title: Human organic anion transporting polypeptide 1A2 (OATP1A2) mediates cellular uptake of all-trans-retinol in human retinal pigmented epithelial cells.
abstract: OBJECTIVE
  Vision depends on retinoid exchange between the retinal pigment epithelium (RPE) and photoreceptors. Defects in any step of the canonical visual cycle can lead to retinal degenerations. All-trans-retinol (atROL) plays an important role in visual signal transduction. However, how atROL enters human RPE from the apical membrane remains unclear. This study investigated the role of human organic anion transporting polypeptide 1A2 (OATP1A2) in atROL uptake in human RPE.
  
  
  METHODS
  Immunoblotting and immunostaining elucidated the expression and localization of OATP1A2 in human RPE. Transporter functional studies were conducted to assess the interaction of OATP1A2 with atROL.
  
  
  RESULTS
  Our study revealed OATP1A2 is expressed in human RPE, mainly at the apical membrane. Our data also indicated atROL inhibited the uptake of the typical OATP1A2 substrate, oestrone-3-sulfate (E3S), in over-expressing cells. Studies on the uptake of (3) H-atROL in these over-expressing cells revealed atROL is a substrate of OATP1A2. We confirmed these findings in human primary RPE cells. The transport of E3S and atROL was significantly reduced in human primary RPE cells with OATP1A2 siRNA silencing.
  
  
  CONCLUSIONS
  Our data provides the first evidence of OATP1A2 expression in human RPE and more importantly, its novel role in the cellular uptake of atROL, which might be essential to the proper functioning of the canonical visual cycle. Our findings contribute to the understanding of the molecular mechanisms involved in retinoid transport between the RPE and photoreceptors and provide novel insights into potential pharmaceutical interventions for visual cycle disruption associated with retinal degenerations.
authors.affiliation: Faculty of Pharmacy, University of Sydney, NSW, Australia.
authors.forename: Ting
authors.initials: T
authors.lastname: Chan
authors.forename: Ling
authors.initials: L
authors.lastname: Zhu
authors.forename: Michele C
authors.initials: MC
authors.lastname: Madigan
authors.forename: Ke
authors.initials: K
authors.lastname: Wang
authors.forename: Weiyong
authors.initials: W
authors.lastname: Shen
authors.forename: Mark C
authors.initials: MC
authors.lastname: Gillies
authors.forename: Fanfan
authors.initials: F
authors.lastname: Zhou
mesh_terms: D000328:Adult; D000368:Aged; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D004970:Estrone / Q000031:analogs & derivatives / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008875:Middle Aged; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism*; D061251:Primary Cell Culture; D034622:RNA Interference; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D014162:Transfection; D014801:Vitamin A / Q000378:metabolism*
chemical_list: D027361:Organic Anion Transporters; C512988:SLCO1A2 protein, human; D014801:Vitamin A; D004970:Estrone; C017296:estrone sulfate