ERK activation and mitogenesis in human airway smooth muscle cells

Mechanisms of biased agonism by Gαi/o-biased stapled peptide agonists of the relaxin-3 receptor

The neuropeptide relaxin-3 is composed of an A chain and a B chain held together by disulfide bonds, and it modulates functions such as anxiety and food intake by binding to and activating its cognate receptor RXFP3, mainly through the B chain. Biased ligands of RXFP3 would help to determine the molecular mechanisms underlying the activation of G proteins and β-arrestins downstream of RXFP3 that lead to such diverse functions. We showed that the i, i+4 stapled relaxin-3 B chains, 14s18 and d(1-7)14s18, were Gαi/o-biased agonists of RXFP3. These peptides did not induce recruitment of β-arrestin1/2 to RXFP3 by GPCR kinases (GRKs), in contrast to relaxin-3, which enabled the GRK2/3-mediated recruitment of β-arrestin1/2 to RXFP3. Relaxin-3 and the previously reported peptide 4 (an i, i+4 stapled relaxin-3 B chain) did not exhibit biased signaling. The staple linker of peptide 4 and parts of both the A chain and B chain of relaxin-3 interacted with extracellular loop 3 (ECL3) of RXFP3, moving it away from the binding pocket, suggesting that unbiased ligands promote a more open conformation of RXFP3. These findings highlight roles for the A chain and the N-terminal residues of the B chain of relaxin-3 in inducing conformational changes in RXFP3, which will help in designing selective biased ligands with improved therapeutic efficacy.

Progress in the development of kinase inhibitors for treating asthma and COPD

Current therapies to mitigate inflammatory responses involved in airway remodeling and associated pathological features of asthma and chronic obstructive pulmonary disease (COPD) are limited and largely ineffective. Inflammation and the release of cytokines and growth factors activate kinase signaling pathways that mediate changes in airway mesenchymal cells such as airway smooth muscle cells and lung fibroblasts. Proliferative and secretory changes in mesenchymal cells exacerbate the inflammatory response and promote airway remodeling, which is often characterized by increased airway smooth muscle mass, airway hyperreactivity, increased mucus secretion, and lung fibrosis. Thus, inhibition of relevant kinases has been viewed as a potential therapeutic approach to mitigate the debilitating and, thus far, irreversible airway remodeling that occurs in asthma and COPD. Despite FDA approval of several kinase inhibitors for the treatment of proliferative disorders, such as cancer and inflammation associated with rheumatoid arthritis and ulcerative colitis, none of these drugs have been approved to treat asthma or COPD. This review will provide a brief overview of the role kinases play in the pathology of asthma and COPD and an update on the status of kinase inhibitors currently in clinical trials for the treatment of obstructive pulmonary disease. In addition, potential issues associated with the current kinase inhibitors, which have limited their success as therapeutic agents in treating asthma or COPD, and alternative approaches to target kinase functions will be discussed.

The extract from Hyssopus cuspidatus Boriss. Prevents bronchial airway remodeling by inhibiting mouse bronchial wall thickening and hASMC proliferation and migration

ETHNOPHARMACOLOGICAL RELEVANCE

Bronchial asthma, a non-communicable chronic respiratory disease, affects people of all ages. An important pathological feature of bronchial asthma is airway remodeling. Hyssopus cuspidatus Boriss. has been used to treat bronchial asthma for over 100 years in Uygur medicine. The ethanol extract of Hyssopus cuspidatus Boriss.(JAX2) can improve airway inflammation in asthma. However, the anti-asthmatic airway-remodeling effect of JAX2 is unclear.

AIM OF THE STUDY

The current study investigated the anti-airway remodeling effect of JAX2 and elucidated its mechanism of action.

MATERIALS AND METHODS

The present study established an ovalbumin-induced mouse model of asthma and platelet-derived growth factor-BB-induced human airway smooth muscle cells (hASMCs) proliferation model, with dexamethasone (DEX) and feining tablets (FNP) designated as positive control drugs. Pathological changes in lung tissues were observed using hematoxylin and eosin staining. Interleukin (IL)-5, IL-10, IL-13, and IL-33 levels in the bronchoalveolar lavage fluid (BALF) and serum of mice were determined using enzyme-linked immunosorbent assay (ELISA). Changes in the expression and distribution of TGF-β1, p-ERK1/2, Smad2/3, and p-Smad3 in lung tissues were determined using immunohistochemistry. Western blotting (WB) was used to determine the protein levels of p-ERK1/2 in lung tissues and cells. MTS assay was used to determine the effects of JAX2 on cell proliferation. IL-5, IL-10, IL-13, MMP-2, and MMP-9 levels in the cell supernatant were determined using ELISA. HASMCs migration was observed using the scratch and transwell methods. The effect of JAX2 on the hASMCs cycle was determined using flow cytometry.

RESULTS

JAX2 significantly improved the pathological status of lung tissues in asthmatic mice. It could also significantly reduce IL-5, IL-13, and IL-33 levels in the BALF and serum of asthmatic mice in a dose-dependent manner and significantly increase IL-10 levels. TGF-β1, p-ERK1/2, Smad2/3, and p-Smad3 expression in lung tissues were decreased in a dose-dependent manner. The protein level of p-ERK1/2 in lung tissues was also reduced. JAX2 could significantly inhibit the proliferation and migration of PDGF-BB-induced hASMCs. IL-5, IL-13, MMP-9, and MMP-2 levels decreased significantly, and IL-10 levels increased significantly in a dose-dependent manner in the cell supernatant. JAX2 could block hASMCs in the G0/G1 phase, thereby inhibiting cell proliferation. p-ERK1/2 protein levels were found to decrease in a dose-dependent manner.

CONCLUSIONS

JAX2 significantly inhibits airway remodeling in asthma. Its mechanism of action may be inhibiting the proliferation and migration of hASMCs, releasing inflammatory factors and metalloproteinases, activating the ERK1/2 signal pathway, and promoting the secretion of anti-inflammatory factors.

Targeted Inhibition of Select Extracellular Signal-regulated Kinases 1 and 2 Functions Mitigates Pathological Features of Asthma in Mice

ERK1/2 (extracellular signal-regulated kinases 1 and 2) regulate the activity of various transcription factors that contribute to asthma pathogenesis. Although an attractive drug target, broadly inhibiting ERK1/2 is challenging because of unwanted cellular toxicities. We have identified small molecule inhibitors with a benzenesulfonate scaffold that selectively inhibit ERK1/2-mediated activation of AP-1 (activator protein-1). Herein, we describe the findings of targeting ERK1/2-mediated substrate-specific signaling with the small molecule inhibitor SF-3-030 in a murine model of house dust mite (HDM)-induced asthma. In 8- to 10-week-old BALB/c mice, allergic asthma was established by repeated intranasal HDM (25 μg/mouse) instillation for 3 weeks (5 days/week). A subgroup of mice was prophylactically dosed with 10 mg/kg SF-3-030/DMSO intranasally 30 minutes before the HDM challenge. Following the dosing schedule, mice were evaluated for alterations in airway mechanics, inflammation, and markers of airway remodeling. SF-3-030 treatment significantly attenuated HDM-induced elevation of distinct inflammatory cell types and cytokine concentrations in BAL and IgE concentrations in the lungs. Histopathological analysis of lung tissue sections revealed diminished HDM-induced pleocellular peribronchial inflammation, mucus cell metaplasia, collagen accumulation, thickening of airway smooth muscle mass, and expression of markers of cell proliferation (Ki-67 and cyclin D1) in mice treated with SF-3-030. Furthermore, SF-3-030 treatment attenuated HDM-induced airway hyperresponsiveness in mice. Finally, mechanistic studies using transcriptome and proteome analyses suggest inhibition of HDM-induced genes involved in inflammation, cell proliferation, and tissue remodeling by SF-3-030. These preclinical findings demonstrate that function-selective inhibition of ERK1/2 signaling mitigates multiple features of asthma in a murine model.

FRET Visualization of Cyclic Stretch-Activated ERK via Calcium Channels Mechanosensation While Not Integrin β1 in Airway Smooth Muscle Cells

Mechanical stretch is one type of common physiological activities such as during heart beating, lung breathing, blood flow through the vessels, and physical exercise. The mechanical stimulations regulate cellular functions and maintain body homeostasis. It still remains to further characterize the mechanical-biomechanical coupling mechanism. Here we applied fluorescence resonance energy transfer (FRET) technology to visualize ERK activity in airway smooth muscle (ASM) cells under cyclic stretch stimulation in airway smooth muscle (ASM) cells, and studied the mechanosensing pathway. FRET measurements showed apparent ERK activation by mechanical stretch, which was abolished by ERK inhibitor PD98059 pretreatment. Inhibition of extracellular Ca²⁺ influx reduced ERK activation, and selective inhibition of inositol 1,4,5-trisphosphate receptor (IP₃R) Ca²⁺ channel or SERCA Ca²⁺ pump on endoplasmic reticulum (ER) blocked the activation. Chemical inhibition of the L-type or store-operated Ca²⁺ channels on plasma membrane, or inhibition of integrin β1 with siRNA had little effect on ERK activation. Disruption of actin cytoskeleton but not microtubule one inhibited the stretch-induced ERK activation. Furthermore, the ER IP₃R-dependent ERK activation was not dependent on phospholipase C-IP₃ signal, indicating possibly more mechanical mechanism for IP₃R activation. It is concluded from our study that the mechanical stretch activated intracellular ERK signal in ASM cells through membrane Ca²⁺ channels mechanosensation but not integrin β1, which was mediated by actin cytoskeleton.

