Cellular retinoic acid bioavailability determines epithelial integrity: Role of retinoic acid receptor alpha agonists in colitis.
The epithelial barrier is determined primarily by intercellular tight junctions (TJs). We have demonstrated previously that all-trans retinoic acid (atRA) plays an important role in forming functional TJs through a specific retinoic acid receptor (RAR)/retinoid X receptor heterodimer in epithelial cells. However, the physiological relevance of retinoic acids (RAs) in maintaining the epithelial integrity remains to be examined. Here, we show that several types of RA, including atRA, promote the barrier function of epithelial TJs. Conversely, RA depletion in the cells by overexpressing CYP26s, cytochrome P450 enzymes specifically involved in the metabolic inactivation of RAs, induces an increase of permeability as measured by two differently sized tracer molecules, inulin and mannitol. This RA-mediated enhancement of barrier function is potentially associated with the increased expression of TJ-associated genes such as occludin, claudin-1, claudin-4, and zonula occludens-1. We also found that RARalpha is a preferential regulator of the epithelial barrier in vitro. Studies of murine experimental colitis, which is characterized by increased gut permeability, reveal that RARalpha stimulation significantly attenuates the loss of the epithelial barrier during colitis in vivo. Our results suggest that cellular RA bioavailability determines the epithelial integrity, because it is a critical regulator for barrier protection during mucosal injuries.
Osanai
Makoto
M
Department of Pathology, Sapporo Medical University School of Medicine, South-1, West-17, Sapporo, Japan. osanaim@sapmed.ac.jp
Nishikiori
Nami
N
Murata
Masaki
M
Chiba
Hideki
H
Kojima
Takashi
T
Sawada
Norimasa
N
D000818:Animals; D018988:Bacterial Translocation; D001682:Biological Availability; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D003092:Colitis / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D004285:Dogs; D006801:Humans; D007668:Kidney; D018168:Receptors, Retinoic Acid / Q000819:agonists*; D011994:Recombinant Proteins / Q000378:metabolism; D000072516:Retinoic Acid 4-Hydroxylase; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014212:Tretinoin / Q000493:pharmacokinetics*; D019459:Urothelium / Q000502:physiology*
D018168:Receptors, Retinoic Acid; D011994:Recombinant Proteins; D014212:Tretinoin; D003577:Cytochrome P-450 Enzyme System; D000072516:Retinoic Acid 4-Hydroxylase