Eosinophil peroxidase induces the expression and function of acid-sensing ion channel-3 in allergic rhinitis: in vitro evidence in cultured epithelial cells.
BACKGROUND
Acid-sensing ion channels (ASIC) are a family of acid-activated ligand-gated cation channels. As tissue acidosis is a feature of inflammatory conditions, such as allergic rhinitis (AR), we investigated the expression and function of these channels in AR.


OBJECTIVE
The aim of the study was to assess expression and function of ASIC channels in the nasal mucosa of control and AR subjects.


METHODS
Immunohistochemical localization of ASIC receptors and functional responses to lactic acid application were investigated. In vitro studies on cultured epithelial cells were performed to assess underlying mechanisms of ASIC function.


RESULTS
Lactic acid at pH 7.03 induced a significant rise in nasal fluid secretion that was inhibited by pre-treatment with the ASIC inhibitor amiloride in AR subjects (n = 19). Quantitative PCR on cDNA isolated from nasal biopsies from control and AR subjects demonstrated that ASIC-1 was equally expressed in both populations, but ASIC-3 was significantly more highly expressed in AR (P < 0.02). Immunohistochemistry confirmed significantly higher ASIC-3 protein expression on nasal epithelial cells in AR patients than controls (P < 0.01). Immunoreactivity for EPO+ eosinophils in both nasal epithelium and submucosa was more prominent in AR compared with controls. A mechanism of induction of ASIC-3 expression relevant to AR was suggested by the finding that eosinophil peroxidase (EPO), acting via ERK1/2, induced the expression of ASIC-3 in epithelial cells. Furthermore, using a quantitative functional measure of epithelial cell secretory function in vitro, EPO increased the air-surface liquid depth via an ASIC-dependent chloride secretory pathway.


CONCLUSIONS
This data suggests a possible mechanism for the observed association of eosinophils and rhinorrhoea in AR and is manifested through enhanced ASIC-3 expression.
Department of Respiratory, Otolaryngology and Molecular Medicine, Education and Research Centre, Dublin, Ireland.
S G
SG
Khoo
M
M
Al-Alawi
M T
MT
Walsh
K
K
Hannigan
S
S
Glynn
M
M
Thornton
S
S
McQuaid
Y
Y
Wang
P W
PW
Hamilton
V
V
Verriere
G J
GJ
Gleich
B J
BJ
Harvey
R W
RW
Costello
L P
LP
McGarvey
D062565:Acid Sensing Ion Channels; D000293:Adolescent; D000328:Adult; D001706:Biopsy; D002478:Cells, Cultured; D047209:Eosinophil Peroxidase / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D019344:Lactic Acid / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009297:Nasal Mucosa / Q000378:metabolism* / Q000473:pathology; D016133:Polymerase Chain Reaction; D006255:Rhinitis, Allergic, Seasonal / Q000378:metabolism* / Q000473:pathology; D015222:Sodium Channels / Q000096:biosynthesis*
C112231:ASIC3 protein, human; D062565:Acid Sensing Ion Channels; D015222:Sodium Channels; D019344:Lactic Acid; D047209:Eosinophil Peroxidase; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3