Role of Carbon Monoxide in Oxidative Stress-Induced Senescence in Human Bronchial Epithelium.

Prolonged or excessive stimulation from inhaled toxins may cause oxidative stress and DNA damage that can lead to stress-induced senescence in epithelial cells, which can contribute to several airway diseases. Mounting evidence has shown carbon monoxide (CO) confers cytoprotective effects. We investigated the effects of CO on oxidative stress-induced senescence in human airway epithelium and elucidated the underlying molecular mechanisms. Here, CO pretreatment reduced H2O2-mediated increases in total reactive oxygen species (ROS) production and mitochondrial superoxide in a human bronchial epithelial cell line (BEAS-2B). H2O2 treatment triggered a premature senescence-like phenotype with enlarged and flattened cell morphology accompanied by increased SA-ß-gal activity, cell cycle arrest in G0/G1, reduced cell viability, and increased transcription of senescence-associated secretory phenotype (SASP) genes. Additionally, exposure to H2O2 increased protein levels of cellular senescence markers (p53 and p21), reduced Sirtuin 3 (SIRT3) and manganese superoxide dismutase (MnSOD) levels, and increased p53 K382 acetylation. These H2O2-mediated effects were attenuated by pretreatment with a CO-containing solution. SIRT3 silencing induced mitochondrial superoxide production and triggered a senescence-like phenotype, whereas overexpression decreased mitochondrial superoxide production and alleviated the senescence-like phenotype. Air-liquid interface (ALI) culture of primary human bronchial cells, which becomes a fully differentiated pseudostratified mucociliary epithelium, was used as a model. We found that apical and basolateral exposure to H2O2 induced a vacuolated structure that impaired the integrity of ALI cultures, increased goblet cell numbers, decreased SCGB1A1+ club cell numbers, increased p21 protein levels, and increased SASP gene transcription, consistent with our observations in BEAS-2B cells. These effects were attenuated in the apical presence of a CO-containing solution. In summary, we revealed that CO has a pivotal role in epithelial senescence by regulating ROS production via the SIRT3/MnSOD/p53/p21 pathway. This may have important implications in the prevention and treatment of age-associated respiratory pathologies.

ß2-Adrenoceptor Activation Stimulates IL-6 Production via PKA, ERK1/2, Src, and Beta-Arrestin2 Signaling Pathways in Human Bronchial Epithelia.

OBJECTIVE: ß2-Adrenoceptor agonists are widely used to treat asthma because of their bronchial-dilation effects. We previously reported that isoprenaline, via the apical and basolateral ß2-adrenoceptor, induced Cl- secretion by activating cyclic AMP (cAMP)-dependent pathways in human bronchial epithelia. Despite these results, whether and how the ß2-adrenoceptor-mediated cAMP-dependent pathway contributes to pro-inflammatory cytokine release in human bronchial epithelia remains poorly understood. METHODS: We investigated ß2-adrenoceptor-mediated signaling pathways involved in the production of two pro-inflammatory cytokines, interleukin (IL)-6 and IL-8, in 16HBE14o- human bronchial epithelia. The effects of isoprenaline or formoterol were assessed in the presence of protein kinase A (PKA), exchange protein directly activated by cAMP (EPAC), Src, and extracellular signal-regulated protein kinase (ERK)1/2 inhibitors. The involvement of ß-arrestin2 was examined using siRNA knockdown. RESULTS: Isoprenaline and formoterol (both ß2 agonists) induced IL-6, but not IL-8, release, which could be inhibited by ICI 118,551 (ß2 antagonist). The PKA-specific inhibitor, H89, partially inhibited IL-6 release. Another intracellular cAMP receptor, EPAC, was not involved in IL-6 release. Isoprenaline-mediated IL-6 secretion was attenuated by dasatinib, a Src inhibitor, and PD98059, an ERK1/2 inhibitor. Isoprenaline treatment also led to ERK1/2 phosphorylation. In addition, knockdown of ß-arrestin2 by siRNA specifically suppressed cytokine release when a high concentration of isoprenaline (1 mM) was used. CONCLUSION: Our results suggest that activation of the ß2-adrenoceptor in 16HBE14o- cells stimulated the PKA/Src/ERK1/2 and/or ß-arrestin2 signaling pathways, leading to IL-6 release. Therefore, our data reveal that ß2-adrenoceptor signaling plays a role in the immune regulation of human airway epithelia.

ß2 adrenoceptor signaling regulates ion transport in 16HBE14o- human airway epithelial cells.

