Abstract 372: The Smad3 Pathway Critically Regulates Myofibroblast Proliferation And Synthetic Activity In Healing Myocardial Infarcts

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Marcin Dobaczewski ◽  
Marcin Bujak ◽  
Carlos Gonzalez ◽  
Na Li ◽  
Xiao-Fan Wang ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Extracellular Matrix ◽  
Proliferative Activity ◽  
Essential Role ◽  
Cardiac Fibroblasts ◽  
Cardiac Fibroblast ◽  
Synthetic Activity ◽  
Dependent Manner ◽  
Tenascin C ◽  
Infarcted Heart

We have recently demonstrated that the Transforming Growth Factor (TGF)-β/Smad3 pathway is activated in healing infarcts and plays an essential role in the pathogenesis of cardiac remodeling. Smad3 −/− mice were protected from the development of ventricular dilation following infarction and exhibited markedly reduced fibrosis of the peri-infarct area and the remodeling non-infarcted heart. Accordingly, we hypothesized that Smad3 signaling plays an essential role in regulating cardiac fibroblast function and gene expression in myocardial infarction. Surprisingly, Smad3 −/− infarcts exhibited increased peak infiltration with myofibroblasts, associated with evidence of enhanced proliferative activity. Smad3 −/− mice had a higher density of Ki-67-positive proliferating myofibroblasts in the infarcted myocardium in comparison with wildtype (WT) animals (Smad3−/− 917±291 cells/mm 2 vs. WT 614±115 cells/mm 2 , p<0.05). In vitro experiments suggested that TGF-β inhibits murine cardiac fibroblast proliferation in a concentration-dependent manner and that the antiproliferative effects of TGF-β are abrogated in Smad3 −/− fibroblasts. On the other hand Smad3 signaling was essential for extracellular matrix protein synthesis by cardiac fibroblasts. TGF-β-mediated induction of procollagen type III and of the matricellular protein tenascin-C in cardiac fibroblasts was dependent on Smad3. In addition, TGF-β-induced Tissue Inhibitor of Metalloproteinases (TIMP)-1 and -2 upregulation was also abrogated in Smad3 −/− fibroblasts, suggesting that Smad3 signaling regulates matrix metabolism. In vivo, Smad3 −/− infarcts exhibited attenuated tenascin-C and collagen deposition in the infarct and in the remodeling non-infarcted heart. Our findings suggest that the Smad3 pathway critically regulates fibroblast function in healing myocardial infarction. In Smad3 −/− mice, the healing infarct contains abundant myofibroblasts that exhibit enhanced proliferative activity, but have markedly decreased ability to synthesize extracellular matrix proteins and to produce TIMPs. In the absence of Smad3, attenuated matrix deposition in the remodeling non-infarcted heart results in decreased dilation and ameliorated diastolic dysfunction. This research has received full or partial funding support from the American Heart Association, AHA South Central Affiliate (Arkansas, New Mexico, Oklahoma & Texas).

scholarly journals Stimulation of cardiac fibroblast Piezo1 channels opposes myofibroblast differentiation and induces IL-6 secretion via Ca2+-mediated p38 MAP kinase activation

2019 ◽  
Author(s):  
Nicola M. Blythe ◽  
Vasili Stylianidis ◽  
Melanie J. Ludlow ◽  
Hamish T. J. Gilbert ◽  
Elizabeth L. Evans ◽  
...  
Keyword(s):  
Map Kinase ◽  
Structural Integrity ◽  
Kinase Inhibitor ◽  
Cardiac Fibroblasts ◽  
Collagen Gel ◽  
Mechanical Stretch ◽  
Cardiac Fibroblast ◽  
Ruthenium Red ◽  
P38 Map Kinase ◽  
Dependent Manner

