Multiple Sclerosis and Related Disorders (2014) 3, 163–175
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/msard
The epigenetics of multiple sclerosis and other related disorders Peter J. van den Elsena,b,n, Marja C.J.A. van Eggermondb, Fabiola Puentesc, Paul van der Valka, David Bakerc, Sandra Amora,c a
Department of Pathology, VU University Medical Center, Amsterdam, The Netherlands Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, The Netherlands c Neuroscience and Trauma Centre, Blizard Institute, Barts and the London School of Medicine and Dentistry, QJ;Queen Mary University of London, London, United Kingdom b
Received 11 June 2013; received in revised form 19 August 2013; accepted 30 August 2013
Epigenetics; Multiple sclerosis; DNA methylation; Histone modiﬁcations; Animal models; Epigenetic drugs
Multiple Sclerosis (MS) is a demyelinating disease characterized by chronic inﬂammation of the central nervous system (CNS) gray and white matter. Although the cause of MS is unknown, it is widely appreciated that innate and adaptive immune processes contribute to its pathogenesis. These include microglia/macrophage activation, pro-inﬂammatory T-cell (Th1) responses and humoral responses. Additionally, there is evidence indicating that MS has a neurodegenerative component since neuronal and axonal loss occurs even in the absence of overt inﬂammation. These aspects also form the rationale for clinical management of the disease. However, the currently available therapies to control the disease are only partially effective at best indicating that more effective therapeutic solutions are urgently needed. It is appreciated that in the immune-driven and neurodegenerative processes MS-speciﬁc deregulation of gene expressions and resulting protein dysfunction are thought to play a central role. These deviations in gene expression patterns contribute to the inﬂammatory response in the CNS, and to neuronal or axonal loss. Epigenetic mechanisms control transcription of most, if not all genes, in nucleated cells including cells of the CNS and in haematopoietic cells. MSspeciﬁc alterations in epigenetic regulation of gene expression may therefore lie at the heart of the deregulation of gene expression in MS. As such, epigenetic mechanisms most likely play an important role in disease pathogenesis. In this review we discuss a role for MS-speciﬁc deregulation of epigenetic features that control gene expression in the CNS and in the periphery. Furthermore, we discuss the application of
Correspondence to: Department of Pathology, VU University Medical Center, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. Tel.: +31 20 444 2898. E-mail address: [email protected]
(P.J. van den Elsen). 2211-0348/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msard.2013.08.007
P.J. van den Elsen et al. small molecule inhibitors that target the epigenetic machinery to ameliorate disease in experimental animal models, indicating that such approaches may be applicable to MS patients. & 2013 Elsevier B.V. All rights reserved.
Contents 1. 2.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Epigenetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 2.1. DNA methylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 2.2. Post-translational histone modiﬁcations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 2.2.1. Enzymes that modify histones by acetylation and methylation . . . . . . . . . . . . . . . . . . . . . . . . 166 2.2.2. Additional histone modiﬁcations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 2.3. Histone code readers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 2.4. miRNA-associated epigenetic regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 3. Epigenetic interference in animal models of MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 3.1. Experimental therapies targeting epigenetic processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 3.2. Epigenetic interference in other inﬂammatory animal models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 4. Epigenetic dysregulation in Multiple Sclerosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 4.1. Histone acetylation patterns in MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 4.2. microRNAs in MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 4.3. Gene-speciﬁc chromatin alterations in the CNS and in MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 5. Epigenetic dysregulation in other neurodegenerative disorders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 6. Conclusions and perspectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Conﬂicts of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
MS is a chronic inﬂammatory demyelinating and neurodegenerative disease of the CNS, the cause of which remains elusive. An estimated 2.5 million people in the world have MS, although there is a distinct distribution with the disease being more common in northern and southern latitudes. The disease onset is mostly in young adults with a prevalence for women. Genetic linkage studies and genome-wide meta-analyses have identiﬁed genes that may confer susceptible individuals to develop disease (Sawcer et al., 2011; Patsopoulos et al., 2011). Many of these genes play a role in the immune system with a prominent role for major histocompatibility complex (MHC) class II molecules in particular deﬁned HLADRB1 alleles (Sawcer et al., 2011). However, if the information contained within the DNA would solely determine disease susceptibility, the concordance rate to develop MS in monozygotic twins should be the same. However, there is a low concordance rate for MS in monozygotic twins (26%) (Ebers et al., 1986) indicating that genetic factors alone do not contribute to disease. This suggests that epigenetic changes may also inﬂuence MS susceptibility (Koch et al., 2013a). It is widely appreciated that environmental factors play an important role in the establishment of the epigenome (Cobiac, 2007; Foley et al., 2009; Jaenisch and Bird, 2003). Since epigenetic alterations accumulate in time, environmental factors consequently have profound effects on the cellular repertoire of expressed genes (Fraga et al., 2005) and may provide an explanation for the impact of the environment to disease pathogenesis.
The inﬂuence of environmental factors on disease susceptibility is illustrated by several studies, which have shown that when migration occurs before the age of ﬁfteen, the migrant acquires the new region's susceptibility to MS. When migration occurs after the age of ﬁfteen, the migrant retains the susceptibility of the home country (Kurtzke, 2000). One of the factors thought to contribute to these manifestations is sunlight exposure reported to have a protective role in MS development, possibly mediated by vitamin D (Kragt et al., 2009). This may explain the geographical prevalence of MS world-wide, due to reduced sunlight exposure in the further northern and southern latitudes. One of the mechanisms by which vitamin D could act is through modulation of the immune response at multiple points by binding to the vitamin D receptor, which is expressed on monocytes, dendritic cells and activated T cells (Smolders et al., 2008). It has been demonstrated in vitro that vitamin D modulates the maturation and differentiation of dendritic cells and therefore could promote a more tolerogenic state of the immune system by the production of IL-10 (Smolders et al., 2008). Further support of a beneﬁcial effect of vitamin D comes from experimental studies in the autoimmune model of MS experimental autoimmune encephalomyelitis (EAE) in which vitamin D has a beneﬁcial effect on onset and severity of the disease (Niino et al., 2008). In addition, the role of environmental factors cooperating with the genetic background to determine the risk for MS has been recently clariﬁed (Handel et al., 2010). For example, sunlight-induced vitamin D, and its effects on epigenetic regulation of MHC gene expression is likely to co-deﬁne the MS risk. Additional environmental factors that possible contribute to this latitude-dependent susceptibility to develop MS are smoking, infections or diet
The epigenetics of multiple sclerosis and other related disorders
(Koch et al., 2013a). In particular Epstein-Barr Virus (EBV) is associated with MS since all patients have the virus (Pakpoor et al., 2013). However, whether the strong epidemiological association between MS and EBV infection is a consequence rather than a cause of the disease remains to be ﬁrmly established (Pakpoor et al., 2013). Interestingly, EBV utilizes DNA methylation to avoid immune recognition (Tao and Robertson, 2003). It is thus tempting to speculate that EBV components could also inﬂuence the well-orchestrated epigenetic cellular programs. Therefore, epigenetic mechanisms inﬂuenced by the environment may play an important role in the onset and progression of the disease in susceptible individuals.
