Rho kinase mediates serum-induced contraction in fibroblast fibers independent of myosin LC20 phosphorylation

Cigarette smoke induces endoplasmic reticulum stress and suppresses efferocytosis through the activation of RhoA

Impaired efferocytosis is a key mechanism of inflammatory lung diseases, including chronic obstructive pulmonary disease and cystic fibrosis. Cigarette smoking activates RhoA and impairs efferocytosis in alveolar macrophages, but the mechanism has not been fully elucidated. We investigated the role of endoplasmic reticulum (ER) stress induced by cigarette smoking in the disruption of efferocytosis. Both tunicamycin (10 μg/ml) and thapsigargin (0.1 and 1 μM), which are ER stress inducers, suppressed efferocytosis in J774 cells, and a Rho-associated coiled-coil-forming kinase (ROCK) inhibitor (Y27632) reversed this effect. We validated the effect of tunicamycin on efferocytosis in experiments using RAW264.7 cells. Then, we investigated the role of the unfolded protein response (UPR) in efferocytosis impaired by ER stress. A PERK inhibitor (GSK2606414) restored the efferocytosis that had been impaired by TM, and an eIF2α dephosphorylation inhibitor (salubrinal) suppressed efferocytosis. Cigarette smoke extract (CSE) induced ER stress in J774 macrophages and RhoA activation in J774 cells, and the CSE-induced ROCK activity was successfully reversed by GSK2606414 and tauroursodeoxycholic acid. Finally, we confirmed that ER stress suppresses efferocytosis in murine alveolar macrophages and that GSK2606414 could rescue this process. These data suggest that cigarette smoke-induced ER stress and the UPR play crucial roles in RhoA activation and suppression of efferocytosis in the lung.

Irradiation-tolerant lung cancer cells acquire invasive ability dependent on dephosphorylation of the myosin regulatory light chain

Radiotherapy is one of the major treatment modalities for malignancies. However, cells surviving irradiation often display high levels of invasiveness. This study shows that irradiation-tolerant lung adenocarcinoma demonstrates high invasive capability depending on dephosphorylation of the myosin regulatory light chain (MRLC). In a collagen gel overlay condition, low-invasive subclones of lung adenocarcinoma (A549P-3) showed a round morphology and diphosphorylation of MRLC. In contrast, irradiation-tolerant A549P-3 cells (A549P-3IR) displayed high invasiveness and a lower level of MRLC diphosphorylation. In addition, inhibition of MRLC phosphatase activity decreased the invasive activity. These findings suggest that A549P-3IR cells acquire high invasiveness through MRLC dephosphorylation.

Regulation of trabecular meshwork cell contraction and intraocular pressure by miR-200c

Lowering intraocular pressure (IOP) delays or prevents the loss of vision in primary open-angle glaucoma (POAG) patients with high IOP and in those with normal tension glaucoma showing progression. Abundant evidence demonstrates that inhibition of contractile machinery of the trabecular meshwork cells is an effective method to lower IOP. However, the mechanisms involved in the regulation of trabecular contraction are not well understood. Although microRNAs have been shown to play important roles in the regulation of multiple cellular functions, little is known about their potential involvement in the regulation of IOP. Here, we showed that miR-200c is a direct postranscriptional inhibitor of genes relevant to the physiologic regulation of TM cell contraction including the validated targets Zinc finger E-box binding homeobox 1 and 2 (ZEB1 and ZEB2), and formin homology 2 domain containing 1 (FHOD1), as well as three novel targets: lysophosphatidic acid receptor 1 (LPAR1/EDG2), endothelin A receptor (ETAR), and RhoA kinase (RHOA). Consistently, transfection of TM cells with miR-200c resulted in strong inhibition of contraction in collagen populated gels as well as decreased cell traction forces exerted by individual TM cells. Finally, delivery of miR-200c to the anterior chamber of living rat eyes resulted in a significant decrease in IOP, while inhibition of miR-200c using an adenoviral vector expressing a molecular sponge led to a significant increase in IOP. These results demonstrate for the first time the ability of a miRNA to regulate trabecular contraction and modulate IOP in vivo, making miR-200c a worthy candidate for exploring ways to alter trabecular contractility with therapeutic purposes in glaucoma.

Mechanical aspects of lung fibrosis: a spotlight on the myofibroblast

Contractile myofibroblasts are responsible for the irreversible alterations of the lung parenchyma that hallmark pulmonary fibrosis. In response to lung injury, a variety of different precursor cells can become activated to develop myofibroblast features, most notably formation of stress fibers and expression of α-smooth muscle actin. Starting as an acute and beneficial repair process, myofibroblast secretion of collagen and contraction frequently becomes excessive and persists. The result is accumulation of stiff scar tissue that obstructs and ultimately destroys lung function. In addition to being a consequence of myofibroblast activities, the stiffened tissue is also a major promoter of the myofibroblast. The mechanical properties of scarred lung and fibrotic foci promote myofibroblast contraction and differentiation. One essential element in this detrimental feed-forward loop is the mechanical activation of the profibrotic growth factor transforming growth factor-β1 from stores in the extracellular matrix. Interfering with myofibroblast contraction and integrin-mediated force transmission to latent transforming growth factor-β1 and matrix proteins are here presented as possible therapeutic strategies to halt fibrosis.

