Abstract 4955: Akt Cooperates with Membrane Type 1-Matrix Metalloproteinase (MT1-MMP) in TNF-Alpha-Induced Signaling Pathways of Endothelial Dysfunction and Haemostasis
Background: Akt is a critical molecule in several signal transduction pathways involved in vascular responses. Membrane type 1-matrix metalloproteinase (MT1-MMP), a membrane-anchored MMP, functions as a signaling molecule in addition to a proteolytic enzyme.
Hypothesis: Akt cooperates with MT1-MMP in tumor necrosis factor (TNF)-alpha-induced signaling pathways of vascular responses including endothelial dysfunction and haemostasis.
Methods and Results: TNF-alpha (10 ng/mL) induced a transient increase in Akt phosphorylation within 15 minutes, followed by the profound decrease of Akt phosphorylation and the increase in MT1-MMP activity within 60 minutes, in cultured human aortic endothelial cells (ECs). To demonstrate the role of MT1-MMP for Akt signaling pathway in TNF-alpha-stimulated ECs, we used siRNA to knockdown MT1-MMP protein in ECs. Silencing of MT1-MMP reversed TNF-alpha-triggered transient upregulation of Akt phosohorylation within 15 minutes and the downregulation within 60 minutes, suggesting that MT1-MMP may be a key regulator of Akt phosphortlation in TNF-alpha stimulated ECs. In the downstream events, TNF-alpha increased tissue factor (TF) expression through NF-kappa B activation and decreased thrombomoduline (TM) expression. Inhibition of Akt by Akt inhibitor X markedly enhanced TNF-alpha-induced upregulation of TF expression and downregulation of TM expression. Silencing of MT1-MMP by siRNA also reversed the changed expression of TF and TM induced by TNF-alpha. These results demonstrated that MT1-MMP-mediated Akt phosphorylation is a critical mechanism in modulation of TNF-alpha-induced signaling pathways and downstream events. Furthermore, we found that pioglitazone, PPAR gamma agonist, suppressed TNF-alpha-induced downregulation of Akt phosphorylation and reversed the upregulated TF expression and upregulated TM expression by TNF-alpha in ECs. This supports a mechanism for pleiotropic effect of pioglitazone on cardiovascular disease.
Conclusions: We show new evidence that Akt is a key modifier for TNF-alpha-induced signaling pathways in cooperation with MT1-MMP for modulation of endothelial dysfunction and haemostasis.