Novel Treatment Approaches to Fibrosis in Scleroderma

Purinergic signaling in systemic sclerosis

Systemic sclerosis (SSc) is a chronic autoimmune rheumatic disease that involves numerous organs and presents major management challenges. The histopathologic hallmarks of SSc include vasculopathy, fibrosis and autoimmune phenomena involving both innate and adaptive immune systems. Purinergic signalling is a pathway that may be implicated in the pathophysiology of several of these disease manifestations. Extracellular purines are potent signalling mediators, which have been shown to be dysregulated in SSc. As examples, purines can exacerbate vasculopathy and provoke platelet dysfunction; as well as contributing to immune dysregulation. Elements of purinergic signalling further promote organ and tissue fibrosis in several disease models. Here, we provide an overview of extracellular purine metabolism in purinergic signalling and link disorders of these to the molecular pathology of SSc. We also discuss targeting the purinergic signalling and explore the translational applications for new therapeutic options in SSc.

Mesenchymal Stem Cells (MSCs) Attenuate Cutaneous Sclerodermatous Graft-Versus-Host Disease (Scl-GVHD) through Inhibition of Immune Cell Infiltration in a Mouse Model

Human chronic graft-versus-host disease (GVHD) shares clinical characteristics with a murine sclerodermatous GVHD model that is characterized by skin thickening and lung fibrosis. A B10.D2 → BALB/c transplant model of sclerodermatous GVHD was used to address the therapeutic effect of mesenchymal stem cells (MSCs) on the development of chronic GVHD. The clinical and pathological severity of cutaneous sclerodermatous GVHD was significantly attenuated in MSC-treated recipients relative to sclerodermatous GVHD control subjects. After MSC treatment, skin collagen production was significantly reduced, with consistent down-regulation of Tgfb expression. Effects of MSCs on molecular markers implicated in persistent transforming growth factor-β signaling and fibrosis, such as PTEN, phosphorylated Smad-2/3, and matrix metalloproteinase-1, were observed in skin tissue. MSCs neither migrate to the skin nor affect the in vivo expansion of immune effector cells, but they inhibited the infiltration of immune effector cells into skin via down-regulation of CCR4 and CCR8 expression on CD4⁺ T cells and CCR1 on CD11b⁺ monocyte/macrophages. MSCs diminished expression of chemokines such as CCL1, CCL3, CCL8, CCL17, and CCL22 in skin. MSCs were also dependent on stimulated splenocytes to suppress fibroblast proliferation. Our findings indicate that MSCs attenuate the cutaneous sclerodermatous GVHD by selectively blocking immune cell migration and down-regulating chemokines and chemokine receptors.

Chemokine receptors CCR2 and CX3CR1 regulate skin fibrosis in the mouse model of cytokine-induced systemic sclerosis

BACKGROUND

Skin fibrotic disorders such as systemic sclerosis (SSc) are characterized by an excessive accumulation of extracellular matrix (ECM), and develop under the influence of certain cytokines. We previously established a mouse model of skin fibrosis induced by exogenous application of cytokines. We have revealed that both the number of macrophages and the levels of macrophage chemoattractant protein-1 (MCP-1) mRNA positively correlate with the extent of skin fibrosis. Macrophages can be divided into two subsets, the first expressing CCR2, and the second expressing CX3CR1.

OBJECTIVE

To elucidate the role of skin infiltrating macrophages based on CCR2 and CX3CR1 in this cytokine-induced murine fibrosis model.

METHODS

We examined the amounts of collagen deposited in granulation tissues, the numbers of macrophages and the levels of several mRNA in wild type (WT) mice, CCR2(-/-) mice, and CX3CR1(-/-) mice during injections of transforming growth factor-β (TGF-β) followed by injections of connective tissue growth factor (CTGF).

RESULTS

TGF-β injection increased the expressions of MCP-1, fractalkine, CCR2 and CX3CR1 mRNA in WT mice. The overproduction of collagen induced by TGF-β was significantly reduced by CCR2 deficiency, while collagen contents induced by CTGF were restored to wild-type levels. In contrast, overproduction of collagen in CX3CR1-deficient mice decreased nearly 50% by both TGF-β and CTGF stimulations.

