p38 mitogen-activated protein kinase targets the production of proinflammatory endothelial microparticles.
BACKGROUND
Endothelial microparticles (EMPs) are irregularly shaped membrane fragments shed into the circulation in patients with vascular diseases, and may themselves act to enhance the endothelial response to inflammation. On the basis of the importance of p38 mitogen-activated protein kinase (MAPK) in endothelial responses to inflammatory stimuli, we sought to define the role of p38 in EMP generation and function.


METHODS
Microparticle generation from cultures of human aortic endothelial cells (hAECs) treated with tumor necrosis factor-alpha (TNF-alpha) and p38 inhibition was quantified via multiple modalities. The response of target endothelial cells was assessed by treatment of cells with EMPs generated under various conditions.


RESULTS
Inhibition of p38 in hAECs, using pharmacologic agents, resulted in a 50% reduction of TNF-alpha-induced EMPs. Importantly, suppression of microparticles was specific to p38 MAPK pathways. EMPs triggered by TNF-alpha activation induced an approximately four-fold increase in soluble intercellular adhesion molecule-1 (sICAM-1) release from targeted cells. However, inhibition of p38 MAPK in the targeted cell prior to EMP treatment did not alter the sICAM1 response.


CONCLUSIONS
Our findings implicate p38 MAPK signaling as significant and selective in the formation and maturation of EMPs. EMPs elicited a proinflammatory response from targeted hAECs that was dependent on the conditions under which EMPs were generated. However, our results imply a unidirectional model in which p38 MAPK is critical at the source of microparticle formation, but not the target cell response to EMPs. These findings indicate a novel mechanism by which p38 inhibition may offer therapeutic benefit in vivo via direct inhibition of EMP formation.
Curtis
A M
AM
GlaxoSmithKline, King of Prussia, PA, USA. Annie.curtis@sfi.ie
Wilkinson
P F
PF
Gui
M
M
Gales
T L
TL
Hu
E
E
Edelberg
J M
JM
D055252:Cell-Derived Microparticles / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000276:immunology / Q000648:ultrastructure*; D004730:Endothelium, Vascular; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*
D018836:Inflammation Mediators; D047428:Protein Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases