Multiple cellular transport and binding processes of unesterified docosahexaenoic acid in outer blood–retinal barrier retinal pigment epithelial cells

Masanori Tachikawa, Shin ichi Akanuma, Tsubasa Imai, Shun Okayasu, Takenori Tomohiro, Yasumaru Hatanaka, Ken ichi Hosoya

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Docosahexaenoic acid (DHA, 22:6) is an essential omega-3 long-chain polyunsaturated fatty acid that plays a pivotal role in vision. The purpose of this study was to clarify the cellular uptake and binding processes of free and protein-bound unesterified DHA in retinal pigment epithelial cell (RPE) line ARPE-19 as a model of the human outer blood–retinal barrier and isolated porcine RPE cell fractions. Uptake of free [14C]DHA by ARPE-19 cells was saturable with a Michaelis–Menten constant of 283µM, and was significantly inhibited by eicosapentaenoic acid, arachidonic acid, and linoleic acid, but not by oleic acid. Further, the uptakes of [14C]DHA associated with retinol-binding protein ([14C]DHA-RBP), [14C]DHA associated with low-density lipoprotein ([14C]DHA-LDL) and [14C]DHA associated with bovine serum albumin ([14C]DHA-BSA) in ARPE-19 cells increased time-dependently at 37°C, and were significantly reduced at 4°C, suggesting the involvement of energy-dependent transport processes. [14C]DHA-LDL uptake by ARPE-19 cells was significantly inhibited by excess unlabeled LDL, but not by an inhibitor of scavenger receptor B type I. Fatty acid transport protein (FATP) 2 and 4 mRNAs were expressed in ARPE-19 cells, and [14C]DHA uptake was observed in FATP2- and FATP4-expressing Xenopus oocytes. Photo-reactive crosslinking and mass spectrometry analyses identified 65-kDa retinal pigment epithelium-specific protein (RPE65) as a DHA-binding protein in porcine RPE cell membrane fractions. Thus, RPE cells possess multiple cellular transport/binding processes for unesterified DHA, involving at least partly FATP2, FATP4, LDL, RBP, and RPE65.

Original languageEnglish
Pages (from-to)1384-1392
Number of pages9
JournalBiological and Pharmaceutical Bulletin
Volume41
Issue number9
DOIs
Publication statusPublished - 2018 Jan 1

Keywords

  • Blood–retinal barrier
  • Docosahexaenoic acid
  • Fatty acid transport protein
  • Low-density lipoprotein
  • Retinal pigment epithelial cell
  • Retinol-binding protein

ASJC Scopus subject areas

  • Pharmacology
  • Pharmaceutical Science

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