Background Systemic sclerosis (SSc) is an autoimmune connective tissue disease characterized by vascular alterations, perivascular mononuclear cell infiltration, and fibrosis of skin and viscera. Microvascular injury, disturbed vascular repair and insufficient angiogenesis result in an overall reduced capillary density, and clinical manifestations such as fingertip ulcers. Expression of vascular endothelial cell growth factor (VEGF), the most potent angiogenic factor, and its receptors VEGFR-1 and VEGFR-2 is highly upregulated in SSc skin, but seems to be uncontrolled and chronic. However, a very high VEGF expression is associated with the lack of fingertip ulcers. Therefore, local administration of VEGF in a form that allows controlled release might be a promising therapeutic approach.
Objectives Based on a proof of concept study in UCD-206 chickens, an animal model showing all hallmarks of the human disease, where we showed that cell demanded release of locally applied exogenous matrix-bound VEGF121-fibrin leads to the formation of stable blood vessels, and clinical improvement of ischemic lesions, we analysed the effect of this therapeutic approach on VEGFR-1 and VEGFR-2 expression.
Methods Early and late ischemic comb and neck skin lesions of UCD-206 chickens were treated locally with VEGF121-fibrin or as a placebo control with fibrin alone. After 7 days the clinical outcome was assessed, and skin biopsies were taken for further analyses. To study the expression of VEGFR-1 and VEGFR-2 on endothelial cells, frozen tissue sections were double stained with the respective VEGF-receptor specific antibody and anti-van Willebrand factor (vWF) antibody by indirect immunofluorescence tests. The numbers of VEGFR-1 positive and VEGFR-2 positive endothelial cells were quantified using Tissuequest. Statistical significance was calculated using the Mann-Whitney-U test.
Results Seven days after treatment with VEGF121-fibrin approximately 80% of the lesions showed clear clinical improvement, whereas 82% of placebo controls and 97% of untreated lesions had deteriorated. Angiogenesis was significantly increased after treatment with VEGF121-fibrin compared to controls. VEGF121-fibrin treatment increased the expression of the pro-angiogenic receptor VEGFR-2, and strongly reduced the endothelial expression of the modulatory or anti-angiogenic receptor VEGFR-1.
Conclusions In the avian SSc model, the cell demanded release of VEGF121 from fibrin seems to result in controlled angiogenesis with formation of morphological normal blood vessels. The released VEGF differentially regulates the expression of VEGFR-1 and VEGFR-2 shifting the balance towards the pro-angiogenic VEGFR-2, thus increasing the angiogenic response. Long term effects of VEGF121-fibrin on vessel stability, the expression of endogenous VEGF, and its receptors will be investigated in a follow up study.
Disclosure of Interest None Declared
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