Toll-like receptor 3 upregulation by type I interferon in healthy and scleroderma dermal fibroblasts
Sandeep K Agarwal
0
Minghua Wu
0
Christopher K Livingston
1
Donald H Parks
1
Maureen D Mayes
0
Frank C Arnett
0
Filemon K Tan
0
0
Division of Rheumatology and Clinical Immunogenetics, Department of Internal Medicine, The University of Texas Health Science Center at Houston
,
6431 Fannin Avenue, Houston, TX 77030
,
USA
1
Division of Plastic and Reconstructive Surgery, Department of Surgery, The University of Texas Health Science Center at Houston
,
6431 Fannin Avenue, Houston, TX 77030
,
USA
Introduction: Increased levels of genes in the type I interferon (IFN) pathway have been observed in patients with systemic sclerosis (SSc), or scleroderma. How type I IFN regulates the dermal fibroblast and its participation in the development of dermal fibrosis is not known. We hypothesized that one mechanism by which type I IFN may contribute to dermal fibrosis is through upregulation of specific Toll-like receptors (TLRs) on dermal fibroblasts. Therefore, we investigated the regulation of TLR expression on dermal fibroblasts by IFN. Methods: The expression of TLRs was assessed in cultured dermal fibroblasts from control and SSc patients stimulated with IFNa2. The ability of IFNa2 to regulate TLR-induced interleukin (IL)-6 and CC chemokine ligand 2 production was also assessed. Immunohistochemical analyses were performed to determine whether TLR3 was expressed in skin biopsies in the bleomycin-induced skin fibrosis model and in patients with SSc. Results: IFNa2 increased TLR3 expression on human dermal fibroblasts, which resulted in enhanced TLR3-induced IL-6 production. SSc fibroblasts have an augmented TLR3 response to IFNa2 relative to control fibroblasts. Pretreatment of fibroblasts with transforming growth factor (TGF)-b increased TLR3 induction by IFNa2, but coincubation of TGF-b did not alter TLR3 induction by IFN. Furthermore, IFNa2 inhibits but does not completely block the induction of connective tissue growth factor and collagen expression by TGF-bin fibroblasts. TLR3 expression was observed in dermal fibroblasts and inflammatory cells from skin biopsies from patients with SSc as well as in the bleomycin-induced skin fibrosis model. Conclusions: Type I IFNs can increase the inflammatory potential of dermal fibroblasts through the upregulation of TLR3.
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Introduction
Systemic sclerosis (SSc), or scleroderma, is a multisystem
autoimmune disease clinically characterized by progressive
fibrosis of the skin and internal organs. Pathologically, SSc
exhibits three cardinal features: inflammation and
autoimmunity, vasculopathy and excessive extracellular matrix
(ECM) deposition [1]. The ECM consists of collagens,
proteoglycans, fibrillins and other matrix molecules [2].
Located within this matrix are fibroblasts and
myofibroblasts, key effectors of the fibrotic process. Resident and
infiltrating cells in the dermis secrete soluble mediators,
such as transforming growth factor b (TGF-b), that
activate fibroblasts and induce differentiation into
myofibroblasts [3,4]. The myofibroblasts subsequently produce
large amounts of ECM, leading to fibrosis. In addition to
their role in ECM deposition, dermal fibroblasts and
myofibroblasts are capable of secreting inflammatory cytokines
and chemokines, such as interleukin (IL)-6 and CC
chemokine ligand 2 (CCL-2), important inflammatory
mediators in SSc pathogenesis [5-8]. Thus, fibroblasts also may
contribute to the development of dermal fibrosis through
the production of these inflammatory mediators.
Current paradigms point toward systemic immune
dysregulation as a central process that ultimately may
lead to fibroblast activation. Biopsies of early SSc skin
demonstrate perivascular infiltrates of mononuclear
inflammatory cells, which produce cytokines and
chemokines that recruit inflammatory cells and promote
ECM deposition [9]. More recent studies in patients
with SSc have identified dysregulation of type I
interferon (IFN) pathways similar to those seen in patients
with systemic lupus erythematosus (SLE) [10-12]. Gene
expression profiling of peripheral blood has
demonstrated the presence of a type I IFN signature in patients
with SSc [12]. These findings have been confirmed in
both circulating CD14+ monocytes and CD4+ T-cells, as
well as in skin biopsies from patients with SSc compared
with healthy controls [13-15]. Together these data
demonstrate the presence of a type I IFN signature in
circulating blood cells and a major target organ (skin) in
patients with SSc.
Type I IFNs are potent regulators of the immune
system, where they modulate the differentiation, survival,
proliferation and cytokine production of T-cells, B-cells
and dendritic cells. Among the critical
immunoregulatory functions of IFN is its ability to stimulate the
expression of Toll-like receptors (TLRs) on dendritic
cells. TLRs are a family of germ line-encoded proteins
that serve as pattern recognition receptors capable of
recognizing highly conserved motifs present in
infectious microorganisms cal (...truncated)