Apoptosis, cell proliferation and modulation of cyclin-dependent kinase inhibitor p21cip1 in vascular remodelling during vein arterialization in the rat

The effectiveness of saphenous vein graft as a coronary bypass conduit is limited by acute thrombotic events or late neo-intimal formation and accelerated atherosclerosis. Although arterial grafts display superior long-term patency, saphenous vein grafts are still widely used since they are readily accessible, have adequate lengths for accessing different vessels in the heart, and the correct diameter to facilitate coronary and aortic anastomoses (Verma et al. 2004). Proliferation of smooth muscle cells (SMC) is one of the main events during the arterializations process, enabling the arterialized veins to sustain the increased hemodynamic stress (higher pressure and shear stress). However, excessive proliferation and migration of SMC to the intima may directly, or indirectly, provide a foundation for the development of atherosclerotic lesions, contributing to late occlusion and vein graft failures (Bourassa et al. 1986; Mehta et al. 1997; Torsney et al. 2004). The proliferative process is finely regulated by the interplay of cyclin-dependent kinases (CDKs) and CDK inhibitors (CDKIs). CDKIs modulate the cyclin-CDK complex activity showing negative regulation of cyclin-mediated cell cycle progression (Sherr & Roberts 1999). The major machinery of the cell cycle is common among different cell types, but some components have been described to better influence the cell proliferation in SMCs. p27Kip1, p21Cip1 and p16INKA are the most studied CDKIs proteins in vascular disorders and it has been tested as therapeutic target in animal models (Chang et al. 1995; Chen et al. 1997; Tanner et al. 1998). It is important to emphasize that most studies have been performed using injured artery models and there is no evidence from venous conduits. The evaluation of CDKI modulation in arterialized veins may represent valuable information to understand the remodelling process and to provide new opportunity of therapeutic approaches to improve the graft patency. Experimental models have been developed to elucidate the morphological and molecular mechanism underlying the vein graft disease (Liu & Fung 1998; Zou et al.1998; Rodriguez et al. 2000; Westerband et al. 2001). In this work, we are showing a model of arteriovenous (AV) connection surgery as an alternative model in rat to study venous arterialization process. It has the advantage of reduced cost, since only one anastomosis is performed, and resembles the morphological changes observed in human vein graft disease. Moreover, we describe the time-related morphological changes during arterialization of the rat jugular vein segment associated to CDKIs modulation for up to 90 days. Early SMC microscopic analysis showed clear evidence that the contractile phenotype gave rise to a synthetic phenotype, followed by late development of elastic fibres and the reappearance of contractile SMC. Finally, we provide evidence for an imbalance of both apoptosis and cell proliferation during the arterialization process and demonstrate that p21Cip1 is the CDKI protein that is modulated during the remodelling response, while p27Kip1 and p16INKA remain unchanged.