HSPA12A improves endothelial integrity to attenuate lung injury during endotoxemia through activating ERKs and Akt-dependent signaling

Acute lung injury (ALI) is a critical manifestation of sepsis/septic shock. Disruption of endothelial barrier function is critical for ALI pathogenesis; however, the regulation of endothelial barrier integrity remains largely unclear. Heat shock protein A12A (HSPA12A) is an atypical member of HSP70 family. We have recently demonstrated that hepatocyte HSPA12A attenuated the bacteria endotoxin (lipopolysaccharide, LPS)-induced liver injury. However, the role of HSPA12A in endothelial barrier function and ALI is unknown. Here in this study, HSPA12A showed upregulation in lungs of mice during bacteria endotoxin (lipopolysaccharide, LPS)-induced lung injury in vivo and in primary human umbilical vein endothelial cells (HUVECs) during LPS-induced barrier disruption in vitro. Knockout of HSPA12A in mice exacerbated LPS-induced ALI. Intriguingly, overexpression of HSPA12A in HUVECs attenuated the LPS-induced endothelial hyperpermeability. In line with this, HSPA12A overexpression increased VE-cadherin and decreased VEGF expression following LPS treatment in HUVECs. Also, knockout of HSPA12A enhanced the LPS-evoked pulmonary endothelial cell apoptosis in mice whereas overexpression of HSPA12A inhibited the LPS-induced death of HUVECs. The levels of ERKs and Akt phosphorylation in HUVECs were promoted by HSPA12A overexpression when cells exposed to LPS. Importantly, inhibition of either ERKs or Akt diminished the HSPA12A-induced protection from LPS-induced endothelial hyperpermeability and death. Taken together, these findings indicated that HSPA12A is a novel regulator of endothelial barrier function through both ERKs and Akt-mediated signaling. HSPA12A might represent a viable strategy for the pulmonary protection against endotoxemia challenge.

TNFα induces mitochondrial fragmentation and biogenesis in human airway smooth muscle

In human airway smooth muscle (hASM), mitochondrial volume density is greater in asthmatic patients compared with normal controls. There is also an increase in mitochondrial fragmentation in hASM of moderate asthmatics associated with an increase in dynamin-related protein 1 (Drp1) and a decrease in mitofusin 2 (Mfn2) expression, mitochondrial fission, and fusion proteins, respectively. Proinflammatory cytokines such TNFα contribute to hASM hyperreactivity and cell proliferation associated with asthma. However, the involvement of proinflammatory cytokines in mitochondrial remodeling is not clearly established. In nonasthmatic hASM cells, mitochondria were labeled using MitoTracker Red and imaged in three dimensions using a confocal microscope. After 24-h TNFα exposure, mitochondria in hASM cells were more fragmented, evidenced by decreased form factor and aspect ratio and increased sphericity. Associated with increased mitochondrial fragmentation, Drp1 expression increased while Mfn2 expression was reduced. TNFα also increased mitochondrial biogenesis in hASM cells reflected by increased peroxisome proliferator-activated receptor-γ coactivator 1α expression and increased mitochondrial DNA copy number. Associated with mitochondrial biogenesis, TNFα exposure also increased mitochondrial volume density and porin expression, resulting in an increase in maximum O2 consumption rate. However, when normalized for mitochondrial volume density, O2 consumption rate per mitochondrion was reduced by TNFα exposure. Associated with mitochondrial fragmentation and biogenesis, TNFα also increased hASM cell proliferation, an effect mimicked by siRNA knockdown of Mfn2 expression and mitigated by Mfn2 overexpression. The results of this study support our hypothesis that in hASM cells exposed to TNFα mitochondria are more fragmented, with an increase in mitochondrial biogenesis and mitochondrial volume density resulting in reduced O2 consumption rate per mitochondrion.

Endoplasmic Reticulum Stress and Mitochondrial Function in Airway Smooth Muscle

Inflammatory airway diseases such as asthma affect more than 300 million people world-wide. Inflammation triggers pathophysiology via such as tumor necrosis factor α (TNFα) and interleukins (e.g., IL-13). Hypercontraction of airway smooth muscle (ASM) and ASM cell proliferation are major contributors to the exaggerated airway narrowing that occurs during agonist stimulation. An emergent theme in this context is the role of inflammation-induced endoplasmic reticulum (ER) stress and altered mitochondrial function including an increase in the formation of reactive oxygen species (ROS). This may establish a vicious cycle as excess ROS generation leads to further ER stress. Yet, it is unclear whether inflammation-induced ROS is the major mechanism leading to ER stress or the consequence of ER stress. In various diseases, inflammation leads to an increase in mitochondrial fission (fragmentation), associated with reduced levels of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2). Mitochondrial fragmentation may be a homeostatic response since it is generally coupled with mitochondrial biogenesis and mitochondrial volume density thereby reducing demand on individual mitochondrion. ER stress is triggered by the accumulation of unfolded proteins, which induces a homeostatic response to alter protein balance via effects on protein synthesis and degradation. In addition, the ER stress response promotes protein folding via increased expression of molecular chaperone proteins. Reduced Mfn2 and altered mitochondrial dynamics may not only be downstream to ER stress but also upstream such that a reduction in Mfn2 triggers further ER stress. In this review, we summarize the current understanding of the link between inflammation-induced ER stress and mitochondrial function and the role played in the pathophysiology of inflammatory airway diseases.

Crosstalk Between Signaling Pathways Involved in the Regulation of Airway Smooth Muscle Cell Hyperplasia

Increased ASM mass, primarily due to ASM hyperplasia, has been recognized as a hallmark of airway remodeling in asthma. Increased ASM mass is the major contributor to the airway narrowing, thus worsening the bronchoconstriction in response to stimuli. Inflammatory mediators and growth factors released during inflammation induce increased ASM mass surrounding airway wall via increased ASM proliferation, diminished ASM apoptosis and increased ASM migration. Several major pathways, such as MAPKs, PI3K/AKT, JAK2/STAT3 and Rho kinase, have been reported to regulate these cellular activities in ASM and were reported to be interrelated at certain points. This article aims to provide an overview of the signaling pathways/molecules involved in ASM hyperplasia as well as the mapping of the interplay/crosstalk between these major pathways in mediating ASM hyperplasia. A more comprehensive understanding of the complexity of cellular signaling in ASM cells will enable more specific and safer drug development in the control of asthma.

The free fatty acid receptor 1 promotes airway smooth muscle cell proliferation through MEK/ERK and PI3K/Akt signaling pathways

Obesity is a risk factor for asthma and influences airway hyperresponsiveness, which is in part modulated by airway smooth muscle proliferative remodeling. Plasma free fatty acids (FFAs) levels are elevated in obese individuals, and long-chain FFAs act as endogenous ligands for the free fatty acid receptor 1 (FFAR1), which couples to both G_q and G_i proteins. We examined whether stimulation of FFAR1 induces airway smooth muscle cell proliferation through classical MEK/ERK and/or phosphoinositide 3-kinase (PI3K)/Akt signaling pathways. The long-chain FFAs (oleic acid and linoleic acid) and a FFAR1 agonist (GW9508) induced human airway smooth muscle (HASM) cell proliferation, which was inhibited by the MEK inhibitor U0126 and the PI3K inhibitor LY294002 . The long-chain FFAs and GW9508 increased phosphorylation of ERK, Akt, and p70S6K in HASM cells and freshly isolated rat airway smooth muscle. Downregulation of FFAR1 in HASM cells by siRNA significantly attenuated oleic acid-induced phosphorylation of ERK and Akt. Oleic acid-induced ERK phosphorylation was blocked by either the Gα_i-protein inhibitor pertussis toxin or U0126 and was partially inhibited by either the Gα_q-specific inhibitor YM-254890 or the Gβγ signaling inhibitor gallein. Oleic acid significantly inhibited forskolin-stimulated cAMP activity, which was attenuated by pertussis toxin. Akt phosphorylation was inhibited by pertussis toxin, the ras inhibitor manumycin A, the Src inhibitor PP1, or LY294002 . Phosphorylation of p70S6K by oleic acid or GW9508 was significantly inhibited by LY294002 , U0126, and the mammalian target of rapamycin (mTOR) inhibitor rapamycin. In conclusion, the FFAR1 promoted airway smooth muscle cell proliferation and p70S6K phosphorylation through MEK/ERK and PI3K/Akt signaling pathways.

