelin-1, and transforming growth factor-β1. Normal atrial tissue showed larger myofibroblast density compared with ventricular tissue, and the difference was exaggerated by congestive heart failure. Congesti...
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TL;DR: The functional changes associated with fibroblast activation, the membrane currents that have been identified in adult cardiac fibroblasts, and recent studies of fibro Blast-myocyte electrical interactions are described to generate new therapeutic approaches for the prevention of arrhythmias associated with cardiac fibrosis.
Abstract: Cardiac fibrosis occurs in a number of cardiovascular diseases associated with a high incidence of arrhythmias. A critical event in the development of fibrosis is the transformation of fibroblasts into an active phenotype or myofibroblast. This transformation results in functional changes including increased proliferation and changes in the release of signaling molecules and extracellular matrix deposition. Traditionally fibroblasts have been considered to affect cardiac electrophysiology indirectly by physically isolating myocytes and creating conduction barriers. There is now increasing evidence that cardiac fibroblasts may play a direct role in modulating the electrophysiological substrate in diseased hearts. The purpose of this review is to summarize the functional changes associated with fibroblast activation, the membrane currents that have been identified in adult cardiac fibroblasts and describe recent studies of fibroblast-myocyte electrical interactions with emphasis on the changes that occur with cardiac injury. Further analysis of fibroblast membrane electrophysiology and their interactions with myocytes will lead to a more complete understanding of the arrhythmic substrate. These studies have the potential to generate new therapeutic approaches for the prevention of arrhythmias associated with cardiac fibrosis.
127 citations
Cites background from "Differential Behaviors of Atrial Ve..."
...Isolated cardiac fibroblasts have also been shown to have chamber-specific differences with respect to morphology and proliferative responses to stimulation with growth factors.(17) Sheets and strands of fibroblasts are arranged in a 3D network that surrounds myocytes and other cell types....
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...In the heart, atrial and ventricular fibroblasts have different cell densities in intact tissue.(17) Isolated cardiac fibroblasts have also been shown to have chamber-specific differences with respect to morphology and proliferative responses to stimulation with growth factors....
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...However, in a different study, proliferation rates were found to be increased in atrial and ventricular fibroblasts isolated from a canine tachypacing model of congestive heart failure.(17) The same study also showed an increase of platelet-derived growth factor levels in response to tachypacing in fibroblasts isolated from atria but not ventricles....
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TL;DR: This review will discuss and highlight developments on spironolactone, as a drug targeted to atrial fibrosis and AF, as well as the distinct and common mechanisms important for regulating atrial and ventricular fibrosis, inclusive of the key extracellular matrix regulatory proteins involved.
123 citations
TL;DR: A comprehensive analysis of the current experimental evidence supporting miRNAs as important factors in AF and their therapeutic implications is provided, followed by experimental evidence for miRNA-mediated regulation of AF, and a comprehensive overview of miRN as potential novel therapeutic targets for AF are provided.
Abstract: Atrial fibrillation (AF), the most common sustained arrhythmia in clinical practice, is an important contributor to cardiac morbidity and mortality. Pharmacological approaches currently available to treat patients with AF lack sufficient efficacy and are associated with potential adverse effects. Even though ablation is generally more effective than pharmacotherapy, this invasive procedure has considerable potential complications and is limited by long-term recurrences. Novel therapies based on the underlying molecular mechanisms of AF can provide useful alternatives to current treatments. MicroRNAs (miRNAs), endogenous short RNA sequences that regulate gene expression, have been implicated in the control of AF, providing novel insights into the molecular basis of the pathogenesis of AF and suggesting miRNA targeting as a potential approach for the management of this common arrhythmia. In this Review, we provide a comprehensive analysis of the current experimental evidence supporting miRNAs as important factors in AF and discuss their therapeutic implications. We first provide background information on the pathophysiology of AF and the biological determinants of miRNA synthesis and action, followed by experimental evidence for miRNA-mediated regulation of AF, and finally provide a comprehensive overview of miRNAs as potential novel therapeutic targets for AF.
118 citations
TL;DR: 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.
Abstract: 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.
117 citations
Cites background from "Differential Behaviors of Atrial Ve..."
...Atria are generally more vulnerable to fibrosis than ventricles (47, 85, 150), which may be due to an enhanced response to multiple growth factors in atrial compared with ventricular CF (17)....
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TL;DR: A better understanding of fibroblasts' biophysical interactions will help to target scar structure and function, and will facilitate the development of novel therapies aimed at modifying scar properties for patient benefit.
