Nasal cytokine responses to natural colds in asthmatic children

Background

The mechanisms by which viruses induce asthma exacerbations are not well understood.

Objective

We characterized fluctuations in nasal aspirate cytokines during naturally occurring respiratory viral infections in children with asthma.

Methods

Sixteen children underwent home collections of nasal aspirates when they were without cold symptoms and again during self‐reported respiratory illnesses. The presence of viral infection was ascertained by multiplex PCR. Cytokines were measured using multiplex immune assay. mRNA expression for selected markers of viral infection was measured using RT‐PCR. A cumulative respiratory symptom score was calculated for each day of measurement. Generalized estimated equations were used to evaluate associations between viral infection and marker elevation, and between marker elevation and symptom score.

Results

The 16 patients completed a total of 37 weeks of assessment (15 ‘well’ weeks; 22 self‐assessed ‘sick’ weeks). Viral infections were detected in 3 of the ‘well’ weeks and 17 of the ‘sick’ weeks (10 rhinovirus, three coronavirus, two influenza A, two influenza B, two respiratory syncytial virus, one parainfluenza). Compared to virus‐negative well weeks, nasal aspirate IFN‐γ, CXCL8/IL‐8, CXCL10/IP‐10, CCL5/RANTES, CCL11/eotaxin‐1, CCL2/MCP‐1, CCL4/MIP‐1β, CCL7/MCP‐3, and CCL20/MIP3α protein levels increased during virus‐positive sick weeks. Only a subset of cytokines (IFN‐γ, CXCL8, CCL2, CCL4, CCL5, and CCL20) correlated with self‐reported respiratory tract symptoms. While many aspirates were dilute and showed no mRNA signal, viral infection significantly increased the number of samples that were positive for IFN‐λ1, IFN‐λ2/3, TLR3, RIG‐I, and IRF7 mRNA.

Conclusions and clinical relevance

We conclude that in children with asthma, naturally occurring viral infections apparently induce a robust innate immune response including expression of specific chemokines, IFNs, and IFN‐responsive genes.

German cockroach extract increases bronchial epithelial cell interleukin-8 expression

BACKGROUND

Cockroach exposure has been recognized as a common trigger for asthma. While dust mite and Aspergillus fumigatus aeroallergens have been noted to have direct effects on airway epithelium, direct effects of cockroach proteins have not been determined.

OBJECTIVE

The purpose of this study was to investigate whether cockroach extract has a direct pro-inflammatory effect on airway epithelium.

METHODS

We examined the effect of crude German cockroach (Blattella germanica) extract on IL-8 expression in a human bronchial epithelial cell line (16HBE14o-cells) and primary human bronchial epithelial cells. Transcription from the IL-8 promoter and protein abundance were determined by reporter assay and enzyme-linked immunosorbent assay (ELISA), respectively. Endotoxin levels in the crude cockroach extracts were determined using the Limulus Amebocyte Lysate assay. Protease activity was assessed using Azocoll as a substrate.

RESULTS

We found that crude cockroach extract induced a synergistic increase in TNF-alpha-induced transcription from the IL-8 promoter. The synergistic effect was observed with as little as 0.3 micro g/mL of crude cockroach extract, while larger concentrations (30 micro g/mL) approximately doubled TNF-alpha-induced IL-8 promoter activity. Similar effects of cockroach extract on IL-8 protein abundance were observed in both 16HBE14o- and primary human bronchial epithelial cells. Addition of endotoxin at concentrations found in the cockroach extract had no effect on TNF-alpha-mediated IL-8 expression. The serine protease inhibitors aprotinin and phenylmethylsulphonyl fluoride abolished cockroach-induced synergy, while the cysteine protease inhibitors E64 and leupeptin had little effect. Measurement of protease activity using Azocoll as a substrate confirmed the presence of protease activity in cockroach extracts. Addition of recombinant Bla g 2, Bla g 3 and Bla g 5 had no effect on TNF-alpha-induced IL-8 promoter activation. Finally, cockroach extract also increased TNF-alpha-induced transcription from the IL-6 promoter.

CONCLUSIONS

German cockroach extract contains novel serine protease activity which has a direct pro-inflammatory effect on airway epithelial cells

Cdc42, but not RhoA, regulates cyclin D1 expression in bovine tracheal myocytes

We previously demonstrated that Rac1 increased cyclin D1 promoter activity in an extracellular signal-regulated kinase (ERK)-independent, antioxidant-sensitive manner. Here, we examined the regulation of cyclin D1 expression by Cdc42 and RhoA. Overexpression of active Cdc42, but not of RhoA, induced transcription from the cyclin D1 promoter. Furthermore, dominant negative Cdc42, but not RhoA, attenuated platelet-derived growth factor-mediated activation of the cyclin D1 promoter. Overexpression of active Cdc42 increased cyclin D1 protein abundance in COS cells. Cdc42-induced cyclin D1 promoter activation was independent of ERK as evidenced by insensitivity to PD-98059, an inhibitor of mitogen-activated protein kinase/ERK kinase (MEK). Furthermore, Cdc42 was neither sufficient nor required for activation of ERK. Similar to Rac1-induced cyclin D1 expression, pretreatment with the antioxidants catalase and ebselen inhibited Cdc42-mediated transcription from the cyclin D1 promoter. Finally, like Rac1, active Cdc42 induced transactivation of the cyclin D1 promoter cAMP response element binding protein/activating transcription factor-2 binding site. Together, these data suggest that in airway smooth muscle cells, Cdc42 and Rac1 share a common signaling pathway to cyclin D1 promoter activation.

p38 MAP kinase negatively regulates cyclin D1 expression in airway smooth muscle cells

We have demonstrated that platelet-derived growth factor (PDGF) stimulates p38 mitogen-activated protein (MAP) kinase activation in bovine tracheal myocytes, suggesting that p38 is involved in growth regulation. We therefore examined whether p38 regulates expression of cyclin D1, a G(1) cyclin required for cell cycle traversal. The chemical p38 inhibitors SB-202190 and SB-203580 each increased basal and PDGF-induced cyclin D1 promoter activity and protein abundance. Overexpression of a dominant negative allele of MAP kinase kinase-3 (MKK3), an upstream activator of p38alpha, had similar effects. Conversely, active MKK3 and MKK6, both of which increase p38alpha activity, each decreased transcription from the cyclin D1 promoter. Together, these data demonstrate that p38 negatively regulates cyclin D1 expression. We tested whether p38 regulates cyclin D1 expression via inhibition of extracellular signal-regulated kinase (ERK) activation. Chemical inhibitors of p38 induced modest ERK phosphorylation and activation. However, dominant negative MKK3 was insufficient to activate ERK, and active MKK3 and MKK6 did not attenuate platelet-derived growth factor-mediated ERK activation. These data are consistent with the notion that p38alpha negatively regulates cyclin D1 expression via an ERK-independent pathway.

Pertussis toxin directly activates endothelial cell p42/p44 MAP kinases via a novel signaling pathway

Bordetella pertussis generates a bacterial toxin utilized in signal transduction investigation because of its ability to ADP ribosylate specific G proteins. We previously noted that pertussis toxin (PTX) directly activates endothelial cells, resulting in disruption of monolayer integrity and intercellular gap formation via a signaling pathway that involves protein kinase C (PKC). We studied the effect of PTX on the activity of the 42- and 44-kDa extracellular signal-regulated kinases (ERK), members of a kinase family known to be activated by PKC. PTX caused a rapid time-dependent increase in bovine pulmonary artery endothelial cell ERK activity that was significantly attenuated by 1) pharmacological inhibition of MEK, the upstream ERK activating kinase, 2) an MEK dominant-negative construct, and 3) PKC inhibition with bisindolylmaleimide. There was little evidence for the involvement of either Gbetagamma-subunits, Ras GTPases, Raf-1, p60(src), or phosphatidylinositol 3'-kinases in PTX-mediated ERK activation. Both the purified beta-oligomer binding subunit of the PTX holotoxin and a PTX holotoxin mutant genetically engineered to eliminate intrinsic ADP ribosyltransferase activity completely reproduced PTX effects on ERK activation, suggesting that PTX-induced ERK activation involves a novel PKC-dependent signaling mechanism that is independent of either Ras or Raf-1 activities and does not require G protein ADP ribosylation.