AbstractPiezo1 is a mechanosensitive cation channel with widespread physiological importance; however its role in the heart is poorly understood. Cardiac fibroblasts are responsible for preserving the structural integrity of the myocardium and play a key role in regulating its repair and remodeling following stress or injury. We investigated expression and function of Piezo1 in cultured human and mouse cardiac fibroblasts. RT-PCR studies confirmed expression ofPiezo1mRNA in cardiac fibroblasts at similar levels to endothelial cells. Fura-2 intracellular Ca2+measurements validated Piezo1 as a functional ion channel that was activated by the Piezo1 agonist, Yoda1. Yoda1-induced Ca2+entry was inhibited by Piezo1 blockers (gadolinium, ruthenium red) and the Ca2+response was reduced proportionally by Piezo1 siRNA knockdown or in cells fromPiezo1+/−mice. Investigation of Yoda1 effects on selected remodeling genes indicated that Piezo1 activation opposed cardiac fibroblast differentiation; data confirmed by functional collagen gel contraction assays. Piezo1 activation using Yoda1 or mechanical stretch also increased the expression of interleukin-6 (IL-6), a mechanosensitive pro-hypertrophic and pro-fibrotic cytokine, in a Piezo1-dependent manner. Multiplex kinase activity profiling combined with kinase inhibitor studies and phospho-specific western blotting, established that Piezo1 activation stimulated IL-6 secretion via a pathway involving p38 MAP kinase, downstream of Ca2+entry. In summary, this study reveals that cardiac fibroblasts express functional Piezo1 channels coupled to reduced myofibroblast activation and increased secretion of paracrine signaling molecules that can modulate cardiac remodeling.

Cardiac Fibroblast Diversity

2020 ◽  
Vol 82 (1) ◽  
pp. 63-78 ◽  
Author(s):  
Michelle D. Tallquist
Keyword(s):  
Extracellular Matrix ◽  
Single Cell ◽  
Future Development ◽  
Cardiac Fibrosis ◽  
Cardiac Fibroblasts ◽  
Pathological Condition ◽  
Cardiac Fibroblast ◽  
Lineage Tracing ◽  
Single Cell Sequencing ◽  
Disease States

Cardiac fibrosis is a pathological condition that occurs after injury and during aging. Currently, there are limited means to effectively reduce or reverse fibrosis. Key to identifying methods for curbing excess deposition of extracellular matrix is a better understanding of the cardiac fibroblast, the cell responsible for collagen production. In recent years, the diversity and functions of these enigmatic cells have been gradually revealed. In this review, I outline current approaches for identifying and classifying cardiac fibroblasts. An emphasis is placed on new insights into the heterogeneity of these cells as determined by lineage tracing and single-cell sequencing in development, adult, and disease states. These recent advances in our understanding of the fibroblast provide a platform for future development of novel therapeutics to combat cardiac fibrosis.

scholarly journals Normal versus Pathological Cardiac Fibroblast-Derived Extracellular Matrix Differentially Modulates Cardiosphere-Derived Cell Paracrine Properties and Commitment

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Francesca Pagano ◽  
Francesco Angelini ◽  
Clotilde Castaldo ◽  
Vittorio Picchio ◽  
Elisa Messina ◽  
...  
Keyword(s):  
Gene Expression ◽  
Extracellular Matrix ◽  
Immunofluorescence Microscopy ◽  
Cardiac Fibroblasts ◽  
Cardiac Fibroblast ◽  
Cardiac Cells ◽  
Cardiac Progenitor Cells ◽  
Therapeutic Success ◽  
Differentiation Potential ◽  
Heart Failure Progression

Human resident cardiac progenitor cells (CPCs) isolated as cardiosphere-derived cells (CDCs) are under clinical evaluation as a therapeutic product for cardiac regenerative medicine. Unfortunately, limited engraftment and differentiation potential of transplanted cells significantly hamper therapeutic success. Moreover, maladaptive remodelling of the extracellular matrix (ECM) during heart failure progression provides impaired biological and mechanical signals to cardiac cells, including CPCs. In this study, we aimed at investigating the differential effect on the phenotype of human CDCs of cardiac fibroblast-derived ECM substrates from healthy or diseased hearts, named, respectively, normal or pathological cardiogel (CG-N/P). After 7 days of culture, results show increased levels of cardiogenic gene expression (NKX2.5, CX43) on both decellularized cardiogels compared to control, while the proportion and staining patterns of GATA4, OCT4, NKX2.5, ACTA1, VIM, and CD90-positive CPCs were not affected, as assessed by immunofluorescence microscopy and flow cytometry analyses. Nonetheless, CDCs cultured on CG-N secreted significantly higher levels of osteopontin, FGF6, FGF7, NT-3, IGFBP4, and TIMP-2 compared to those cultured on CG-P, suggesting overall a reduced trophic and antiremodelling paracrine profile of CDCs when in contact with ECM from pathological cardiac fibroblasts. These results provide novel insights into the bidirectional interplay between cardiac ECM and CPCs, potentially affecting CPC biology and regenerative potential.

scholarly journals Cardiac Fibroblasts and the Extracellular Matrix in Regenerative and Nonregenerative Hearts

