Airway Smooth Muscle Remodeling In Asthma Research Articles

Asthma: Pharmacological degradation of the airway smooth muscle layer.

Asthma: A disease characterised by excessive and variable airway narrowing, and pathologies of inflammation and remodelling, particularly thickening of the airway smooth muscle (ASM). Treatment approaches dilate narrowed airways and reduce inflammation; however, remodelling seems largely neglected. This review considers the evolution of remodelling in asthma and whether conventional hypotheses that inflammation causes ASM thickening has mislead the medical community into thinking that anti-inflammatories will remedy this ASM defect. There is instead reasonable evidence that ASM thickening occurs independently of inflammation, such that therapies should employ strategies to directly modify ASM growth. Lessons have been learned from the use of untargeted bronchial thermoplasty and there should also be consideration of pharmacological therapies to ablate ASM. We discuss several new approaches to target ASM remodelling in asthma. A major current obstacle is our inability to image the ASM layer and assess treatment response. In this regard, polarisation-sensitive optical coherence tomography offers future promise.

Bnip3 regulates airway smooth muscle cell focal adhesion and proliferation.

Increased airway smooth muscle (ASM) mass is a key contributor to airway narrowing and airway hyperresponsiveness in asthma. Besides conventional pathways and regulators of ASM proliferation, recent studies suggest that changes in mitochondrial morphology and function play a role in airway remodeling in asthma. In this study, we aimed at determining the role of mitochondrial Bcl-2 adenovirus E1B 19 kDa-interacting protein, Bnip3, in the regulation of ASM proliferation. Bnip3 is a member of the Bcl-2 family of proteins critical for mitochondrial health, mitophagy, and cell survival/death. We found that Bnip3 expression is upregulated in ASM cells from asthmatic donors compared with that in ASM cells from healthy donors and transient downregulation of Bnip3 expression in primary human ASM cells using an siRNA approach decreased cell adhesion, migration, and proliferation. Furthermore, Bnip3 downregulation altered the structure (electron density) and function (cellular ATP levels, membrane potential, and reacitve oxygen species generation) of mitochondria and decreased expression of cytoskeleton proteins vinculin, paxillin, and actinin. These findings suggest that Bnip3 via regulation of mitochondria functions and expression of adhesion proteins regulates ASM adhesion, migration, and proliferation. This study reveals a novel role for Bnip3 in ASM functions and establishes Bnip3 as a potential target in mitigating ASM remodeling in asthma.

Suppression of Eosinophil Integrins Prevents Remodeling of Airway Smooth Muscle in Asthma.

Background: Airway smooth muscle (ASM) remodeling is an important component of the structural changes to airways seen in asthma. Eosinophils are the prominent inflammatory cells in asthma, and there is some evidence that they contribute to ASM remodeling via released mediators and direct contact through integrin–ligand interactions. Eosinophils express several types of outer membrane integrin, which are responsible for cell–cell and cell–extracellular matrix interactions. In our previous study we demonstrated that asthmatic eosinophils show increased adhesion to ASM cells and it may be important factor contributing to ASM remodeling in asthma. According to these findings, in the present study we investigated the effects of suppression of eosinophil integrin on eosinophil-induced ASM remodeling in asthma.Materials and Methods: Individual combined cell cultures of immortalized human ASM cells and eosinophils from peripheral blood of 22 asthmatic patients and 17 healthy controls were prepared. Eosinophil adhesion was evaluated using eosinophil peroxidase activity assay. Genes expression levels in ASM cells and eosinophils were measured using quantitative real-time PCR. ASM cell proliferation was measured using alamarBlue® solution. Eosinophil integrins were blocked by incubating with Arg-Gly-Asp-Ser peptide.Results: Eosinophils from the asthma group showed increased outer membrane α4β1 and αMβ2 integrin expression, increased adhesion to ASM cells, and overexpression of TGF-β1 compared with eosinophils from the healthy control group. Blockade of eosinophil RGD-binding integrins by Arg-Gly-Asp-Ser peptide significantly reduced adhesion of eosinophils to ASM cells in both groups. Integrin-blocking decreased the effects of eosinophils on TGF-β1, WNT-5a, and extracellular matrix protein gene expression in ASM cells and ASM cell proliferation in both groups. These effects were more pronounced in the asthma group compared with the control group.Conclusion: Suppression of eosinophil-ASM interaction via RGD-binding integrins attenuates eosinophil-induced ASM remodeling in asthma.Trial Registration: ClinicalTrials.gov Identifier: NCT02648074.

Functional Effects of WNT1-Inducible Signaling Pathway Protein-1 on Bronchial Smooth Muscle Cell Migration and Proliferation in OVA-Induced Airway Remodeling.