CONCLUSION

The involvement of CCR2/MCP-1 interaction (CCR2-dependent loop) was during the TGF-β phase. In contrast, the fractalkine/CX3CR1 interaction contributes to the initiation of fibrosis by TGF-β and its maintenance by CTGF. Collectively, two subsets of macrophages both cooperatively and independently play important roles in the development of fibrosis.

Understanding fibrosis in systemic sclerosis: shifting paradigms, emerging opportunities

Fibrosis in multiple organs is a prominent pathological finding and distinguishing hallmark of systemic sclerosis (SSc). Findings during the past 5 years have contributed to a more complete understanding of the complex cellular and molecular underpinning of fibrosis in SSc. Fibroblasts, the principal effector cells, are activated in the profibrotic cellular milieu by cytokines and growth factors, developmental pathways, endothelin 1 and thrombin. Innate immune signaling via Toll-like receptors, matrix-generated biomechanical stress signaling via integrins, hypoxia and oxidative stress seem to be implicated in perpetuating the process. Beyond chronic fibroblast activation, fibrosis represents a failure to terminate tissue repair, coupled with an expanded population of mesenchymal cells originating from bone marrow and transdifferentiation of epithelial cells, endothelial cells and pericytes. In addition, studies have identified intrinsic alterations in SSc fibroblasts resulting from epigenetic changes, as well as altered microRNA expression that might underlie the cell-autonomous, persistent activation phenotype of these cells. Precise characterization of the deregulated extracellular and intracellular signaling pathways, mediators and cellular differentiation programs that contribute to fibrosis in SSc will facilitate the development of selective, targeted therapeutic strategies. Effective antifibrotic therapy will ultimately involve novel compounds and repurposing of drugs that are already approved for other indications.

[Scleroderma]

Scleroderma (synonyms: systemic sclerosis, systemic scleroderma) is a systemic disease which affects the skin as well as internal organs such as the lungs, gastrointestinal tract, kidneys, and the heart. Pathogenetically a distinction should be made between uncontrolled formation of extracellular matrix proteins (fibrosis) and vasculopathy. In addition to organ fibrosis, this leads to a clinical picture of vascular manifestations. These include fingertip ulcers, pulmonary arterial hypertension, and acute renal crisis. Localized forms of scleroderma, such as morphea, which do not involve organ complications, should be differentiated from systemic sclerosis. Due to its clinical heterogeneity and high rate of morbidity and mortality, systemic sclerosis poses an enormous diagnostic and therapeutic challenge in everyday clinical practice. This review article summarizes the current status of classification and epidemiology, pathogenesis, and the most important clinical manifestations such as interstitial fibrosis, pulmonary arterial hypertension, acute renal crisis, and peripheral vasculopathy and provides an overview of current and future treatment options.

Cutaneous Connective Tissue Diseases: Epidemiology, Diagnosis, and Treatment

Connective tissue diseases (CTDs) are a group of clinical disorders that have an underlying autoimmune pathogenesis. These include a diverse set of diseases such as relapsing polychondritis, rheumatoid arthritis, and eosinophilic fasciitis, along with more common entities like Sjogren's syndrome, dermatomyositis, scleroderma, and lupus erythematosus. The latter three will be the focus of this review, as they constitute the most significant and common CTD with cutaneous manifestations. The cutaneous signs often represent the preliminary stages of disease and the presenting clinical symptoms. Therefore, comprehensive knowledge of CTD manifestations is essential for accurate diagnosis, better assessment of prognosis, and effective management. Although the precise etiologies of CTDs remain obscure, recent advances have allowed for further understanding of their pathogenesis and improved disease classifications. In addition, there have been developments in therapeutic options for CTDs. This review provides an overview of the epidemiology, clinical presentations, and current treatment options of cutaneous lupus erythematous, dermatomyositis and scleroderma.