SOX Transcription Factors in Endothelial Differentiation and Endothelial-Mesenchymal Transitions

Abstract

The SRY (Sex Determining Region Y)-related HMG box of DNA binding proteins, referred to as SOX transcription factors, were first identified as critical regulators of male sex determination but are now known to play an important role in vascular development and disease. SOX7, 17, and 18 are essential in endothelial differentiation and SOX2 has emerged as an essential mediator of endothelial-mesenchymal transitions (EndMTs), a mechanism that enables the endothelium to contribute cells with abnormal cell differentiation to vascular disease such as calcific vasculopathy. In the following paper, we review published information on the SOX transcription factors in endothelial differentiation and hypothesize that SOX2 acts as a mediator of EndMTs that contribute to vascular calcification.

Keywords: differentiation; endothelial-mesenchymal transition; endothelium; sex determining region y-box; vascular calcification.

Figure 1

SOX2 plays a role in endothelial differentiation. Time course of expression of (left panels) SOX2, and (right panels) fetal liver kinase 1 (Flk1), VE-cadherin (VE-Cad) and cluster of differentiation 31 (CD31), as determined by real-time PCR during endothelial cell derivation from wild type embryonic stem cells (15 days). (A) Scrambled siRNA (SCR) or (B) specific Sox2 siRNAs were transfected into the embryonic stem cells on day 3. Gene expression is shown as fold change compared to the expression on day 0 (n = 5).

Figure 2

Endothelial differentiation co-exists with neural differentiation. (A) Schematic diagram of the temporal induction patterns of coordinated endothelial (EC) and neuronal (NE) differentiation. (B–F) Marker expression during neuronal differentiation in wild type embryonic stem cells with or without suppression of SOX2 (n = 5). Scrambled siRNA (SCR) or specific Sox2 siRNAs were transfected into the cells on day 3. Expression was determined by real-time PCR and calculated as fold change compared to the expression on day 0. (B–D) Time course of expression of SOX2, and the neural progenitor markers SOX1, paired box protein (Pax6), and nestin. (E,F) Time course expression of the endothelial markers VE-cadherin (VE-Cad), fetal liver kinase 1 (Flk1) and cluster of differentiation 31 (CD31).

Figure 3

Serine proteases degrade Mgp-/- aortic tissue (A) Wild type (Mgp^+/+) and Mgp^−/− aortic endothelium at 4 weeks of age was examined by scanning electron microscopy (magnification 5 × 10²). The image shows significant disruption of the Mgp^−/− endothelium and elastic lamina (n = 3). Top, schematic diagram indicating the locations of lumen and endothelium. (B) Expression of elastase (ELA) 1 and 2 and kallikrein (KLK) 1, 5, and 6 and SOX2 in Mgp^−/− aortas at 1–4 weeks of age, as determined by immunoblotting. Beta-actin was used as a loading control (n = 3). (C) Immunofluorescent staining of aortic elastin of wild type (Mgp^+/+) and Mgp^−/− mice at 1–4 weeks of age. The images reveal the degradation of Mgp^−/− aortic elastin starting at 2 weeks of age (n = 5). (D) Immunoblotting demonstrates that kallikrein (KLK) 1, 5, and 6 degrade matrix components of aortic tissues including collagen (Col) 1, II, III, and IV, fibronectin, fibrinogen and laminin in vitro. One mg of substrate protein was mixed with 100 ng of enzyme or control at 37°C for 1 h before the samples were analyzed by immunoblotting (n = 3).

Figure 4

Schematic diagram of the hypothesis that SOX2 acts as a mediator of endothelial-mesenchymal transitions (EndMTs).