Objective: The objective of this study is to identify mechanisms of mechanical stretch on neointima formation. Methods and Results: By a microarray analysis, we found that mechanical cyclic stretch (15% elongation) stimulated the transcription of SGK-1 (serum-, glucocorticoid-regulated kinase-1). Mechanical stretch-induced SGK-1 mRNA expression was blocked by actinomycin D. The mechanism for the SGK-1 expression involved MEK1 but not p38 or JNK signaling pathway. SGK-1 activation in response to stretch is blocked by insulin-like growth factor (IGF)-1 receptor inhibitor and mammalian target of rapamycin complex (mTORC)2 inhibitor (Ku-0063794) but not mTORC1 inhibitor (rapamycin). Mechanical stretch-induced bromodeoxyuridine incorporation was reduced by 83.5% in venous SMCs isolated from SGK-1 knockout mice. In contrast, inhibition of Akt, another downstream signal of PI3K resulted in only partial inhibition of mechanical stretch-induced proliferation of venous SMCs. Mechanical stretch also induced phosphorylation and nuclear exportation of p27 kip1 , whereas knockout of SGK-1 attenuated this effect of mechanical stretch on p27
kip1. In vivo, we found that placement of a vein graft into artery increased SGK-1 expression. Knockout of SGK-1 effectively prevented neointima formation in vein graft. There is significant lower level of p27 kip1 located in the nucleus of neointima cells in SGK-1 knockout mice compared with that of wild-type vein graft. In addition, we also found that wire injury of artery or growth factors in vitro increased expression of SGK-1. Key Words: mechanical stretch Ⅲ serum-, glucocorticoid-regulated kinase-1 Ⅲ neointima formation Ⅲ mTORC Ⅲ mammalian target of rapamycin complex I ncreased growth of venous smooth muscle cells (SMCs) is a hallmark of vein graft failure. [1][2][3][4] After implantation of a vein graft into the arterial circulation, the venous wall is immediately exposed to mechanical stimuli. Those include arterial pressure, wall tension, shear stress, and pulsatile flow, all of which modulate graft physiology. [5][6][7] Such alteration could lead to the activation of many intracellular signaling pathways. Mechanical stress could also stimulate the synthesis and/or secretion of various bioactive molecules including platelet-derived growth factor (PDGF), basic fibroblast growth factor, and the transcriptional factors. 8 -10 Recently, we have shown that mechanical stretch stimulates expression and activation of insulin-like growth factor (IGF)-1 and its receptor in venous SMCs, and we found that activated IGF-1R/phosphatidylinositol 3-kinase (PI3K) is essential for mechanical stretch-induced proliferation of venous SMCs. 11 However, the downstream targets of IGF-1/ PI3K signaling that mediate mechanical stretch-induced proliferation of venous SMCs are still unknown.
Conclusions:Belonging to the AGC subfamily, the catalytic domain of SGK-1 (serum-, glucocorticoid-regulated kinase-1) is 54% identical to that of AKT, and it shares common downstream substrates with AKT. 12,13 Activation...