Stent Implantation Activates Akt in the Vessel Wall

Abstract

Objective-The long-term efficacy of stent implantation is affected by in-stent restenosis (ISR). Multiple factors can contribute to ISR, and the underlying mechanism remains elusive. We investigated the possible role of mechanical stretch and the associated molecular signaling in ISR. Methods and Results-Stent implantation in rat abdominal aortas induced neointima formation. Immunohistochemical studies revealed the activation of Akt in the media and neointima of the stented vessels. Western blotting showed increased phosphorylation of Akt at both Thr308 and Ser473 and phosphorylation of GSK-3␤ in the stented vessels. A stretch device applying static equibiaxial stretch on cultured vascular smooth muscle cells was used to delineate the molecular mechanism underlying the stretch activation of Akt. Static mechanical stretch induced the sustained activation of Akt and its upstream phosphoinositide 3-kinase (PI3K) and the phosphorylation of GSK-3␤, its downstream effector in vascular smooth muscle cells. LY294002, a PI3K inhibitor, and N-acetylcysteine, a scavenger of reactive oxygen species, inhibited the stretch activation of Akt. Furthermore, N-acetylcysteine and wortmannin, another PI3K inhibitor, reduced the neointima formation after stent implantation. Key Words: vascular smooth muscle cells Ⅲ stent Ⅲ Akt Ⅲ mechanical stretch Ⅲ in-stent restenosis S tenosis of blood vessels leads to ischemia and infarction of the supplied tissues and organs. Besides surgical bypass, stent implantation has been a popular angioplasty procedure for many vascular occlusive diseases. Stents can be implanted in many different vessels, including coronary, carotid, iliac, mesenteric, and intracranial arteries, as well as the aorta. Despite the high success rate of stenting in the treatment of vascular occlusive diseases, the major drawback of this procedure is in-stent restenosis (ISR), which involves late arterial renarrowing at the site of stenting. With the increased usage of stents, ISR has become a common clinical problem and hence is presently under extensive investigation. 1 ISR is largely a result of the formation of neointima, the cellular component of which is mainly the proliferated smooth muscle cells (SMCs). 2,3 Some areas of neointima, especially those surrounding the stent struts, are composed of SMCs exclusively. 3 Although factors such as thrombosis, inflammation, and stent strut stimulation are known to increase the risk of ISR, the underlying mechanism of ISR remains elusive. Conclusions-MechanicalSeveral recent studies have shown that medial damage and stent oversizing are positively correlated with the severity of ISR. 2,4 The amount of stenting-induced intimal hyperplasia is proportional to the degree of circumferential vascular stretch. 5 Stenting exerts its lumen-opening effect by mechanical distention and providing a static luminal scaffolding to eliminate recoil and keep the lumen patent. After stenting, the local vascular wall, including the regions in contact with and adjacent to the stent struts, is subject...

Phosphatidylinositol-3-kinase signaling mediates vascular smooth muscle cell expression of periostin in vivo and in vitro

“…Wortmannin (dissolved in 2%DMSO/PBS) was given by intravenous injection at 60 and 5 minutes before balloon injury followed by daily injections, at a dose of 10 μg per rat. This dosing regimen has been showed to effectively inhibit the activation of Akt, but not ERK1/2 kinases in rat carotid arteries after balloon injury (17,18). The wortmannin treatment of rats inhibited the Akt phosphorylation (Figure 2A) and the periostin mRNA upregulation ( Figure 2B) in the 3-day injured carotid arteries.…”

“…This pathway has been showed to be rapidly activated by growth factors such as PDGF and angiotensin II in vitro (20,21) and by mechanical vascular injury in vivo (17,18). Inhibition of the PI3-kinase/Akt signaling pathway has been showed to limit the neointima formation in rat vascular injury models.…”

“…The involvement of the PI3-kinase signaling in regulation of periostin expression in the vasculature was examined by using the PI3 kinase inhibitor wortmannin. Although the LY294002 compound is a more potent and highly selective PI3-kinase inhibitor, it appears not to be suitable for in vivo studies as it is very insoluble and thus unable to achieve an effective concentration in the artery in vivo according to previous reports (17,18). Wortmannin (dissolved in 2%DMSO/PBS) was given by intravenous injection at 60 and 5 minutes before balloon injury followed by daily injections, at a dose of 10 μg per rat.…”

Akt Mediates Mechanical Strain-Induced Collagen Production by Mesangial Cells

“…In vitro, Akt is phosphorylated in endothelial cells by fluid shear stress (23) and by cyclic stretch in pericytes, osteoblasts, and aortic and bladder smooth muscle cells (24,25,27,45). In vivo, myocardial pressure overload and aortic stent implantation stimulate activation of Akt (46,47). The events leading to PI3K/Akt activation by mechanical strain, however, remain largely unexplored.…”

The application of multiscale modelling to the process of development and prevention of stenosis in a stented coronary artery

“…Care needs to be taken when extrapolating data from in vitro studies, as the precise contribution of individual pathways and the relationship between pathway and cellular response is species and cell type specific (Goncharova et al 2002). Activation of the PI3K/Akt pathway following stent implantation has also been observed in vivo (Zhou et al 2003).…”