Stimulation of Cholesterol Efflux by LXR Agonists in Cholesterol-Loaded Human Macrophages Is ABCA1-Dependent but ABCG1-Independent

Abstract The nuclear oxysterol receptors liver X receptor-α [LXRα (NR1H3)] and LXRβ (NR1H2) coordinately regulate genes involved in cholesterol homeostasis. Although both LXR subtypes are expressed in the brain, their roles in this tissue remain largely unexplored. In this report, we show that LXR agonists have marked effects on gene expression in murine brain tissue both in vitro and in vivo. In primary astrocyte cultures, LXR agonists regulated several established LXR target genes, including ATP binding cassette transporter A1, and enhanced cholesterol efflux. In contrast, little or no effect on gene expression or cholesterol efflux was detected in primary neuronal cultures. Treatment of mice with a selective LXR agonist resulted in the induction of several LXR target genes related to cholesterol homeostasis in the cerebellum and hippocampus. These data provide the first evidence that the LXRs regulate cholesterol homeostasis in the central nervous system. Because dysregulation of cholesterol balance is implicated in central nervous system diseases such as Alzheimer’s and Niemann-Pick disease, pharmacological manipulation of the LXRs may prove beneficial in the treatment of these disorders.

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Internalization of the Membrane Attack Complex Triggers NLRP3 Inflammasome Activation and IL-1β Secretion in Human Macrophages

Frontiers in Immunology ◽

10.3389/fimmu.2021.720655 ◽

2021 ◽

Vol 12 ◽

Author(s):

Ines Diaz-del-Olmo ◽

Jonathan Worboys ◽

Fatima Martin-Sanchez ◽

Anna Gritsenko ◽

Ashley R. Ambrose ◽

...

Keyword(s):

Nlrp3 Inflammasome ◽

Pore Formation ◽

Membrane Attack Complex ◽

Inflammasome Activation ◽

Adapter Protein ◽

Human Macrophages ◽

Danger Signals ◽

Nlrp3 Inflammasome Activation ◽

Golgi Network ◽

Stimulation Of

Interleukin 1β (IL-1β) plays a major role in inflammation and is secreted by immune cells, such as macrophages, upon recognition of danger signals. Its secretion is regulated by the inflammasome, the assembly of which results in caspase 1 activation leading to gasdermin D (GSDMD) pore formation and IL-1β release. During inflammation, danger signals also activate the complement cascade, resulting in the formation of the membrane attack complex (MAC). Here, we report that stimulation of LPS-primed human macrophages with sub-lytic levels of MAC results in activation of the NOD-like receptor 3 (NLRP3) inflammasome and GSDMD-mediated IL-1β release. The MAC is first internalized into endosomes and then colocalizes with inflammasome components; adapter protein apoptosis associated speck-like protein containing a CARD (ASC) and NLRP3. Pharmacological inhibitors established that MAC-triggered activation of the NLRP3 inflammasome was dependent on MAC endocytosis. Internalization of the MAC also caused dispersion of the trans-Golgi network. Thus, these data uncover a role for the MAC in activating the inflammasome and triggering IL-1β release in human macrophages.

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Apolipoprotein A-I stimulates the transport of intracellular cholesterol to cell-surface cholesterol-rich domains (caveolae)

Biochemical Journal ◽

10.1042/bj3580079 ◽

2001 ◽

Vol 358 (1) ◽

pp. 79-86 ◽

Cited By ~ 18

Author(s):

Dmitri SVIRIDOV ◽

Noel FIDGE ◽

Gabrielle BEAUMIER-GALLON ◽

Christopher FIELDING

Keyword(s):

Cell Surface ◽

Cholesterol Efflux ◽

Partial Purification ◽

Cholesterol Transport ◽

Dependent Manner ◽

Cholesterol Trafficking ◽

Apolipoprotein A ◽

Intracellular Cholesterol ◽

Plasma Apolipoprotein ◽

Stimulation Of

We have studied the effect of lipid-free human plasma apolipoprotein A-I (apoA-I) on the transport of newly synthesized cholesterol to cell-surface cholesterol-rich domains, which in human skin fibroblasts are mainly represented by caveolae. Changes in transport of newly synthesized cholesterol were assessed after labelling cells with [14C]acetate at 15°C and warming cells to permit the transfer of cholesterol, followed by the selective oxidation of cholesterol in cholesterol-rich domains (caveolae) in the plasma membrane before their partial purification. ApoA-I, but not BSA added in an equimolar concentration, enhanced the transport of cholesterol to the caveolae up to 5-fold in a dose- and time-dependent manner. The effect of apoA-I on cholesterol transport exceeded its effect on cholesterol efflux, resulting in an accumulation of intracellular cholesterol in caveolae. Methyl-β-cyclodextrin, added at a concentration promoting cholesterol efflux to the same extent as apoA-I, also stimulated cholesterol trafficking, but was 3-fold less effective than apoA-I. Progesterone inhibited the transport of newly synthesized cholesterol to the caveolae. Treatment of cells with apoA-I stimulated the expression of caveolin, increasing the amount of caveolin protein and mRNA by approx. 2-fold. We conclude that apoA-I induces the transport of intracellular cholesterol to cell-surface caveolae, possibly in part through the stimulation of caveolin expression.

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