Matrix Gla protein (MGP) and bone morphogenetic protein-2 in aortic calcified lesions of aging rats

Authors


Reidar Wallin, Rheumatology, Department of Internal Medicine, Wake Forest University School of Medicine, Medical Center Blv., Winston-Salem, NC 27157, USA.Tel.: + 1 336 716 6166; fax: + 1 336 716 9821; e-mail: rwallin@wfubmc.edu

Abstract

Summary.  The vitamin K-dependent protein, matrix Gla protein (MGP) is a binding protein for bone morphogenetic protein-2 (BMP-2). Here we present additional evidence that the Ca2+-induced conformer of the vitamin K-dependent Gla region in MGP is involved in BMP-2 binding. Recombinant BMP-2 binds to the Gla-containing region of MGP in the presence of Ca2+. Immunohistochemistry showed that calcified lesions in the aortic wall of aging rats contained elevated concentrations of MGP that was poorly γ-carboxylated and did not bind BMP-2. In contrast, we were able to identify glandular structures in the mucosa of the rat nasal septum that gave bright fluorescent signals with both antigens; confocal microscopy confirmed their colocalization. These results demonstrate that the BMP-2/MGP complex exists in vivo, consistent with a role for MGP as a BMP-2 inhibitor. Age-related arterial calcification may be a consequence of under-γ-carboxylation of MGP, allowing unopposed BMP-2 activity.

Ancillary