Knockdown of FSTL1 inhibits PDGF‑BB‑induced human airway smooth muscle cell proliferation and migration

Abnormal proliferation and migration of airway smooth muscle (ASM) cells serve roles in airway remodeling, and contribute to airway hyper‑responsiveness. Follistatin‑like protein 1 (FSTL1) is a secreted glycoprotein that belongs to the follistatin family of proteins. It was reported that in the lungs of patients suffering from severe asthma, FSTL1 is highly expressed by macrophages. However, the role of FSTL1 in ASM cell proliferation and migration remains unknown. The present study aimed to investigate the role of FSTL1 in cell proliferation and migration mediated by platelet‑derived growth factor subunit B (PDGF‑BB) in human ASM cells. The results of the present study demonstrated that PDGF‑BB stimulation upregulated FSTL1 expression levels in ASM cells in vitro. Knockdown of FSTL1 inhibited cell proliferation and arrested the cell cycle in the G2/M phase in PDGF‑BB‑stimulated ASM cells. Additionally, knockdown of FSTL1 inhibited PDGF‑BB‑induced ASM cell migration. Furthermore, FSTL1 knockdown caused the downregulation of phosphorylated (p)‑extracellular signal‑regulated kinase (ERK) and p‑protein kinase B (AKT) expression levels induced by PDGF‑BB in ASM cells. In conclusion, the present study demonstrated that knockdown of FSTL1 inhibited ASM cell proliferation and migration induced by PDGF‑BB, at least partially via inhibiting the activation of ERK and AKT. FSTL1 may therefore represent a novel therapeutic target for airway remodeling in childhood asthma.

Chrysin inhibits human airway smooth muscle cells proliferation through the extracellular signal-regulated kinase 1/2 signaling pathway

Asthma is a chronic airway inflammatory disease characterized by an increased mass of airway smooth muscle (ASM). Chrysin (5,7-dihydroxyflavone), a natural flavonoid, has been shown to exert multiple biological activities, including anti-inflammatory, anti-proliferative and anti-oxidant effects, as well as the potency to ameliorate asthma in animal models. The objective of the present study was to identify the underlying mechanism of the therapeutic effects of chrysin. The impact of chrysin on basal and platelet-derived growth factor (PDGF)-induced proliferation and apoptosis of human airway smooth muscle cells (HASMCs) was investigated. Furthermore, the activation of the extracellular signal-regulated protein kinase (ERK) signaling pathway was evaluated in HASMCs. The results revealed that chrysin significantly inhibited basal as well as PDGF-induced HASMC proliferation, most likely through the suppression of ERK1/2 phosphorylation. However, chrysin did not significantly reduce PDGF-induced apoptosis of HASMCs. The present study indicated that chrysin may be a promising medication for controlling airway remodeling and clinical manifestations of asthma.

Interleukin-17A promotes functional activation of systemic sclerosis patient-derived dermal vascular smooth muscle cells by extracellular-regulated protein kinases signalling pathway

INTRODUCTION

Dermal vascular smooth muscle cells (DVSMCs) are important for vascular wall fibrosis in microangiopathy of systemic sclerosis (SSc). T helper 17 cell-associated cytokines, particularly interleukin-17A (IL-17A), have been demonstrated to play a role in the pathogenesis of SSc. However, the effect of IL-17A on the DVSMCs in microangiopathy of SSc has not been established. In the present study, we investigated the effect of IL-17A on the SSc patient-derived DVSMCs.

METHODS

DVSMCs from patients with SSc and healthy subjects were incubated using IL-17A or serum derived from patients with SSc. Subsequently, the proliferation, collagen synthesis and secretion, and migration of DVSMCs were analysed using a cell counting kit-8 (CCK-8), dual-luciferase reporter assay, real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blot, enzyme-linked immunosorbent assay (ELISA) and transwell assay. The protein phosphorylation of signalling pathways in the process of IL-17A-mediated DVSMC activation was investigated and validated by specific signalling pathway inhibitor.

RESULTS

IL-17A and serum from patients with SSc could promote the proliferation, collagen synthesis and secretion, and migration of DVSMCs. IL-17A neutralising antibody could inhibit the IL-17A-induced activation of DVSMCs. Additionally, IL-17A induced the activation of extracellular-regulated protein kinases 1/2 (ERK1/2) in DVSMCs, and ERK1/2 inhibitor could block the IL-17A-elicited activation of DVSMCs.

CONCLUSIONS

Our results suggested that IL-17A derived from patients with SSc might induce the proliferation, collagen synthesis and secretion, and migration of DVSMCs via ERK1/2 signalling pathway, raising the likelihood that IL-17A and ERK1/2 might be promising therapeutic targets for the treatment of SSc-related vasculopathy.

A-kinase anchoring proteins: cAMP compartmentalization in neurodegenerative and obstructive pulmonary diseases

The universal second messenger cAMP is generated upon stimulation of Gs protein-coupled receptors, such as the β2 -adreneoceptor, and leads to the activation of PKA, the major cAMP effector protein. PKA oscillates between an on and off state and thereby regulates a plethora of distinct biological responses. The broad activation pattern of PKA and its contribution to several distinct cellular functions lead to the introduction of the concept of compartmentalization of cAMP. A-kinase anchoring proteins (AKAPs) are of central importance due to their unique ability to directly and/or indirectly interact with proteins that either determine the cellular content of cAMP, such as β2 -adrenoceptors, ACs and PDEs, or are regulated by cAMP such as the exchange protein directly activated by cAMP. We report on lessons learned from neurons indicating that maintenance of cAMP compartmentalization by AKAP5 is linked to neurotransmission, learning and memory. Disturbance of cAMP compartments seem to be linked to neurodegenerative disease including Alzheimer's disease. We translate this knowledge to compartmentalized cAMP signalling in the lung. Next to AKAP5, we focus here on AKAP12 and Ezrin (AKAP78). These topics will be highlighted in the context of the development of novel pharmacological interventions to tackle AKAP-dependent compartmentalization.

Roxithromycin suppresses airway remodeling and modulates the expression of caveolin-1 and phospho-p42/p44MAPK in asthmatic rats

Roxithromycin (RXM) expresses anti-asthmatic effects that are separate from its antibiotic activity, but its effects on airway remodeling are still unknown. Here, we evaluated the effects of RXM on airway remodeling and the expression of caveolin-1 and phospho-p42/p44mitogen-activated protein kinase (phospho-p42/p44MAPK) in chronic asthmatic rats. The chronic asthma was induced by ovalbumin/Al(OH)3 sensitization and ovalbumin challenge, RXM (30mg/kg) or dexamethasone (0.5mg/kg) was given before airway challenge initiation. We measured the thickness of bronchial wall and bronchial smooth muscle cell layer to indicate airway remodeling, and caveolin-1 and phospho-p42/p44MAPK expression in lung tissue and airway smooth muscle were detected by immunohistochemistry and western blot analysis, respectively. The results demonstrated that RXM treatment decreased the thickness of bronchial wall and bronchial smooth muscle cell layer, and also downregulated the phospho-p42/p44MAPK expression and upregulated the caveolin-1 expression. The above effects of RXM were similar to dexamethasone. Our results suggested that pretreatment with RXM could suppress airway remodeling and regulate the expression of caveolin-1 and phospho-p42/p44MAPK in chronic asthmatic rats.

Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca(2+) regulation in airway smooth muscle (ASM)

Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNFα and IL-13) increase cytosolic Ca(2+) ([Ca(2+)]cyt) responses to agonist stimulation and Ca(2+) sensitivity of force generation, thereby enhancing airway smooth muscle (ASM) contractility (hyper-reactive state). Inflammation also induces ASM proliferation and remodeling (synthetic state). In normal ASM, the transient elevation of [Ca(2+)]cyt induced by agonists leads to a transient increase in mitochondrial Ca(2+) ([Ca(2+)]mito) that may be important in matching ATP production with ATP consumption. In human ASM (hASM) exposed to TNFα and IL-13, the transient increase in [Ca(2+)]mito is blunted despite enhanced [Ca(2+)]cyt responses. We also found that TNFα and IL-13 induce reactive oxidant species (ROS) formation and endoplasmic/sarcoplasmic reticulum (ER/SR) stress (unfolded protein response) in hASM. ER/SR stress in hASM is associated with disruption of mitochondrial coupling with the ER/SR membrane, which relates to reduced mitofusin 2 (Mfn2) expression. Thus, in hASM it appears that TNFα and IL-13 result in ROS formation leading to ER/SR stress, reduced Mfn2 expression, disruption of mitochondrion-ER/SR coupling, decreased mitochondrial Ca(2+) buffering, mitochondrial fragmentation, and increased cell proliferation.

