Cardiac Pericytes Acquire a Fibrogenic Phenotype and Contribute to Vascular Maturation After Myocardial Infarction

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 NG(2Dsred);PDGFR alpha(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-beta (TGF-beta) signaling in regulation of pericyte phenotype was investigated in vivo using pericyte-specific TGF-beta 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 a (PDGFRa) 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 similar to 4% of PDGFRa+ 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-beta as a potentially causative mediator in fibrogenic activation of infarct pericytes. However, pericyte-specific TGF-beta receptor 2 disruption had no significant effects on infarct myofibroblast infiltration and collagen deposition. Pericyte-specific TGF-beta 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 matrixsynthetic and matrix-remodeling profiles. A fraction of infarct pericytes exhibits expression of fibroblast identity markers. Pericyte-specific TGF-beta signaling plays a central role in maturation of the infarct vasculature and protects from adverse dilative remodeling, but it does not modulate fibrotic remodeling.

Automated summary

This study found that pericytes in the heart play a role in tissue repair, remodeling, and fibrosis. After myocardial infarction, a subpopulation of pericytes exhibits transient expression of fibroblast markers and contributes to the formation of fibrotic tissue. Pericyte-specific TGF-beta signaling is involved in the maturation of blood vessels in the infarcted area and protects against adverse remodeling.