27-Hydroxycholesterol

Neuroscience. 2015 Aug 6;300:163-73.

27-Hydroxycholesterol contributes to disruptive effects on learning and memory by modulating cholesterol metabolism in the rat brain.[Pubmed: 25987203]

Cholesterol metabolism is important for neuronal function in the central nervous system (CNS). The oxysterol 27-Hydroxycholesterol (27-OHC) is a cholesterol metabolite that crosses the blood-brain barrier (BBB) and may be a useful substitutive marker for neurodegenerative diseases. However, the effects of 27-Hydroxycholesterol on learning and memory and the underlying mechanisms are unclear.
METHODS AND RESULTS:
To determine this mechanism, we investigated learning and memory and cholesterol metabolism in rat brain following the injection of various doses of 27-Hydroxycholesterol into the caudal vein. We found that 27-Hydroxycholesterol increased cholesterol levels and upregulated the expression of liver X receptor-α (LXR-α) and adenosine triphosphate (ATP)-binding cassette transporter protein family member A1 (ABCA1). In addition, 27-Hydroxycholesterol decreased the expression of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CR) and low-density lipoprotein receptor (LDLR) in rat brain tissues.
CONCLUSIONS:
These findings suggest that 27-Hydroxycholesterol may negatively modulate cognitive effects and cholesterol metabolism in the brain.

Behav Brain Res. 2015 Feb 1;278:356-9.

27-hydroxycholesterol mediates negative effects of dietary cholesterol on cognition in mice.[Pubmed: 25453744]

In spite of the fact that cholesterol does not pass the blood-brain barrier, treatment of mice with dietary cholesterol causes significant effects on a number of genes in the brain and in addition a memory impairment.
METHODS AND RESULTS:
We have suggested that these effects are mediated by 27-Hydroxycholesterol, which is able to pass the blood-brain barrier. To test this hypothesis we utilized Cyp27-/- mice lacking 27-Hydroxycholesterol. The negative effect on memory observed after treatment of wildtype mice with dietary cholesterol was not observed in these mice. The cholesterol diet reduced the levels of the "memory protein" Arc (Activity Regulated Cytoskeleton associated protein) in the hippocampus of the wildtype mice but not in the hippocampus of the Cyp27-/- mice.
CONCLUSIONS:
The results are consistent with 27-Hydroxycholesterol as the mediator of the negative effects of cholesterol on cognition.

Aging Cell. 2015 Aug;14(4):569-81.

Relation between TLR4/NF-κB signaling pathway activation by 27-hydroxycholesterol and 4-hydroxynonenal, and atherosclerotic plaque instability.[Pubmed: 25757594]

It is now thought that atherosclerosis, although due to increased plasma lipids, is mainly the consequence of a complicated inflammatory process, with immune responses at the different stages of plaque development. Increasing evidence points to a significant role of Toll-like receptor 4 (TLR4), a key player in innate immunity, in the pathogenesis of atherosclerosis.
METHODS AND RESULTS:
This study aimed to determine the effects on TLR4 activation of two reactive oxidized lipids carried by oxidized low-density lipoproteins, the oxysterol 27-Hydroxycholesterol (27-OH) and the aldehyde 4-hydroxynonenal (HNE), both of which accumulate in atherosclerotic plaques and play a key role in the pathogenesis of atherosclerosis. Secondarily, it examined their potential involvement in mediating inflammation and extracellular matrix degradation, the hallmarks of high-risk atherosclerotic unstable plaques. In human promonocytic U937 cells, both 27-OH and HNE were found to enhance cell release of IL-8, IL-1β, and TNF-α and to upregulate matrix metalloproteinase-9 (MMP-9) via TLR4/NF-κB-dependent pathway; these actions may sustain the inflammatory response and matrix degradation that lead to atherosclerotic plaque instability and to their rupture. Using specific antibodies, it was also demonstrated that these inflammatory cytokines increase MMP-9 upregulation, thus enhancing the release of this matrix-degrading enzyme by macrophage cells and contributing to plaque instability.
CONCLUSIONS:
These innovative results suggest that, by accumulating in atherosclerotic plaques, the two oxidized lipids may contribute to plaque instability and rupture. They appear to do so by sustaining the release of inflammatory molecules and MMP-9 by inflammatory and immune cells, for example, macrophages, through activation of TLR4 and its NF-κB downstream signaling.

J Hepatol. 2015 Feb;62(2):430-6.

Hematopoietic overexpression of Cyp27a1 reduces hepatic inflammation independently of 27-hydroxycholesterol levels in Ldlr(-/-) mice.[Pubmed: 25281859 ]

Non-alcoholic steatohepatitis (NASH) is characterized by hepatic lipid accumulation and inflammation. Currently, the underlying mechanisms, leading to hepatic inflammation, are still unknown. The breakdown of free cholesterol inside Kupffer cells (KCs) by the mitochondrial enzyme CYP27A1 produces 27-Hydroxycholesterol (27HC). We recently demonstrated that administration of 27HC to hyperlipidemic mice reduced hepatic inflammation. In line, hematopoietic deletion of Cyp27a1 resulted in increased hepatic inflammation. In the current manuscript, the effect of hematopoietic overexpression of Cyp27a1 on the development of NASH and cholesterol trafficking was investigated. We hypothesized that Cyp27a1 overexpression in KCs will lead to reduced hepatic inflammation.
METHODS AND RESULTS:
Irradiated Ldlr(-/-) mice were transplanted (tp) with bone marrow from mice overexpressing Cyp27a1 (Cyp27a1(over)) and wild type (Wt) mice and fed either chow or a high-fat, high-cholesterol (HFC) diet for 3 months. Additionally, gene expression was assessed in bone marrow-derived macrophages (BMDM) from Cyp27a1(over) and Wt mice. In line with our hypothesis, hepatic inflammation in HFC-fed Cyp27a1(over)-tp mice was reduced and KCs were less foamy compared to Wt-tp mice. Remarkably, these changes occurred even though plasma and liver levels of 27HC did not differ between both groups. BMDM from Cyp27a1(over) mice revealed reduced inflammatory gene expression and increased expression of cholesterol transporters compared to Wt BMDM after lipopolysaccharide (LPS) stimulation.
CONCLUSIONS:
Our data suggest that overexpression of Cyp27a1 in KCs reduces hepatic inflammation independently of 27HC levels in plasma and liver, further pointing towards KCs as specific target for improving the therapy of NASH.