title: Identification of active retinaldehyde dehydrogenase isoforms in the postnatal human eye.
abstract: OBJECTIVE
  Retinaldehyde 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.
  
  
  METHODS
  Retina, 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.
  
  
  RESULTS
  In 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
  Results 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.
authors: Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors: Angelica R
authors: AR
authors: Harper
authors: Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors: Allan F
authors: AF
authors: Wiechmann
authors: Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors: Gennadiy
authors: G
authors: Moiseyev
authors: Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors: Jian-Xing
authors: JX
authors: Ma
authors: Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America.
authors: Jody A
authors: JA
authors: Summers
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D055162:Biocatalysis / Q000187:drug effects; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005123:Eye / Q000187:drug effects / Q000201:enzymology*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009243:NAD / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D050697:Retinal Dehydrogenase / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology
chemical_list: D007527:Isoenzymes; D009243:NAD; D014212:Tretinoin; D050697:Retinal Dehydrogenase