Key role of PI3Kgamma in monocyte chemotactic protein-1-mediated amplification of PDGF-induced aortic smooth muscle cell migration

BACKGROUND AND PURPOSE: Vascular smooth muscle cell (SMC) migration within the arterial wall is a crucial event in atherogenesis and restenosis. Monocyte chemotactic protein-1/CC-chemokine receptor 2 (MCP-1/CCR2) signalling is involved in SMC migration processes but the molecular mechanisms have not been well characterized. We investigated the role of PI3Kgamma in SMC migration induced by MCP-1. EXPERIMENTAL APPROACHES: A pharmacological PI3Kgamma inhibitor, adenovirus encoding inactive forms of PI3Kgamma and genetic deletion of PI3Kgamma were used to investigate PI3Kgamma functions in the MCP-1 and platelet-derived growth factor (PDGF) signalling pathway and migration process in primary aortic SMC. KEY RESULTS: The gamma isoform of PI3K was shown to be the major signalling molecule mediating PKB phosphorylation in MCP-1-stimulated SMC. Using a PI3Kgamma inhibitor and an adenovirus encoding a dominant negative form of PI3Kgamma, we demonstrated that PI3Kgamma is essential for SMC migration triggered by MCP-1. PDGF receptor stimulation induced MCP-1 mRNA and protein accumulation in SMCs. Blockade of the MCP-1/CCR2 pathway or pharmacological inhibition of PI3Kgamma reduced PDGF-stimulated aortic SMC migration by 50%. Thus PDGF promotes an autocrine loop involving MCP-1/CCR2 signalling which is required for PDGF-mediated SMC migration. Furthermore, SMCs isolated from PI3Kgamma-deficient mice (PI3Kgamma(-/-)), or mice expressing an inactive PI3Kgamma (PI3Kgamma(KD/KD)), migrated less than control cells in response to MCP-1 and PDGF. CONCLUSIONS AND IMPLICATIONS: PI3Kgamma is essential for MCP-1-stimulated aortic SMC migration and amplifies cell migration induced by PDGF by an autocrine/paracrine loop involving MCP-1 secretion and CCR2 activation. PI3Kgamma is a promising target for the treatment of aortic fibroproliferative pathologies.