115 citations
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TL;DR: It is shown that cardiac fibrosis is associated with the emergence of fibroblasts originating from endothelial cells, suggesting an endothelial-mesenchymal transition (EndMT) similar to events that occur during formation of the atrioventricular cushion in the embryonic heart.
Abstract: Cardiac fibrosis, associated with a decreased extent of microvasculature and with disruption of normal myocardial structures, results from excessive deposition of extracellular matrix, which is mediated by the recruitment of fibroblasts. The source of these fibroblasts is unclear and specific anti-fibrotic therapies are not currently available. Here we show that cardiac fibrosis is associated with the emergence of fibroblasts originating from endothelial cells, suggesting an endothelial-mesenchymal transition (EndMT) similar to events that occur during formation of the atrioventricular cushion in the embryonic heart. Transforming growth factor-β1 (TGF-β1) induced endothelial cells to undergo EndMT, whereas bone morphogenic protein 7 (BMP-7) preserved the endothelial phenotype. The systemic administration of recombinant human BMP-7 (rhBMP-7) significantly inhibited EndMT and the progression of cardiac fibrosis in mouse models of pressure overload and chronic allograft rejection. Our findings show that EndMT contributes to the progression of cardiac fibrosis and that rhBMP-7 can be used to inhibit EndMT and to intervene in the progression of chronic heart disease associated with fibrosis.
1,908 citations
TL;DR: Experimental CHF strongly promotes the induction of sustained AF by causing interstitial fibrosis that interferes with local conduction, with important potential implications for understanding, treating, and preventing AF related to CHF.
Abstract: Background—Studies of atrial fibrillation (AF) due to atrial tachycardia have provided insights into the remodeling mechanisms by which “AF begets AF” but have not elucidated the substrate that initially supports AF before remodeling occurs. We studied the effects of congestive heart failure (CHF), an entity strongly associated with clinical AF, on atrial electrophysiology in the dog and compared the results with those in dogs subjected to rapid atrial pacing (RAP; 400 bpm) with a controlled ventricular rate (AV block plus ventricular pacemaker at 80 bpm). Methods and Results—CHF induced by 5 weeks of rapid ventricular pacing (220 to 240 bpm) increased the duration of AF induced by burst pacing (from 8±4 seconds in control dogs to 535±82 seconds; P<0.01), similar to the effect of 1 week of RAP (713±300 seconds). In contrast to RAP, CHF did not alter atrial refractory period, refractoriness heterogeneity, or conduction velocity at a cycle length of 360 ms; however, CHF dogs had a substantial increase in th...
1,343 citations
TL;DR: Cultured fetal and adult human fibroblasts maintained key features of HOX gene expression patterns established during embryogenesis, suggesting that HOX genes may direct topographic differentiation and underlie the detailed positional memory in fibro Blasts.
Abstract: A fundamental feature of the architecture and functional design of vertebrate animals is a stroma, composed of extracellular matrix and mesenchymal cells, which provides a structural scaffold and conduit for blood and lymphatic vessels, nerves, and leukocytes. Reciprocal interactions between mesenchymal and epithelial cells are known to play a critical role in orchestrating the development and morphogenesis of tissues and organs, but the roles played by specific stromal cells in controlling the design and function of tissues remain poorly understood. The principal cells of stromal tissue are called fibroblasts, a catch-all designation that belies their diversity. We characterized genome-wide patterns of gene expression in cultured fetal and adult human fibroblasts derived from skin at different anatomical sites. Fibroblasts from each site displayed distinct and characteristic transcriptional patterns, suggesting that fibroblasts at different locations in the body should be considered distinct differentiated cell types. Notable groups of differentially expressed genes included some implicated in extracellular matrix synthesis, lipid metabolism, and cell signaling pathways that control proliferation, cell migration, and fate determination. Several genes implicated in genetic diseases were found to be expressed in fibroblasts in an anatomic pattern that paralleled the phenotypic defects. Finally, adult fibroblasts maintained key features of HOX gene expression patterns established during embryogenesis, suggesting that HOX genes may direct topographic differentiation and underlie the detailed positional memory in fibroblasts.
1,055 citations
TL;DR: The two PDGF null phenotypes reveal analogous morphogenetic functions for myofibroblast-type cells in lung and kidney organogenesis, and show that PDGF-B is required in the ontogeny of kidney mesangial cells.
854 citations
TL;DR: TGF-beta induces proliferation of connective tissue cells at low concentrations by stimulating autocrine PDGF-AA secretion, which at higher concentrations of TGF- beta, is decreased by down-regulation of PDGF receptor alpha subunits and perhaps by direct growth inhibition.
760 citations