Angiogenesis is induced by airway smooth muscle strain

Mechanopharmacology of Rho-kinase antagonism in airway smooth muscle and potential new therapy for asthma

The principle of mechanopharmacology of airway smooth muscle (ASM) is based on the premise that physical agitation, such as pressure oscillation applied to an airway, is able to induce bronchodilation by reducing contractility and softening the cytoskeleton of ASM. Although the underlying mechanism is not entirely clear, there is evidence to suggest that large-amplitude stretches are able to disrupt the actomyosin interaction in the crossbridge cycle and weaken the cytoskeleton in ASM cells. Rho-kinase is known to enhance force generation and strengthen structural integrity of the cytoskeleton during smooth muscle activation and plays a key role in the maintenance of force during prolonged muscle contractions. Synergy in relaxation has been observed when the muscle is subject to oscillatory length change while Rho-kinase is pharmacologically inhibited. In this review, inhibition of Rho-kinase coupled to therapeutic pressure oscillation applied to the airways is explored as a combination treatment for asthma.

YAP1, targeted by miR-375, enhanced the pro-angiogenesis of airway smooth muscle cells in asthma via STAT3 activation

YAP1 was previously reported to regulate the development of multiple tumors, angiogenesis included. Angiogenesis was a specific process of remodeling in asthma. In a recent study, YAP1 was correlated with the progression of asthma. However, the role of YAP1 in airway smooth muscle cell and the asthmatic airway angiogenesis was unclear. In the present study, we used cytokine-stimulated airway smooth muscle cells as asthma cell model in vitro. The results showed a significant up-regulation of YAP1 in asthmatic airway smooth muscle tissue and cytokine-stimulated asthmatic cell model by Western blot. The experimental results of YAP1 loss-of-function combined with STAT3 inhibitor (WP1066) showed that YAP1 knockdown inhibited the expression of VEGF by deactivating STAT3 in cytokine-stimulated ASM cells, which hindered the pro-angiogenesis ability of ASM cells. Besides, by combining prediction and binding site mutation along with luciferase reporter gene experiments, we confirmed direct binding between miR-375 and YAP1. Based on that, the decreased expression level of miR-375 was found to be correlated with the pathogenesis of asthma. Finally, miR-375 was verified to participate in the YAP1-regulated pro-angiogenesis ability of ASM cells. To sum up, we provided the evidence that YAP1 directly binds to miR-375 and takes part in the regulation of the pro-angiogenic ability of ASM cells by activating STAT3 and VEGF signaling.

Phosphoinositide 3-Kinase in Asthma: Novel Roles and Therapeutic Approaches

Asthma manifests as airway hyperresponsiveness and inflammation, including coughing, wheezing, and shortness of breath. Immune cells and airway structural cells orchestrate asthma pathophysiology, leading to mucus secretion, airway narrowing, and obstruction. Phosphoinositide 3-kinase, a lipid kinase, plays a crucial role in many of the cellular and molecular mechanisms driving asthma pathophysiology and represents an attractive therapeutic target. Here, we summarize the diverse roles of phosphoinositide 3-kinase in the pathogenesis of asthma and discuss novel therapeutic approaches to treatment.

STAT3 potentiates the ability of airway smooth muscle cells to promote angiogenesis by regulating VEGF signalling

NEW FINDINGS

What is the central question of this study? Airway angiogenesis occurs in asthma, and airway smooth muscle (ASM) cells have been reported to be capable of promoting airway angiogenesis. What is the potential mechanism by which ASM cells harvested from patients with asthma are capable of promoting airway angiogenesis? What is the main finding and its importance? Endogenous STAT3 mediated the pro-angiogenic ability of ASM cells by directly activating VEGF signalling. These findings contribute to the understanding of airway angiogenesis in pathology and could represent a possible therapeutic target for asthma. Airway angiogenesis indicates the specific vascular structure remodelling that occurs in asthma. Airway smooth muscle (ASM) cells have been reported to be capable of promoting airway angiogenesis; however, the potential mechanism is not yet fully defined. Herein, we investigated the role of signal transducer and activator of transcription 3 (STAT3) in the progress of airway angiogenesis. Western blot analysis showed that STAT3 activation was aberrantly upregulated in ASM tissues of patients with asthma and ASM cells that were exposed to cytokines to imitate the airway conditions in patients with asthma. Compared with the control group, both the inhibition of STAT3 activation and the silencing of endogenous STAT3 in ASM cells significantly reduced the proliferation, migration and tube-forming ability of human lung microvascular endothelial cells induced by the conditioned medium (CM) of ASM cells. The increased proliferation and migration of human aortic vascular smooth muscle cells were also repressed by inhibition of STAT3 in ASM cells. Besides, the increased activity of VEGF signalling was observed in ASM cells and the CM by RT-PCR and Western blotting assay, whereas this increased activity was reduced by STAT3 silencing. Further studies indicated that STAT3 regulated VEGF activation by directly interacting with the binding site on the 5' region of the VEGF gene. The increase in STAT3-induced pro-angiogenic activity of ASM cells was significantly decreased by administration of VEGF neutralizing antibody. In conclusion, we provided evidence that endogenous STAT3 mediates the pro-angiogenic ability of ASM cells by directly activating VEGF signalling, which could represent a possible therapeutic target for asthma.

Comparative analysis of the mechanical signals in lung development and compensatory growth

This review compares the manner in which physical stress imposed on the parenchyma, vasculature and thorax and the thoraco-pulmonary interactions, drive both developmental and compensatory lung growth. Re-initiation of anatomical lung growth in the mature lung is possible when the loss of functioning lung units renders the existing physiologic-structural reserves insufficient for maintaining adequate function and physical stress on the remaining units exceeds a critical threshold. The appropriate spatial and temporal mechanical interrelationships and the availability of intra-thoracic space, are crucial to growth initiation, follow-on remodeling and physiological outcome. While the endogenous potential for compensatory lung growth is retained and may be pharmacologically augmented, supra-optimal mechanical stimulation, unbalanced structural growth, or inadequate remodeling may limit functional gain. Finding ways to optimize the signal-response relationships and resolve structure-function discrepancies are major challenges that must be overcome before the innate compensatory ability could be fully realized. Partial pneumonectomy reproducibly removes a known fraction of functioning lung units and remains the most robust model for examining the adaptive mechanisms, structure-function consequences and plasticity of the remaining functioning lung units capable of regeneration. Fundamental mechanical stimulus-response relationships established in the pneumonectomy model directly inform the exploration of effective approaches to maximize compensatory growth and function in chronic destructive lung diseases, transplantation and bioengineered lungs.

