Rodopi Stamatiou

Azithromycin has an antiproliferative and autophagic effect on airway smooth muscle cells.

Azithromycin is used in long-term, low-dose treatment of airway diseases where airway wall remodelling is present. Since it improves total score symptom and respiratory function of such patients, we hypothesise that azithromycins additional clinical benefits are due to an inhibition of airway smooth muscle cell (SMC) proliferation. Rabbit tracheal SMCs were treated with azithromycin (10−5 to 10−6 M) in the presence or absence of 10% fetal bovine serum (FBS). The proliferation was estimated using the Cell Titer 96® AQueous One Solution Assay (Promega, Madison, WI, USA). Cell viability was assessed with Trypan blue staining and flow cytometry after 7-aminoactinomycin D (7-AAD) staining. Induction of autophagy was studied by indirect immmunofluorescence and/or Western blotting with antibodies against human smooth muscle α-actin, beclin 1, light chain 3 and caspase 3. The involvement of the phosphoinositide 3-kinase pathway was investigated with the inhibitors LY294002 and wortmannin. Incubation with azithromycin for 72 h in the presence of FBS reduced SMC proliferation and viability in a dose-dependent manner. Azithromycin treatment was accompanied by the formation of cytoplasmic vacuoles, characteristic of autophagy. All these effects were reversible after azithromycin removal and prevented by the autophagy inhibitor, 3-methyladenine, or LY294002, but not by wortmannin. In conclusion, azithromycin reduces proliferation and causes autophagy of airway SMCs.

The mitogenic effect of testosterone and 17β-estradiol on airway smooth muscle cells.

Airway disease distribution and/or severity exhibit sex differences suggesting that sex hormones are involved in the respiratory system physiology and pathophysiology. The implication of airway smooth muscle cells (ASMCs) in the physiology of the airways and the pathogenetic mechanism of airway remodeling is of great interest. Therefore, we studied the effect of testosterone and 17β-estradiol on ASMC proliferation and the mechanisms involved. Cell proliferation was estimated using the methyl-[³H]thymidine incorporation and Cell Titer 96® AQueous One Solution Assay methods. ASMC isolated from adult male or female rabbit trachea were incubated with testosterone (1 pM-1 μM) or 17β-estradiol (1 pM-1 μM), in the presence or absence of the androgen receptor antagonist flutamide (10 nM) or estrogen receptor antagonist ICI182780 (10 nM), as well as of the PI3K inhibitors LY294002 (20 μM) or wortmannin (1 μM), or the MAPK inhibitors PD98059 (100 μM) or U0126 (1 μM). After 24 h of incubation, testosterone and 17β-estradiol increased methyl-[³H]thymidine incorporation and cell number, in ASMC isolated from male or female animals. The induction of ASMC proliferation by testosterone or 17β-estradiol was inhibited by flutamide or ICI182780 respectively, as well as by LY294002, wortmannin, PD98059 or U0126. In conclusion, testosterone and 17β-estradiol have a mitogenic effect on ASMC, which is receptor-mediated and involves the MAPK and PI3K signaling pathways. Moreover, their effect is the same for ASMC from male and female animals. It is possible that gender-related differences in ASMC remodeling, may be influenced by the different patterns of sex steroid hormone secretion in males and females.

Cytokines and Growth Factors Promote Airway Smooth Muscle Cell Proliferation

Chronic airway diseases, such as asthma or chronic obstructive pulmonary disease, are characterized by the presence in the airways of inflammation factors, growth factors and cytokines, which promote airway wall remodelling. The aim of this study was to investigate the effect of cytokines and growth factors on airway smooth muscle cell (ASMC) proliferation, phenotype and responsiveness. Incubation of serum starved human bronchial ASMCs with TNF-α, TGF, bFGF, and PDGF, but not IL-1β, increased methyl-[3H]thymidine incorporation and cell number, mediated by the PI3K and MAPK signalling pathways. Regarding rabbit tracheal ASMC proliferation, TNF-α, IL-1β, TGF, and PDGF increased methyl-[3H]thymidine incorporation in a PI3K- and MAPK-dependent manner. bFGF increased both methyl-[3H]thymidine incorporation and cell number. Moreover, incubation with TGF, bFGF and PDGF appears to drive human ASMCs towards a synthetic phenotype, as shown by the reduction of the percentage of cells expressing SM-α actin. In addition, the responsiveness of epithelium-denuded rabbit tracheal strips to carbachol was not significantly altered after 3-day treatment with bFGF. In conclusion, all the tested cytokines and growth factors increased ASMC proliferation to a different degree, depending on the specific cell type, with bronchial ASMCs being more prone to proliferation than tracheal ASMCs.

TNFα induces expression of HIF-1α mRNA and protein but inhibits hypoxic stimulation of HIF-1 transcriptional activity in airway smooth muscle cells.

