VTN and age-related macular degeneration: Interactions with lipids, glycosaminoglycans, collagens, plasminogen activator inhibitor-1 (PAI-1) and adhesion receptors make vitronectin a multifunctional protein involved in the regulation of a variety of cellular events that are also known to be affected by AMD, such as ECM deposition, cell adhesion and migration, immune response, angiogenesis and fibrinolysis [8,9,10,11,12,13,14,15].