| The objective of this thesis work was to understand how the dynamic cross talk that occurs between vascular smooth muscle cells (SMCs) and macrophages recruited to regions of arterial injury promotes the pathogenesis of neointimal hyperplasia.;Macrophages were the predominant myeloid cell type recruited to wire-injured femoral arteries in mouse, as assessed by flow cytometry. Recruited macrophages from injured vessels exhibited a distinct expression profile relative to circulating peripheral blood mononuclear cells. This phenotype was largely recapitulated in vitro by maturing rat bone marrow cells in the presence of macrophage-colony stimulating factor (M-CSF) and 20% conditioned media from cultured rat SMC, compared to maturation in M-CSF alone (M0). The physical parameters of the active factor present in SMC conditioned medium were consistent with the properties of TGF-beta. Recombinant TGF-beta1 recapitulated the effect of SMC conditioned medium on macrophage phenotypic modulation. Macrophage maturation studies performed in the presence of a pan-TGF-beta neutralizing antibody, a TGF-beta receptor 1 inhibitor, or conditioned medium from TGF-beta-depleted SMCs confirmed that the SMC-derived factor responsible for macrophage activation was TGF-beta. Finally, we assessed the effect of SMC-mediated macrophage activation state on SMC biology. SMCs cocultured with smooth muscle conditioned medium-matured macrophages; exhibited increased rates of proliferation relative to SMCs cultured alone or with M0 macrophages.;We assessed whether macrophage phenotype is differentially modulated in mice with targeted deletion of the protein and lipid phosphatase PTEN in SMC (PTEN iKO). At 15 days following injury there was an increase in the number of macrophages present in PTEN iKO lesions, and a larger percentage of macrophages were Ly6chigh by flow cytometry. This suggests that, at this time point, monocyte recruitment in PTEN iKO lesions is enhanced relative to recruitment in wild type lesions.;These data are significant since macrophages have been shown to play an important role in promotion of neointima formation following vascular injury, and these results begin to explain the mechanisms involved. Our data show that TGF-beta produced by SMCs is critical for promoting a macrophage phenotype representative of that observed in injured vessels. These activated macrophages would be predicted to signal to the SMC in vivo, resulting in feed-forward promotion of neointima formation. |