Thrombin enhances NGF-mediated neurite extension via increased and sustained activation of p44/42 MAPK and p38 MAPK

Rapid neurite remodeling is fundamental to nervous system development and plasticity. It involves neurite extension that is regulated by NGF through PI3K/AKT, p44/42 MAPK and p38 MAPK. It also involves neurite retraction that is regulated by the serine protease, thrombin. However, the intracellular signaling pathway by which thrombin causes neurite retraction is unknown. Using the PC12 neuronal cell model, we demonstrate that thrombin utilizes the PI3K/AKT pathway for neurite retraction in NGF-differentiated cells. Interestingly, however, we found that thrombin enhances NGF-induced neurite extension in differentiating cells. This is achieved through increased and sustained activation of p44/42 MAPK and p38 MAPK. Thus, thrombin elicits opposing effects in differentiated and differentiating cells through activation of distinct signaling pathways: neurite retraction in differentiated cells via PI3K/AKT, and neurite extension in differentiating cells via p44/42 MAPK and p38 MAPK. These findings, which also point to a novel cooperative role between thrombin and NGF, have significant implications in the development of the nervous system and the disease processes that afflicts it as well as in the potential of combined thrombin and NGF therapy for impaired learning and memory, and spinal cord injury which all require neurite extension and remodeling.

Mitogen Activated Protein Kinase Family Proteins and c-jun Signaling in Injury-induced Schwann Cell Plasticity

Schwann cells (SCs) in the peripheral nerves myelinate axons during postnatal development to allow saltatory conduction of nerve impulses. Well-organized structures of myelin sheathes are maintained throughout life unless nerves are insulted. After peripheral nerve injury, unidentified signals from injured nerves drive SC dedifferentiation into an immature state. Dedifferentiated SCs participate in axonal regeneration by producing neurotrophic factors and removing degenerating nerve debris. In this review, we focus on the role of mitogen activated protein kinase family proteins (MAP kinases) in SC dedifferentiation. In addition, we will highlight neuregulin 1 and the transcription factor c-jun as upstream and downstream signals for MAP kinases in SC responses to nerve injury.

Cell-specific and endothelium-dependent regulations of matrix metalloproteinase-2 in rat aorta

Chronic activation of angiotensin II (ANGII) and matrix metalloproteinase-2 (MMP-2) during hypertension contributes to increased aortic stiffness. We studied signalling mechanisms employed by ANGII in the regulation of latent (pro-) and active forms of MMP-2 in rat aortic endothelial and smooth muscle cells, along with isolated rat aorta. Using western blotting, we demonstrate that ANGII (1 µmol/L) significantly (P < 0.01) increases pro-MMP-2 protein expression after 8 h not only in endothelial and smooth muscle cells, but also in isolated rat aorta. We demonstrate that ANGII acts via AT1 receptor-activated cell-specific pathways. In endothelial cells, the JNK1/c-jun pathway is activated, whereas in smooth muscle cells, the JAK2/STAT3 pathway. Activation of JAK2/STAT3 pathway in response to ANGII was EGF receptor-dependent. Results obtained in cell culture are in agreement with the results obtained in isolated aorta. However, active MMP-2 was not found under cell culture conditions, whereas in isolated aorta, active MMP-2 was significantly (P < 0.05) increased after stimulation with ANGII, as detected by gelatine zymography. This increase of MMP-2 activity was not inhibited by blocking the pathways we identified to control pro-MMP-2 protein expression, but was abolished in the absence of endothelium. Our findings demonstrate that ANGII regulates pro-MMP-2 protein expression via cell-specific pathways in rat aorta. The endothelium may play an essential role in the activation of pro-MMP-2. These results may lead to new strategies for inhibiting MMP-2 expression and activity in distinct cell types of the aortic wall.

Cigarette smoke-induced mitochondrial fragmentation and dysfunction in human airway smooth muscle

The balance between mitochondrial fission and fusion is crucial for mitochondria to perform its normal cellular functions. We hypothesized that cigarette smoke (CS) disrupts this balance and enhances mitochondrial dysfunction in the airway. In nonasthmatic human airway smooth muscle (ASM) cells, CS extract (CSE) induced mitochondrial fragmentation and damages their networked morphology in a concentration-dependent fashion, via increased expression of mitochondrial fission protein dynamin-related protein 1 (Drp1) and decreased fusion protein mitofusin (Mfn) 2. CSE effects on Drp1 vs. Mfn2 and mitochondrial network morphology involved reactive oxygen species (ROS), activation of extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), protein kinase C (PKC) and proteasome pathways, as well as transcriptional regulation via factors such as NF-κB and nuclear erythroid 2-related factor 2. Inhibiting Drp1 prevented CSE effects on mitochondrial networks and ROS generation, whereas blocking Mfn2 had the opposite, detrimental effect. In ASM from asmatic patients, mitochondria exhibited substantial morphological defects at baseline and showed increased Drp1 but decreased Mfn2 expression, with exacerbating effects of CSE. Overall, these results highlight the importance of mitochondrial networks and their regulation in the context of cellular changes induced by insults such as inflammation (as in asthma) or CS. Altered mitochondrial fission/fusion proteins have a further potential to influence parameters such as ROS and cell proliferation and apoptosis relevant to airway diseases.

Transcriptome analysis in prenatal IGF1-deficient mice identifies molecular pathways and target genes involved in distal lung differentiation

Background

Insulin-like Growth Factor 1 (IGF1) is a multifunctional regulator of somatic growth and development throughout evolution. IGF1 signaling through IGF type 1 receptor (IGF1R) controls cell proliferation, survival and differentiation in multiple cell types. IGF1 deficiency in mice disrupts lung morphogenesis, causing altered prenatal pulmonary alveologenesis. Nevertheless, little is known about the cellular and molecular basis of IGF1 activity during lung development.

Methods/Principal Findings

Prenatal Igf1^−/− mutant mice with a C57Bl/6J genetic background displayed severe disproportional lung hypoplasia, leading to lethal neonatal respiratory distress. Immuno-histological analysis of their lungs showed a thickened mesenchyme, alterations in extracellular matrix deposition, thinner smooth muscles and dilated blood vessels, which indicated immature and delayed distal pulmonary organogenesis. Transcriptomic analysis of Igf1^−/− E18.5 lungs using RNA microarrays identified deregulated genes related to vascularization, morphogenesis and cellular growth, and to MAP-kinase, Wnt and cell-adhesion pathways. Up-regulation of immunity-related genes was verified by an increase in inflammatory markers. Increased expression of Nfib and reduced expression of Klf2, Egr1 and Ctgf regulatory proteins as well as activation of ERK2 MAP-kinase were corroborated by Western blot. Among IGF-system genes only IGFBP2 revealed a reduction in mRNA expression in mutant lungs. Immuno-staining patterns for IGF1R and IGF2, similar in both genotypes, correlated to alterations found in specific cell compartments of Igf1^−/− lungs. IGF1 addition to Igf1^−/− embryonic lungs cultured ex vivo increased airway septa remodeling and distal epithelium maturation, processes accompanied by up-regulation of Nfib and Klf2 transcription factors and Cyr61 matricellular protein.

Conclusions/Significance

We demonstrated the functional tissue specific implication of IGF1 on fetal lung development in mice. Results revealed novel target genes and gene networks mediators of IGF1 action on pulmonary cellular proliferation, differentiation, adhesion and immunity, and on vascular and distal epithelium maturation during prenatal lung development.

Up-regulation of KCa3.1 promotes human airway smooth muscle cell phenotypic modulation

Airway smooth muscle (ASM) cell phenotype modulation, characterized by reversible switching between contractile and proliferative phenotypes, is considered to contribute to proliferative diseases such as allergic asthma and chronic obstructive pulmonary disease (COPD). KCa3.1 has been suggested to be involved in regulating ASM cell activation, proliferation, and migration. However, little is known regarding the exact role of KCa3.1 in ASM cell phenotypic modulation. To elucidate the role of KCa3.1 in regulating ASM cell phenotypic modulation, we investigated the effects of KCa3.1 channels on ASM contractile marker protein expression, proliferation and migration of primary human bronchial smooth muscle (BSM) cells. We found that PDGF increased KCa3.1 channel expression in BSM cells with a concomitant marked decrease in the expression of contractile phenotypic marker proteins including smooth muscle myosin heavy chain (SMMHC), smooth muscle α-actin (α-SMA), myocardin and KCa1.1. These changes were significantly attenuated by the KCa3.1 blocker, TRAM-34, or gene silencing of KCa3.1. Pharmacological blockade or gene silencing of KCa3.1 also suppressed PDGF-induced human BSM cell migration and proliferation accompanied by a decrease in intracellular free Ca(2+) levels as a consequence of membrane depolarization, resulting in a reduction in cyclin D1 level and cell cycle arrest at G0-G1 phase. Additionally, PDGF-induced up-regulation of KCa3.1 and down-regulation of BSM contractile marker proteins were regulated by the ERK inhibitor U0126 and the AKT inhibitor LY294002. These findings highlight a novel role for the KCa3.1 channel in human BSM cell phenotypic modulation and provide a potential target for therapeutic intervention for proliferative airway diseases.

