Mechanisms altering airway smooth muscle cell Ca+ homeostasis in two asthma models.
BACKGROUND
Asthma is characterized by airway remodeling, altered mucus production and airway smooth muscle cell (ASMC) contraction causing extensive airway narrowing. In particular, alterations of ASMC contractility seem to be of crucial importance. The elevation of the cytoplasmic Ca(2+) concentration is a key event leading to ASMC contraction and changes in the agonist-induced Ca(2+) increase in ASMC have been reported in asthma.


OBJECTIVE
The aim of this study was to investigate mechanisms underlying these changes.


METHODS
Murine tracheal smooth muscle cells (MTSMC) from T-bet KO mice and human bronchial smooth muscle cells (HBSMC) incubated with IL-13 and IL-4 served as asthma models. Acetylcholine-induced changes in the cytoplasmic Ca(2+) concentration were recorded using fluorescence microscopy and the expression of Ca(2+) homeostasis regulating proteins was investigated with Western blot analysis.


RESULTS
Acetylcholine-induced Ca(2+) transients were elevated in both asthma models. This correlated with an increased Ca(2+) content of the sarcoplasmic reticulum (SR). In MTSMC from T-bet KO mice, the expression of the SR Ca(2+) buffers calreticulin and calsequestrin was higher compared to wild-type mice. In HBSMC incubated with IL-13 or IL-4, the expression of ryanodine receptors, inositol-3-phosphate receptors and sarcoplasmic/endoplasmic reticulum Ca(2+) ATPases 2 was increased compared to HBSMC without incubation with interleukins. The enlarged acetylcholine-induced Ca(2+) transients could be reversed by blocking inositol-3-phosphate receptors.


CONCLUSIONS
We conclude that in the murine asthma model the SR Ca(2+) buffer capacity is increased, while in the human asthma model the expression of SR Ca(2+) channels is altered. The investigation of the Ca(2+) homeostasis of ASMC has the potential to provide new therapeutical options in asthma.
Kellner
Julia
J
Pneumology, Medizinische Klinik Innenstadt, Ludwig Maximilian University, Munich, Germany.
Tantzscher
Juliane
J
Oelmez
Hamza
H
Edelmann
Martin
M
Fischer
Rainald
R
Huber
Rudolf Maria
RM
Bergner
Albrecht
A
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D037282:Calreticulin / Q000378:metabolism; D002155:Calsequestrin / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D007377:Interleukin-3 / Q000378:metabolism; D015847:Interleukin-4 / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism; D014132:Trachea / Q000166:cytology; D000098815:T-bet Transcription Factor
D037282:Calreticulin; D002155:Calsequestrin; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007377:Interleukin-3; D019837:Ryanodine Receptor Calcium Release Channel; D020825:T-Box Domain Proteins; D000098815:T-bet Transcription Factor; D015847:Interleukin-4; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium