Inhibition of histone deacetylases protects septic mice from lung and splenic apoptosis

Abstract

Background

Epigenetic programming, dynamically regulated by histone acetylation, may play a key role in the pathophysiology of sepsis. We examined whether histone deacetylase (HDAC) can contribute to sepsis-associated inflammation and apoptosis.

Materials and methods

Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in BALB/c mice. An intraperitoneal injection of CG200745 (10 mg/kg), a novel broad-spectrum HDAC inhibitor, or valproic acid (500 mg/kg), a predominant inhibitor of class I HDACs, was given 3 h before surgery.

Results

HDAC1, HDAC2, and HDAC3 protein levels were decreased in lungs after CLP. Furthermore, CLP-induced sepsis increased both histone H3 and H4 acetylation levels in lungs. When CG200745 was given, apoptosis induction was strongly suppressed in lungs and spleens of septic mice. This antiapoptotic effect of CG200745 was not accompanied by upregulation of antiapoptotic and downregulation of proapoptotic Bcl-2 family member proteins. Treatment with CG200745 failed to inhibit elevated levels of serum cytokines and prevent lung inflammation in septic mice. Valproic acid also showed antiapoptotic but not anti-inflammatory effects in septic mice.

Conclusions

These findings imply that HDAC inhibitors are a unique agent to prevent cell apoptosis in sepsis at their doses that do not improve inflammatory features, indicating that septic inflammation and apoptosis may not necessarily be essential for one another's existence. This study also represents the first report that CLP-induced sepsis downregulates HDACs. Nevertheless, the data with HDAC inhibitors suggest that imbalance in histone acetylation may play a contributory role in expression or repression of genes involved in septic cell apoptosis.

Introduction

Epigenetic regulation primarily works through modifying the secondary and tertiary structures of DNA (chromatin), making it more or less accessible to transcription. Many types of epigenetic processes have been identified. These modifications include acetylation, methylation, ubiquitylation, phosphorylation, and sumoylation. Epigenetics is being implicated in increasing numbers of diseases [1], [2], [3]. The basic unit of chromatin is a nucleosome which is made up of wrapped around an octamer of core histone proteins. Histones are acetylated by histone acetyltransferases (HATs), which is one of the steps that allow for transcription of genes [4]. The activity of HATs is balanced by histone deacetylases (HDACs), which remove the acetyl group from the histones and impair gene transcription [5]. Epigenetic pharmacology witnessed a real explosion of interest in the development of HDAC inhibitors [6]. They are potent compounds capable of unbalancing cellular acetylation toward a hyperacetylation status, thereby affecting overall gene expression profiles [7]. It is interesting to note that HDAC inhibitors are currently evaluated in several clinical trials for neoplastic disorders [8].

Sepsis is associated with inappropriate changes in the transcription of a vast number of harmful genes. In this regard, epigenetic mechanisms may play a modifying role in harmful gene expression during sepsis. In the present study, we asked whether histone acetylation is a significant pathologic event in lung tissues of mice with cecal ligation and puncture (CLP)–induced sepsis. Furthermore, we looked at HDAC protein expression and activity during sepsis as a marker of potential epigenetic change. A number of in vitro and in vivo studies emerged in the recent decade indicating the anti-inflammatory properties of HDAC inhibitors [9], [10], [11]. The HDAC inhibitors can also control the process of cell apoptosis through multiple pathways, including transcriptional activation or repression of target genes [12]. Although the seriousness of sepsis results from an unbridled inflammatory response, dysregulated apoptotic cell death during sepsis is considered to be a potential cause leading to tissue damage and resultant multiple organ failure [13], [14], [15]. However, whether these two important pathogenic events, inflammation and apoptosis, are closely related for sepsis development is still a matter of considerable debate. Hence, we examined the effect of treatment with the novel broad-spectrum HDAC inhibitor CG200745 ((E)-N¹-3-(dimethylamino)propyl)-N⁸-hydroxy-2-((naphthalene-1-loxy)methyl)oct-2-enediamide) [16] and valproic acid (VPA), which can inhibit both class I and class II HDACs, with a higher potency for class I HDACs [17], on lung inflammation and apoptosis in CLP-induced septic mice.