Fibrosis in systemic sclerosis: emerging concepts and implications for targeted therapy.
Systemic sclerosis (SSc) is a complex and incompletely understood disease associated with fibrosis in multiple organs. Recent findings identify transforming growth factor-ß (TGF-ß), Wnt ligands, toll-like receptor-mediated signaling, hypoxia, type I interferon, type 2 immune responses and mechanical stress as extracellular cues that modulate fibroblast function and differentiation, and as potential targets for therapy. Moreover, fibrillin-1 has a major role in storing and regulating the bioavailability of TGF-ß and other cytokines, and fibrillin-1 mutations are implicated in a congenital form of scleroderma called stiff skin syndrome. Fibrosis is due not only to the activation of tissue-resident fibroblasts and their transdifferentiation into myofibroblasts, but also the differentiation of bone marrow-derived fibrocytes, and transition of endothelial and epithelial cells, pericytes and adipocytes into activated mesenchymal cells. These responses are modulated by signaling mediators and microRNAs that amplify or inhibit TGF-ß and Wnt signaling. Gain-of-function and loss-of-function abnormalities of these mediators may account for the characteristic activated phenotype of SSc fibroblasts. The nuclear orphan receptor PPAR-γ plays a particularly important role in limiting the duration and intensity of fibroblast activation and differentiation, and impaired PPAR-γ expression or function in SSc may underlie the uncontrolled progression of fibrosis. Identifying the perturbations in signaling pathways, mediators and differentiation programs that are responsible for SSc tissue damage allows their selective targeting. This in turn opens the door for therapies utilizing novel compounds, or drug repurposing by innovative uses of already-approved drugs. In view of the heterogeneous clinical presentation and unpredictable course of SSc, as well as its complex pathogenesis, only robust clinical trials incorporating the judicious application of biomarkers will be able to clarify the clinical utility of these innovative approaches.
Wei
Jun
J
Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, United States.
Bhattacharyya
Swati
S
Tourtellotte
Warren G
WG
Varga
John
J
D017667:Adipocytes / Q000378:metabolism / Q000473:pathology; D000818:Animals; D015415:Biomarkers / Q000032:analysis; D054338:Cell Transdifferentiation; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D000071838:Fibrillin-1; D000071837:Fibrillins; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D005355:Fibrosis / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D006801:Humans; D000860:Hypoxia / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D058990:Molecular Targeted Therapy / Q000379:methods; D047495:PPAR gamma / Q000378:metabolism; D020286:Pericytes / Q000378:metabolism / Q000473:pathology; D012595:Scleroderma, Systemic / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism; D054392:Adipokines
D015415:Biomarkers; D000071838:Fibrillin-1; D000071837:Fibrillins; D008840:Microfilament Proteins; D047495:PPAR gamma; D051193:Toll-Like Receptors; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D051176:beta Catenin; C000605722:FBN1 protein, human; D054392:Adipokines; C000605724:Fbn1 protein, mouse