RESUMO
BACKGROUND: Although multiple clinical studies have found an association between vitamin D (Vit D) deficiency and asthma, a recent clinical study suggested lack of therapeutic effect of Vit D supplementation. Nonetheless, the mechanisms by which Vit D influences airway structure and function in the context of inflammation and asthma remains undefined. In this regard, Vit D effects on airway smooth muscle (ASM) are important, given the role of this cell type in the hypercontractility and remodeling. We assessed the mechanisms by which Vit D modulates the enhancing effects of proinflammatory cytokines tumor necrosis factor-α (TNF-α) and IL-13 on intracellular Ca(2+) ([Ca(2+)]i) levels and remodeling in nonasthmatic versus asthmatic human ASM. METHODS: Human ASM was enzymatically isolated from surgical lung specimens of patients with clinically defined mild to moderate asthma versus no asthma. Cells were treated with 10 ng/ml TNF-α and 50 ng/ml IL-13 in the presence or absence of 100 nM calcitriol. MEASUREMENTS AND MAIN RESULTS: Interestingly, Vit D receptor (VDR) and retinoic X receptor-α levels were maintained, even increased, in subjects with asthma when treated with TNF-α and IL-13. Compared with untreated cells, calcitriol blunted the heightened effect of TNF-α on [Ca(2+)]i response to histamine in ASM. Calcitriol particularly blunted TNF-α and IL-13 effects on collagen and fibronectin deposition, especially in asthmatic ASM. Calcitriol stimulated VDR/retinoic X receptor dimerization and VDR activity even in subjects with asthma and with IL-13, highlighting retained functionality. Expression of Class I histone deacetylases 1-3 (HDAC) and overall HDAC activity were lower in IL-13-exposed ASM, but calcitriol enhanced HDAC expression/activity. CONCLUSIONS: In asthmatic ASM, Vit D functionality is maintained, allowing calcitriol to reduce the procontractile and proremodeling effects of inflammatory cytokines, particularly IL-13, which is relevant to asthma. These findings highlight a potential role for Vit D in asthma pathogenesis, particularly in the context of airway structure and functional changes early in disease.
RESUMO
Airway hyperresponsiveness and inflammation are fundamental hallmarks of allergic asthma that are accompanied by increases in certain polycations, such as eosinophil cationic protein. Levels of these cations in body fluids correlate with asthma severity. We show that polycations and elevated extracellular calcium activate the human recombinant and native calcium-sensing receptor (CaSR), leading to intracellular calcium mobilization, cyclic adenosine monophosphate breakdown, and p38 mitogen-activated protein kinase phosphorylation in airway smooth muscle (ASM) cells. These effects can be prevented by CaSR antagonists, termed calcilytics. Moreover, asthmatic patients and allergen-sensitized mice expressed more CaSR in ASMs than did their healthy counterparts. Indeed, polycations induced hyperreactivity in mouse bronchi, and this effect was prevented by calcilytics and absent in mice with CaSR ablation from ASM. Calcilytics also reduced airway hyperresponsiveness and inflammation in allergen-sensitized mice in vivo. These data show that a functional CaSR is up-regulated in asthmatic ASM and targeted by locally produced polycations to induce hyperresponsiveness and inflammation. Thus, calcilytics may represent effective asthma therapeutics.
