CD38/cADPR Signaling Pathway in Airway Disease: Regulatory Mechanisms

Asthma is an inflammatory disease in which proinflammatory cytokines have a role in inducing abnormalities of airway smooth muscle function and in the development of airway hyperresponsiveness. Inflammatory cytokines alter calcium (Ca2+) signaling and contractility of airway smooth muscle, which results in nonspecific airway hyperresponsiveness to agonists. In this context, Ca2+ regulatory mechanisms in airway smooth muscle and changes in these regulatory mechanisms encompass a major component of airway hyperresponsiveness. Although dynamic Ca2+ regulation is complex, phospholipase C/inositol tris-phosphate (PLC/IP3) and CD38-cyclic ADP-ribose (CD38/cADPR) are two major pathways mediating agonist-induced Ca2+ regulation in airway smooth muscle. Altered CD38 expression or enhanced cyclic ADP-ribosyl cyclase activity associated with CD38 contributes to human pathologies such as asthma, neoplasia, and neuroimmune diseases. This review is focused on investigations on the role of CD38-cyclic ADP-ribose signaling in airway smooth muscle in the context of transcriptional and posttranscriptional regulation of CD38 expression. The specific roles of transcription factors NF-kB and AP-1 in the transcriptional regulation of CD38 expression and of miRNAs miR-140-3p and miR-708 in the posttranscriptional regulation and the underlying mechanisms of such regulation are discussed

Crosstalk Between Diacylglycerol Kinase and Protein Kinase a in the Regulation of Airway Smooth Muscle Cell Proliferation

Background: Diacylglycerol kinase (DGK) regulates intracellular signaling and functions by converting diacylglycerol (DAG) into phosphatidic acid. We previously demonstrated that DGK inhibition attenuates airway smooth muscle (ASM) cell proliferation, however, the mechanisms mediating this effect are not well established. Given the capacity of protein kinase A (PKA) to effect inhibition of ASM cells growth in response to mitogens, we employed multiple molecular and pharmacological approaches to examine the putative role of PKA in the inhibition of mitogen-induced ASM cell proliferation by the small molecular DGK inhibitor I (DGK I). Methods: We assayed cell proliferation using CyQUANT™ NF assay, protein expression and phosphorylation using immunoblotting, and prostaglandin E2 (PGE2) secretion by ELISA. ASM cells stably expressing GFP or PKI-GFP (PKA inhibitory peptide-GFP chimera) were stimulated with platelet-derived growth factor (PDGF), or PDGF + DGK I, and cell proliferation was assessed. Results: DGK inhibition reduced ASM cell proliferation in cells expressing GFP, but not in cells expressing PKI-GFP. DGK inhibition increased cyclooxygenase II (COXII) expression and PGE2 secretion over time to promote PKA activation as demonstrated by increased phosphorylation of (PKA substrates) VASP and CREB. COXII expression and PKA activation were significantly decreased in cells pre-treated with pan-PKC (Bis I), MEK (U0126), or ERK2 (Vx11e) inhibitors suggesting a role for PKC and ERK in the COXII-PGE2-mediated activation of PKA signaling by DGK inhibition. Conclusions: Our study provides insight into the molecular pathway (DAG-PKC/ERK-COXII-PGE2-PKA) regulated by DGK in ASM cells and identifies DGK as a potential therapeutic target for mitigating ASM cell proliferation that contributes to airway remodeling in asthma

Anti-mitogenic effects of bitter taste receptor (BTR) agonists on human airway smooth muscle cells

