Purpose. We explored the role of bone morphogenic protein 2 (BMP2) in defocus-induced ocular growth using gene expression changes in RPE as a surrogate. Methods. Young White-Leghorn chickens were used in this study. Normal gene expression of BMP2 and its receptors was examined in retina, RPE, and choroid, and BMP2 protein expression assessed in the same tissues using Western blots and immunohistochemistry. Quantitative PCR (qPCR) was used to assess the effects of short-term exposure (2 or 48 hours) to monocular +10 and −10 diopter (D) lenses, on RPE gene expression of BMP2 and its receptors. Ocular growth was assessed using A-scan ultrasonography. Results. In the eyes of untreated chickens, BMP2 mRNA was expressed more highly in RPE compared to retina and choroid and all three tissues expressed BMP2 protein. The gene expression for all three receptors also was detected in these tissues, with BMPR2 showing highest and BMPR1B lowest expression. BMP2 was up-regulated in the RPE from eyes wearing +10 D lenses, which exhibited shorter than normal vitreous chambers (VCDs) and thickened choroids, while BMP2 was down-regulated in the RPE from eyes wearing −10 D lenses, which developed enlarged VCDs. These treatments did not induce differential expression of BMP receptors in RPE. Conclusions. That mRNA expression of BMP2 in chick RPE shows bidirectional, defocus sign-dependent changes is suggestive of a role for BMP2 in eye growth regulation, although the diffuse ocular expression of BMP2 and its receptors suggests complex growth-modulatory signal pathways.

This study investigated the gene expression of TGFβ isoforms and their receptors in chick retina, retinal pigment epithelium (RPE), and choroid and the effects of short-term imposed optical defocus. The expression of TGFβ isoforms (TGF-β1, 2, 3) and TGFβ receptors (TGFBR1, 2, 3) was examined in the retina, RPE, and choroid of young White-Leghorn untreated chicks (19 days-old). The effects on the expression of the same genes of monocular +10 and -10 D defocusing lenses, worn for either 2 or 48 h by age-matched chicks, were also examined by comparing expression in treated and untreated fellow eyes. RNA was purified, characterized and then reverse transcribed to cDNA. Differential gene expression was quantified using real-time PCR. All 3 isoforms of TGFβ and all 3 receptor subtypes were found to be expressed in all 3 ocular tissues, with apparent tissue-dependent differences in expression profiles. Data are reported as mean normalized expression relative to GAPDH. Sign-dependent optical defocus effects were also observed. Optical defocus did not affect retinal gene expression but in the RPE, TGF-β2 expression was significantly up-regulated with +10 D lenses, worn for either 2 h (349% increase ± 88%, p < 0.01) or 48 h (752% increase ± 166%, p < 0.001), and in the choroid, the expression of TGF-β3 was up-regulated with -10 D lenses, worn for 48 h (147% increase ± 9%, p < 0.01). The effects of short term exposure to optical defocus on TGFβ gene expression in the RPE and choroid, which were sign-dependent and isoform specific, provide further supporting evidence for important roles of members of the TGFβ family and these two tissues in local signal cascades regulating ocular growth.

Recent studies have demonstrated the defocus sign-dependent, bidirectional gene expression regulation of bone morphogenetic proteins, BMP2, 4 and 7 in chick RPE. In this study, we examined the effects of imposed positive (+10 D) and negative (−10 D) lenses on the gene expression of these BMPs and BMP receptors (BMPR1A, BMPR1B, BMPR2) in chick retina and choroid after monocular lens treatment for 2 or 48 h, as indicators of the roles of retinal and choroidal BMPs and receptors in postnatal eye growth regulation. In retina, although all genes were expressed, neither +10 nor −10 D lenses, worn for either 2 or 48 h, significantly altered gene expression. In contrast, treatment-related differential gene expression was detected in the choroid for both BMPs and their receptors, although interestingly, with the +10 D lens, BMP2 was up-regulated by 156.7 ± 19.7% after 2 h, while BMPR1A was down-regulated to 82.3 ± 12.5% only after 48 h. With the −10 D lens, only the gene expression of BMPR1B was significantly altered, being up-regulated by 162.3 ± 21.2% after 48 h. Untreated birds showed no difference in expression between their two eyes, for any of the genes examined. The finding that retinal gene expression for BMP2, 4, 7 and their receptors are not affected by short-term optical defocus contrasts with previous observations of sign-dependent expression changes for the same genes in the RPE. The latter changes were also larger and more consistent in direction than the choroidal gene expression changes reported here. The interrelationship between these various changes and their biological significance for eye growth regulation are yet to be elucidated.