Simvastatin suppresses LPS-induced Akt phosphorylation in the human monocyte cell line THP-1

BACKGROUND: Activation of the small GTPase, Rac, requires post-translational modification by isoprenylation. Statins interfere with this process by blocking the synthesis of isoprenoid intermediates. The protein kinase Akt is a multifunctional regulator of cell behavior that has been linked to Rac activation. We have shown that lipopolysaccharide (LPS) stimulation leads to Rac activation in THP-1 cells. Therefore, we hypothesized that LPS stimulation would also activate Akt, a downstream effector of Rac, and that this may be blocked by statin pretreatment. MATERIALS AND METHODS: THP-1 cells were maintained in 1% fetal calf serum with or without 20 microM simvastatin for 24 h, followed by LPS stimulation for increasing time. Cytoskeletal changes were observed using Alexa-Phalloidin. Akt was immunoprecipitated from total cell lysate. Activated Akt was detected by immunoblotting with a phospho-Akt antibody and was quantified by image densitometry. RESULTS: LPS stimulation of THP-1 cells results in membrane ruffling and cell polarization. Furthermore, LPS increased Akt activation in THP-1 cells when compared with the nonstimulated controls. Akt phosphorylation peaked after 15 min of LPS stimulation and was suppressed by pretreatment with simvastatin. CONCLUSIONS: These data demonstrate that LPS stimulation leads to increased Akt phosphorylation, which can be suppressed with simvastatin pretreatment. This suggests one possible mechanism through which simvastatin could modulate LPS-induced signaling events in monocytes to improve the host response to Gram-negative infections.