Involvement of reactive oxygen species in thrombin-induced pulmonary vasoconstriction

RATIONALE

Pulmonary vascular thrombosis and thrombotic arteriopathy are common pathological findings in pulmonary arterial hypertension. Thrombin may thus play an important role in the pathogenesis and pathophysiology of pulmonary arterial hypertension.

OBJECTIVES

The present study aimed to elucidate the contractile effect of thrombin in the pulmonary artery and clarify its underlying mechanisms.

METHODS

The changes in cytosolic Ca²(+) concentrations ([Ca²(+)](i)), 20-kD myosin light chain (MLC20) phosphorylation, and contraction were monitored in the isolated porcine pulmonary artery. The production of reactive oxygen species (ROS) was evaluated by fluorescence imaging.

MEASUREMENTS AND MAIN RESULTS

In the presence of extracellular Ca²(+), thrombin induced a sustained contraction accompanied by an increase in [Ca²(+)](i) and the phosphorylation of MLC20. In the absence of extracellular Ca²(+), thrombin induced a contraction without either [Ca²(+)](i) elevation or MLC20 phosphorylation. This Ca²(+)- and MLC20 phosphorylation-independent contraction was mimicked by hydrogen peroxide and inhibited by N-acetyl cysteine. Fluorescence imaging revealed thrombin to induce the production of ROS. A Rho-kinase inhibitor, Y27632, inhibited not only the thrombin-induced Ca²(+)- and MLC20 phosphorylation-dependent contraction, but also the Ca²(+)- and MLC20 phosphorylation-independent contraction and the ROS production. These effects of thrombin were mimicked by a proteinase-activated receptor 1 (PAR₁)-activating peptide.

CONCLUSIONS

This study elucidated the Ca²(+)- and MLC20 phosphorylation-independent ROS-mediated noncanonical mechanism as well as Ca²(+)- and MLC20 phosphorylation-dependent canonical mechanism that are involved in the thrombin-induced PAR₁-mediated pulmonary vasoconstriction. Rho-kinase was suggested to play multiple roles in the development of thrombin-induced pulmonary vasoconstriction.

Regulation of myofibroblast activities: calcium pulls some strings behind the scene

Myofibroblast-induced remodeling of collagenous extracellular matrix is a key component of our body's strategy to rapidly and efficiently repair damaged tissues; thus myofibroblast activity is considered crucial in assuring the mechanical integrity of vital organs and tissues after injury. Typical examples of beneficial myofibroblast activities are scarring after myocardial infarct and repair of damaged connective tissues including dermis, tendon, bone, and cartilage. However, deregulation of myofibroblast contraction causes the tissue deformities that characterize hypertrophic scars as well as organ fibrosis that ultimately leads to heart, lung, liver and kidney failure. The phenotypic features of the myofibroblast, within a spectrum going from the fibroblast to the smooth muscle cell, raise the question as to whether it regulates contraction in a fibroblast- or muscle-like fashion. In this review, we attempt to elucidate this point with a particular focus on the role of calcium signaling. We suggest that calcium plays a central role in myofibroblast biological activity not only in regulating contraction but also in mediating intracellular and extracellular mechanical signals, structurally organizing the contractile actin-myosin cytoskeleton, and establishing lines of intercellular communication.

Myofibroblast communication is controlled by intercellular mechanical coupling

Neoformation of intercellular adherens junctions accompanies the differentiation of fibroblasts into contractile myofibroblasts, a key event during development of fibrosis and in wound healing. We have previously shown that intercellular mechanical coupling of stress fibres via adherens junctions improves contraction of collagen gels by myofibroblasts. By assessing spontaneous intracellular Ca2+ oscillations, we here test whether adherens junctions mechanically coordinate myofibroblast activities. Periodic Ca2+ oscillations are synchronised between physically contacting myofibroblasts and become desynchronised upon dissociation of adherens junctions with function-blocking peptides. Similar uncoupling is obtained by inhibiting myofibroblast contraction using myosin inhibitors and by blocking mechanosensitive ion channels using Gd3+ and GSMTx4. By contrast, gap junction uncouplers do not affect myofibroblast coordination. We propose the following model of mechanical coupling for myofibroblasts: individual cell contraction is transmitted via adherens junctions and leads to the opening of mechanosensitive ion channels in adjacent cells. The resulting Ca2+ influx induces a contraction that can feed back on the first cell and/or stimulate other contacting cells. This mechanism could improve the remodelling of cell-dense tissue by coordinating the activity of myofibroblasts.

