title: Characterization of vitamin D production by human ocular barrier cells.
abstract: OBJECTIVE
  Vitamin D3 is a secosteroid mainly synthesized from the conversion of the skin precursor 7-dehydrocholesterol (7DHC) to vitamin D3 by ultraviolet (UV) B sunlight. Extrarenal synthesis of vitamin D3 has been reported in many tissues and cells, including barrier sites. This study characterizes the expression of components of vitamin D3 signaling in human ocular barrier cells.
  
  
  METHODS
  Primary human scleral fibroblasts (HSF), human corneal endothelial (HCEC-12), nonpigmented ciliary body epithelial (ODM-2), and adult retinal pigment epithelial (ARPE-19) cell lines were analyzed for the expression of vitamin D receptor (VDR), the vitamin D3 activating enzymes 1α-hydroxylase (CYP27B1), 25-hydroxylases (CYP27A1 and CYP2R1), the vitamin D3 inactivating enzyme 24-hydroxylase (CYP24A1), and the endocytic receptors cubilin and megalin using a combination of RT-PCR, immunocytochemistry, and enzyme immunoassay (EIA).
  
  
  RESULTS
  The HSF, HCEC-12, ODM-2, and ARPE-19 express mRNA and protein for all vitamin D3 synthesizing and metabolizing components. The cell types tested, except HSF, are able to convert inactive 25-hydroxyvitamin D3 (25[OH]D3) into active 1,25-hydroxyvitamin D3 (1,25[OH]2D3).
  
  
  CONCLUSIONS
  This novel study demonstrated that ocular barrier epithelial cells express the machinery for vitamin D3 and can produce 1,25(OH)2D3. We suggest that vitamin D3 might have a role in immune regulation and barrier function in ocular barrier epithelial cells.
authors.affiliation: Centre for Translational Inflammation, School of Immunity and Infection, University of Birmingham, Birmingham, United Kingdom.
authors.forename: Jawaher A
authors.initials: JA
authors.lastname: Alsalem
authors.forename: Deepali
authors.initials: D
authors.lastname: Patel
authors.forename: Radhika
authors.initials: R
authors.lastname: Susarla
authors.forename: Miguel
authors.initials: M
authors.lastname: Coca-Prados
authors.forename: Rosemary
authors.initials: R
authors.lastname: Bland
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Walker
authors.forename: Saaeha
authors.initials: S
authors.lastname: Rauz
authors.forename: Graham R
authors.initials: GR
authors.lastname: Wallace
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000096:biosynthesis / Q000235:genetics*; D002460:Cell Line; D002762:Cholecalciferol / Q000096:biosynthesis*; D004728:Endothelium, Corneal / Q000166:cytology / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007124:Immunoenzyme Techniques; D007150:Immunohistochemistry; D012333:RNA, Messenger / Q000235:genetics*; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012590:Sclera / Q000166:cytology / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D002762:Cholecalciferol; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase
keywords: blood–ocular barrier; epithelial cells; vitamin D3