Serine Protease Activation Essential for Endothelial–Mesenchymal Transition in Vascular Calcification

Abstract

Rationale Endothelial cells have the ability to undergo endothelial-mesenchymal transitions (EndMTs), by which they acquire a mesenchymal phenotype and stem-cell like characteristics. We previously found that EndMTs ocurred in the endothelium deficient in matrix Gla protein (MGP) enabling endothelial cells to contribute cells to vascular calcification. However, the mechanism responsible for initiating EndMTs is not fully understood. Objective To determine the role of specific serine proteases and sex determining region Y-box 2 (Sox2) in the initiation of EndMTs. Methods and Results In this study, we used in vivo and in vitro models of vascular calcification to demonstrate that serine proteases and Sox2 are essential for the initiation of EndMTs in MGP-deficient endothelium. We showed that expression of a group of specific serine proteases was highly induced in endothelial cells at sites of vascular calcification in Mgp null aortas. Treatment with serine protease inhibitors decreased both stem-cell marker expression and vascular calcification. In human aortic endothelial cells, this group of serine proteases also induced EndMTs, and the activation of proteases was mediated by Sox2. Knockdown of the serine proteases or Sox2 diminished EndMTs and calcification. Endothelial-specific deletion of Sox2 decreased expression of stem-cell markers and aortic calcification in MGP-deficient mice. Conclusions Our results suggest that Sox2-mediated activation of specific serine proteases is essential for initiating EndMTs, and thus, may provide new therapeutic targets for treating vascular calcification.

Roles of High Mobility Group Box 1 in Cardiovascular Calcification

“…Aortic and valvular endothelial cells also have been shown to transition to cells that undergo osteochondrogenesis via the endothelial to mesenchymal transition (EMT) [58, 59]. Cells exhibiting an osteochondrogenic phenotype have the potential to generate mineralized matrix, resulting in calcified deposits [60].…”

Endothelial-mesenchymal transition in atherosclerotic lesion calcification

“…An inhibitor of BMP type I receptor kinases also reduces the lesion calcification in Ldlr −/− mice (12). Recently, it was found that excess BMP activity triggers EndMT allowing the endothelium to contribute cells to the calcifying process (10, 13, 14). …”

“…EndMT is a process through which ECs transit into mesenchymal stem cells and gain multipotency (15), prior to differentiating into various cell lineages (13). EndMT has been shown in normal development, such as neural crest formation and cardiogenesis (16, 17).…”

The Vascular Wall: a Plastic Hub of Activity in Cardiovascular Homeostasis and Disease

“…Numerous studies using lineage tracing of endothelial cells have revealed that a significant portion of ECM-producing cells in various pathological conditions is of endothelial origin (estimates vary but usually range between 20 and 30%). Specifically, this has been shown in various models of lung fibrosis and pulmonary hypertension [41][42][43][44]; kidney fibrosis after acute or chronic injury [45][46][47]; the heart after acute ischemic injury such as myocardial infarction and chronic fibrosis caused by constant pressure overload [ [57]; diabetic retinopathy [58]; valve thickening [59]; and the generation of fibroblast-like cells that support tumor growth [60]. However, the field is not without controversy, since other studies have refuted the extent of EndMT contribution in fibrosis and pointed to proliferation and activation of resident fibroblasts as the main source of myofibroblasts after acute or chronic injury [61•, 62•].…”