Elsevier

Journal of Autoimmunity

Volume 41, March 2013, Pages 175-181
Journal of Autoimmunity

Epigenetic dysregulation in salivary glands from patients with primary Sjögren's syndrome may be ascribed to infiltrating B cells

https://doi.org/10.1016/j.jaut.2013.02.002Get rights and content

Abstract

Sjögren's syndrome (SS) is an autoimmune exocrinopathy characterized by an epithelium injury with dense lymphocytic infiltrates, mainly composed of activated T and B cells. Present at the interface of genetic and environmental risk factors, DNA methylation is suspected to play a key role in SS. To clarify this point, global DNA methylation was tested within salivary gland epithelial cells (SGEC), peripheral T cells and B cells from SS patients. Global DNA methylation was reduced in SGEC from SS patients, while no difference was observed in T and B cells. SGEC demethylation in SS patients was associated with a 7-fold decrease in DNA methyl transferase (DNMT) 1 and a 2-fold increase in Gadd45-alpha expression. The other DNA methylation/demethylation partners, tested by real time PCR (DNMT3a/b, PCNA, UHRF1, MBD2, and MBD4), were not different. Interestingly, SGEC demethylation may be attributed in part to the infiltrating B cells as suspected in patients treated with anti-CD20 antibodies to deplete B cells. Such hypothesis was confirmed using co-culture experiments with human salivary gland cells and B cells. Furthermore, B cell-mediated DNA demethylation could be ascribed to an alteration of the PKC delta/ERK/DNMT1 pathway. As a consequence, part of the SGEC dysfunction in SS may be linked to epigenetic modifications, thus opening new therapeutic perspectives in SS.

Highlights

► In the etiology of Sjogren's syndrome (SS), epigenetic modifications are suspected. ► DNMT1 expression and global DNA methylation are altered in SS. ► Epigenetic defects are restricted to salivary gland epithelial cells. ► In exocrine glands, DNA methylation is controlled by infiltrating B cells.

Introduction

Sjögren's syndrome (SS) is a chronic autoimmune disease affecting exocrine glands, mainly the salivary and lacrimal glands, leading to its designation as an autoimmune epithelitis [1]. Systemic features may be present [2], autoantibodies are detected, and patients with SS have a 20–40 fold increased risk of developing B cell lymphoma [3]. Activated mononuclear cells infiltrate exocrine glands, mainly T and B cells, and such infiltration evolves with the lesion severity and disease manifestations. According to Christodoulou et al., B cells predominate in severe inflammatory lesions, and a B/T cell positive ratio correlated with the infiltration grade and the biopsy focus score [4].

The etiology of SS is multifactorial and arises from an interplay of genetic predispositions, immunological dysregulation, environmental factors and epigenetic modifications [5]. Experimental models support a role for DNA methylation in SS and lupus. Indeed, hydralazine and procainamide, two DNA methylation inhibitors, induce SS with immunological features of a systemic lupus erythematosus (SLE)-like disease [6], [7]. DNA methylation at the 5-carbon position of cytosines (5MeCyt) in CpG dinucleotides is tightly regulated during cell development and the cell cycle. The DNA methyl transferases DNMT3a/b and DNMT1 are responsible for the establishment and maintenance of CpG methylation patterns, respectively. To be effective, DNMTs need to be associated with DNA binding proteins such as the proliferation cell nuclear antigen (PCNA) and the DNA repair/transcription factor ubiquitin-like PHD and RING finger domains 1 (UHRF1) [8]. In contrast, DNA demethylation is related to the methyl-CpG-binding domain (MBD) protein-2 and -4 when associated with the stress protein Gadd-45α that can initiate DNA demethylation by replacing a 5MeCyt with an unmethylated cytosine [9].

Most of our knowledge regarding DNA demethylation in autoimmune diseases came from the analysis of CD4+ T cells and B cells in patients with SLE [10], [11], [12]. Several mechanisms have been described to explain DNA demethylation in SLE patients. The first one, described by Gorelik et al., is related to a defective PKC delta (PKCδ)/ERK pathway observed both in idiopathic and drug-induced SLE patients [13]. Interestingly, the PKCδ−/− mice reproduce the SS disease with reduced salivary gland function, B cell infiltration and autoantibody production [14]. The second mechanism is related to the expression of miRNAs that down regulate DNMT1 [15], [16], and the third to the overexpression of DNA demethylating factors such as Gadd-45α [17], and MBD2/4 [18].

