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J Thorac Cardiovasc Surg 2003;126:1449-1454
© 2003 The American Association for Thoracic Surgery

Cardiopulmonary support and physiology

Cartilaginous metaplasia and calcification in aortic allograft is associated with transforming growth factor ß1 expression

^a Quebec Heart Institute, Hôpital Laval, Sainte-Foy, Quebec, Canada
^b Institut National de la Santé et de la Recherche Médicale (INSERM), Nantes, France

Received for publication January 27, 2002; revisions received April 30, 2002; accepted for publication September 17, 2002.

^* Address for reprints: Patrick Mathieu, MD, Quebec Heart Institute, Hôpital Laval, 2725 Chemin Sainte-Foy, Sainte-Foy, Quebec GIV 4G5, Canada
prmathieu{at}hotmail.com

BACKGROUND: Calcification of homografts and vascular conduits is poorly understood. Mechanisms leading to calcification were studied in a rat model of aortic allografts.

METHODS: Rat aortas from Lew1W (RT1^u) were transplanted into Lew1A (RT1^a). Animals were killed at 30 days and 180 days, and aortic grafts were removed and analyzed for histologic and immunohistologic studies.

RESULTS: Intimal surface increased progressively over 6 months and was the site of important modifications. Intimal cellular population changed from a leukocyte (CD45, OX1-OX30)- and macrophage (CD68, ED-1)-based population at 30 days to predominantly -smooth muscle actin-expressing cells at 180 days. At 180 days, allografts were characterized by an abundant extracellular matrix composed of collagen and elastic fibers associated with extensive calcification (von Kossa staining) located in the intima and media. Osteoblastic activity was present in calcified lesion as shown by alkaline phosphatase activity. At 180 days, numerous chondrocytes (protein S100-positive and -smooth muscle actin-negative) were present focally in the media. However, double immunostaining revealed that a cellular population within the media with a chondrocyte-like morphology was -smooth muscle actin-positive and S100-negative. Active form of transforming growth factor ß1 was expressed from 30 to 80 days in the medial and intimal layers.

CONCLUSIONS: These observations suggest that -smooth muscle actin-positive cells within aortic allografts are eventually transformed to a chondrocyte-like structure, leading to vascular cartilaginous metaplasia associated with the expression of transforming growth factor ß1 and could be a potential pathway leading to extensive vascular wall calcification in allografts through endochondral ossification.

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