The degradation of airway tight junction protein under acidic conditions is probably mediated by transient receptor potential vanilloid 1 receptor.
Acidic airway microenvironment is one of the representative pathophysiological features of chronic inflammatory respiratory diseases. Epithelial barrier function is maintained by TJs (tight junctions), which act as the first physical barrier against the inhaled substances and pathogens of airway. As previous studies described, acid stress caused impaired epithelial barriers and led the hyperpermeability of epithelium. However, the specific mechanism is still unclear. We have showed previously the existence of TRPV (transient receptor potential vanilloid) 1 channel in airway epithelium, as well as its activation by acidic stress in 16HBE cells. In this study, we explored the acidic stress on airway barrier function and TJ proteins in vitro with 16HBE cell lines. Airway epithelial barrier function was determined by measuring by TER (trans-epithelial electrical resistance). TJ-related protein [claudin-1, claudin-3, claudin-4, claudin-5, claudin-7 and ZO-1 (zonula occluden 1)] expression was examined by western blotting of insoluble fractions of cell extraction. The localization of TJ proteins were visualized by immunofluorescent staining. Interestingly, stimulation by pH 6.0 for 8 h slightly increased the epithelial resistance in 16HBE cells insignificantly. However, higher concentration of hydrochloric acid (lower than pH 5.0) did reduce the airway epithelial TER of 16HBE cells. The decline of epithelial barrier function induced by acidic stress exhibited a TRPV1-[Ca2+]i-dependent pathway. Of the TJ proteins, claudin-3 and claudin-4 seemed to be sensitive to acidic stress. The degradation of claudin-3 and claudin-4 induced by acidic stress could be attenuated by the specific TRPV1 blocker or intracellular Ca2+ chelator BAPTA/AM [1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester)].
*Department of Respiratory Medicine, the Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China.
Rui
R
Xu
*Department of Respiratory Medicine, the Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China.
Qi
Q
Li
†Department of Respiratory Medicine, the First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, China.
Jia
J
Zhou
*Department of Respiratory Medicine, the Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, China.
Xiang-dong
XD
Zhou
‡Far Eastern Scientific Center of Physiology and Pathology of Respiration, Russian Academy of Medical Sciences, Blagoveschensk 675000, Russia.
Juliy M
JM
Perelman
‡Far Eastern Scientific Center of Physiology and Pathology of Respiration, Russian Academy of Medical Sciences, Blagoveschensk 675000, Russia.
Victor P
VP
Kolosov
D000142:Acidosis, Respiratory / Q000378:metabolism; D001980:Bronchi / Q000473:pathology; D020013:Calcium Signaling; D002460:Cell Line; D002470:Cell Survival; D062465:Claudin-3 / Q000378:metabolism*; D062506:Claudin-4 / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D017097:Electric Impedance; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010539:Permeability; D059748:Proteolysis; D013312:Stress, Physiological; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019108:Tight Junctions / Q000378:metabolism
C568122:CLDN3 protein, human; C568157:CLDN4 protein, human; D062465:Claudin-3; D062506:Claudin-4; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid