In healing myocardial infarction, myofibroblast- and cardiomyocyte-specific activation of Smad3 has contrasting functional outcomes that may involve activation of an integrin/reactive oxygen axis.

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. Objective: To investigate the role of macrophage-specific TGF-β Smad3 signaling in a mouse model of myocardial infarction and to dissect the mechanisms mediating Smad-dependent modulation of macrophage function. Methods and Results: TGF-βs markedly activated Smad3 in macrophages, without affecting Smad-independent pathways. Phagocytosis rapidly and directly activated macrophage Smad3, in the absence of active TGF-β release. MyS3KO (myeloid cell–specific Smad3 knockout) mice had no baseline defects but exhibited increased late mortality and accentuated dilative postmyocardial infarction remodeling. Adverse outcome in infarcted MyS3KO mice was associated with perturbations in phagocytic activity, defective transition of macrophages to an anti-inflammatory phenotype, scar expansion, and accentuated apoptosis of border zone cardiomyocytes. In vitro, Smad3 null macrophages exhibited reduced expression of genes associated with eat-me signals, such as Mfge8 (milk fat globule-epidermal growth factor factor 8), and reduced capacity to produce the anti-inflammatory mediators IL (interleukin)-10 and TGF-β1, and the angiogenic growth factor VEGF (vascular endothelial growth factor). Mfge8 partly rescued the phagocytic defect of Smad3 null macrophages, without affecting inflammatory activity. Impaired anti-inflammatory actions of Smad3 null macrophages were associated with marked attenuation of phagocytosis-induced PPAR (peroxisome proliferator-activated receptor) expression. MyS3KO mice had no significant alterations in microvascular density and interstitial fibrosis in remodeling myocardial segments. Conclusions: We demonstrate that Smad3 critically regulates function of infarct macrophages, by mediating acquisition of a phagocytic phenotype and by contributing to anti-inflammatory transition. Smad3-dependent actions in macrophages protect the infarcted heart from adverse remodeling.

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 extracellular matrix protein synthesis, and promoting fibrosis and diastolic dysfunction. Members of the Transforming Growth Factor (TGF)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, and through Smad-independent pathways. Objectives: To examine the role of fibroblast-specific TGF-β/Smad3 signaling in the remodeling pressure-overloaded myocardium. Methods and Results: We examined the effects of cell-specific Smad3 loss in activated periostin-expressing myofibroblasts using a mouse model of cardiac pressure overload, induced through transverse aortic constriction (TAC). Surprisingly, myofibroblast-specific Smad3 knockout (FS3KO) mice exhibited accelerated systolic dysfunction following pressure overload, evidenced by an early 40% reduction in ejection fraction after 7 days of TAC. Accelerated systolic dysfunction in pressure-overloaded FS3KO mice was associated with accentuated matrix degradation and generation of collagen-derived matrikines, accompanied by cardiomyocyte myofibrillar loss and apoptosis, and by enhanced macrophage-driven inflammation. In vitro, TGF-β1, TGF-β2 and TGF-β3 stimulated a Smad3-dependent matrix-preserving phenotype in cardiac fibroblasts, suppressing matrix metalloproteinase (MMP)3 and MMP8 synthesis and inducing tissue inhibitor of metalloproteinases (TIMP)1. In vivo, administration of an MMP8 inhibitor attenuated early systolic dysfunction in pressure-overloaded FS3KO mice, suggesting that the protective effects of activated cardiac myofibroblasts in the pressure-overloaded myocardium are,

The immune system plays a critical role in both repair and remodeling of the infarcted myocardium. Danger signals released by dying cardiomyocytes mobilize, recruit, and activate immune cells, triggering an inflammatory reaction. CXC chemokines containing the ELR motif attract neutrophils, while CC chemokines mediate recruitment of mononuclear cell subpopulations, contributing to clearance of the infarct from dead cells and matrix debris. Immune cell subsets also participate in suppression and containment of the postinfarction inflammatory response by secreting anti-inflammatory mediators, such as IL-10 and TGF-β. As proinflammatory signaling is suppressed, macrophage subpopulations, mast cells and lymphocytes, activate fibrogenic and angiogenic responses, contributing to scar formation. In the viable remodeling myocardium, chronic activation of immune cells may promote fibrosis and hypertrophy. This review discusses the role of immune cells in repair and remodeling of the infarcted myocardium. Understanding the role of immune cells in myocardial infarction is critical for the development of therapeutic strategies aimed at protecting the infarcted heart from adverse remodeling. Moreover, modulation of immune cell phenotype may be required in order to achieve the visionary goal of myocardial regeneration.