Role of licochalcone A in VEGF-induced proliferation of human airway smooth muscle cells: implications for asthma

Asthma is a chronic respiratory disease characterized by reversible airway obstruction with persistent airway inflammation and airway remodeling, which is associated with increased airway smooth muscle (ASM) mass. Licochalcone A is the predominant characteristic chalcone in licorice root. We found that licochalcone A inhibited vascular endothelial growth factor (VEGF)-induced ASM cell proliferation and induced cell cycle arrest. Additionally, VEGF-induced ASM cell proliferation was suppressed via inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) activity, but not that of Akt. Furthermore, licochalcone A treatment inhibited VEGF-induced activation of VEGF receptor 2 (VEGFR2) and ERK and blocked the downregulation of caveolin-1 in a concentration-dependent manner. Collectively, our findings suggested that licochalcone A inhibited VEGF-induced ASM cell proliferation by suppressing VEGFR2 and ERK1/2 activation and downregulating caveolin-1. Further studies of these mechanisms are needed to facilitate the development of treatments for smooth muscle hyperplasia-associated diseases of the airway, such as asthma.

Effect of active vitamin D3 on VEGF-induced ADAM33 expression and proliferation in human airway smooth muscle cells: implications for asthma treatment

BACKGROUND

Asthma is a chronic respiratory disease characterized by reversible airway obstruction with persistent airway inflammation and airway remodeling, which is associated with increased airway smooth muscle (ASM) mass. Vascular endothelial growth factor (VEGF) has been implicated in inflammatory and airway blood vessel remodeling in asthma. Recent evidence indicates that a deficiency of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) may influence asthma pathogenesis. A disintegrin and metalloproteinase (ADAM)33 has been identified as playing a role in the pathophysiology of asthma. ADAM33, which is expressed in ASM cells, is suggested to play a role in the function of these cells. Recent studies show that 1,25-(OH)2D3 exerts direct inhibitory effects on passively sensitized human ASM cells in vitro, including inhibition of ADAM33 expression and cell proliferation; however, the mechanism has not been fully understood.

METHODS

In order to elucidate the precise mechanism underlying the effect of 1,25(OH)2D3 on VEGF-induced ADAM33 expression and ASM cell proliferation, we tested the effects of 1,25(OH)2D3 on cell cycle progression and evaluated the levels of phospho-VEGF receptor 2 (VEGFR2), phospho-extracellular signal-regulated kinase 1/2 (ERK1/2), and phospho-Akt in VEGF-stimulated ASM cells.

RESULTS

We found that 1,25(OH)2D3 inhibited VEGF-induced ADAM33 expression and ASM cell proliferation, as well as cell cycle arrest. Additionally, VEGF-induced ADAM33 expression and ASM cell proliferation was suppressed via inhibition of ERK1/2 activity, but not that of Akt. Furthermore, 1,25(OH)2D3 treatment inhibited VEGF-induced activation of VEGFR2 as well as that of ERK and Akt in a concentration-dependent manner. 1,25(OH)2D3 also inhibited transforming growth factor (TGF)-β-induced VEGF secretion by ASM cells.

CONCLUSIONS

Collectively, our findings suggest that 1,25(OH)2D3 inhibits VEGF-induced ASM cell proliferation by suppressing VEGFR2 and ERK1/2 activation and downregulating ADAM33. Further studies of these mechanisms are needed to facilitate the development of treatments for smooth muscle hyperplasia-associated diseases of the airway such as asthma.

Upregulation of a disintegrin and metalloproteinase-33 by VEGF in human airway smooth muscle cells: Implications for asthma

Asthma is a chronic respiratory disease characterized by reversible airway obstruction with persistent airway inflammation and airway remodeling. Features of airway remodeling include increased airway smooth muscle (ASM) mass. A disintegrin and metalloproteinase (ADAM)-33 has been identified as playing a role in the pathophysiology of asthma. ADAM-33 is expressed in ASM cells and is suggested to play a role in the function of these cells. However, the regulation of ADAM-33 is not fully understood. Vascular endothelial growth factor (VEGF) has been implicated in inflammatory and airway blood vessel remodeling in asthmatics. Although VEGF was initially thought of as an endothelial-specific growth factor, recent reports have found that VEGF can promote proliferation of other cell types, including ASM cells. To investigate the precise mechanism of VEGF's effect on ASM cell proliferation, we tested the expression of ADAM-33, phospho-extracellularsignal-regulated kinase 1/2 (ERK1/2), and phospho-Akt in VEGF-stimulated ASM cells. We found that VEGF up-regulates ADAM-33 mRNA and protein levels in a dose- and time-dependent manner as well as phosphorylation of ERK1/2 and Akt. We also found that VEGF-induced ASM cell proliferation is inhibited by both ADAM-33 knockdown and a selective VEGF receptor 2 (VEGFR2) inhibitor (SU1498). Furthermore, VEGF-induced ADAM-33 expression and ASM cell proliferation were suppressed by inhibiting ERK1/2 activity, but not by inhibiting Akt activity. Collectively, our findings suggest that VEGF enhances ADAM-33 expression and ASM cell proliferation by activating the VEGFR2/ERK1/2 signaling pathway, which might be involved in the pathogenesis of airway remodeling. Further elucidation of the mechanisms underlying these observations might help develop therapeutic strategies for airway diseases associated with smooth muscle hyperplasia such as asthma.

