Session Information
Title: Systemic Sclerosis, Fibrosing Syndromes and Raynaud's - Pathogenesis, Animal Models and Genetics
Session Type: Abstract Submissions (ACR)
Background/Purpose
Systemic sclerosis (SSc) is a multisystem inflammatory and vascular disease resulting in fibrosis of the skin and certain internal organs. Although the pathogenesis of SSc still remains unknown, we have recently demonstrated that Fli1 deficiency at least partially due to epigenetic suppression contributes to the development of fibrosis and vasculopathy characteristically seen in this disease. A critical complication associated with SSc vasculopathy is refractory and recurrent skin ulcers which largely affect morbidity of SSc patients. To elucidate a potential mechanism rendering skin ulcers refractory to the treatments in SSc, we employed endothelial cell-specific Fli1 knockout (Fli1 ECKO) mice and carried out a wound healing experiment.
Methods
Fli1 ECKO mice were generated by crossing Fli1flox/flox mice with Tie2-Cre transgenic mice under a C57B/6 background. An 8 mm full-thickness skin wound was generated on the back of wild type (WT) and Fli1 ECKO mice with a punch biopsy. Vascular structure was visualized by FITC-dextran injection. The expression levels of target molecules were determined by immunohistochemistry in vivo and immunoblotting and quantitative reverse transcription-PCR in vitro using murine dermal microvascular endothelial cells (MDMECs). Promoter occupancy was evaluated by chromatin immunoprecipitation in MDMECs
Results
Wound healing was markedly delayed in Fli1 ECKO mice compared with WT mice. When vascular structure around scars was visualized with FITC-dextran injection, newly formed blood vessels were oriented toward the central area of scars in WT mice, while Fli1 ECKO mice lacked blood vessels around the central area of scars, suggesting that angiogenesis is impaired in Fli1 ECKO mice. At day 7 after wounding, many newly formed blood vessels filled with erythrocytes were present in granulation tissue in WT mice, while there were many dilated vessels with a few or no erythrocytes and a small number of vessels filled with erythrocytes in Fli1 ECKO mice. Since day 7 is a time point when newly formed blood vessels connect with pre-existing ones, it suggested that anastomosis may be impaired in Fli1 ECKO mice. In line with this idea, mRNA levels of the Notch1 and Dll4 genes, which code key molecules regulating anastomosis, were markedly decreased in ECs derived from Fli1 ECKO mice compared with those from WT mice. Furthermore, Fli1 occupied the promoter region of these genes in MDMECs.
Conclusion
Fli1 deficiency decelerates wound healing by inhibiting anastomosis of newly formed vessels with pre-existing ones and a similar process may contribute to the delayed wound healing associated with SSc.
Disclosure:
Y. Asano,
None;
M. Trojanowska,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/endothelial-fli1-deficiency-delays-wound-healing-due-to-impaired-anastomosis-of-newly-formed-vessels-a-possible-mechanism-of-refractory-skin-ulcers-in-systemic-sclerosis/