VEGF and SPARC Immunoreactivities in the Rat Retina

Hann, Hoo Jae

Abstract

Normal angiogenesis is very important in the embryonic period and even in the postnatal period. If the vascularization is inadequate or excessive, several pathologic conditions may develop. Angiogenesis is well controlled and there are several angiogenic factors. Vascular endothelial growth factor (VEGF) has been identiified as an endothelial cell specific mitogen with potent angiogenic properties. Recently, a matricellular protein known as SPARC (secreted protein, acidic and rich in cysteine) is also proposed as one of new angiogenic factors. So, I planned to investigate the expression pattern of these two factors in the rat retina and to correlate their expression pattern with intraretinal vascularization. I used Sprague-Dawley rat as the experimental animals and divided them into 7 groups according to their postnatal age: 0-day, 3-day, 7-day, 14-day, 21-day, 28-day and adult. Immunohistochemistry was done. The results were as follows. 1. No SPARC immunoreactivity is observed in neural retina until postnatal day 7. At that time, weak immunore-activity is noted and it is gradually increased. The most intense immunoreactivity is noted at postnatal day 21 and 28. SPARC immunoreactivity is restricted in the nerve fiber layer and especially prominent around the blood vessels. Although SPARC immunoreactivity is much weaker than that of GFAP, the expression patterns of both factors are similar to each other. But, no SPARC immunoreactivity is observed in the adult retina. 2. Weak VEGF immunoreactivity is observed in the nerve fiber layer, ganglion cell layer and inner portion of inner nuclear layer even at postnatal day 0. After postnatal day 14, VEGF immunoreactivity is dramatically decreased in the nerve fiber layer, but it still remained in the ganglion cell layer and inner portion of inner nuclear layer. Although immunoreactivity is most intense at postnatal day 14 and 21, VEGF immunoreactivity is still observed in the ganglion cells at postnatal day 28 and adult. The spatial and temporal patterns of VEGF expression suggest that VEGF may function as a direct angiogenic factor in the retinal angiogenesis of rat. In the contrary, SPARC immunoreactivity is observed transiently in some period. So, SPARC is seemed to be a regulator that is involved only in limited steps of the retinal angiogenesis.