Upregulation of WISP1 has been demonstrated in lung remodeling. Moreover, it has been recently found that some signaling components of WNT pathway can activate GSK3β signaling to mediate remodeling of airway smooth muscle (ASM) in asthma. Therefore, we hypothesized that WISP1, a signaling molecule downstream of the WNT signaling pathway, is involved in PI3K/GSK3β signaling to mediate ASM remodeling in asthma. Our results showed that WISP1 depletion partly suppressed OVA-induced ASM hypertrophy in vivo. In vitro, WISP1 could induce hBSMC hypertrophy and proliferation, accompanied by upregulation of levels of PI3K, p-Akt, p-GSK3β, and its own expression. TGF-β treatment could increase expression of PI3K, p-Akt, p-GSK3β, and WISP1. SH-5 treatment could partly suppress TGF-β-induced hypertrophy and proliferation of hBSMC, and depress expression of p-GSK3β and WISP1. In conclusion, WISP1 may be a potential inducer of ASM proliferation and hypertrophy in asthma. The pro-remodeling effect of WISP1 is likely due to be involved in PI3K-GSK3β-dependent noncanonical TGF-β signaling.

L-thyroxine promotes a proliferative airway smooth muscle phenotype in the presence of TGF-β1.

Hypothyroidism may reduce, whereas hyperthyroidism may aggravate, asthma symptoms. The mechanisms underlying this relationship are largely unknown. Since thyroid hormones have central roles in cell growth and differentiation, we hypothesized that airway remodeling, in particular increased airway smooth muscle (ASM) mass, may be involved. To address this hypothesis, we investigated the effects of triiodothyronine (T3) and l-thyroxine (T4) in the absence and presence of the profibrotic transforming growth factor (TGF)-β1 on human ASM cell phenotype switching. T3 (1-100 nM) and T4 (1-100 nM) did not affect basal ASM proliferation. However, when combined with TGF-β1 (2 ng/ml), T4 synergistically increased the proliferative response, whereas only a minor effect was observed for T3. In line with a switch from a contractile to a proliferative ASM phenotype, T4 reduced the TGF-β1-induced contractile protein expression by ∼50%. Cotreatment with T3 reduced TGF-β1-induced contractile protein expression by ∼25%. The synergistic increase in proliferation was almost fully inhibited by the integrin αvβ3 antagonist tetrac (100 nM), whereas no significant effects of the thyroid receptor antagonist 1-850 (3 μM) were observed. Inhibition of MEK1/2, downstream of the integrin αvβ3, also inhibited the T4- and TGF-β1-induced proliferative responses. Collectively, the results indicate that T4, and to a lesser extent T3, promotes a proliferative ASM phenotype in the presence of TGF-β1, which is predominantly mediated by the membrane-bound T4 receptor αvβ3. These results indicate that thyroid hormones may enhance ASM remodeling in asthma, which could be of relevance for hyperthyroid patients with this disease.

5-Aza-2′-deoxycytidine inhibited PDGF-induced rat airway smooth muscle cell phenotypic switching

Airway smooth muscle (ASM) cell phenotypic switching played an important role in airway remodeling in asthma. In vitro platelet-derived growth factor (PDGF) induced ASM cell phenotypic switching from a mature to pro-remodeling phenotype, but the mechanism remained incompletely understood. This study was to explore the effect of DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (Aza-CdR) on PDGF-induced rat ASM cell phenotypic switching and biological behaviors. Rat airway smooth muscle (RASM) cells were obtained by primary explant techniques. Western blot, 3-dimensional gel contraction, transwell and wound healing assay, and MTT were applied to detect cell phenotypic switching, contractility, migration and proliferation, respectively. Cytoskeleton rearrangement was observed by immunofluorescence. Results showed Aza-CdR inhibited PDGF-induced down-regulation of contractile markers in RASM cells and increased cell contractility. Aza-CdR inhibited PDGF-induced RASM cell migration by abrogating cell morphology change and cytoskeletal reorganization and attenuated the effect of PDGF on proliferating cell nuclear antigen expression and cell cycle progression, ultimately cell proliferation. PDGF-induced DNA methyltransferase 1 (DNMT1) expression was mediated by activation of PI3K/Akt and ERK signaling in RASM cells. Selective depletion of DNMT1 protein by Aza-CdR inhibited PDGF-induced RASM cell phenotypic switching, revealing DNMT1-mediated DNA methylation was implicated in asthmatic ASM remodeling. We proposed for the first time that DNMT1 played a key role in PDGF-induced RASM cell phenotypic switching and Aza-CdR is promising in intervening ASM remodeling in asthma. Although study of abnormal DNA methylation in PDGF-stimulated ASM cells is in its infancy, this work contributes to providing new insights into the mechanism of ASM remodeling and may be helpful for developing effective treatments for airway remodeling in asthma.

