EphA2 regulation of atherosclerotic smooth muscle phenotype

PROJECT SUMMARY The guidance receptor EphA2 promotes atherogenic inflammation driving an unstable plaque phenotype and promotes smooth muscle cell (SMC) fibroproliferative expansion enhancing plaque stability. While most cells within the plaque express EphA2, only endothelial cells and leukocytes express its ephrinA1 ligand, and endothelial EphA2 ligation with ephrinA1 enhances proinflammatory gene expression and monocyte recruitment. SMCs express EphA2 during phenotypic transition, associated with loss of contractile markers and a transition to a fibroproliferative phenotype. A known oncogene, EphA2 expression enhances smooth muscle proliferation and extracellular matrix deposition in vitro, and global EphA2 deletion reduces atherosclerosis associated with diminished inflammation and reduced smooth muscle content and matrix deposition. While EphA2 expression promotes SMC fibroproliferative remodeling, EphA2 ligation reduces smooth muscle proliferation and migration, suggesting that ligand-dependent EphA2 signaling may reduce plaque stability by promoting inflammation and preventing fibroproliferative remodeling. EphA2 ligand-independent signaling, involving canonical S897 phosphorylation and non-canonical Y772 transphosphorylation in focal adhesions, likely mediates EphA2's positive effects on fibroproliferative remodeling and fibrous cap formation. SMCs show EphA2 S897 phosphorylation during atherogenic vascular remodeling in vivo, and S897 phosphorylation enhances smooth muscle migration in vitro. EphA2 Y772 transphosphorylation drives fibronectin deposition, and our preliminary data suggest that Y772-dependent matrix remodeling likely mediates EphA2-dependent phenotypic transition and fibroproliferative remodeling by activating a novel EphA2-binding transcription factor. In addition, EphA2 strongly inhibits tumor suppressor expression, and our preliminary data show a key role for one of these tumor suppressors in regulating atherosclerotic smooth muscle phenotype. Therefore, we hypothesize that EphA2 ligand-dependent signaling promotes inflammation and reduces fibroproliferative remodeling, whereas ligand-independent signaling drives fibroproliferative remodeling directly through fibronectin-dependent regulation of an EphA2-binding transcription factor and indirectly through tumor suppressor inhibition. This proposal will assess how EphA2 and ephrinA1 expression affects atherosclerotic inflammation and plaque stability, to characterize the mechanisms of EphA2 ligand-independent signaling regulating smooth muscle phenotype, and to characterize how EphA2-dependent tumor suppressor regulation affects smooth muscle phenotype in vitro and in vivo. Successful completion of these Aims will characterize novel signaling mechanisms driving EphA2-dependent plaque stability and may identify novel therapeutic mechanisms targeting EphA2 signaling to stabilize atherosclerotic plaques.