Abstract 5513: p38 MAPK Targets the Generation and Formation of Pro-Inflammatory Endothelial Microparticles but not the Microparticle Derived Response
Endothelial microparticles (EMPs) are submicron vesicles which form directly from the surface membrane under conditions of cellular activation and apoptosis. EMPs are shed into circulation in patients with vascular diseases and may themselves act as central paracrine inflammatory mediators, conferring further inflammatory activity. Despite this, our knowledge of the inflammatory pathways that govern EMP formation and function is lacking. Given the established TNFα-induction of EMPs, and the pivotal role of p38 in TNFα-mediated pathways, we hypothesized that p38 signaling may impact EMPs. EMPs derived from cultures of human aortic endothelial cells (hAECs) treated with TNFα and highly selective inhibitors of p38 (SB-239036AN & SB-239063) were investigated. p38 inhibition in hAECs resulted in ~50% reduction (P≤.0001) in the membrane formation and release of TNFα induced EMPs as determined by scanning electron microscopy on the membrane surface, and flow cytometry and ELISA based assays from the cell supernatant. Importantly, suppression of microparticle release was specific to p38 MAPK pathways as inhibition of JNK and ERK had no effect. TNFα and TNFα+p38i derived-EMPs induce approximately four-fold increase (P≤.001) in Icam1 expression and soluble protein release from targeted hAECs versus baseline EMPs. However, p38 signaling, although critical for vesicle formation in the originator cell, does not function in the cells response to microparticles. Our findings implicate p38 MAPK signaling as significant and selective in the formation and maturation of EMPs. EMPs elicited a pro-inflammatory response from targeted hAECs, and highly dependant on the conditions under which those EMPs were generated. However, our results imply a unidirectional model in which p38 MAPK is critical at the junction of microparticle formation, but not the target cell response to EMPs. These findings indicate a novel mechanism by which p38 inhibitors may offer therapeutic benefit in-vivo via the ability to uncouple the EMP-mediated paracrine inflammatory cascade.