Stimulation of Rho signaling by pathologic mechanical stretch is a “second hit” to Rho-independent lung injury induced by IL-6

Abstract

Birukova AA, Tian Y, Meliton A, Leff A, Wu T, Birukov KG. Stimulation of Rho signaling by pathologic mechanical stretch is a "second hit" to Rho-independent lung injury induced by IL-6. Am J Physiol Lung Cell Mol Physiol 302: L965-L975, 2012. First published February 17, 2012 doi:10.1152/ajplung.00292.2011.-Most patients with acute lung injury (ALI) and acute respiratory distress syndrome of septic and nonseptic nature require assisted ventilation with positive pressure, which at suboptimal range may further exacerbate lung dysfunction. Previous studies described enhancement of agonist-induced Rho GTPase signaling and endothelial cell (EC) permeability in EC cultures exposed to pathologically relevant cyclic stretch (CS) magnitudes. This study examined a role of pathologic CS in modulation of pulmonary EC permeability caused by IL-6, a cytokine increased in sepsis and acting in a Rho-independent manner. IL-6 increased EC permeability, which was associated with activation of Jak/signal transducers and activators of transcription, p38 MAP kinase, and NF-B signaling and was augmented by EC exposure to 18% CS. Rho kinase inhibitor Y-27632 suppressed the synergistic effect of 18% CS on IL-6-induced EC monolayer disruption but did not alter the IL-6 effects on static EC culture. 18% CS also increased IL-6-induced ICAM-1 expression by pulmonary EC and neutrophil adhesion, which was attenuated by Y-27632. Intratracheal IL-6 administration in C57BL/6J mice increased protein content and cell count in bronchoalveolar lavage fluid. These changes were augmented by high tidal volume mechanical ventilation (HTV; 30 ml/kg, 4 h). Intravenous injection of Y-27632 suppressed IL6/HTV-induced lung injury. In conclusion, this study proposes a novel mechanism contributing to two-hit model of ALI: in addition to synergistic effects on Rho-dependent endothelial hyper-permeability triggered by thrombin, TNF␣, LPS, or other agonists, ventilator-induced lung injury-relevant CS may also exacerbate Rho-independent mechanisms of EC permeability induced by other inflammatory mediators such as IL-6 via mechanisms involving Rho activity. cyclic stretch; actin; interleukin-6; vascular permeability; endothelium VENTILATOR SUPPORT IS AN INDISPENSABLE treatment for critically ill patients. However, suboptimal regimen of mechanical ventilation leading to ventilator-induced lung injury (VILI), multiorgan dysfunction, and high rates of morbidity and mortality remain one of the most important problems in the management of patients with preexisting respiratory complications in the intensive care unit (31, 34).Pathologic mechanical forces leading to VILI trigger several signaling mechanisms including activation of signaling kinases, ion channels, small GTPases, second messengers, inflammatory signaling, and gene expression (14,16,39). Increased vascular endothelial permeability (2), inflammatory cytokine production (41), and apoptosis (18) induced by pathological mechanical stimulation causes alveolar flooding, leukocyte infiltration, and hypoxemia leadi...

IL-6 trans-signaling promotes pancreatitis-associated lung injury and lethality

“…Moreover, we found that the effects on the liver and kidney were only transient (Supplemental Figure 1, F-J). This model of pancreatitis-associated lung injury revealed activation of the signaling pathways IκB/NF-κB, p38, and RhoA (Supplemental Figure 2, A and B), which are known to be important for mediating damage in the lung (18,19).…”

“…Because IL-6R is only minimally expressed (mainly on hepatocytes and leukocytes), IL-6 trans-signaling dramatically increases the number of potential IL-6 target cells (16). The complexes involve the downstream kinase Jak-2 in order to phosphorylate the transcription factor STAT3 at Y705 (18,19). Tyrosine phosphorylation of Y705 is required for formation of homodimers and subsequent nuclear translocations.…”

Selective Role of Vinculin in Contractile Mechanisms of Endothelial Permeability

“…By contrast, the EC permeability response to IL-6 was not accompanied by significant changes in FA arrangement ( Figure 1C). Previous studies have shown more delayed EC permeability response to IL-6, which developed after 0.5-5.0 hours of stimulation (24) in contrast to more rapid (5-20 min) development of permeability caused by thrombin, which also was followed by recovery of EC barrier by 60 minutes after treatment (29). These time points were further used for analysis of thrombin-and IL-6-induced EC signaling and cytoskeletal remodeling.…”

“…The signaling pathways activated in pulmonary endothelium by IL-6 are not clearly understood, and the precise mechanisms of IL-6-mediated EC barrier dysfunction remain to be elucidated. Our previous study suggests that IL-6-induced EC permeability is independent of RhoA signaling (24). In the current study, we used thrombin and IL-6 as model agents to investigate a role of vinculin in contractiledependent and contractile-independent mechanisms of EC barrier failure relevant to pathological conditions of lung vascular barrier dysfunction caused by circulating vasoactive agonists and proinflammatory cytokines.…”

Control of Vascular Permeability by Atrial Natriuretic Peptide via a GEF-H1-dependent Mechanism

“…The pathologic role of Rho activation in animal models of acute lung injury and EC cultures stimulated with ALI-relevant agonists or high magnitude cyclic stretch is well recognized (29,39,40), and pharmacologic inhibition of the Rho pathway by prostanoids, simvastatin, S1P receptor agonist FTY720, or Rho kinase inhibitor Y-27632 has been proposed as a potential treatment of ALI (41)(42)(43)(44)(45). However, endogenous regulators of excessive Rho activation in ALI are not well characterized.…”