Insulin-like growth factor-I induces reactive oxygen species production and cell migration through Nox4 and Rac1 in vascular smooth muscle cells.

AIMS: We showed previously that insulin-like growth factor-I (IGF-I)-induced vascular smooth muscle cells (VSMCs) proliferation through the production of reactive oxygen species (ROS). However, how IGF-I-induced ROS was unknown. The aim of this study is to investigate the mechanisms by which IGF-I induces ROS production in VSMCs. Methods results Reverse transcription-PCR, real-time PCR, immunoblotting, and confocal microscopic image analysis were employed to determine protein expression, small Rho-GTPase Rac1 activation, and ROS production. Inhibition of NADPH oxidase 4 (Nox4) or Rac1 was performed by means of siRNA technology. Inhibition of Rac1 activity was accomplished using dominant-negative form of Rac1 (N17Rac1) plasmid. VSMCs from Sprague-Dawley rat thoracic aortas were used in this work.IGF-I enhanced ROS production in rat VSMCs. IGF-I increased the protein level of Nox4 but had little effect on its mRNA level. IGF-I induced the activation of Rac1. Either knockdown of Nox4 or inactivation of Rac1 impaired IGF-I-induced ROS. Over-expression of Nox4 increased NADPH oxidase activity, which was not influenced by inactivation of Rac1. Neither over-expression nor knockdown of Rac1 influenced Nox4 expression. Knockdown of Nox4 did not affect IGF-I-induced activation of Rac1. IGF-I increased matrix metalloproteinase (MMP)-2 and 9 activity and promoted VSMC migration, which was inhibited by knockdown of Nox4 and inactivation of Rac1.
CONCLUSION: Our results suggest that Nox4 and Rac1 mediate IGF-I-induced ROS production and cell migration in VSMCs and that Nox4 is not regulated by Rac1.