Epigenetics is one of the most promising and rapidly expanding ﬁelds in biomedical research. It refers to the study of mitotically and/or meiotically heritable changes in gene expression that occur without a change in the DNA sequence (Berger et al., 2009). Epigenetic mechanisms control gene expression by determining the accessibility of the transcriptional machinery to regulatory regions of genes. Since all nucleated cells contain the same genetic material, epigenetic mechanisms determine the function of cells in a speciﬁc manner by controlling its gene expression proﬁle. As such, epigenetic mechanisms play an essential and fundamental role in the transcriptional control of genes, maintenance of cellular identity, cell activation, cellular repair and stress processes. It can therefore be envisioned that disturbances in epigenetic processes lead to oncogenic transformation of cells as well as monogenic or complex diseases. Moreover, these epigenetically controlled gene expression patterns can be passed to daughter cells upon cell division or even transgenerationally (GuerreroBosagna and Skinner, 2012). This latter effect is illustrated by several studies, which show the transgenerational effect of maternal and paternal environmental exposures on the offspring of next generation(s) (Bygren et al., 2001; Kaati et al., 2002; Pembrey et al., 2006). In its natural state DNA in the nucleus is packaged into chromatin, a highly organized and dynamic protein-DNA complex, which consists of DNA, histones and non-histone proteins (Luger et al., 1997; Kouzarides, 2007). The fundamental subunit of chromatin is the nucleosome which is composed of an octamer of four core histones: two each of H2A, H2B, H3 and H4, surrounded by 147 base pairs of DNA (Luger et al., 1997; Kouzarides, 2007) (Figure 1). Epigenetic mechanisms alter the structure of chromatin by modiﬁcation of DNA and by modiﬁcation or rearrangement of nucleosomes, which include post-translational modiﬁcations of histones (Jenuwein and Allis, 2001). Accessible or relaxed chromatin (euchromatin) allows transcription factors to interact with their cognate binding sites within regulatory regions of genes, such as proximal promoters and enhancer/ silencers, while inaccessible or compressed chromatin (heterochromatin) does not permit these protein/DNA interactions. Of note is that these epigenetic modiﬁcations are reversible allowing the chromatin structure to switch between open and closed states. In this way, global gene activation and local control of gene-speciﬁc transcription is
Fig. 1 Schematic representation of chromatin. Euchromatin is recognized by low levels of DNA methylation (open white circles), and high levels of acetylated histones (light green triangles) and histone methylation modiﬁcations correlated with activation (dark green circles). These histone modiﬁcations are recognized by code-readers associated with open chromatin (alternatively shaped ﬁgures). Heterochromatin is hallmarked by high density of DNA methylation (black circles) and high levels of repressive histone methylation modiﬁcations (closed red circles). These histone modiﬁcations are recognized by code-readers associated with repressed chromatin (alternatively shaped ﬁgures). KATs are responsible for acetylation of histone tails whereas HDACs remove these acetylation modiﬁcations associated with active chromatin. Methylation of histone tails is catalyzed by KMTs whereas KDMs remove these modiﬁcations. DNA methylation is catalyzed by DNMTs. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)
exerted by components of the epigenetic machinery. Importantly, epigenetic processes are not static, but dynamic, changing e.g. during differentiation and in response to environmental factors (Alkemade et al., 2010; Fraga et al., 2005; Kaminsky et al., 2009).
DNA methylation is the best-studied epigenetic modiﬁcation that involves the addition of a methyl group to the C5 position of cytosine residues in a CpG dinucleotide context, converting cytosine residues into 5-methylcytosines. This reaction is exerted by DNA methyltransferases (DNMTs) and Sadenosylmethionine as a methyl group donor. Of the DNMTs, DNMT3A and DNMT3B are responsible for de novo methylation; whereas the maintenance DNA methyltransferase, DNMT1, ensures that the epigenetically modiﬁed cytosine residues are maintained after cell division. The reversible nature of this modiﬁcation is underscored by the ﬁnding that DNMTs are also involved in removing the methyl group from 5-methylcytosines (Kangaspeska et al., 2008; Metivier et al., 2008; Kim et al., 2009). In addition, the Ten-Eleven Translocation (TET) family of enzymes have the capacity to convert 5-methylcytosine into 5-hydroxymethylcytosine (Williams et al., 2012). This conversion could be followed by passive or active demethylation restoring the unmethylated state of CpG islands.
P.J. van den Elsen et al.
CpG residues are underrepresented in the human genome but are highly enriched in so-called CpG islands in most gene promoters (Takai and Jones, 2002). In general, gene expression is associated with unmethylated CpGs in gene promoters, while CpG methylation is associated with transcriptional repression (Kulis and Esteller, 2010) (Figure 1). More recently, the involvement of so-called CpG island shores, at more distal locations from gene promoters in gene transcription, has become apparent (Irizarry et al., 2009). In addition, the crucial role that diet plays in epigenetic processes is shown by the requirement of co-factors folate and vitamins B12 and B6 by enzymes involved in the DNA methylation cycle (Fuso, 2013).
Post-translational histone modiﬁcations
Post-translational modiﬁcations of histone proteins are also key-components in the epigenetic regulation of genes. Histones are subject to many modiﬁcations mostly in the N-terminal tails (Bernstein et al., 2007; Brunner et al., 2012; Wang et al., 2007). Modiﬁcations of histone tails involved in gene transcription include acetylation and methylation of lysine residues. Whereas acetylation of lysine residues in histone tails is correlated with gene activation (Struhl, 1998), the inﬂuence of histone methylation on gene transcription depends on the exact lysine residue methylated and the number of added methyl groups: mono-, di- or trimethyl (Kouzarides, 2007). For instance, tri-methylation of histone H3 at lysine 9 (3MeK9H3) and at lysine 27 (3MeK27H3), and of histone H4 at lysine 20 (3MeK20H4) are marks of gene repression (Cao and Zhang, 2004; Li et al., 2007; Martin and Zhang, 2005; Rice et al., 2003; Schotta et al., 2004). Counteracting these repressive modiﬁcations are the transcriptionally permissive modiﬁcations tri-methylation of histone H3 at lysine 4 (3MeK4H3) and at lysines 36 and 79 (Li et al., 2007; Martin and Zhang, 2005; Wang et al., 2009; Yan and Boyd, 2006). Together these modiﬁcations form a ‘histone code,’ like the genetic code, that controls transcription levels of genes (Strahl and Allis, 2000).
Table 1 Class I IIa IIb III IV
HDAC: HDAC: HDAC: HDAC: HDAC:
1,2,3,8 4,5,7,9 6,10 SIRT1-7 11
expressed genes. Besides their important role in the modiﬁcation of histones, these enzymes also modify and thereby inﬂuence the activities of non-histone targets involved in many cellular processes including in axonal degeneration (Egorova et al., 2010; Yao and Yang, 2011).
2.2.2. Additional histone modiﬁcations While lysine methylation and acetylation are the most studied modiﬁcations, there are many more histone modiﬁcations known. Arginine residues can also be methylated and acetylated. In the case of methylation, repression or activation of transcription depends on which arginine residue is methylated and the type of methylation i.e. mono- or di-(asymmetric or symmetric) (Bannister and Kouzarides, 2011). Sumoylation and ubiquitination of lysine residues have also been observed (Wang et al., 2007). Sumoylation appears to be associated with transcriptional repression (Garcia-Dominguez and Reyes, 2009), whereas ubiquitination has been suggested to play a role in transcriptional activation and elongation (Shukla et al., 2009). Other post-translational histone modiﬁcations that have been described include phosphorylation of serine and threonine residues, ADP-ribosylation of glutamic acid and arginine, deimination of arginine residues which are converted to citrulline and proline isomerisation (Bannister and Kouzarides, 2011).
2.3. 2.2.1. Enzymes that modify histones by acetylation and methylation Enzymes that chemically modify histones by adding or removing speciﬁc acetylation or methylation modiﬁcations on lysine residues of core histones have been, and continue to be identiﬁed. Histone acetylation depends on the activities of lysine acetyltransferases (KATs), and histone deacetylases (HDACs) and SIRTUINS (SIRTS). HDACs may be classiﬁed into four subfamilies (class-I, -IIa/IIb, -III and -IV), which possess in general non-overlapping functions and each having a unique expression pattern (Kortenhorst et al., 2006) (Table 1). Likewise, histone methylation relies on the activities of lysine methyltransferases (KMTs) and lysine demethylases (KDMs). In this way the enzymes promote a return to respectively repressive or active chromatin structure (Bannister and Kouzarides, 2011). Of note is that the enzymes that modify histones act in concert with DNA methyltransferases (Vaissiere et al., 2008; Vire et al., 2006). In this way, these enzymes control global gene activation and local control of genespeciﬁc transcription, and establish the cellular portrait of
Families of histone deacetylases.