Blebbistatin inhibits the chemotaxis of vascular smooth muscle cells by disrupting the myosin II-actin interaction

Blebbistatin is a myosin II-specific inhibitor. However, the mechanism and tissue specificity of the drug are not well understood. Blebbistatin blocked the chemotaxis of vascular smooth muscle cells (VSMCs) toward sphingosylphosphorylcholine (IC(50) = 26.1 +/- 0.2 and 27.5 +/- 0.5 microM for GbaSM-4 and A7r5 cells, respectively) and platelet-derived growth factor BB (IC(50) = 32.3 +/- 0.9 and 31.6 +/- 1.3 muM for GbaSM-4 and A7r5 cells, respectively) at similar concentrations. Immunofluorescence and fluorescent resonance energy transfer analysis indicated a blebbistatin-induced disruption of the actin-myosin interaction in VSMCs. Subsequent experiments indicated that blebbistatin inhibited the Mg(2+)-ATPase activity of the unphosphorylated (IC(50) = 12.6 +/- 1.6 and 4.3 +/- 0.5 microM for gizzard and bovine stomach, respectively) and phosphorylated (IC(50) = 15.0 +/- 0.6 microM for gizzard) forms of purified smooth muscle myosin II, suggesting a direct effect on myosin II motor activity. It was further observed that the Mg(2+)-ATPase activities of gizzard myosin II fragments, heavy meromyosin (IC(50) = 14.4 +/- 1.6 microM) and subfragment 1 (IC(50) = 5.5 +/- 0.4 microM), were also inhibited by blebbistatin. Assay by in vitro motility indicated that the inhibitory effect of blebbistatin was reversible. Electron-microscopic evaluation showed that blebbistatin induced a distinct conformational change (i.e., swelling) of the myosin II head. The results suggest that the site of blebbistatin action is within the S1 portion of smooth muscle myosin II.

Embracing emerging paradigms of G protein-coupled receptor agonism and signaling to address airway smooth muscle pathobiology in asthma

G protein-coupled receptors (GPCRs) regulate numerous airway cell functions, and signaling events transduced by GPCRs are important in both asthma pathogenesis and therapy. Indeed, most asthma therapies target GPCRs either directly or indirectly. Within recent years, our understating of how GPCRs signal and are regulated has changed significantly as new concepts have emerged and traditional ideas have evolved. In this review, we discuss current concepts regarding constitutive GPCR activity and receptor agonism, functional selectivity, compartmentalized signaling, and GPCR desensitization. We further discuss the relevance of these ideas to asthma and asthma therapy, while emphasizing their potential application to the GPCR signaling in airway smooth muscle that regulates airway patency and thus disease severity.

Expression of angiotensin-converting enzyme changes major histocompatibility complex class I peptide presentation by modifying C termini of peptide precursors

We recently reported a mouse model called ACE 10/10 in which macrophages overexpress the carboxypeptidase angiotensin-converting enzyme (ACE). These mice have an enhanced inflammatory response to tumors that markedly inhibits tumor growth. Here, we show that ACE modifies the C termini of peptides for presentation by major histocompatibility complex (MHC) class I molecules. The peptide-processing activity of ACE applies to antigens from either the extracellular environment (cross-presentation) or antigens produced endogenously. Consistent with its role in MHC class I antigen processing, ACE localizes to the endoplasmic reticulum. ACE overexpression does not appear to change the overall supply of peptides available to MHC class I molecules. The immunization of wild type mice previously given ACE 10/10 macrophages enhances the efficiency of antigen-specific CD8+ T cell priming. These data reveal that ACE is a dynamic participant in fashioning the peptide repertoire for MHC class I molecules by modifying the C termini of peptide precursors. Manipulation of peptidase expression by antigen-presenting cells may ultimately prove a useful strategy to enhance the immune response.

Inhibition of rho-kinase impairs fibroblast stress fiber formation, confluence, and contractility in vitro

Rho kinase is an enzyme that has been implicated in pathological wound healing. In our study, we aimed to characterize the dosages of Y-27632 (a competitive inhibitor of rho kinase) at which fibroblast stress fiber formation is inhibited, to determine the effect of Y-27632 on fibroblast confluence, and to determine the effect of varying concentrations of Y-27632 on fibroblast-mediated gel contraction. First, 3T3 fibroblasts were exposed to various concentrations of Y-27632, and stress fiber dissolution was assessed with immunofluorescence. Next, 10 microM Y-27632 was applied to 3T3 fibroblast monolayer cultures immediately after plating and at 8 hours after plating to determine the effect on fibroblast confluence. Finally, a three-dimensional model was used to assess the effect of Y-27632 on gel contraction. Increasing doses of Y-27632 resulted in a dose-dependent increase in stress fiber dissolution as well as a dose-dependent inhibition of gel contraction. Median number of days to confluence were 3, 5, and 6 after no, immediate, and delayed incubation with Y-27632, respectively (P < .05). Our results further characterize the dosages at which Y-27632 may be most effective in the modulation of wound contraction in burn patients. In addition, our confluence study suggests that patients need not necessarily be pretreated with Y-27632.

