Coronary Artery Disease Associated Transcription Factor TCF21 Regulates Smooth Muscle Precursor Cells That Contribute to the Fibrous Cap

Abstract

Recent genome wide association studies have identified a number of genes that contribute to the risk for coronary heart disease. One such gene, TCF21, encodes a basic-helix-loop-helix transcription factor believed to serve a critical role in the development of epicardial progenitor cells that give rise to coronary artery smooth muscle cells (SMC) and cardiac fibroblasts. Using reporter gene and immunolocalization studies with mouse and human tissues we have found that vascular TCF21 expression in the adult is restricted primarily to adventitial cells associated with coronary arteries and also medial SMC in the proximal aorta of mouse. Genome wide RNA-Seq studies in human coronary artery SMC (HCASMC) with siRNA knockdown found a number of putative TCF21 downstream pathways identified by enrichment of terms related to CAD, including “vascular disease,” “disorder of artery,” and “occlusion of artery,” as well as disease-related cellular functions including “cellular movement” and “cellular growth and proliferation.” In vitro studies in HCASMC demonstrated that TCF21 expression promotes proliferation and migration and inhibits SMC lineage marker expression. Detailed in situ expression studies with reporter gene and lineage tracing revealed that vascular wall cells expressing Tcf21 before disease initiation migrate into vascular lesions of ApoE-/- and Ldlr-/- mice. While Tcf21 lineage traced cells are distributed throughout the early lesions, in mature lesions they contribute to the formation of a subcapsular layer of cells, and others become associated with the fibrous cap. The lineage traced fibrous cap cells activate expression of SMC markers and growth factor receptor genes. Taken together, these data suggest that TCF21 may have a role regulating the differentiation state of SMC precursor cells that migrate into vascular lesions and contribute to the fibrous cap and more broadly, in view of the association of this gene with human CAD, provide evidence that these processes may be a mechanism for CAD risk attributable to the vascular wall.

Genetic lineage tracing defines myofibroblast origin and function in the injured heart

“…More recently, epicardial derived fibroblasts, as traced with Wt1 CreERT2 or Tbx18 CreERT2 alleles, were shown to give rise to 80% or more of the total fibroblasts in the left ventricle of a failing mouse heart1131 Thus, there is strong support for the conclusion that tissue-resident fibroblasts in the adult heart are the primary cell type that generates myofibroblasts upon injury. This same paradigm appears to be present in the fibrotic cap of diseased vasculature in atherosclerotic mice where Tcf21 lineage-traced cells were shown to uniformly express αSMA, periostin and PDGFRα41.…”

Genetics of Coronary Artery Disease

“…The same group demonstrated that TCF21 regulates the development of the epicardial progenitor cells that give risk to smooth muscle cells that contribute to the fibrous cap. 140 Similar approaches have provided new insight into the roles of PHACTR1 141 and ADAMTS7 142 in atherosclerosis. ADAMTS7 plays a role in the regulation of vascular smooth muscle cell migration, and Bauer et al 143 recently demonstrated that Adamsts7 −/− mice were protected from atherosclerosis on an Ldlr −/− or Apoe −/− background and showed reduced neointimal formation after femoral wire injury and that Adamsts7 −/− vascular smooth muscle cells showed reduced migration in the setting of tumor necrosis factor-α stimulation, consistent with a proatherogenic effect of ADAMTS7.…”

Tracking Adventitial Fibroblast Contribution to Disease

“…A tool for identifying Tcf21 lineage cells was generated by inserting an inducible Cre recombinase at the Tcf21 locus 118 ( Tcf21 mCrem ). Tcf21 lineage cells were present in the adventitia of coronary arteries and the aortic root, as well as aortic root media and fibrous cap after injury 102, 115 . In addition to cells of the heart, adult induction of Tcf21 mCrem recombination also lineage tags splenic interstitial cells 119 , kidney podocytes and mesangial cells, lung interstitial cells, and liver interstitial cells 8, 118 .…”

“…Tcf21 LacZ reporter mice 114 have expression of β-galactosidase in coronary adventitia, aortic root, and interstitial cells of the heart 115 . In atherosclerotic lesions, β-galactosidase activity was observed on the luminal side of lesions and in the fibrous cap 115 . In the kidney, another Tcf21 LacZ 116 reporter line showed β-galactosidase activity in adventitial cells 117 .…”