Osteopontin (OPN) is required for vascular smooth muscle cells (VSMC) migration in collagen gels.

OPN, a secreted extracellular matrix protein, is induced by angiotensin II (Ang) and other growth agonists which play a role in the vascular remodelling seen in hypertension and atherosclerosis. OPN is postulated to facilitate VSMC adhesion and migration. To test this, rat aortic VSMC lines were isolated after infection with recombinant retroviruses harboring OPN sense (S) or antisense (AS) constructs. All lines grew normally in monolayer culture. When tested for adhesion and migration in a 3D collagen gel culture system, normal VSMC and lines containing the OPN S construct (n=15) or the empty vector (EV, N=10) attached to the surface of the gel and invaded the substance of the matrix, forming lattice-like cell connections. 4 of 5 AS clones did not migrate or form cell connections. All 5 AS clones, 4 S clones and 2 clones containing the EV were chosen for more detailed evaluation. AS clones had lower OPN levels (257±102 ng/ml) following maximal stimulation with Ang, than S clones(473±104) or clones containing the EV (434±66). Non-migrating VSMC clones had significantly lower mean OPN levels following maximal stimulation with Ang (161±47) than migrating clones (486±63; unpaired t-Test, p<0.005). To verify that the effect was due to OPN, exogenous OPN was added back to the media of all non-migrating AS clones. Migration was fully restored with addition of 100-200 ng/ml exogenous OPN. In conclusion, OPN appears to be critical for VSMC migration.