Pivotal role of serum- and glucocorticoid-inducible kinase 1 in vascular inflammation and atherogenesis

Abstract

Objective-Atherosclerosis, an inflammatory disease of arterial vessel walls, requires migration and matrix metalloproteinase (MMP)-9-dependent invasion of monocytes/macrophages into the vascular wall. MMP-9 expression is stimulated by transcription factor nuclear factor-κB, which is regulated by inhibitor κB (IκB) and thus IκB kinase. Regulators of nuclear factor-κB include serum- and glucocorticoid-inducible kinase 1 (SGK1). The present study explored involvement of SGK1 in vascular inflammation and atherogenesis. Approach and Results-Gene-targeted apolipoprotein E (ApoE)-deficient mice without (apoe-/- sgk1+/+ ) or with (apoe-/- sgk1-/- ) additional SGK1 knockout received 16-week cholesterol-rich diet. According to immunohistochemistry atherosclerotic lesions in aorta and carotid artery, vascular CD45+ leukocyte infiltration, Mac-3+ macrophage infiltration, vascular smooth muscle cell content, MMP-2, and MMP-9 positive areas in atherosclerotic tissue were significantly less in apoe-/- sgk1-/- mice than in apoe-/- sgk1+/+ mice. As determined by Boyden chamber, thioglycollate-induced peritonitis and air pouch model, migration of SGK1-deficient CD11b+ F4/80+ macrophages was significantly diminished in vitro and in vivo. Zymographic MMP-2 and MMP-9 production, MMP-9 activity and invasion through matrigel in vitro were significantly less in sgk1-/- than in sgk1+/+ macrophages and in control plasmid-transfected or inactive K127N SGK1-transfected than in constitutively activeS422D SGK1-transfected THP-1 cells. Confocal microscopy revealed reduced macrophage number and macrophage MMP-9 content in plaques of apoe-/- sgk1-/- mice. In THP-1 cells, MMP-inhibitor GM6001 (25 μmol/L) abrogatedS422D SGK1-induced MMP-9 production and invasion. According to reverse transcription polymerase chain reaction, MMP-9 transcript levels were significantly reduced in sgk1-/- macrophages and strongly upregulated inS422D SGK1-transfected THP-1 cells compared with control plasmid-transfected or K127N SGK1-transfected THP-1 cells. According to immunoblotting and confocal microscopy, phosphorylation of IκB kinase and inhibitor κB and nuclear translocation of p50 were significantly lower in sgk1-/- macrophages than in sgk1+/+ macrophages and significantly higher inS422D SGK1-transfected THP-1 cells than in control plasmid-transfected or K127N SGK1-transfected THP-1 cells. Treatment of S422D SGK1-transfected THP-1 cells with IκB kinase-inhibitor BMS-345541 (10 μmol/L) abolished S422DSGK1-induced increase of MMP-9 transcription and gelatinase activity. Conclusions-SGK1 plays a pivotal role in vascular inflammation during atherogenesis. SGK1 participates in the regulation of monocyte/macrophage migration and MMP-9 transcription via regulation of nuclear factor-κB.