Histone code readers
The ‘histone code’ can be read by so-called code-readers, chromatin-associated factors that speciﬁcally interact with modiﬁed histones (Bannister and Kouzarides, 2011). For instance Heterochromatin Protein 1 (HP1) recognizes and binds to the 3MeK9H3 mark, while Polycomb Group Proteins interact with the 3MeK27H3 mark for maintenance of repressive chromatin states. The 3MeK4H3 mark is bound by an ATP-dependent remodeling enzyme chromodomain helicase DNA binding protein 1 (CHD1), which is capable of repositioning nucleosomes facilitating transcription (Bannister and Kouzarides, 2011). Methylated CpG dinucleotides are bound by methyl CpG binding protein 2 (MeCP2) which can also be regarded as a code-reader. MeCP2 subsequently acts as a platform for recruitment of HDACs and transcriptional repressors, and of HMTs (Bird, 2002; Fuks et al., 2003). This leads to deacetylation and methylation of histones associated with CpG methylated DNA, which ultimately results in a stable transcriptionally repressive chromatin environment and gene silencing.
The epigenetics of multiple sclerosis and other related disorders
miRNA-associated epigenetic regulation
3.1. Experimental therapies targeting epigenetic processes
MicroRNAs (miRNA) are a class of endogenous small noncoding RNAs that consist of about 22 nucleotides and play critical roles in various cellular processes including in differentiation. miRNAs can act in several ways in epigenetic regulation by post-transcriptional silencing through target mRNA degradation or by translational inhibition of mRNAs encoding DNMTs, histone modifying activities or code readers (Sato et al., 2011) (Figure 2). Notably, transcription of the genes encoding miRNAs themselves is regulated by epigenetic processes such as DNA methylation (Kulis and Esteller, 2010). Several miRNAs appear to play a role in oligodendrocyte differentiation, and in immune system development and regulation (Li and Yao, 2012; Thamilarasan et al., 2012). Due to the reversible nature of epigenetic histone modiﬁcations, the chromatin-modifying enzymes are interesting therapeutic targets (Adcock, 2006; Cole, 2008). A myriad of small molecule inhibitors that can inﬂuence the enzymatic activity of these chromatin-modifying enzymes are currently being tested for their efﬁcacy in a variety of pathologies including neurological disorders (Mai, 2007). Some of these issues, summarized in Table 2 are discussed below.
3. Epigenetic interference in animal models of MS Animal models of MS are crucial for investigating the mechanisms underlying the disease as well as the design and testing of therapeutic strategies (Van der Star et al., 2012). The autoimmune model of MS is experimental autoimmune encephalomyelitis (EAE) in which inﬂammation, myelin damage and neurodegeneration can be induced in susceptible animals following immunization with CNS proteins in a strong adjuvant. The course of disease, and histological and neurological signs heavily depend on the immunization regimen, as well as the strain and species of animal.
A potential role for epigenetic acetylation processes in disease pathogenesis emerges from several studies in EAE, including our own, and in experimental autoimmune neuritis (EAN, an animal model of inﬂammatory demyelinating peripheral neuropathies). A number of these studies are also summarized in Table 2. In these studies the therapeutic potential of small molecule inhibitors that target the activities of the enzymes involved in modiﬁcation of lysine residues in histones and non-histone proteins by acetylation has been evaluated. For instance, Camelo et al. showed that intraperitoneal administration of the histone deacetylase inhibitor (HDACi) Trichostatin A (TSA) reduces spinal cord inﬂammation, demyelination, neuronal and axonal loss and ameliorates disability in the relapsing phase of EAE in C57BL/6 female mice (Camelo et al., 2005). TSA treatment promoted neuronal survival and inhibited anti-inﬂammatory pathways leading to signiﬁcant reduction in the cell inﬁltration in the CNS. The HDACi, vorinostat (SAHA), was shown to reduce neurological signs of EAE in C57BL/6 female mice (Ge et al., 2013). In vitro studies revealed that mature DC-induced allogeneic T-cell responses and DC-derived Th1 and Th17 polarizing cytokines are reduced by exposure of DCs to vorinostat, possibly explaining the mechanism of action in EAE. The therapeutic effect of the HDACi, valproic acid (VPA), on EAE in Lewis rats was revealed following daily administration, which greatly reduced the severity and duration of EAE (Zhang et al., 2012). VPA administration also suppressed mRNA levels in spinal cords of the pro-inﬂammatory cytokines IFNγ, TNFα, IL-1β and IL-17, while an increase in the anti-inﬂammatory cytokine IL-4 was also noted. Preventive VPA treatment also greatly attenuated accumulation of macrophages and lymphocytes in EAE spinal cords while at the same time shifting the Th1 and Th17 proﬁle to a Th2 and Treg proﬁle (Zhang et al., 2012). VPA also reduces neurological disease in chronic relapsing EAE in Biozzi ABH mice as we have explored. As shown in
miRNA gene Drosha Pre-miRNA
Mature miRNA Target gene
RISC Target mRNA
Figure 2 Schematic representation of translational repression and mRNA degradation by miRNAs. A miRNA gene is transcribed to yield pre-miRNA, which is cleaved by Drosha and transported out of the nucleus. Pre-miRNA is then cleaved by Dicer to form a short double stranded mature miRNA. The double stranded miRNA separated into two single strands and complexes with Risc. The miRNA/ Risc complex binds to its target mRNA, which is translationally repressed or degraded.
P.J. van den Elsen et al.
Epigenetic therapies in experimental models of CNS autoimmune and neurodegenerative diseases.
HDAC class I and IIa, inhibitor
EAE in rats Inhibits neurological disease. Decreased macrophage and T cell inﬁltration. Th1, Th17 switch to Th2 and T reg. AD mouse Inhibits Abeta production. Reduces neuronal loss, plaque formation and behavioral deﬁcits HD mouse Alleviated locomotor deﬁcits, depressive- and model anxiety-like behaviors. Improved motor skill, learning and coordination.
Zhang et al. (2012)
Long et al. (2012) Qing et al. (2008) Chiu et al. (2011)
HDAC class I, EAE IIa, IIb and IV AD mouse inhibitor R6/2 HD mouse
Inhibition of Th1 and Th17 responses Restored contextual memory Improved the motor impairment
Ge et al. (2013) Kilgore et al. (2010) Hockly et al. (2003)
HDAC-1 and HDAC-3 inhibitor
Attenuates accumulation of macrophages, T cells and B cells, and demyelination. Reduces pro-inﬂammatory cytokines. Increases Foxp3 + cells and M2 macrophages Ameliorates inﬂammation and cerebral amyloidosis
Zhang et al. (2010)
AD cerebral amyloidosis D-β-hydroxy butyrate HDAC class I and IIa inhibitor
transgenic R6/2 mice HD
HDAC class I, EAE IIa, IIb and IV inhibitor
Sirt 1 activator (HDAC class III)
Extends life span and attenuates motor deﬁcits Lim et al. (2011)
Reduces spinal cord inﬂammation, demyelination, neuronal and axonal loss and decreases neurological disease
Reduced optic neuritis attenuates neuronal damage. Reduces clinical disease 6-OHDA-PD Neuroprotective effect due to decreased the rat model levels of COX-2 and TNFα mRNA in the substantia nigra
KAT inhibitor EAE AD model MTPT PD model
Zhang and Schluesener (2013)
Camelo et al. (2005)
Shindler et al. (2010) Jin et al. (2008)
Decreased inﬂammation and IL-17, TGFβ, IL-6, Xie et al. (2009) IL-21 STAT3, RORγ Interferes with plaque formation Lim et al. (2001) Reduces monoamine oxidase activity Rajeswari and Sabesan (2008)
VPA—Valproic acid; HDAC—histone deacetylase; EAE—experimental autoimmune encephalomyelitis; AD—Alzheimer's disease; HD— Huntingtons' disease; SAHA—Suberoylanilide hydroxamic acid; EAN—experimental autoimmune neuritis; KAT—lysine acetyltransferase; EAN—experimental autoimmune neuritis; PD-0 Parkinsons disease; TSA—Trichostatin A.
