Abstract
Background/ObjectivesRetinaldehyde dehydrogenase 2 (RALDH2) has been implicated in regulating all-trans-retinoic acid (atRA) synthesis in response to visual signals in animal models of myopia. To explore the potential role of retinaldehyde dehydrogenase (RALDH) enzymes and atRA in human postnatal ocular growth, RALDH activity, along with the distribution of RALDH1, RALDH2, and RALDH3 in the postnatal eye was determined.MethodologyRetina, retinal pigment epithelium (RPE), choroid, and sclera were isolated from donor human eyes. RALDH catalytic activity was measured in tissue homogenates using an in vitro atRA synthesis assay together with HPLC quantification of synthesized atRA. Homogenates were compared by western blotting for RALDH1, RALDH2, and RALDH3 protein. Immunohistochemistry was used to determine RALDH1 and RALDH2 localization in posterior fundal layers of the human eye.Principal FindingsIn the postnatal human eye, RALDH catalytic activity was detected in the choroid (6.84 ± 1.20 pmol/hr/ug), RPE (5.46 ± 1.18 pmol/hr/ug), and retina (4.21 ± 1.55 pmol/hr/ug), indicating the presence of active RALDH enzymes in these tissues. RALDH2 was most abundant in the choroid and RPE, in moderate abundance in the retina, and in relatively low abundance in sclera. RALDH1 was most abundant in the choroid, in moderate abundance in the sclera, and substantially reduced in the retina and RPE. RALDH3 was undetectable in human ocular fundal tissues. In the choroid, RALDH1 and RALDH2 localized to slender cells in the stroma, some of which were closely associated with blood vessels.Conclusions/SignificanceResults of this study demonstrated that: 1) Catalytically active RALDH is present in postnatal human retina, RPE, and choroid, 2) RALDH1 and RALDH2 isoforms are present in these ocular tissues, and 3) RALDH1 and RALDH2 are relatively abundant in the choroid and/or RPE. Taken together, these results suggest that RALDH1 and 2 may play a role in the regulation of postnatal ocular growth in humans through the synthesis of atRA.
Highlights
Postnatal ocular growth is regulated by a vision-dependent process that coordinates the growth of the eye such that the ocular axial length will align the retina with the focal plane to give clear, uncorrected vision [1]
Results of this study demonstrated that: 1) Catalytically active retinaldehyde dehydrogenase (RALDH) is present in postnatal human retina, retinal pigment epithelium (RPE), and choroid, 2) RALDH1 and Retinaldehyde dehydrogenase 2 (RALDH2) isoforms are present in these ocular tissues, and 3) RALDH1 and RALDH2 are relatively abundant in the choroid and/or RPE
These results suggest that RALDH1 and 2 may play a role in the regulation of postnatal ocular growth in humans through the synthesis of All-trans-retinoic acid (atRA)
Summary
Postnatal ocular growth is regulated by a vision-dependent process that coordinates the growth of the eye such that the ocular axial length will align the retina with the focal plane to give clear, uncorrected vision [1]. Interruption of this process can result in abnormal axial elongation of the eye, often leading to the development of myopia or nearsightedness due to altered scleral extracellular matrix remodeling at the posterior pole of the eye [2,3,4]. AtRA may represent a chemical signal that can directly modulate ocular size and refraction in many vertebrate species
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