Increased amount of type III pN-collagen in human abdominal aortic aneurysms: Evidence for impaired type III collagen fibrillogenesis

Purpose: This study aimed to characterize the distribution of structural do mains of type I and III collagens in the wall of abdominal aortic aneurysms (AAAs), by the use of undilated atherosclerotic aortas (aortoiliac occlusi ve disease [AOD]) and healthy abdominal aortas as controls. Methods: Immunohistochemical staining was applied with antibodies for the a minoterminal propeptides of type I (PINP) and type III (PIIINP) procollagen s, which represent newly synthesized type I and III pN-collagens. In additi on, an antibody against the aminoterminal telopeptide of type III collagen (IIINTP) was used as a means of detecting maturely cross-linked type III co llagen fibrils. Results: The newly synthesized type III procollagen detected by means of PI IINP staining was concentrated in the media in aneurysmal aortas, whereas t ype I pN-collagen was localized in the intima in both AAAs and AODs. The he althy aortas showed no immunoreactivity for either PIIINP or PINP. The cros s-linked type III collagen, detected by means of IIINTP staining, stained t ransmurally in all study groups, but appeared more abundant in the media in AAAs. Conclusion: Our results strongly suggest that the metabolism of type III co llagen is enhanced in AAAs. Intensive type III pN-collagen staining was pre sent mainly in the media layer in AAAs, suggesting a role of type III colla gen in aneurysm formation, whereas type I pN-collagen was present in the in tima in both AAAs and AODs, suggesting that type I collagen synthesis is a fibroproliferative response related to the atherosclerotic process. The inc reased type III pN-collagen in AAAs may result in impaired fibril formation and, thus, in decreased tensile strength of aneurysmal tissue.