Treatment of experimental asthma using a single small molecule with anti-inflammatory and BK channel-activating properties

Large conductance voltage- and calcium-activated potassium (BK) channels are highly expressed in airway smooth muscle (ASM). Utilizing the ovalbumin (OVA) and house dust mite (HDM) models of asthma in C57BL/6 mice, we demonstrate that systemic administration of the BK channel agonist rottlerin (5 μg/g) during the challenge period reduced methacholine-induced airway hyperreactivity (AHR) in OVA- and HDM-sensitized mice (47% decrease in peak airway resistance in OVA-asthma animals, P<0.01; 54% decrease in HDM-asthma animals, P<0.01) with a 35-40% reduction in inflammatory cells and 20-35% reduction in Th2 cytokines in bronchoalveolar lavage fluid. Intravenous rottlerin (5 μg/g) reduced AHR within 5 min in the OVA-asthma mice by 45% (P<0.01). With the use of an ex vivo lung slice technique, rottlerin relaxed acetylcholine-stimulated murine airway lumen area to 87 ± 4% of the precontracted area (P<0.01 vs. DMSO control). Rottlerin increased BK channel activity in human ASM cells (V50 shifted by 73.5±13.5 and 71.8±14.6 mV in control and asthmatic cells, respectively, both P<0.05 as compared with pretreatment) and reduced the frequency of acetylcholine-induced Ca(2+) oscillations in murine ex vivo lung slices. These findings suggest that rottlerin, with both anti-inflammatory and ASM relaxation properties, may have benefit in treating asthma.

Exchange protein directly activated by cAMP (epac): a multidomain cAMP mediator in the regulation of diverse biological functions

Since the discovery nearly 60 years ago, cAMP is envisioned as one of the most universal and versatile second messengers. The tremendous feature of cAMP to tightly control highly diverse physiologic processes, including calcium homeostasis, metabolism, secretion, muscle contraction, cell fate, and gene transcription, is reflected by the award of five Nobel prizes. The discovery of Epac (exchange protein directly activated by cAMP) has ignited a new surge of cAMP-related research and has depicted novel cAMP properties independent of protein kinase A and cyclic nucleotide-gated channels. The multidomain architecture of Epac determines its activity state and allows cell-type specific protein-protein and protein-lipid interactions that control fine-tuning of pivotal biologic responses through the "old" second messenger cAMP. Compartmentalization of cAMP in space and time, maintained by A-kinase anchoring proteins, phosphodiesterases, and β-arrestins, contributes to the Epac signalosome of small GTPases, phospholipases, mitogen- and lipid-activated kinases, and transcription factors. These novel cAMP sensors seem to implement certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Agonists and antagonists selective for Epac are developed and will support further studies on the biologic net outcome of the activation of Epac. This will increase our current knowledge on the pathophysiology of devastating diseases, such as diabetes, cognitive impairment, renal and heart failure, (pulmonary) hypertension, asthma, and chronic obstructive pulmonary disease. Further insights into the cAMP dynamics executed by the Epac signalosome will help to optimize the pharmacological treatment of these diseases.

Hydrogen-rich saline attenuates vascular smooth muscle cell proliferation and neointimal hyperplasia by inhibiting reactive oxygen species production and inactivating the Ras-ERK1/2-MEK1/2 and Akt pathways

Hydrogen-rich saline has been reported to prevent neointimal hyperplasia induced by carotid balloon injury. The purpose of the present study was to further investigate the molecular mechanisms underlying this phenomenon. Daily injection of a hydrogen-rich saline solution (HRSS) in rats was employed to study the effect of hydrogen on balloon injury-induced neointimal hyperplasia and the neointima/media ratio was assessed. HRSS significantly decreased the neointima area and neointima/media ratio in a dose-dependent manner. In vitro effects of hydrogen on fetal bovine serum (FBS)-induced vascular smooth muscle cell (VSMC) proliferation were also investigated. Hydrogen-rich medium (HRM) inhibited rat VSMC proliferation and migration induced by 10% FBS. FBS-induced reactive oxygen species (ROS) production and activation of intracellular Ras, MEK1/2, ERK1/2, proliferative cell nuclear antigen (PCNA), Akt were significantly inhibited by HRM. In addition, HRM blocked FBS-induced progression from the G0/G1 to the S-phase and increased the apoptosis rate of VSMCs. These results showed that hydrogen-rich saline was able to attenuate FBS-induced VSMC proliferation and neointimal hyperplasia by inhibiting ROS production and inactivating the Ras-ERK1/2-MEK1/2 and Akt pathways. Thus, HRSS may have potential therapeutic relevance for the prevention of human restenosis.

Reduced adult endothelial cell EphB4 function promotes venous remodeling

Reduced EphB4 expression is observed during vein graft adaptation and is associated with increased venous wall thickening. These findings suggest that EphB4 may mediate normal adult venous endothelial cell (EC) function and vein graft adaptation. We therefore tested the functional significance of EphB4 using EC with genetically reduced EphB4 signaling. EC were isolated from EphB4(+/+) and EphB4(+/-) mice. In vitro function was assessed through EC proliferation, migration, nitric oxide (NO) synthesis, and chemokine production. A mouse vein graft model was used to correlate in vitro findings with in vivo vein grafts. Smooth muscle cells (SMC) were subjected to proliferation and migration assays using EphB4(+/+) and EphB4(+/-) EC-conditioned medium. EphB4(+/-) EC exhibited diminished proliferation (P < 0.0001, n = 6), migration (P < 0.0001, n = 3), and NO production (P = 0.0012, n = 3). EphB4(+/-) EC had increased VEGF-A mRNA (P = 0.0006, n = 6) and protein (P = 0.0106, n = 3) as well as increased secretion of VEGF-A (P = 0.0010, n = 5), PDGF-BB (P < 0.0001, n = 6), and TGF-β1 (P < 0.0001, n = 6). EphB4(+/-)-conditioned medium promoted SMC proliferation (P < 0.0001, n = 7) and migration (P = 0.0358, n = 3). Vein grafts and EphB4(+/-) EC showed similarity with regard to VEGF-A and eNOS mRNA and protein expression. In conclusion, reduced venous EC EphB4 function is associated with a proangiogenic and mitogenic phenotype. EphB4(+/-) EC have increased secretion of SMC mitogens and reduced NO production that correlate with the thickened neointima formed during vein graft adaptation. These findings suggest that EphB4 remains active in adult venous EC and that loss of EphB4 plays a role in vein graft adaptation.

Th17-associated cytokines promote human airway smooth muscle cell proliferation

Increased airway smooth muscle (ASM) mass is a hallmark of airway remodeling in severe asthma. Th17-associated cytokines, particularly IL-17A, IL-17F, and IL-22, have been postulated to play a role in the pathogenesis of asthma. To investigate the in vitro effect of Th17 cytokines on the proliferation and survival of airway smooth muscle cells (ASMCs), human ASMCs from asthmatic and nonasthmatic subjects were incubated with IL-17A, IL-17F, or IL-22. The aforementioned cytokines demonstrated an ability to promote proliferation and survival of ASMCs from asthmatic and nonasthmatic subjects, which were mediated by selective activation of their corresponding receptors on ASMCs, including IL-17RA, IL-17RC, or IL-22R1, respectively. IL-17A and IL-17F-induced proliferation of ASMCs was dependent on ERK1/2 MAPK pathway, while IL-22-induced proliferation involved both ERK1/2 MAPK and NF-κB pathways. The involvement of signaling pathways was further confirmed by the inhibition of proliferation by knockdown of ERK1/2 MAPK or NF-κB p65 expression with pathway-specific siRNA. Together, our results show that Th17-associated cytokines promote proliferation and reduce the apoptotic rate of human ASMCs, raising the possibility that Th17 cytokines may contribute to increasing airway smooth muscle mass and airway remodeling in asthma.

Corticosteroids and β₂-agonists upregulate mitogen-activated protein kinase phosphatase 1: in vitro mechanisms

BACKGROUND AND PURPOSE

Airway remodelling is a consequence of long-term inflammation and MAPKs are key signalling molecules that drive pro-inflammatory pathways. The endogenous MAPK deactivator--MAPK phosphatase 1 (MKP-1)--is a critical negative regulator of the myriad pro-inflammatory pathways activated by MAPKs in the airway.

EXPERIMENTAL APPROACH

Herein we investigated the molecular mechanisms responsible for the upregulation of MKP-1 in airway smooth muscle (ASM) by the corticosteroid dexamethasone and the β₂-agonist formoterol, added alone and in combination.