2019 ◽  
Vol 6 (3) ◽  
pp. 29 ◽  
Author(s):  
Luis Hortells ◽  
Anne Katrine Z. Johansen ◽  
Katherine E. Yutzey
Keyword(s):  
Extracellular Matrix ◽  
Collagen Fiber ◽  
Cellular Proliferation ◽  
Cardiac Fibroblasts ◽  
Postnatal Period ◽  
Cardiac Fibroblast ◽  
Scar Formation ◽  
Cardiac Cells ◽  
Fiber Organization

During the postnatal period in mammals, the heart undergoes significant remodeling and cardiac cells progressively lose their embryonic characteristics. At the same time, notable changes in the extracellular matrix (ECM) composition occur with a reduction in the components considered facilitators of cellular proliferation, including fibronectin and periostin, and an increase in collagen fiber organization. Not much is known about the postnatal cardiac fibroblast which is responsible for producing the majority of the ECM, but during the days after birth, mammalian hearts can regenerate after injury with only a transient scar formation. This phenomenon has also been described in adult urodeles and teleosts, but relatively little is known about their cardiac fibroblasts or ECM composition. Here, we review the pre-existing knowledge about cardiac fibroblasts and the ECM during the postnatal period in mammals as well as in regenerative environments.

MiR-150 Attenuates Maladaptive Cardiac Remodeling Mediated by Long Noncoding RNA MIAT and Directly Represses Profibrotic Hoxa4

2022 ◽  
Author(s):  
Tatsuya Aonuma ◽  
Bruno Moukette ◽  
Satoshi Kawaguchi ◽  
Nipuni P. Barupala ◽  
Marisa N. Sepúlveda ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Cardiac Remodeling ◽  
Long Noncoding Rna ◽  
Noncoding Rna ◽  
Molecular Mechanisms ◽  
Cardiac Fibroblasts ◽  
Cardiac Fibroblast ◽  
Null Mouse ◽  
Increased Risk

Background: MicroRNA-150 (miR-150) plays a protective role in heart failure (HF). Long noncoding RNA, myocardial infarction–associated transcript (MIAT) regulates miR-150 function in vitro by direct interaction. Concurrent with miR-150 downregulation, MIAT is upregulated in failing hearts, and gain-of-function single-nucleotide polymorphisms in MIAT are associated with increased risk of myocardial infarction (MI) in humans. Despite the correlative relationship between MIAT and miR-150 in HF, their in vivo functional relationship has never been established, and molecular mechanisms by which these 2 noncoding RNAs regulate cardiac protection remain elusive. Methods: We use MIAT KO (knockout), Hoxa4 (homeobox a4) KO, MIAT TG (transgenic), and miR-150 TG mice. We also develop DTG (double TG) mice overexpressing MIAT and miR-150. We then use a mouse model of MI followed by cardiac functional, structural, and mechanistic studies by echocardiography, immunohistochemistry, transcriptome profiling, Western blotting, and quantitative real-time reverse transcription-polymerase chain reaction. Moreover, we perform expression analyses in hearts from patients with HF. Lastly, we investigate cardiac fibroblast activation using primary adult human cardiac fibroblasts and in vitro assays to define the conserved MIAT/miR-150/HOXA4 axis. Results: Using novel mouse models, we demonstrate that genetic overexpression of MIAT worsens cardiac remodeling, while genetic deletion of MIAT protects hearts against MI. Importantly, miR-150 overexpression attenuates the detrimental post-MI effects caused by MIAT. Genome-wide transcriptomic analysis of MIAT null mouse hearts identifies Hoxa4 as a novel downstream target of the MIAT/miR-150 axis. Hoxa4 is upregulated in cardiac fibroblasts isolated from ischemic myocardium and subjected to hypoxia/reoxygenation. HOXA4 is also upregulated in patients with HF. Moreover, Hoxa4 deficiency in mice protects the heart from MI. Lastly, protective actions of cardiac fibroblast miR-150 are partially attributed to the direct and functional repression of profibrotic Hoxa4 . Conclusions: Our findings delineate a pivotal functional interaction among MIAT, miR-150, and Hoxa4 as a novel regulatory mechanism pertinent to ischemic HF.

scholarly journals Identification of Human CD4+ Sub-population of Resident Cardiac Fibroblasts Linked to Inflammation-Mediated Cardiac Fibrosis