Effect of Traditional Chinese Medicine on Inflammatory Mediators in Pediatric Asthma

Objective. To observe the effects of empirical prescriptions of traditional Chinese medicine (TCM) on inflammatory mediators in pediatric asthma and to explore the underlying molecular mechanism in the treatment of asthma. Methods. A total of 182 children with asthma were randomly placed into either the TCM group (n = 97) or the salbutamol and montelukast (SM) group (n = 85). Patients in the TCM group were treated with a series of empirical prescriptions of TCM, while those in the SM group received salbutamol and montelukast. Both groups received their respective treatment for 12 weeks. There were 35 patients in TCM group and 34 patients in SM group providing venous blood. Real-time PCR was used to determine the mRNA expression levels of interleukin- (IL-) 10, IL-17, matrix metalloproteinase-9 (MMP-9), and transforming growth factor β1 (TGF-β1) in peripheral blood mononuclear cells before and after treatment. Enzyme-linked immunosorbent assay was used to measure the levels of IL-10, IL-17, MMP-9, and TGF-β1 in peripheral blood before and after treatment. Results. The mRNA expression of TGF-β1 in the SM group was downregulated (P = 0.00) after treatment. No significant differences were found between the TCM group and the SM group after treatment (P > 0.05). In the TCM group, the levels of IL-10, IL-17, and MMP-9 significantly decreased after treatment (P = 0.01, 0.04, and 0.03, resp.). In the SM group, IL-17, MMP-9, and TGF-β1 levels significantly decreased after treatment (P = 0.00, 0.03, and 0.00, resp.). There was no significant difference between the two groups regarding the levels of IL-10, IL-17, TGF-β1, and MMP-9 (P > 0.05). The difference of the level of IL-17 was negatively correlated with the change of C-ACT score in TCM group and SM group. Conclusion. TCM has a regulatory effect on the balance of some inflammatory mediators in pediatric asthma.

Transplantation of cyclic stretched fibroblasts accelerates the wound-healing process in streptozotocin-induced diabetic mice

Mechanical stimulation is a known modulator of survival and proliferation for many cells, including endothelial cells, smooth muscle cells, and bone marrow-derived mesenchymal stem cells. In this study, we found that mechanical strain prevents apoptosis and increases the adhesive ability of dermal fibroblasts in vitro and thus confers the survival advantage in vivo after transplantation of fibroblasts into the full-thickness wound of diabetic mice. Cyclic stretch at a frequency of 0.5 Hz and maximum elongation of 20% stimulates cellular survival mediated by the activation of extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and the serine/threonine kinase Akt (AKT). Stretching of the fibroblasts increases the synthesis of extracellular matrix proteins and the formation of denser focal adhesion structures, both of which are required for fibroblast adhesion. The stretched fibroblasts also upregulate the expression of vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1α (SDF-1α), which enhanced wound healing in vivo. Indeed, preconditioning with mechanical stretch allows better survival of the transplanted fibroblasts, when compared to unstretched control cells, in the wound environment of mice with streptozotocin-induced diabetes and thus accelerates the wound-healing process in these mice.

Airway smooth muscle in asthma: linking contraction and mechanotransduction to disease pathogenesis and remodelling

Asthma is an obstructive airway disease, with a heterogeneous and multifactorial pathogenesis. Although generally considered to be a disease principally driven by chronic inflammation, it is becoming increasingly recognised that the immune component of the pathology poorly correlates with the clinical symptoms of asthma, thus highlighting a potentially central role for non-immune cells. In this context airway smooth muscle (ASM) may be a key player, as it comprises a significant proportion of the airway wall and is the ultimate effector of acute airway narrowing. Historically, the contribution of ASM to asthma pathogenesis has been contentious, yet emerging evidence suggests that ASM contractile activation imparts chronic effects that extend well beyond the temporary effects of bronchoconstriction. In this review article we describe the effects that ASM contraction, in combination with cellular mechanotransduction and novel contraction-inflammation synergies, contribute to asthma pathogenesis. Specific emphasis will be placed on the effects that ASM contraction exerts on the mechanical properties of the airway wall, as well as novel mechanisms by which ASM contraction may contribute to more established features of asthma such as airway wall remodelling.

Airway remodelling in asthma: role for mechanical forces

Asthma is a chronic airway inflammatory disease with functional and structural changes, leading to bronchial hyperresponsiveness and airflow obstruction. Airway structural changes or airway remodelling consist of epithelial injury, goblet cell hyperplasia, subepithelial layer thickening, airway smooth muscle hyperplasia and angiogenesis. These changes were previously considered as a consequence of chronic airway inflammation. Even though inhaled corticosteroids can suppress airway inflammation, the natural history of asthma is still unaltered after inhaled corticosteroid treatment. As such there is increasing evidence for the role of mechanical forces within the asthmatic airway contributing to airway structural changes.

Reduced flow after tubularized incised plate urethroplasty--increased fibrogenesis, elastin fiber loss or neither?

PURPOSE

Low urinary flow rates are common after tubularized incised plate urethroplasty but the etiology remains unclear and may be related to low urethral compliance due to abnormal collagen concentrations and/or fewer elastic fibers in the healed urethral plate. We hypothesized that inserting a preputial mucosal graft over the dorsal raw area after the midline incision may avoid scarring and improve urethral compliance.

MATERIALS AND METHODS

Adult rabbits were submitted to tubularized incised plate urethroplasty with or without inlay preputial graft according to a previously described protocol. Tissular concentrations of collagens I, III, IV, VI, VIII and XIII were measured. Histomorphometric analysis was used to quantify elastic fibers in the urethra. Tubularized incised plate urethroplasty with and without inlay preputial graft was compared to normal rabbit urethras (controls).

RESULTS

mRNA concentrations for collagens I, II and XIII were similar between controls and operated rabbits. The proportions between collagens I and III were 1.05, 0.87 and 1.21, respectively, in controls and animals undergoing tubularized incised plate urethroplasty with and without inlay preputial graft. mRNA concentrations for collagen IV and collagens VI/VIII tended to be higher and lower, respectively, in the operated urethras, despite showing statistical significance only for collagen VIII in animals undergoing tubularized incised plate urethroplasty with inlay preputial graft vs controls (p=0.02). The operated animals did not demonstrate a reduced number of elastic fibers in the urethral tissues compared to controls.

CONCLUSIONS

Elastic fiber number and distribution were similar between tubularized incised plate urethroplasty cases and controls, suggesting that decreased concentrations of elastic fibers do not explain the reduced urethral compliance after tubularized incised plate urethroplasty. The raw area determined by the dorsal urethral incision regenerated after standard tubularized incised plate urethroplasty, while cicatrization with fibrosis occurred in correspondence to the grafted areas after tubularized incised plate urethroplasty with inlay preputial graft.

