Pivotal Role of Serum- and Glucocorticoid-Inducible Kinase 1 in Vascular Inflammation and Atherogenesis
Authors: Borst Oliver , Schaub Malte , Walker Britta , Schmid Evi , Münzer Patrick , Voelkl Jakob , Alesutan Ioana , Rodríguez José M. , Vogel Sebastian , Schoenberger Tanja , Metzger Katja , Rath Dominik , Umbach Anja , Kuhl Dietmar , Müller Iris I. , Seizer Peter , Geisler Tobias , Gawaz Meinrad , Lang Florian 
Published: January 2015

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 active
S422D
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) abrogated
S422D
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 in
S422D
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 in
S422D
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
S422D
SGK1-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.