Regulation of cyclin D(1) expression and DNA synthesis by phosphatidylinositol 3-kinase in airway smooth muscle cells

We have shown in bovine tracheal myocytes that extracellular signal-regulated kinase (ERK) and Rac1 function as upstream activators of transcription from the cyclin D(1) promoter. We now examine the role of phosphatidylinositol (PI) 3-kinase in this process. PI 3-kinase activity was increased by platelet-derived growth factor (PDGF) and attenuated by the PI 3-kinase inhibitors wortmannin and LY294002. These inhibitors also decreased cyclin D(1) promoter activity, protein abundance, and DNA synthesis. Overexpression of the active catalytic subunit of PI 3-kinase (p110(PI) (3-K)CAAX) was sufficient to activate the cyclin D(1) promoter. Wortmannin and LY294002 failed to attenuate PDGF-induced ERK activation, and overexpression of p110(PI) (3-K)CAAX was insufficient to activate ERK. p110(PI) (3-K)CAAX-induced cyclin D(1) promoter activity was not blocked by PD98059, an inhibitor of mitogen-activated protein kinase/ERK kinase. We next examined whether PI 3-kinase and the 21-kD guanidine triphosphatase Rac1 regulate cyclin D(1) promoter activity by similar mechanisms. p110(PI) (3-K)CAAX-induced cyclin D(1) promoter activity was decreased by two inhibitors of Rac1-mediated signaling, catalase and diphenylene iodonium. Further, PDGF, PI 3-kinase, and Rac1 each activated the cyclin D(1) promoter at the cyclic adenosine monophosphate response element binding protein (CREB)/activating transcription factor (ATF)-2 binding site, as evidenced by expression of a CREB/ATF-2 reporter plasmid. Finally, PI 3-kinase and Rac1-induced CREB/ATF-2 transactivation were each inhibited by catalase. Together, these data suggest that in airway smooth muscle (ASM) cells, PI 3-kinase regulates transcription from the cyclin D(1) promoter and DNA synthesis in an ERK-independent manner. Further, PI 3-kinase and Rac1 regulate ASM cell cycle traversal via a common cis-regulatory element in the cyclin D(1) promoter.

Physiological control of smooth muscle-specific gene expression through regulated nuclear translocation of serum response factor

Prolonged serum deprivation induces a structurally and functionally contractile phenotype in about 1/6 of cultured airway myocytes, which exhibit morphological elongation and accumulate abundant contractile apparatus-associated proteins. We tested the hypothesis that transcriptional activation of genes encoding these proteins accounts for their accumulation during this phenotypic transition by measuring the transcriptional activities of the murine SM22 and human smooth muscle myosin heavy chain promoters during transient transfection in subconfluent, serum fed or 7 day serum-deprived cultured canine tracheal smooth muscle cells. Contrary to our expectation, SM22 and smooth muscle myosin heavy chain promoter activities (but not viral murine sarcoma virus-long terminal repeat promoter activity) were decreased in long term serum-deprived myocytes by at least 8-fold. Because serum response factor (SRF) is a required transcriptional activator of these and other smooth muscle-specific promoters, we evaluated the expression and function of SRF in subconfluent and long term serum-deprived cells. Whole cell SRF mRNA and protein were maintained at high levels in serum-deprived myocytes, but SRF transcription-promoting activity, nuclear SRF binding to consensus CArG sequences, and nuclear SRF protein were reduced. Furthermore, immunocytochemistry revealed extranuclear redistribution of SRF in serum-deprived myocytes; nuclear localization of SRF was restored after serum refeeding. These results uncover a novel mechanism for physiological control of smooth muscle-specific gene expression through extranuclear redistribution of SRF and consequent down-regulation of its transcription-promoting activity.

Role of ras-dependent ERK activation in phorbol ester-induced endothelial cell barrier dysfunction

The treatment of endothelial cell monolayers with phorbol 12-myristate 13-acetate (PMA), a direct protein kinase C (PKC) activator, leads to disruption of endothelial cell monolayer integrity and intercellular gap formation. Selective inhibition of PKC (with bisindolylmaleimide) and extracellular signal-regulated kinases (ERKs; with PD-98059, olomoucine, or ERK antisense oligonucleotides) significantly attenuated PMA-induced reductions in transmonolayer electrical resistance consistent with PKC- and ERK-mediated endothelial cell barrier regulation. An inhibitor of the dual-specificity ERK kinase (MEK), PD-98059, completely abolished PMA-induced ERK activation. PMA also produced significant time-dependent increases in the activity of Raf-1, a Ser/Thr kinase known to activate MEK ( approximately 6-fold increase over basal level). Similarly, PMA increased the activity of Ras, which binds and activates Raf-1 ( approximately 80% increase over basal level). The Ras inhibitor farnesyltransferase inhibitor III (100 microM for 3 h) completely abolished PMA-induced Raf-1 activation. Taken together, these data suggest that the sequential activation of Ras, Raf-1, and MEK are involved in PKC-dependent endothelial cell barrier regulation.

Mitogen-activated signaling and cell cycle regulation in airway smooth muscle

Increased airway smooth muscle mass has been demonstrated in patients with bronchopulmonary dysplasia and asthma. These data highlight the need for a precise understanding of the events involved in airway smooth muscle mitogenesis. To that end, investigators have developed cell culture systems adopting tracheal and bronchial myocytes from different species. A growing body of literature suggests that common signal transduction pathways regulate airway smooth muscle cell cycle entry across species lines. This review summarizes what is known about mitogen-activated signal transduction in airway smooth muscle cells. The extracellular signal regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI 3-kinase) pathways appear to be major positive regulators of airway smooth muscle proliferation. It is also conceivable that growth factor stimulation of airway smooth muscle simultaneously elicits signaling through negative regulatory pathways such as the p38 mitogen-activated protein (MAP) kinase pathway, perhaps as a safeguard against excessive growth.

Bronchoalveolar lavage fluid from asthmatic subjects is mitogenic for human airway smooth muscle

Airway smooth muscle proliferation may contribute to the airway wall remodeling seen in asthma. In this study we tested for the presence of airway smooth muscle mitogenic activity in bronchoalveolar lavage (BAL) fluid obtained from 12 atopic asthmatics before and serially after segmental allergen challenge, and from four normal subjects who did not undergo allergen challenge. Mitogenic effect was assessed by coincubating BAL fluid with human airway smooth muscle cells, and measuring its effect on (3)[H]thymidine incorporation and cell number. Induction of ERK phosphorylation and cyclin D(1) protein abundance were also assessed. Compared with serum-free medium alone, BAL fluid obtained from normal subjects increased thymidine incorporation, cell number, ERK phosphorylation, and cyclin D(1) abundance. BAL fluid from asthmatic subjects prior to allergen challenge induced even greater increases in all measures, except for cell number, which was similar to that observed with normal subjects' BAL fluid. Incubation with lavage fluid obtained 48 h after segmental allergen challenge in atopic asthmatics caused yet further increases in thymidine incorporation, cell number, and cyclin D(1) protein abundance. Molecular sieving of prechallenge BAL fluid from three asthmatic subjects demonstrated that mitogenic activity was present exclusively in the > 10 kD fraction. These results provide the first direct demonstration that fluid lining the airways of asthmatics contains excess mitogenic activity for human airway smooth muscle, and that this activity increases further after allergen challenge.

Characterization of a Rac1 signaling pathway to cyclin D(1) expression in airway smooth muscle cells

We examined the importance of the Rho family GTPase Rac1 for cyclin D(1) promoter transcriptional activation in bovine tracheal myocytes. Overexpression of active Rac1 induced transcription from the cyclin D(1) promoter, whereas platelet-derived growth factor (PDGF)-induced transcription was inhibited by a dominant-negative allele of Rac1, suggesting that Rac1 functions as an upstream activator of cyclin D(1) in this system. Rac1 forms part of the NADPH oxidase complex that generates reactive oxygen species such as H(2)O(2). PDGF stimulated a substantial increase in intracellular reactive oxygen species, as measured by the fluorescence of dichlorofluorescein-loaded cells, and this was blocked by the glutathione peroxidase mimetic ebselen. Pretreatment with ebselen, catalase, and the flavoprotein inhibitor diphenylene iodonium each attenuated PDGF- and Rac1-mediated cyclin D(1) promoter activation, while having no effect on the induction of cyclin D(1) by mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase-1 (MEK1), the upstream activator of ERKs. Antioxidant treatment also inhibited PDGF-induced cyclin D(1) protein expression and DNA synthesis. Overexpression of an N-terminal fragment of p67(phox), a component of NADPH oxidase which interacts with Rac1, attenuated PDGF-induced cyclin D(1) promoter activity, whereas overexpression of the wild-type p67 did not. Finally, Rac1 was neither required nor sufficient for ERK activation. Taken together, these data suggest a model by which two distinct signaling pathways, the ERK and Rac1 pathways, positively regulate cyclin D(1) and smooth muscle growth.

