Objective: To investigate the effects of platelet-derived growth factor (PDGF)-BB on the vascular smooth muscle cell (VSMC)-monocyte interaction and the mechanism thereof.
Methods: Rat aortic VSMC were pretreated with PDGF-BB of the concentrations of 0, 2.5, 5, 10, and 20 ng/ml for 8 hours and then co-incubated with human monocytes of the line THP-1 labeled with PKH26, a cellular membrane fluorescent marker, i.e., to be subjected to binding assay to observe the dose-effect relationship. Other VSMC were co-cultured with PDGF of the concentration of 10 ng/ml for 1, 2, 4, 12, and 24 hours respectively and then interacted with PKH26-abeled THP-1 cells so as to observe the time-response relationship. Monoclonal antibody against integrin beta1 was co-cultured with VSMC for 30 min, and then PKH26-labeled THP-1 cells were added to block the effect of PDGF. After the incubation of THP-1 cells and VSMC, the amount of bound cells was counted using fluorescent phase-contrast microscopy. The effect of PDGF on the expression of integrin beta1 was detected by Western blotting.
Results: The amounts of THP-1 cells bound to VSMC pretreated with PDGF of the concentrations of 2.5, 5, 10, and 20 ng/ml respectively were 1.1, 2.1, 3.1, and 4.4 times that of the untreated cells. Incubated with 10 ng/ml PDGF for 0-18 h, the adhesion rate between the VSMC and THP-1 cells increased time-1dependently. After the blocking by the antibody against integrin beta1, the adhesion rate between the VSMC and THP-1 cells decreased from (25.4+/-11.4)% to (9.2+/-4.1)% (P<0.01). Western blotting showed that the level of integrin beta1 of the VSMC treated by 10 ng/ml PDGF increased since 4 h after the treatment, peaked 8 h later, and then decreased gradually.
Conclusion: PDGF-BB can induce the binding of monocytes to VSMC via the integrin-beta1 signaling pathway. The effect may therefore facilitate the progression of atherosclerosis by augmenting the VSMC-monocyte adhesive interaction.