Claudin-19 and the barrier properties of the human retinal pigment epithelium.
OBJECTIVE
The retinal pigment epithelium (RPE) separates photoreceptors from choroidal capillaries, but in age-related macular degeneration (AMD) capillaries breach the RPE barrier. Little is known about human RPE tight junctions or the effects of serum on the retinal side of the RPE.


METHODS
Cultured human fetal RPE (hfRPE) was assessed by the transepithelial electrical resistance (TER) and the transepithelial diffusion of methylated polyethylene glycol (mPEG). Claudins and occludin were monitored by quantitative RT-PCR, immunoblotting, and immunofluorescence.


RESULTS
Similar to freshly isolated hfRPE, claudin-19 mRNA was 25 times more abundant than claudin-3. Other detectable claudin mRNAs were found in even lesser amounts, as little as 3000 times less abundant than claudin-19. Claudin-1 and claudin-10b were detected only in subpopulations of cells, whereas others were undetectable. Knockdown of claudin-19 by small interfering RNA (siRNA) eliminated the TER. siRNAs for other claudins had minimal effects. Serum affected tight junctions only when presented to the retinal side of the RPE. The TER increased 2 times, and the conductance of K(+) relative to Na(+) decreased without affecting the permeability of mPEG. These effects correlated with increased steady-state levels of occludin.


CONCLUSIONS
Fetal human RPE is a claudin-19-dominant epithelium that has regional variations in claudin-expression. Apical serum decreases RPE permeability, which might be a defense mechanism that would retard the spread of edema due to AMD.
Department of Surgery, Yale University School of Medicine, New Haven, Connecticut 06520-8062, USA.
Shaomin
S
Peng
Veena S
VS
Rao
Ron A
RA
Adelman
Lawrence J
LJ
Rizzolo
D002478:Cells, Cultured; D057167:Claudins; D017097:Electric Impedance; D019084:Fluorescent Antibody Technique, Indirect; D020868:Gene Silencing / Q000502:physiology; D005865:Gestational Age; D006801:Humans; D015151:Immunoblotting; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D062793:Occludin; D010539:Permeability; D011092:Polyethylene Glycols / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D055213:Retinal Pigment Epithelium / Q000196:embryology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019108:Tight Junctions / Q000502:physiology*
C508912:CLDN19 protein, human; D057167:Claudins; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011092:Polyethylene Glycols; C028210:monomethoxypolyethylene glycol