Calcium sensors as new therapeutic targets for airway hyperresponsiveness and asthma

Abstract

Airway hyperresponsiveness and epithelial damage are key features in asthma, a disease reaching epidemic proportions in the developed world. To investigate and modulate airway hyperresponsiveness, we used two novel peptides, CALP1 and CALP2, which interact with calcium-binding EF hand motifs and regulate calcium channels. We found that CALP1 induced, whereas CALP2 blocked, airway hyperresponsiveness. Both effects were epithelium-dependent. In epithelial cells, CALP1 blocked agonist-induced increase in [Ca 2+ ] i , whereas CALP2 increased agonist-induced elevation in [Ca 2+ ] i . CALP2 causes the release of nitric oxide (NO), a mediator that relaxes airway smooth muscle. We conclude that epithelial calcium channels play a key role in regulating airway hyperresponsiveness by controlling [Ca 2+ ] i and consequently the production of NO. These results bring new insights into the mechanism of airway hyperresponsiveness and suggest new therapeutic targets for asthma.Key words: calcium-like peptide • nitric oxide • epithelium • tracheal reactivity sthma is a chronic airway disease characterized by infiltration of inflammatory cells, epithelial cell damage, and airway hyperresponsiveness to a variety of specific and nonspecific stimuli. The degree of epithelial damage is associated with the degree of airway hyperresponsiveness (1). The airway epithelium is a physical barrier that protects sensory nerves and smooth muscle from stimulation by inhaled irritants (2). Epithelial cells also release mediators that can inhibit bronchoconstriction by relaxing the underlying smooth muscle. These "epithelium-derived relaxing factors," such as prostaglandin E 2 and nitric oxide (NO), protect the airways from excessive bronchoconstriction (reviewed in 3).Inhaled NO causes bronchodilation in asthmatic patients (4), and inhibition of NO production by NO synthase inhibitors increases airway responsiveness in patients with mild asthma (5, 6). Viral A respiratory infections induce airway hyperresponsiveness in healthy individuals and exacerbate it in asthmatic subjects. These infections are estimated to underlie about 85% and 45% of asthma exacerbations in children and adults, respectively (7-9). NO plays a protective role after an experimental viral infection in asthmatics (10). These results are consistent with our earlier findings that, in guinea pigs, NO synthase inhibitors induce airway hyperresponsiveness in vivo and in vitro (11) and that the NO production in tracheal tubes from virus-inoculated guinea pigs is reduced by 75% (12).Calmodulin (CaM), the ubiquitous calcium-sensing regulatory protein, binds and regulates different target proteins, including protein kinases, ion channels, and NO synthases (13). The constitutively expressed NO synthase (cNOS), present in the airway epithelium (14, 15), is activated by CaM in a calcium-dependent manner (16). NO produced by cNOS is an important regulator of tone and responsiveness of airway smooth muscle (reviewed in (14)). Agonist stimulation increases the intracellular calcium concentra...

Loss-of-function of inositol polyphosphate-4-phosphatase reversibly increases the severity of allergic airway inflammation

“…As PEST sequences are calpain protease target sites, and a characteristic PEST motif was also seen in mouse INPP4A, we hypothesized that increased calpain-protease-mediated degradation of INPP4A in mouse lungs may be important in experimental asthma pathogenesis. As an increase in the intracellular free calcium is known to activate the calpain family of proteases 30 , and abnormal calcium homeostasis has been observed in asthma 31,32 , it is very likely to be one of the underlying mechanisms for calpain-mediated INPP4A degradation. Various types of calpain inhibitors have been known to alleviate a myriad of disorders 33,34 .…”

Specific modulation of calmodulin activity induces a dramatic production of superoxide by alveolar macrophages

“…For the latter, guinea-pigs were intratracheally inoculated with PI-3 virus (culture infective dose 50 ¼ 10 7.8 /ml) and four days later BAL cells were obtained. 18 Alveolar neutrophils were obtained from guinea-pigs treated with aerosolized LPS (endotoxin, Escherichia coli, 75 mg/ml, Sigma, St Louis, MO, USA) for 30 min. The cells were obtained 24 h after LPS treatment.…”

“…15 Interestingly, this resulted in an increase of [Ca 2 þ ] i . 18 Therefore, we hypothesized that the action of CALP2 on superoxide production by alveolar macrophages is due to the inhibition of CaM activation and therefore an increase of [Ca 2 þ ] i in these cells. The basal fluorescence ratio (F 340 /F 380 ) in alveolar macrophages was 1.8570.01 ( Figure 9).…”

“…15,16 The peptide binds EF hand motifs of the calcium-binding proteins CaM and troponin C. Moreover, we showed that CALP2 inhibited the action of CaM, 15,17 but increased [Ca 2 þ ] i in airway epithelial cells, the latter being accompanied by an increased NO production by these cells. 18 Moreover, the effects of CALP2 were likely due to the sustained opening of calcium channels present in epithelial cells. 18,19 In the present study, we used CALP2 to investigate the importance of CaM in radical production.…”

“…18 Moreover, the effects of CALP2 were likely due to the sustained opening of calcium channels present in epithelial cells. 18,19 In the present study, we used CALP2 to investigate the importance of CaM in radical production. For this purpose, radical production by bronchoalveolar lavage (BAL) cells from guinea-pigs was measured using lucigenin-enhanced chemiluminescence.…”