Signaling mechanism of thrombin-induced gingival fibroblast-populated collagen gel contraction

1.--Thrombin is activated during gingival tissue injury and inflammation. Thrombin (platelet)-rich plasma has been used for periodontal regeneration with success. Thrombin and other bacterial proteases also affect the functions of adjacent periodontal cells via stimulation of protease-activated receptors (PARs). 2.--We noted that thrombin (0.1-2 U ml(-1)), human, and frog PAR-1 agonist peptide (20-240 microM) induced the gingival fibroblast (GF)-populated collagen gel contraction within 2 h of exposure. However, PAR-2, PAR-3, and PAR-4 agonist peptide (20-240 microM) showed little effect on collagen gel contraction. U73122 (phospholipase C inhibitor) and 2-APB (IP3 antagonist) were effective in inhibition of GF contraction. 3.--Thrombin-induced GF contraction was inhibited by 5 mM EGTA (an extracellular calcium chelator) and verapamil (an L-type calcium channel blocker). In addition, W7 (10 and 25 microM, a calcium/calmodulin (CaM) inhibitor), ML-7 (50 microM, myosin light chain kinase (MLCK) inhibitor), and HA1077 (100 microM, Rho kinase inhibitor) completely inhibited the thrombin-induced collagen gel contraction. Thrombin also induced the phosphorylation of ERK1/ERK2 and elevated the Rho-GTP levels in GF. 4.--However, U0126 only partially inhibited the thrombin-induced GF contraction. Similarly, wortmannin (100 nM), LY294002 (20 microM) (two PI3K inhibitor) and genistein also showed partial inhibition. Moreover, NAC was not able to suppress the GF contraction, as supported by the slight decrease in reactive oxygen species production in GF by thrombin. 5.--Thrombin also stimulated metalloproteinase-2 (MMP-2) and MMP-3 production in GF. But addition of GM6001 or 1,10-phenanthroline, two MMP inhibitors, could not inhibit the thrombin-induced GF contraction. 6.--These results indicate that thrombin is crucial in the periodontal inflammation and wound healing by promoting GF contraction. This event is mainly mediated via PAR-1 activation, PLC activation, extracellular calcium influx via L-type calcium channel, and the calcium/CaM-MLCK and Rho kinase activation pathway.

Oxidative stress and lipid-derived inflammatory mediators during acute exacerbations of cystic fibrosis

BACKGROUND AND OBJECTIVE

In cystic fibrosis (CF) very few studies have assessed sputum 8-iso-PGF2alpha levels during pulmonary exacerbations as a direct measure of airway oxidative stress. The role of other lipid-derived inflammatory mediators, such as the cysteinyl leukotrienes (cys-LTs) and prostaglandin (PG)-E2, during exacerbations is also poorly defined and the effect of conventional antibiotic therapy on these components of the inflammatory process is unclear.

METHODS

Sputum 8-iso-PGF2alpha, total cys-LT and PGE2 levels were measured in 17 CF patients experiencing a pulmonary exacerbation and repeated analysis were performed in 15 of these patients after antibiotic treatment. Eight stable CF and nine healthy subjects provided control data.

RESULTS

Sputum 8-iso-PGF2alpha was significantly elevated in acute, but not stable CF patients versus healthy controls (P < 0.001). Similarly, sputum cys-LT and PGE2 levels were increased in acute compared with stable CF patients and healthy controls (P <or= 0.001). Although substantially lower than in acute patients, sputum cys-LT levels in stable patients were also significantly higher than in normal controls (P = 0.01). There were strong associations between cys-LT levels and sputum total cell counts, and blood neutrophils in acute patients (r2 = 0.53, P = 0.001 and r2 = 0.33, P < 0.05, respectively). Overall in the CF patients, FEV1% predicted was strongly and negatively correlated with sputum 8-iso-PGF2alpha (r2 = 0.34, P = 0.006), cys-LT (r2 = 0.40, P = 0.002) and PGE2 (r2 = 0.52, P < 0.001) levels. Antibiotic treatment reduced sputum total cell count (P = 0.03), but did not affect 8-iso-PGF2alpha, cys-LT or PGE2 levels.

CONCLUSIONS

CF exacerbations are characterized by increased oxidative stress and sputum concentrations of bioactive lipid mediators. Treatment does not modulate these aspects of inflammation and more targeted therapy needs further study.

Comparison of norepinephrine responsiveness of mucosal veins in vivo with that of isolated mucosal tissue in vitro in guinea pig nasal mucosa

BACKGROUND

The vascular responsiveness of nasal mucosa has been determined frequently by using isolated mucosal tissues although it is not clear whether the response of the whole tissue truly reflects the response of the vasculature (especially veins) in mucosa. In this study, the in vivo responsiveness of mucosal veins was compared with in vitro responsiveness of isolated mucosal tissue in guinea pig nasal septa.

METHODS

The in vivo venous responsiveness to norepinephrine (NE) of guinea pig nasal septal mucosa was measured by changes in the diameters of mucosal veins, stereomicroscopically. The in vitro responsiveness to NE of isolated nasal septal mucosae from guinea pigs also was determined by standard organ-bath technique.

RESULTS

Application of NE induced concentration-dependent contractile responses both in vivo and in vitro with the pD2 (negative logarithm for 50% effective concentration [M] of NE) values of 5.23 +/- 0.29 and 5.00 +/- 0.17, respectively.

CONCLUSION

The equal potencies obtained by the in vivo and in vitro experiments suggest that an increase in tension of isolated nasal mucosal tissue might be caused by the contraction of mucosal veins. Both the in vivo and the in vitro methods used in this study might be useful for determining vasoreactivity of nasal mucosa in experimental animals.

