Regulation of Macrophage Cholesterol Efflux through Hydroxymethylglutaryl-CoA Reductase Inhibition

Abstract

The cholesterol biosynthetic pathway produces numerous signaling molecules. Oxysterols through liver X receptor (LXR) activation regulate cholesterol efflux, whereas the non-sterol mevalonate metabolite, geranylgeranyl pyrophosphate (GGPP), was recently demonstrated to inhibit ABCA1 expression directly, through antagonism of LXR and indirectly through enhanced RhoA geranylgeranylation. We used HMG-CoA reductase inhibitors (statins) to test the hypothesis that reduced synthesis of mevalonate metabolites would enhance cholesterol efflux and attenuate foam cell formation. Preincubation of THP-1 macrophages with atorvastatin, dose dependently (1-10 M) stimulated cholesterol efflux to apolipoprotein AI (apoAI, 10 -60%, p < 0.05) and high density lipoprotein (HDL 3 ) (2-50%, p < 0.05), despite a significant decrease in cholesterol synthesis (2-90%). Atorvastatin also increased ABCA1 and ABCG1 mRNA abundance (30 and 35%, p < 0.05). Addition of mevalonate, GGPP or farnesyl pyrophosphate completely blocked the statin-induced increase in ABCA1 expression and apoAI-mediated cholesterol efflux. A role for RhoA was established, because two inhibitors of Rho protein activity, a geranylgeranyl transferase inhibitor and C3 exoenzyme, increased cholesterol efflux to apoAI (20 -35%, p < 0.05), and macrophage expression of dominant-negative RhoA enhanced cholesterol efflux to apoAI (20%, p < 0.05). In addition, atorvastatin increased the RhoA levels in the cytosol fraction and decreased the membrane localization of RhoA. Atorvastatin treatment activated peroxisome proliferator activated receptor ␥ and increased LXR-mediated gene expression suggesting that atorvastatin induces cholesterol efflux through a molecular cascade involving inhibition of RhoA signaling, leading to increased peroxisome proliferator activated receptor ␥ activity, enhanced LXR activation, increased ABCA1 expression, and cholesterol efflux. Finally, statin treatment inhibited cholesteryl ester accumulation in macrophages challenged with atherogenic hypertriglyceridemic very low density lipoproteins indicating that statins can regulate foam cell formation.

Identification and pharmacological characterization of cholesterol-5,6-epoxide hydrolase as a target for tamoxifen and AEBS ligands

“…α-CE is the only epimer of CE found in the adrenal cortex, where it is produced by an as-yet-unidentified cytochrome p450 (35). α-CE can be esterified by Sult2B1b (36) to give a 3β-sulfated product that antagonizes liver X-receptor sig- naling (37,38), or it can be transformed by glutathione transferase into 3β,5α-dihydroxycholestan-6β-yl-S-glutathione (39,40). In addition, we have reported that the aminolysis of α-CE by biogenic amines under catalytic conditions is possible and generates powerful cell-differentiating alkylaminooxysterols (30).…”

Cholesterol 24S-Hydroxylase Overexpression Inhibits the Liver X Receptor (LXR) Pathway by Activating Small Guanosine Triphosphate-Binding Proteins (sGTPases) in Neuronal Cells

“…LXR ligands have been previously shown to have differential effects on the activation of Rho family members, namely by inhibiting RhoA and activating Cdc42 [50,51]. Moreover, RhoA has been reported to inhibit LXR [45][46][47][48][49], suggesting integration between Rho-dependent functions and LXR activation. Our experiments on the effect of CYP46A1 overexpression on the LXR pathway show that, in contrast to the effect of added 24OHC, increased levels of CYP46A1 reduced the expression of LXR target genes ABCA1 and APOE, which are critical for cholesterol efflux in neurons [52][53][54][55][56].…”

“…Since activation of Rho GTPases has been associated with an inhibition of the LXR pathway [45][46][47][48][49] and we have observed that CYP46A1 overexpression and 24OHC treatment differentially affect RhoA membrane levels, we hypothesize that CYP46A1-dependent decrease in LXR target genes was dependent on the increase in RhoA prenylation. To test our hypothesis, we incubated cells transfected with pFLAGhCYP46A1 in the presence or absence of GGTi-2133 and observed that inhibition of prenylation abolished the CYP46A1-dependent decrease in ABCA1 and APOE mRNA levels (Fig.…”

Selective Up-regulation of LXR-regulated Genes ABCA1, ABCG1, and APOE in Macrophages through Increased Endogenous Synthesis of 24(S),25-Epoxycholesterol

“…For experiments, cells were cultured at 4.0 ϫ 10 6 cells/35-mm plate (Falcon Scientific, BD Biosciences) or 3.0 ϫ 10 7 cells/100-mm plate in RPMI 1640 supplemented with 10% fetal bovine serum (Sigma), ␤-mercaptoethanol (5 ϫ 10 Ϫ5 M), 100 units/ml penicillin, and 100 g/ml streptomycin and differentiated with 300 nM phorbol 12,13-dibutyrate (PDB) for 1 week prior to use in experiments as described (20). The OSCi designated as RO0714565 with an IC 50 of 5 nM for human liver microsomal OSC activity was provided by J. Aebi (F. Hoffmann-La Roche AG (Pharmaceuticals Division, Basal, Switzerland)) and dissolved in Me 2 SO.…”