Platelet-derived growth factor stimulation of mitogen-activated protein kinases and cyclin D1 promoter activity in cultured airway smooth-muscle cells. Role of Ras

We hypothesized that in bovine tracheal myocytes, growth factor treatment induces transcription from the cyclin D1 promoter that is dependent on the activation of both Ras and extracellular signal-related kinase (ERK). We found that platelet-derived growth factor (PDGF) treatment induced substantial activation of ERK2 that was blocked by expression of a dominant-negative Ha-Ras. Further, expression of a constitutively active Ha-Ras induced substantial ERK2 activity, consistent with the notion that Ras is required and sufficient for ERK activation. PDGF treatment induced only modest activation of the Jun amino terminal kinase-1 (JNK1) and p38 mitogen-activated protein kinases (MAPKs). Active Ras induced similar responses, implying that complete activation of the JNK and p38 pathways requires additional or alternative upstream signaling intermediates besides Ras. In contrast, expression of a constitutively active Rac1, an alternative guanosine triphosphatase involved in intracellular signaling, produced a high level of JNK1 activation, suggesting that Rac1 is an important upstream activator of JNK in this system. Active Ras and MAPK/ ERK kinase-1 (MEK1) (the upstream activator of ERK) each induced cyclin D1 promoter activity, whereas active stress-activated protein kinase/ERK kinase-1 (SEK1), an upstream activator of JNK, did not. Finally, the synthetic MEK inhibitor PD98059 blocked Ras-induced cyclin D1 promoter activity. Together, these data suggest that in bovine tracheal myocytes: (1) activation of MAPK by PDGF is dependent on Ras; (2) active Ras is sufficient for ERK activation but is insufficient for maximal activation of JNK or p38; (3) activation of Rac1 is sufficient for maximal JNK activation; and (4) Ras, MEK, and ERK constitute a distinct pathway to cyclin D1 transcriptional activation.

Partial characterization of a novel mitogen-activated protein kinase/extracellular signal-regulated kinase activator in airway smooth-muscle cells

We demonstrated previously that in bovine tracheal myocytes, pretreatment with either forskolin or histamine significantly reduces both platelet-derived growth factor (PDGF)- and epidermal growth factor- induced Raf-1 activation but fails to inhibit extracellular signal-regulated kinase (ERK) activation substantially, evidence of a Raf-1-independent ERK activation pathway. To identify Raf-1-independent upstream signaling intermediates of mitogen-activated protein kinase/ERK kinase-1 (MEK1), the dual-function kinase required and sufficient for ERK activation in these cells, lysates from forskolin and PDGF-treated bovine tracheal myocytes were resolved using ion exchange chromatography. Kinase activity for MEK1 was assessed by in vitro phosphorylation assay. In all experiments, the major peak of MEK1 phosphorylation activity was detected in fractions 18 through 26 (80 to 160 mM NaCl), with the peak fraction eluting at a NaCl concentration of 140 mM. The ability of these fractions to activate MEK1 was confirmed by examining the phosphorylation of myelin basic protein, a known substrate for ERKs, in the presence of functional MEK1 and ERK1. Fractions containing kinase activity were also probed with antibodies against MEK kinase-1, Raf-1, A-Raf, B-Raf, Mos, and Tpl-2. None of these proteins was detected in fractions containing peak kinase activity, suggesting the presence of a novel PDGF-stimulated, forskolin-insensitive MEK1 kinase. Further separation of fractions holding peak MEK phosphorylation activity by gel filtration suggested an apparent molecular mass of 40 to 45 kD. We conclude that PDGF-induced activation of MEK1 in bovine tracheal myocytes is mediated at least in part by a novel kinase.

Extracellular signal-regulated kinase 7 (ERK7), a novel ERK with a C-terminal domain that regulates its activity, its cellular localization, and cell growth

Mitogen-activated protein (MAP) kinases play distinct roles in a variety of cellular signaling pathways and are regulated through multiple mechanisms. In this study, a novel 61-kDa member of the MAP kinase family, termed extracellular signal-regulated kinase 7 (ERK7), has been cloned and characterized. Although it has the signature TEY activation motif of ERK1 and ERK2, ERK7 is not activated by extracellular stimuli that typically activate ERK1 and ERK2 or by common activators of c-Jun N-terminal kinase (JNK) and p38 kinase. Instead, ERK7 has appreciable constitutive activity in serum-starved cells that is dependent on the presence of its C-terminal domain. Interestingly, the C-terminal tail, not the kinase domain, of ERK7 regulates its nuclear localization and inhibition of growth. Taken together, these results elucidate a novel type of MAP kinase whereby interactions via its C-terminal tail, rather than extracellular signal-mediated activation cascades, regulate its activity, localization, and function.

Forskolin inhibits cyclin D1 expression in cultured airway smooth-muscle cells

Accumulation of intracellular cyclic adenosine monophosphate (cAMP) has been shown to inhibit the growth of cultured airway smooth-muscle cells, but the precise mechanism underlying the antimitogenic action of cAMP in these cells is unknown. We examined the effects of forskolin, an activator of adenylate cyclase, on DNA synthesis, cyclin D1 expression, and cAMP response element-binding protein (CREB) phosphorylation and DNA binding in bovine tracheal myocytes. DNA synthesis was assessed by measurement of [3H]thymidine incorporation. Cyclin D1 protein abundance and CREB phosphorylation were assessed by immunoblotting. Cyclin D1 promoter transcriptional activation was determined by measurement of luciferase activity in cells transiently cotransfected with complementary DNAs encoding the full-length cyclin D1 promoter subcloned into a luciferase reporter and beta-galactosidase (to normalize for transfection efficiency). The binding of nuclear proteins to the cyclin D1 promoter cAMP response element (CRE) was determined by electrophoretic mobility shift assay. We found that forskolin attenuated platelet-derived growth factor-induced DNA synthesis in a concentration-dependent manner. In addition, forskolin pretreatment decreased both cyclin D1 promoter activity and protein levels. Forskolin treatment induced the phosphorylation of CREB and increased the binding of nuclear protein to the cyclin D1 promoter CRE. Finally, addition of an antibody against CREB1 induced supershift of at least one protein-DNA complex. Together, these data suggest that cAMP suppresses cyclin D1 gene expression via phosphorylation and transactivation of CREB. Further studies are needed to determine whether this is the primary mechanism of cAMP-induced growth inhibition, or whether additional pathways are also involved.

Divergent differentiation paths in airway smooth muscle culture: induction of functionally contractile myocytes

We tested the hypothesis that prolonged serum deprivation would allow a subset of cultured airway myocytes to reacquire the abundant contractile protein content, marked shortening capacity, and elongated morphology characteristic of contractile cells within intact tissue. Passage 1 or 2 canine tracheal smooth muscle (SM) cells were grown to confluence, then serum deprived for up to 19 days. During serum deprivation, two differentiation pathways emerged. One-sixth of the cells developed an elongated morphology and aligned into bundles. Elongated myocytes contained cables of contractile myofilaments, dense bodies, gap junctions, and membrane caveoli, ultrastructural features of contractile SM in tissue. These cells immunostained intensely for SM alpha-actin, SM myosin heavy chain (MHC), and SM22 (an SM-specific actin-binding protein), and Western analysis of culture lysates disclosed 1.8 (SM alpha-actin)-, 7.7 (SM MHC)-, and 5.8 (SM22)-fold protein increases during serum deprivation. Immunoreactive M3 muscarinic receptors were present in dense foci distributed throughout elongated, SM MHC-positive myocytes. ACh (10(-3) M) induced a marked shortening (59.7 +/- 14.4% of original length) in 62% of elongated myocytes made semiadherent by gentle proteolytic digestion, and membrane bleb formation (a consequence of contraction) occurred in all stimulated cells that remained adherent and so did not shorten. Cultured airway myocytes that did not elongate during serum deprivation instead became short and flattened, lost immunoreactivity for contractile proteins, lacked the M3 muscarinic-receptor expression pattern seen in elongated cells, and exhibited no contractile response to ACh. Thus we demonstrate that prolonged serum deprivation induces distinct differentiation pathways in confluent cultured tracheal myocytes and that one subpopulation acquires an unequivocally functional contractile phenotype in which structure and function resemble contractile myocytes from intact tissue.

Airway remodeling: potential contributions of subepithelial fibrosis and airway smooth muscle hypertrophy/hyperplasia to airway narrowing in asthma

Recently, much attention has been focused on the airway structural changes accompanying chronic, severe asthma, and the potential ramifications of these changes for airway function and medical management. Airway remodeling may exaggerate airway narrowing by: (i) thickening of the airway wall internal to the smooth muscle, thereby increasing the luminal obstruction generated by a given degree of smooth muscle shortening; (ii) increasing the amount of smooth muscle, thereby increasing shortening; and/or (iii) reducing the load on the smooth muscle, either by increasing the compliance of the airway wall or by reducing airway-parenchymal interdependence. The possibility also exists that airway remodeling represents a protective mechanism against excessive airway narrowing. The major airway structural changes occurring in asthma are subepithelial protein deposition and increased airway smooth muscle mass (hypertrophy, hyperplasia, or both). Several investigators have found correlations between the magnitudes of subepithelial thickening and smooth muscle hypertrophy/hyperplasia and the severity of airways disease, though interpretation has been made difficult by study differences in patient population, treatment, indices of disease severity, and morphometric technique. Taken together, these data suggest that increases in airway remodeling may contribute significantly to the airflow obstruction observed in patients with asthma. However, data proving a causal relationship between airway remodeling and asthma severity remain elusive.