KEY RESULTS

MKP-1 is a corticosteroid-inducible gene whose expression is enhanced by long-acting β₂-agonists in an additive manner. Formoterol induced MKP-1 expression via the β₂-adrenoceptor and we provide the first direct evidence (utilizing overexpression of PKIα, a highly selective PKA inhibitor) to show that PKA mediates β₂-agonist-induced MKP-1 upregulation. Dexamethasone activated MKP-1 transcription in ASM cells via a cis-acting corticosteroid-responsive region located between -1380 and -1266 bp of the MKP-1 promoter. While the 3'-untranslated region of MKP-1 contains adenylate + uridylate elements responsible for regulation at the post-transcriptional level, actinomycin D chase experiments revealed that there was no increase in MKP-1 mRNA stability in the presence of dexamethasone, formoterol, alone or in combination. Rather, there was an additive effect of the asthma therapeutics on MKP-1 transcription.

CONCLUSIONS AND IMPLICATIONS

Taken together, these studies allow us a greater understanding of the molecular basis of MKP-1 regulation by corticosteroids and β₂-agonists and this new knowledge may lead to elucidation of optimized corticosteroid-sparing therapies in the future.

Altered CD38/Cyclic ADP-Ribose Signaling Contributes to the Asthmatic Phenotype

CD38 is a transmembrane glycoprotein expressed in airway smooth muscle cells. The enzymatic activity of CD38 generates cyclic ADP-ribose from β-NAD. Cyclic ADP-ribose mobilizes intracellular calcium during activation of airway smooth muscle cells by G-protein-coupled receptors through activation of ryanodine receptor channels in the sarcoplasmic reticulum. Inflammatory cytokines that are implicated in asthma upregulate CD38 expression and increase the calcium responses to contractile agonists in airway smooth muscle cells. The augmented intracellular calcium responses following cytokine exposure of airway smooth muscle cells are inhibited by an antagonist of cyclic ADP-ribose. Airway smooth muscle cells from CD38 knockout mice exhibit attenuated intracellular calcium responses to agonists, and these mice have reduced airway response to inhaled methacholine. CD38 also contributes to airway hyperresponsiveness as shown in mouse models of allergen or cytokine-induced inflammatory airway disease. In airway smooth muscle cells obtained from asthmatics, the cytokine-induced CD38 expression is significantly enhanced compared to expression in cells from nonasthmatics. This differential induction of CD38 expression in asthmatic airway smooth muscle cells stems from increased activation of MAP kinases and transcription through NF-κB, and altered post-transcriptional regulation through microRNAs. We propose that increased capacity for CD38 signaling in airway smooth muscle in asthma contributes to airway hyperresponsiveness.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Airway smooth muscle in asthma: just a target for bronchodilation?

Airway smooth muscle (ASM) has long been recognized as the main cell type responsible for bronchial hyperresponsiveness. It has, thus, been considered as a target for bronchodilation. In asthma, however, there is a complex relationship between ASM and inflammatory cells, such as mast cells and T lymphocytes. Moreover, the increased ASM mass in asthmatic airways is one of the key features of airway remodeling. This article aims to review the main concepts about the 3 possible roles of ASM in asthma: (1) contractile tone, (2) inflammatory response, and (3) remodeling.

Identification of SRC as a potent drug target for asthma, using an integrative approach of protein interactome analysis and in silico drug discovery

Network-biology inspired modeling of interactome data and computational chemistry have the potential to revolutionize drug discovery by complementing conventional methods. We consider asthma, a complex disease characterized by intricate molecular mechanisms, for our study. We aim to integrate prediction of potent drug targets using graph-theoretical methods and subsequent identification of small molecules capable of modulating activity of the best target. In this work, we construct the protein interactome underlying this disease: Asthma Protein Interactome (API). Using a strategy based on network analysis of the interactome, we identify a set of potential drug targets for asthma. Topologically and dynamically, v-src sarcoma (Schmidt-Ruppin A-2) viral oncogene homolog (SRC) emerges as the most central target in API. SRC is known to play an important role in promoting airway smooth muscle cell growth and facilitating migration in airway remodeling. From interactome analysis, and with the reported role in respiratory mechanisms, SRC emerges as a promising drug target for asthma. Further, we proceed to identify leads for SRC from a public database of small molecules. We predict two potential leads for SRC using ligand-based virtual screening methodology.

Urotensin upregulates transforming growth factor-β1 expression of asthma airway through ERK-dependent pathway

Airway smooth muscle cells (ASMCs) play a key role in the process of asthma airway remodeling. Urotensin II (UII) and transforming growth factor (TGF)-β are potent mitogens for ASMCs proliferation. The study was aimed to determine whether UII-upregulated TGF-β-mediated ASMCs proliferation and extracellular signal-regulated kinase (ERK) was required for such an effect. OVA-sensitized rats were challenged to induce asthma. Lung morphology and airway dynamic parameters were monitored. ASMCs from control and asthma rats were purified for the measurement of UII and TGF-β1 expression. In vitro experiments were conducted to determine the direct effect of UII on TGF-β1 expression by ASMCs. Finally, U0126, an ERK inhibitor was used to examine the role of ERK pathway in UII mediated TGF-β1 upregulation. We found that both UII and TGF-β1 were upregulated in asthma lung tissues. In vitro study on ASMCs further revealed that UII may render its effect on ASMCs cells through the upregulation of TGF-β1. Data also supported the conclusion that ERK pathway was required, but not sufficient in UII-induced TGF-β1 upregulation. The current study provides new evidence that UII is involved in the TGF-β mediated mitogenic effect on ASMCs. UII, at least partially, uses ERK pathway to render such effect.

PDGF-induced airway smooth muscle proliferation is associated with Human antigen R activation and could be weakened by AMPK activation

CyclinD1 over-expression is the key pathogenetic event underlying airway smooth muscle (ASM) proliferation. Human antigen R (HuR) is a ubiquitously expressed RNA-binding protein, and is known to regulate the expression of multiple cell cycle regulators. The aim of the study is to investigate whether HuR might also be involved in ASM proliferation. In cultured ASM cells, PDGF treatment induced a significant elevation of HuR expression at both mRNA and protein levels. Immunofluorescence analysis demonstrated PDGF might promote HuR translocation from nucleus to cytoplasma as well. RNA-interference of HuR effectively decreased PDGF-induced cyclinD1 over-expression in ASM cells. Furthermore, AMPK activation by AICAR could effectively decrease PDGF-induced HuR cytoplasmatic translocation, cyclinD1 expression and ASM cells proliferation. In conclusion, altered expression and activity of HuR might participate in PDGF-induced ASM cells cyclinD1 expression and proliferation. The effectiveness of AMPK activation indicated a novel intervention method for airway remodeling.

TAK1 plays a major role in growth factor-induced phenotypic modulation of airway smooth muscle

Increased airway smooth muscle (ASM) mass is a major feature of airway remodeling in asthma and chronic obstructive pulmonary disease. Growth factors induce a proliferative ASM phenotype, characterized by an increased proliferative state and a decreased contractile protein expression, reducing contractility of the muscle. Transforming growth factor-β-activated kinase 1 (TAK1), a mitogen-activated protein kinase kinase kinase, is a key enzyme in proinflammatory signaling in various cell types; however, its function in ASM is unknown. The aim of this study was to investigate the role of TAK1 in growth factor-induced phenotypic modulation of ASM. Using bovine tracheal smooth muscle (BTSM) strips and cells, as well as human tracheal smooth muscle cells, we investigated the role of TAK1 in growth factor-induced proliferation and hypocontractility. Platelet-derived growth factor- (PDGF; 10 ng/ml) and fetal bovine serum (5%)-induced increases in DNA synthesis and cell number in bovine and human cells were significantly inhibited by pretreatment with the specific TAK1 inhibitor LL-Z-1640-2 (5Z-7-oxozeaenol; 100 nM). PDGF-induced DNA synthesis and extracellular signal-regulated kinase-1/2 phosphorylation in BTSM cells were strongly inhibited by both LL-Z-1640-2 pretreatment and transfection of dominant-negative TAK1. In addition, LL-Z-1640-2 inhibited PDGF-induced reduction of BTSM contractility and smooth muscle α-actin expression. The data indicate that TAK1 plays a major role in growth factor-induced phenotypic modulation of ASM.

Monocyte 15-lipoxygenase gene expression requires ERK1/2 MAPK activity

IL-13 induces profound expression of 15-lipoxygenase (15-LO) in primary human monocytes. Our studies have defined the functional IL-13R complex, association of Jaks with the receptor components, and the tyrosine phosphorylation of several Stat molecules in response to IL-13. Furthermore, we identified both p38MAPK and protein kinase Cδ as critical regulators of 15-LO expression. In this study, we report an ERK1/2-dependent signaling cascade that regulates IL-13-mediated 15-LO gene expression. We show the rapid phosphorylation/activation of ERK1/2 upon IL-13 exposure. Our results indicate that Tyk2 kinase is required for the activation of ERK1/2, which is independent of the Jak2, p38MAPK, and protein kinase Cδ pathways, suggesting bifurcating parallel regulatory pathways downstream of the receptor. To investigate the signaling mechanisms associated with the ERK1/2-dependent expression of 15-LO, we explored the involvement of transcription factors, with predicted binding sites in the 15-LO promoter, in this process including Elk1, early growth response-1 (Egr-1), and CREB. Our findings indicate that IL-13 induces Egr-1 nuclear accumulation and CREB serine phosphorylation and that both are markedly attenuated by inhibition of ERK1/2 activity. We further show that ERK1/2 activity is required for both Egr-1 and CREB DNA binding to their cognate sequences identified within the 15-LO promoter. Furthermore, by transfecting monocytes with the decoy oligodeoxyribonucleotides specific for Egr-1 and CREB, we discovered that Egr-1 and CREB are directly involved in regulating 15-LO gene expression. These studies characterize an important regulatory role for ERK1/2 in mediating IL-13-induced monocyte 15-LO expression via the transcription factors Egr-1 and CREB.

