Mechanisms of Statin-mediated Inhibition of Small G-protein Function

Andrew Cordle,Jessica Koenigsknecht-Talboo,Brandy Wilkinson,Allison Limpert,Gary Landreth

doi:10.1074/jbc.m505268200

Andrew Cordle, Jessica Koenigsknecht-Talboo + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m505268200

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Abstract

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been reported to reduce the risk of Alzheimer disease. We have shown previously that statins inhibit a beta-amyloid (Abeta)-mediated inflammatory response through mechanisms independent of cholesterol reduction. Specifically, statins exert anti-inflammatory actions through their ability to prevent the isoprenylation of members of the Rho family of small G-proteins, resulting in the functional inactivation of these G-proteins. We report that statin treatment of microglia results in perturbation of the cytoskeleton and morphological changes due to alteration in Rho family function. Statins also block Abeta-stimulated phagocytosis through inhibition of Rac action. Paradoxically, the statin-mediated inactivation of G-protein function was associated with increased GTP loading of Rac and RhoA, and this effect was observed in myeloid lineage cells and other cell types. Statin treatment disrupted the interaction of Rac with its negative regulator the Rho guanine nucleotide dissociation inhibitor (RhoGDI), an interaction that is dependent on protein isoprenylation. We propose that lack of negative regulation accounts for the increased GTP loading. Isoprenylation of Rac is also required for efficient interaction with the plasma membrane, and we report that statin treatment dramatically reduces the capacity of Rac to interact with membranes. These results suggest a mechanism by which statins inhibit the actions of Rho GTPases and attenuate Abeta-stimulated inflammation.

Highlights

Isoprenoids farnesyl pyrophosphate or geranylgeranyl pyrophosphate (GGpp) is negatively affected by statin-mediated inhibition of HMGCoA reductase
We reported that the anti-inflammatory actions of statins in A␤-stimulated microglia are independent of cholesterol reduction but are a consequence of the reduction of cellular levels of the isoprenoid GGpp [16]
Statin Treatment Alters Cell Morphology—We observed that BV-2 microglia exposed to statins exhibit altered cellular morphology

Summary

EXPERIMENTAL PROCEDURES

Materials and Reagents—␤-Amyloid (A␤) peptides A␤-(25–35) and A␤-(1– 42), purchased from the American Peptide Company (Sunnyvale, CA), were dissolved in sterile water at a concentration of 2 mM and. Phalloidin Staining—BV-2 cells (1.5 ϫ 105) were collected, plated on coverslips resting in 24-well plates, and incubated in serum-free DMEM in the presence or absence of increasing concentrations of simvastatin and lovastatin overnight at 37 °C and 5% CO2. The percentage of phagocytic cells was determined Both simvastatin and lovastatin reduced fA␤-(1– 42)-stimulated phagocytosis to basal levels at concentrations as low as 250 nM (Fig. 2, A and B). Supplementing the medium of statin-treated cells with mevalonic acid, the product of HMG-CoA reductase, reversed the statin-mediated inhibition of phagocytosis (Fig. 2E). Prevention of isoprenylation with the geranylgeranyl transferase inhibitor GTI-286 mimicked the anti-phagocytic actions of statins (Fig. 2F) These data demonstrate that statins disrupt Rac function via perturbation of isoprenylation, inhibiting A␤-stimulated phagocytosis. A Tukey-Kramer post test was used to determine p values

RESULTS

Statins Inhibit the Interactions between Rac and Its Negative Regulator RhoGDI

Statins Prevent Rac Translocation to the Plasma Membrane

DISCUSSION

Although we propose that the lack of interaction with RhoGDI

Gary Landreth