Epithelial Notch signaling regulates lung alveolar morphogenesis and airway epithelial integrity

Abnormal enlargement of the alveolar spaces is a hallmark of conditions such as chronic obstructive pulmonary disease and bronchopulmonary dysplasia. Notch signaling is crucial for differentiation and regeneration and repair of the airway epithelium. However, how Notch influences the alveolar compartment and integrates this process with airway development remains little understood. Here we report a prominent role of Notch signaling in the epithelial-mesenchymal interactions that lead to alveolar formation in the developing lung. We found that alveolar type II cells are major sites of Notch2 activation and show by Notch2-specific epithelial deletion (Notch2(cNull)) a unique contribution of this receptor to alveologenesis. Epithelial Notch2 was required for type II cell induction of the PDGF-A ligand and subsequent paracrine activation of PDGF receptor-α signaling in alveolar myofibroblast progenitors. Moreover, Notch2 was crucial in maintaining the integrity of the epithelial and smooth muscle layers of the distal conducting airways. Our data suggest that epithelial Notch signaling regulates multiple aspects of postnatal development in the distal lung and may represent a potential target for intervention in pulmonary diseases.

Augmented acetylcholine-induced translocation of RhoA in bronchial smooth muscle from antigen-induced airway hyperresponsive rats

Acetylcholine (ACh)-induced translocation of RhoA in bronchial smooth muscle of repeatedly antigen-challenged rats that have a marked airway hyperresponsiveness (AHR) was examined. ACh induced time- and concentration-dependent translocation of RhoA to the plasma membrane, indicating an activation of RhoA in bronchial smooth muscle. The level of ACh-induced RhoA translocation was further increased markedly in the AHR group as compared to that in the control group. It is suggested that the augmented activation of RhoA observed in the hyperresponsive bronchial smooth muscle might be responsible for the enhanced ACh-induced Ca(2+) sensitization of bronchial smooth muscle contraction associated with AHR.

RGS4 Overexpression in Lung Attenuates Airway Hyperresponsiveness in Mice

A cardinal feature of asthma is airway hyperresponsiveness (AHR) to spasmogens, many of which activate G protein-coupled receptors (GPCRs) on airway smooth muscle (ASM) cells. Asthma subtypes associated with allergy are characterized by eosinophilic inflammation in the lung due to the type 2 immune response to allergens and proinflammatory mediators that promote AHR. The degree to which intrinsic abnormalities of ASM contribute to this phenotype remains unknown. The regulators of G protein signaling (RGS) proteins are a large group of intracellular proteins that inhibit GPCR signaling pathways. RGS2- and RGS5-deficient mice develop AHR spontaneously. Although RGS4 is upregulated in ASM from patients with severe asthma, the effects of increased RGS4 expression on AHR in vivo are unknown. Here, we examined the impact of forced RGS4 overexpression in lung on AHR using transgenic (Tg) mice. Tg RGS4 was expressed in bronchial epithelium and ASM in vivo, and protein expression in lung was increased at least 4-fold in Tg mice compared with wild-type (WT) mice. Lung slices from Tg mice contracted less in response to the m3 muscarinic receptor agonist methacholine compared with the WT, although airway resistance in live, unchallenged mice of both strains was similar. Tg mice were partially protected against AHR induced by fungal allergen challenge due to weakened contraction signaling in ASM and reduced type 2 cytokine (IL-5 and IL-13) levels in Tg mice compared with the WT. These results provide support for the hypothesis that increasing RGS4 expression and/or function could be a viable therapeutic strategy for asthma.