Cyclooxygenase-1 overexpression decreases Basal airway responsiveness but not allergic inflammation

Pharmacological inhibition or genetic disruption of cyclooxygenase (COX)-1 or COX-2 exacerbates the inflammatory and functional responses of the lung to environmentally relevant stimuli. To further examine the contribution of COX-derived eicosanoids to basal lung function and to allergic lung inflammation, transgenic (Tr) mice were generated in which overexpression of human COX-1 was targeted to airway epithelium. Although no differences in basal respiratory or lung mechanical parameters were observed, COX-1 Tr mice had increased bronchoalveolar lavage fluid PGE(2) content compared with wild-type littermates (23.0 +/- 3.6 vs 8.4 +/- 1.4 pg/ml; p < 0.05) and exhibited decreased airway responsiveness to inhaled methacholine. In an OVA-induced allergic airway inflammation model, comparable up-regulation of COX-2 protein was observed in the lungs of allergic wild-type and COX-1 Tr mice. Furthermore, no genotype differences were observed in allergic mice in total cell number, eosinophil content (70 vs 76% of total cells, respectively), and inflammatory cytokine content of bronchoalveolar lavage fluid, or in airway responsiveness to inhaled methacholine (p > 0.05). To eliminate the presumed confounding effects of COX-2 up-regulation, COX-1 Tr mice were bred into a COX-2 null background. In these mice, the presence of the COX-1 transgene did not alter allergen-induced inflammation but significantly attenuated allergen-induced airway hyperresponsiveness, coincident with reduced airway leukotriene levels. Collectively, these data indicate that COX-1 overexpression attenuates airway responsiveness under basal conditions but does not influence allergic airway inflammation.

Asthma: is it due to an abnormal airway smooth muscle cell?

Asthma is an airway disease highly prevalent in westernized countries and of unknown etiology. Often, asthma is associated with atopy, but not all atopic individuals have asthma. Some patients with asthma outgrow symptoms, whereas many others acquire asthma later in life. Still other patients suffer from asthma their entire life. How can we explain these different patterns? It may be that asthma should be regarded as the clinical manifestation of a group of diseases with similar pathology due to a common factor. In this Pulmonary Perspective, we propose that an aberrant phenotype of airway smooth muscle (ASM) cells could be sufficient to explain the pathology of asthma. We will argue an abnormal ASM cell is a prerequisite to the development of asthma. Our postulate is that inadequate levels of C/EBPalpha, a protein that is pivotal for the suppression of both inflammation and proliferation responses, confer on ASM cells an activated phenotype that is more susceptible to mitogenic and contractile stimuli.

Multiple signaling pathways mediate compaction of collagen matrices by EGF-stimulated fibroblasts

Fibroblasts stimulated by EGF within collagen matrices generate contraction forces that are likely of importance to cell migration and matrix compaction during wound healing. We have employed an in vitro fibroblast-embedded collagen matrix compaction assay to ascertain signaling pathway components downstream of EGFR activation leading to generation and transmission of contractile force. EGF compacts this floating collagen matrix to a similar extent as PDGF. We demonstrate that compaction requires EGFR kinase activity, yet is maximal in magnitude at intermediate EGF concentrations. This suggests that transmission of EGFR-induced contractile force to the matrix can be mitigated by consequent anti-adhesive effects of EGFR signaling in a dose-dependent manner. Treatment with pharmacological inhibitors demonstrated involvement of the signaling components extracellular signal-regulated kinase (ERK), Rho kinase, and myosin light chain kinase (MLCK) in the force generation and/or transmission process. Moreover, treatment with the pan-calpain inhibitor ALLN and isoform-specific downregulation of m-calpain (CAPN2) using RNA interference determined m-calpain to be a key component of the EGF-induced force response. ALLN treatment modulated the compaction response in a biphasic manner, enhancing matrix deformation to the greatest extent at intermediate concentrations. Our findings have thus identified key signals downstream of EGFR, which integrate in a complex manner to generate and transmit contractile forces to yield matrix deformation.

Modulation of respiratory syncytial virus-induced prostaglandin E2 production by n-3 long-chain polyunsaturated fatty acids in human respiratory epithelium

Infection with respiratory syncytial virus (RSV) results in substantial infant morbidity and has been associated with the subsequent development of childhood asthma. Inflammatory mediators produced by both the epithelium and tissue leukocytes during RSV infection stimulate the release of chemotactic factors by the respiratory epithelium and the subsequent influx of inflammatory cells, predominantly neutrophils. We investigated the production of inflammatory mediators [prostaglandin E2 (PGE2), interleukin (IL)-1beta, tumor necrosis factor alpha] and chemokines [IL-8, RANTES (regulation on activation, normal T cell expressed and secreted)] by alveolar epithelial cells in response to RSV infection. Infection of a human alveolar epithelial transformed cell line (A549 cells) with live RSV substantially increased production of PGE2, IL-8, and RANTES. By altering cell membrane FA through incorporation of the long-chain PUFA (LCPUFA) arachidonic acid, EPA, and DHA, we were subsequently able to significantly modulate PGE2 production by the infected epithelium. Because of the dynamic nature of the effects of PGE2 on lung function, regulation of this prostaglandin during RSV infection by n-3 LCPUFA has the potential to significantly alter the disease process.