Figure 3 intraperitoneally administration of VPA after induction of disease signiﬁcantly delayed onset and severity of EAE in these mice. The HDACi VPA and MS275 both attenuate the inﬂammatory reaction in EAN in Lewis rats resulting in a greatly reduced severity and duration of the disease (Zhang et al., 2008, 2010). VPA administration resulted in reduced mRNA levels in the lymph nodes of IFNγ, TNFα, IL-1β, IL-4, IL-6 and IL-17. At the same time FoxP3+ cells were increased but IL17+ cells were decreased in peripheral blood and sciatic nerves (Zhang et al., 2008). Administration of MS275 also resulted in a signiﬁcant reduction in the transcript levels of the pro-inﬂammatory cytokines IFNγ, IL-1β and IL-17 in
sciatic nerves (Zhang et al., 2010). In lymph nodes, MS275 also depressed the expression of these cytokines but at the same time an increase in expression of the anti-inﬂammatory cytokine IL-10 and of FOXP3 was noted. In addition both drugs attenuated the accumulation of macrophages, T-cells and B-cells, and demyelination in sciatic nerves (Zhang et al., 2008, 2010). By using the naturally occurring polyphenolic phytochemical curcumin, which inhibits the activity of lysine acetyltransferases (KATs), Xie et al. showed that clinical severity of EAE was signiﬁcantly reduced in Lewis rats (Xie et al., 2009). Moreover, it was revealed that curcumin treatment also affected the amount of inﬂammatory cells inﬁltration in the
The epigenetics of multiple sclerosis and other related disorders
A Complete time course
B Results to day 21
Figure 3 Therapeutic valproic acid (VPA) treatment attenuates onset and severity of EAE in Biozzi ABH mice. VPA inhibits the activities of class I and class IIa lysine deacetylases. (A) Animals were injected with 1 mg syngeneic spinal cord homogenate emulsiﬁed in CFA on days 0 and 7 (Al-Izki et al., 2011). Animals were also injected intraperitoneally (i.p.) with 200 ng of pertussis toxin that was repeated 24 h later. Mice were injected i.p. daily with VPA (400 mg/kg in 200 μl PBS) or PBS from day 10 until day 24 after immunization. Clinical scores (0 =normal, 1 =limp tail, 2 =impaired righting reﬂex, 3 =hind-limb paresis, 4 =complete hindlimb paralysis and 5=moribund/death) were measured daily post immunization. Animals were housed and monitored consistent with the principles of the ARRIVE guidelines as described previously (Baker and Amor, 2012; Baker et al., 2011). (A) VPA treatment signiﬁcantly delayed onset and severity of EAE. (B) Table detailing reduction in EAE score and day of onset. aMean 7 SEM of maximum clinical score of EAE from all animals in the group. bMean 7 SEM of maximum clinical score from animals exhibiting EAE within a group. cMean 7 SD of day of onset of clinical disease. *po0.05; **po0.01.
spinal cord. Interestingly, curcumin treatment resulted in a decrease of IL-17, TGFβ, IL-6, IL-21, STAT3 and RORγ expression, which had a bearing on differentiation and development of Th17 cells (Xie et al., 2009). Interference in SIRT's activities is also of interest as they play a key role in neuroprotection (recently reviewed by Albani et al., 2010). This is illustrated by the ﬁnding that Sirt1 activation by resveratrol confers neuroprotection in experimental optic neuritis (Shindler et al., 2007). In addition, oral administration of resveratrol reduces neuronal damage in EAE in female SJL/J mice. However, in this model Sirt1 activation did not prevent inﬂammation (Shindler et al., 2010). In summary, the studies in experimental animal models demonstrate that small molecule inhibitors known to interfere in epigenetic acetylation processes modulate immune reactivity thereby suppressing systemic and local inﬂammation ameliorating disease. While Sirt activators do not seem to have an effect on inﬂammation, they clearly have neuroprotective properties. The promising observations made in these experimental animal models support the notion that interference in epigenetic processes might be a promising novel therapeutic option for treatment of MS.
3.2. Epigenetic interference in other inﬂammatory animal models Similar studies in a number of other experimental disease models also reveal a critical role for epigenetic processes in onset and severity of disease (summarized in Table 2). As an example, in collagen-induced arthritis VPA, SAHA and MS-275 have anti-rheumatic activities and show a decrease in incidence and severity of disease amongst others by an increase in regulatory T cell function (Lin et al., 2007; Saouaf et al., 2009). In collagen antibody-induced arthritis TSA suppresses synovial inﬂammation (Nasu et al., 2008). In a mouse model of Alzheimers disease, VPA treatment was shown to have beneﬁcial effect on disease severity by inhibiting Abeta production, neuritic plaque formation and behavioral deﬁcits (Qing et al., 2008). Also, in an animal model of cerebral amyloidosis for Alzheimer disease, MS-275 ameliorated neuroinﬂammation and cerebral amyloidosis (Zhang and Schluesener, 2013). In other animal models such as for autoimmune lymphoproliferative syndrome (ALPS), renal injury, and experimental autoimmune prostatitis various HDACi were shown to display effective therapeutic potential (Dowdell et al., 2009; Noh et al., 2009; Zhang and Schluesener, 2012).
P.J. van den Elsen et al.
Together, data from these various animal models reveals that interference in HDAC activities is very effective in ameliorating disease indicting that translational studies may very well show similar effects in humans.
4. Epigenetic dysregulation in Multiple Sclerosis 4.1.
Histone acetylation patterns in MS
The question therefore remains whether in the human disease MS alterations in epigenetic processes can be observed. Indeed, in MS apparent changes in histone acetylation patterns in normal-appearing white matter (NAWM) and in early MS lesions have been documented (Pedre et al., 2011). A shift towards histone acetylation in the white matter of the frontal lobes of aged subjects and in patients with chronic MS was observed. Furthermore, increased immunoreactivity for acetylated histone H3 in nuclei of mature (NogoA + ) oligodendrocytes in a subset of MS samples was found (Pedre et al., 2011). Previously it was shown that histone acetylation is associated with increased levels of transcriptional inhibitors of oligodendrocyte differentiation (Li et al., 2009). The high level of histone acetylation observed in NogoA + oligodendrocytes was associated with increased levels of transcriptional inhibitors of oligodendrocyte differentiation in female MS patients compared with non-neurological controls and correlated with disease duration. However, the opposite was true for early MS lesions where a marked reduction in oligodendrocyte histone acetylation was observed (Pedre et al., 2011).
Together, these observations reveal the ﬂuidity of histone acetylation during the disease course resulting in increased levels of histone acetylation in NogoA + oligodendrocytes at later stages of the disease. The dynamics of global histone acetylation patterns in MS lesions and NAWM is underscored also by our unpublished observations, which are indicative of a increase in histone acetylation in NAWM of MS patients when compared with non-neurological controls (Figure 4A). Furthermore, altered histone acetylation patterns in NAWM and lesional areas in MS patients can also be observed (Figure 4B). Together, similar to other inﬂammatory autoimmune diseases, alterations in global levels of histone acetylation modiﬁcations can be observed. How these global alterations in histone acetylation or additional epigenetic histone and DNA modiﬁcations translate to transcription of speciﬁc genes involved in inﬂammation, oligodendrocyte differentiation or post-translation modiﬁcation of non-histone gene products and the bearing this has on the function of their protein product will be discussed below.
microRNAs in MS
In MS, by using whole blood, peripheral blood-derived lymphocytes or serum samples, several studies have shown differential expression of various miRNAs (reviewed in Fenoglio et al., 2012; Huynh and Casaccia, 2013; Junker et al., 2011; Thamilarasan et al., 2012). In particular miR223 was found upregulated in blood and in Tregs from MS patients in comparison with healthy controls (Keller et al., 2009). miR-223 modulates the NF-κB pathway and as such
Figure 4 Expression of epigenetic markers in multiple sclerosis. (A) Enhanced display of the acetylated histone H4 mark (blue staining, upper panel) in pre-active lesions appearing in the NAWM of an MS patient (Van der Valk and Amor, 2009). LN3 (HLA-DR) brown staining. (B) Nuclei displaying the acetylated histone H3 (Ac-H3) mark (brown staining). Left panel above: PLP staining revealing lesional area (L), an area of remyelination (R) and the NAWM (N). Right panel above: all nuclei in the NAWM display the Ac-H3 mark. In the lesional area only 60% of the nuclei display the Ac-H3 mark, while in the remyelinated area about 80% of the nuclei display the Ac-H3 mark (Bottom left and right panel, respectively). (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)
The epigenetics of multiple sclerosis and other related disorders plays a central role inﬂammatory responses (Li et al., 2010). In addition to miR-223, proﬁling in MS lesions revealed the upregulation of miR34a, miR-155 and miR-326 in active lesions when compared to normal brain white matter (Junker et al., 2009). Since miR34a, miR-155 and miR-326 target CD47 these observations suggest that in MS lesions CD47 is reduced in brain resident cells, releasing macrophages from inhibitory control, thereby promoting phagocytosis of myelin (Junker et al., 2009). miR-155 together with miR-338 and miR-491 were also found to be upregulated in cerebral white matter of MS patients (Noorbakhsh et al., 2011). As a result levels of important neurosteroids were suppressed in white matter of MS patients. These observations are in support of dysregulated miRNA levels in MS (Koch et al., 2013b). Further studies are required to establish the potential role for these miRNAs in MS pathogenesis.