Transcriptional regulation of smooth muscle contractile apparatus expression

The transcriptional regulatory mechanisms that control gene expression during differentiation and contractile protein accumulation are becoming well understood in skeletal and cardiac muscle lineages. Current understanding of smooth muscle-specific gene transcription is much more limited, though recent studies have begun to shed light on this topic. In this review, we summarize some of the themes emerging from these studies and identify transcriptional regulatory elements common to several smooth muscle genes. These include potential binding sites for serum response factor, Sp1, AP2, Mhox, and YY1, as well as a potential transforming growth factor-beta control element. We speculate that it may be possible to manipulate smooth muscle-specific gene expression in asthma or pulmonary arterial hypertension as an eventual therapy.

Catalytic activation of extracellular signal-regulated kinases induces cyclin D1 expression in primary tracheal myocytes

We have demonstrated that extracellular signal-regulated kinases (ERKs) and cyclin D1 are required for bovine tracheal myocyte DNA synthesis. We hypothesized that catalytic activation by ERKs may regulate cyclin D1 expression in these cells. To test this hypothesis, we examined the effects of two inhibitors of ERKs and two reagents that increase the level of activated ERKs on cyclin D1 protein abundance and promoter activity. ERK activity was inhibited either by PD98059, a synthetic inhibitor of mitogen-activated protein kinase (MAPK)/ERK kinase (MEK), the upstream signaling intermediate required and sufficient for ERK activation, or by transient transfection with a dominant-negative mutant of MEK1 (MEK-2A). The level of activated ERKs was increased by transient transfection with either a constitutively active form of MEK1 (MEK-2E) or wild-type ERK2 (MAPKwt). Cyclin D1 expression was assessed either by immunoblot or cotransfection with the full-length cyclin D1 promoter subcloned into a luciferase reporter. We found that pretreatment of bovine tracheal myocytes with PD98059 significantly attenuated platelet- derived growth factor (PDGF)-induced cyclin D1 protein abundance. Furthermore, transfection with MEK-2A reduced PDGF-induced cyclin D1 promoter activity. Finally, transfection with either MEK-2E or MAPKwt induced cyclin D1 promoter activity in the absence of growth factor treatment. We conclude that catalytic activation of ERKs regulates cyclin D1 expression in airway smooth-muscle cells.

Hydrogen peroxide activates extracellular signal-regulated kinase via protein kinase C, Raf-1, and MEK1

We have previously demonstrated that hydrogen peroxide (H2O2) treatment of bovine tracheal myocytes increases the activity of extracellular signal-regulated kinases (ERK), serine/threonine kinases of the mitogen-activated protein (MAP) kinase superfamily thought to play a key role in the transduction of mitogenic signals to the cell nucleus. Moreover, H2O2-induced ERK activation was partially reduced by pretreatment with phorbol 12,13-dibutyrate, which depletes protein kinase C (PKC). In this study, we further examined the signaling intermediates responsible for ERK activation by H2O2 in airway smooth muscle, focusing on MAP kinase/ERK kinase (MEK), a dual-function kinase which is required and sufficient for ERK activation in bovine tracheal myocytes; Raf-1, a serine/threonine kinase known to activate MEK; and PKC. Pretreatment of cells with inhibitors of MEK (PD98059), Raf-1 (forskolin), and PKC (chelerythrine) each reduced H2O2-induced ERK activity. In addition, H2O2 treatment significantly increased both MEK1 and Raf-1 activity. No activation of MEK2 was detected. Together these data suggest that H2O2 may stimulate ERK via successive activation of PKC, Raf-1, and MEK1.

Adhesion of bovine airway smooth muscle cells activates extracellular signal-regulated kinases

Extracellular signal-regulated kinases (ERKs) phosphorylate and regulate cytoskeletal components of contractile cells and have been implicated in integrin-mediated adhesion. In this study, we examined the contributions of adherence, cell flattening, and cytoskeletal reorganization to adhesion-induced ERK activation in cultured bovine tracheal myocytes. We found, as evidenced by a reduction in electrophoretic mobility, that adhesion to fibronectin induced phosphorylation of both p44ERK1 and p42ERK2. In-gel kinase assays confirmed activation of both p44ERK1 and p42ERK2 in fibronectin-adherent cells, consistent with the notion that ligand-integrin binding is required for adhesion-induced ERK activation. However, ERK activation was maximal 2-4 h after plating, and adherence to either polystyrene or poly-L-lysine also caused ERK activation (fold increase 4 h after plating: fibronectin, 3.75 +/- 0.33; polystyrene, 3.95 +/- 0.78; poly-L-lysine, 2.14 +/- 0.36). Inspection of myocytes following passage onto fibronectin showed near 100% adhesion and cell spreading after 4 h, whereas cells plated onto poly-L-lysine demonstrated adherence but minimal spreading. To test whether the cytoskeletal reorganization accompanying cell spreading is required for adhesion-induced ERK activation, we assessed ERK activity following pretreatment with cytochalasin D, an inhibitor of actin polymerization. Cytochalasin inhibited both cell spreading and ERK activation following adhesion to fibronectin, but had no effect on growth factor-induced ERK activation in adherent cells. We conclude that adhesion-induced ERK activation in bovine tracheal myocytes may occur independently of ligand-integrin binding and is primarily related to the cell spreading that follows adhesion.

Src tyrosine kinase mediates stimulation of Raf-1 and mitogen-activated protein kinase by the tumor promoter thapsigargin

Thapsigargin is a non-phorbol ester-type tumor promoter that elevates the intracellular Ca2+ (Ca(i)2+) levels by blocking the microsomal Ca2+ ATPase. At present, the consequence of this Ca(i)2+ increase and the nature of the tumorigenicity of thapsigargin still remain to be elucidated. Previously, we demonstrated that thapsigargin activates the mitogen-activated protein (MAP) kinase via Ca(i)2+ but independently of protein kinase C or Ca2+ influx. Here, we show that thapsigargin also rapidly stimulates the Src tyrosine kinase. Transfection of a v-Src gene into a hippocampal cell line (H19-7) renders a constitutive activation of MAP kinase, whereas transfection of a kinase-deficient Src mutant blocks the activation by thapsigargin, suggesting that Src is required for the thapsigargin-induced MAP kinase activation. Cotransfection of a dominant-inhibitory Raf-1 and the v-Src genes into H19-7 cells results in an inhibition of the otherwise constitutively elevated MAP kinase activity, suggesting that Raf-1 is required for the Src-dependent activation of MAP kinase. Similarly, in the LA-90 cells, expression of a temperature-sensitive allele of v-Src constitutively activates Raf-1 and MAP kinase, whereas expression of a dominant-inhibitory Raf-1 mutant abolishes the MAP kinase activation induced by either v-Src or thapsigargin treatment. Together, these results suggest that thapsigargin stimulates MAP kinase signaling via Src and Raf-1. The activation of this Src-MAP kinase pathway suggests a biochemical mechanism for the tumorigenic nature of thapsigargin.

Mitogen-activated signaling in cultured airway smooth muscle cells

Airway hyperresponsiveness and excess smooth muscle mass coexist in patients with asthma and bronchopulmonary dysplasia. This increase in airway smooth muscle mass, which in part relates to smooth muscle proliferation, may increase bronchoconstrictor-induced airway narrowing, even in the absence of excessive force generation. Thus, there is need for a precise understanding of the events involved in airway smooth muscle mitogenesis. This review examines the inflammatory substances and growth factors that induce airway smooth muscle proliferation, and the signaling pathways that may be involved in the transduction of these extracellular signals to the cell nucleus. Also discussed are various antimitogenic substances and potential mechanisms underlying the inhibition of cell proliferation. Central to the discussion are the extracellular signal regulated kinases (ERKs), serine/threonine kinases of the mitogen-activated protein kinase (MAP kinase) superfamily, which upon activation, translocate from the cytoplasm to the nucleus after mitogenic stimulation. Insight gained from studies of cultured airway smooth muscle growth and mitogen-activated signaling may shed light on parallel mechanisms that may operate in asthma and in bronchopulmonary dysplasia, and may lead to therapeutic interventions against airway remodeling.

