All-trans-retinol generated by rhodopsin photobleaching induces rapid recruitment of TIP47 to lipid droplets in the retinal pigment epithelium.
OBJECTIVE
To investigate the effect of light stimulation on lipid droplets (LDs) and LD proteins in the retinal pigment epithelium (RPE).


METHODS
Dark-adapted mouse eyes were exposed to intense flashes of light, and ARPE-19 cells were treated with all-trans-retinol. The two specimens were labeled with BODIPY493/503 for LDs and with antibodies for three LD proteins: adipocyte differentiation-related protein (ADRP), TIP47, and Rab18. The labeling intensity in fluorescence microscopy was quantified by image analysis. Localization of mutated TIP47 was also examined. Immunoelectron microscopy was performed for ADRP in mouse RPE. Expression of TIP47 in ARPE-19 cells was knocked down by RNA interference (RNAi), and its effect on retinyl ester storage was measured by HPLC.


RESULTS
Both flashes of light on mouse eyes and all-trans-retinol on ARPE-19 cells caused rapid translocation of TIP47 from the cytosol to LDs, whereas ADRP distributed constitutively in LDs. The density of LDs did not show visible changes by any treatment. The localization of TIP47 to LDs was abolished when either the amino-terminal or the carboxyl-terminal half of the molecule was deleted, but was enhanced by a short deletion in the carboxyl terminus. Manipulation of TIP47 expression by RNAi or cDNA transfection did not affect the retinyl ester amounts in ARPE-19 cells significantly.


CONCLUSIONS
All-trans-retinol generated by photobleaching in the retina induces rapid translocation of TIP47 to LDs in the RPE.
Tsuiki
Eiko
E
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan. t-eiko@net.nagasaki-u.ac.jp
Fujita
Akikazu
A
Ohsaki
Yuki
Y
Cheng
Jinglei
J
Irie
Toshiaki
T
Yoshikawa
Kiwamu
K
Senoo
Haruki
H
Mishima
Kazuaki
K
Kitaoka
Takashi
T
Fujimoto
Toyoshi
T
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003623:Dark Adaptation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D050356:Lipid Metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D008807:Mice, Inbred BALB C; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D000070780:Perilipin-2; D000070796:Perilipin-3; D010775:Photic Stimulation; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D011257:Pregnancy Proteins / Q000378:metabolism*; D021381:Protein Transport; D034622:RNA Interference; D012243:Rhodopsin / Q000528:radiation effects*; D033921:Vesicular Transport Proteins; D014801:Vitamin A / Q000494:pharmacology / Q000502:physiology*; D020691:rab GTP-Binding Proteins / Q000378:metabolism / Q000648:ultrastructure
D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C000602982:PLIN2 protein, human; C038196:PLIN3 protein, human; D000070780:Perilipin-2; D000070796:Perilipin-3; C000602983:Plin2 protein, mouse; D011257:Pregnancy Proteins; C083879:Rab18 protein, mouse; D033921:Vesicular Transport Proteins; D014801:Vitamin A; D012243:Rhodopsin; D020691:rab GTP-Binding Proteins