4.3. Gene-speciﬁc chromatin alterations in the CNS and in MS As discussed in the previous section, alterations in global levels of histone acetylation in NogoA+ oligodendrocytes has a bearing on the levels of transcriptional inhibitors of oligodendrocyte differentiation (Pedre et al., 2011). This is particularly revealed by chromatin immunoprecipitation (ChIP) showing that the promoter of the TCF7L2 gene, which plays a critical role in modulating oligodendrocyte differentiation, displays an increase in histone acetylation in chromatin encompassing the TCF7L2 gene promoter in MS in comparison to controls (Pedre et al., 2011). That epigenetic post-translational modiﬁcations impact on disease is supported by the demonstration that in MS white matter hypomethylation of the promoter of the peptidyl arginine deaminase 2 (PAD2) gene is correlated with an increase in the levels of PAD2 expression (Mastronardi et al., 2007; Moscarello et al., 2007). The PAD2 enzyme catalyzes MBP citrullination and increased levels of citrullinated myelin basic protein (MBP) can result in a loss of myelin stability in MS brains (D’Souza et al., 2005). With respect to immune genes, increased expression of MHC class I and class II molecules is noted in various types of lesions in MS, when compared with NAWM (Gobin et al., 2001). Expression of both classes of MHC genes is also determined by epigenetic processes. In particular because the transcriptional co-activators which play an important role in the transcriptional activation of these genes act as platforms for the recruitment of histone modifying activities for adequate expression (Kobayashi and van den Elsen, 2012; Van den Elsen et al., 2004). Furthermore, it is now ﬁrmly established that remyelination is controlled by the activities of enzymes that modify histones by acetylation (Shen et al., 2008).
5. Epigenetic dysregulation in other neurodegenerative disorders In addition to MS, it has become apparent in recent years that epigenetic dysregulation is also frequently observed in other neurodegenerative disorders including Alzheimer
disease, Huntington's disease, Parkinson's disease, ischemia, mood disorders (depression and anxiety), neurodevelopmental disorders (Rubinstein–Taybi syndrome, Rett syndrome, Fragile X syndrome), Immunodeﬁciency with Centromeric Instability and Facial anomalies (ICF) syndrome, Angelman and Prader–Willi syndromes, and in inﬂammatory disorders (reviewed in Abel and Zukin, 2008; Chuang et al., 2009; De Greef et al., 2011; Lalande and Calciano, 2007; Urdinguio et al., 2009; Wierda et al., 2010). For example, Angelman and Prader-Willi syndromes are recognized by DNA methylation imprinting defects encompassing human chromosome 15q11-q13, which affect allelespeciﬁc expression in the brain of disease-associated genes (Lalande and Calciano, 2007). In Rubinstein–Taybi syndrome the genetic defect is in the transcriptional co-activator CREB-binding protein (CBP), which possesses lysine acetyltransferase activities (Petrij et al., 1995). ICF1 syndrome is recognized by mutations in DNMT3b (Xu et al., 1999), while in ICF2 the mutations are in the zinc-ﬁnger- and BTB (bric-abric, tramtrack, broad complex)-domain-containing 24 (ZBTB24), which belongs to a large family of transcriptional repressors (De Greef et al., 2011). Both ICF1 and ICF2 patients share the same immunological and epigenetic features, including hypomethylation of juxtacentromeric repeat sequences (De Greef et al., 2011; Weemaes et al., 2013). Loss of function mutations in MeCP2 is characteristic for RETT syndrome (Amir et al., 1999). Early life experiences seem to determine anxietymediated behaviors and disorders later in life. These events are mediated by epigenetic processes which is illustrated by the observation that maternal care inﬂuences methylation of the glucocorticoid receptor (GR) at promoter CpG residues in the hippocampus is. Early in life pup licking and grooming, and arched-back nursing were found to inﬂuence the methylation status of the GR in the hippocampus. These alterations in DNA methylation were associated with altered histone acetylation and transcription factor (NGFI-A) binding to the GR promoter and ultimately affected the hypothalamic-pituitary-adrenal (HPA) responses to stress in the offspring (Weaver et al., 2004). TSA treatment eliminates maternal effect on histone acetylation and NGFI-A binding (Weaver et al., 2004). Moreover, treatment of the offspring with TSA also reverses the earlyin-life induced maternal care effects on the hippocampal transcriptome and anxiety-mediated behaviors in the offspring in adulthood (Weaver et al., 2006).
Conclusions and perspectives
Epigenetic control of gene expression and maintenance of cellular identity is one of the most fundamental regulatory systems within the cell. Not surprisingly it fulﬁls essential roles in processes involved CNS homeostasis. Disturbances of the delicate interplay between the various activities that modify histones (and also non-histone targets) may lead to cellular dysfunction as observed in pathological conditions. In the case of MS this contributes to the neuro-inﬂammatory and neuro-degenerative character of the disease. Intervention in epigenetic gene regulation in disease states might prove to be a beneﬁcial therapeutic option for the near future, especially in complex multi-factorial diseases such
P.J. van den Elsen et al. Astrocyte
Figure 5 Therapeutic potential of inhibitors of epigenetic processes in the treatment of multiple sclerosis. Epigenetic drugs such as histone deacetylase inhibitors, lysine acetyltransferase inhibitors or DNA demethylating drugs have the capacity to rescue the distorted epigenetic processes that affect the expression of genes in MS. In this way these drugs mediate peripheral immunosuppressive activities either through skewing of dendritic cell function, or directly by inhibiting the activities of Th1/Th17 cells or by promoting the activities of Tregs. At the same these drugs may also exhibit neuroprotective properties or interfere in disease-associated pathogenic processes in astrocytes or microglia.
as MS. Epigenetic interference in the treatment of MS may be targeted at relevant immune components such as dendritic cells, Tregs and Th17 cells, or cells of the CNS such as microglia, neurons or astrocytes (Figure 5). However, caution should be taken as most of the currently available drugs display a broad spectrum of activity, which could lead to severe side-effects thereby limiting their clinical efﬁcacy. Additionally, in case of MS, most-likely simultaneous targeting of the CNS and the peripheral immune system is required to obtain the desired clinical efﬁcacy. In that case these inhibitors should also be able to cross the blood-brain barrier. Therefore, further studies are required to identify the histone and DNA modifying activities, and epigenetic effectors displaying altered expression characteristics and protein function in MS. The identiﬁcation of MS-associated epigenetic activities allows the design of more speciﬁc drugs, which can be evaluated for their clinical efﬁcacy. In summary, the results from various preclinical studies indicate that epigenetic therapy by using inhibitors that target disease-associated components of the epigenetic machinery may prove to be beneﬁcial in the treatment of MS.
Conﬂicts of interest The authors declare no conﬂicts of interests.
Acknowledgments We apologize to our colleagues whose work was not cited in this review. The authors greatly acknowledge the support of the MS Research Foundation of the Netherlands, the Multiple Sclerosis Society of Great Britain and Northern Ireland, the National Multiple Sclerosis Society USA and the National Center for the Reﬁnement, Reduction and Replacement of Animals in Research.