Cyclin D1 is required for S phase traversal in bovine tracheal myocytes

We examined the role of cyclin D1 in cultured bovine tracheal myocyte mitogenesis. Immunoblots using a polyclonal antibody against cyclin D1 showed the appearance of this protein 4 h after treatment with platelet-derived growth factor (PDGF), a potent mitogen for these cells. Immunoblots utilizing an antibody against the 110-kDa retinoblastoma protein (Rb), a downstream phosphorylation target of the cyclin D1/cyclin-dependent kinase 4 (cdk4) complex, showed reduced electrophoretic mobility of this protein as early as 8 h after PDGF treatment, suggesting phosphorylation of Rb by the cyclin D1/cdk4 dimer in vivo. Epidermal growth factor (EGF), a nonmitogen, failed to induce either cyclin D1 synthesis or Rb phosphorylation. PDGF treatment of cells transiently transfected with the full-length cyclin D1 promoter subcloned into a luciferase reporter increased luciferase activity almost threefold, demonstrating transcriptional activation of the cyclin D1 promoter with mitogenic stimulation. Finally, microinjection of individual myocytes with an affinity-purified antibody against cyclin D1 reduced the percentage of cells traversing S phase after serum stimulation, as assessed by fractional bromodeoxyuridine labeling (isotype control antibody, 0.74 +/- 0.10; anti-cyclin D1, 0.22 +/- 0.04; P = 0.0001). We conclude that 1) mitogenic stimulation of cultured bovine tracheal myocytes by PDGF induces cyclin D1 transcriptional activation and protein expression, 2) cyclin D1 expression is accompanied by Rb phosphorylation, which is evidence of increased cyclin D1-associated kinase activity in vivo, and 3) microinjection of anti-cyclin D1 antibodies inhibits cellular DNA synthesis, which is evidence that cyclin D1 is required for airway smooth muscle S phase traversal.

MEK1 is required for PDGF-induced ERK activation and DNA synthesis in tracheal myocytes

We tested whether activation of mitogen-activated protein kinase/ extracellular signal-regulated kinase kinase-1 (MEK1) is required and sufficient for extracellular signal-regulated kinase (ERK) activation in airway smooth muscle cells. First, we transiently cotransfected bovine tracheal myocytes with an epitope-tagged ERK2 and a dominant-negative or a constitutively active form of the gene encoding MEK1 and assessed ERK2 activation by in vitro phosphorylation assay. Expression of the dominant-negative MEK1 inhibited platelet-derived growth factor (PDGF)-induced ERK2 activation, whereas expression of the constitutively active MEK1 induced ERK2 activation, suggesting that MEK1 is required and sufficient for ERK activation in these cells. Next, we assessed the effect of PD-98059, a synthetic MEK inhibitor, on PDGF-induced MEK1 and ERK activation. PD-98059 (10 microM) inhibited MEK1 and ERK activation, confirming that MEK1 is required for ERK activation in bovine tracheal myocytes. PD-98059 had no effect on Src or Raf-1 activity, evidence that PD-98059 is a specific inhibitor of MEK in this system. Finally, PD-98059 reduced PDGF-induced [(3)H]thymidine incorporation in a concentration-dependent manner, suggesting that catalytic activation of MEK1 and ERKs is required for DNA synthesis. We conclude that MEK1 is required for PDGF-induced ERK activation in bovine tracheal myocytes and that MEK1 and ERKs are required for PDGF-induced DNA synthesis in these cells.

p172: An alveolar type II and Clara cell specific protein with late developmental expression and upregulation by hyperoxic lung injury

The epithelium of the alveolus and distal airway meets unique requirements, functioning as a gas exchange membrane and barrier to alveolar flooding by vascular contents as well as to bloodstream contamination by airborne toxins and pathogens. Gene products specifically expressed by this epithelium, notably the surfactant apoproteins, have had important clinical application. No cell surface antigen specific for alveolar type II and Clara cells has been described. We report the biochemical characterization, tissue and developmental expression, and upregulation by injury of a 172 kD protein recognized by a monoclonal antibody, 3F9, synthesized in response to immunization with freshly isolated rat alveolar type II cells. p172 is expressed in a polarized fashion by the apical surface of rat alveolar type II and Clara cells. An immunohistochemical survey of various rat tissues and organs reveals lung specificity. p172 is first detectable in rare epithelial cells at 19 days of gestation, a time when the fully differentiated alveolar type II cell is identified by the first detection of lamellar bodies. There is a dramatic increase in p172 expression just prior to birth. Hyperoxic lung injury results in increased expression of p172. The upregulation of p172 by hyperoxia and its cell-specific expression suggests an important adaptive function.

Hyperoxia alone causes changes in lung proteoglycans and hyaluronan in neonatal rat pups

Specific changes in composition and content of lung extracellular matrix (ECM) proteoglycans (PGs) and hyaluronan (HA) have been observed during the acute response to damage in several forms of injury including infant respiratory distress syndrome (IRDS). These ECM components are thought to modulate the healing response. Hyperoxia, a contributing factor to IRDS, is known to damage both adult and developing lung, however, the extent and pattern of impairment depends on lung maturity. We hypothesized that exposing neonatal rats to hyperoxia alone might result in changes in lung HA, as well as in age-specific changes in lung PGs, similar to those shown to occur in IRDS. In control rats, lung HA decreased over the first 10 days of life, whereas rats exposed to hyperoxia exhibited a time-dependent, time-limited increase in both lung HA and lung wet weight. Histochemistry showed the HA in hyperoxia-exposed lungs to be accumulated in perivascular cuffs of medium sized arteries, and in the alveolar walls. Rats were then exposed to normoxia or hyperoxia for 7 days beginning at either 3 days of life (neonatal) or 21 days (adolescent), and lung tissue was cultured in the presence of [35S]-sulfate to label newly synthesized PGs. Proteoglycans were extracted, and analyzed by isopycnic CsCl gradient centrifugation, sequential enzymatic deglycosylation, size chromatography, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). When controlled for total protein extracted, 63% more label was incorporated into large molecular weight material in the tissue exposed to hyperoxia, with a 95% increase in incorporation in the most dense fraction, D1. [35S]-Sulfate incorporation into chondroitin and dermatan sulfate in hyperoxic tissue specifically increased 116% (242% in the D1 fraction), while incorporation into heparan sulfate remained essentially unchanged. There was a nearly fivefold increase in [35S]-sulfate incorporation into chondroitin sulfate chains in the D1 fraction. When the D1 fractions of extracts of treated and control rat lungs were compared on SDS-PAGE, a large chondroitin sulfate proteoglycan (CSPG; core protein of 195 kDa) was upregulated in the D1 fraction from hyperoxic tissue of neonatal rats, but was not detected in the lungs of adolescent animals exposed to hyperoxia. This CSPG and four additional large CSPGs were noted to be upregulated on western blotting by a polyclonal antibody directed against the G1 domain of the aggrecan protein core. We conclude that hyperoxia alone causes an increase in lung HA and lung water, and speculate that this contributes significantly to the clinical syndrome of IRDS. In addition, several large CSPGs are upregulated by hyperoxic exposure in a developmentally specific manner. We speculate that this increase in CSPGs may interfere with the normal developmental sequence of events, contributing to hypoalveolarization.

Histamine antagonizes serotonin and growth factor-induced mitogen-activated protein kinase activation in bovine tracheal smooth muscle cells

We examined the effects of the bronchoconstrictor agonists serotonin (5-hydroxytryptamine; 5-HT) and histamine on mitogen-activated protein (MAP) kinase activation in cultured bovine tracheal myocytes. Kinase renaturation assays demonstrated activation of the 42- and 44-kDa MAP kinases within 2 min of 5-HT exposure. MAP kinase activation was mimicked by alpha-methyl-5-HT and reduced by pretreatment with either phorbol 12,13-dibutyrate or forskolin, suggesting activation of the 5-HT2 receptor, protein kinase C, and Raf-1, respectively. Raf-1 activation was confirmed by measurement of Raf-1 activity, and the requirement of Raf-1 for 5-HT-induced MAP kinase activation was demonstrated by transient transfection of cells with a dominant-negative allele of Raf-1. Histamine pretreatment significantly inhibited 5-HT and insulin-derived growth factor-1-induced MAP kinase activation. Attenuation of MAP kinase activation was reversed by cimetidine, mimicked by forskolin, and accompanied by cAMP accumulation and inhibition of Raf-1, suggesting activation of the H2 receptor and cAMP-dependent protein kinase A. However, histamine treatment inhibited Raf-1 but not MAP kinase activation following treatment with either platelet-derived growth factor or epidermal growth factor, implying a Raf-1-independent MAP kinase activation pathway. In summary, our data suggest a model whereby 5-HT activates MAP kinase via a protein kinase C/Raf-1 pathway, and histamine attenuates MAP kinase activation by serotonin via activation of cAMP-dependent protein kinase A and inhibition of Raf-1.

