SSc Basic Science: Fibrosis
Britta Maurer, MD
WHO Collaborating Center for Molecular Biology and Novel Therapeutic Strategies for
Rheumatic Diseases, Dpt. of Rheumatology, University Hospital Zurich, Switzerland
Given the large numbers of submitted and accepted abstracts, fibrosis as one key feature of SSc
pathogenesis was one main topic in SSc sessions and presentations of this year’s ACR meeting in
Boston. This report aims to highlight some selected novel aspects of key pathways and targets for
molecular therapy of fibrosis, epigenetics, animal models, and should therefore not be considered as a
Key pathways and targets for molecular therapy
Since imatinib (Gleevec) has been proven to be successful in the prevention of accumulated
extracellular matrix proteins in the SSc animal model of bleomycin induced skin fibrosis, there is
raising hope that targeting key molecules in fibrogenesis might be more efficient than the use of anti-
inflammatory and/or immunosuppressive drugs. The anti-fibrotic potential of inhibitors of different
signalling pathways (PPARγ, c-kit, imatinib, src kinases, nilotinib and dasatinib, TSA) has now been
investigated by several groups in vitro and in vivo with promising results (presentation no 2144, 2145,
2146, 2147, 43, 44). The introduction of PPARγ as an endogenous anti-fibrotic molecule suggests an
anti-fibrotic role of adipose tissue, since its repression in SSc elegantly links skin fibrosis and
subcutaneous adipose atrophy.
A presentation of outstanding interest was part of the ACR plenary session “Discovery 2007: Insights
into Autoimmunity”. The in vitro and in vivo studies with caveolin-1 knock out mice of Francesco Del
Galdo and his co-workers proved caveolin-1 downregulation in SSc to play a key role in the
development of fibrosis of the skin as well as the internal organs. The restoration of caveolin-1
bioavailability in SSc fibroblasts by cell permeable recombinant caveolin-1 peptides reduced the
collagen production as well as the TGFbeta induced up-regulation of profibrotic genes without
cytotoxic effects. If these results could be confirmed in vivo by the application of recombinant
caveolin-1 peptides to animal models of SSc, recombinant caveolin-1 might represent another
promising anti-fibrotic drug (presentation no 2058). In summary, these findings might represent the
experimental background for the initiation of clinical trials with anti-fibrotic agents.
There is some evidence that the onset of SSc is triggered by exogenous stimuli on the basis of a
genetic susceptibility. Therefore, the epigenetic regulation of profibrotic genes in SSc pathogenesis
represents an interesting but yet not well investigated aspect of SSc research. Two abstracts of a group
of the University of Toledo showed DNA methylation to be involved in epigenetic gene silencing
(presentation no 60, 2148). A previous study of this group gives evidence that epigenetic repression of
FLI1 results in uncontrolled expression of extracellular matrix genes and accumulation of extracellular
matrix proteins. By high throughput DNA methylation profiling of SSc fibroblasts and microvascular
endothelial cells (MVEC), the authors identified thousands of hypermethylated loci in both cell types,
of which most of the examined genes were underexpressed. Epigenetic repression of FLI1 in SSc
fibroblasts and of NOS3 in SSc MVEC was the most prominent feature. The knockdown of FLI1 in
normal fibroblasts and of NOS3 in normal MVEC by stealth siRNA resulted in SSc characteristic
phenotypes of both cell types (presentation no 2148). The still ongoing analysis of this study’s results
will probably reveal interesting new insights of the implication of epigenetic mechanisms in SSc
Another presentation gives evidence that not only methylation but also acetylation as epigenetic
phenomenon might play a role in SSc, since treatment with the HDAC inhibitor TSA, which effects
are mainly mediated by the inhibition of HDAC7, results in decrease of collagen synthesis in SSc in
vitro and in vivo experiments (presentation no 44).
Animal models like the tight skin mouse, the bleomycin induced skin fibrosis model or the TGFbeta
receptor II knock out mouse are well established in vivo models for the examination of SSc
pathogenesis. Among others, this year 2 mouse models addressing novel aspects were introduced: one
investigating the role of type I interferons (presentation no 46), a second one examining adenosine
deaminase (ADA) deficiency for the development of fibrosis (presentations 42, 41).
Out of the large number of interesting abstracts dealing with fibrogenesis in SSc, only few
presentations with partially yet not well defined but promising novel pathogenic molecules will be
One presentation suggests COMP as a promising biomarker for skin involvement in SSc since COMP
levels in affected skin and in serum were found positively correlated with the mRSS. Changes of the
extent of skin involvement were not only reflected by the mRSS but also by the modification of serum
COMP levels (presentation no 66). The functional relevance of these findings as well as the
pathogenic role of COMP in SSc pathogenesis will have to be addressed in further studies.
