Substrate-induced phenotypic switches of human smooth muscle cells: an in vitro study of in-stent restenosis activation pathways

Abstract

In-stent restenosis is a clinical complication following coronary angioplasty caused by the implantation of the metal device in the atherosclerotic vessel. Histological examination has shown a clear contribution of both inflammatory and smooth muscle cells (SMCs) to the deposition of an excess of neointimal tissue. However, the sequence of events leading to clinically relevant restenosis is unknown. This paper aims to study the phenotype of SMCs when adhering on substrates and exposed to biochemical stimuli typical of the early phases of stent implantation. In particular, human SMC phenotype was studied when adhering on extracellular matrix-like material (collagen-rich gel), thrombus-like material (fibrin gel) and stent material (stainless steel) in the presence or absence of a platelet-derived growth factor (PDGF) stimulus. Cells on the collagen and fibrin-rich substrates maintained their contractile phenotype. By contrast, cells on stainless steel acquired a secretory phenotype with a proliferation rate 50 per cent higher than cells on the natural substrates. Cells on stainless steel also showed an increase in PDGF-BB receptor expression, thus explaining the increase in proliferation observed when cells were subject to PDGF-BB stimuli. The stainless steel substrate also promoted a different pattern of β1-integrin localization and an altered expression of hyaluronan (HA) synthase isoforms where the synthesis of high-molecular-weight HA seemed to be favoured. These findings highlighted the induction of a phenotypic pattern in SMC by the stainless steel substrate whereby the formation of a HA-rich neointimal tissue is enhanced.

Figure 1.

SMCs adhering on the different substrates. (a) TCP, (b) ECM, and (c) St.

Figure 2.

SMC proliferation on the different substrates with or without PDGF-BB spiking (2 ng ml⁻¹). Suc indicates 0.2 M sucrose treatment. Asterisk indicates values significantly different from the relative control (<0.01).

Figure 3.

PDGF-BBr immunolabelling of SMCs adhering on the different substrates. (a) TCP, (b) ECM, and (c) St. Arrows indicate areas of PDGF-BBr localization.

Figure 4.

β1-Integrin immunolabelling of SMCs adhering on the different substrates. (a) TCP, (b) ECM, and (c) St. Arrows indicate areas of β1-integrin localization in SMCs adhering on ECM. Arrowheads show areas of β1-integrin localization in SMCs adhering on St.

Figure 5.

Gene expression of hyaluronan synthase isoforms (HAS1, HAS2, HAS3) in SMCs adhering on the different substrates with or without PDGF-BB (2 ng ml⁻¹). Lane 1, TCP; lane 2, Fib; lane 3, ECM; lane 4, St; lane 5, TCP with PDGF-BB spiking; lane 6, Fib with PDGF-BB spiking; lane 7, ECM with PDGF-BB spiking; lane 8, St with PDGF-BB spiking. Ladder is shown on the left-hand side. GAPDH was used as the housekeeping gene.