Muscarinic receptor stimulation augments TGF-β1-induced contractile protein expression by airway smooth muscle cells

Acetylcholine (ACh) is the primary parasympathetic neurotransmitter in the airways. Recently, it was established that ACh, via muscarinic receptors, regulates airway remodeling in animal models of asthma and chronic obstructive pulmonary disease (COPD). The mechanisms involved are not well understood. Here, we investigated the functional interaction between muscarinic receptor stimulation and transforming growth factor (TGF)-β(1) on the expression of contractile proteins in human airway smooth muscle (ASM) cells. ASM cells expressing functional muscarinic M(2) and M(3) receptors were stimulated with methacholine (MCh), TGF-β(1), or their combination for up to 7 days. Western blot analysis revealed a strong induction of sm-α-actin and calponin by TGF-β(1), which was increased by MCh in ASM cells. Immunocytochemistry confirmed these results and revealed that the presence of MCh augmented the formation of sm-α-actin stress fibers by TGF-β(1). MCh did not augment TGF-β(1)-induced gene transcription of contractile phenotype markers. Rather, translational processes were involved in the augmentation of TGF-β(1)-induced contractile protein expression by muscarinic receptor stimulation, including phosphorylation of glycogen synthase kinase-3β and 4E-binding protein 1, which was enhanced by MCh. In conclusion, muscarinic receptor stimulation augments functional effects of TGF-β(1) in human ASM cells on cellular processes that underpin ASM remodeling in asthma and COPD.

T Cells Localize with Proliferating Smooth Muscle α-Actin+ Cell Compartments in Asthma

Airway remodeling in asthma comprises increased airway smooth muscle (ASM), an alteration linked to airway hyperresponsiveness and disease severity. Experimental studies showed that T cells adhere to ASM through vascular cell adhesion molecule-1 (VCAM-1) and drive ASM growth through direct contact between the T cells and smooth muscle alpha-actin (alpha-SMA)(+) cells. To support the hypothesis of a T-cell/alpha-SMA(+) cell contact mechanism of ASM remodeling in asthma, using bronchial biopsies. We performed quantitative morphology on T cells, proliferating cell nuclear antigen (PCNA), alpha-SMA, and VCAM-1 on biopsies from subjects with moderate and severe asthma and healthy control subjects. We demonstrate ASM cell proliferation and infiltration by T cells in proportion to severity in the subjects with asthma. T cells localized with alpha-SMA(+)PCNA(+) cells, suggesting direct intercellular contact and a relationship with alpha-SMA(+) cell proliferation. Furthermore, the subjects with asthma developed a proliferating compartment of subepithelial alpha-SMA(+), nonorganized airway contractile elements (NOACE), suggesting a phenotype gradient from undifferentiated cells to smooth muscle-like cells. T-cell juxtaposition events were also observed in this compartment and correlated to its mass. The subjects with asthma showed VCAM-1 expression in postcapillary venules and clusters of VCAM-1 immunoreactivity in ASM and NOACE, consistent with a role of VCAM-1 in T-cell/alpha-SMA(+) cell interaction. T cells may induce alpha-SMA(+) cell proliferation through direct intercellular contact. NOACE may in part contribute to ASM growth through differentiation and translocation of alpha-SMA(+) cells. The findings support the role of the T cell in ASM remodeling in asthma.

Interferons modulate mitogen-induced protein synthesis in airway smooth muscle.

Severe asthma is characterized by increased airway smooth muscle (ASM) mass due, in part, to ASM cell growth and contractile protein expression associated with increased protein synthesis. Little is known regarding the combined effects of mitogens and interferons on ASM cytosolic protein synthesis. We demonstrate that human ASM mitogens including PDGF, EGF, and thrombin stimulate protein synthesis. Surprisingly, pleiotropic cytokines IFN-beta and IFN-gamma, which inhibit ASM proliferation, also increased cytosolic protein content in ASM cells. Thus IFN-beta alone significantly increased protein synthesis by 1.62 +/- 0.09-fold that was further enhanced by EGF to 2.52 +/- 0.17-fold. IFN-gamma alone also stimulated protein synthesis by 1.91 +/- 0.15-fold; treatment of cells with PDGF, EGF, and thrombin in the presence of IFN-gamma stimulated protein synthesis by 2.24 +/- 0.3-, 1.25 +/- 0.17-, and 2.67 +/- 0.34-fold, respectively, compared with growth factors alone. The mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) inhibition with rapamycin inhibited IFN- and EGF-induced protein synthesis, suggesting that IFN-induced protein synthesis is modulated by mTOR/S6K1 activation. Furthermore, overexpression of tumor suppressor protein tuberous sclerosis complex 2 (TSC2), which is an upstream negative regulator of mTOR/S6K1 signaling, also inhibited mitogen-induced protein synthesis in ASM cells. IFN-beta and IFN-gamma stimulated miR143/145 microRNA expression and increased SM alpha-actin accumulation but had little effect on ASM cell size. In contrast, EGF increased ASM cell size but had little effect on miR143/145 expression. Our data demonstrate that both IFNs and mitogens stimulate protein synthesis but have differential effects on cell size and contractile protein expression and suggest that combined effects of IFNs and mitogens may contribute to ASM cell growth, contractile protein expression, and ASM remodeling in asthma.