Substrate-induced phenotypical change of monocytes/macrophages into myofibroblast-like cells: a new insight into the mechanism of in-stent restenosis.

Stented coronary angioplasty is the procedure of choice to re-establish patency in obstructed coronary arteries. However, the stent implantation procedure often leads to in-stent restenosis, a process that is characterized by stent strut colonization by macrophages and smooth muscle cells and by neointima formation. The present in vitro study investigates the effect of stent materials on the phenotypical features of monocyte/macrophages. Human peripheral blood monocytes from healthy donors (n = 7) were cultured up to 7 days on substrates mimicking: (i) the stent surface (i.e., electropolished stainless steel), (ii) the de-endothelialized vessel wall (collagen-based extracellular matrix gel), and (iii) thrombus (i.e., fibrin gel). The cells were analyzed by immunocytochemistry for their ability to express alpha-actin, a typical myofibroblast marker, by ELISA to determine PDGF-BB and TGF-beta1 secretion and by PCR to evaluate hyaluronan synthase 1, 2, and 3 genes expression. Data were statistically analyzed by ANOVA (Dunnett's test) and data considered significantly different at p </= 0.05. The data demonstrated that mononuclear cells adhering to stainless steel acquire a phenotype capable of expressing alpha-actin while secreting significantly higher levels of PDGF-BB and TGF-beta. The expression of the three hyaluronan synthase isoforms was also altered by the metal substrate, where cells expressed genes only for the isoforms synthesizing high molecular weight hyaluronan. This study therefore suggests that mononuclear cells adhering on the stent metal surface undergo phenotypical transformation into myofibroblast-like cells that are able to contribute to neointimal tissue synthesis.