Wogonin promotes cholesterol efflux by increasing protein phosphatase 2B-dependent dephosphorylation at ATP-binding cassette transporter-A1 in macrophages

Wogonin, one component in Scutellaria baicalensis Georgi extracts, has several beneficial properties for cancers and inflammatory diseases. However, the efficacy of wogonin in cholesterol metabolism of macrophages remains unknown. In macrophages, cholesterol uptake is controlled by scavenger receptors (SR-A and CD36) and cholesterol efflux by SR-BI, ATP-binding cassette transporter-A1 (ABCA1) and ABCG1. In the present study, we investigated the effect and underlying molecular mechanism of wogonin on the formation of macrophage foam cells by murine J774.A1 macrophages. Wogonin attenuated oxidized low-density lipoprotein (oxLDL)-induced cholesterol accumulation in macrophages. The binding of oxLDL to macrophages and protein expression of SR-A and CD36 were not affected by wogonin. Wogonin enhanced cholesterol efflux and increased the protein level of ABCA1 without affecting the protein expression of SR-BI or ABCG1. Inhibition of ABCA1 by pharmacological inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid disodium salt or neutralizing antibody abolished this suppressive effect of wogonin on lipid accumulation. Moreover, the up-regulation of ABCA1 protein by wogonin resulted from a decrease in degradation rate of ABCA1 protein, with no effect on ABCA1 mRNA expression. This reduction in ABCA1 degradation was due to increased protein phosphatase 2B (PP2B)-mediated ABCA1 dephosphorylation, as evidenced by increased interaction between ABCA1 and PP2B; pharmacological inhibition of PP2B would prevent wogonin-induced ABCA1 protein expression, dephosphorylation and attenuation of lipid accumulation. Collectively, wogonin increases the protein stability of ABCA1 via PP2B-mediated dephosphorylation, thus leading to reduced cholesterol accumulation in macrophage foam cells.