Arachidonate-regulated Ca(2+) influx in human airway smooth muscle

Plasma membrane Ca(2+) influx, especially store-operated Ca(2+) entry triggered by sarcoplasmic reticulum (SR) Ca(2+) release, is a key component of intracellular calcium concentration ([Ca(2+)]i) regulation in airway smooth muscle (ASM). Agonist-induced Ca(2+) oscillations in ASM that involve both influx and SR mechanisms have been previously demonstrated. In nonexcitable cells, [Ca(2+)]i oscillations involve Ca(2+) influx via arachidonic acid (AA) -stimulated channels, which show similarities to store-operated Ca(2+) entry, although their molecular identity remains undetermined. Little is known about AA-regulated Ca(2+) channels or their regulation in ASM. In enzymatically dissociated human ASM cells loaded with the Ca(2+) indicator, fura-2, AA (1-10 μM) triggered [Ca(2+)]i oscillations that were inhibited by removal of extracellular Ca(2+). Other fatty acids, such as the diacylglycerol analog, 1-oleoyl-2-acetyl-SN-glycerol, oleic acid, and palmitic acid (10 μM each), failed to elicit similar [Ca(2+)]i responses. Preincubation with LaCl3 (1 μM or 1 mM) inhibited AA-induced oscillations. Inhibition of receptor-operated channels (SKF96,365 [10 μM]), lipoxygenase (zileuton [10 μM]), or cyclooxygenase (indomethacin [10 μM]) did not affect oscillation parameters. Inhibition of SR Ca(2+) release (ryanodine [10 μM] or inositol 1,4,5-trisphosphate receptor inhibitor, xestospongin C [1 μM]) decreased [Ca(2+)]i oscillation frequency and amplitude. Small interfering RNA against caveolin-1, stromal interaction molecule 1, or Orai3 (20 nM each) reduced the frequency and amplitude of AA-induced [Ca(2+)]i oscillations. In ASM cells derived from individuals with asthma, AA increased oscillation amplitude, but not frequency. These results are highly suggestive of a novel AA-mediated Ca(2+)-regulatory mechanism in human ASM, reminiscent of agonist-induced oscillations. Given the role of AA in ASM intracellular signaling, especially with inflammation, AA-regulated Ca(2+) channels could potentially contribute to increased [Ca(2+)]i in diseases such asthma.

Intranasal administration of recombinant progranulin inhibits bronchial smooth muscle hyperresponsiveness in mouse allergic asthma

Progranulin (PGRN) is a growth factor with multiple biological functions and has been suggested as an endogenous inhibitor of Tumor necrosis factor-α (TNF-α)-mediated signaling. TNF-α is believed to be one of the important mediators of the pathogenesis of asthma, including airway hyperresponsiveness (AHR). In the present study, effects of recombinant PGRN on TNF-α-mediated signaling and antigen-induced hypercontractility were examined in bronchial smooth muscles (BSMs) both in vitro and in vivo. Cultured human BSM cells (hBSMCs) and male BALB/c mice were used. The mice were sensitized and repeatedly challenged with ovalbumin antigen. Animals also received intranasal administrations of recombinant PGRN into the airways 1 h before each antigen inhalation. In hBSMCs, PGRN inhibited both the degradation of IκB-α (an index of NF-κB activation) and the upregulation of RhoA (a contractile machinery-associated protein that contributes to the BSM hyperresponsiveness) induced by TNF-α, indicating that PGRN has an ability to inhibit TNF-α-mediated signaling also in the BSM cells. In BSMs of the repeatedly antigen-challenged mice, an augmented contractile responsiveness to acetylcholine with an upregulation of RhoA was observed: both the events were ameliorated by pretreatments with PGRN intranasally. Interestingly, a significant decrease in PGRN expression was found in the airways of the repeatedly antigen-challenged mice rather than those of control animals. In conclusion, exogenously applied PGRN into the airways ameliorated the antigen-induced BSM hyperresponsiveness, probably by blocking TNF-α-mediated response. Increasing PGRN levels might be a promising therapeutic for AHR in allergic asthma.

Functional Cooperation between KCa3.1 and TRPV4 Channels in Bronchial Smooth Muscle Cell Proliferation Associated with Chronic Asthma

Airway smooth muscle cells (SMC) proliferation contributes to the airways remodeling and irreversible airway obstruction during severe asthma, but the mechanisms of airway SMC proliferation are poorly understood. Intracellular Ca²⁺ levels play an important role in regulating cell proliferation. We have previously reported KCa3.1 channels regulated human bronchial smooth muscle (HBSM) cells proliferation via the Ca²⁺ influx as a consequence of membrane hyperpolarization. However, the role of potassium channels KCa3.1 in airway remodeling as well as the mechanism for extracellular Ca²⁺ influx induced by the activation of KCa3.1 remains unknown. Here we demonstrated that KCa3.1 channels deficiency attenuated airway remodeling, airway inflammation, and airway hyperresponsiveness (AHR) in a mouse model of chronic asthma. The gene expressions of repressor element 1-silencing transcription factor (REST) and c-Jun, two transcriptional regulators of KCa3.1 channels, were correlated negatively or positively with KCa3.1 channels expressions both in vivo and in vitro using real-time PCR and Western blot analyses. RNAi-mediated knockdown or pharmacological blockade of KCa3.1 and TRPV4 significantly attenuated HBSM cells proliferation. Using confocal imaging and custom data analysis software, blockade of TRPV4 decreased the Ca²⁺ influx induced by 1-EBIO-mediated KCa3.1 activation. Double-labeled staining showed that KCa3.1 and TRPV4 channels colocalized in HBSM cells. These results demonstrate that KCa3.1 channels regulate the proliferation phenotype of HBSM cells via TRPV4 channels in the process of chronic asthma, making it a potential therapeutic target to treat chronic asthma.