Viscoelastic retraction of single living stress fibers and its impact on cell shape, cytoskeletal organization, and extracellular matrix mechanics

Cells change their form and function by assembling actin stress fibers at their base and exerting traction forces on their extracellular matrix (ECM) adhesions. Individual stress fibers are thought to be actively tensed by the action of actomyosin motors and to function as elastic cables that structurally reinforce the basal portion of the cytoskeleton; however, these principles have not been directly tested in living cells, and their significance for overall cell shape control is poorly understood. Here we combine a laser nanoscissor, traction force microscopy, and fluorescence photobleaching methods to confirm that stress fibers in living cells behave as viscoelastic cables that are tensed through the action of actomyosin motors, to quantify their retraction kinetics in situ, and to explore their contribution to overall mechanical stability of the cell and interconnected ECM. These studies reveal that viscoelastic recoil of individual stress fibers after laser severing is partially slowed by inhibition of Rho-associated kinase and virtually abolished by direct inhibition of myosin light chain kinase. Importantly, cells cultured on stiff ECM substrates can tolerate disruption of multiple stress fibers with negligible overall change in cell shape, whereas disruption of a single stress fiber in cells anchored to compliant ECM substrates compromises the entire cellular force balance, induces cytoskeletal rearrangements, and produces ECM retraction many microns away from the site of incision; this results in large-scale changes of cell shape (> 5% elongation). In addition to revealing fundamental insight into the mechanical properties and cell shape contributions of individual stress fibers and confirming that the ECM is effectively a physical extension of the cell and cytoskeleton, the technologies described here offer a novel approach to spatially map the cytoskeletal mechanics of living cells on the nanoscale.

Horse Chestnut Extract Induces Contraction Force Generation in Fibroblasts through Activation of Rho/Rho Kinase

Contraction forces generated by non-muscle cells such as fibroblasts play important roles in determining cell morphology, vasoconstriction, and/or wound healing. However, few factors that induce cell contraction forces are known, such as lysophosphatidic acid and thrombin. Our study analyzed various plant extracts for ingredients that induce generation of cell contraction forces in fibroblasts populating collagen gels. We found that an extract of Horse chestnut (Aesculus hippocastanum) is able to induce such contraction forces in fibroblasts. The involvement of actin polymerization and stress fiber formation in the force generation was suggested by inhibition of this effect by cytochalasin D and by Rhodamine phalloidin. Rho kinase inhibitors (Y27632 and HA1077) and a Rho inhibitor (exoenzyme C3) significantly inhibited the force generation induced by the Horse chestnut extract. H7, which inhibits Rho kinase as well as other protein kinases, also significantly inhibited induction of force generation. However, inhibitors of other protein kinases such as myosin light chain kinase (ML-9), protein kinase C (Calphostin), protein kinase A (KT5720), and tyrosine kinase (Genistein, Herbimycin A) had no effect on force generation induced by Horse chestnut extract. These results suggest that the Horse chestnut extract induces generation of contraction forces in fibroblasts through stress fiber formation followed by activation of Rho protein and Rho kinase but not myosin light chain kinase or other protein kinases.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Gene expression profiles in rat intestine identify pathways for 1,25-dihydroxyvitamin D(3) stimulated calcium absorption and clarify its immunomodulatory properties

Microarray technology has been used to discover 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) induced gene expression changes in rat small intestine in vivo. Here, we report gene expression changes related to intestinal absorption or transport, the immune system and angiogenesis in response to 1,25-(OH)(2)D(3). Vitamin D deficient rats were intrajugularly given vehicle or vehicle containing 730 ng of 1,25-(OH)(2)D(3)/kg of body weight. Intestinal mRNA was harvested from duodenal mucosa at 15 min, 1, 3, and 6 h post-injection and studied by Affymetrix microarrays. Genes significantly affected by 1,25-(OH)(2)D(3) were confirmed by quantitative RT-PCR with remarkable agreement. The most strongly affected gene in intestine was CYP24 with 97-fold increase at 6 h post-1,25-(OH)(2)D(3) treatment. Intestinal calcium absorption genes: TRPV5, TRPV6, calbindin D(9k), and Ca(2+) dependent ATPase all were up-regulated in response to 1,25-(OH)(2)D(3), supporting the currently accepted mechanism of 1,25-(OH)(2)D(3) induced transcellular calcium transport. However, a 1,25-(OH)(2)D(3) suppression of several intra-/intercellular matrix modeling proteins such as sodium/potassium ATPase, claudin 3, aquaporin 8, cadherin 17, and RhoA suggests a vitamin D regulation of tight junction permeability and paracellular calcium transport. Several other genes related to the immune system and angiogenesis whose expression was changed in response to 1,25-(OH)(2)D(3) provided evidence for an immunomodulatory and anti-angiogenic role of 1,25-(OH)(2)D(3).

