Redox sensitive regulation of thioredoxin interacting protein (TxnIP) gene expressions in mouse vascular smooth muscle cells

Abstract

Since nitric oxide (NO) is a redox-sensitive signaling molecule, reactive oxygen species (ROS) level influences the efficiency of NO-related signaling. However, much of the knowledge has not been accumulated on how NO regulates ROS level. Here, we take the thioredoxin (Trx) system as a model of regulatory mechanism of ROS by NO. The functional availability of Trx is strictly regulated through the binding with thioredoxin interacting protein (TxnIP); TxnIP is a known regulatory factor involved in atherosclerosis and vascular endothelial cell functions. Hence, we studied effects of NO on TxnIP in mouse vascular smooth muscle cells (VSMC), where NO from vascular endothelial cells works as an intercellular signal in various degree. Following a treatment with S-nitrosoglutathione (GSNO), TxnIP mRNA level analyzed by real-time PCR method in mouse VSMC decreased 1/6 to the control (untreated) within an hour. The decrease was then followed by an increase 5-fold over control within 4–5 h. This bi-phasic response of TxnIP mRNA to GSNO was triggered by the consumption of GSNO in cells. Interestingly, the induction of TxnIP mRNA was not observed under the anaerobic condition. TxnIP proteins decreased in parallel with mRNA change. Thereby, GSNO-treated cells exhibited higher resistance to H 2 O 2 exposure (up to 30 μM) than control cells. It is probably resulting from a complementary increase of Trx and activation of peroxidase activity coupled with Trx. These results suggest NO suppresses ROS levels through the inhibition of TxnIP, which may extend the effect of NO.