Endothelial Myocyte Enhancer Factor 2c Inhibits Migration of Smooth Muscle Cells Through Fenestrations in the Internal Elastic Lamina

Abstract

Objective Laminar flow activates MEF2 transcription factors in vitro to induce expression of atheroprotective genes in the endothelium. Here we sought to establish the role of Mef2c in the vascular endothelium in vivo. Approach and Results To study endothelial Mef2c, we generated endothelial-specific deletion of Mef2c using Tie2-Cre or Cdh5-Cre-ERT2 and examined aortas and carotid arteries by en face immunofluorescence. We observed enhanced actin stress fiber formation in the Mef2c-deleted thoracic aortic endothelium (laminar flow region), similar to those observed in normal aortic inner curvature (disturbed flow region). Furthermore, Mef2c deletion resulted in the de novo formation of subendothelial intimal cells expressing markers of differentiated smooth muscle in the thoracic aortas and carotids. Lineage-tracing showed that these cells were not of endothelial origin. To define early events in intimal development, we induced endothelial deletion of Mef2c and examined aortas at 4 and 12 weeks post induction. The number of intimal cell clusters increased from 4 to 12 weeks, but the number of cells within a cluster peaked at 2 cells in both cases, suggesting ongoing migration but minimal proliferation. Moreover, we identified cells extending from the media through fenestrations in the internal elastic lamina into the intima, indicating trans-fenestral smooth muscle migration. Similar trans-fenestral migration was observed in wild-type carotid arteries ligated to induce neointimal formation. Conclusions These results indicate that endothelial Mef2c regulates the endothelial actin cytoskeleton and inhibits smooth muscle cell migration into the intima.

Cell chirality regulates intercellular junctions and endothelial permeability

“…Mice with mixed background without genetic deletion were maintained in accordance with protocols approved by the Institutional Animal Care and Use Committee in Albany Medical College. En face immunofluorescence staining of mouse vessels was described previously ( 49 ). Briefly, mice were euthanized with an intraperitoneal injection of sodium pentobarbital (0.1 mg/g of animal).…”

MEF2 and the Right Ventricle: From Development to Disease

“…MEF2A and MEF2C are the MEF2 isoforms most highly expressed in endothelium (58). MEF2C promotes endothelial survival, regulates endothelial cytoskeleton and inhibits smooth muscle migration into the intima of the vasculature (59, 60). Endothelial specific knock out of Mef2c in mice with subsequent exposure to hypoxia leads to increased PH, RV hypertrophy (RVH), and muscularization of pulmonary arterioles (61).…”

Therapeutic Engagement of the Histone Deacetylase IIA–Myocyte Enhancer Factor 2 Axis Improves Experimental Pulmonary Hypertension

“…Pulmonary arterial hypertension (PAH) is a fatal disease of the pulmonary vasculature, characterized by abnormal remodeling of pulmonary vessels and elevated pulmonary arterial pressure, ultimately leading to right ventricular (RV) failure and death. MEF2 (myocyte enhancer factor 2) is a transcription factor that regulates multiple genes that are important during cardiovascular development and for vascular homeostasis (1), with MEF2C known to play a crucial role in regulating endothelial integrity, survival, and angiogenesis (2). A wealth of evidence supports regulation of MEF2 activity by the class IIA subset of HDACs (histone deacetylases), which directly bind to and inhibit its transcriptional activity (3).…”