Abstract Rationale: Obstructive diseases of airways such as asthma and COPD are characterized by airway remodeling. Clinical studies and animal models have demonstrated that ASM mass is increased in asthma, and ASM thickness is correlated with severity of the disease. Current asthma medications control inflammation and reverse airway obstruction effectively, yet have very limited effects in deterring airway remodeling. Recently we identified the expression of BTRs on human ASM cells. Activation with known BTR agonists resulted in elevation of intracellular calcium, membrane hyperpolarization and ASM relaxation. Aerosol challenge in normal and allergen sensitized- and challenged- mice resulted in a robust bronchodilation. Another recent study demonstrated that BTR expression, signaling and bronchodilatory effects are preserved during human asthma. These studies suggest that BTRs can be used as new therapeutic targets in the clinical management of obstructive lung diseases. The current study aimed at determining the effect of BTR agonists on ASM growth. Methods: Primary human ASM cells maintained in culture were pretreated with different concentrations of BTR agonists, chloroquine and quinine or vehicle, then stimulated with ASM mitogens fetal bovine serum (FBS), platelet-derived growth factor (PDGF) or epithelial growth factor (EGF). Regulation of ASM growth was subsequently assessed by cell counts, CyQuant assay and 3H-thymidine-incorporation assays. Parallel studies assessed the effects of BTR agonists on key mitogenic signaling pathways in the ASM by Western blotting. Results: In CyQuant assays, chloroquine and quinine significantly inhibited growth of normal and astmatic human ASM cells induced by each mitogen in a concentration-dependent manner. BTR agonists also inhibited increases in ASM cell number suggesting their anti-mitogenic effect is mediated via inhibition of hyperplasia. BTR agonists did not induce apoptosis or cell death in human ASM. Growth inhibitory effects of BTR agonists in ASM cells were not dependent on protein kinase A (PKA) as demonstrated for other Gs coupled G protein coupled receptor agonists (e.g. β-agonists and PGE2). Western blot analyses of key mitogenic signaling demonstrated that BTR agonists inhibit mitogen-induced activation of p42/p44, p38 and Akt pathways. Conclusion: Collectively, these data suggest that BTR agonists inhibit ASM cell growth by inhibiting key mitogenic signaling pathways in ASM via PKA-independent mechanism, suggesting a novel and unexploited mode of inhibiting ASM growth. Future studies are needed to establish in vivo effectiveness of BTR agonists on airway remodeling

Bitter taste receptors: novel therapeutic targets for asthma

Objectives: Understand identification of new class of receptors on airway cells Discuss potential therapeutic implications of bitter taste receptor signaling in airway diseases Explore experimental tools and animal models to study molecular pathogenesis of obstructive pulmonary diseases Overall Goals and Objectives: Following this activity, a participant should be able to: 1. Recognize recent advances and developments in Pulmonary Medicine & Critical Care and translate into clinical practice 2. Integrate perspectives of multiple disciplines into decision-making on behalf of patients through structured plans for patient care. 3. Develop areas for future research and discuss appropriate methods to address these needs. 4. Summarize and continually improve communications as a team, caring for Pulmonary/Critical Care patients. Presentation: 1 hou

OGR1-dependent regulation of the allergen-induced asthma phenotype

The proton-sensing receptor, ovarian cancer G protein-coupled receptor (OGR1), has been shown to be expressed in airway smooth muscle (ASM) cells and is capable of promoting ASM contraction in response to decreased extracellular pH. OGR1 knockout (OGR1KO) mice are reported to be resistant to the asthma features induced by inhaled allergen. We recently described certain benzodiazepines as OGR1 activators capable of mediating both procontractile and prorelaxant signaling in ASM cells. Here we assess the effect of treatment with the benzodiazepines lorazepam or sulazepam on the asthma phenotype in wild-type (WT) and OGR1KO mice subjected to inhaled house dust mite (HDM; Dermatophagoides pteronyssius) challenge for 3 wk. In contrast to previously published reports, both WT and OGR1KO mice developed significant allergen-induced lung inflammation and airway hyperresponsiveness (AHR). In WT mice, treatment with sulazepam (a Gs-biased OGR1 agonist), but not lorazepam (a balanced OGR1 agonist), prevented allergen-induced AHR, although neither drug inhibited lung inflammation. The protection from development of AHR conferred by sulazepam was absent in OGR1KO mice. Treatment of WT mice with sulazepam also resulted in significant inhibition of HDM-induced collagen accumulation in the lung tissue. These findings suggest that OGR1 expression is not a requirement for development of the allergen-induced asthma phenotype, but OGR1 can be targeted by the Gs-biased OGR1 agonist sulazepam (but not the balanced agonist lorazepam) to protect from allergen-induced AHR, possibly mediated via suppression of chronic bronchoconstriction and airway remodeling in the absence of effects on airway inflammation