Silencing carboxylesterase 1 in human THP-1 macrophages perturbs genes regulated by PPARγ/RXR and RAR/RXR: down-regulation of CYP27A1–LXRα signaling

Abstract

Macrophage foam cells store excess cholesterol as cholesteryl esters, which need to be hydrolyzed for cholesterol efflux. We recently reported that silencing expression of carboxylesterase 1 (CES1) in human THP-1 macrophages (CES1KD macrophages) reduced cholesterol uptake and decreased expression of CD36 and scavenger receptor-A in cells loaded with acetylated low-density lipoprotein (acLDL). Here, we report that CES1KD macrophages exhibit reduced transcription of cytochrome P450 27A1 (CYP27A1) in non-loaded and acLDL-loaded cells. Moreover, levels of CYP27A1 protein and its enzymatic product, 27-hydroxycholesterol, were markedly reduced in CES1KD macrophages. Transcription of LXRα and ABCA1 was also decreased in acLDL-loaded CES1KD macrophages, suggesting reduced signaling through PPARγ-CYP27A1-LXRα. Consistent with this, treatment of CES1KD macrophages with agonists for PPARγ, RAR, and/or RAR/RXR partially restored transcription of CYP27A1 and LXRα, and repaired cholesterol influx. Conversely, treatment of control macrophages with antagonists for PPARγ and/or RXR decreased transcription of CYP27A1 and LXRα. Pharmacologic inhibition of CES1 in both wildtype THP-1 cells and primary human macrophages also decreased CYP27A1 transcription. CES1 silencing did not affect transcript levels of PPARγ and RXR in acLDL-loaded macrophages, whereas it did reduce the catabolism of the endocannabinoid 2-arachidonoylglycerol. Finally, the gene expression profile of CES1KD macrophages was similar to that of PPARγ knockdown cells following acLDL exposures, further suggesting a mechanistic link between CES1 and PPARγ. These results are consistent with a model in which abrogation of CES1 function attenuates the CYP27A1-LXRα-ABCA1 signaling axis by depleting endogenous ligands for the nuclear receptors PPARγ, RAR, and/or RXR that regulate cholesterol homeostasis.

Long non‑coding RNA MALAT1 regulates cholesterol accumulation in ox‑LDL‑induced macrophages via the microRNA‑17‑5p/ABCA1 axis

“…Macrophages regulate cholesterol homeostasis via several factors including scavenger receptors, cholesterol metabolism enzymes and cholesterol transporters (25,36). a series of scavenger receptors, including Sr-a and Sr-B1, mediate the binding of modified LDL (37).…”

Free radical oxidation in liver mitochondria of tumor-bearing rats and its correction by essential lipophilic nutrients

“…As a result, ω3 PUFAs can inhibit the hydroxylation of retinol acetate to toxic metabolites [12]. On the other hand, the combined administration of ω3 PUFAs and retinol acetate facilitates the formation of nuclear receptor heterodimers (PPARγ/ RXR і RAR/RXR), which modulate the expression of the corresponding genes [10].…”

“…The function of PPARs is regulated by the exact form of the ligand-binding domain, which is due to the attachment of the ligand and coactivator proteins or corepressor proteins. The endogenous PPARs ligands include free fatty acids and eicosanoids, which are synthesized from PUFAs [10,11]. As follows from the above, the effects of ω3 PUFA and retinoids can be interrelated through their effects on PPAR and RXR.…”

Carboxylesterases: Pharmacological Inhibition Regulated Expression and Transcriptional Involvement of Nuclear Receptors and other Transcription Factors

“…Many nuclear receptors have been established or implicated in the regulation such as constitutive androstane receptor [27], farnesoid X receptor [125], glucocorticoid receptor [76], peroxisome proliferator-activated receptors [126] and pregnane X receptor [27,28]. It should be noted that expression of CES1 regulates the signal transduction supported by peroxisome proliferator-activated receptors and liver X receptor [127]. These receptors are ligand-dependent transcription factors and majority of them are traditionally called orphan receptors [128].…”