Attenuation of relaxing response induced by pituitary adenylate cyclase-activating polypeptide in bronchial smooth muscle of experimental asthma

Bronchomotor tone is regulated by contraction and relaxation of airway smooth muscle (ASM). A weakened ASM relaxation might be a cause of airway hyperresponsiveness (AHR), a characteristic feature of bronchial asthma. Pituitary adenylyl cyclase-activating polypeptide (PACAP) is known as a mediator that causes ASM relaxation. To date, whether or not the PACAP responsiveness is changed in asthmatic ASM is unknown. The current study examined the hypothesis that relaxation induced by PACAP is reduced in bronchial smooth muscle (BSM) of allergic asthma. The ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Twenty-four hours after the last antigen challenge, the main bronchial smooth muscle (BSM) tissues were isolated. Tension study showed a BSM hyperresponsiveness to acetylcholine in the OA-challenged mice. Both quantitative RT-PCR and immunoblot analyses revealed a significant decrease in PAC₁ receptor expression in BSMs of the diseased mice. Accordingly, in the antigen-challenged group, the PACAP-induced PAC₁ receptor-mediated BSM relaxation was significantly attenuated, whereas the relaxation induced by vasoactive intestinal polypeptide was not changed. These findings suggest that the relaxation induced by PACAP is impaired in BSMs of experimental asthma due to a downregulation of its binding partner PAC₁ receptor. Impaired BSM responsiveness to PACAP might contribute to the AHR in asthma.

Stimulation of airway sensory nerves by cyclosporin A and FK506 in guinea-pig isolated bronchus

We have investigated the contractile property of cyclosporin A and FK506 in guinea-pig isolated bronchus. Cyclosporin A (10 microM) failed to significantly attenuate the excitatory non-adrenergic non-cholinergic (eNANC) and cholinergic contractile response (per cent methacholine Emax) induced by electrical field stimulation (EFS). In contrast, eNANC responses were significantly attenuated by both the neurokinin (NK)-1 and (NK)-2 receptor antagonists, N-acetyl-L-tryptophan 3,5-bis (trifluoromethyl)-benzyl and SR48968, respectively. Cyclosporin A and FK506 caused a concentration-dependent contraction in guinea-pig isolated bronchus, which was significantly attenuated by NK-1 and NK-2 receptor antagonists. The capsaicin receptor antagonist, capsazepine (10 microM) significantly reduced the contractile response to cyclosporin A and capsaicin, but not to FK506. The N-type calcium channel blocker, omega-Conotoxin (omegaCTX: 10 nM), significantly reduced the contractile response to FK506 and the eNANC response following EFS. In contrast, omega-CTX failed to significantly reduce the contractile potency to capsaicin or cyclosporin A. In bronchial preparations desensitized by repeated application of capsaicin (1 microM), the contractile responses to both cyclosporin A (100 microM) and FK506 (100 microM), were significantly reduced. In contrast, the contractile responses to substance P and neurokinin A (10 microM) were not altered. Furthermore, repeated application of cyclosporin A (100 microM) significantly inhibited the contractile response to capsaicin (1 microM). The findings from this study would indicate that cyclosporin A and FK506 mediate contraction of guinea-pig isolated bronchus secondary to the release of neuropeptides from airway sensory nerves. However, the release of sensory neuropeptides appears to be mediated via different mechanisms for cyclosporin A and FK506, the former by stimulation of the vanilloid receptor and the latter via opening of N-type calcium channels.