References Abel T, Zukin RS. Epigenetic targets of HDAC inhibition in neurodegenerative and psychiatric disorders. Current Opinion in Pharmacology 2008;8:57–64. Adcock IM. Histone deacetylase inhibitors as novel anti-inﬂammatory agents. Current Opinion in Investigational Drugs 2006;7: 966–73. Albani D, Polito L, Signorini A, Forloni G. Neuroprotective properties of resveratrol in different neurodegenerative disorders. Biofactors 2010;36:370–6. Al-Izki S, Pryce G, Jackson SJ, Giovannoni G, Baker D. Immunosuppression with FTY720 is insufﬁcient to prevent secondary progressive neurodegeneration in experimental autoimmune encephalomyelitis. Multiple Sclerosis 2011;17:939–48. Alkemade FE, Van Vliet P, Henneman P, Van Dijk KW, Hierck BP, Van Munsteren JC, et al. Prenatal exposure to apoE deﬁciency and postnatal hypercholesterolemia are associated with altered cellspeciﬁc lysine methyltransferase and histone methylation patterns in the vasculature. American Journal of Pathology 2010;176:542–8. Amir RE, Van den Veyver IB, Wan M, Tran CQ, Francke U, Zoghbi HY. Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2. Nature Genetics 1999;23:185–8. Baker D, Gerritsen W, Rundle J, Amor S. Critical appraisal of animal models of multiple sclerosis. Multiple Sclerosis 2011;17:647–57. Baker D, Amor S. Publication guidelines for refereeing and reporting on animal use in experimental autoimmune encephalomyelitis. Journal of Neuroimmunology 2012;242:78–83. Bannister AJ, Kouzarides T. Regulation of chromatin by histone modiﬁcations. Cell Research 2011;21:381–95. Berger SL, Kouzarides T, Shiekhattar R, Shilatifard A. An operational deﬁnition of epigenetics. Genes and Development 2009;23:781–3. Bernstein BE, Meissner A, Lander ES. The mammalian epigenome. Cell 2007;128:669–81. Bird A. DNA methylation patterns and epigenetic memory. Genes and Development 2002;16:6–21. Brunner AM, Tweedie-Cullen RY, Mansuy IM. Epigenetic modiﬁcations of the neuroproteome. Proteomics 2012;12:2404–20.
The epigenetics of multiple sclerosis and other related disorders Bygren LO, Kaati G, Edvinsson S. Longevity determined by paternal ancestors' nutrition during their slow growth period. Acta Biotheoretica 2001;49:53–9. Camelo S, Iglesias AH, Hwang D, Due B, Ryu H, Smith K, et al. Transcriptional therapy with the histone deacetylase inhibitor trichostatin A ameliorates experimental autoimmune encephalomyelitis. Journal of Neuroimmunology 2005;164:10–21. Cao R, Zhang Y. The functions of E(Z)/EZH2-mediated methylation of lysine 27 in histone H3. Current Opinion in Genetics and Development 2004;14:155–64. Chuang DM, Leng Y, Marinova Z, Kim HJ, Chiu CT. Multiple roles of HDAC inhibition in neurodegenerative conditions. Trends in Neurosciences 2009;32:591–601. Cobiac L. Epigenomics and nutrition. Forum of Nutrition 2007;60: 31–41. Chiu CT, Liu G, Leeds P, Chuang DM. Combined treatment with the mood stabilizers lithium and valproate produces multiple beneﬁcial effects in transgenic mouse models of Huntington's disease. Neuropsychopharmacology 2011;36:2406–21. Cole PA. Chemical probes for histone-modifying enzymes. Nature Chemical Biology 2008;4:590–7. D’Souza CA, Wood DD, She YM, Moscarello MA. Autocatalytic cleavage of myelin basic protein: an alternative to molecular mimicry. Biochemistry 2005;44:12905–13. De Greef JC, Wang J, Balog J, den Dunnen JT, Frants RR, Straasheijm KR, et al. Mutations in ZBTB24 are associated with immunodeﬁciency, centromeric instability, and facial anomalies syndrome type 2. American Journal of Human Genetics 2011;88:796–804. Dowdell KC, Pesnicak L, Hoffmann V, Steadman K, Remaley AT, Cohen JI, et al. Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, diminishes lymphoproliferation in the Fas -deﬁcient MRL/lpr(-/-) murine model of autoimmune lymphoproliferative syndrome (ALPS). Experimental Hematology 2009;37:487–94. Ebers GC, Bulman DE, Sadovnick AD, Paty DW, Warren S, Hader W, et al. A population-based study of multiple sclerosis in twins. New England Journal of Medicine 1986;315:1638–42. Egorova KS, Olenkina OM, Olenina LV. Lysine methylation of nonhistone proteins is a way to regulate their stability and function. Biochemistry (Mosc) 2010;75:535–48. Fenoglio C, Ridolﬁ E, Galimberti D, Scarpini E. MicroRNAs as active players in the pathogenesis of multiple sclerosis. International Journal of Molecular Sciences 2012;13:13227–39. Foley DL, Craig JM, Morley R, Olsson CJ, Dwyer T, Smith K, et al. Prospects for epigenetic epidemiology. American Journal of Epidemiology 2009;169:389–400. Fraga MF, Ballestar E, Paz MF, Ropero S, Setien F, Ballestar ML, et al. Epigenetic differences arise during the lifetime of monozygotic twins. Proceedings of the National Academy of Sciences of the United States of America 2005;102:10604–9. Fuks F, Hurd PJ, Wolf D, Nan X, Bird AP, Kouzarides T. The methylCpG-binding protein MeCP2 links DNA methylation to histone methylation. Journal of Biological Chemistry 2003;278:4035–40. Fuso A. The ‘golden age’ of DNA methylation in neurodegenerative diseases. Clinical Chemistry and Laboratory Medicine 2013;51: 523–34. Garcia-Dominguez M, Reyes JC. SUMO association with repressor complexes, emerging routes for transcriptional control. Biochimica et Biophysica Acta 2009;1789:451–9. Ge Z, Da Y, Xue Z, Zhang K, Zhuang H, Peng M, et al. Vorinostat, a histone deacetylase inhibitor, suppresses dendritic cell function and ameliorates experimental autoimmune encephalomyelitis. Experimental Neurology 2013;241:56–66. Gobin SJ, Montagne L, Van Zutphen M, Van der Valk P, Van den Elsen PJ, De Groot CJ. Upregulation of transcription factors controlling MHC expression in multiple sclerosis lesions. Glia 2001;36: 68–77.
