ab2005

Increased but imbalanced expression of VEGF and its receptors has no positive effect on angiogenesis in systemic sclerosis skin

Z. Mackiewicz^1,2, A. Sukura³, D. Povilenaité¹, A. Ceponis⁴, I. Virtanen², M. Hukkanen², Y.T. Konttinen^2,5,6

¹Institute of Experimental and Clinical Medicine, Vilnius, Lithuania; ²Institute of Biomedicine/Anatomy, University of Helsinki, Finland; ³Department of Veterinary Pathology, University of Helsinki, Finland; ⁴RW Jonsson Pharmaceutical Research Institute, San Diego, California, USA; ⁵Department of Medicine/ InvŠrtes medicin, Helsinki University Hospital, Helsinki; ⁶ORTON Research Institute and the Orthopaedic Hospital of the Invalid Foundation, Helsinki, Finland.

ABSTRACT
Objective
To investigate the expression of vascular endothelial growth factor (VEGF) and its vascular and lymphatic receptors in skin in systemic sclerosis (SSc) compared to systemic lupus erythematosus (SLE), Raynaud's phenomenon (RP) and normal healthy control skin.

Methods
Staining was performed using rabbit anti-human antibodies in DAKO TechMate™ Horizon staining robot programmed for the biotin-streptavidin protocol.

Results
VEGF was sporadically and weakly expressed in normal skin, but in spite of vascular damage in diseased skin, VEGF expression was only slightly upregulated. In contrast, its vascular receptors VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1), were clearly upregulated. Finally, the lymphatic VEGFR-3 (Flt-4) receptor was also upregulated in diseased skin and ectopically expressed also in blood vessels. Negative staining and positive sample controls confirmed the specificity of the staining.

Conclusion
The imbalanced expression of VEGF and its vascular receptors suggest that the compensatory efforts to angiogenesis fail in SSc, in part due to insufficient local production of VEGF, which was low compared to VEGFR expression. This is compatible with the recent observations on the lack of aVb3+ newly formed blood vessels in SSc skin. Since microvascular angiogenic stimuli normally induce first VEGF and then VEGFR, these findings also suggest that the angiogenic cascade is turned on, but there is a defect in the finalisation of its effects. Normalization of angiogenic cascade in SSc could provide a future therapeutic target.

Key words
Systemic sclerosis, angiogenesis, lymphangiogenesis.

Supported by the Finnish Center for the Advancement of Technology, the Academy, Helsinki University Finnish Central Hospital (Evo Grant), Finska Läkaresällskapet, Finland, the Sigrid Juselius Foundation, and Ministery of Higher Education of Lithuania.
Please address correspondence to: Prof. Y.T. Konttinen, Biomedicum Helsinki, P.O. Box 700 (Haartmaninkatu 8), FIN-00029 Helsinki University Hospital, Finland.
E-mail: Yrjo.Konttinen@helsinki.fi