Inhibition of protein kinase C delta attenuates allergic airway inflammation through suppression of PI3K/Akt/mTOR/HIF-1 alpha/VEGF pathway

Vascular endothelial growth factor (VEGF) is supposed to contribute to the pathogenesis of allergic airway disease. VEGF expression is regulated by a variety of stimuli such as nitric oxide, growth factors, and hypoxia-inducible factor-1 alpha (HIF-1α). Recently, inhibition of the mammalian target of rapamycin (mTOR) has been shown to alleviate cardinal asthmatic features, including airway hyperresponsiveness, eosinophilic inflammation, and increased vascular permeability in asthma models. Based on these observations, we have investigated whether mTOR is associated with HIF-1α-mediated VEGF expression in allergic asthma. In studies with the mTOR inhibitor rapamycin, we have elucidated the stimulatory role of a mTOR-HIF-1α-VEGF axis in allergic response. Next, the mechanisms by which mTOR is activated to modulate this response have been evaluated. mTOR is known to be regulated by phosphoinositide 3-kinase (PI3K)/Akt or protein kinase C-delta (PKC δ) in various cell types. Consistent with these, our results have revealed that suppression of PKC δ by rottlerin leads to the inhibition of PI3K/Akt activity and the subsequent blockade of a mTOR-HIF-1α-VEGF module, thereby attenuating typical asthmatic attack in a murine model. Thus, the present data indicate that PKC δ is necessary for the modulation of the PI3K/Akt/mTOR signaling cascade, resulting in a tight regulation of HIF-1α activity and VEGF expression. In conclusion, PKC δ may represent a valuable target for innovative therapeutic treatment of allergic airway disease.

Role of vascular endothelial growth factor antagonism on airway remodeling in asthma

BACKGROUND

Vascular endothelial growth factor (VEGF) is an important mediator of the neoangiogenesis component of remodeling in asthma.

OBJECTIVE

To evaluate the influence of VEGF blockage on airway remodeling, specifically epithelium thickness, subepithelial smooth muscle thickness, number of mast and goblet cells, and basement membrane thickness, in a mouse model of chronic asthma.

METHODS

We used 30 BALB/c mice. The control group was not exposed to ovalbumin or any medication (group 1). Other groups were exposed to intraperitoneal and inhaled ovalbumin to achieve chronic asthma. Each of these groups received intraperitoneal saline (group 2), intraperitoneal dexamethasone (group 3), or intraperitoneal bevacizumab (group 4). Histomorphologic examination for epithelium thickness, subepithelial smooth muscle thickness, number of mast and goblet cells, and basement membrane thickness was performed from the middle zone of the left lung.

RESULTS

Treatment with anti-VEGF caused significant reduction in epithelial, subepithelial muscle, and basement membrane thickness compared with untreated asthmatic mice (P = .001, P = .03, and P = .009, respectively). Goblet and mast cell numbers were significantly lower in mice treated with anti-VEGF than in untreated mice (P = .02 and P = .007, respectively). Dexamethasone treatment resulted in improvement of all histomorphologic markers, except goblet cell number. Influences of dexamethasone and anti-VEGF on epithelial and basement membrane thickness and mast and goblet cell numbers did not differ (P > .05), but subepithelial muscle layer was thinner in the former (P = .003).

CONCLUSION

VEGF blockage may provide adjunctive therapeutic options as steroid-sparing agents for more effective treatment of remodeling in asthma.

Estimating cyclic shear strain in the common carotid artery using radiofrequency ultrasound

There is increasing evidence that supports the hypothesis that elevated cyclic shear strain in the adventitia of the common carotid artery promotes plaque progression. In this article, we estimated cyclic shear strain in the carotid arterial wall in 16 asymptomatic human participants using radio-frequency (RF) ultrasound. In each participant, we acquired two separate RF ultrasound recordings. We correlated the cyclic shear strain with the distension waveform (representing the blood pressure waveform) of the carotid artery and the brachial blood pressure. There were no significant differences between the shear strains estimated from the two separate RF ultrasound recordings. The point-in-time of the maximum shear strain showed a significant correlation with that of the dicrotic notch in the distension waveform (Spearman's coefficient = 0.7, p < 0.001). The pulse shear strain (difference between maximum and minimum shear strain) was significantly correlated with the pulse pressure as measured in the brachial artery (Spearman's coefficient = 0.4, p < 0.01). In this study, we show that the cyclic shear strain in the adventitia of the common carotid artery can be estimated using RF ultrasound. We found indications that the estimated cyclic shear strain was induced by the pulsating blood pressure and it was found to be higher in participants with an elevated pulse pressure.

Paradoxical effects of rapamycin on experimental house dust mite-induced asthma

The mammalian target of rapamycin (mTOR) modulates immune responses and cellular proliferation. The objective of this study was to assess whether inhibition of mTOR with rapamycin modifies disease severity in two experimental murine models of house dust mite (HDM)-induced asthma. In an induction model, rapamycin was administered to BALB/c mice coincident with nasal HDM challenges for 3 weeks. In a treatment model, nasal HDM challenges were performed for 6 weeks and rapamycin treatment was administered during weeks 4 through 6. In the induction model, rapamycin significantly attenuated airway inflammation, airway hyperreactivity (AHR) and goblet cell hyperplasia. In contrast, treatment of established HDM-induced asthma with rapamycin exacerbated AHR and airway inflammation, whereas goblet cell hyperplasia was not modified. Phosphorylation of the S6 ribosomal protein, which is downstream of mTORC1, was increased after 3 weeks, but not 6 weeks of HDM-challenge. Rapamycin reduced S6 phosphorylation in HDM-challenged mice in both the induction and treatment models. Thus, the paradoxical effects of rapamycin on asthma severity paralleled the activation of mTOR signaling. Lastly, mediastinal lymph node re-stimulation experiments showed that treatment of rapamycin-naive T cells with ex vivo rapamycin decreased antigen-specific Th2 cytokine production, whereas prior exposure to in vivo rapamycin rendered T cells refractory to the suppressive effects of ex vivo rapamycin. We conclude that rapamycin had paradoxical effects on the pathogenesis of experimental HDM-induced asthma. Thus, consistent with the context-dependent effects of rapamycin on inflammation, the timing of mTOR inhibition may be an important determinant of efficacy and toxicity in HDM-induced asthma.