Guerrero-Bosagna C, Skinner MK. Environmentally induced epigenetic transgene rational inheritance of phenotype and disease. Molecular and Cellular Endocrinology 2012;354:3–8. Handel AE, Giovannoni G, Ebers GC, Ramagopalan SV. Environmental factors and their timing in adult-onset multiple sclerosis. Nature Reviews Neurology 2010;6:156–66. Hockly E, Richon VM, Woodman B, Smith DL, Zhou X, Rosa E, et al. Suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, ameliorates motor deﬁcits in a mouse model ofHuntington's disease. Proceedings of the National Academy of Sciences of the United States of America 2003;100:2041–6. Huynh JL, Casaccia P. Epigenetic mechanisms in multiple sclerosis: implications for pathogenesis and treatment. Lancet Neurology 2013;12:195–206. Irizarry RA, Ladd-Acosta C, Wen B, Wu Z, Montano C, Onyango P, et al. The human colon cancer methylome shows similar hypoand hypermethylation at conserved tissue-speciﬁc CpG island shores. Nature Genetics 2009;41:178–86. Jaenisch R, Bird A. Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals. Nature Genetics 2003;33(Suppl):245–54. Jenuwein T, Allis CD. Translating the histone code. Science 2001;293: 1074–80. Jin F, Wu Q, Lu YF, Gong QH, Shi JS. Neuroprotective effect of resveratrol on 6-OHDA-induced Parkinson's disease in rats. European Journal of Pharmacology 2008;600:78–82. Junker A, Krumbholz M, Eisele S, Mohan H, Augstein F, Bittner R, et al. MicroRNA proﬁling of multiple sclerosis lesions identiﬁes modulators of the regulatory protein CD47. Brain 2009;132: 3342–52. Junker A, Hohlfeld R, Meinl E. The emerging role of microRNAs in multiple sclerosis. Nature Reviews Neurology 2011;7:56–9. Kaati G, Bygren LO, Edvinsson S. Cardiovascular and diabetes mortality determined by nutrition during parents' and grandparents' slow growth period. European Journal of Human Genetics 2002;10:682–8. Kaminsky ZA, Tang T, Wang SC, Ptak C, Oh GH, Wong AH, et al. DNA methylation proﬁles in monozygotic and dizygotic twins. Nature Genetics 2009;41:240–5. Kangaspeska S, Stride B, Metivier R, Polycarpou-Schwarz M, Ibberson D, Carmouche RP, et al. Transient cyclical methylation of promoter DNA. Nature 2008;452:112–5. Keller A, Leidinger P, Lange J, Borries A, Schroers H, Schefﬂer M, et al. Multiple sclerosis: microRNA expression proﬁles accurately differentiate patients with relapsing-remitting disease from healthy controls. PLoS One 2009;4:e7440. Kilgore M, Miller CA, Fass DM, Hennig KM, Haggarty SJ, Sweatt JD, et al. Inhibitors of class 1 histone deacetylases reverse contextual memory deﬁcits in a mouse model of Alzheimer's disease. Neuropsychopharmacology 2010;35:870–80. Kim JK, Samaranayake M, Pradhan S. Epigenetic mechanisms in mammals. Cellular and Molecular Life Sciences 2009;66: 596–612. Kobayashi KS, van den Elsen PJ. NLRC5: a key regulator of MHC class I-dependent immune responses. Nature Reviews Immunology 2012;12:813–20. Koch MW, Metz LM, Kovalchuk O. Epigenetic changes in patients with multiple sclerosis. Nature Reviews Neurology 2013a;9: 35a–43a. Koch MW, Metz LM, Kovalchuk O. Epigenetics and miRNAs in the diagnosis and treatment of multiple sclerosis. Trends in Molecular Medicine 2013b;19:23b–30b. Kortenhorst MS, Carducci MA, Shabbeer S. Acetylation and histone deacetylase inhibitors in cancer. Cellular Oncology 2006;28: 191–222. Kouzarides T. Chromatin modiﬁcations and their function. Cell 2007;128:693–705.
174 Kragt J, van Amerongen B, Killestein J, Dijkstra C, Uitdehaag B, Polman Ch, et al. Higher levels of 25-hydroxyvitamin D are associated with a lower incidence of multiple sclerosis only in women. Multiple Sclerosis 2009;15:9–15. Kulis M, Esteller M. DNA methylation and cancer. Advances in Genetics 2010;70:27–56. Kurtzke JF. Multiple sclerosis in time and space—geographic clues to cause. Journal of Neurovirology 2000;6:S134–40. Lalande M, Calciano MA. Molecular epigenetics of Angelman syndrome. Cellular and Molecular Life Sciences 2007;64:947–60. Li B, Carey M, Workman JL. The role of chromatin during transcription. Cell 2007;128:707–19. Li H, He Y, Richardson WD, Casaccia P. Two-tier transcriptional control of oligodendrocyte differentiation. Current Opinion in Neurobiology 2009;19:479–85. Li T, Morgan MJ, Choksi S, Zhang Y, Kim YS, Liu ZG. MicroRNAs modulate the noncanonical transcription factor NF-kappaB pathway by regulating expression of the kinase IKKalpha during macrophage differentiation. Nature Immunology 2010;11:799–805. Li JS, Yao ZX. MicroRNAs: novel regulators of oligodendrocyte differentiation and potential therapeutic targets in demyelination-related diseases. Molecular Neurobiology 2012;45: 200–12. Lim GP, Chu T, Yang F, Beech W, Frautschy SA, Cole GM. The curry spice curcumin reduces oxidative damage and amyloid pathology in an Alzheimer transgenic mouse. Journal of Neuroscience 2001;21:8370–7. Lim S, Chesser AS, Grima JC, Rappold PM, Blum D, Przedborski S. Tieu KD-β-hydroxybutyrate is protective in mouse models of Huntington's disease. PLoS One 2011;6:e24620. Lin HS, Hu CY, Chan HY, Liew YY, Huang HP, Lepescheux L, et al. Anti-rheumatic activities of histone deacetylase (HDAC) inhibitors in vivo in collagen-induced arthritis in rodents. British Journal of Pharmacology 2007;150:862–72. Long Z, Zheng M, Zhao L, Xie P, Song C, Chu Y, et al. Valproic acid attenuates neuronal loss in the brain of APP/PS1 double transgenic Alzheimer's diseasemice model. Current Alzheimer Research 2013;10:261–9. Luger K, Mader AW, Richmond RK, Sargent DF, Richmond TJ. Crystal structure of the nucleosome core particle at 2.8 A resolution. Nature 1997;389:251–60. Mai A. The therapeutic uses of chromatin-modifying agents. Expert Opinion on Therapeutic Targets 2007;11:835–51. Martin C, Zhang Y. The diverse functions of histone lysine methylation. Nature Reviews Molecular Cell Biology 2005;6:838–49. Mastronardi FG, Noor A, Wood DD, Paton T, Moscarello MA. Peptidyl argininedeiminase 2 CpG island in multiple sclerosis white matter is hypomethylated. Journal of Neuroscience Research 2007;85:2006–16. Metivier R, Gallais R, Tiffoche C, Le PC, Jurkowska RZ, Carmouche RP, et al. Cyclical DNA methylation of a transcriptionally active promoter. Nature 2008;452:45–50. Moscarello MA, Mastronardi FG, Wood DD. The role of citrullinated proteins suggests a novel mechanism in the pathogenesis of multiple sclerosis. Neurochemical Research 2007;32:251–6. Nasu Y, Nishida K, Miyazawa S, Komiyama T, Kadota Y, Abe N, et al. Trichostatin A, a histone deacetylase inhibitor, suppresses synovial inﬂammation and subsequent cartilage destruction in a collagen antibody-induced arthritis mouse model. Osteoarthritis and Cartilage 2008;16:723–32. Niino M, Fukazawa T, Kikuchi S, Sasaki H. Therapeutic potential of vitamin D for multiple sclerosis. Current Medicinal Chemistry 2008;15:499–505. Noh H, Oh EY, Seo JY, Yu MR, Kim YO, Ha H, et al. Histone deacetylase-2 is a key regulator of diabetes- and transforming growth factor-beta1-induced renal injury. American Journal of Physiology—Renal Physiology 2009;297:F729–39.
