Autocrine secretion of osteopontin by vascular smooth muscle cells regulates their adhesion to collagen gels

Osteopontin (OPN) is a secreted protein postulated to facilitate vascular smooth muscle cell (VSMC) adhesion and migration. Rat aortic VSMC lines were isolated after infection with recombinant retroviruses harboring OPN sense and antisense constructs. All lines grew normally in monolayer culture. On three-dimensional collagen gels, normal VSMCs and lines containing sense constructs (n = 15) or empty vector (n = 10) attached to the gel and invaded the matrix. Four of five antisense clones did not adhere or invade. Antisense clones had lower OPN levels after stimulation with angiotensin II than sense clones or clones containing the empty vector (antisense, 257 ± 102 ng/ml; sense, 473 ± 104; vector, 434 ± 66). Non- adhering antisense clones bad lower mean OPN levels after angiotensin II stimulation (161 ± 47 ng/ml) than sense or antisense lines with normal adhesion (486 ± 63 ng/ml). The ability to adhere correlated with OPN levels >250 ng/ml. Adhesion and invasion were fully restored with addition of 100 to 200 ng/ml of exogenous OPN and were inhibited in normal VSMCs by incubation with 1 μg/ml anti-OPN antibody. The autocrine secretion of OPN appears to play an important role in VSMC adhesion, spreading, and invasion.