Regulation of connexin expression after balloon injury: possible mechanisms for antiproliferative effect of statins.

Statins, the 3-hydroxy-3-methylglutaryl-cooenzyme A (HMG-CoA) reductase inhibitors, have been shown to inhibit the migration of macrophages and smooth muscle cell proliferation leading to an antiproliferative effect. Although this beneficial effect of statins has been suggested to be independent of lipid lowering properties, the possible mechanisms responsible for this action is largely unknown. Gap junctions, which serve as channels for direct intercellular exchange of ions, secondary messengers, and small signaling molecules, play an important role in tissue homeostasis and regulation of growth, differentiation, and development. This study was designed to test the hypothesis that expression of the component proteins of gap junctions, connexins 40 and 43 (Cx40 and Cx43), is upregulated in arteries subjected to balloon injury and that this upregulation can be suppressed by statin therapy. Male New Zealand white rabbits were subjected to injury in which an angioplasty catheter was introduced into the right iliac artery from the femoral artery under fluoroscopic guidance. Five groups of rabbits (n = 6 to 7) were treated for 2 weeks with one of the following: balloon injury (BL); BL+lovastatin (BL+L, 10 mg/kg/day); BL+fluvastatin (BL+F, 10 mg/kg/day); sham operation (Sham); and control (Con). Immunohistochemistry studies showed that Cx40 and Cx43 were expressed in normal smooth muscle cells (SMC) throughout the media. Reverse transcription-polymerase chain reaction and Western blot analysis showed that Cx40 and Cx43 mRNA and protein expression was elevated after injury (P < .001 for both proteins and both assays), and these elevations were suppressed by lovastatin and fluvastatin to a similar degree (P < .05 for both drugs and both assays). Immunostaining of Cx40 and Cx43 was consistently enhanced in the neointimal area after injury and lovastatin and fluvastatin reduced staining of these proteins in the lessened neointimal layer. Transmission electron microscopy revealed that there were abundant gap junctions between neointimal SMC as well as fewer and smaller gap junctions after statin treatment. Therefore, balloon injury causes upregulation of Cx40 and Cx43 in neointimal SMC. Lovastatin and fluvastatin suppress upregulated Cx40 and Cx43 expression and reduce neointimal proliferation, suggesting that Cx40 and Cx43 may play a role in statin-induced antiproliferative effect.