Stretching mechanotransduction from the lung to the lab: approaches and physiological relevance in drug discovery

Recent years have shown a great deal of interest and research into the understanding of the biological and physiological roles of mechanical forces on cellular behavior. Despite these reports, in vitro screening of new molecular entities for lung ailments is still performed in static cell culture models. Failure to incorporate the effects of mechanical forces during early stages of screening could significantly reduce the success rate of drug candidates in the highly expensive clinical phases of the drug discovery pipeline. The objective of this review is to expand our current understanding of lung mechanotransduction and extend its applicability to cellular physiology and new drug screening paradigms. This review covers early in vivo studies and the importance of mechanical forces in normal lung development, use of different types of bioreactors that simulate in vivo movements in a controlled in vitro cell culture environment, and recent research using dynamic cell culture models. The cells in lungs are subjected to constant stretching (mechanical forces) in regular cycles due to involuntary expansion and contraction during respiration. The effects of stretch on normal and abnormal (disease) lung cells under pathological conditions are discussed. The potential benefits of extending dynamic cell culture models (screening in the presence of forces) and the associated challenges are also discussed in this review. Based on this review, the authors advocate the development of dynamic high throughput screening models that could facilitate the rapid translation of in vitro biology to animal models and clinical efficacy. These concepts are translatable to cardiovascular, digestive, and musculoskeletal tissues and in vitro cell systems employed routinely in drug-screening applications.

Mechanical regulation of glycogen synthase kinase 3β (GSK3β) in mesenchymal stem cells is dependent on Akt protein serine 473 phosphorylation via mTORC2 protein

Mechanical signals can inactivate glycogen synthase kinase 3β (GSK3β), resulting in stabilization of β-catenin. This signaling cascade is necessary for the inhibition of adipogenesis in mesenchymal stem cells (MSC) that is produced by a daily strain regimen. We investigated whether Akt is the mechanically activated kinase responsible for phosphorylation and inactivation of GSK3β in MSC. Mechanical strain (2% magnitude, 0.17 Hz) induced phosphorylation of Akt at Ser-473 and Thr-308 in parallel with phosphorylation of GSK3β at Ser-9. Inhibiting Akt (Akt1/2 kinase inhibitor treatment or Akt knockdown) prevented strain-induced phosphorylation of GSK3β at Ser-9. Inhibition of PI3K prevented Thr-308 phosphorylation, but strain-induced Ser-473 phosphorylation was measurable and induced phosphorylation of GSK3β, suggesting that Ser-473 phosphorylation is sufficient for the downstream mechanoresponse. As Rictor/mTORC2 (mammalian target of rapamycin complex 2) is known to transduce phosphorylation of Akt at Ser-473 by insulin, we investigated whether it contributes to strain-induced Ser-473 phosphorylation. Phosphorylation of Ser-473 by both mechanical and insulin treatment in MSC was prevented by the mTOR inhibitor KU0063794. When mTORC2 was blocked, mechanical GSK3β inactivation was prevented, whereas insulin inhibition of GSK3β was still measured in the absence of Ser-473 phosphorylation, presumably through phosphorylation of Akt at Thr-308. In sum, mechanical input initiates a signaling cascade that is uniquely dependent on mTORC2 activation and phosphorylation of Akt at Ser-473, an effect sufficient to cause inactivation of GSK3β. Thus, mechanical regulation of GSK3β downstream of Akt is dependent on phosphorylation of Akt at Ser-473 in a manner distinct from that of growth factors. As such, Akt reveals itself to be a pleiotropic signaling molecule whose downstream targets are differentially regulated depending upon the nature of the activating input.

Mechanical loading activates β-catenin signaling in periodontal ligament cells

OBJECTIVE

To determine whether β-catenin signaling is responsive to mechanical loading in periodontal ligament (PDL) cells.

MATERIALS AND METHODS

To determine whether Wnt/β-catenin signaling pathway components are present and functional, PDL cells were treated with lithium chloride or Wnt3a-conditioned media. To determine whether mechanical strain activates β-catenin signaling, PDL cells were subjected to compressive loading. Activation of the β-catenin signaling pathway was determined by immunofluorescence, Western immunoblotting, and TOPflash assay.

RESULTS

Mimicking Wnt signaling stimulates β-catenin nuclear translocation and T-cell factor/lymphoid enhancer binding factor-dependent transcriptional activation in PDL cells. Mechanical loading stimulates a transient accumulation of dephosphorylated β-catenin in the cytoplasm and its translocation to the nucleus. This effect of strain acts through activation of protein kinase B and phosphorylation of glycogen synthase kinase-3 beta. These strain-related changes do not involve the low-density lipoprotein receptor-related protein 5/Wnt receptor.

CONCLUSIONS

The Wnt/β-catenin signaling pathway components are functional and activated by mechanical loading in PDL cells. β-catenin serves as an effector of mechanical signals in PDL cells.

Role and mechanism of arsenic in regulating angiogenesis

Arsenic is a wide spread carcinogen associated with several kinds of cancers including skin, lung, bladder, and liver cancers. Lung is one of the major targets of arsenic exposure. Angiogenesis is the pivotal process during carcinogenesis and chronic pulmonary diseases, but the role and mechanism of arsenic in regulating angiogenesis remain to be elucidated. In this study we show that short time exposure of arsenic induces angiogenesis in both human immortalized lung epithelial cells BEAS-2B and adenocarcinoma cells A549. To study the molecular mechanism of arsenic-inducing angiogenesis, we find that arsenic induces reactive oxygen species (ROS) generation, which activates AKT and ERK1/2 signaling pathways and increases the expression of hypoxia-inducible factor 1 (HIF-1) and vascular endothelial growth factor (VEGF). Inhibition of ROS production suppresses angiogenesis by decreasing AKT and ERK activation and HIF-1 expression. Inhibition of ROS, AKT and ERK1/2 signaling pathways is sufficient to attenuate arsenic-inducing angiogenesis. HIF-1 and VEGF are downstream effectors of AKT and ERK1/2 that are required for arsenic-inducing angiogenesis. These results shed light on the mechanism of arsenic in regulating angiogenesis, and are helpful to develop mechanism-based intervention to prevent arsenic-induced carcinogenesis and angiogenesis in the future.