Role of MAP kinase activation in bovine tracheal smooth muscle mitogenesis

Abnormal growth of airway smooth muscle may play an important role in the pathogenesis of human airway diseases. Little is known about the proliferative responses of cultured airway smooth muscle cells, nor of the precise pathways responsible for mitogenesis in these cells. We assessed DNA synthesis, cell proliferation, and mitogen-activated protein (MAP) kinase activation in bovine tracheal myocytes after exposure to four potential mitogens: platelet-derived growth factor (PDGF), epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and 5-hydroxytryptamine (5-HT). Stimulation with either PDGF or IGF-1 induced substantial increases in DNA synthesis and cell number, as reflected by [3H]thymidine incorporation, flow cytometry, and methylene blue staining. Treatment with EGF or 5-HT, on the other hand, induced only modest DNA synthesis and no increase in cell number. Immunoblots and kinase renaturation assays of cell extracts demonstrated activation of both the 42- and 44-kDa MAP kinases within minutes of either PDGF, IGF-1, EGF, or 5-HT exposure. However, relative to EGF and 5-HT stimulation, late-phase MAP kinase activation was significantly greater after treatment with the mitogens PDGF and IGF-1. We conclude that in cultured bovine tracheal myocytes 1) PDGF and IGF-1 are potent mitogens; 2) MAP kinase may be activated subsequent to stimulation of either receptor tyrosine kinases (PDGF, EGF, IGF-1) or G protein-linked receptors lacking in known tyrosine kinase activity (5-HT); and 3) unsustained MAP kinase activation is insufficient for mitogenesis. Finally, the finding that mitogenicity correlates with the late phase of MAP kinase activation is consistent with the notion that sustained MAP kinase activation is important for bovine tracheal myocyte proliferation.

Bronchoalveolar lavage fluid from immature rats with hyperoxia-induced airway remodeling is mitogenic for airway smooth muscle

We previously demonstrated that hyperoxia-exposed immature rats develop airway smooth muscle layer thickening; this remodeling appears partially attributable to smooth muscle hyperplasia. In this study, we tested the hypothesis that excess mitogenic activity for airway smooth muscle cells is present within the lungs of hyperoxia-exposed immature rats. We assessed the proliferative effect of bronchoalveolar lavage (BAL) fluid from air- and O2-exposed animals on cultured rat tracheal smooth muscle cells. BAL fluids from air- or O2-exposed immature rats increased DNA synthesis ([3H]-thymidine incorporation at 24 h of incubation) and cell number (compared with DMEM-treated control cells, at 2 days of incubation), but BAL fluid from O2-exposed animals had significantly greater mitogenic effects. This excess mitogenic activity was lipid inextractable and was ablated by trypsin digestion, indicating that at least one polypeptide growth factor was responsible; molecular sieve fractionation demonstrated a molecular weight of > 10 kD. Because platelet-derived growth factor (PDGF) has been identified in other models of hyperoxia exposure, we tested the further hypothesis that PDGF contributes to the observed excess mitogenic activity. Addition of neutralizing anti-PDGF antibodies to BAL-stimulated smooth muscle cultures did not reduce BAL fluid-induced mitogenesis. These data indicate that the lungs of O2-exposed rats contain excess mitogenic activity for airway smooth muscle, attributable to non-PDGF polypeptide growth factors. It is conceivable that this abnormal mitogenic activity contributes to O2-induced airway smooth muscle remodeling observed in immature rats in vivo.

Concentration-dependent effects of cocaine on monoamine-induced constriction of cannulated, pressurized cerebral arteries from fetal sheep

Drugs, such as cocaine, which may alter monoamine neurotransmitter responsiveness, could adversely affect the regulation of cerebral vasculature. Cocaine exhibits at least two mechanisms that may alter vascular responsiveness: synaptic uptake inhibition, which may augment response to stimulation, and Na+ channel inhibition, which may attenuate response. To help elicit the concentration-dependent effects of cocaine, the effects of cocaine on monoamine neurotransmitter responsiveness were studied in vitro on fetal sheep cerebral arteries (120 days gestation). The changes in diameter of segments of cannulated, pressurized fetal sheep cerebral artery were measured with a videomicroscaler system. Cumulative concentration-response curves (10(-10) to 10(-4)M) were generated for two monoamines, norepinephrine and serotonin, alone and in the presence of cocaine (10(-5) or 10(-4)M). Cocaine caused concentration-dependent alteration of response. At 10(-4)M, cocaine attenuated mean maximal norepinephrine-induced vasoconstriction 46.2% (P < 0.05). At 10(-5)M, cocaine increased sensitivity to norepinephrine (log EC50 decreased -6.63 +/- 0.09 to -7.11 +/- 0.03) and to serotonin (log EC50 decreased -7.24 +/- 0.04 to -7.81 +/- 0.09) (P < 0.05). The higher concentration of cocaine (10(-4)M) did not significantly decrease log EC50 norepinephrine. Cocaine (10(-4)M) also attenuated the response to single doses of norepinephrine (10(-6)M) and serotonin (10(-6)M) by 26.5% and 40.0%, respectively (P < or = 0.05). It is concluded that cocaine has concentration-dependent effects on vasoconstriction of the fetal sheep cerebral artery in vitro. This cocaine-induced alteration of cerebral vascular responsiveness to monoamines may be important in the regulation of fetal cerebral blood flow.

In vivo hyperoxic exposure increases cultured lung fibroblast proliferation and c-Ha-ras expression

Exposure to hyperoxia has been demonstrated to alter the cell number of lung fibroblasts in vivo. The precise mechanism of lung fibroblast proliferation after hyperoxic exposure has not been elucidated, however. We examined the growth characteristics of lung fibroblasts isolated from 21-day-old rats exposed to air or 100% O2 for 8 days. Cell proliferation was assessed by hemocytometry, [3H]thymidine incorporation, and fractional labeling with the thymidine analog bromodeoxyuridine. Under all conditions tested, fibroblasts isolated from O2-exposed rats grew more rapidly than those from air-exposed rats. Conditioned medium from fibroblasts isolated from hyperoxia-exposed rats failed to increase the [3H]thymidine incorporation of control cells to that observed in cells isolated from hyperoxia-exposed animals, suggesting that an autocrine growth factor was not responsible for the excess proliferation. Sensitivity to exogenous growth factors was assessed by measuring the response to increasing concentrations of insulin-like growth factor-1 (IGF-1). Relative to 1% fetal bovine serum (FBS), concentrations of IGF-1 between 3 and 30 ng/ml significantly increased the [3H]thymidine incorporation of fibroblasts derived from hyperoxic animals, whereas control cells were unresponsive to IGF-1 stimulation. The apparent sensitivity to IGF-1 led us to assess the effect of in vivo hyperoxic exposure on the expression of c-Ha-ras, which encodes a membrane-bound, GTP-binding/hydrolyzing protein essential for progression through G1 in the cell cycle. ras mRNA levels in quiescent, control cells were minimal but increased following serum stimulation. The c-Ha-ras expression of lung fibroblasts from hyperoxia-exposed animals, on the other hand, was substantial in quiescent cells and remained high after serum exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrogen peroxide stimulates mitogen-activated protein kinase in bovine tracheal myocytes: implications for human airway disease

We have shown that hyperoxic exposure of immature rats induces airway smooth muscle layer thickening and cell turnover parallel to that found in the airways of patients with bronchopulmonary dysplasia and chronic, severe asthma. We hypothesized that reactive oxygen species could promote the observed airway remodeling by directly stimulating signal transduction pathways that regulate cell growth. To test this hypothesis in cultured cells, we assessed the effects of hydrogen peroxide (H2O2) on mitogen-activated protein (MAP) kinase activation in bovine tracheal myocytes. The MAP kinases are a family of 40 to 46 kD cytosolic serine/threonine kinases that participate in the transduction of mitogenic signals to the cell nucleus. Quiescent cells were exposed to H2O2 (25 to 200 microns; 2 to 60 min), after which SDS-PAGE of cell extracts was performed. Western analysis using an anti-MAP kinase antiserum revealed a decrease in the mobility of the 42 and 44 kD MAP kinase bands after H2O2 exposures of 5 to 30 min, reflecting the phosphorylation at threonine and tyrosine residues required for enzymatic activity. MAP kinase activation was demonstrated by kinase renaturation assays, which showed an almost 4-fold increase in 42 and 44 kD MAP kinase activity. Down-regulation of protein kinase C (PKC) with phorbol 12,13-dibutyrate (PDBu) partially reduced H2O2-stimulated MAP kinase activity, suggesting that H2O2 induces MAP kinase activation via both PKC-dependent and PKC-independent pathways. Western analysis using a phosphotyrosine monoclonal antibody revealed increased tyrosine phosphorylation of proteins with approximate molecular weights of 72 and 125 kD after H2O2 exposure, demonstrating that H2O2 can stimulate the tyrosine phosphorylation of multiple cytosolic proteins, including MAP kinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperoxia increases airway cell S-phase traversal in immature rats in vivo

Exposure of 21-day-old Sprague-Dawley rats to hyperoxia (> 95% O2 for 8 days) causes thickening of the airway epithelial and smooth muscle layers. To test the hypothesis that hyperoxic exposure increases airway layer DNA synthesis, we labeled the nuclei of cells undergoing S-phase by administering the thymidine analog bromodeoxyuridine (BrdU). BrdU was administered on days 3 and 4, 5 and 6, or 7 and 8 of air or O2 exposure, and the lungs were harvested immediately thereafter. Histologic sections were stained with an avidin-biotin-immunoperoxidase stain that revealed BrdU incorporation into nuclei, and a hematoxylin counterstain. After 4 days of air or O2 exposure, there was no difference in BrdU fractional labeling between control and hyperoxic animals. Thereafter, fractional BrdU labeling of the small airway (circumference < 1,000 microns) epithelium and smooth muscle layer was significantly increased in O2-exposed animals (P < 0.01, unpaired t test). The fractional labeling of larger, central airway smooth muscle layer cells was also increased after 8 days of O2 exposure (P < 0.01). In another cohort of O2-exposed animals, measurements of airway layer dimensions demonstrated increases in small airway epithelial and smooth muscle layer thickness that paralleled the time course seen for BrdU incorporation. We conclude that O2 exposure of immature rats increases airway epithelial and smooth muscle layer cellular DNA synthesis. These data suggest that hyperplasia of airway epithelial and smooth muscle layer cells may contribute to hyperoxia-induced airway remodeling.

