Expression of matrix Gla protein and osteonectin mRNA by human aortic smooth muscle cells

Recent data indicate that matrix proteins such as matrix Gla protein (MGP) and osteonectin (ON) influence not only mineralization of vasculature but smooth muscle cell (SMC) differentiation.

We examined whether MGP and ON are expressed by human aortic SMCs in vivo using Northern blotting, in situ hybridization and immunohistochemistry.

MGP and ON mRNAs were strongly expressed in the aorta without atherosclerosis from newborn and four young subjects up to 10 years old. In the aorta from 15 adult cases, MGP and ON mRNAs were decreased as atherosclerosis developed. We determined cell type and distribution of the MGP- and ON mRNA-expressing cells by in situ hybridization and immunohistochemistry. In the aorta obtained from newborn and young subjects, SMCs in the media and thin intima expressed MGP mRNA and, to a lesser extent, ON mRNA. In the adult aorta with fibrous thickening, MGP mRNA was expressed by intimal SMCs and subpopulation of medial SMCs. Osteonectin mRNA was expressed mainly by intimal SMCs and few medial SMCs. Double immunohistochemical staining revealed that both MGP- and ON protein-expressing cells were positive for anti-alpha-smooth muscle actin antibody, aortic SMCs.

These results suggested that MGP and ON expression by aortic SMCs might be regulated by the degree of atherosclerosis and SMC differentiation in human aorta.