Abstract
Purpose: :
Erythropoietin (EPO) and its receptor (EPOR) play an important role in brain development. However, little is known about the impact of EPO and EPOR on the eye development. To gain insight into the role of EPO/EPOR on retinal neurons and lens cells differentiation during eye development, the protein expression of EPO and EPOR, signal transducer and activator transcripts 5 (STAT5) and pro-apoptotic protein BAX were investigated across various developmental stages.
Methods: :
The whole eyes of SD rats from a late embryonic stage (E) 19 to postnatal stage (P) 1, 2, 3, 4, 5, 7, 12, 15, 20, 25, 30, 35, 45 and 60 were collected (n=4 eyes per time point). In a separate study, the ocular tissues from adult rats were collected as whole eye or dissected into anterior segment, lens and attached vitreous, retina, and posterior segment (without retina). All collected tissues were stored at -70ºC for tissue protein preparation using a whole protein extract kit (Biochain Institute, Inc.). The total protein lysate (15µl) was subject to 12% SDS-PAGE followed by western blotting procedure with specific primary antibodies of EPO, EPOR, STAT5, and BAX. Quantitative densitometry of protein expression and statistical analysis were then performed.
Results: :
EPO was detected in the eye throughout the entire investigated period. The expression increased slightly after birth. EPOR displayed two distinct isoforms in the eye: the neural EPOR (32-kDa, termed EPOR-C) and the lens isoform (59-kDa). The expression of EPOR-C increased gradually and reached the maximum level by P30 and was maintained thereafter. The lens isoform was not detected before birth, but then its expression was up-regulated to the adult level at P12. STAT5 was expressed at all time points with peak expression during P12-P20, but decreased to the adult level during P25 to P60. BAX was detected in the retina (35-kDa isoform) during the studied period, but significantly upregulated after birth. In the lens, BAX is 55 kDa and was not detected before P7. From P12 to P60, the lens BAX gradually increased.
Keywords: growth factors/growth factor receptors • development • retina