P.J. van den Elsen et al. Noorbakhsh F, Ellestad KK, Maingat F, Warren KG, Han MH, Steinman L, et al. Impaired neurosteroid synthesis in multiple sclerosis. Brain 2011;134:2703–21. Pakpoor J, Giovannoni G, Ramagopalan SV. Epstein-Barr virus and multiple sclerosis: association or causation? Expert Review of Neurotherapeutics 2013;13:287–97. Patsopoulos NA, Esposito F, Reischl J, Lehr S, Bauer D, Heubach J, et al. Genome-wide meta-analysis identiﬁes novel multiple sclerosis susceptibility loci. Annals of Neurology 2011;70:897–912. Pedre X, Mastronardi F, Bruck W, López-Rodas G, Kuhlmann T, Casaccia P. Changed histone acetylation patterns in normalappearing white matter and early multiple sclerosis lesions. Journal of Neuroscience 2011;31:3435–45. Pembrey ME, Bygren LO, Kaati G, Edvinsson S, Northstone K, Sjöström M, et al. ALSPAC Study Team. Sex-speciﬁc, male-line transgenerational responses in humans. European Journal of Human Genetics 2006;14:159–66. Petrij F, Giles RH, Dauwerse HG, Saris JJ, Hennekam RC, Masuno M, et al. Rubinstein–Taybi syndrome caused by mutations in the transcriptional co-activator CBP. Nature 1995;376:348–51. Qing H, He G, Ly PT, Fox CJ, Staufenbiel M, Cai F, et al. Valproic acid inhibits Abeta production, neuritic plaque formation, and behavioral deﬁcits in Alzheimer's disease mouse models. Journal of Experimental Medicine 2008;205:2781–9. Rajeswari A, Sabesan M. Inhibition of monoamine oxidase-B by the polyphenolic compound, curcumin and its metabolite tetrahydrocurcumin, in a model of Parkinson's disease induced by MPTP neurodegeneration in mice. Inﬂammopharmacology 2008;16: 96–9. Rice JC, Briggs SD, Ueberheide B, Barber CM, Shabanowitz J, Hunt DF, et al. Histone methyltransferases direct different degrees of methylation to deﬁne distinct chromatin domains. Molecular Cell 2003;12:1591–8. Saouaf SJ, Li B, Zhang G, Shen Y, Furuuchi N, Hancock WW, et al. Deacetylase inhibition increases regulatory T cell function and decreases incidence and severity of collagen-induced arthritis. Experimental and Molecular Pathology 2009;87:99–104. Sato F, Tsuchiya S, Meltzer SJ, Shimizu K. MicroRNAs and epigenetics. FEBS Journal 2011;278:1598–609. Sawcer S, Hellenthal G, Pirinen M, Spencer CC, Patsopoulos NA, Moutsianas L, et al. Genetic risk and a primary role for cellmediated immune mechanisms in multiple sclerosis. Nature 2011;476:214–9. Schotta G, Lachner M, Sarma K, Ebert A, Sengupta R, Reuter G, et al. A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin. Genes and Development 2004;18:1251–62. Shen S, Sandoval J, Swiss VA, Li J, Dupree J, Franklin RJ, et al. Agedependent epigenetic control of differentiation inhibitors is critical for remyelination efﬁciency. Nature Neuroscience 2008;11: 1024–34. Shindler KS, Ventura E, Rex TS, Elliot P, Rostami A. SIRT1 activation confers neuroprotection in experimental optic neuritis. Investigative Ophthalmology and Visual Science 2007;48:3602–9. Shindler KS, Ventura E, Dutt M, Elliott P, Fitzgerald DC, Rostami A. Oral resveratrol reduces neuronal damage in a model of multiple sclerosis. Journal of Neuroophthalmology 2010;30:328–39. Shukla A, Chaurasia P, Bhaumik SR. Histone methylation and ubiquitination with their cross-talk and roles in gene expression and stability. Cellular and Molecular Life Sciences 2009;66: 1419–33. Smolders J, Damoiseaux J, Menheere P, Hupperts R. Vitamin D as an immune modulator in multiple sclerosis, a review. Journal of Neuroimmunology 2008;194:7–17. Strahl BD, Allis CD. The language of covalent histone modiﬁcations. Nature 2000;403:41–5. Struhl K. Histone acetylation and transcriptional regulatory mechanisms. Genes and Development 1998;12:599–606.
The epigenetics of multiple sclerosis and other related disorders Takai D, Jones PA. Comprehensive analysis of CpG islands in human chromosomes 21 and 22. Proceedings of the National Academy of Sciences of the United States of America 2002;99:3740–5. Tao Q, Robertson KD. Stealth technology: how Epstein-Barr virus utilizes DNA methylation to cloak itself from immune detection. Clinical Immunology 2003;109:53–63. Thamilarasan M, Koczan D, Hecker M, Paap B, Zettl UK. MicroRNAs in multiple sclerosis and experimental autoimmune encephalomyelitis. Autoimmunity Reviews 2012;11:174–9. Urdinguio RG, Sanchez-Mut JV, Esteller M. Epigenetic mechanisms in neurological diseases: genes, syndromes, and therapies. Lancet Neurology 2009;8:1056–72. Van den Elsen PJ, Holling TM, Kuipers HF, Van der Stoep N. Transcriptional regulation of antigen presentation. Current Opinion in Immunology 2004;16:67–75. Van der Star BJ, Vogel DY, Kipp M, Puentes F, Baker D, Amor S. In vitro and in vivo models of multiple sclerosis. CNS and Neurological Disorders—Drug Targets 2012;11:570–88. Van der Valk P, Amor S. Preactive lesions in multiple sclerosis. Current Opinion in Neurology 2009;22:207–13. Vaissiere T, Sawan C, Herceg Z. Epigenetic interplay between histone modiﬁcations and DNA methylation in gene silencing. Mutation Research 2008;659:40–8. Vire E, Brenner C, Deplus R, Blanchon L, Fraga M, Didelot C, et al. The Polycomb group protein EZH2 directly controls DNA methylation. Nature 2006;439:871–4. Wang GG, Allis CD, Chi P. Chromatin remodeling and cancer, Part I: covalent histone modiﬁcations. Trends in Molecular Medicine 2007;13:363–72. Wang P, Lin C, Smith ER, Guo H, Sanderson BW, Wu M, et al. Global analysis of H3K4 methylation deﬁnes MLL family member targets and points to a role for MLL1-mediated H3K4 methylation in the regulation of transcriptional initiation by RNA polymerase II. Molecular and Cellular Biology 2009;29:6074–85. Weaver IC, Cervoni N, Champagne FA, D’Alessio AC, Sharma S, Seckl JR, et al. Epigenetic programming by maternal behavior. Nature Neuroscience 2004;7:847–54. Weaver IC, Meaney MJ, Szyf M. Maternal care effects on the hippocampal transcriptome and anxiety-mediated behaviors in the offspring that are reversible in adulthood. Proceedings of the National Academy of Sciences of the United States of America 2006;103:3480–5.
Weemaes CMR, Van Tol MJD, Wang J, Van Ostaijen-ten Dam MM, Van Eggermond MCJA, Aytekin C, et al. Heterogeneous clinical presentation in ICF syndrome: correlation with underlying gene defects. European Journal of Human Genetics 2013, . http://dx. doi.org/10.1038/ejhg.2013.40. ([Epub ahead of print]). Wierda RJ, Geutskens SB, Quax PHA, Jukema JW, Van den Elsen PJ. Epigenetics in atherosclerosis and inﬂammation. Journal of Cellular and Molecular Medicine 2010;14:1225–40. Williams K, Christensen J, Helin K. DNA methylation: TET proteinsguardians of CpG islands? EMBO Reports 2012;13:28–35. Xie L, Li XK, Funeshima-Fuji N, Kimura H, Matsumoto Y, Isaka Y, et al. Amelioration of experimental autoimmune encephalomyelitis by curcumin treatment through inhibition of IL-17 production. International Immunopharmacology 2009;9:575–81. Xu GL, Bestor TH, Bourc’his D, Hsieh CL, Tommerup N, Bugge M, et al. Chromosome instability and immunodeﬁciency syndrome caused by mutations in a DNA methyltransferase gene. Nature 1999;402:187–91. Yan C, Boyd DD. Histone H3 acetylation and H3 K4 methylation deﬁne distinct chromatin regions permissive for transgene expression. Molecular and Cellular Biology 2006;26:6357–71. Yao YL, Yang WM. Beyond histone and deacetylase: an overview of cytoplasmic histone deacetylases and their nonhistone substrates. Journal of Biomedicine and Biotechnology 2011;2011: 146493. Zhang Z, Zhang ZY, Fauser U, Schluesener HJ. Valproic acid attenuates inﬂammation in experimental autoimmune neuritis. Cellular and Molecular Life Sciences 2008;65:4055–65. Zhang ZY, Zhang Z, Schluesener HJ. MS-275 an histone deacetylase inhibitor, reduces the inﬂammatory reaction in rat experimental autoimmune neuritis. Neuroscience 2010;169:370–7. Zhang Z, Zhang ZY, Wu Y, Schluesener HJ. Valproic acid ameliorates inﬂammation in experimental autoimmune encephalomyelitis rats. Neuroscience 2012;221:140–50. Zhang ZY, Schluesener HJ. HDAC inhibitor MS-275 attenuates the inﬂammatory reaction in rat experimental autoimmune prostatitis. Prostate 2012;72:90–9. Zhang ZY, Schluesener HJ. Oral administration of histone deacetylase inhibitor MS-275 ameliorates neuroinﬂammation and cerebral amyloidosis and improves behavior in a mouse model. Journal of Neuropathology and Experimental Neurology 2013;72: 178–85.