Inflammation contributes to development of atherosclerosis. Atherosclerosis is decreased in regions of steady flow associated with high shear stress (termed s-flow), compared to regions of disturbed and low flow (termed d-flow). This finding has yielded the concept that s-flow is atheroprotective and d-flow is atheropromoting, in part by causing endothelial cell (EC) dysfunction. Previously we showed that s-flow activated thioredoxin-1 (Trx1) in EC, decreased expression of the Trx1 interacting protein (Txnip), and inhibited tumor necrosis factor (TNF) signaling. Several findings indicate that Txnip-dependent signaling represents a unique atheropromoting mechanism. 1) Txnip expression is increased by d-flow and promotes the adhesive phenotype of EC, by stimulating VCAM-1 expression. 2) Txnip specifically inhibits Trx1 function and contributes to oxidative stress in EC. 3) Txnip is required for TNF- mediated JNK and caspase-3 activation in EC. 4) Exciting preliminary data show that TNF causes Trx1 and Txnip to translocate to the plasma membrane and stimulate a tyrosine kinase receptor (TKR) signaling pathway that inhibits apoptosis via Akt activation (Fig. 1). Recently, SHP2, a protein tyrosine phosphatase (PTPase), was shown to stimulate the Apoptosis Signal-regulated Kinase (ASK1)-JNK-VCAM1 pathway. 5) Our data show that Txnip binding to SHP2 also activates this pathway (Fig. 1). Thus our major hypothesis is Txnip, like NF-kB, stimulates both pro-survival and pro-inflammatory pathways in EC. In the proposed aims we will identify mechanisms to separate the Txnip-Trx1-TKR-Akt survival pathway from the Txnip-SHP2-ASK1 inflammation pathway.
Aim 1 : Show that Trx-Txnip stimulates TKR activation and survival by assembling signal complexes and inhibiting PTPases.
Aim 2 : Show that Txnip regulates SHP2 activity and subcellular location modulating ASK1 activity.
Aim 3 : Show that d-flow alters Txnip expression and location inhibiting Trx1 activity and activating ASK1.
Aim 4 : Show that EC-specific Txnip knockout mice exhibit improved EC function and decreased atherosclerosis. These studies should provide insight into mechanisms by which flow inhibits inflammation and facilitate development of therapeutic approaches to limit atherosclerosis.
Strokes and heart attacks are the leading cause of death in the US. Interventions such as bypass surgery and angioplasty treat acute events, but there are limited therapies to prevent the underlying disease termed atherosclerosis. We have found that thioredoxin interacting protein is increased in blood vessels at sites where atherosclerosis develops. Here we will focus on novel approaches to inhibit the function of this protein. Elucidating the specific pathways by which thioredoxin interacting protein modulates vessel function will provide the basis to develop new therapies to prevent atherosclerosis.
