Justin C. Mason

Increased Endothelial Mitogen-Activated Protein Kinase Phosphatase-1 Expression Suppresses Proinflammatory Activation at Sites That Are Resistant to Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of arteries. It is triggered by proinflammatory mediators which induce adhesion molecules (eg, vascular cell adhesion molecule [VCAM]-1) in endothelial cells (ECs) by activating p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein (MAP) kinases by phosphorylation. Blood flow influences atherosclerosis by exerting shear stress (mechanical drag) on the inner surface of arteries, a force that alters endothelial physiology. Regions of the arterial tree exposed to high shear are protected from endothelial activation, inflammation, and atherosclerosis, whereas regions exposed to low or oscillatory shear are susceptible. We examined whether MAP kinase phosphatase (MKP)-1, a negative regulator of p38 and JNK, mediates the antiinflammatory effects of shear stress. We observed that expression of MKP-1 in cultured ECs was elevated by shear stress, whereas the expression of VCAM-1 was reduced. MKP-1 induction was shown to be necessary for the antiinflammatory effects of shear stress because gene silencing of MKP-1 restored VCAM-1 expression in sheared ECs. Immunostaining revealed that MKP-1 is preferentially expressed by ECs in a high-shear, protected region of the mouse aorta and is necessary for suppression of EC activation at this site, because p38 activation and VCAM-1 expression was enhanced by genetic deletion of MKP-1. We conclude that MKP-1 induction is required for the antiinflammatory effects of shear stress. Thus, our findings reveal a novel molecular mechanism contributing to the spatial distribution of vascular inflammation and atherosclerosis.

Decay‐accelerating factor induction by tumour necrosis factor‐α, through a phosphatidylinositol‐3 kinase and protein kinase C‐dependent pathway, protects murine vascular endothelial cells against complement deposition

We have shown that human endothelial cells (EC) are protected against complement‐mediated injury by the inducible expression of decay‐accelerating factor (DAF). To understand further the importance of DAF regulation, we characterized EC DAF expression on murine EC in vitro and in vivo using a model of glomerulonephritis. Flow cytometry using the monoclonal antibody (mAb) Riko‐3 [binds transmembrane‐ and glycosylphosphatidylinositol (GPI)‐anchored DAF], mAb Riko‐4 (binds GPI‐anchored DAF) and reverse transcription–polymerase chain reaction (RT–PCR), demonstrated that murine EC DAF is GPI‐anchored. Tumour necrosis factor‐α (TNF‐α) increased EC DAF expression, detectable at 6u2003hr and maximal at 24–48u2003hr poststimulation. DAF upregulation required increased steady‐state DAF mRNA and protein synthesis. In contrast, no increased expression of the murine complement receptor‐related protein‐Y (Crry) was seen with TNF‐α. DAF upregulation was mediated via a protein kinase C (PKC)α, phosphoinositide‐3 kinase (PI‐3 kinase), p38 mitogen‐activated protein kinase (MAPK) and nuclear factor‐κB (NF‐κB)‐dependent pathway. The increased DAF was functionally relevant, resulting in a marked reduction in C3 deposition following complement activation. In a nephrotoxic nephritis model, DAF expression on glomerular capillaries was significantly increased 2u2003hr after the induction of disease. The demonstration of DAF upregulation above constitutive levels suggests that this may be important in the maintenance of vascular integrity during inflammation, when the risk of complement‐mediated injury is increased. The mouse represents a suitable model for the study of novel therapeutic approaches by which vascular endothelium may be conditioned against complement‐mediated injury.