Inhibition of the p38 MAP kinase pathway destabilizes smooth muscle length during physiological loading

Abstract

Lakser, Oren J., Robert P. Lindeman, and Jeffrey J. Fredberg. Inhibition of the p38 MAP kinase pathway destabilizes smooth muscle length during physiological loading. Am J Physiol Lung Cell Mol Physiol 282: L1117-L1121, 2002 10.1152/ajplung.00230.2000.-We tested the hypothesis that mechanical plasticity of airway smooth muscle may be mediated in part by the p38 mitogen-activated protein (MAP) kinase pathway. Bovine tracheal smooth muscle (TSM) strips were mounted in a muscle bath and set to their optimal length, where the active force was maximal (Fo). Each strip was then contracted isotonically (at 0.32 Fo) with ACh (maintained at 10 Ϫ4 M) and allowed to shorten for 180 min, by which time shortening was completed and the static equilibrium length was established. To simulate the action of breathing, we then superimposed on this steady distending force a sinusoidal force fluctuation with zero mean, at a frequency of 0.2 Hz, and measured incremental changes in muscle length. We found that TSM strips incubated in 10 M SB-203580-HCl, an inhibitor of the p38 MAP kinase pathway, demonstrated a greater degree of fluctuation-driven lengthening than did control strips, and upon removal of the force fluctuations they remained at a greater length. We also found that the force fluctuations themselves activated the p38 MAP kinase pathway. These findings are consistent with the hypothesis that inhibition of the p38 MAP kinase pathway destabilizes muscle length during physiological loading. mitogen-activated protein; contraction; plasticity; perturbed myosin binding ASTHMA IS CHARACTERIZED by reversible airway obstruction, airway inflammation, and airway hyperresponsiveness to nonspecific agonists. The end result is excessive airway narrowing. Airway narrowing is driven by the action of airway smooth muscle and its actomyosin contractile machinery, but myosin exerts its mechanical effects within a cytoskeletal scaffolding that is extensible and in a continuous state of remodeling (6,8,21,23,24).In this connection, load fluctuations are imposed continuously on airway smooth muscle by the tidal action of breathing. These fluctuations are known to inhibit the development of active force and stiffness (7,9,22,27) and result in smooth muscle lengthening (4). Although the direct effects of tidal stretch on actomyosin bridge dynamics can explain much of the force and stiffness inhibition (4), it is thought that important changes in the cytoskeleton are also induced by changes of the muscle load in time (8, 21).Here we have investigated the hypothesis that activation of p38 mitogen-activated protein (MAP) kinase may modulate muscle mechanical responses to imposed load fluctuations during contractile stimulation. We show that the p38 MAP kinase inhibitor SB-203580-HCl increased the degree of smooth muscle lengthening induced by load fluctuations. As such, these data suggest that activation of p38 MAP kinase stabilizes airway smooth muscle subjected to dynamic loading conditions that approximate those that prevail in vivo. Moreover, t...

Force Fluctuation induced Relengthening of Acetylcholine-contracted Airway Smooth Muscle

“…Here we have reviewed a number of possible theories for this difference. We have presented published data that strongly implicate FFIR as a key component of this breathing effect (1)(2)(3)(4). Furthermore, we have suggested, based on our previous work, that actin filament length is a major determinant of FFIR (1).…”

“…That is, it seems that the airways (airway smooth muscle) of healthy individuals reacted differently to the stretch from a DI than did those of individuals with asthma. Therefore, we designed in vitro experiments (1,4) to assess whether oscillating (to simulate breathing) contracted and shortened airway smooth muscle (to simulate narrowed bronchi) could be relengthened (airway opening) and to determine whether the relengthening could be physiologically regulated.…”

Latrunculin B increases force fluctuation-induced relengthening of ACh-contracted, isotonically shortened canine tracheal smooth muscle

“…Our approach is modeled after that of Fredberg's laboratory (13,14), but it was modified to allow for comparison of results before and after pharmacological intervention. Where Fredberg et al used increasing amplitudes of fluctuation from Ϯ2 to 16% of the maximal isometric force elicited by ACh (Fmax) over several hours, we used a single amplitude of Ϯ16% Fmax for 20 min.…”

“…Fredberg and coworkers (13,14) studied the influence on airway smooth muscle shortening of the load fluctuations imposed by breathing. They stimulated bovine trachealis strips with ACh and allowed them to shorten isotonically against a constant load to a steady-state length and then superimposed sinusoidal force oscillations of increasing amplitudes (to simulate tidal breathing) on the constant mean load (5).…”

“…Subsequent studies showed that oscillation-induced relengthening of contracted airway smooth muscle is a physiologically regulated phenomenon. For example, treatment with the p38 MAPK inhibitor SB-203580 enhanced force fluctuation-induced relengthening (13). One potential consequence of p38 MAPK inhibition is shortening of contractile actin filaments, because p38 MAPK activation leads to the phosphorylation of heat shock protein 27 (HSP27), an actin "capping protein."…”