Dept. of Cellular & Integrative Physiology, Indiana Univ. School of Medicine, Indianapolis, IN 46202, USA.
Am J Physiol Lung Cell Mol Physiol. 2011 Sep;301(3):L275-84. doi: 10.1152/ajplung.00043.2011. Epub 2011 Jun 3.
Airway smooth muscle phenotype may be modulated in response to external stimuli under physiological and pathophysiological conditions. The effect of mechanical forces on airway smooth muscle phenotype were evaluated in vitro by suspending weights of 0.5 or 1 g from the ends of canine tracheal smooth muscle tissues, incubating the weighted tissues for 6 h, and then measuring the expression of the phenotypic marker protein, smooth muscle myosin heavy chain (SmMHC). Incubation of the tissues at a high load significantly increased expression of SmMHC compared with incubation at low load. Incubation of the tissues at a high load also decreased activation of PKB/Akt, as indicated by its phosphorylation at Ser 473. Inhibition of Akt or phosphatidylinositol-3,4,5 triphosphate-kinase increased SmMHC expression in tissues at low load but did not affect SmMHC expression at high load. IL-13 induced a significant increase in Akt activation and suppressed the expression of SmMHC protein at both low and high loads. The role of integrin signaling in mechanotransduction was evaluated by expressing a PINCH (LIM1-2) fragment in the muscle tissues that prevents the membrane localization of the integrin-binding IPP complex (ILK/PINCH/α-parvin), and also by expressing an inactive integrin-linked kinase mutant (ILK S343A) that inhibits endogenous ILK activity. Both mutants inhibited Akt activation and increased expression of SmMHC protein at low load but had no effect at high load. These results suggest that mechanical stress and IL-13 both act through an integrin-mediated signaling pathway to oppositely regulate the expression of phenotypic marker proteins in intact airway smooth muscle tissues. The stimulatory effects of mechanical stress on contractile protein expression oppose the suppression of contractile protein expression mediated by IL-13; thus the imposition of mechanical strain may inhibit changes in airway smooth muscle phenotype induced by inflammatory mediators.
在生理和病理条件下，气道平滑肌表型可能会对外界刺激做出反应进行调节。通过将 0.5 或 1 克的砝码悬挂在犬气管平滑肌组织的两端来评估机械力对气道平滑肌表型的影响，孵育加重量的组织 6 小时，然后测量表型标记蛋白，平滑肌肌球蛋白重链（SmMHC）的表达。与低负荷孵育相比，高负荷孵育显著增加 SmMHC 的表达。高负荷孵育还降低了 PKB/Akt 的激活，这表现为其在 Ser 473 处的磷酸化。Akt 或磷脂酰肌醇-3,4,5 三磷酸激酶的抑制增加了低负荷组织中 SmMHC 的表达，但不影响高负荷组织中 SmMHC 的表达。IL-13 诱导 Akt 激活显著增加，并抑制低负荷和高负荷时 SmMHC 蛋白的表达。通过在肌肉组织中表达阻止整合素结合 IPP 复合物（ILK/PINCH/α-辅肌动蛋白）膜定位的 PINCH（LIM1-2）片段，以及通过表达抑制内源性 ILK 活性的无活性整合素连接激酶突变体（ILK S343A）来评估整合素信号在机械转导中的作用。这两种突变体均抑制 Akt 激活并增加低负荷时 SmMHC 蛋白的表达，但在高负荷时没有影响。这些结果表明，机械应力和 IL-13 都通过整合素介导的信号通路作用，相反调节完整气道平滑肌组织中表型标记蛋白的表达。机械应力对收缩蛋白表达的刺激作用与 IL-13 介导的收缩蛋白表达抑制作用相反；因此，施加机械应变可能会抑制由炎症介质引起的气道平滑肌表型变化。
