2. Academic Validation
  3. Quantitative Protein Expression in the Human Retinal Pigment Epithelium: Comparison Between Apical and Basolateral Plasma Membranes With Emphasis on Transporters

Quantitative Protein Expression in the Human Retinal Pigment Epithelium: Comparison Between Apical and Basolateral Plasma Membranes With Emphasis on Transporters

  • Invest Ophthalmol Vis Sci. 2019 Dec 2;60(15):5022-5034. doi: 10.1167/iovs.19-27328.
Laura Hellinen 1,  Kazuki Sato 2,  Mika Reinisalo 1 3,  Heidi Kidron 4,  Kirsi Rilla 5,  Masanori Tachikawa 2,  Yasuo Uchida 2,  Tetsuya Terasaki 2,  Arto Urtti 1 4 6
Affiliations

Affiliations

  • 1 School of Pharmacy, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland.
  • 2 Division of Membrane Transport and Drug Targeting, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.
  • 3 Institute of Clinical Medicine, Department of Ophthalmology, Faculty of Health Sciences, University of Eastern Finland, Kuopio, Finland.
  • 4 Drug Research Programme, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
  • 5 School of Medicine, Institute of Biomedicine, University of Eastern Finland, Kuopio, Finland.
  • 6 Laboratory of Biohybrid Technologies, Institute of Chemistry, St. Petersburg State University, St. Petersburg, Russian Federation.
PMID: 31791063 DOI: 10.1167/iovs.19-27328
Abstract

Purpose: Retinal pigment epithelium (RPE) limits the xenobiotic entry from the systemic blood stream to the eye. RPE surface transporters can be important in ocular drug distribution, but it has been unclear whether they are expressed on the apical, basal, or both cellular surfaces. In this paper, we provide quantitative comparison of apical and basolateral RPE surface proteomes.

Methods: We separated the apical and basolateral membranes of differentiated human fetal RPE (hfRPE) cells by combining apical membrane peeling and sucrose density gradient centrifugation. The membrane fractions were analyzed with quantitative targeted absolute proteomics (QTAP) and sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) to reveal the membrane protein localization on the RPE cell surfaces. We quantitated 15 transporters in unfractionated RPE cells and scaled their expression to tissue level.

Results: Several proteins involved in visual cycle, cell adhesion, and ion and nutrient transport were expressed on the hfRPE plasma membranes. Most drug transporters showed similar abundance on both RPE surfaces, whereas large neutral Amino acids transporter 1 (LAT1), P-glycoprotein (P-gp), and Monocarboxylate Transporter 1 (MCT1) showed modest apical enrichment. Many solute carriers (SLC) that are potential prodrug targets were present on both cellular surfaces, whereas putative sodium-coupled neutral amino acid transporter 7 (SNAT7) and riboflavin transporter (RFT3) were enriched on the basolateral and sodium- and chloride-dependent neutral and basic amino acid transporter (ATB0+) on the apical membrane.

Conclusions: Comprehensive quantitative information of the RPE surface proteomes was reported for the first time. The scientific community can use the data to further increase understanding of the RPE functions. In addition, we provide insights for transporter protein localization in the human RPE and the significance for ocular pharmacokinetics.

Figures