2021 ◽  
Author(s):  
Jamila H Siamwala ◽  
Francesco Pagano ◽  
Patrycja M Dubielecka ◽  
Alexander Zhao ◽  
Sonja Chen ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
T Cell ◽  
Right Ventricle ◽  
Cardiac Fibrosis ◽  
Cardiac Fibroblasts ◽  
Interleukin 1 ◽  
Cardiac Fibroblast ◽  
Mass Cytometry ◽  
Phenotype Switching ◽  
Cardiac Myofibroblasts

Background: Infiltration with inflammatory CD4+ T-cells and the accumulation of heterogeneous cardiac myofibroblasts are hallmarks of cardiac fibrosis and remodeling. The origin, identity, states, and functions of the resident cells involved in the transition from adaptive to maladaptive fibrotic remodeling, as well as the pathways of inflammatory regulation are unclear. Methods: We performed mass cytometry profiling of resident human ventricular cardiac fibroblasts (hVCF) and determined the identity of cells contained in fibrotic right ventricle autopsy tissues from individuals diagnosed with pulmonary hypertension and tissue from SUGEN/hypoxia rats exhibiting cardiac fibrosis. We further characterized the resident cardiac fibroblast sub-population morphologically, structurally and functionally using transcriptome and secretome analysis of the secreted cytokines, chemokines, proteins, metabolites using milliplex panels, proteomics and metabolomics pipelines. Results: Single-cell mass cytometry identified remarkable plasticity of resident human cardiac fibroblasts. We provide evidence of a sub-population of resident cardiac myofibroblasts expressing high levels of CD4+, a helper T-cell surface marker in addition to mesenchymal markers, αSMA and Vimentin in all the human donors. These cardiac cells co-expressing lymphoid CD4+and αSMA+ were localized to the fibrotic regions of the human right ventricular tissue and were a common feature in the interstitial and perivascular lesions of SUGEN/Hypoxia (SuHx) rats. CD3+CD4+ T-cell numbers were higher in the right ventricle compared with the left ventricle of SuHx, as determined by flow cytometry. In vitro, T-cell homing receptors CD44, Interleukin-1 receptor (IL-1R), and CCR2 were upregulated in cardiac fibroblasts in response to IL-1β. Exposure of cardiac fibroblasts to IL-1β led to upregulation of genes regulating extracellular matrix, collagen deposition and inflammation-related genes, and induced secretion of cytokines, chemokines, and metabolites involved in innate and adaptive humoral immune responses. Cell clustering, elevated phosphorylation of MAPK p38 and inflammatory NF-κB p65 and cell phenotype switching upon IL-1β stimulation reverted with the administration of an IL-1R antagonist. Conclusions: Our data expand concepts of heterogeneity of resident cardiac fibroblasts and plasticity in response to pro-inflammatory cytokines by the demonstration of a unique subpopulation of cardiac fibroblasts exhibiting attributes of both mesenchymal and lymphoid cells. Exposure of cardiac fibroblasts to the pro-inflammatory cytokine, IL-1β, induces a robust phenotypic response linked to extracellular matrix deposition and up-regulates an immune-associated phenotype linked to expression of immune markers and secretion of immunomodulatory cytokines and chemokines. We also propose that resident cardiac fibroblast transdifferentiation and phenotype switching maybe the key process involved in adaptive to maladaptive remodeling leading to fibrosis and failure. Non-standard abbreviations: CD4; Cluster of differentiation, αSMA; alpha smooth muscle actin, IL-1R; Interleukin-1-receptor, CCR2; C-X-C Motif Chemokine Receptor 2

Matrix metalloproteinase-2 stimulates collagen-I expression through phosphorylation of focal adhesion kinase in rat cardiac fibroblasts

2012 ◽  
Vol 303 (9) ◽  
pp. C947-C953 ◽  
Author(s):  
Yasutomo Hori ◽  
Takashige Kashimoto ◽  
Tomohiro Yonezawa ◽  
Naoya Sano ◽  
Ryuta Saitoh ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Matrix Metalloproteinase ◽  
Focal Adhesion Kinase ◽  
Focal Adhesion ◽  
Cardiac Fibroblasts ◽  
Primary Cultures ◽  
Collagen I ◽  
Matrix Metalloproteinase 2 ◽  
Dependent Manner ◽  
Simultaneous Treatment

