Involvement of Interleukin-1 Receptor–Associated Kinase-1 in Vascular Smooth Muscle Cell Proliferation and Neointimal Formation After Rat Carotid Injury

Abstract

Objective— Reduced frequency of atherosclerotic plaques is observed in interleukin-1 receptor–associated kinase-1 (IRAK1)–deficient mice; however, the underlying mechanism is not clear. Therefore, this study investigate the role of IRAK1 in vascular smooth muscle cell proliferation and neointimal hyperplasia. Approach and Results— Stimulation of rat primary vascular smooth muscle cells with fetal bovine serum (10%) or platelet-derived growth factor-BB (20 ng/mL) for 15 minutes to 24 hours induced a time-dependent increase in IRAK1 and extracellular signal–regulated kinase (ERK) activation, proliferating cell nuclear antigen upregulation and p27Kip1 downregulation as assessed by Western blotting. Inhibitors of ERK pathway (U0126, 10 μmol/L), IRAK (IRAK1/4, 3 μmol/L), protein kinase C (PKC; Ro-31-8220, 1 μmol/L), siRNA of toll-like receptor-4 (200 nmol/L), and PKC-ε (200 nmol/L) significantly attenuated these changes. Platelet-derived growth factor induced endogenous IRAK–ERK–PKC-ε association in a toll-like receptor-4 and PKC-ε–dependent manner. A time-dependent increase in IRAK1 and ERK activation was observed after 15 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours of carotid balloon injury in rats. Balloon injury induced endogenous IRAK–ERK–PKC-ε interaction. Perivascular application of IRAK1/4 inhibitor (100 μmol/L), U0126 (100 μmol/L), and IRAK1 siRNA (220 and 360 nmol/L) in pluronic gel abrogated balloon injury–induced ERK phosphorylation, activation, and p27Kip1 downregulation. Hematoxylin and eosin staining and immunohistochemistry of proliferating cell nuclear antigen and smooth muscle actin demonstrated that balloon injury–induced intimal thickening and neointimal vascular smooth muscle cell proliferation were significantly abrogated in the presence of IRAK1/4 inhibitor, IRAK1 siRNA, and U0126. Conclusions— IRAK1 mediates vascular smooth muscle cell proliferation and neointimal hyperplasia by regulating PKC-ε–IRAK1–ERK axis.