We investigated the regulation of Cl- secretion by adrenoceptors in polarized 16HBE14o- human bronchial epithelial cells. Treatment with the nonselective ß adrenoceptor agonist isoprenaline stimulated an increase in short-circuit current (ISC ), which was inhibited by the ß adrenoceptor blocker propranolol. Treatment with procaterol, an agonist specific for the ß2 adrenoceptor subtype, stimulated a similar increase in ISC , which was inhibited by the ß2 adrenoceptor antagonist ICI 118551. Inhibitors of cystic fibrosis transmembrane conductance regulator (CFTR) and calcium-activated Cl- channel (CaCC), but not K+ channel blockers, were able to inhibit the increase in ISC . "Trimultaneous" recording of ISC and intracellular cyclic adenosine monophosphate (cAMP) and Ca2+ levels in 16HBE14o- epithelia confirmed that the ISC induced by isoprenaline or procaterol involved both cAMP and Ca2+ signaling. Our results demonstrate that ß2 adrenoceptors regulate Cl- secretion in the human airway epithelium by activating apical CFTRs and CaCCs via cAMP-dependent and intracellular Ca2+ -dependent mechanisms, respectively.

Anti-inflammatory action of HO-1/CO in human bronchial epithelium in response to cationic polypeptide challenge.

Carbon monoxide (CO) is an anti-inflammatory gaseous molecule produced endogenously by heme oxygenases (HOs) HO-1 and HO-2. However, the mechanisms underlying the anti-inflammatory effects of CO in the human bronchial epithelium are still not fully understood. In this study, the cationic peptide poly-l-arginine (PLA) was utilized to induce bronchial epithelial damage and subsequent pro-inflammatory cytokine release in the human bronchial epithelial cell line 16HBE14o-. Expression of both HO-1 and HO-2 after PLA exposure was examined. The polarized secretion of two pro-inflammatory cytokines, interleukin (IL)-6 and IL-8, was determined by ELISA. The anti-inflammatory effects of CO liberated from CO-releasing molecules (CORMs) were examined by both ELISA and western blot analysis. Our results indicate that PLA exposure leads to upregulation of HO-1 expression and p65 NF-κB phosphorylation, as well as IL-6 and IL-8 release. HO-1 induction by hemin or CORMs significantly suppressed IL-6 and IL-8 release. In addition, HO-1 knockdown further increased IL-6 and IL-8 release under basal and PLA-stimulated conditions. Our results thereby demonstrate that the HO-1/CO axis exerts significant anti-inflammatory activity during bronchial epithelial damage caused by cationic protein.

Carbon Monoxide Inhibits Cytokine and Chloride Secretion in Human Bronchial Epithelia.

BACKGROUND/AIMS: Carbon monoxide (CO) is an important gas produced endogenously by heme oxygenase (HO) that functions as an anti-inflammatory and in ion channel modulation, but the effects of CO on airway inflammation and ion transport remains unclear. METHODS: The effect of CO on cell damage- and nucleotide-induced pro-inflammatory cytokine release in primary human bronchial epithelia cells (HBE) and in the 16HBE14o- human bronchial epithelial cell line were investigated. The effects of CO on calcium- and cAMP-dependent chloride (Cl-) secretion were examined using a technique that allowed the simultaneous measurement and quantification of real-time changes in signalling molecules (cAMP and Ca2+) and ion transport in a polarised epithelium. RESULTS: CO suppressed the release of interleukin (IL)-6 and IL-8 and decreased the phosphorylation of ERK1/2 and NF-κB p65. Furthermore, CO inhibited UTP-induced increases in calcium and Cl- secretion, and forskolin-induced increases in cAMP and Cl- secretion. CONCLUSIONS: These findings suggest a novel anti-inflammatory role of CO in human bronchial epithelia via interactions with purinergic signalling pathways. Further, CO modulated both the Ca2+- and cAMP-dependent secretion of Cl-.

Regulation of Intracellular Calcium by Carbon Monoxide in Human Bronchial Epithelial Cells.

BACKGROUND/AIMS: Carbon monoxide (CO) is an important autocrine/paracrine messenger involved in a variety of physiological and pathological processes. This study aimed to investigate the regulatory role of CO released by CO-releasing molecule-2 (CORM-2) in a P2Y receptor-mediated calcium-signaling pathway in the human bronchial epithelial cell line, 16HBE14o-. METHODS: Intracellular calcium ([Ca2+]i) was measured by fura-2 microspectrofluorimetry. D-myo-inositol-1-phosphate (IP1) levels and cGMP-dependent protein kinase activity (PKG) were also quantified. RESULTS: The exogenous application of CORM-2 increased both intracellular Ca2+ and IP1, which are inhibited by U73122, a phospholipase C (PLC) inhibitor. In contrast, the P2Y2/P2Y4 receptor-mediated intracellular Ca2+ release and influx induced by UTP were inhibited in the presence of CORM-2. However, CORM-2 did not affect the store-operated Ca2+ entry (SOCE) induced by thapsigargin (Tg). Moreover, the inhibitory effect of CORM-2 on UTP-induced calcium increase could be attenuated by a soluble guanylyl cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), or a Protein Kinase G (PKG) inhibitor, KT5823, suggesting the involvement of sGC/PKG signaling in this process. CONCLUSION: CORM-2 serves a dual role in modulating [Ca2+]i in 16HBE14o- cells. Thus, CO released by CORM-2 may act as a regulator of calcium homeostasis in human airway epithelia. These findings help further elucidate the function of CO in many physiological and pathological conditions.