Literature-based and estimated parameter values used in the ASM growth model.

<p>(^* indicates the values estimated from <i>in vitro</i> experiments.)</p

The role of individual inflammation history in the case of slow inflammation resolution (IR <<1).

<p>(a–c) ASM population size dynamics (<i>c</i>-cells, red; <i>p</i>-cells, blue; total population <i>s</i>, black) and (d–f) the corresponding inflammatory status evolution (μ, solid black; inflammatory thresholds μ₁ and μ₂, dashed), characterized by the same inflammation resolution rate, magnitude and average stimulus frequency (λ_d/λ_p  = 0.08, <i>a</i>/μ₁  = 0.5, ω/λ_p  = 0.25). (d) Regular series of inflammatory events; (e–f) two realisations of a series of inflammatory events at random times for the same mean frequency (about once a fortnight) as in (d). (g) Distribution of fold-increase in ASM mass after 300 days for a random sequence of inflammatory events with the same characteristics as in panels (b, c); arrows indicate the fold-increase corresponding to (a–c). (h) The distribution of outcomes with an increase of 25% in the inflammation resolution rate (λ_d/λ_p  = 0.1). (The outcome histograms (g,h) are computed for <i>N</i> = 1000 instances).</p

Survey of ASM growth scenarios, showing fold-increase in ASM population size after 300 days (colour scale) as a function of the inflammation resolution rate IR = λ_d/λ_p and (a) inflammation magnitude <i>a</i>/μ₁ (for fixed frequency ω/λ_p = 0.25) or (b) inflammation frequency ω/λ_p (for fixed magnitude <i>a</i>/μ₁ = 5).

<p>White dots indicate the growth regimes shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090162#pone-0090162-g002" target="_blank">Fig. 2</a>. Solid black lines are the computed isolines of the 2- and 8-fold ASM growth, which agree with the theoretically predicted dependence λ_d ∼ ω log <i>a</i>/μ₂ (dashed white lines; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090162#pone.0090162.s001" target="_blank">Materials S1</a>).</p

A schematic of the model design.

<p>(a) Schematic representation of the model with <i>p</i> being the amount of ASM cells in proliferating state, <i>c</i> the amount of non-proliferative cells and μ the inflammatory status; λ_p is the proliferation rate, λ_a is the apoptosis rate, λ_cp and λ_pc are the switching rates between non-proliferative and proliferative states, λ_d is the inflammation clearance rate, and <i>f</i>(<i>t</i>) is a time-dependent external inflammatory stimulus. (b) Dependence of the model parameters on the inflammatory status μ (three levels of inflammation are characterised by the thresholds μ₁ and μ₂; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090162#pone-0090162-t001" target="_blank">Table 1</a> for reference values). Rates are plotted on a logarithmic vertical scale. (c) An illustration of the inflammatory status dynamics induced by a series of environmental stimuli such as shown in (a), illustrating graphically the parameters λ_d, <i>a</i>, and ω. (d) A simulation of the ASM cell population response (<i>p</i>, blue dash-dotted; <i>c</i>, red dashed; <i>s</i> = <i>p</i>+<i>c</i>, thick black solid) to a stepwise variation in the inflammation status (thin solid); the arrows show the direction of change in the ASM subpopulations. Although the inflammatory status returns to its initial state at the end of the simulation, the total ASM cell population has irreversibly increased, showing thereby “effective” hysteresis. Only the time spent in “severe” regime (μ>μ₂) contributes to substantial growth (over weeks); however, the “moderate” regime (μ₁<μ<μ₂) can also give rise to substantial growth over a longer timescale (months). Note that the proportion of proliferative cells (blue dash-dotted) is significant only during the “severe inflammation” regime (3).</p

Possible pathways of chronic ASM mass accumulation in asthma (solid lines indicate the mechanisms included in the mathematical model).

<p>Possible pathways of chronic ASM mass accumulation in asthma (solid lines indicate the mechanisms included in the mathematical model).</p

Representative ASM cell population growth dynamics over a period of 300 days, starting from a “healthy” state (<i>c</i> = 0.1, <i>p</i> = 0.01), for different values of normalised inflammation magnitude <i>a</i>/μ₁, frequency ω/λ_p and inflammation resolution rate λ_d/λ_p: <i>a</i>/μ₁ = {2 (a), 5 (b,c), 8 (d), 1.5 (e)}, ω/λ_p = {0.25 (a,c–e), 0.125 (b)} and λ_d/λ_p = {7 (a), 5 (b,c), 2 (d), 0.22 (e)}.

<p>(a,b) show no substantial ASM accumulation, (c,e) show “moderate” and (d) “severe” ASM hyperplasia. The amount of <i>c</i>-cells is depicted by the red line, <i>p</i>-cells (blue) and total population size <i>s</i> = <i>p</i>+<i>c</i> (thick black). Insets plot the corresponding inflammatory status μ (solid black) and the inflammation level thresholds (horizontal dashed lines).</p

<i>AGER</i> mRNA expression levels in total lung and airway cells.

<p>Q-PCR analysis identified <i>AGER</i> mRNA was highly expressed in total lung and at lower levels in human airway smooth muscle cells (HASM) cells, human bronchial epithelial cells (HBEC) and the BEAS-2BR1 bronchial epithelial cell line, (n = 3).</p

<i>AGER</i> isoform expression in three HBEC donors using RNA Seq.

<p>Structure and abundance of known <i>AGER</i> isoforms in three human bronchial epithelial cell donors illustrating heterogeneity in expression levels. Percentage abundances (% FPKM) were calculated for each donor. Transcripts for full length and soluble <i>AGER</i> were identified at similar low abundancies. FPKM; fragments per kilobase of transcript per million mapped reads.</p

Immunohistochemical analysis of RAGE expression in healthy and COPD lung.

<p>In healthy lung tissue, RAGE was found to be localised to the cytoplasm and membrane. RAGE expression was high in the pneumocytes of alveolar regions (a). The bronchial epithelium showed variable weak to moderate staining (e). In lung tissue of individuals with COPD, RAGE was very strongly immunopositive in the membrane and cytoplasm of the pneumocytes in the alveolar regions (b). The bronchial epithelium from individuals with COPD was weak or immunonegative for the RAGE protein (f). All isotype controls were negative (c, d, g and h). Representative images of one healthy and one COPD lung shown. x10 magnification.</p

Baseline characteristics of UK smoker population used for genetic association studies.

<p>Baseline characteristics of UK smoker population used for genetic association studies.</p