Role of TRPP2 in mouse airway smooth muscle tension and respiration

The transient receptor potential polycystin-2 (TRPP2) is encoded by the Pkd2 gene, and mutation of this gene can cause autosomal dominant polycystic kidney disease (ADPKD). Some patients with ADPKD experience extrarenal manifestations, including radiologic and clinical bronchiectasis. We hypothesized that TRPP2 may regulate airway smooth muscle (ASM) tension. Thus, we used smooth muscle-Pkd2 conditional knockout (Pkd2^SM-CKO) mice to investigate whether TRPP2 regulated ASM tension and whether TRPP2 deficiency contributed to bronchiectasis associated with ADPKD. Compared with wild-type mice, Pkd2^SM-CKO mice breathed more shallowly and faster, and their cross-sectional area ratio of bronchi to accompanying pulmonary arteries was higher, suggesting that TRPP2 may regulate ASM tension and contribute to the occurrence of bronchiectasis in ADPKD. In a bioassay examining isolated tracheal ring tension, no significant difference was found for high-potassium-induced depolarization of the ASM between the two groups, indicating that TRPP2 does not regulate depolarization-induced ASM contraction. By contrast, carbachol-induced contraction of the ASM derived from Pkd2^SM-CKO mice was significantly reduced compared with that in wild-type mice. In addition, relaxation of the carbachol-precontracted ASM by isoprenaline, a β-adrenergic receptor agonist that acts through the cAMP/adenylyl cyclase pathway, was also significantly attenuated in Pkd2^SM-CKO mice compared with that in wild-type mice. Thus, TRPP2 deficiency suppressed both contraction and relaxation of the ASM. These results provide a potential target for regulating ASM tension and for developing therapeutic alternatives for some ADPKD complications of the respiratory system or for independent respiratory disease, especially bronchiectasis.

Increased Rac1 Activation in the Enhanced Carbachol-Induced Bronchial Smooth Muscle Contraction of Repeatedly Antigen-Challenged Mice

Recently, we demonstrated that Rac1 upregulation is involved in augmented bronchial smooth muscle (BSM) contractions of antigen-challenged mice. However, change in G protein-coupled receptor (GPCR)-induced Rac1 activation remains unknown in BSMs of repeatedly antigen-challenged (Chal.) mice. We here examined carbachol (CCh)-induced Rac1 activation in BSMs of Chal. mice. Gene expression levels of both Rac1 and Rac-guanine nucleotide exchange factors (GEFs), such as Tiam1 and Trio, were increased in BSMs of Chal. mice. Furthermore, CCh-induced Rac1 activation was inhibited by pretreatment with Rac1-GEF inhibitor NSC23766 and Rac1 inhibitor EHT1864 in BSMs of sensitized-control (S.C.) and Chal. mice. Compared with S.C. mice, CCh-induced Rac1 activation was increased in BSMs of Chal. mice. In conclusion, we reported that increased CCh-induced Rac1 activation via Tiam1 and Trio upregulation, in addition to upregulate Rac1, may be involved in increased CCh-induced BSM contractions in Chal. mice.

Beta-Hydroxybutyrate Attenuates Bronchial Smooth Muscle Pro-Inflammatory Cytokine Production

Asthma is a common airway condition causing breathing difficulties due to reversible airflow obstruction. It often affects obese individuals, with symptoms triggered by environmental factors that induce immune responses, leading to inflammation and bronchoconstriction. Bronchial smooth muscle (BSM) plays a central role in airway narrowing, driven by type 2 immune responses involving cytokines like IL-4, IL-5, and IL-13, along with leukocytes including eosinophils and type 2 T-helper cells. These responses cause structural changes such as fibrosis and airway thickening, while BSM cells worsen asthma by releasing pro-inflammatory cytokines in response to allergens, microbial signals, or inflammatory cytokines from other cells. While current treatments manage asthma in most patients, alternative therapies are needed for difficult-to-treat cases, particularly prevalent in obese, allergic individuals. Emerging research suggests that therapeutic ketosis, induced by dietary changes or ketone supplementation, may reduce airway hyperresponsiveness and inflammation. The primary ketone body, β-hydroxybutyrate (BHB), produced during carbohydrate scarcity, acts via cell-surface receptors and transporters, potentially mitigating asthma symptoms. Weight loss and caloric restriction increase ketone levels, correlating with reduced inflammation and improved asthma outcomes. We hypothesized that β-hydroxybutyrate (BHB) reduces bronchoconstriction and inflammation in asthma by targeting bronchial smooth muscle. Using human bronchial smooth muscle cells (HBSMC) in vitro, we demonstrate herein that BHB suppresses IL-1β-induced pro-inflammatory cytokine production through Free Fatty Acid Receptor 3 (FFAR3) activation. These findings suggest that bronchial smooth muscle is a key target of therapeutic ketosis, supporting BHB's potential benefits in preclinical asthma models.

