| Endomucin is a type I transmembrane sialomucin of the endothelial glycocalyx that localizes predominantly to venous and capillary endothelium and functions as an anti‑adhesive and signaling modulator in vascular homeostasis, angiogenesis, and inflammation. The protein has an extensively O‑glycosylated, negatively charged extracellular domain that projects into the vascular lumen, a single membrane‑spanning region, and a short cytoplasmic tail that associates with intracellular partners and links the glycocalyx to cytoskeletal and signaling machinery, allowing endomucin to act as both a physical barrier and a transducer of extracellular cues. High luminal expression on post‑capillary venules interferes with leukocyte rolling and firm adhesion by masking or functionally antagonizing adhesion molecules such as E‑selectin and ICAM‑1, and loss of endomucin from quiescent endothelium permits leukocyte–endothelial interactions and facilitates recruitment during inflammatory activation. As a component of angiogenic endothelium, endomucin regulates VEGF receptor 2 signaling and cytoskeletal dynamics: its presence supports VEGF‑induced VEGFR2 phosphorylation, ERK and p38 activation, proliferation, migration, and tube morphogenesis, whereas silencing of endomucin reduces VEGFR2 signaling, impairs retinal vascular expansion, decreases vessel density, and suppresses choroidal sprouting. Interactions with actin‑associated proteins allow endomucin to influence F‑actin organization, membrane protrusions, and stress fiber formation independently of VEGFR2, indicating a direct role in coupling the endothelial glycocalyx to cytoskeletal remodeling pathways that control cell shape changes and rearrangements during angiogenic growth. Distribution analyses identify endomucin as a robust marker of venous and capillary endothelial cells and of specialized vascular structures such as high endothelial venules and hematopoietic clusters, which makes it useful for mapping microvascular beds and tracking vascular remodeling in tissues with active angiogenesis. Dysregulated expression is linked to vascular pathology and cancer: reduced or altered endomucin on venular endothelium favors leukocyte adhesion and chronic vascular inflammation, whereas tumor‑derived endomucin is overexpressed in colorectal cancer, promotes proliferation, metastasis, and epithelial–mesenchymal transition, and associates with networks of carcinogenesis‑related binding partners, highlighting distinct roles in tumor vasculature and tumor cells. |
