A Narrative Review: Syndecans in Aortic Aneurysm Pathogenesis and Course-Biomarkers and Targets?

The maintenance of the integrity of the entire endothelium, glycocalyx included, and, therefore, of tissue aorta's homeostasis, depends on the expressions of several molecular pathways and their interactions, such as syndecan molecules. Alterations in syndecans, i.e., quantitative alterations or linking to their shedding, contributes to invoking endothelium dysfunction, which causes damage to the vessel wall due to the increased production of growth-stimulating and pro-inflammatory gene products. Inflammatory processes negatively affect the integrity of the endothelial glycocalyx, a dynamic layer of the luminal portion of endothelial cells composed of proteoglycans, glycoproteins, and glycosaminoglycans, i.e., syndecans. In turn, structural alterations in the endothelial glycocalyx influence the coagulative state, increasing pro-thrombotic processes. The family of syndecans constitutes a major component of glycocalyx or, more accurately, the major source of cell surface heparan sulfate. It encompasses four components: syndecan-1, syndecan-2, and syndecan-4 (with syndecan-3 only expressed in neural tissue), which have a fundamental role in regulating the events of acute and chronic aorta damage subsequently correlated with the formation of aneurysms. As such, the aim of our review is to highlight the current knowledge on the roles of syndecans and to analyze their relationship with the pathological processes of the aortic wall based on the most recent literature.