Airway smooth muscle cells (ASMCs) participate in tissue remodeling characteristic of airway inflammatory diseases like asthma. Inflammation and hypoxia pathways are often interconnected and the regulatory subunit of the hypoxia inducible factor, HIF‐1α, has been recently shown to be induced by cytokines. Here we investigate the effect of individual or combined treatment of ASMCs with the inflammatory mediator TNFα and/or hypoxia on the expression of HIF‐1α, HIF‐1 targets and inflammation markers. TNFα enhances HIF‐1α protein and mRNA levels, under both normoxia and hypoxia. TNFα‐mediated induction of HIF‐1α gene transcription is repressed by inhibition of the NF‐κB pathway. Despite the up‐regulation of HIF‐1α protein, the transcription of HIF‐1 target genes remains low in the presence of TNFα at normoxia and is even reduced at hypoxia. We show that the reduction in HIF‐1 transcriptional activity by TNFα is due to inhibition of the interaction of HIF‐1α with ARNT and subsequent blocking of its binding to HREs. Comparison between hypoxia and TNFα for their effects on the expression of inflammatory markers shows significant differences: hypoxia up‐regulates the expression of IL‐6, but not RANTES or ICAM, and reduces the induction of VCAM by TNFα. Finally, ex vivo treatment of rabbit trachea strips with TNFα increases HIF‐1α protein levels, but reduces the expression of HIF‐1 targets under hypoxia. Overall, TNFα induces HIF‐1α mRNA synthesis via an NF‐κB dependent pathway but inhibits binding of HIF‐1α to ARNT and DNA, while hypoxia and TNFα have distinct effects on ASMC inflammatory gene expression. J. Cell. Physiol. 228: 1745–1753, 2013.

Azithromycin reduces the viability of human bronchial smooth muscle cells

The macrolide antibiotic azithromycin has an antiproliferative and autophagic effect on rabbit tracheal smooth muscle cells (SMCs). The purpose of this study is to investigate the effect of azithromycin on human bronchial SMCs. Human bronchial SMCs were treated with azithromycin (10−5 M) in the presence or absence of 10% fetal bovine serum (FBS). Cell number was estimated using the Cell Titer 96 AQueous One Solution Assay. Induction of autophagy was studied by observation of cell morphology in cells treated or not with the autophagy inhibitor, 3-methyladenine (3-MA), as well as by Lysotracker Red staining of lysosomes. Activation of apoptosis was assessed with flow cytometry after annexin staining. Incubation with azithromycin for 24, 48 or 72 h reduced viability in FBS-deprived cells, as well as cells cultured in FBS-containing medium. Azithromycin treatment resulted in the formation of cytoplasmic vacuoles that could not be prevented by 3-MA. Furthermore, 3-MA did not reverse the effect of azithromycin on the viability of SMCs. There was an increase in the number of lysosomes in cells treated with azithromycin. Finally, azithromycin increased the percentage of early apoptotic cells. In conclusion, azithromycin reduces the viability of human bronchial SMCs possibly by leading to apoptotic cell death.

The muscarinic antagonist gallamine induces proliferation of airway smooth muscle cells regardless of the cell phenotype

BACKGROUND Muscarinic receptor antagonists are a usual treatment for chronic airway diseases, with increased bronchoconstriction, like asthma and chronic obstructive pulmonary disease. These diseases are usually accompanied by airway remodeling, involving airway smooth muscle cell (ASMC) proliferation. The purpose of this study was to examine the effect of the muscarinic receptor modulator gallamine on rabbit tracheal ASMC proliferation. METHODS ASMCs were incubated with gallamine (1 nM-10 mM), atropine (1 fM-10 mM), and/or acetylcholine (1 nM-1 mM), in the presence or absence of FBS (1% or 10%). Cell proliferation was estimated by incorporation of radioactive thymidine, the Cell Titer AQueous One Solution method and cell number counting after Trypan blue exclusion. The mechanisms mediating cell proliferation were studied using the PI3K and MAPK inhibitors LY294002 (20 μM) and PD98059 (100 μM), respectively. Cell phenotype was studied by indirect immunofluorescence for α-actin, Myosin Heavy Chain and desmin. RESULTS ASMC incubation with the muscarinic receptor allosteric modulator gallamine or the muscarinic receptor antagonist atropine increased methyl-[3H]thymidine incorporation and cell number in a dose-dependent manner. ASMC proliferation was mediated via PI3K and MAPK activation and was transient. Gallamine antagonized the mitogenic effect of 1% FBS. Furthermore, gallamine had a similar effect on contractile ASMCs, without synergizing with or affecting acetylcholine induced proliferation, or altering the percentage of ASMCs expressing contractile phenotype marker proteins. CONCLUSIONS Gallamine, in the absence of any agonist, has a transient mitogenic effect on ASMCs, regardless of the cell phenotype, mediated by the PI3K and the MAPK signaling pathways.