FBN1 and aortic aneurysm: Additionally, specific immunofluorescent staining was used to detect three highly interactive extracellular matrix proteins that are known to have roles in the pathogenesis of aortic aneurysm in humans: fibrillin-1 (FBN1), latent transforming growth factor beta binding protein 4 (LTBP4) and fibronectin (FN).