Inhibitory effects of cilostazol on proliferation of vascular smooth muscle cells (VSMCs) through suppression of the ERK1/2 pathway

AIM

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenic factor of vascular disorders such as atherosclerosis and restenosis after angioplasty. During atherogenesis or in response to vessel injury, VSMC proliferation is induced by a number of peptide growth factors released from platelets and VSMCs. Cilostazol is a phosphodiesterase (PDE) 3 inhibitor that increases intracellular cAMP levels and decreases intracellular Ca(2+) levels, inhibiting platelet aggregation and inducing vasodilatation. Cilostazol is also known to have an inhibitory effect on the proliferation of VSMCs, but the anti-proliferative mechanism of cilostazol in VSMCs has not yet been established. In the present study, we investigated whether the anti-proliferative mechanism of cilostazol is associated with the suppression of extracellular signal-regulated kinases (ERK) and phosphatidylinositol 3 kinase (PI3K) signaling pathways.

METHODS

To confirm the anti-proliferative effects of cilostazol on VSMCs, VSMCs were induced to proliferate by serum-induced mitogenesis and then were treated with cilostazol for 24 h. And, to investigate whether the anti-proliferative mechanism of cilostazol in VSMCs involves the suppression of the ERK and PI3K pathways, expression of the phosphorylated forms of ERK1/2, Raf, Akt, and glycogen synthase kinase (GSK)-3 were evaluated by western blot.

RESULTS

Cilostazol inhibited VSMC proliferation in a dose-dependent manner. Phosphorylated ERK1/2 and Raf were significantly reduced in a dose-dependent manner, whereas phosphorylated Akt and GSK-3 were not changed.

CONCLUSION

These results suggest that suppression of the ERK pathway but not the PI3K pathway is an important mechanism in the anti-proliferative effect of cilostazol on VSMCs.

Up-regulation of cyclin D1 expression in asthma serum-sensitized human airway smooth muscle promotes proliferation via protein kinase C alpha

Abnormal hypertrophy and hyperplasia of airway smooth muscle cells play an important role in airway remodeling in chronic asthma. The authors' previous studies have indicated that protein kinase C alpha (PKC alpha) is involved in the proliferation of passively sensitized human airway smooth muscle cells (HASMCs). However, the underlying mechanisms remain unknown. Here, the authors examined the possible role of the alpha isoform of PKC in the control of cyclin D1 expression, using HASMCs passively sensitized on human atopic asthmatic serum as a model system. Cultured HASMCs were passively sensitized with serum from atopic asthmatic patients. Cell proliferation was measured by [(3)H]thymidine incorporation and an MTT assay. Cell cycle status was analyzed by flow cytometry. The mRNA and protein expression profiles of cyclin D1 were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting, respectively. Furthermore, the authors assessed the role of cyclin D1 in PKC alpha-induced HASMC proliferation by transfection with a recombinant cyclin D1 antisense construct. The activation of PKC alpha with phorbol myristate acetate (PMA), a PKC activator, up-regulated cyclin D1 expression and increased the proliferation of passively sensitized HASMCs. This effect was significantly decreased by specific inhibition of PKC alpha with Go6976. In addition, the authors showed that transfection with antisense cyclin D1 abolished PMA-induced G1/S progression and HASMC proliferation. These results demonstrate that PKC alpha promotes the proliferation of HASMCs sensitized with atopic asthmatic serum via up-regulation of cyclin D1 expression.

Cigarette smoke and lipopolysaccharide induce a proliferative airway smooth muscle phenotype

Background

A major feature of chronic obstructive pulmonary disease (COPD) is airway remodelling, which includes an increased airway smooth muscle (ASM) mass. The mechanisms underlying ASM remodelling in COPD are currently unknown. We hypothesized that cigarette smoke (CS) and/or lipopolysaccharide (LPS), a major constituent of CS, organic dust and gram-negative bacteria, that may be involved in recurrent airway infections and exacerbations in COPD patients, would induce phenotype changes of ASM.

Methods

To this aim, using cultured bovine tracheal smooth muscle (BTSM) cells and tissue, we investigated the direct effects of CS extract (CSE) and LPS on ASM proliferation and contractility.

Results

Both CSE and LPS induced a profound and concentration-dependent increase in DNA synthesis in BTSM cells. CSE and LPS also induced a significant increase in BTSM cell number, which was associated with increased cyclin D1 expression and dependent on activation of ERK 1/2 and p38 MAP kinase. Consistent with a shift to a more proliferative phenotype, prolonged treatment of BTSM strips with CSE or LPS significantly decreased maximal methacholine- and KCl-induced contraction.

Conclusions

Direct exposure of ASM to CSE or LPS causes the induction of a proliferative, hypocontractile ASM phenotype, which may be involved in airway remodelling in COPD.

Adenosine activates a2b receptors and enhances chloride secretion in kidney inner medullary collecting duct cells

In the kidney, defects in the regulation of urine salt excretion can result in extracellular fluid volume expansion, leading to salt-sensitive hypertension. Previous studies have demonstrated that, when rats are maintained on a high sodium chloride (NaCl) diet, adenosine production increases in the renal medulla with parallel changes in adenosine receptor expression. These studies suggest that adenosine signaling in the kidney can respond to high NaCl loading; however, the functional consequences of these changes in adenosine signaling are not clear. We used the immortalized cell line mIMCD-K2, a murine model system for the renal inner medullary collecting duct, to study the direct effects of adenosine on NaCl transport across the inner medullary collecting duct epithelium with an Ussing chamber system. When epithelial Na(+) channels were inhibited, the addition of adenosine to the apical side of mIMCD-K2 cell sheets stimulated short-circuit current in a dose-dependent manner. This increase in short-circuit current was inhibited by a cystic fibrosis transmembrane conductance regulator Cl(-) channel inhibitor. Pharmacological studies with a panel of adenosine receptor agonists and antagonists demonstrated that adenosine activates apical A2b adenosine receptors to enhance the short-circuit current. Furthermore, adenosine application to mIMCD-K2 cell sheets increased intracellular cAMP, whereas inhibition of protein kinase A completely blocked the adenosine response. Together, our findings indicate that adenosine stimulates Cl(-) secretion through the cystic fibrosis transmembrane conductance regulator in mIMCD-K2 cells by activating apical A2b receptors and signaling through cAMP/protein kinase A. We propose that this adenosine receptor pathway may provide one mechanism for enhancing urine NaCl excretion in the setting of high dietary NaCl intake.

Noncontractile functions of airway smooth muscle cells in asthma

Although pivotal in regulating bronchomotor tone in asthma, airway smooth muscle (ASM) also modulates airway inflammation and undergoes hypertrophy and hyperplasia, contributing to airway remodeling in asthma. ASM myocytes secrete or express a wide array of immunomodulatory mediators in response to extracellular stimuli, and in chronic severe asthma, increases in ASM mass may render the airway irreversibly obstructed. Although the mechanisms by which ASM secretes cytokines and chemokines are the same as those regulating immune cells, there exist unique ASM signaling pathways that may provide novel therapeutic targets. This review provides an overview of our current understanding of the proliferative as well as the synthetic properties of ASM.

Transcriptional regulation of cytokine function in airway smooth muscle cells

The immuno-modulatory properties of airway smooth muscle have become of increasing importance in our understanding of the mechanisms underlying chronic inflammation and structural remodeling of the airway wall in asthma and chronic obstructive pulmonary disease (COPD). ASM cells respond to many cytokines, growth factors and lipid mediators to produce a wide array of immuno-modulatory molecules which may in turn orchestrate and perpetuate the disease process in asthma and COPD. Despite numerous studies of the cellular effects of cytokines on cultured ASM, few have identified intracellular signaling pathways by which cytokines modulate or induce these cellular responses. In this review we provide an overview of the transcriptional mechanisms as well as intracellular signaling pathways regulating cytokine functions in ASM cells. The recent discovery of toll-like receptors in ASM cells represents a significant development in our understanding of the immuno-modulatory capabilities of ASM cells. Thus, we also review emerging evidence of the inflammatory response to toll-like receptor activation in ASM cells.