Collagen-I is thought to be the main component of the extracellular matrix in cardiac fibrosis, the accumulation of which occurs with excessive activation of matrix metalloproteinase-2 (MMP-2). MMP-2 degrades the extracellular matrix; however, the relative importance of MMP-2 to collagen-I synthesis in cardiac fibroblasts remains unclear. We investigated whether extracellular activation of MMP-2 regulates collagen-I synthesis and phosphorylation of focal adhesion kinase (FAK) in rat cardiac fibroblasts. Primary cultures of rat cardiac fibroblasts were incubated with purified active MMP-2 to determine whether extracellular MMP-2 affects collagen-I synthesis and FAK phosphorylation in cardiac fibroblasts. Exogenous MMP-2 significantly stimulated FAK (Tyr397) phosphorylation and induced collagen-I expression in a time-dependent manner. Simultaneous treatment with the FAK inhibitor PF573228 abolished exogenous MMP-2-enhanced FAK (Tyr397) phosphorylation and collagen-I expression. Cells were then stimulated with norepinephrine (NE) to investigate whether endogenous MMP-2 could also induce collagen-I expression through FAK (Tyr397) phosphorylation. NE-stimulated endogenous MMP-2 activation in conditioned medium was significantly attenuated by simultaneous treatment with the MMP inhibitor PD166793. Similarly, NE-induced FAK (Tyr397) phosphorylation and collagen-I expression were significantly inhibited by simultaneous treatment with PD166793 or PF573228. Furthermore, MMP-2 knockdown induced by small interfering RNA (siRNA) significantly abolished endogenous MMP-2 expression and activation. MMP-2 siRNA significantly abolished NE-induced FAK (Tyr397) phosphorylation and collagen-I expression. These findings suggest that the extracellular activation of MMP-2 accelerated collagen-I synthesis in rat cardiac fibroblasts and that FAK phosphorylation (Tyr397) plays a pivotal role in MMP-2-stimulated collagen-I synthesis.

Abstract 12519: Regulation of Cardiac Fibroblast Phenotype by Scleraxis

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Rushita Bagchi ◽  
Patricia Roche ◽  
Ronen Schweitzer ◽  
Michael P Czubryt
Keyword(s):  
Extracellular Matrix ◽  
Cardiac Fibroblasts ◽  
Gene Promoter ◽  
Cardiac Fibroblast ◽  
Fiber Formation ◽  
Luciferase Reporter ◽  
Collagen Gels ◽  
Contractile Phenotype ◽  
Extracellular Matrix Components ◽  
E Boxes

Cardiac fibroblasts constitute the primary extracellular matrix synthesis machinery in the myocardium. Activation of fibroblasts into a hyper-synthetic and contractile phenotype potentiates fibrosis, impairs cardiac function and contributes to heart failure. Our laboratory previously reported that the transcription factor scleraxis regulates human cardiac collagen Iα2 expression and has shown its up-regulation in the post-infarct scar. Here we demonstrate a novel regulatory role for scleraxis in governing cardiac fibroblast function and phenoconversion. Cell contractility assays using collagen gels demonstrated the abrogation of pro-fibrotic TGF-β-mediated contractility of myofibroblasts in response to scleraxis knockdown. The de novo expression of α-smooth muscle actin (αSMA) and its incorporation into stress fibers is a key feature of myofibroblasts - key causative cells of fibrosis. Scleraxis over-expression in isolated primary cardiac fibroblasts induced αSMA gene expression and stress fiber formation, and rescued the αSMA loss observed in cardiac fibroblasts from scleraxis null mice. Luciferase reporter assays demonstrated a significant transactivation of the αSMA gene promoter by scleraxis. Mutation analysis revealed that scleraxis interacts with two E-boxes within the αSMA promoter, a finding confirmed by chromatin immunoprecipitation of scleraxis in primary cardiac fibroblasts. An increase in scleraxis binding to the αSMA promoter was observed in cardiac myofibroblasts compared to fibroblasts, and also in response to TGF-β, further supporting a direct role of scleraxis in regulation of myofibroblast αSMA expression and its contractile phenotype. Gel shift assays also confirmed the direct interaction of scleraxis with E-boxes within the αSMA gene promoter. Our data indicates that scleraxis plays a required role in cardiac fibroblast phenotype and contractile function. Taken in context with our finding that scleraxis regulates expression of multiple extracellular matrix components, including fibrillar collagens, our data reveals that scleraxis exerts broad and potent pro-fibrotic effects on cardiac fibroblast form and function, and may thus represent a novel target for fibrosis therapy.

scholarly journals Helix-Loop-Helix Protein p8, a Transcriptional Regulator Required for Cardiomyocyte Hypertrophy and Cardiac Fibroblast Matrix Metalloprotease Induction

