VEGF, Ang-2 and SRIF associated abnormal postnatal development of the retinal capillary network in the Royal College of Surgeons rat

To examine retinal angiogenesis in the Royal College of Surgeons rat (RCS) serving as a model for ischemic proliferative retinopathies at morphological, proteomic and mRNA levels in order to evaluate the interplay of morphological and molecular changes in the course of the disease.Photoreceptor degeneration was confirmed by histological cross-sections and optical coherence tomography. The capillary retinal network was visualized in RCS rats aged between 14 and 45 days (P14–P45) by perfusion with high molecular weight fluorescein isothiocyanate-labeled dextran and compared with corresponding Sprague-Dawley rats. Vascular crosstalks within central areas to peripheral retinal eccentricities were analyzed. The expression of vascular growth-associated factors and their receptors in the course of the abnormal vascular development, namely vascular endothelial growth factor (VEGF), VEGF receptor subtype 1 (VEGF-R1) and -2 (VEGF-R2), somatostatin (SRIF), somatostatin receptor subtype 2 (Sstr-2), angiopoietin-2 (Ang-2) and tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (Tie-2), was analyzed by immunohistochemistry, western blotting and quantitative real-time polymerase chain reaction.Underperfused areas without capillarization were found in the middle and peripheral retinal eccentricities of RCS rats until P29. Through the course of vascularization previously low perfused areas became completely perfused, but were characterized by significantly increased neovascularizations. Western blotting revealed specific expression of growth-associated factors and their receptors in the course of capillary development. VEGF was significantly increased until P29 in RCS rats, while SRIF was significantly upregulated at P21 and P29 at proteomic level in SD rats. At mRNA level Ang-2 was significantly upregulated in RCS rats at P29, VEGF-R1 and VEGF-R2 at P36 and SRIF at P36.Initial incomplete perfusion is followed by aberrant vessel formation. VEGF, SRIF, Ang-2 and their receptors are regulated at protein and mRNA levels, providing therapeutic possibilities for treating ischemic proliferative retinopathies in the course of the disease.

Research highlights
► This study is the first to analyze the vessel-growth associated factors VEGF, Ang-2, SRIF and their specific receptors in the course of IPR in an animal model of photoreceptor dystrophy.
► RCS rats are suitable models to study developmental changes in the course of IPRs, mimicking the pathophysiology of IPRs showing a vaso-obliterative phase until P29, followed by a vaso-proliferative phase.
► The expression of the growth-associated factors VEGF, Ang-2 and SRIF is affected throughout the course of the disease showing a specific regulation of those angiopoietic factors in the phases of vaso-obliteration and vaso-proliferation at genetical and proteomic level.