Expression of bone morphogenetic protein in sclera of form deprivation myopic eye

Abstract

Background It is well known that sclera remodeling occurs during axial elongation in myopia under the control of growth hormone or its downstream effectors.The role of transforming growth factor-β (TGF-β) in myopia has been determined in previous studies.Bone morphogenetic protein (BMP) is one of members of the TGF-β superfamily,but if it plays an important role in the genesis and development of myopia is not completely clear.Objective This study was to identify the presence of BMPs in normal guinea pigs sclera and investigate the change of BMPs in the sclera in form-deprivation myopia (FDM) of guinea pigs.Methods Thirty young guinea pigs were randomized into normal control group and experimental group using table of random number.FDM models were established by occluding unilateral eyes of guinea pigs with a translucent lens for 14 days in the experimental group,and the fellow eyes served as the controls.Diopter of all eyes was tested by retinoscopy optometry,and ocular axial length was measured by A-sonography before and after modeling.Posterior sclera tissue of the animals was obtained on 14 days,and the relative expression level of BMPs mRNA and protein were assayed by reverse transcription PCR (RT-PCR) and Western blot.The use and care of the animals complied with ARVO Statement.Results On 14 days after occluding of unilateral eyes,the refraction diopter of the experimental group was (-0.48±0.51) D,and that of the fellow eyes was (3.22 ±0.34) D,showing a significant difference between them (t =-12.814,P =0.000).Also,a significant difference in the diopter was seen between the experimental group and normal control group ([-0.48±0.51]D vs.[2.97±0.70]D,t =-11.878,P=0.000).Axial length was (8.30 ± 0.05) mm in the experimental group,(8.11 ±0.06) mm in the fellow eyes and (8.06±0.06) mm in the normal control group,showing a significant increase in the experimental group compared with the fellow eyes and normal control group (t =7.230,P =0.000 ; t =9.084,P=0.000).The expressions of BMP-2 mRNA,BMP-4 mRNA,BMP-5 mRNA in posterior sclera were detected in the normal guinea pigs.Fourteen days after the induction of myopia,the relative levels of BMP-2 mRNA and BMP-5 mRNA in sclera were 0.41 ± 0.11 and 0.65 ± 0.06 in the experimental eyes,which were significantly lower than 0.62 ± 0.07 and 0.84 ± 0.03 in the fellow eyes with the descent range of 34.48％ and 23.67％ respectively (t=2.838,P=0.017; t=2.524,P=0.028).The relative values of BMP-2 protein and BMP-5 protein were 0.44±0.06 and 0.70±0.05 in the experimental eyes,and those of the fellow eyes were 0.61±0.05 and 0.82±0.03,showing significant decline in the experimental eyes with the lowing range of 23.42％ and 15.21％,respectively (t =2.465,P =0.030;t =2.445,P=0.031).No significant differences were found in the expression of BMP-4 mRNA and protein in posterior sclera between the experimental eyes and the normal control eyes (mRNA:t =0.704,P=0.460;protein:t=0.987,P=0.365).Conclusions The expressions of the BMP-2 and BMP-5 in sclera down-regulate significantly in FDM eyes,which suggest that BMP-2 and BMP-5 participate in sclera remodeling during myopia induction. Key words: Transforming growth factor-β/bone morphogenetic protein; Form-deprivation myopia; Sclera