Recovery of airway structure and function after hyperoxic exposure in immature rats

We have previously demonstrated that hyperoxic exposure (> 95% O2 for 8 d) induces airway cholinergic hyperresponsiveness and remodeling in 21-d-old rats. To examine the potential relationship between airway hyperresponsiveness and remodeling in these animals, we exposed rats to air or hyperoxia for 8 d, returned them to air-breathing, and measured airway responsiveness to inhaled acetylcholine (ACh) and layer thicknesses immediately after or 16 or 48 d after cessation of air or O2 exposure. The ACh concentration required to increase resistance by 100% (EC200ACh) was calculated by linear interpolation. Small airway (circumference < 1,000 microns) and medium-sized, conducting airway (1,000 to 3,000 microns) epithelial and smooth muscle layer mean thicknesses and fractional areas (layer area/luminal cross-sectional area) were determined from lung sections by contour tracing using a digitizing pad and computer. As we reported previously, after 8 d of O2 exposure, group mean log EC200ACh was significantly reduced relative to that in control animals (p < 0.001). Similarly, hyperoxic exposure was associated with significant increases in all parameters of airway layer thickness assessed (p < 0.05). However, by 16 d after cessation of O2 exposure, there were no longer statistically significant differences in log EC200ACh, airway layer thickness, or fractional area between control and O2-exposed animals. Further studies, in a second cohort of animals killed 0, 3, 6, 8, or 13 d after cessation of O2 exposure, demonstrated progressive reductions in small airway epithelial and smooth muscle layer thicknesses, confirming that hyperoxia-induced airway remodeling resolves by approximately 2 wk after termination of O2 exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure of immature rats to hyperoxia increases tracheal smooth muscle stress generation in vitro

Recently, we demonstrated that chronic exposure to hyperoxia causes in vivo airway muscarinic receptor hyperresponsiveness in the developing rat [Am. J. Physiol. 262 (Lung Cell. Mol. Physiol. 6): L263-L269, 1992]. To test whether airway cholinergic hyperresponsiveness might result from intrinsic alterations in smooth muscle contractility, we measured the effect of in vivo hyperoxia on the contractile force elicited by acetylcholine (ACh) of isometrically mounted tracheal rings in vitro. Tracheal rings were obtained from 3-wk-old rats exposed to air or to > 95% O2 for 8 days. Muscarinic responses were determined by measuring the force elicited by exposure to increasing concentrations of ACh. Responses were normalized to the morphometrically determined tracheal smooth muscle cross-sectional area in a plane perpendicular to the axis of force generation. In vivo O2 exposure significantly increased maximal ACh-induced stress generation (response to 10(-3) M ACh: air, 15.92 +/- 1.37 g/mm2; O2, 21.78 +/- 1.52 g/mm2; P = 0.010). The ACh-induced stress generation of cylinders from hyperoxic rats was substantially reduced by both epithelial removal and treatment with the cyclooxygenase inhibitor indomethacin. We conclude that in vivo hyperoxic exposure increases tracheal smooth muscle contractile function in vitro and that epithelium-derived prostaglandin(s) contributes to the observed increase in maximal contractile responsiveness.

Impaired sensorineural function after allergen-induced mediator release

We tested the hypothesis that allergen-induced mediator release augments the magnitude of isocapnic dry gas hyperpnea-induced bronchoconstriction in sensitized guinea pigs. Male Hartley guinea pigs were sensitized by spontaneous inhalation of ovalbumin (OA) aerosol on days 0 and 7 of the study. On day 14, sensitized animals again breathed OA aerosol and were prospectively divided into a group that exhibited labored breathing (LB), presumably reflecting OA-induced inflammatory mediator release, and a group that did not exhibit LB at this time. Control guinea pigs breathed saline aerosol on days 0, 7, and 14. Bronchoalveolar lavage on day 17 disclosed relative eosinophilia in OA+LB, but not in OA-LB, animals. On day 17, the bronchoconstrictor responses to increasing intravenous (i.v.) doses of acetylcholine (ACh), substance P (SP), neurokinin A (NKA), and capsaicin, as well as dry gas hyperpnea, were measured in vivo in animals from each group. Control and OA-LB guinea pigs exhibited similar responses, but OA+LB animals demonstrated augmented bronchoconstriction induced by i.v. administration of ACh, SP, or NKA. However, despite their augmented responsiveness to these exogenous constrictor agonists, OA+LB animals displayed no greater bronchoconstriction after dry gas hyperpnea or i.v. capsaicin administration. It is known that both dry gas hyperpnea and i.v. capsaicin cause bronchoconstriction in guinea pigs by releasing endogenous tachykinins from airway sensory C-fibers. Thus, our results suggest that allergen-induced mediator release impairs endogenous tachykinin release from airway sensory C-fibers in guinea pigs.

Proliferation of guinea pig tracheal epithelial cells induced by calcitonin gene-related peptide

Calcitonin gene-related peptide (CGRP) is contained within and secreted by nerves and neuroepithelial bodies in the airway epithelium. To determine whether CGRP is mitogenic for airway epithelial cells, tracheal epithelial cells isolated from 26 guinea pigs were grown in primary culture for 2 days. Subconfluent cells were exposed to 10(-13) to 10(-9) M CGRP for 4 h and then returned to CGRP-free medium. Proliferation was quantified by direct cell count and by measurement of fractional labeling with the thymidine analog, bromodeoxyuridine (BrdU). CGRP exposure increased both cell number (53,980 +/- 9,870 cells after 10(-9) M CGRP versus 33,910 +/- 5,150 cells after control, P < 0.05) and fractional BrdU labeling (12.9 +/- 2.2% after 10(-11) M CGRP versus 3.9 +/- 0.9%, control; P < 0.01, n = 9) at 24 h after exposure. The mitogenic effect of CGRP persisted at least 3 days after exposure. CGRP-induced proliferation was attenuated by co-incubation with the CGRP receptor antagonist, hCGRP-(8-37). These data demonstrate that CGRP causes proliferation of guinea pig tracheal epithelial cells in primary culture through stimulation of a specific receptor, and suggest a role for this neuropeptide in regulating airway epithelial cell growth.

Hyperoxia-induced airway remodeling in immature rats. Correlation with airway responsiveness

We recently found that exposure of 21-day-old rats to hyperoxia (> 95% O2 for 8 days) significantly increased in vivo airway cholinergic responsiveness and that O2 exposure also increased airway epithelial and smooth muscle layer thicknesses in a separate cohort of animals. There was substantial variation in the magnitude of both the functional and structural responses to hyperoxia. The present study was designed to test whether the magnitude of O2-induced airway remodeling could account for individual differences in airway responsiveness after O2 exposure, as well as for the difference in responsiveness between air- and O2-exposed animals. We assessed in vivo airway responsiveness to aerosolized acetylcholine (ACh) and airway architecture in 14 O2- and 5 air-exposed, immature rats. Total respiratory system resistance was determined using a plethysmographic method. The mean thicknesses and fractional areas of the airway epithelial and smooth muscle layers were determined by contour tracing using a digitizing pad and microcomputer. Both the small (circumference < 1,000 microns) and central (circumference 1,000 to 4,000 microns) airways were studied. For O2-exposed rats, individual values of EC200 ACh correlated negatively with small airway smooth muscle layer thickness (r = -0.59, p < 0.05; ANOVA), small airway smooth muscle layer fractional area (r = -0.75, p < 0.01), small airway epithelial thickness (r = -0.54, p < 0.05), small airway epithelial fractional area (r = -0.69, p < 0.01), and central airway smooth muscle layer thickness (r = -0.53, p < 0.05). When both air- and O2-exposed animals were considered, EC200 ACh correlated negatively with all eight parameters of airway layer thickness and fractional area.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of series compliance on twitches superimposed on voluntary contractions

The activation of skeletal muscle during voluntary isometric contraction has been assessed by measuring the increase in force caused by a superimposed maximal shock to the motor nerve (the twitch-interpolation technique). When the muscle is held isometric, the increase in force with stimulation (superimposed twitch force) decreases with increasing voluntary force, and a line fit through the data can be extrapolated to maximal voluntary force at the zero twitch force axis. In a previous paper we questioned the applicability of this technique in situations where a high series compliance allows the muscle to shorten during the superimposed twitch. To explore effects of series compliance, we measured force of the adductor pollicis during voluntary isometric contractions with noncompliant and compliant loading devices. With the compliant loading device, superimposed twitch force was systematically less than with the noncompliant device, and the plot of superimposed twitch force vs. voluntary force was often concave upward, preventing easy extrapolation to maximal voluntary force. These findings are consistent with force-velocity characteristics of muscle and suggest that twitch-interpolation data must be interpreted with caution when the muscle is not held isometric during the superimposed twitch.