No abstract

No abstract

TGF-βs regulate fibroblast responses, by activating Smad2 or Smad3 signaling, or via Smad independent pathways. We have previously demonstrated that myofibroblast-specific Smad3 is critically implicated in repair of the infarcted heart. However, the role of fibroblast Smad2 in myocardial infarction remains unknown. This study investigates the role of myofibroblast specific Smad2 signaling in myocardial infarction, and explores the mechanisms responsible for the distinct effects of Smad2 and Smad3. In a mouse model of non-reperfused myocardial infarction, Smad2 activation in infarct myofibroblasts peaked 7 days after coronary occlusion. In vitro, TGF-β1, -β2 and -β3, but not angiotensin 2 and bone morphogenetic proteins-2, −4 and −7, activated fibroblast Smad2. Myofibroblast-specific Smad2 and Smad3 knockout mice (FS2KO, FS3KO) and corresponding control littermates underwent non-reperfused infarction. In contrast to the increase in rupture rates and adverse remodeling in FS3KO mice, FS2KO animals had mortality comparable to Smad2 fl/fl controls, and exhibited a modest but transient improvement in dysfunction after 7 days of coronary occlusion. At the 28 day timepoint, FS2KO and Smad2 fl/fl mice had comparable adverse remodeling. Although both FS3KO and FS2KO animals had increased myofibroblast density in the infarct, only FS3KO mice exhibited impaired scar organization, associated with perturbed alignment of infarct myofibroblasts. In vitro, Smad3 but not Smad2 knockdown downmodulated fibroblast α2 and α5 integrin expression. Moreover, Smad3 knockdown reduced expression of the GTPase RhoA, whereas Smad2 knockdown markedly increased fibroblast RhoA levels. Smad3-dependent integrin expression may be important for fibroblast activation, whereas RhoA may transduce planar cell polarity pathway signals, essential for fibroblast alignment. Myofibroblast-specific Smad3, but not Smad2 is required for formation of aligned myofibroblast arrays in the infarct. The distinct in vivo effects of myofibroblast Smad2 and Smad3 may involve Smad3-dependent integrin synthesis, and contrasting effects of Smad2 and Smad3 on RhoA expression.

Type 2 diabetes mellitus (T2DM) has insulin resistance (IR) or reduced β-cell mass, partially due to an increased β-cell apoptosis rate. Pancreatic stone protein/regenerating protein (PSP/reg) is a secretory protein produced in the pancreas and up-regulated dramatically during pancreatic disease. Recent studies revealed that β-cells undergoing apoptosis induce PSP/reg expression in surviving neighboring cells. Further experiments demonstrated that PSP/reg was elevated during disease progression in type 1 diabetes mellitus (T1DM). However, the association between PSP/reg and T2DM patients is unknown. The aim of this pilot study was to investigate PSP/reg in different clinical stages of T2DM and evaluate its correlation with chronic complications of diabetes. A total of 1,121 participants (479 males, 642 females; age range 23-80 years) were enrolled in this study. PSP/reg serum values were measured by a newly developed enzyme-linked immunosorbent assay (ELISA). We analyzed its correlation with clinical and biochemical parameters in subjects with T2DM at different clinical phases. Statistical analyses were conducted using SPSS 17.0 software. Correlations of PSP/reg and clinical parameters were performed using Spearman's rank correlation coefficient. Differences between groups were determined by Nemenyi test. PSP/reg was elevated in high-risk and impaired glucose regulation (IGR) patients (p<0.05). PSP/reg was significantly up-regulated in newly diagnosed T2DM patients and long-term diabetes patients with complications (p<0.001). PSP/reg levels correlated with the duration of diabetes (p<0.001). The area under the curve (AUC) for presence of diabetes-onset and its chronic complications was 0.640 and 0.754, respectively. PSP/reg is significantly up-regulated in T2DM patients, and PSP/reg levels are related to the duration of diabetes. Therefore, PSP/reg might be useful as a predictor of T2DM and disease progression.