Transcriptional regulation of cholesterol 24-hydroxylase by histone deacetylase inhibitors

Abstract

Keywords:24S-hydroxycholesterol CYP46A1 CYP39A1 Epigentics Histone deacetylase inhibitor Oxysterol Brain cholesterol a b s t r a c tThe mechanistic basis for the tissue specific expression of cholesterol elimination pathways is poorly understood. To gain additional insight into this phenomenon we considered it of interest to investigate if epigenetic mechanisms are involved in the regulation of the brain-specific enzyme cholesterol 24-hydroxylase (CYP46A1), a key regulator of brain cholesterol elimination. We demonstrated a marked time-dependent derepression of the expression of CYP46A1, in response to treatment with the potent histone deacetylase (HDAC) inhibitor Trichostatin A. The pattern of expression of the genes in the genomic region surrounding CYP46A1 was found to be diametrically opposite in brain and liver. Intraperitoneal injection of HDAC inhibitors in mice led to a significant derepression of hepatic Cyp46a1 mRNA expression and tissue specific changes in Hmgcr and Cyp39a1 mRNA expression. These results are discussed in the context of the phenomenology of tissue specific cholesterol balance.Ó 2008 Elsevier Inc. All rights reserved.Although all nucleated cells are capable of cholesterol synthesis, their ability to do so varies over several orders of magnitude. In the adult state most organisms have established a certain level of tissue specialisation [1]. The rate of cholesterol synthesis and the cholesterol content of a given tissue are not necessarily directly related, e.g. the adult brain contains more than 25% of whole body cholesterol but turns over only 0.03% of its cholesterol content each day. This turnover is much lower than the developing brain [1] where cholesterol rich myelin is being formed. The slow turnover of brain cholesterol is in marked contrast to that in most other organs [1,2]. The mechanistic basis for these differences is unknown, although they are probably a result of the functional isolation of brain and blood cholesterol [3][4][5].According to current concepts, the synthesis and elimination of cholesterol in the adult brain is compartmentalised-astroglial cells are believed to be responsible for the majority of synthesis in the adult brain while they contribute relatively little to brain elimination. The neuron specific cytochrome P450 cholesterol 24-hydroxylase (CYP46A1) is responsible for the elimination of about two thirds of the cholesterol synthesised by the brain [6,7]. Recently it was shown that deletion of this gene led to a reduction in the rate of brain cholesterol synthesis while the level of brain cholesterol was maintained [8]. Due to the importance of this enzyme for brain cholesterol balance we have previously investigated its transcriptional regulation [9], with an expectation that a gene so important for brain cholesterol balance would be subject to complex mechanisms of regulation. Surprisingly we found the opposite-expression of CYP46A1 was insensitive to mechanisms known to regulate the key genes in cholesterol synthesis and elimination, HMGCR and CYP7A1,...

Okadaic acid inhibits the trichostatin A-mediated increase of human CYP46A1 neuronal expression in a ERK1/2-Sp3-dependent pathway

“…The 0.12pGL2 promoter reporter construct was transfected in SH-SY5Y cells and 24 h after cells were arising from overexpressing this enzyme in a mouse model of AD ( 9 ). We and others have shown that HDACi are one of the few classes of compounds known to induce CYP46A1 expression ( 10,11 ). In our previous study, we showed that the histone deacetylase inhibitor TSA induced a transient histone hyperacetylation of CYP46A1 promoter, which signifi cantly increased CYP46A1 transcription in SH-SY5Y neuroblastoma cells ( 11 ).…”

Epigenetic regulation of oxysterol formation

“…This effect was time dependentmRNA levels were reduced during the first 24 hours of treatment but the suppression was lost by 48 hours. In contrast, Shafaati et al reported that in SH-SY5Y neuroblastoma cells, the levels of CYP27A1 mRNA increase by a factor of five following treatment with the same HDAC inhibitor [30]. A possible reason for this discrepancy is that HepG2 cells are known to express a relatively large amount of CYP27A1 mRNA in comparison to SH-SY5Y cells and the basal chromatin architecture may and accessory proteins, including HDACs, are likely to be different and respond differently to the broad acting HDAC inhibitor used in these studies.…”

“…In this study they reported that HDAC inhibitor treatment led to an increase in the expression of Cyp46a1 mRNA by approximately ten-fold in primary cultures of mouse cortical neurons. Later contemporaneous studies by Shafaati et al and Nunes et al reported that HDAC inhibition led to a profound upregulation of the mRNA expression of CYP46A1 (over 50-fold) in several different cell systems [30,33]. In addition Shafaati et al also reported that treatment of mice with HDAC inhibitors modestly increased the expression of Cyp46a1 in murine liver [30].…”

“…Evidence has also been presented that Hnf-1α and Runt-related transcription factor 2 (Runx2) (which is known to be involved in maintenance of epigenetic bookmarking in the context of bone cell development) may have a role in the expression of this gene [58]. Shafaati et al have described that HDACi treatment led to an increase of Cyp39a1 in the brain with a decrease in hepatic expression [30]. In addition, preliminary data suggests that epigenetic mechanisms may have a role in the observed sexual dimorphism of Cyp39a1 (unpublished observations).…”

“…Epigenetic regulators of GROS may have potential as anti-atherosclerotic agents whereby these pathways are enhanced following transcriptional therapy with epigenetic regulators. Theoretically, reduction in CYP7B1 and induction of CYP27A1 would optimize this pathway, and evidence has been presented that HDACi may shift the expression of these genes in this manner, at least under in vitro conditions [30]. Epigenetic regulation of the oxidative pathway for cholesterol removal may thus represent a novel anti-atherosclerotic therapy.…”