Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC285
The long acting beta agonist formoterol and the cAMP raising agent forskolin both cause reduced expression of SERCA2 in human airway smooth muscle cells
O. O. Ojo1,2, D. B. Wright1,2, T. H. Lee1,2, J. P. Ward1
1. Asthma Allergy and Respiratory Science, King''s College London, London, United Kingdom. 2. MRC & Asthma UK Centre in Allergic Mechanisms of Asthma, King's College London, London, United Kingdom.
There is strong evidence that airway smooth muscle (ASM) from asthmatic patients has an altered phenotype, with increased rates of proliferation, migration and secretion of pro-inflammatory cytokines. It has been suggested that a central underlying factor for these changes is a defect in ASM calcium homeostasis (e.g. Mahn et al, 2010). Our laboratory has previously shown that ASM cells from asthmatics exhibit a reduced expression of the sarcoendoplasmic reticulum calcium ATPase (SERCA2), and that knockdown of SERCA2 in healthy ASM cells recapitulates the asthmatic phenotype (Mahn et al, 2009). Whilst the reduced expression of SERCA2 may be primarily associated with inflammatory cytokines, it is unclear what effect current therapies might have. Notably, it has been reported that the long acting beta agonist (LABA) formoterol causes reduced expression of SERCA2 in cardiac myocytes (Ryall et al, 2008), and use of LABAs has been linked with adverse effects in asthmatic patients. We therefore examined whether formoterol also reduced SERCA2 expression inhuman ASM cells, and whether this was related to an increase in cAMP. ASM cells were treated with formoterol (1-30nM) for 24 hours. SERCA2 expression was estimated using western blot. Formoterol caused a dose dependent reduction in SERCA2 expression (10nM: to 48 +/- 11% control, p<0.05; 30nM: to 32 +/- 6% control, n=4, p<0.02). To determine whether this was mediated by cAMP, similar experiments were performed using forskolin. Preliminary experiments determined that 10 and 100uM forskolin induced approximately equivalent increases in cAMP in ASM cells to 10 and 30nM formoterol. Forskolin also reduced SERCA2 expression (10uM: to 70 +/- 6% control; 100uM: to 25 +/- 3% control, n=4, P<0.001). This strongly implies that formoterol acts via raising cAMP, and implicates CREB signalling. Consistent with this and the known role of ERK in CREB signalling, the ERK inhibitor UO126 prevented the effect of formoterol on SERCA2 expression. These results may possibly explain some of the adverse effects of LABAs in asthmatic patients.
Where applicable, experiments conform with Society ethical requirements