Fibroblast-specific TGF-β signaling mediates cardiac dysfunction, fibrosis, and hypertrophy in obese diabetic mice.

Aims: Transforming growth factor (TGF)-β is up-regulated in the diabetic myocardium and may mediate fibroblast activation. We aimed at examining the role of TGF-β-induced fibroblast activation in the pathogenesis of diabetic cardiomyopathy.

Methods And Results: We generated lean and obese db/db mice with fibroblast-specific loss of TbR2, the Type 2 receptor-mediating signaling through all three TGF-β isoforms, and mice with fibroblast-specific Smad3 disruption.

Macrophages in the infarcted heart acquire a fibrogenic phenotype, expressing matricellular proteins, but do not undergo fibroblast conversion.

Although some studies have suggested that macrophages may secrete structural collagens, and convert to fibroblast-like cells, macrophage to fibroblast transdifferentiation in infarcted and remodeling hearts remains controversial. Our study uses linage tracing approaches and single cell transcriptomics to examine whether macrophages undergo fibroblast conversion, and to characterize the extracellular matrix expression profile of myeloid cells in myocardial infarction. To examine whether infarct macrophages undergo fibroblast conversion, we identified macrophage-derived progeny using the inducible CX3CR1 mice crossed with the PDGFRα reporter line for reliable fibroblast identification.

Fibroblast Smad7 Induction Protects the Remodeling Pressure-Overloaded Heart.

Background: Cardiac fibroblast activation contributes to adverse remodeling, fibrosis, and dysfunction in the pressure-overloaded heart. Although early fibroblast TGF-β (transforming growth factor-β)/Smad (small mother against decapentaplegic)-3 activation protects the pressure-overloaded heart by preserving the matrix, sustained TGF-β activation is deleterious, accentuating fibrosis and dysfunction. Thus, endogenous mechanisms that negatively regulate the TGF-β response in fibroblasts may be required to protect from progressive fibrosis and adverse remodeling.

Protective effects of macrophage-specific integrin α5 in myocardial infarction are associated with accentuated angiogenesis.

Macrophages sense changes in the extracellular matrix environment through the integrins and play a central role in regulation of the reparative response after myocardial infarction. Here we show that macrophage integrin α5 protects the infarcted heart from adverse remodeling and that the protective actions are associated with acquisition of an angiogenic macrophage phenotype. We demonstrate that myeloid cell- and macrophage-specific integrin α5 knockout mice have accentuated adverse post-infarction remodeling, accompanied by reduced angiogenesis in the infarct and border zone.

BAK contributes critically to necrosis and infarct generation during reperfused myocardial infarction.

At least seven cell death programs are activated during myocardial infarction (MI), but which are most important in causing heart damage is not understood. Two of these programs are mitochondrial-dependent necrosis and apoptosis. The canonical function of the pro-cell death BCL-2 family proteins BAX and BAK is to mediate permeabilization of the outer mitochondrial membrane during apoptosis allowing apoptogen release.

Diabetes Induces Cardiac Fibroblast Activation, Promoting a Matrix-Preserving Nonmyofibroblast Phenotype, Without Stimulating Pericyte to Fibroblast Conversion.

Background Interstitial and perivascular fibrosis may contribute to diabetes-associated heart failure. Pericytes can convert to fibroblasts under conditions of stress and have been implicated in the pathogenesis of fibrotic diseases. We hypothesized that in diabetic hearts, pericytes may convert to fibroblasts, contributing to fibrosis and to the development of diastolic dysfunction.

Differential effects of Smad2 and Smad3 in regulation of macrophage phenotype and function in the infarcted myocardium.

TGF-βs regulate macrophage responses, by activating Smad2/3. We have previously demonstrated that macrophage-specific Smad3 stimulates phagocytosis and mediates anti-inflammatory macrophage transition in the infarcted heart. However, the role of macrophage Smad2 signaling in myocardial infarction remains unknown.

The role of endogenous Smad7 in regulating macrophage phenotype following myocardial infarction.

Smad7 restrains TGF-β responses, and has been suggested to exert both pro- and anti-inflammatory actions that may involve effects on macrophages. Myocardial infarction triggers a macrophage-driven inflammatory response that not only plays a central role in cardiac repair, but also contributes to adverse remodeling and fibrosis. We hypothesized that macrophage Smad7 expression may regulate inflammation and fibrosis in the infarcted heart through suppression of TGF-β responses, or via TGF-independent actions.

Properties and Functions of Fibroblasts and Myofibroblasts in Myocardial Infarction.

The adult mammalian heart contains abundant interstitial and perivascular fibroblasts that expand following injury and play a reparative role but also contribute to maladaptive fibrotic remodeling. Following myocardial infarction, cardiac fibroblasts undergo dynamic phenotypic transitions, contributing to the regulation of inflammatory, reparative, and angiogenic responses. This review manuscript discusses the mechanisms of regulation, roles and fate of fibroblasts in the infarcted heart.

Smad7 effects on TGF-β and ErbB2 restrain myofibroblast activation and protect from postinfarction heart failure.

Repair of the infarcted heart requires TGF-β/Smad3 signaling in cardiac myofibroblasts. However, TGF-β-driven myofibroblast activation needs to be tightly regulated in order to prevent excessive fibrosis and adverse remodeling that may precipitate heart failure. We hypothesized that induction of the inhibitory Smad, Smad7, may restrain infarct myofibroblast activation, and we examined the molecular mechanisms of Smad7 actions.

Collagen denaturation in the infarcted myocardium involves temporally distinct effects of MT1-MMP-dependent proteolysis and mechanical tension.

Tissue injury results in profound alterations in the collagen network, associated with unfolding of the collagen triple helix, proteolytic degradation and generation of fragments. In the infarcted myocardium, changes in the collagen network are critically involved in the pathogenesis of left ventricular rupture, adverse remodeling and chronic dysfunction. We hypothesized that myocardial infarction is associated with temporally and spatially restricted patterns of collagen denaturation that may reflect distinct molecular mechanisms of collagen unfolding.

The role of Smad signaling cascades in cardiac fibrosis.

Most myocardial pathologic conditions are associated with cardiac fibrosis, the expansion of the cardiac interstitium through deposition of extracellular matrix (ECM) proteins. Although replacement fibrosis plays a reparative role after myocardial infarction, excessive, unrestrained or dysregulated myocardial ECM deposition is associated with ventricular dysfunction, dysrhythmias and adverse prognosis in patients with heart failure. The members of the Transforming Growth Factor (TGF)-β superfamily are critical regulators of cardiac repair, remodeling and fibrosis.

Inflammatory Cytokines and Chemokines as Therapeutic Targets in Heart Failure.

Heart failure exhibits remarkable pathophysiologic heterogeneity. A large body of evidence suggests that regardless of the underlying etiology, heart failure is associated with induction of cytokines and chemokines that may contribute to the pathogenesis of adverse remodeling, and systolic and diastolic dysfunction. The pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1, and IL-6 have been extensively implicated in the pathogenesis of heart failure.

Validation of diagnostic criteria and histopathological characterization of cardiac rupture in the mouse model of nonreperfused myocardial infarction.

In patients with myocardial infarction (MI), cardiac rupture is an uncommon but catastrophic complication. In the mouse model of nonreperfused MI, reported rupture rates are highly variable and depend not only on the genetic background and sex of animals but also on the method used for documentation of rupture. In most studies, diagnosis of cardiac rupture is based on visual inspection during autopsy; however, criteria are poorly defined.

The role of Smad2 and Smad3 in regulating homeostatic functions of fibroblasts in vitro and in adult mice.

The heart contains an abundant fibroblast population that may play a role in homeostasis, by maintaining the extracellular matrix (ECM) network, by regulating electrical impulse conduction, and by supporting survival and function of cardiomyocytes and vascular cells. Despite an explosion in our understanding of the role of fibroblasts in cardiac injury, the homeostatic functions of resident fibroblasts in adult hearts remain understudied. TGF-β-mediated signaling through the receptor-activated Smads, Smad2 and Smad3 critically regulates fibroblast function.

Macrophage Smad3 Protects the Infarcted Heart, Stimulating Phagocytosis and Regulating Inflammation.

Rationale: TGF (transforming growth factor)-β is critically involved in myocardial injury, repair, and fibrosis, activating both Smad (small mothers against decapentaplegic)-dependent and non-Smad pathways. The in vivo role of TGF-β signaling in regulation of macrophage function is poorly understood. We hypothesized that in the infarcted myocardium, activation of TGF-β/Smad signaling in macrophages may regulate repair and remodeling.

Protective Effects of Activated Myofibroblasts in the Pressure-Overloaded Myocardium Are Mediated Through Smad-Dependent Activation of a Matrix-Preserving Program.

Rationale: The heart contains abundant interstitial and perivascular fibroblasts. Traditional views suggest that, under conditions of mechanical stress, cytokines, growth factors, and neurohumoral mediators stimulate fibroblast activation, inducing ECM (extracellular matrix) protein synthesis and promoting fibrosis and diastolic dysfunction. Members of the TGF (transforming growth factor)-β family are upregulated and activated in the remodeling myocardium and modulate phenotype and function of all myocardial cell types through activation of intracellular effector molecules, the Smads (small mothers against decapentaplegic), and through Smad-independent pathways.