Abstract 468: Smooth Muscle Cells Accelerate Endothelial Regeneration Through a Protein Kinase C-delta-Dependent Secretion of CXCR2 Ligands

Background: Efficient regeneration of denuded endothelial cells (ECs) is an important process that counteracts the pro-stenotic activities. Unfortunately, this natural healing process is frequently compromised by disease conditions such as diabetes. Protein kinase C-delta (PKCδ) plays a complex role in the arterial injury response by regulating apoptosis of vascular smooth muscle cells (SMCs) as well as production of chemokines capable of attracting resident and circulating cells. In this study, we explored whether SMCs participate in endothelial repair through a PKCδ-dependent paracrine mechanism. Methods and Results: Following balloon injury to the rat carotid, SMC-specific gene transfer of Prkcd accelerated reendothelialization compared to the empty vector, reflected by a larger area excluded from Evans blue measured 14 days post injury (59.60±5.01% vs 25.38±7.52%). In contrast, SMC-specific knockdown of endogenous Prkcd delayed reendothelialization compared to the non-targeting shRNA control (41.31±6.54% vs 70.31±5.97%). In vitro , media conditioned by AdPKCδ-infected SMCs increased endothelial wound healing without affecting their proliferation and viability. In addition, SMCs in a PKCδ-dependent fashion attracted circulating angiogenic cells (CACs), a cell population that promotes neovascularization via production of angiogenic factors. A PCR-based array analysis identified Cxcl1 and Cxcl7 among others as PKCδ-mediated chemokines produced by SMCs. Blocking CXCL7 or CXCR2 significantly inhibited endothelial wound healing and CAC migration in response to AdPKCδ-infected SMC conditioned media. In vivo , PKCδ overexpression in SMCs following balloon injury increased CXCL7 production and stimulated CACs recruitment to injured arteries. Furthermore, insertion of a Cxcl7 cDNA in the lentiviral vector that carries a Prkcd shRNA overcame the negative effects of Prkcd knockdown on reendothelialization. Conclusions: Regeneration of denuded endothelium involves multiple cell types from the vascular wall as well as circulation. SMCs stimulate reendothelialization in a PKCδ-dependent paracrine mechanism, likely through CXCL7-mediated recruitment of ECs from uninjured endothelium and CACs from circulation.