Regulation of cysteinyl leukotriene type 1 receptor internalization and signaling

Cysteinyl leukotrienes activate the cysteinyl leukotriene type 1 receptor (CysLT1R) to regulate numerous cell functions important in inflammatory processes and diseases such as asthma. Despite its physiologic importance, no studies to date have examined the regulation of CysLT1R signaling or trafficking. We have established model systems for analyzing recombinant human CysLT1R and found regulation of internalization and signaling of the CysLT1R to be unique among G protein-coupled receptors. Rapid and profound LTD4-stimulated internalization was observed for the wild type (WT) CysLT1R, whereas a C-terminal truncation mutant exhibited impaired internalization yet signaled robustly, suggesting a region within amino acids 310-321 as critical to internalization. Although overexpression of WT arrestins significantly increased WT CysLT1R internalization, expression of dominant-negative arrestins had minimal effects, and WT CysLT1R internalized in murine embryonic fibroblasts lacking both arrestin-2 and arrestin-3, suggesting that arrestins are not the primary physiologic regulators of CysLT1Rs. Instead, pharmacologic inhibition of protein kinase C (PKC) was shown to profoundly inhibit CysLT1R internalization while greatly increasing both phosphoinositide (PI) production and calcium mobilization stimulated by LTD4 yet had almost no effect on H1 histamine receptor internalization or signaling. Moreover, mutation of putative PKC phosphorylation sites within the CysLT1R C-tail (CysLT1RS(313-316)A) reduced receptor internalization, increased PI production and calcium mobilization by LTD4, and significantly attenuated the effects of PKC inhibition. These findings characterized the CysLT1R as the first G protein-coupled receptor identified to date in which PKC is the principal regulator of both rapid agonist-dependent internalization and rapid agonist-dependent desensitization.

Neutral endopeptidase and angiotensin-converting enzyme - key enzymes terminating the action of neuroendocrine mediators

Zinc-metalloproteases, such as neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE), effectively control the bioavailability of peptide mediators released from sensory nerves, immune and skin cells during the cutaneous response to endogenous or exogenous noxious stimuli. Functional inactivation of NEP or ACE by transient inhibition or permanent genomic deletion results in a relative abundance of substance P (SP) and bradykinin (BK); this augments murine allergic contact dermatitis (ACD) by affecting ACD sensitization and elicitation, which involves neurokinin 1 receptors (NK1), BK receptors (B2) and an intact cutaneous sensory nervous system. Present evidence suggests that increased SP via NK(1) is capable of boosting important functions of SP- and NK1-expressing dendritic cells (DCs) and T cells (TCs) in an auto- or paracrine manner, which promotes ACD antigen sensitization. Moreover, skin inflammation or wounding in vivo, as well as treatment of epidermal and dermal cells by UV light and inflammatory mediators in vitro, regulates NEP and ACE expression and activity. Likewise, NEP and ACE are capable of processing neuroendocrine hormones, such as adrenocorticotropin and alpha-melanocyte-stimulating hormone. Thus, present data indicate that ACE and NEP, via proteolytic cleavage of peptide mediators and growth factors, represent important control factors for the inflammatory response in skin disorders such as psoriasis or allergic inflammation, but may also be capable of affecting pigmentation, cell survival, wound healing and tissue regeneration.

Wrch1 is a GTPase-deficient Cdc42-like protein with unusual binding characteristics and cellular effects

The Rho family of small GTPases controls many biological processes, including cytoskeletal regulation, membrane trafficking, cell adhesion, cell polarization, transcriptional activity, apoptosis, and cell proliferation. Wrch1, which belongs to the Cdc42 subfamily, is one of the least characterized family member. Despite its homology to other Cdc42-like proteins, we found that Wrch1 has unique characteristics. Biochemical experiments showed that Wrch1 has no detectable GTPase activity in vitro and that its intrinsic nucleotide exchange rate is very high in comparison to Cdc42. Furthermore, NIH3T3 cells transiently transfected with Wrch1 showed an up-rounded, retracted phenotype. In addition, Wrch1 was shown to be more efficient than Cdc42 in triggering the formation of filopodia. Serum stimulation of cells expressing Wrch1 induces vigorous membrane blebbing, a phenomenon dependent on the activity of ROCK. In a search for proteins interacting with Wrch1, PAK1 and NCKbeta were identified as binding partners. Interestingly, the interaction to NCKbeta was shown to be mediated via PxxP motifs present in an N-terminal extension of Wrch1 to the second and third SH3 domains of NCKbeta.

Omalizumab and the treatment of allergic rhinitis

Anti-IgE therapy affects mechanisms in the allergic response that are IgE-dependent or IgE-mediated and common to both allergic asthma and allergic rhinitis. Clinical trials of omalizumab in the treatment of patients with allergic rhinitis or comorbid allergic rhinitis and moderate to severe allergic asthma have recorded significant reductions in symptom severity scores of both conditions. This novel therapy has increased the knowledge base concerning IgE-mediated allergic responses, and, in keeping with its actions established in the treatment of asthma, appears to be useful in the treatment of moderate to severe allergic rhinitis, as well.

