Apolipoprotein J inhibits the migration, adhesion, and proliferation of vascular smooth muscle cells

Purpose: Apolipoprotein J (ApoJ) is expressed during tissue injury and remodeling and has been implicated in vascular smooth muscle cell (VSMC) differentiation. Recently, the gene for ApoJ was identified as upregulated in distal anastomotic intimal hyperplasia after prosthetic arterial grafting. In this study we investigate the effect of ApoJ on VSMC migration, adhesion, proliferation, and gene expression. Methods: To study the effect of ApoJ on cell migration, we used a microchemotaxis chamber with an intervening 8-mum pore semipermeable polycarbonate membrane. Assays were performed with ApoJ alone (1-50 mug/mL) or in combination with platelet-derived growth factor homodimer bb (PDGF-bb; 10 ng/mL) or 2% fetal bovine serum (FBS; n=8) in the lower wells. The influence of extracellular matrix interactions on ApoJ and chemotaxis was studied in a similar way, except membranes were collagen coated. Furthermore, cells were exposed to ApoJ 15 minutes before or after seeding on the coated membrane (n=10). The influence of ApoJ on cell adhesion to collagen was assessed with cell exposure to ApoJ 15 minutes before or after seeding on a collagen-coated membrane (n=10). Migration and adhesion were quantified by counting the number of cells per three independent high-power fields with light microscopy. The effect of ApoJ in 0.4% FBS with or without PDGF-bb on VSMC proliferation (n=12) was assessed by means of [Methyl-H-3] thymidine incorporation. The transcriptional profile of VSMCs in 2% FBS exposed to ApoJ and a control for 24 hours was analyzed with an oligonucleotide microarray containing 12,560 genes. Results. ApoJ alone was not chemotactic for VSMCs. Without collagen, ApoJ decreased the migration of VSMCs toward 2% PBS by 96% or more starting at 10 mug/mL (P<.05) and toward PDGF-bb by 60.9% or more starting at 25 <mu>g/mL (P<.05) compared with the control. When collagen was introduced, ApoJ (25 <mu>g/mL) decreased migration toward 2% FBS by 64% (P<.01) and toward PDGF-bb by 67.5% (P<.01) and decreased adhesion by 26.8% (P<.01) only when VSMCs in solution were exposed to ApoJ before placement on collagen. ApoJ did not induce VSMC proliferation. ApoJ alone decreased VSMC thymidine incorporation by 41.1% at 25 <mu>g/mL (P<.05). ApoJ decreased thymidine incorporation of PDGF-bb stimulated VSMCs by 42.8% at 50 <mu>g/mL (P<.05). Interleukin-8 and endothelin-1 were demonstrated by means of the microarray to be differentially expressed more than twofold in VSMCs that were exposed to ApoJ. Conclusion: ApoJ is a potent inhibitor of VSMC migration, adhesion, and proliferation. Its genetic targets are linked to cell senescence and differentiation. Therefore, ApoJ may play a role, in part, in modulating the VSMC response to injury.