A new procedure for determining the genetic basis of a physiological process in a non-model species, illustrated by cold induced angiogenesis in the carp

BACKGROUND

Physiological processes occur in many species for which there is yet no sequenced genome and for which we would like to identify the genetic basis. For example, some species increase their vascular network to minimise the effects of reduced oxygen diffusion and increased blood viscosity associated with low temperatures. Since many angiogenic and endothelial genes have been discovered in man, functional homolog relationships between carp, zebrafish and human were used to predict the genetic basis of cold-induced angiogenesis in Cyprinus Carpio (carp). In this work, carp sequences were collected and built into contigs. Human-carp functional homolog relationships were derived via zebrafish using a new Conditional Stepped Reciprocal Best Hit (CSRBH) protocol. Data sources including publications, Gene Ontology and cDNA libraries were then used to predict the identity of known or potential angiogenic genes. Finally, re-analyses of cold carp microarray data identified carp genes up-regulated in response to low temperatures in heart and muscle.

RESULTS

The CSRBH approach outperformed all other methods and attained 8,726 carp to human functional homolog relationships for 16,650 contiguous sequences. This represented 3,762 non-redundant genes and 908 of them were predicted to have a role in angiogenesis. The total number of up-regulated differentially expressed genes was 698 and 171 of them were putatively angiogenic. Of these, 5 genes representing the functional homologs NCL, RHOA, MMP9, GRN and MAPK1 are angiogenesis-related genes expressed in response to low temperature.

CONCLUSION

We show that CSRBH functional homologs relationships and re-analyses of gene expression data can be combined in a non-model species to predict genes of biological interest before a genome sequence is fully available. Programs to run these analyses locally are available from http://www.cbrg.ox.ac.uk/~jherbert/.

Why is effective treatment of asthma so difficult? An integrated systems biology hypothesis of asthma

A hypothesis is presented that asthma is not only an airway disease, but that the disease involves the entire lung, and that the chronicity of asthma and asthma exacerbations can perhaps be explained if one considers asthma as a systemic disease. Increased lung-not only airway-vascularity may be the result of the action of angiogenesis factors, such as vascular endothelial growth factor (VEGF) and sphingosine-1-phosphate (S1P). A bone-marrow lung axis can be postulated as one element of the systemic nature of the asthma syndrome, in which the inflamed lung emits chemotactic signals, which the bone marrow responds to by releasing cells that contribute to lung angiogenesis. A molecular model of the pathobiology of asthma can be built by connecting hypoxia-inducible transcription factor-1 alpha, VEGF S1P, and bone-marrow precursor cell mobilization and acknowledging that angiogenesis is part of the inflammatory response.

Exposure to environmental tobacco smoke induces angiogenesis and leukocyte trafficking in lung microvessels

Exposure to environmental tobacco smoke (ETS) is known to contribute to and exacerbate inflammatory diseases of the lung such as chronic obstructive pulmonary disease (COPD) and asthma. The effect of ETS on angiogenesis and leukocyte recruitment, both of which promote lung inflammation, was investigated using lung tissue from mice exposed to aged and diluted sidestream cigarette smoke or fresh air for 12 weeks and transplanted into dorsal skin-fold chambers in nude mice. Lung tissue from mice exposed to cigarette smoke for 12 weeks exhibited significantly increased vascular density (angiogenesis) associated with selectin-mediated increased intravascular leukocyte rolling and adhesion compared to fresh air-exposed lung tissue by intravital microscopy. Further, neutrophils from nicotine-exposed mice displayed significantly increased rolling and adhesion compared to control neutrophils in microvessels of nicotine-exposed lungs versus control lung microvessels, suggesting that nicotine in cigarette smoke can augment leukocyte-endothelial interactions. ETS-induced angiogenesis and leukocyte trafficking may play a key role in airway recruitment of inflammatory cells in ETS-associated disorders such as COPD bronchitis or asthma.

Airway vascular reactivity and vascularisation in human chronic airway disease

Altered bronchial vascular reactivity and remodelling including angiogenesis are documented features of asthma and other chronic inflammatory airway diseases. Expansion of the bronchial vasculature under these conditions involves both functional (vasodilation, hyperperfusion, increased microvascular permeability, oedema formation, and inflammatory cell recruitment) and structural changes (tissue and vascular remodelling) in the airways. These changes in airway vascular reactivity and vascularisation have significant pathophysiological consequences, which are manifest in the clinical symptoms of airway disease. Airway vascular reactivity is regulated by a wide variety of neurotransmitters and inflammatory mediators. Similarly, multiple growth factors are implicated in airway angiogenesis, with vascular endothelial growth factor amongst the most important. Increasing attention is focused on the complex interplay between angiogenic growth factors, airway smooth muscle and the various collagen-derived fragments that exhibit anti-angiogenic properties. The balance of these dynamic influences in airway neovascularisation processes and their therapeutic implications is just beginning to be elucidated. In this review article, we provide an account of recent developments in the areas of vascular reactivity and airway angiogenesis in chronic airway diseases.

An imbalance in C/EBPs and increased mitochondrial activity in asthmatic airway smooth muscle cells: novel targets in asthma therapy?

The asthma prevalence was increasing over the past two decades worldwide. Allergic asthma, caused by inhaled allergens of different origin or by food, is mediated by inflammatory mechanisms. The action of non-allergic asthma, induced by cold air, humidity, temperature or exercise, is not well understood. Asthma affects up to 15% of the population and is treated with anti-inflammatory and muscle relaxing drugs which allow symptom control. Asthma was first defined as a malfunction of the airway smooth muscle, later as an imbalanced immune response of the lung. Recent studies placed the airway smooth muscle again into the focus. Here we summarize the molecular biological basis of the deregulated function of the human airway smooth muscle cell as a cause or important contributor to the pathology of asthma. In the asthmatic human airway smooth muscle cells, there is: (i) a deregulation of cell differentiation due to low levels of maturation-regulating transcription factors such as CCAAT/enhancer binding proteins and peroxisome proliferator-activated receptors, thereby reducing the cells threshold to proliferate and to secrete pro-inflammatory cytokines under certain conditions; (ii) a higher basal energy turnover that is due to increased number and activity of mitochondria; and (iii) a modified feedback mechanism between cells and the extracellular matrix they are embedded in. All these cellular pathologies are linked to each other and to the innate immune response of the lung, but the sequence of events is unclear and needs further investigation. However, these findings may present the basis for the development of novel curative asthma drugs.