Role of muscarinic receptor subtypes in the constriction of peripheral airways: studies on receptor-deficient mice

In the airways, increases in cholinergic nerve activity and cholinergic hypersensitivity are associated with chronic obstructive pulmonary disease and asthma. However, the contribution of individual muscarinic acetylcholine receptor subtypes to the constriction of smaller intrapulmonary airways that are primarily responsible for airway resistance has not been analyzed. To address this issue, we used videomicroscopy and digital imaging of precision-cut lung slices derived from wild-type mice and mice deficient in either the M1 (mAChR1-/- mice), M2 (mAChR2-/- mice), or M3 receptor subtype (mAChR3-/- mice) or lacking both the M2 and M3 receptor subtypes (mAChR2/3-/- double-knockout mice). In peripheral airways from wild-type mice (mAChR+/+ mice), muscarine induced a triphasic concentration-dependent response, characterized by an initial constriction, a transient relaxation, and a sustained constriction. The bronchoconstriction was diminished by up to 60% in mAChR3-/- lungs and was completely abolished in mAChR2/3-/- lungs. The sustained bronchoconstriction was reduced in mAChR2-/- bronchi, and, interestingly, the transient relaxation was absent; the bronchoconstriction in response to 10-8 M muscarine was increased by 158% in mAChR1-/- mice. Quantitative reverse transcriptase-polymerase chain reaction analysis revealed that the disruption of specific mAChR genes had no significant effect on the expression levels of the remaining mAChR subtypes. These results demonstrate that cholinergic constriction of murine peripheral airways is mediated by the concerted action of the M2 and M3 receptor subtypes and suggest the existence of pulmonary M1 receptor activation, which counteracts cholinergic bronchoconstriction. Given the important role of muscarinic cholinergic mechanisms in pulmonary disease, these findings should be of considerable therapeutic relevance.

Fibroblast fiber contraction: role of C and Rho kinase in activation by thromboxane A2

We investigated the mechanisms underlying regulation of contraction with measurements of isometric force and intracellular Ca2+ concentration ([Ca2+]i) in NIH 3T3 fibroblast reconstituted into fibers with the use of a collagen matrix. Treatment with the major phospholipids, neurotransmitters, and growth factors had little effect on baseline isometric force. However, U-46619, a thromboxane A2 (TxA2) analog, increased force and [Ca2+]i; EC50 values were 11.0 and 10.0 nM, respectively. The time courses were similar to those induced by calf serum (CS), and the maximal force was 65% of a CS-mediated contraction. The selective TxA2 receptor antagonist SQ-29548 abolished the U-46619-induced responses. CS-induced contractions are dependent on an intracellular Ca2+ store function; however, the U-46619 response depended not only on intracellular Ca2+ stores, but also on Ca2+ influx from the extracellular medium. Inhibition of Rho kinase suppressed U-46619- and CS-induced responses; in contrast, inhibition of C kinase (PKC) reduced only the U-46619 response. Moreover, addition of U-46619 to a CS contracture enhanced force and [Ca2+]i responses. These results indicate that U-46619-induced responses involve PKC and Rho kinase pathways, in contrast to activation by CS. Thus TxA2 may have a role in not only the initial step of wound repair as an activator of blood coagulation, but also in fibroblast contractility in later stages.

Rho-kinase inhibitor inhibits both myosin phosphorylation-dependent and -independent enhancement of myofilament Ca2+ sensitivity in the bovine middle cerebral artery

The role of Rho kinase in Ca2+ sensitization of the contractile apparatus in smooth muscle was investigated in the bovine middle cerebral artery. U46619, a thromboxane A2 analog, induced a greater sustained contraction with a smaller [Ca2+]i elevation than that seen with 118 mm K+. The level of myosin light chain (MLC) phosphorylation obtained in the initial phase of the contraction was higher than that seen with 118 mm K+; thereafter, it gradually declined to a comparable level in the late phase. During the steady state of the U46619-induced contraction, Y27632 (10 microM), a Rho-kinase inhibitor, partially inhibited [Ca2+]i, although it substantially inhibited tension and MLC phosphorylation. Wortmannin (10 microM), an MLC kinase inhibitor, had no significant effect on [Ca2+]i, but it completely inhibited MLC phosphorylation and partially inhibited tension. The wortmannin-resistant tension development was thus not associated with MLC phosphorylation, and this component was completely inhibited by Y27632. In conclusion, U46619 enhanced Ca2+ sensitivity in a manner both dependent and independent of MLC phosphorylation in the bovine middle cerebral artery. Both mechanisms of Ca2+ sensitization can be inhibited by the Rho-kinase inhibitor.

Different molecular motors mediate platelet-derived growth factor and lysophosphatidic acid-stimulated floating collagen matrix contraction

Fibroblast-collagen matrix contraction has been used as a model system to study how cells organize connective tissue. Previous work showed that lysophosphatidic acid (LPA)-stimulated floating collagen matrix contraction is independent of Rho kinase, whereas platelet-derived growth factor (PDGF)-stimulated contraction is Rho kinase-dependent. The current studies were carried out to learn more about the molecular motors responsible for LPA- and PDGF-stimulated contraction. We found that neither PDGF nor LPA-dependent contractile mechanisms require myosin II regulatory light chain kinase or increased phosphorylation of myosin II regulatory light chain (measured as diphosphorylation). Low concentrations of the specific myosin II inhibitor blebbistatin blocked PDGF-stimulated matrix contraction and LPA-stimulated retraction of fibroblast dendritic extensions but not LPA-stimulated matrix contraction. These data suggest that PDGF- and LPA-stimulated floating matrix contraction utilize myosin II-dependent and -independent mechanisms, respectively. LPA-dependent, Rho kinase-independent force generation also was detected during fibroblast spreading on collagen-coated coverslips.