Altered CD38/Cyclic ADP-Ribose Signaling Contributes to the Asthmatic Phenotype

Estrogenic Modulation of Ionic Channels, Pumps and Exchangers in Airway Smooth Muscle

To preserve ionic homeostasis (primarily Ca²⁺, K⁺, Na⁺, and Cl^-), in the airway smooth muscle (ASM) numerous transporters (channels, exchangers, and pumps) regulate the influx and efflux of these ions. Many of intracellular processes depend on continuous ionic permeation, including exocytosis, contraction, metabolism, transcription, fecundation, proliferation, and apoptosis. These mechanisms are precisely regulated, for instance, through hormonal activity. The lipophilic nature of steroidal hormones allows their free transit into the cell where, in most cases, they occupy their cognate receptor to generate genomic actions. In the sense, estrogens can stimulate development, proliferation, migration, and survival of target cells, including in lung physiology. Non-genomic actions on the other hand do not imply estrogen's intracellular receptor occupation, nor do they initiate transcription and are mostly immediate to the stimulus. Among estrogen's non genomic responses regulation of calcium homeostasis and contraction and relaxation processes play paramount roles in ASM. On the other hand, disruption of calcium homeostasis has been closely associated with some ASM pathological mechanism. Thus, this paper intends to summarize the effects of estrogen on ionic handling proteins in ASM. The considerable diversity, range and power of estrogens regulates ionic homeostasis through genomic and non-genomic mechanisms.

High-fat-diet induces airway hyperresponsiveness partly through activating CD38 signaling pathway

CD38 is a plasma membrane bound multifunctional enzyme. It can be activated by inflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-13, inducing calcium responses to agonist in airway smooth muscle cells (ASMC). Previous studies have found that high-fat-diet (HFD) induced obesity exhibited innate airway hyperresponsiveness (AHR). This study aimed to detect the effect of CD38 signaling pathway on the AHR of overweight/obese mice. The HFD-fed mice exhibited a significantly higher baseline airway resistance (Rn), and the increasing rates of Rn responded to increasing doses of methacholine compared with the LFD-fed mice. High-fat-diet increased CD38 expressions both in lung tissues and primary cultured ASMCs. Besides, preincubation with TNF-α led to a higher expression of CD38 protein and increased intracellular calcium in ASMC of the HFD-fed mice. Furthermore, CD38 gene knockdown through transfection of CD38 siRNA decreased the concentration of intracellular calcium. Additionally, the upregulations of CD38 protein and CD38 mRNA were also found in the lung tissues of HFD-fed mice challenged by ovalbumin (OVA). Collectively, our findings demonstrated a role of CD38 signaling pathway on the AHR of obesity and might be a potential therapeutic target for treating difficult-to-control obese asthma phenotype.

Gene expression analysis in asthma using a targeted multiplex array

Background

Gene expression changes in the structural cells of the airways are thought to play a role in the development of asthma and airway hyperresponsiveness. This includes changes to smooth muscle contractile machinery and epithelial barrier integrity genes. We used a targeted gene expression arrays to identify changes in the expression and co-expression of genes important in asthma pathology.

Methods

RNA was isolated from the airways of donor lungs from 12 patients with asthma (8 fatal) and 12 non-asthmatics controls and analyzed using a multiplexed, hypothesis-directed platform to detect differences in gene expression. Genes were grouped according to their role in airway dysfunction: airway smooth muscle contraction, cytoskeleton structure and regulation, epithelial barrier function, innate and adaptive immunity, fibrosis and remodeling, and epigenetics.

Results

Differential gene expression and gene co-expression analyses were used to identify disease associated changes in the airways of asthmatics. There was significantly decreased abundance of integrin beta 6 and Ras-Related C3 Botulinum Toxin Substrate 1 (RAC1) in the airways of asthmatics, genes which are known to play an important role in barrier function. Significantly elevated levels of Collagen Type 1 Alpha 1 (COL1A1) and COL3A1 which have been shown to modulate cell proliferation and inflammation, were found in asthmatic airways. Additionally, we identified patterns of differentially co-expressed genes related to pathways involved in virus recognition and regulation of interferon production. 7 of 8 pairs of differentially co-expressed genes were found to contain CCCTC-binding factor (CTCF) motifs in their upstream promoters.

Conclusions

Changes in the abundance of genes involved in cell-cell and cell-matrix interactions could play an important role in regulating inflammation and remodeling in asthma. Additionally, our results suggest that alterations to the binding site of the transcriptional regulator CTCF could drive changes in gene expression in asthmatic airways. Several asthma susceptibility loci are known to contain CTCF motifs and so understanding the role of this transcription factor may expand our understanding of asthma pathophysiology and therapeutic options.

Electronic supplementary material

The online version of this article (10.1186/s12890-017-0545-9) contains supplementary material, which is available to authorized users.

Abnormal corticosteroid signalling in airway smooth muscle: mechanisms and perspectives for the treatment of severe asthma

Growing in vivo evidence supports the concept that airway smooth muscle produces various immunomodulatory factors that could contribute to asthma pathogenesis via the regulation of airway inflammation, airway narrowing and remodelling. Targeting ASM using bronchial thermoplasty has provided undeniable clinical benefits for patients with uncontrolled severe asthma who are refractory to glucocorticoid therapy. The present review will explain why the failure of glucocorticoids to adequately manage patients with severe asthma could derive from their inability to affect the immunomodulatory potential of ASM. We will support the view that ASM sensitivity to glucocorticoid therapy can be blunted in severe asthma and will describe some of the factors and mechanisms that could be responsible for glucocorticoid insensitivity.

Ryanodine receptor sensitization results in abnormal calcium signaling in airway smooth muscle cells

Intracellular Ca(2+) dynamics of airway smooth muscle cells (ASMCs) are believed to play a major role in airway hyperresponsiveness and remodeling in asthma. Prior studies have underscored a prominent role for inositol 1,4,5-triphosphate (IP3) receptors in normal agonist-induced Ca(2+) oscillations, whereas ryanodine receptors (RyRs) appear to remain closed during such Ca(2+) oscillations, which mediate ASMC contraction. Nevertheless, RyRs have been hypothesized to play a role in hyperresponsive Ca(2+) signaling. This could be explained by RyRs being "sensitized" to open more frequently by certain compounds. We investigate the implications of RyR sensitization on Ca(2+) dynamics in ASMC using a combination of mathematical modeling and experiments with mouse precision-cut lung slices. Caffeine is used to increase the sensitivity of RyRs to cytosolic Ca(2+) concentration ([Ca(2+)]i) and sarcoplasmic reticulum Ca(2+) ([Ca(2+)]SR). In ASMCs, high caffeine concentrations (>10 mM) induce a sustained elevation of [Ca(2+)]i. Our mathematical model accounts for this by the activation of store-operated Ca(2+) entry that results from a large increase in the RyR sensitivity to [Ca(2+)]SR and the associated Ca(2+) release, which leads to a reduction of [Ca(2+)]SR. Importantly, our model also predicts that: (1) moderate RyR sensitization induces slow Ca(2+) oscillations, a result experimentally confirmed with low concentrations of caffeine; and (2) high RyR sensitization suppresses fast, agonist-induced Ca(2+) oscillations by inducing substantial store-operated Ca(2+) entry and elevated [Ca(2+)]i. These results suggest that RyR sensitization could play a role in ASMC proliferation (by inducing slow Ca(2+) oscillations) and in airway hyperresponsiveness (by inducing greater mean [Ca(2+)]i for similar levels of contractile agonist).

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.