Osteoblasts express claudins and tight junction-associated proteins.
Osteoblasts were previously reported to form tight junctions, which may play an important role in the regulation of ion transport across the epithelial-like bone membrane. However, the evidence for the presence of tight junction-associated proteins in osteoblasts is lacking. We therefore studied the expression of tight junction-associated genes in primary rat osteoblasts and bone tissues. Quantitative real-time PCR showed that osteoblasts expressed ZO-1, -2, -3, cingulin, occludin, claudin-1 to -12, -14 to -20, -22 and -23. By using western blot analyses of selected claudins, expression of claudin-5, -11, -14 and -15, but not claudin-3, were identified in osteoblasts. A confocal immunofluorescent study in undecalcified tibial sections confirmed that claudin-16 was localized on the trabecular surface, normally covered by osteoblasts and bone-lining cells. In addition, immunohistochemical studies in decalcified tibial sections demonstrated the expression of claudin-5, -11, -14, -15 and -16 in bone-lining cells (inactive osteoblasts). Primary osteoblasts cultured in the Snapwell for 19-26 days were found to form a monolayer with measurable transepithelial resistance of approximately 110-180 Omegacm(2), confirming the presence of barrier functions of the tight junction. It was concluded that osteoblasts expressed several tight junction-associated proteins, which possibly regulated ion transport across the bone membrane.
Wongdee
Kannikar
K
Consortium for Calcium and Bone Research, Faculty of Science, Mahidol University, Rama VI Road, Bangkok, 10400, Thailand.
Pandaranandaka
Jantarima
J
Teerapornpuntakit
Jarinthorn
J
Tudpor
Kukiat
K
Thongbunchoo
Jirawan
J
Thongon
Narongrit
N
Jantarajit
Walailak
W
Krishnamra
Nateetip
N
Charoenphandhu
Narattaphol
N
D000818:Animals; D001842:Bone and Bones / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression; D008565:Membrane Proteins / Q000096:biosynthesis*; D008855:Microscopy, Electron, Scanning; D062793:Occludin; D010006:Osteoblasts / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D019108:Tight Junctions / Q000378:metabolism* / Q000648:ultrastructure
D008565:Membrane Proteins; D062793:Occludin; C568987:Ocln protein, rat