Interleukin-21-mediated suppression of the Pax3-Id3 pathway exacerbates the development of Sjögren’s syndrome via follicular helper T cells
Introduction
Sjögren’s syndrome (SS) is a chronic systemic autoimmune disease characterized by infiltration of immune cells into the exocrine glands and inflammation, which ultimately results in diminished glandular secretory function. Destruction of lacrimal and salivary glands causes keratoconjunctivitis sicca (dry eyes) and xerostomia (oral dryness). SS is also frequently accompanied by extraglandular manifestations, including fatigue, as well as symptoms involving the skin, muscles, kidneys, joints, peripheral nervous system, and blood vessels. In addition, SS is associated with increased risk of the development of non-Hodgkin lymphomas that may significantly affect morbidity [1], [2].
The pathogenesis of SS is frequently related to infiltration of lymphocytes, mainly T and B cells, into the target organs. In the salivary and lacrimal glands, focal sialadenitis, consisting of aggregates of B and T cells, is a major site of autoantibody production [3], [4]. Hyperactivity of B cells, characterized by hypergammaglobulinemia and germinal center (GC) formation, results in the production of autoantibodies, such as anti-SSA/Ro and anti-SSB/La antibodies directed against intracellular ribonucleoprotein [5], [6]. Follicular helper T (Tfh) cells are required for T cell-dependent activation of B cells leading to affinity maturation, generation of high-affinity antibodies, and the formation and maintenance of the GC [7]. Tfh cells are involved in a number of autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, and SS [8], [9], [10]. The frequency of Tfh cells in peripheral blood is positively correlated with disease activity in SS patients [10], [11].
Inhibitor of DNA binding 3 (Id3) is a helix-loop-helix protein lacking a basic region, which is essential for exerting its effects as a transcriptional regulator through direct binding with DNA [12]. Deficiency of Id3 results in lymphocyte infiltration into the exocrine glands, decreased tear and saliva secretion, and increased autoantibody production in mice, which can be used as an animal model of SS [13]. Furthermore, Id3-deficient mice show a high frequency of effector memory cells and increased levels of chemokine receptor C-X-C motif receptor 5 (CXCR5) and transcription factor B cell lymphoma 6 (Bcl6) expression, which are necessary in Tfh cells [14]. Id3 is a direct transcriptional target for Pax7/Pax3 in quiescent satellite cells [15]. However, the transcriptional mechanism between Pax and Id3 underlying the development of Tfh cells has not yet been determined.
The present study was performed to investigate whether interleukin (IL)-21, a key cytokine involved in the promotion of Tfh cell differentiation, could modulate the Pax-Id3 molecular mechanism and whether activation of Pax-Id3 could regulate the severity of SS in NOD/ShiLtJ mice. Treatment with IL-21 could inhibit the expression of Pax3 and Id3 via signal transducer and activator of transcription 3 (STAT3) in splenic T cells in vitro. Administration of pCMV14-3xFlag PAX3 vector ameliorated the development of SS by suppressing the number of Tfh cells in NOD/ShiLtJ mice. Blockade of the IL-21 signal enhanced the number of Pax3+ and Id3+ cells in the salivary glands and the populations of Tfh cells and IL-17-producing T (Th17) cells were reduced in NOD/ShiLtJ mice. The levels of Pax3 and Id3 were reduced in the salivary glands of human SS patients compared with healthy controls.
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Animals
Seven-week-old NOD/ShiLtJ mice were purchased from the Jackson Laboratory (Bar Harbor, ME, USA). Animals were maintained under specific pathogen-free conditions at the Institute of Medical Science of the Catholic University of Korea and fed standard mouse chow and water ad libitum. All experimental procedures were examined and approved by the Animal Research Ethics Committee of the Catholic University of Korea; the procedure conformed to all National Institutes of Health of the USA guidelines
IL-21 suppresses Pax3 and Id3 expression in splenic CD4+ cells
Publicly available microarray data (GSE23117) and the Encyclopedia of DNA Elements (ENCODE) were analyzed to investigate the possible factors involved in binding to the promoter of Id3 among the transcription factors reduced with Id3 in the salivary glands of SS patients. The analysis indicated that the expression of Pax3, which can bind to the promoter of Id3, was reduced in SS salivary tissues (data not shown). Next, we investigated whether treatment with IL-21, the primary cytokine secreted
Discussion
The results presented here indicated that IL-21-mediated STAT3 activation is associated with expression of Pax3-Id3 in CD4+ cells. Upregulation of Pax3 ameliorated the development of SS by regulating the GC response between GC B cells, plasma cells, and Tfh cells in NOD/ShiLtJ mice. Inhibition of IL-21 increased the numbers of Pax3+ cells and Id3+ cells, while the numbers of Tfh cells and Th17 cells were decreased in the salivary glands of NOD/ShiLtJ mice.
In previous reports, Id3 is known to
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was supported by a grant of the Korean Health Technology R&D Project, Ministry of Health & Welfare Republic of Korea (HI13C0016) and by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (HI15C1062).
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Cited by (0)
- 1
Jin-Sil Park and Sung-Min Kim contributed equally to this work.
- 2
Sung-Hwan Park and Mi-La Cho contributed to this work.