TGF-beta effects on airway smooth muscle cell proliferation, VEGF release and signal transduction pathways

BACKGROUND AND OBJECTIVE

Airway smooth muscle (ASM) cell hyperplasia is a key feature of airway remodelling. Mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) are key components in signal transduction associated with cell proliferation; MAPK consists of the extracellular signal-regulated kinase (ERK), p38MAPK and c-Jun NH(2)-terminal kinase (JNK). The effect of transforming growth factor (TGF)-beta on the proliferation of ASM cells, the release of vascular endothelial growth factor (VEGF) by ASM cells and relevant signal transduction pathways were investigated.

METHODS

ASM cells were growth-arrested for 48 h then stimulated with platelet-derived growth factor (PDGF), TGF-beta and dexamethasone. ASM cells were also treated with specific inhibitors of MAPK (PD98059), PI3K (wortmannin) and JNK (SP600125). Cell proliferation and VEGF concentrations were measured.

RESULTS

TGF-beta neither augmented ASM cell proliferation nor showed a synergistic effect on PDGF-mediated ASM cell proliferation. Dexamethasone did not suppress ASM cell proliferation. VEGF release was augmented by TGF-beta stimulation in a time-dependent manner, and was further enhanced by co-stimulation with PDGF and TGF-beta. Dexamethasone suppressed VEGF release significantly. TGF-beta enhanced PI3K phosphorylation, while PDGF augmented both ERK and PI3K phosphorylation. Wortmannin inhibited both TGF-beta- and PDGF-stimulated VEGF release.

CONCLUSIONS

TGF-beta may facilitate airway remodelling by promoting VEGF release through the PI3K pathway, rather than via ASM cell proliferation.

Mechanical strain inhibits adipogenesis in mesenchymal stem cells by stimulating a durable beta-catenin signal

The ability of exercise to decrease fat mass and increase bone mass may occur through mechanical biasing of mesenchymal stem cells (MSCs) away from adipogenesis and toward osteoblastogenesis. C3H10T1/2 MSCs cultured in highly adipogenic medium express peroxisome proliferator-activated receptor gamma and adiponectin mRNA and protein, and accumulate intracellular lipid. Mechanical strain applied for 6 h daily inhibited expression of peroxisome proliferator-activated receptor gamma and adiponectin mRNA by up to 35 and 50%, respectively, after 5 d. A decrease in active and total beta-catenin levels during adipogenic differentiation was entirely prevented by daily application of mechanical strain; furthermore, strain induced beta-catenin nuclear translocation. Inhibition of glycogen synthase kinase-3beta by lithium chloride or SB415286 also prevented adipogenesis, suggesting that preservation of beta-catenin levels was important to strain inhibition of adipogenesis. Indeed, mechanical strain inactivated glycogen synthase kinase-3beta, which was preceded by Akt activation, indicating that strain transmits antiadipogenic signals through this pathway. Cells grown under adipogenic conditions showed no increase in osteogenic markers runt-related transcription factor (Runx) 2 and osterix (Osx); subsequent addition of bone morphogenetic protein 2 for 2 d increased Runx2 but not Osx expression in unstrained cultures. When cultures were strained for 5 d before bone morphogenetic protein 2 addition, Runx2 mRNA increased more than in unstrained cultures, and Osx expression more than doubled. As such, mechanical strain enhanced MSC potential to enter the osteoblast lineage despite exposure to adipogenic conditions. Our results indicate that MSC commitment to adipogenesis can be suppressed by mechanical signals, allowing other signals to promote osteoblastogenesis. These data suggest that positive effects of exercise on both fat and bone may occur during mesenchymal lineage selection.

Strain-induced proliferation requires the phosphatidylinositol 3-kinase/AKT/glycogen synthase kinase pathway

The intestinal epithelium is repetitively deformed by shear, peristalsis, and villous motility. Such repetitive deformation stimulates the proliferation of intestinal epithelial cells on collagen or laminin substrates via ERK, but the upstream mediators of this effect are poorly understood. We hypothesized that the phosphatidylinositol 3-kinase (PI3K)/AKT cascade mediates this mitogenic effect. PI3K, AKT, and glycogen synthase kinase-3beta (GSK-3beta) were phosphorylated by 10 cycles/min strain at an average 10% deformation, and pharmacologic blockade of these molecules or reduction by small interfering RNA (siRNA) prevented the mitogenic effect of strain in Caco-2 or IEC-6 intestinal epithelial cells. Strain MAPK activation required PI3K but not AKT. AKT isoform-specific siRNA transfection demonstrated that AKT2 but not AKT1 is required for GSK-3beta phosphorylation and the strain mitogenic effect. Furthermore, overexpression of AKT1 or an AKT chimera including the PH domain and hinge region of AKT2 and the catalytic domain and C-tail of AKT1 prevented strain activation of GSK-3beta, but overexpression of AKT2 or a chimera including the PH domain and hinge region of AKT1 and the catalytic domain and C-tail of AKT2 did not. These data delineate a role for PI3K, AKT2, and GSK-3beta in the mitogenic effect of strain. PI3K is required for both ERK and AKT2 activation, whereas AKT2 is sequentially required for GSK-3beta. Furthermore, AKT2 specificity requires its catalytic domain and tail region. Manipulating this pathway may prevent mucosal atrophy and maintain the mucosal barrier in conditions such as ileus, sepsis, and prolonged fasting when peristalsis and villous motility are decreased and the mucosal barrier fails.

