Objective. Imatinib is a small-molecule tyrosine kinase inhibitor capable of selective, dual inhibition of the transforming growth factor ␤ and platelet-derived growth factor (PDGF) pathways. Imatinib has previously been shown to prevent the development of inflammation-driven experimental fibrosis when treatment was initiated before administration of the profibrotic stimulus. The aim of this study was to confirm the efficacy of imatinib in a murine model of systemic sclerosis (SSc) that is less driven by inflammation and to investigate whether imatinib is also effective for the treatment of established fibrosis.Methods. The tight skin 1 (TSK-1) mouse model of SSc was used to evaluate the antifibrotic effects of imatinib in a genetic model of the later stages of SSc. In addition, the efficacy of imatinib for the treatment of preestablished fibrosis was analyzed in a modified model of bleomycin-induced dermal fibrosis in which the application of bleomycin was prolonged and the onset of treatment was late.Results. Treatment with imatinib reduced dermal and hypodermal thickening in TSK-1 mice and prevented the differentiation of resting fibroblasts into myofibroblasts. In the model of preestablished dermal fibrosis, imatinib not only stopped further progression of fibrosis but also induced regression of preexisting dermal fibrosis, with a reduction in dermal thickness below pretreatment levels.Conclusion. These results indicate that combined inhibition of the tyrosine kinase c-Abl and PDGF receptor might be effective in the later, less inflammatory stages of SSc and for the treatment of established fibrosis. Thus, imatinib might be an interesting candidate for clinical trials in patients with longstanding disease and preexisting tissue fibrosis.

Objective. The cannabinoid receptor CB2 is predominantly expressed in non-neuronal tissue and exerts potent immunomodulatory effects. This study was undertaken to evaluate the role of CB2 in the pathogenesis of dermal fibrosis.Methods. Mice deficient in CB2 (CB2 ؊/؊ mice) and their wild-type littermates (CB2 ؉/؉ mice) were injected with bleomycin to induce experimental fibrosis. Mice were treated with selective agonists and antagonists of CB2. Lesional skin was evaluated for dermal thickness and numbers of infiltrating leukocytes. Bone marrow transplantation experiments were performed.Results. CB2 ؊/؊ mice were more sensitive to bleomycin-induced dermal fibrosis than were CB2 ؉/؉ mice, and showed increased dermal thickness. Leukocyte counts were significantly higher in the lesional skin of CB2 ؉/؉ mice. Increased dermal fibrosis was also observed upon treatment with the CB2 antagonist AM-630. In contrast, the selective CB2 agonist JWH-133 reduced leukocyte infiltration and dermal thickening. The phenotype of CB2 ؊/؊ mice was mimicked by transplantation of CB2

Background— Microvascular damage is one of the first pathological changes in systemic sclerosis. In this study, we investigated the role of Fos-related antigen-2 (Fra-2), a transcription factor of the activator protein-1 family, in the peripheral vasculopathy of systemic sclerosis and examined the underlying mechanisms. Methods and Results— Expression of Fra-2 protein was significantly increased in skin biopsies of systemic sclerosis patients compared with healthy controls, especially in endothelial and vascular smooth muscle cells. Fra-2 transgenic mice developed a severe loss of small blood vessels in the skin that was paralleled by progressive skin fibrosis at 12 weeks of age. The reduction in capillary density was preceded by a significant increase in apoptosis in endothelial cells at week 9 as detected by immunohistochemistry. Similarly, suppression of Fra-2 by small interfering RNA prevented human microvascular endothelial cells from staurosporine-induced apoptosis and improved both the number of tubes and the cumulative tube lengths in the tube formation assay. In addition, cell migration in the scratch assay and vascular endothelial growth factor–dependent chemotaxis in a modified Boyden chamber assay were increased after transfection of human microvascular endothelial cells with Fra-2 small interfering RNA, whereas proliferation was not affected. Conclusions— Fra-2 is present in human systemic sclerosis and may contribute to the development of microvasculopathy by inducing endothelial cell apoptosis and by reducing endothelial cell migration and chemotaxis. Fra-2 transgenic mice are a promising preclinical model to study the mechanisms and therapeutic approaches of the peripheral vasculopathy in systemic sclerosis.

Objective. Src kinases are nonreceptor tyrosine kinases, which have been implicated in cytoskeletal organization and cell mobility. This study was undertaken to evaluate the potential of Src kinases as novel targets of antifibrotic therapies.Methods. Fibroblast cultures were obtained from 10 patients with systemic sclerosis (SSc) and 5 healthy subjects. Src signaling was inhibited using smallmolecule inhibitors and overexpression of a dominantnegative mutant of Src and of the endogenous inhibitor Csk. The expression of extracellular matrix proteins was analyzed by real-time polymerase chain reaction and by SirCol collagen assay. Toxic effects were excluded by MTT assay and staining for annexin V and propidium iodide. The mouse model of bleomycin-induced dermal fibrosis was used to assess the role of Src kinases in dermal fibrosis in vivo.Results. Stimulation with transforming growth factor ␤ and platelet-derived growth factor activated Src signaling in dermal fibroblasts from patients with SSc and healthy donors. Incubation with the Src kinase inhibitors or overexpressed mutant Src or Csk reduced the synthesis of messenger RNA for COL1A1, COL1A2, and fibronectin 1. A dose-dependent reduction in collagen release was also observed at the protein level. No inhibitory effects on proliferation and no increase in the number of apoptotic or necrotic fibroblasts were observed. Consistent with the in vitro data, inhibition of Src kinases prevented experimental dermal fibrosis. Dermal thickness, the amount of collagen protein, and the number of myofibroblasts were reduced in a dosedependent manner.Conclusion. These findings indicate that Src kinases play important roles in the activation of fibroblasts and in the development of experimental fibrosis. Thus, Src kinases might be interesting targets for novel antifibrotic therapies in SSc.

Systemic sclerosis (SSc) is a systemic autoimmune disease that is characterized by microangiopathy with progressive loss of capillaries and tissue fibrosis. Imatinib exerts potent anti-fibrotic effects and is currently evaluated in clinical trials. The aim of the present study was to exclude that the anti-fibrotic effects of imatinib are complicated by inhibitory effects on endothelial cell functions, which might augment vascular disease in SSc. Endothelial cells and mice were treated with pharmacologically relevant concentrations of imatinib. The expression of markers of vascular activation was assessed with real-time PCR. Proliferation was analysed with the cell counting experiments and the MTT assay. Apoptosis was quantified with caspase 3 assays, annexin V in vitro and with TUNEL staining in vivo. Migration was studied with scratch and transwell assays. Tube forming was investigated with the matrigel assay. Imatinib did not alter the expression of markers of vascular activation. Imatinib did not increase the percentage of annexin V positive cells or the activity of caspase 3. No reduction in proliferation or metabolic activity of endothelial cells was observed. Imatinib did not affect migration of endothelial cells and did not reduce the formation of capillary tubes. Consistent with the in vitro data, no difference in the number of apoptotic endothelial cells was observed in vivo in mice treated with imatinib. Imatinib does not inhibit activation, viability, proliferation, migration or tube forming of endothelial cells in vitro and in vivo. Thus, treatment with imatinib might not augment further endothelial cell damage in SSc.