Another presentation investigated the interaction of T cells and fibroblasts with regard to early stages
of SSc pathogenesis. Previous studies of the same authors have shown that infiltrating T cells in SSc
tissue express AIF-1 (anti-inflammatory factor 1) and that soluble factors derived from these cells
induced a profibrotic phenotype of normal fibroblasts. Based on these results, the current investigation
revealed MIF (macrophage inhibitory factor) to be among the most abundant proteins produced by
AIF-1 overexpressing T cells. Further experiments showed that treatment of normal fibroblasts with
MIF resulted in the upregulation of collagen gene expression. Taken together, the presentation
suggests that AIF-1 expressing T cells might induce the profibrotic phenotype of SSc fibroblast and
might thus play a triggering role in early SSc development (presentation no 52). However, the
relevance of MIF induced upregulation of collagen gene expression in normal fibroblasts should
additionally be confirmed on the protein level. Furthermore, it would be interesting to examine if the
promising effects of MIF neutralizing antibodies in the suppression of collagen gene expression in
vitro could be confirmed by in vivo experiments.
Another presented study investigated the role of icIL-1Ra (intracellular interleukin 1 receptor
antagonist) with respect to the localized inhibition of MMP-1 expression in fibrotic vs. non-fibrotic
skin of SSc patients. The authors found the expression of MMP-1 decreased in SSc fibroblasts derived
from affected vs. non-affected skin. Furthermore, there was a negative correlation of the expression of
MMP-1 and icIL-1Ra (presentation no 68). However, based on these interesting findings, the
pathogenic role of icIL-1Ra in MMP-1 inhibition warrants further elucidation. Functional experiments
as well as in vivo studies should be performed to confirm the functional relevance of the current
SSc : Basic Science: Fibrosis
Key pathways and targets for molecular therapy
Abstract no. 2144:
Gosh AK et al: Novel function of PPAR_: endogenous anti -fibrotic that ameliorates murine
scleroderma and may be defective in systemic scle rosis (SSc).
Abstract no. 2145:
Del Papa N et al.: Clinical and molecular evidence for c -kit receptor as a therapeutic target in
systemic sclerosis (SSc).
Abstract no. 2146:
Shiwen X et al: Imatinib alleviates the pro -fibrotic phenotype of scleroderma fibr oblasts.
Abstract no. 43:
Akhmetshina A et al: Nilotinib and dasatinib, two novel and more potent inhibitors of c -abl
and PDGF signalling, for the treatment of experimental dermal fibrosis.
Abstr act no. 2058:
Del Gado F et al: Down -regulation of caveolin -1 (cav -1) in systemic sclerosis plays a key role
in the fibrotic process and can be reversed by cell permeable recombinant cav - 1 peptides.
Abstract no. 60:
Wang Y et al: DNA methylation induction by a circulating activity in SSc sera: possible role
for oxidation and auto -antibodies related mechanisms.
Abstract no. 2148:
Wang Y et al: Epigenetic regulation in scleroderma: high -throughput DNA methylation
profiling of SSc fibroblasts and microvascular endothelial cells and the central role for Nos3
and Fli1 epigenetic repression in the emergence of SSc cellular phenotype.
Abstract no. 44:
Hemmatazad H et al.: The anti -fibrotic effects of trichostatin A are mediated through the
down-regulation of histone deacetylase 7.
Abstract no. 46:
Delaney TA et al: Role of type I interferon in a murine model of scleroderma.
Abstract no. 42:
Fernandez P et al: Pharmacological blockade of adenosine A2A receptors reduces IL - 13
production and fibrotic features in a novel model of skin fibrosis.
Abstrac t no. 41:
Liu H et al: Adenosine A2A receptor occupancy regulates the expression of multiple genes
involved in fibrosis.
Abstract no. 66:
Hesselstrand R et al: Serum COMP in systemic sclerosis – a promising new biomarker for
Abstract no. 52:
Del Gado F et al: Macrophage migration inhibitory factor (MIF) production by T cells is
strongly up -regulated by allograft inflammatory factor -1 (AIF -1) expression and contributes to
the pro -fibrotic effects of AIF -1.
Abstract no. 68:
Hasty KA et al: Collagenase expression is inhibited in fibroblasts from fibrotic, but not non -
fibrotic scleroderma skin: The role of intracellular interleukin -1 receptor antagonist.