Augmented bronchial smooth muscle contractility induced by aqueous cigarette smoke extract in rats

Cigarette smoking is the main risk factor for the development of chronic obstructive pulmonary disease (COPD). However, little is known about the mechanisms of cigarette smoke-induced bronchial smooth muscle (BSM) hyperresponsiveness. In the present study, we investigated the effects of aqueous cigarette smoke extract (ACSE) on the BSM contraction in rats. The bronchial strips of rats were incubated with ACSE or control-extract for 24 h. The acetylcholine (ACh), high K(+) depolarization and sodium fluoride (NaF)-induced BSM contraction of the ACSE-treated group was significantly augmented as compared to that of the control one. The expression levels of both myosin light-chain kinase (MLCK) and RhoA were significantly increased in the ACSE-treated BSM. These findings suggest that the water-soluble components of cigarette smoke may cause BSM hyperresponsiveness via an increase in MLCK and RhoA.

Extracellular acidification attenuates bronchial contraction via an autocrine activation of EP2 receptor: Its diminishment in murine experimental asthma

PURPOSE

Extracellular acidification is a major component of tissue inflammation, including airway inflammation in asthmatics. However, its physiological/pathophysiological significance in bronchial function is not fully understood. Currently, the functional role of extracellular acidification on bronchial contraction was explored.

METHODS

Left main bronchi were isolated from male BALB/c mice. Epithelium-removed tissues were exposed to acidic pH under submaximal contraction induced by 10-5 M acetylcholine in the presence or absence of a COX inhibitor indomethacin (10-6 M). Effects of AH6809 (10-6 M, an EP2 receptor antagonist), BW A868C (10-7 M, a DP receptor antagonist) and CAY10441 (3×10-6 M, an IP receptor antagonist) on the acidification-induced change in tension were determined. The release of prostaglandin E2 (PGE2) from epithelium-denuded tissues in response to acidic pH was assessed using an ELISA.

RESULTS

In the bronchi stimulated with acetylcholine, change in the extracellular pH from 7.4 to 6.8 caused a transient augmentation of contraction followed by a sustained relaxing response. The latter inhibitory response was abolished by indomethacin and AH6809 but not by BW A868C or CAY10441. Both indomethacin and AH6809 significantly increased potency and efficacy of acetylcholine at pH 6.8. Stimulation with low pH caused an increase in PGE2 release from epithelium-denuded bronchi. Interestingly, the acidic pH-induced bronchial relaxation was significantly reduced in a murine asthma model that had a bronchial hyperresponsiveness to acetylcholine.

CONCLUSION

Taken together, extracellular acidification could inhibit the bronchial contraction via autocrine activation of EP2 receptors. The diminished acidic pH-mediated inhibition of bronchial tone may contribute to excessive bronchoconstriction in inflamed airways such as asthma.

Bariatric surgery decreases the capacity of plasma from obese asthmatic subjects to augment airway epithelial cell proinflammatory cytokine production

Obesity is a risk factor for asthma. Individuals with asthma and obesity often have poor asthma control and do not respond as well to therapies such as inhaled corticosteroids and long-acting bronchodilators. Weight loss improves asthma control, with a 5%-10% loss in body mass necessary and sufficient to lead to clinically relevant improvements. Preclinical studies have demonstrated the pathogenic contribution of adipocytes from obese mice to the augmented production of proinflammatory cytokines from airway epithelial cells and the salutary effects of diet-induced weight loss to decrease these consequences. However, the effects of adipocyte-derived products on airway epithelial function in human obesity remain incompletely understood. We utilized samples collected from a 12-mo longitudinal study of subjects with obesity undergoing weight loss (bariatric) surgery including controls without asthma and subjects with allergic and nonallergic obese asthma. Visceral adipose tissue (VAT) samples were collected during bariatric surgery and from recruited normal weight controls without asthma undergoing elective abdominal surgery. Human bronchial epithelial (HBEC3-KT) cells were exposed to plasma or conditioned media from cultured VAT adipocytes with or without agonists. Human bronchial smooth muscle (HBSM) cells were similarly exposed to adipocyte-conditioned media. Proinflammatory cytokines were augmented in supernatants from HBEC3-KT cells exposed to plasma as compared with subsequent visits. Whereas exposure to obese adipocyte-conditioned media induced proinflammatory responses, there were no differences between groups in both HBEC3-KT and HBSM cells. These data show that bariatric surgery and subsequent weight loss beneficially change the circulating factors that augment human airway epithelial and bronchial smooth muscle cell proinflammatory responses.NEW & NOTEWORTHY This longitudinal study following subjects with asthma and obesity reveals that weight loss following bariatric surgery decreases the capacity for plasma to augment proinflammatory cytokine secretion by human bronchial epithelial cells, implicating that circulating but not adipocyte-derived factors are important modulators in obese asthma.