Ion channel regulation of intracellular calcium and airway smooth muscle function

Airway hyper-responsiveness associated with asthma is mediated by airway smooth muscle cells (SMCs) and has a complicated etiology involving increases in cell contraction and proliferation and the secretion of inflammatory mediators. Although these pathological changes are diverse, a common feature associated with their regulation is a change in intracellular Ca(2+) concentration ([Ca(2+)](i)). Because the [Ca(2+)](i) itself is a function of the activity and expression of a variety of ion channels, in both the plasma membrane and sarcoplasmic reticulum of the SMC, the modification of this ion channel activity may predispose airway SMCs to hyper-responsiveness. Our objective is to review how ion channels determine the [Ca(2+)](i) and influence the function of airway SMCs and emphasize the potential of ion channels as sites for therapeutic approaches to asthma.

Beta-catenin levels influence rapid mechanical responses in osteoblasts

Mechanical loading of bone initiates an anabolic, anticatabolic pattern of response, yet the molecular events involved in mechanical signal transduction are not well understood. Wnt/beta-catenin signaling has been recognized in promoting bone anabolism, and application of strain has been shown to induce beta-catenin activation. In this work, we have used a preosteoblastic cell line to study the effects of dynamic mechanical strain on beta-catenin signaling. We found that mechanical strain caused a rapid, transient accumulation of active beta-catenin in the cytoplasm and its translocation to the nucleus. This was followed by up-regulation of the Wnt/beta-catenin target genes Wisp1 and Cox2, with peak responses at 4 and 1 h of strain, respectively. The increase of beta-catenin was temporally related to the activation of Akt and subsequent inactivation of GSK3beta, and caveolin-1 was not required for these molecular events. Application of Dkk-1, which disrupts canonical Wnt/LRP5 signaling, did not block strain-induced nuclear translocation of beta-catenin or up-regulation of Wisp1 and Cox2 expression. Conditions that increased basal beta-catenin levels, such as lithium chloride treatment or repression of caveolin-1 expression, were shown to enhance the effects of strain. In summary, mechanical strain activates Akt and inactivates GSK3beta to allow beta-catenin translocation, and Wnt signaling through LRP5 is not required for these strain-mediated responses. Thus, beta-catenin serves as both a modulator and effector of mechanical signals in bone cells.

Induction of angiogenesis by airway smooth muscle from patients with asthma

RATIONALE

Airway remodeling in asthma involves accumulation of airway smooth muscle (ASM) and increased vascularity due to angiogenesis. Bronchial blood vessels and ASM are found in close proximity, and ASM releases multiple proinflammatory mediators, including vascular endothelial growth factor (VEGF).

OBJECTIVES

We examined whether release of proangiogenic mediators is increased in ASM from subjects with asthma and whether this is translated to induction of angiogenesis.

METHODS

Biopsy-derived ASM cells were cultured from 12 subjects with mild asthma, 8 with moderate asthma, and 9 healthy control subjects. Angiogenesis induced by cell-conditioned medium (CM) from ASM was evaluated in a tubule formation assay. Anti-CD31-labeled tubules were quantified by image analysis. Angiogenic factors in CM were quantified by antibody arrays and by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Induction of angiogenesis by CM from unstimulated ASM was increased in subjects with mild asthma (twofold) and moderate asthma (threefold), compared with healthy CM (P < 0.001). Levels of angiogenic factors (VEGF, angiopoietin [Ang]-1, angiogenin) were similarly elevated in CM from subjects with asthma compared with that from healthy subjects (P < 0.05), whereas antiangiogenic factors (endostatin, Ang-2) were unchanged. VEGF, Ang-1, and angiogenin in combination increased vascularity (twofold, P < 0.01) in cultured intact biopsies. Selective VEGF immunodepletion abolished enhanced tubule formation by CM from asthmatic ASM (P < 0.01), but CM depletion of Ang-1 or angiogenin had no effect.

CONCLUSIONS

ASM cultured from subjects with mild or moderate asthma, but not from healthy control subjects, promotes angiogenesis in vitro. This proangiogenic capacity resides in elevated VEGF release and suggests that ASM regulates airway neovascularization in asthma.

Mechanical signals modulated vascular endothelial growth factor-A (VEGF-A) alternative splicing in osteoblastic cells through actin polymerisation

Since VEGF-A is involved in mechanically induced bone gain and because vegf exists under 6 isoforms exerting various biological effects, we studied vegf isoform expression and VEGF protein production in osteoblastic cells (rat Ros17/2.8 and human osteoblasts) submitted to 4 mechanical regimens. Mechanical regimens (1% stretch deformation) were designed with a fixed number of cycles (450) delivered at various frequencies (0.05 to 5 Hz). We found a negative correlation (R(2)=0.76, p<0.0001) between production of soluble VEGF and mechanical stretch frequency and a positive correlation (R(2)=0.99, p<0.0001) between production of matrix-bound VEGF and mechanical stretch frequency. mRNA expressions of soluble VEGF isoforms (121, 165) were specifically expressed under low frequency while matrix-bound VEGF isoforms (206, 189, 165, 145) were specifically expressed under high frequency in human osteoblasts. As f-actin stress fiber formation was significantly increased selectively in high frequency conditions, we disrupted actin fibers in Ros17/2.8 and found that immobilisation of VEGF was abolished. Conversely, Jasplakinolide treatment which increases stress fiber formation was able to mimic high frequency stretch-induced immobilisation of VEGF. Thus, we speculate that the stretch-induced increase in cell tension is responsible for matrix-bound vegf isoform production. Mechanically induced selection of soluble or matrix-bound VEGF production may modify osteoblast and endothelial cell crosstalk crucial during osteogenesis and fracture healing.

Airway modeling and remodeling in the pathogenesis of asthma

PURPOSE OF REVIEW

Asthma remains a severe health problem since current therapies are directed to suppressing, rather than preventing or reversing, the primary disease process. Clearly, a greater understanding of the pathogenesis of asthma is critical to the development of better therapeutic modalities. In this review, we discuss the recent advancements in research targeting the role of airway remodeling in asthma.

RECENT FINDINGS

Epithelial fragility and abnormalities are being recognized as important facets of asthma, as are other features of remodeling such as angiogenesis, goblet cell hyperplasia and thickened lamina reticularis. Significantly, these anomalies occur early in disease pathogenesis. However, their impact on disease severity remains unclear.

SUMMARY

Although an altered immune response is undoubtedly important to the pathogenesis of asthma, there is increasing evidence that the tissue-specific manifestations occur independently of inflammation and significantly impact on disease development and severity.