Objective: Smooth muscle cell (SMC) migration and proliferation are the key steps in the development of atherosclerosis and restenosis. Matricellular proteins have been implicated in cell adhesion, migration and proliferation. Here we investigated the role of the matricellular protein galectin-1 (Gal-1), a beta-galactoside-binding lectin, in SMC proliferation in atheroma and DNA synthesis in cell culture.
Methods: Protein expression was visualised by tissue section immunostaining. RNA expression was analysed using Northern blot analysis. DNA synthesis of human vascular SMCs was determined by 3H-thymidine incorporation. Recombinant glutathione S-transferase-galectin-1 fusion protein (Gal FP) binding to extracellular matrix (ECM) proteins was measured by ELISA. Gal-1 binding to cells and ECM was estimated using 125I-labelled Gal FP.
Results: Prominent Gal-1 staining coincided with SMC proliferation in human coronary endarterectomy samples in organoid culture. In cell culture, Gal-1 mRNA was upregulated in growing SMCs. Gal FP increased serum-induced DNA synthesis of human SMCs on plastic or endogenous ECM, but not of a rat PAC1 SM cell line. Also, Gal FP slightly increased SMC adhesion to ECM. SMCs exhibited a complex pattern of receptor-ligand interactions with Gal FP. The Gal-1 binding to SMCs was much stronger than to ECM, produced by these SMCs. We identified new ECM proteins: thrombospondin, vitronectin and osteopontin, which bound to Gal FP in a dose- and beta-galactoside-dependent manner in ELISA.
Conclusions: Gal-1 binding to SMCs was stronger than to ECM, although ECM of atherosclerotic blood vessels contained additional ECM proteins which bound to Gal-1. Gal-1 was upregulated during SMC growth and Gal FP enhanced serum-induced DNA synthesis in SMCs. Overall, Gal-1 upregulation is likely to provide a reinforcement of serum-induced events during vascular injury.