Endogenous sensory neuropeptide release enhances nonspecific airway responsiveness in guinea pigs

To test whether endogenous sensory neuropeptide release results in airway hyperresponsiveness to exogenous bronchoconstrictor stimuli, male Camm-Hartley guinea pigs were exposed either to capsaicin aerosol for 10 min (CAP-AER) or to saline aerosol (SAL-AER) as a control condition. The following day, animals were anesthetized, tracheostomized, and beta-adrenergically blocked with propranolol, and their bronchoconstrictor responses to intravenously administered acetylcholine (ACh), neurokinin A (NKA), or capsaicin were measured. The bronchoconstriction induced by isocapnic dry gas hyperpnea also was assessed. Compared with the SAL-AER control group, the CAP-AER-treated animals exhibited augmented bronchoconstrictor responses to ACh and NKA. In contrast, the SAL-AER and CAP-AER groups had equivalent bronchoconstrictor responses to dry gas hyperpnea and to intravenously administered capsaicin. CAP-AER treatment caused neutrophilic airway inflammation, as reflected in increased numbers of neutrophils in bronchoalveolar lavage fluid obtained from CAP-AER-treated animals. Ablation of airway c-fiber neuron function (by chronic pretreatment with capsaicin prior to capsaicin aerosol inhalation) eliminated the ACh hyperresponsiveness observed in the CAP-AER-treated animals, demonstrating that sensory nerve products play a key role in the development of this nonspecific hyperresponsiveness. Our results demonstrate that sensory nerve stimulation with capsaicin aerosol leads to nonspecific bronchoconstrictor hyperresponsiveness and cellular airway inflammation, and thus disclose another potentially important role of sensory nerves in regulating airway function.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of fatigue on maximal inspiratory pressure-flow capacity

The inspiratory muscles can be fatigued by repetitive contractions characterized by high force (inspiratory resistive loads) or high velocities of shortening (hyperpnea). The effects of fatigue induced by inspiratory resistive loaded breathing (pressure tasks) or by eucapnic hyperpnea (flow tasks) on maximal inspiratory pressure-flow capacity and rib cage and diaphragm strength were examined in five healthy adult subjects. Tasks consisted of sustaining an assigned breathing frequency, duty cycle, and either a "pressure-time product" of esophageal pressure (for the pressure tasks) or peak inspiratory flow rate (for the flow tasks). Esophageal pressure was measured during maximal inspiratory efforts against a closed glottis (Pesmax), maximal transdiaphragmatic pressure was measured during open-glottis expulsive maneuvers (Pdimax), and maximal inspiratory flow (VImax) was measured during maximal inspiratory efforts with no added external resistance before and after fatiguing pressure and flow tasks. The reduction in Pesmax) with pressure fatigue (-25 +/- 7%) was significantly greater than the change in Pesmax with flow fatigue (-8 +/- 8%, P less than 0.01). In contrast, the reductions in Pdimax (-11 +/- 8%) and VImax (-16 +/- 3%) with flow fatigue were greater than the changes in Pdimax (-0.6 +/- 4%, P less than 0.05) or VImax (-3 +/- 4%, P less than 0.05) with pressure fatigue. We conclude that respiratory muscle performance is dependent not only on the presence of fatigue but whether fatigue was induced by pressure tasks or flow tasks. The specific impairment of Pesmax and not of Pdimax or flow with pressure fatigue may reflect selective fatigue of the rib cage muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperoxia-induced airway hyperresponsiveness and remodeling in immature rats

We exposed 21-day-old rats to either normoxia or hyperoxia (greater than 95% O2) for 8 days and assessed in vivo airway responsiveness to aerosolized and intravenous methacholine (MCh) and airway architecture. Airway responsiveness was determined using a plethysmographic method. Hyperoxia increased airway cholinergic responsiveness, as reflected in a decreased mean ED200 (concentration of MCh required to increase respiratory system resistance by 100%) for both aerosolized MCh [air exposed, 5.94 +/- 2.50 vs. O2 exposed, 0.29 +/- 3.34 (SD) mg/ml, P = 0.0013, unpaired t test] and intravenous MCh (air, 1.40 x 10(-8) vs. O2, 2.45 x 10(-10) mol/kg, P = 0.0002). Airway morphometry was studied in a separate cohort of animals. After fixation by distension with Formalin at 25 cmH2O pressure, each airway cross section was photographed, and airway circumference, epithelial area, and smooth muscle layer area were determined by means of contour tracing using a digitizing pad and microcomputer. For the small airways (circumference less than 1,000 microns), hyperoxia increased both mean epithelial thickness (air, 4.88 +/- 0.53; O2, 8.64 +/- 0.90 microns) and mean smooth muscle layer thickness (air, 2.69 +/- 0.11; O2, 4.79 +/- 0.56 microns; P less than 0.0001 for each). O2 had similar effects on the larger (1,000-3,000 microns) central airways (P less than 0.0001 for both layers). We conclude that chronic hyperoxic exposure induces both airway hyperresponsiveness and airway wall thickening in immature rats.

Efficacy of adrenaline, lignocaine-adrenaline and isoprenaline as a test dose in halothane-anaesthetized lambs

It has been shown that an epidural test dose with adrenaline does not always detect an intravascular injection in halothane-anaesthetized children. To ascertain whether test dosing with other agents might be more useful, we sought to determine if and at what dose levels three different intravenous drugs (adrenaline, isoprenaline and 1% lignocaine with 1/200,000 adrenaline) produced an increase in heart rate (HR) in halothane-anaesthetized lambs. Eight 2-week-old lambs were anaesthetized with 1% halothane in oxygen. The lambs were intubated and ventilated in order to maintain end-tidal and arterial CO2 within normal limits; HR and blood pressure before and 15-180 s after the injection of four increasing doses of each drug were recorded. The same set of measurements was repeated after the intravenous injection of atropine 10 micrograms kg-1. Adrenaline-containing doses produced a more sustained increase in HR (P less than 0.05, ANOVA) at lower doses of adrenaline when atropine was injected first. This increase did not occur in all lambs, and dysrhythmias were manifest in some. Isoprenaline always produced a significant increase in HR without dysrhythmias whether atropine was given or not. We conclude that in halothane-anaesthetized lambs, isoprenaline is a more reliable indicator of intravascular injection than adrenaline.

Tolerance and dependence in neonates sedated with fentanyl during extracorporeal membrane oxygenation

We undertook a retrospective chart review of 37 neonates who received fentanyl by continuous infusion while undergoing extracorporeal membrane oxygenation (ECMO) between May 1986 and October 1988. We quantified the doses of all sedatives utilized, determined the incidence of neonatal abstinence syndrome (NAS), and identified risk factors associated with NAS. We determined peak fentanyl infusion rate, mean fentanyl infusion rate, total fentanyl dose, and duration of ECMO therapy. NAS was observed in 21 of 37 neonates (57%). In both the NAS and non-NAS neonates, mean infusion rate increased steadily during ECMO therapy, from a mean of 11.6 +/- 6.9 (SD) micrograms.kg-1.h-1 on day 1 to a mean of 52.5 +/- 19.4 (SD) micrograms.kg-1.h-1 by day 8. Total fentanyl dose and duration of ECMO were significantly greater in neonates with NAS. We found that neonates with a total dose greater than 1.6 mg/kg or an ECMO duration greater than 5 days had a significantly greater incidence of NAS (chi-squared test, P less than 0.01 and P less than 0.005; odds ratios = 7.0 and 13.9, respectively). With multiple logistic regression, ECMO duration was found to be the most powerful predictor of the occurrence of NAS. We also measured plasma fentanyl concentrations in a separate group of 5 neonates receiving fentanyl by continuous infusion for sedation. Fentanyl concentrations increased steadily during the period of infusion, suggesting the development of tolerance to the sedating effects. We conclude that continuous administration of fentanyl for sedation is associated with the uniform development of tolerance and a significant incidence of dependence. Alternative approaches to sedation should be investigated.