2006 ◽  
Vol 27 (3) ◽  
pp. 993-1006 ◽  
Author(s):  
Sandro Goruppi ◽  
Richard D. Patten ◽  
Thomas Force ◽  
John M. Kyriakis
Keyword(s):  
Heart Failure ◽  
Ventricular Remodeling ◽  
Cardiac Fibroblasts ◽  
Cardiac Fibroblast ◽  
Matrix Metalloproteases ◽  
Cardiomyocyte Hypertrophy ◽  
Matrix Remodeling ◽  
Dependent Manner ◽  
Helix Loop Helix ◽  
Cellular Events

ABSTRACT Cardiomyocyte hypertrophy and extracellular matrix remodeling, primarily mediated by inflammatory cytokine-stimulated cardiac fibroblasts, are critical cellular events in cardiac pathology. The molecular components governing these processes remain nebulous, and few genes have been linked to both hypertrophy and matrix remodeling. Here we show that p8, a small stress-inducible basic helix-loop-helix protein, is required for endothelin- and α-adrenergic agonist-induced cardiomyocyte hypertrophy and for tumor necrosis factor-stimulated induction, in cardiac fibroblasts, of matrix metalloproteases (MMPs) 9 and 13—MMPs linked to general inflammation and to adverse ventricular remodeling in heart failure. In a stimulus-dependent manner, p8 associates with chromatin containing c-Jun and with the cardiomyocyte atrial natriuretic factor (anf) promoter and the cardiac fibroblast mmp9 and mmp13 promoters, established activator protein 1 effectors. p8 is also induced strongly in the failing human heart by a process reversed upon therapeutic intervention. Our results identify an unexpectedly broad involvement for p8 in key cellular events linked to cardiomyocyte hypertrophy and cardiac fibroblast MMP production, both of which occur in heart failure.

scholarly journals Targeting 5-HT 2B Receptor Signaling Prevents Border Zone Expansion and Improves Microstructural Remodeling after Myocardial Infarction

Circulation ◽  
2021 ◽  
Author(s):  
J. Caleb Snider ◽  
Lance A. Riley ◽  
Noah T. Mallory ◽  
Matthew R. Bersi ◽  
Prachi Umbarkar ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Rna Sequencing ◽  
Cardiac Fibroblasts ◽  
Left Ventricular ◽  
Cardiac Fibroblast ◽  
Scar Formation ◽  
Border Zone ◽  
Ventricular Contractility ◽  
Fibrotic Process

Background: Myocardial infarction (MI) induces an intense injury response which ultimately generates a collagen-dominated scar. While required to prevent ventricular rupture, the fibrotic process is often sustained in a manner detrimental to optimal recovery. Cardiac myofibroblasts are the cells tasked with depositing and remodeling collagen and are a prime target to limit the fibrotic process post-MI. Serotonin 2B receptor (5-HT 2B ) signaling has been shown to be harmful in a variety of cardiopulmonary pathologies and could play an important role in mediating scar formation after MI. Methods: We employed two pharmacologic antagonists to explore the effect of 5-HT 2B inhibition on outcomes post-MI and characterized the histological and microstructural changes involved in tissue remodeling. Inducible, 5-HT 2B ablation driven by Tcf21 MCM and Postn MCM were used to evaluate resident cardiac fibroblast- and myofibroblast-specific contributions of 5-HT 2B , respectively. RNA sequencing was used to motivate subsequent in vitro analyses to explore cardiac fibroblast phenotype. Results: 5-HT 2B antagonism preserved cardiac structure and function by facilitating a less fibrotic scar, indicated by decreased scar thickness and decreased border zone area. 5-HT 2B antagonism resulted in collagen fiber redistribution to thinner collagen fibers which were more anisotropic, enhancing left ventricular contractility, while fibrotic tissue stiffness was decreased, limiting the hypertrophic response of uninjured cardiomyocytes. Using a tamoxifen-inducible Cre, we ablated 5-HT 2B from Tcf21 -lineage resident cardiac fibroblasts and saw similar improvements to the pharmacologic approach. Tamoxifen-inducible Cre-mediated ablation of 5-HT 2B after onset of injury in Postn -lineage myofibroblasts also improved cardiac outcomes. RNA sequencing and subsequent in vitro analyses corroborate a decrease in fibroblast proliferation, migration, and remodeling capabilities through alterations in Dnajb4 expression and Src phosphorylation. Conclusions: Together, our findings illustrate that 5-HT 2B expression in either cardiac fibroblasts or activated myofibroblasts directly contributes to excessive scar formation, resulting in adverse remodeling and impaired cardiac function after MI.

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