Abstract
Purpose: :
This study examined the gene expression of BMPs (BMP3, 6, 7), TGF-β2, and Noggin (NOG), a BMP antagonist protein, in chick retinal pigment epithelium (RPE) after exposure to imposed optical defocus. It is part of a larger investigation into the role in early eye growth regulation of TGF-β family (including BMPs) in RPE, which we believe to be involved because of its strategic location between the retina and choroid.
Methods: :
White-Leghorn chicks wore monocular -10 or +10 D lenses from 19 days of age for 2 or 48 h. Age-matched non-treated chicks were included. At the end of the lens treatment periods, chicks were sacrificed, eyes enucleated, RPE isolated and RNA extracted. RNA from the RPE and retina of age-matched non-treated chick was also purified. RNA was subjected to cDNA synthesis and then real-time PCR amplification. Primers for chick BMP3, BMP6, BMP7, NOG, TGFB2, and GAPDH (house-keeping gene) were designed using Primer Express 3.0 and gene information in the NCBI database. Expression levels for lens-treated eyes were compared to those of their fellow eyes, and these data were compared with values from untreated chicks.
Results: :
All five genes (BMP3, 6, 7, TGFB2, NOG) were highly expressed in chick RPE compare to retina (459, 15, 599, 6 & 28 fold higher respectively). Expression of BMP7 in RPE was down-regulated by 2.2 and 2.0 fold after 2 and 48 h of -10 D lens wear compared to levels in fellow eyes (p < 0.01, n = 16; p < 0.05, n = 13), but not affected by +10 D lens wear. Likewise, expression of NOG in RPE appeared to be up-regulated after 2 and 48 h of the -10 D lens treatment, i.e. by 2.0 and 5.9 fold (p = 0.06, n = 6; p < 0.05, n = 14), although compared to levels for control chicks, the latter trends reflected down-regulation in fellow eyes rather than up-regulation in treated eyes. In contrast, expression of TGF-β2 in RPE was not affected by -10 D lens wear, but was up-regulated by 3.9 and 8.6 fold after 2 and 48 hours +10 D lens wear respectively (p < 0.01, n = 14, 14). Neither the expression of BMP3 nor that of BMP6 was affected by -10 D and +10D lens treatments.
Conclusions: :
Our finding that expression levels of BMP7, TGF-β2, and NOG in chick RPE are all sensitive to imposed optical defocus, albeit with defocus sign-dependent differences in sensitivity, is consistent with roles of these members of the TGF-β superfamily as RPE-based signal relays or modulators in the early eye growth regulation.