Endothelial activation and fibrotic changes are impeded by laminar flow-induced CHK1-SENP2 activity through mechanisms distinct from endothelial-to-mesenchymal cell transition

Blood flow patterns have been shown to have a profound effect on the progression of atherosclerosis; specifically, disturbed flow correlates with pro-atherogenic features, while laminar flow promotes atheroprotection.  The Abe group linked disturbed flow to the enhancement of SUMOylation of key target proteins in endothelial cells through the phosphorylation of the deSUMOylase SENP2 at T368 via a redox-sensitive ribosomal S6 kinase, p90RSK. In this recent study, the group discovered that laminar flow can also regulate SENP2, but in a fashion independent of T368 phosphorylation, to produce an atheroprotective effect. Based on available mass spectrometry SENP2 S344 was identified as a potential post-translational modification of interest.  The lab developed a phospho-specific antibody to S344 of SENP2 and used it to confirm laminar flow on endothelial cells led to enhanced phosphorylation at this site.  They then discovered that CHK1 phosphorylates SENP2 as S344 and utilized a chemical inhibitor of CHK1 to further link its role. They then developed a knock-in mouse model where SENP2 S344A was expressed.  As expected, endothelial cells isolated from these mice had reduced phosphorylation at S344 in response to laminar flow.  Importantly, these cells also showed elevated SUMOylation of key target proteins ERK5 and p53 in response to laminar flow when compared to WT endothelial cells.  Interestingly, SENP2 S344A KI mice exposed to a high-fat diet had significantly larger lipid-laden lesions and displayed other features that supported the hypothesis that phosphorylation of S344 SENP2 may be atheroprotective.  RNA-Seq and functional studies were performed to show that phosphorylation of SENP2 was important for regulating endothelial cell activation, which was mediated by several signaling pathways through ERK5, which SENP2 regulated through SUMOylation.  Cytoskeleton Inc’s SUMOylation 2/3 Detection Kit (Cat. # BK162) was essential for confirming that phosphorylation of SENP2 at S344 augmented its ability to regulate ERK5 and p53 SUMOylation state.  Understanding the mechanisms by which patterned blood flow affects atherosclerosis will be pivotal for identifying potential targets for intervention.