Stewart, Alecia

Abstract 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 Ca2+ ([Ca2+]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 [Ca2+]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.

Exposure to moderate hyperoxia in prematurity contributes to subsequent airway dysfunction and increases the risk of developing recurrent wheeze and asthma. The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic GMP (cGMP) axis modulates airway tone by regulating airway smooth muscle (ASM) intracellular Ca2+([Ca2+]i) and contractility. However, the effects of hyperoxia on this axis in the context of Ca2+/contractility are not known. In developing human ASM, we explored the effects of novel drugs that activate sGC independent of NO on alleviating hyperoxia (50% oxygen)-induced enhancement of Ca2+responses to bronchoconstrictor agonists. Treatment with BAY 41–2272 (sGC stimulator) and BAY 60-2770 (sGC activator) increased cGMP levels during exposure to 50% O2. Although 50% O2did not alter sGCα1or sGCβ1expression, BAY 60-2770 did increase sGCβ1expression. BAY 41-2272 and BAY 60-2770 blunted Ca2+responses to histamine in cells exposed to 50% O2. The effects of BAY 41-2272 and BAY 60-2770 were reversed by protein kinase G inhibition. These novel data demonstrate that BAY 41-2272 and BAY 60-2770 stimulate production of cGMP and blunt hyperoxia-induced increases in Ca2+responses in developing ASM. Accordingly, sGC stimulators/activators may be a useful therapeutic strategy in improving bronchodilation in preterm infants.

Calcilytics reduce airway hyperresponsiveness and inflammation and may represent effective asthma therapeutics.

Neurally derived tachykinins such as substance P (SP) play a key role in modulating airway contractility (especially with inflammation). Separately, the neurotrophin brain-derived neurotrophic factor (BDNF; potentially derived from nerves as well as airway smooth muscle; ASM) and its tropomyosin-related kinase receptor, TrkB, are involved in enhanced airway contractility. In this study, we hypothesized that neurokinins and neurotrophins are linked in enhancing intracellular Ca2+ concentration ([Ca2+]i) regulation in ASM. In rat ASM cells, 24 h exposure to 10 nM SP significantly increased BDNF and TrkB expression ( P < 0.05). Furthermore, [Ca2+]i responses to 1 μM ACh as well as BDNF (30 min) effects on [Ca2+]i regulation were enhanced by prior SP exposure, largely via increased Ca2+ influx ( P < 0.05). The enhancing effect of SP on BDNF signaling was blunted by the neurokinin-2 receptor antagonist MEN-10376 (1 μM, P < 0.05) to a greater extent than the neurokinin-1 receptor antagonist RP-67580 (5 nM). Chelation of extracellular BDNF (chimeric TrkB-Fc; 1 μg/ml), as well as tyrosine kinase inhibition (100 nM K252a), substantially blunted SP effects ( P < 0.05). Overnight (24 h) exposure of ASM cells to 50% oxygen increased BDNF and TrkB expression and potentiated both SP- and BDNF-induced enhancement of [Ca2+]i ( P < 0.05). These results suggest a novel interaction between SP and BDNF in regulating agonist-induced [Ca2+]i regulation in ASM. The autocrine mechanism we present here represents a new area in the development of bronchoconstrictive reflex response and airway hyperreactive disorders.