Formation of macrophage phenotupe in inflammatory and fibrogenic response: The role of mevalonate pathway and nuclear receptors LXR

   Free cholesterol (Ch) and its oxidative derivatives, oxysterols (OS), are often accumulated in macrophages during chronic inflammation and atherogenesis. The effects of Ch and OS on the balance of pro- and anti-inflammatory cytokines in inflammatory response and the role of mevalonate pathway in the effects of these sterols are studied poorly. Both Ch and OS are able to affect mevalonate pathway activity and activity of nuclear hormonal receptors LXR. However the roles of LXR and mevalonate pathway in Ch and OS effects on macrophage polarization are unknown. We studied the effects of Ch, OS, atorvastatin, and mevalonic acid on the LPS-induced TNF-α, IL-10 and TGF-β1 production in macrophage cell culture. The study was carried out in murine peritoneal macrophages preincubated for 4 h with Ch (5 μg/mL), 25-hydroxycholesterol (25-OH-Ch) (5 μg/mL), 7-keto-Ch (5 μg/mL), farnesol (10 μM), or atorvastatin (5 μmol/mL) in the presence or absence of 1 mM of mevalonate. The cells were further incubated in the presence or absence of E. coli 0111:B4 lipopolysaccharide (LPS) for 24 h, and cytokine concentrations in incubation media were determined. Macrophages preincubation with Ch, 25-OH-Ch, or atorvastatin decreased LPS-induced TNF-α production in cell cultures, while supplementation of preincubation medium with mevalonic acid abrogated the effects of atorvastatin and Ch. The Ch, 25-OH-Ch, 7-keto-Ch and atorvastatin significantly reduced IL-10 production by LPS–stimulated macrophages, while farnesol had no effect. Supplementation of Ch or atorvastatin-containing preincubation medium with mevalonate restored IL-10 production. The TGF-β1 production was significantly enhanced by the presence of Ch or atorvastatin in preincubation medium as compared to the control level in non-treated macrophages, while 25-OH-Ch or farnesol decreased profoundly TGF-β1 production. Mevalonate abrogated the effect of Ch or atorvastatin but not of 25-OH-Ch or farnesol. These results allow to conclude, that the presence of Ch in micro-environment of inflammatory macrophages promotes anti-inflammatory and fibrogenic macrophage response; the latter is connected, at least in part, with the deficiency of mevalonate pathway intermediates, particularly to the deficiency of farnesol. At the same time hydroxysterols suppress both pro- and anti-inflammatory macrophage response independently of the impact of these compounds on mevalonate pathway. Apparently, pharmacological interference in the process of farnesylation could be a new approach to the control of chronic inflammation, including atherogenesis.

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