Because DNA demethylation is commonly observed in autoimmune diseases [19], and suspected to be associated with autoantibody production [20], we decided to characterize DNA methylation in SS. The results indicate that salivary gland epithelial cells (SGEC) are demethylated in SS and that this defect may be attributed in part to the presence of infiltrating B cells.

Section snippets

Patients and controls

Eight patients fulfilling the American–European consensus group criteria for primary SS that displayed salivary gland (SG) focus score of at least 3 were enrolled in the study [21]. Peripheral blood was collected by phlebotomy using lithium heparin tubes, and minor labial SGs were obtained by biopsy. SGs obtained before and after two infusions of anti-CD20 at 4 months (Rituximab, Roche) were available for two patients [22], [23]. Peripheral blood controls were obtained from 8 healthy subjects

DNA global demethylation characterizes salivary glands epithelial cells from SS patients

To determine whether global DNA methylation may be altered in SS, 5MeCyt content was evaluated salivary gland (SG) epithelial cells, in peripheral T cells, and in peripheral B cells obtained from 8 patients with primary SS. As reported in Fig. 1, global DNA methylation was reduced in minor SG biopsy sections and in long term cultured SG epithelial cells (SGEC) from SS patients in contrast with the control group (5MeCyt: 36.3 ± 3.2% in SS versus 43.1 ± 3.3% in controls, P = 0.01). Surprisingly,

Discussion

Our study reveals that DNA demethylation characterizes SG from SS patients and that this defect persists in long term SGEC culture. In this context, it is not surprising that mice treated long term with demethylating drugs such as procainamide or 5-azacytidine, in addition to developing an SLE-like disease, present clinical features of SS (reviewed in Ref. [5]). Yin et al., have recently reported a decrease in TNFSF7 promoter methylation status in SS CD4+ T cells [26]. Testing global DNA

Acknowledgments

Thanks are due to Dr. Wesley H. Brooks for editorial assistance and to Geneviève Michel and Simone Forest for their help with typing of the paper. We are also grateful to the “Association Française du Gougerot Sjögren et des Syndromes Secs” for their support. Yosra Thabet is funded by the Islamic development bank merit scholarship program.

References (46)

  • Y. Thabet et al.

    Altered patterns of epigenetic changes in systemic lupus erythematosus and auto-antibody production: is there a link?

    J Autoimmun

    (2012)
  • H. Yin et al.

    Hypomethylation and overexpression of CD70 (TNFSF7) in CD4+ T cells of patients with primary Sjogren's syndrome

    J Dermatol Sci

    (2010)
  • A. Saraux

    The point on the ongoing B-cell depleting trials currently in progress over the world in primary Sjogren's syndrome

    Autoimmun Rev

    (2010)
  • M.M. Varin et al.

    In Sjogren's syndrome, B lymphocytes induce epithelial cells of salivary glands into apoptosis through protein kinase C delta activation

    Autoimmun Rev

    (2012)
  • C. Selmi et al.

    Heritability versus the role of the environment in autoimmunity

    J Autoimmun

    (2012)
  • F.W. Miller et al.

    Epidemiology of environmental exposures and human autoimmune diseases: findings from a National Institute of Environmental Health Sciences Expert Panel Workshop

    J Autoimmun

    (2012)
  • O. Ngalamika et al.

    Epigenetics, autoimmunity and hematologic malignancies: a comprehensive review

    J Autoimmun

    (2012)
  • Q. Lu et al.

    Epigenetics in autoimmune disorders: highlights of the 10th Sjogren's syndrome symposium

    Autoimmun Rev

    (2010)
  • C.L. Dantec et al.

    Epigenetics and Sjogren's syndrome

    Curr Pharm Biotechnol

    (2012)
  • J. Sharif et al.

    The SRA protein Np95 mediates epigenetic inheritance by recruiting Dnmt1 to methylated DNA

    Nature

    (2007)
  • S. Garaud et al.

    IL-6 modulates CD5 expression in B cells from patients with lupus by regulating DNA methylation

    J Immunol

    (2009)
  • G. Gorelik et al.

    Impaired T cell protein kinase C delta activation decreases ERK pathway signaling in idiopathic and hydralazine-induced lupus

    J Immunol

    (2007)
  • G.P. Banninger et al.

    Loss of PKCdelta results in characteristics of Sjogren's syndrome including salivary gland dysfunction

    Oral Dis

    (2011)
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