Molecular mechanisms underlying airway smooth muscle contraction and proliferation: implications for asthma

Airway smooth muscle (ASM) plays a key role in bronchomotor tone, as well as in structural remodeling of the bronchial wall. Therefore, ASM contraction and proliferation significantly participate in the development and progression of asthma. Many contractile agonists also behave as mitogenic stimuli, thus contributing to frame a hyperresponsive and hyperplastic ASM phenotype. In this review, the molecular mechanisms and signaling pathways involved in excitation-contraction coupling and ASM cell growth will be outlined. Indeed, the recent advances in understanding the basic aspects of ASM biology are disclosing important cellular targets, currently explored for the implementation of new, more effective anti-asthma therapies.

Pharmacology of airway smooth muscle proliferation

Airway smooth muscle thickening is a pathological feature that contributes significantly to airflow limitation and airway hyperresponsiveness in asthma. Ongoing research efforts aimed at identifying the mechanisms responsible for the increased airway smooth muscle mass have indicated that hyperplasia of airway smooth muscle, due in part to airway myocyte proliferation, is likely a major factor. Airway smooth muscle proliferation has been studied extensively in culture and in animal models of asthma, and these studies have revealed that a variety of receptors and mediators contributes to this response. This review aims to provide an overview of the receptors and mediators that control airway smooth muscle cell proliferation, with emphasis on the intracellular signalling mechanisms involved.

Inhibition of human airway smooth muscle cell proliferation by beta 2-adrenergic receptors and cAMP is PKA independent: evidence for EPAC involvement

Mechanisms by which beta-adrenergic receptor (beta AR) agonists inhibit proliferation of human airway smooth muscle (HASM) cells were investigated because of their potential relevance to smooth muscle hyperplasia in asthma. We hypothesized that beta AR agonists would inhibit mitogenesis in HASM cells via the beta 2AR, an increase in cAMP, and PKA activation. HASM cells were treated for 24 h with various agents and then analyzed for [3H]thymidine incorporation as a measure of cell proliferation. EGF stimulated proliferation by approximately 10-fold. The nonselective beta AR agonist isoproterenol and the beta 2AR-selective agonists albuterol and salmeterol inhibited EGF-stimulated proliferation by more than 50%, with half-maximal effects at 4.8 nM, 110 nM, and 6.7 nM, respectively. A beta 2AR-selective antagonist inhibited the isoproterenol effect with 100-fold greater potency than a beta 1AR-selective antagonist, confirming beta 2AR involvement in the inhibition of proliferation. The cAMP-elevating agents PGE2 and forskolin decreased EGF-induced proliferation, suggesting cAMP as the mediator. beta 2AR agonists and forskolin also inhibited proliferation stimulated by lysophosphatidic acid (LPA) as well as the synergistic proliferation stimulated by LPA+EGF. Importantly, PKA-selective cAMP analogs did not inhibit proliferation at concentrations that maximally activated PKA (10-100 microM), whereas a cAMP analog selective for the exchange protein directly activated by cAMP (EPAC), 8-(4-chlorophenylthio)-2'-O-methyl-cAMP, maximally inhibited proliferation at a concentration that did not activate PKA (10 microM). These data show that beta 2AR agonists and other cAMP-elevating agents decrease proliferation in HASM cells via a PKA-independent mechanism, and they provide pharmacological evidence for involvement of EPAC or an EPAC-like cAMP effector protein instead.

ERK1/2 signaling pathway modulates the airway smooth muscle cell phenotype in the rat model of chronic asthma

BACKGROUND

It has been demonstrated that the phenotypic modulation of airway smooth muscle cells (ASMCs) is important to the pathogenesis of airway remodeling in chronic asthma. The extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway is one of the most important transduction pathways involved in the process of asthma; however, its role in the phenotypic transition of ASMCs remains unclear.

OBJECTIVES

To examine the role of ERK1/2 in the phenotypic modulation of ASMCs in the rat model of chronic asthma.

METHODS

Bronchial smooth muscle strips were cultured in vitro in the presence of the ERK1/2 agonist epidermal growth factor or/and the MEK inhibitor PD98059. The phenotype of ASMCs was determined by observing these cells under an electron microscope and analyzing expression of phenotypic markers (smooth muscle alpha-actin for the contractile phenotype and osteopontin for the synthetic) by using Western blot and reverse-transcriptase polymerase chain reaction, respectively.

RESULTS

The phenotype of the ASMCs from the chronic asthmatic rats changed from the contractile type to the synthetic type with synthetic organelles abundantly gathered around the nucleus and altered expression of phenotypic markers. ERK1/2 was strongly expressed in the ASMCs of the chronic asthmatic rats and its activation by epidermal growth factor excessively promoted the synthetic function of ASMCs; the MEK inhibitor PD98059, however, reversed this phenotypic change in the ASMCs.

CONCLUSIONS

Our results reveal a key role of the ERK1/2 signaling pathway in the phenotypic modulation of ASMCs in chronic asthmatic rats, indicating that specific inhibition of ERK1/2 in ASMCs may be therapeutically valuable in the control of airway remodeling in chronic asthma.

Raf-1 kinase mediates adenylyl cyclase sensitization by TNF-alpha in human airway smooth muscle cells

Tumor necrosis factor (TNF)-alpha is a potent inflammatory cytokine implicated in the exacerbation of asthma. Chronic exposure to TNF-alpha has been reported to induce G protein-coupled receptor desensitization, but adenylyl cyclase sensitization, in airway smooth muscle cells by an unknown mechanism. Cyclic AMP, which is synthesized by adenylyl cyclases in response to G protein-coupled receptor signals, is an important second messenger involved in the regulation of the airway muscle proliferation, migration, and tone. In other cell types, TNF-alpha receptors transactivate the EGF receptor, which activates raf-1 kinase. Further studies in transfected cells show that raf-1 kinase can phosphorylate and activate some isoforms of adenylyl cyclase. Cultured human airway smooth muscle cells were treated with TNF-alpha in the presence or absence of inhibitors of prostaglandin signaling, protein kinases, or G(i) proteins. TNF-alpha caused a significant dose- (1-10 ng/ml) and time-dependent (24 and 48 h) increase in forskolin-stimulated adenylyl cyclase activity, which was abrogated by pretreatment with GW5074 (a raf-1 kinase inhibitor), was partially inhibited by an EGF receptor inhibitor, but was unaffected by pertussis toxin. TNF-alpha also increased phosphorylation of Ser(338) on raf-1 kinase, indicative of activation. IL-1beta and EGF sensitization of adenylyl cyclase activity was also sensitive to raf-1 kinase inhibition by GW5074. Taken together, these studies link two signaling pathways not previously characterized in human airway smooth muscle cells: TNF-alpha transactivation of the EGF receptor, with subsequent raf-1 kinase-mediated activation of adenylyl cyclase.

CysLT1 receptor-induced human airway smooth muscle cells proliferation requires ROS generation, EGF receptor transactivation and ERK1/2 phosphorylation

Background

Cysteine-containing leukotrienes (cysteinyl-LTs) are pivotal inflammatory mediators that play important roles in the pathophysiology of asthma, allergic rhinitis, and other inflammatory conditions. In particular, cysteinyl-LTs exert a variety of effects with relevance to the aetiology of asthma such as smooth muscle contraction, eosinophil recruitment, increased microvascular permeability, enhanced mucus secretion and decreased mucus transport and, finally, airway smooth muscle cells (ASMC) proliferation. We used human ASMC (HASMC) to identify the signal transduction pathway(s) of the leukotriene D₄ (LTD₄)-induced DNA synthesis.

Methods

Proliferation of primary HASMC was measured by [³H]thymidine incorporation. Phosphorylation of EGF receptor (EGF-R) and ERK1/2 was assessed with a polyclonal anti-EGF-R or anti-phosphoERKl/2 monoclonal antibody. A Ras pull-down assay kit was used to evaluate Ras activation. The production of reactive oxygen species (ROS) was estimated by measuring dichlorodihydrofluorescein (DCF) oxidation.

Results

We demonstrate that in HASMC LTD₄-stimulated thymidine incorporation and potentiation of EGF-induced mitogenic signaling mostly depends upon EGF-R transactivation through the stimulation of CysLT₁-R. Accordingly, we found that LTD₄ stimulation was able to trigger the increase of Ras-GTP and, in turn, to activate ERK1/2. We show here that EGF-R transactivation was sensitive to pertussis toxin (PTX) and phosphoinositide 3-kinase (PI3K) inhibitors and that it occurred independently from Src activity, despite the observation of a strong impairment of LTD₄-induced DNA synthesis following Src inhibition. More interestingly, CysLT₁-R stimulation increased the production of ROS and N-acetylcysteine (NAC) abolished LTD₄-induced EGF-R phosphorylation and thymidine incorporation.

Conclusion

Collectively, our data demonstrate that in HASMC LTD₄ stimulation of a G_i/o coupled CysLT₁-R triggers the transactivation of the EGF-R through the intervention of PI3K and ROS. While PI3K and ROS involvement is an early event, the activation of Src occurs downstream of EGF-R activation and is followed by the classical Ras-ERK1/2 signaling pathway to control G1 progression and cell proliferation.