BACKGROUND: Pericytes have been implicated in tissue repair, remodeling, and fibrosis. Although the mammalian heart contains abundant pericytes, their fate and involvement in myocardial disease remains unknown. METHODS: We used NG2 Dsred ;PDGFRα EGFP pericyte:fibroblast dual reporter mice and inducible NG2 CreER mice to study the fate and phenotypic modulation of pericytes in myocardial infarction. The transcriptomic profile of pericyte-derived cells was studied using polymerase chain reaction arrays and single-cell RNA sequencing. The role of transforming growth factor–β (TGF-β) signaling in regulation of pericyte phenotype was investigated in vivo using pericyte-specific TGF-β receptor 2 knockout mice and in vitro using cultured human placental pericytes. RESULTS: In normal hearts, neuron/glial antigen 2 (NG2) and platelet-derived growth factor receptor α (PDGFRα) identified distinct nonoverlapping populations of pericytes and fibroblasts, respectively. After infarction, a population of cells expressing both pericyte and fibroblast markers emerged. Lineage tracing demonstrated that in the infarcted region, a subpopulation of pericytes exhibited transient expression of fibroblast markers. Pericyte-derived cells accounted for ~4% of PDGFRα+ infarct fibroblasts during the proliferative phase of repair. Pericyte-derived fibroblasts were overactive, expressing higher levels of extracellular matrix genes, integrins, matricellular proteins, and growth factors, when compared with fibroblasts from other cellular sources. Another subset of pericytes contributed to infarct angiogenesis by forming a mural cell coat, stabilizing infarct neovessels. Single-cell RNA sequencing showed that NG2 lineage cells diversify after infarction and exhibit increased expression of matrix genes, and a cluster with high expression of fibroblast identity markers emerges. Trajectory analysis suggested that diversification of infarct pericytes may be driven by proliferating cells. In vitro and in vivo studies identified TGF-β as a potentially causative mediator in fibrogenic activation of infarct pericytes. However, pericyte-specific TGF-β receptor 2 disruption had no significant effects on infarct myofibroblast infiltration and collagen deposition. Pericyte-specific TGF-β signaling was involved in vascular maturation, mediating formation of a mural cell coat investing infarct neovessels and protecting from dilative remodeling. CONCLUSIONS: In the healing infarct, cardiac pericytes upregulate expression of fibrosis-associated genes, exhibiting matrix-synthetic and matrix-remodeling profiles. A fraction of infarct pericytes exhibits expression of fibroblast identity markers. Pericyte-specific TGF-β signaling plays a central role in maturation of the infarct vasculature by protecting from adverse dilative remodeling, but it does not modulate fibrotic remodeling.
The heart contains a population of resident macrophages that markedly expands following injury through recruitment of monocytes and through proliferation of macrophages. In myocardial infarction, macrophages have been implicated in both injurious and reparative responses. In coronary atherosclerotic lesions, macrophages have been implicated in disease progression and in the pathogenesis of plaque rupture. Following myocardial infarction, resident macrophages contribute to initiation and regulation of the inflammatory response. Phagocytosis and efferocytosis are major functions of macrophages during the inflammatory phase of infarct healing, and mediate phenotypic changes, leading to acquisition of an anti-inflammatory macrophage phenotype. Infarct macrophages respond to changes in the cytokine content and extracellular matrix composition of their environment and secrete fibrogenic and angiogenic mediators, playing a central role in repair of the infarcted heart. Macrophages may also play a role in scar maturation and may contribute to chronic adverse remodeling of non-infarcted segments. Single cell studies have revealed a remarkable heterogeneity of macrophage populations in infarcted hearts; however, the relations between transcriptomic profiles and functional properties remain poorly defined. This review manuscript discusses the fate, mechanisms of expansion and activation, and role of macrophages in the infarcted heart. Considering their critical role in injury, repair and remodeling, macrophages are important, but challenging, targets for therapeutic interventions in myocardial infarction.
Background: 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), which are widely used to lower plasma cholesterol levels, have been reported to have various pleiotropic effects such as protective effect of endothelial cells, angiogenic effect, antioxidant effect and anti-inflammatory effect. It is unclear, however, whether statins have any effects on the progression from left ventricular (LV) hypertrophy to heart failure in the established hypertrophied heart. Methods and Results: C57BL/6 mice were treated with pitavastatin (pitava) or vehicle (control) from 2 weeks (established hypertrophy stage) after transverse aortic constriction (TAC) and the treatment was continued for 4 weeks. Pitavastatin significantly inhibited the progression from LV hypertrophy to heart failure as assessed on echocardiography. The cardiomyocyte cross-sectional area was significantly increased in the control group compared to the sham-operated mice (sham group), but it was not significantly different between the control group and the pitava group at 6 weeks after TAC. Moreover, pitavastatin induced myocardial angiogenesis (ratio of number of endothelial cells to cardiomyocytes) and decreased the myocardial fibrosis and oxidative stress. The expression of angiopoietin-1 in the heart was significantly increased by pitavastatin at 6 weeks after TAC. Conclusions:Pitavastatin has preventive effects on the progression of heart failure even in the hypertrophied heart. (Circ J 2012; 76: 1159 - 1168
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