PML- and Smyd1-dependent regulatory mechanisms and effects on inflammatory responses of vascular endothelial cells

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Endothelial cells (ECs) line as a single layer the interior surface of lymphatic and blood vessels. Loss of proper endothelial functions lead to potentially life-threatening conditions. They may emerge as a chronic inflammatory disease with specific anatomical localization, as in the case of arteriosclerosis, but can also arise acute, as in the case of a sepsis or of an ischemic-reperfusion injury, which in contrast to sepsis is typically restricted to single organs. In these, per se very different situations, inflammatory alterations of the endothelium play a pivotal role for the functional integrity of the endothelium of affected blood vessels. Preliminary experiments of the proposed project revealed a protein-protein-interaction of Smyd1 (SET And MYND Domain Containing 1) and PML (Promyelocytic Leukemia Protein) and a PML-dependent SUMOylation of Symd1 in ECs. Overexpression of Smyd1 in ECs induced by gene transfection showed increased expression levels of PML and NFB. Remarkably, the effect of Smyd1 on NFB expression was caused by the histone methyltransferase activity of Smyd1. Overexpression of both, Smyd1 and PML, resulted in an increased expression of the major histocompatibility complex class II transactivator CIITA. An increased endothelial MHC class II expression is associated with autoimmune diseasesand endothelial dysfunction. The expression of PML and Smyd1 in ECs was augmented by treatment with liposaccharide. Hypoxia showed a similar effect. In contrast, atherogenic flow profiles decreased PML and Smyd1 expression. These findings provided experimental evidence that PML and Smyd1 interact with each other to influence inflammatory responses of vascular endothelial cells.In the current proposal, we want to explore in more detail the role of PML and Smyd1 in inflammatory reactions of vascular endothelial cells, blood vessels and organ perfusion. Special stimulation protocols will be applied to mimic inflammatory reactions characteristic for the initiation of arteriosclerosis, sepsis and ischemic-reperfusion injury. The systematic comparison of these stimulation protocols ought to deepen the understanding for varieties and similarities in the investigated endothelial dysfunctions. The underlying cellular mechanisms, which include transcriptional regulation of putative target genes via Smyd1-dependent histone modifications, PML nuclear bodies-mediated SUMOylation of proteins, as well as interaction of both proteins, will be identified and characterized in detail. Implications for endothelial cell function will be experimentally quantified. Finally, translational applications will be prepared by analysis of the obtained findings, the development of Smyd1-inhibitors including the comparison with cardiovascular databases.