Distribution of biglycan and its propeptide form in rat and bovine aortic tissue

The matrix proteoglycan biglycan was identified in bovine and rat aortic tissue by Western blot analysis and by immunohistochemistry, using polyclonal antibodies raised against peptides of the propeptide and the hypervariable region of the rat biglycan core protein. Western blot analysis of proteoglycans isolated from bovine and rat aortas by ion exchange chromatography and treated with chondroitin ABC lyase, with antibody against propeptide, demonstrated core proteins with molecular weights ranging from 43,000 to 45,000 daltons. Similar results were obtained with Western blot studies using the peptide antibody to the hypervariable region of biglycan, except the antibody did not recognize the core protein of bovine biglycan. Location of biglycan within bovine and rat aortic tissue sections by immunoperoxidase histochemistry using the antibody raised against the propeptide revealed intense intracellular staining of medial myocytes and endothelial cells but no extracellular staining. In contrast, immunohistochemistry performed with the purified antibody to the hypervariable region revealed significant extracellular staining of the adventitia proximate to the media and of the endothelial lining but no intracellular staining of rat aortic tissue, with no observable staining of bovine aortic tissue. These data demonstrate that, in contrast to cultured smooth muscle cells, biglycan containing the propeptide is not secreted and deposited within the extracellular matrix by smooth muscle cells and endothelial cells from aortic tissue.