Background/Purpose:

Systemic sclerosis (SSc) is a multisystem autoimmune disease characterized by initial vascular injuries and resultant fibrosis of skin and certain internal organs. Although the pathogenesis of SSc still remains unknown, our latest data have demonstrated that epigenetic suppression of transcription factor Fli1 is deeply involved in the constitutive activation of fibroblasts and endothelial cells in this disease. In murine models, Fli1 haploinsufficiency results in increased expression of type I collagen at mRNA and protein levels in the back skin, but fibrosis does not occur at least partly because the expression of CTGF, which plays a critical role to establish and maintain tissue fibrosis, remains unchanged. Since our pilot studies have revealed that transcription factor KLF5 is a potent repressor of the CTGF gene and its expression is epigenetically suppressed in SSc dermal fibroblasts, we generated mice with heterozygous deletions of Fli1 and KLF5 and evaluated whether they recapitulated the clinical and histopathological features of SSc.

Methods:

mRNA and protein levels of target molecules were determined by quantitative real-time PCR and by immunoblotting, immunohistochemistry and ELISA, respectively. Vascular structure in the back skin was visualized by FITC-dextran intravenously injected. Ultrastructue of collagen fibers was evaluated by electron microscopy. Auto-antibodies were detected by indirect immunofluorescence with Hep2 cells.

Results:

Klf5^+/-;Fli1^+/-mice (C57BL/6) were fertile, born in Mendelian ratio, and did not display any apparent early developmental abnormalities. Notably, these mice spontaneously recapitulated cardinal features of SSc, including peripheral vasculopathy, fibrosis of skin and lung, autoimmunity and inflammation. Dermal vascular abnormalities, including stenosis of arterioles with a moth-eaten pattern and bushy capillary tips, occurred around the age of 1 month prior to the development of dermal fibrosis with ultrastructural changes of collagen fibrils similar to those seen in SSc. Interstitial lung disease with B cell lymphoid aggregates and vascular changes characteristic of pulmonary arterial hypertension and pulmonary veno-occlusive disease appeared around the age of 2-4 months and progressed along with disease duration. Serum IL-6 levels and IL-6 mRNA levels in the skin and lung were elevated around the age of 2 months and splenic B cells secreted a greater amount of IL-6 in response to toll-like receptor 4 stimulation with LPS and/or T cell help in the form of an anti-CD40 antibody. Importantly, anti-nuclear antibodies were also detected.

Conclusion:

These studies underscore the concept of epigenetic reprogramming underlying pathogenic changes in SSc and implicate the Fli1 and KLF5 pathways as central mediators of this disease.

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« Back to 2013 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/downregulation-of-klf5-and-fli1-cooperatively-contribute-to-distinct-manifestations-of-systemic-sclerosis-in-vitro-and-in-vivo/