Heat shock proteins and ventilator-induced lung injury

TLR4 is required for macrophage efferocytosis during resolution of ventilator-induced lung injury

Mechanical ventilation is a life-sustaining therapy for patients with respiratory failure but can cause further lung damage known as ventilator-induced lung injury (VILI). However, the intrinsic molecular mechanisms underlying recovery of VILI remain unknown. Phagocytosis of apoptotic cells (also known as efferocytosis) is a key mechanism orchestrating successful resolution of inflammation. Here we show the positive regulation of macrophage Toll-like receptor (TLR) 4 in efferocytosis and resolution of VILI. Mice were depleted of alveolar macrophages and then subjected to injurious ventilation (tidal volume, 20 mL/kg) for 4 h. On day 1 after mechanical ventilation, Tlr4^+/+ or Tlr4^-/- bone marrow-derived macrophages (BMDMs) were intratracheally administered to alveolar macrophage-depleted mice. We observed that mice depleted of alveolar macrophages exhibited defective resolution of neutrophilic inflammation, exuded protein, lung edema, and lung tissue injury after ventilation, whereas these delayed responses were reversed by administration of Tlr4^+/+ BMDMs. Importantly, these proresolving effects by Tlr4^+/+ BMDMs were abolished in mice receiving Tlr4^-/- BMDMs. The number of macrophages containing apoptotic cells or bodies in bronchoalveolar lavage fluid was much less in mice receiving Tlr4^-/- BMDMs than that in those receiving Tlr4^+/+ BMDMs. Macrophage TLR4 deletion facilitated a disintegrin and metalloprotease 17 maturation and enhanced Mer cleavage in response to mechanical ventilation. Heat shock protein 70 dramatically increased Mer tyrosine kinase surface expression, phagocytosis of apoptotic neutrophils, and rescued the inflammatory phenotype in alveolar macrophage-depleted mice receiving Tlr4^+/+ BMDMs, but not Tlr4^-/- BMDMs. Our results suggest that macrophage TLR4 promotes resolution of VILI via modulation of Mer-mediated efferocytosis.

Heat shock protein 70 secretion by neonatal tracheal tissue during mechanical ventilation: association with indices of tissue function and modeling

Mechanical ventilation (MV) of the neonatal airway alters mechanical properties and activates tissue-modeling pathways. Heat shock protein (HSP70) is a marker of tissue injury and modulates inflammation, which may influence subsequent pulmonary tissue modeling by matrix metalloproteinases (MMPs). HSP70 secretion is up-regulated in MV airway tissues and associated with changes in airway elasticity and secretion of MMPs. Proximal tracheal segments were isolated in 13 newborn lambs and were either MV for 4 h or SHAM. At baseline and hourly, tracheal segments were flushed and tracheal elasticity was determined. Tracheal wash fluid was assayed for HSP70 by ELISA and for MMPs by substrate zymography. HSP70 secretion increased from baseline to a peak at 1 h in both groups (p < 0.01), greater in the MV group (p < 0.05), and returned to baseline values by 2 h. This response was in contrast to the progressive decrease in tracheal elasticity (p < 0.05). The HSP70 elevation pattern was noted in MMP-2, but beyond 1 h, MMP-2 returned to baseline values in MV group but remained elevated in SHAM (p < 0.05). HSP70 secretion is associated with the degree of biophysical tracheal injury as well as the time course of MMP-2 secretion by tracheal tissues.

Hypoxia attenuates effector-target cell interaction in the airway and pulmonary vascular compartment

Leucocyte infiltration is known to play an important role in hypoxia-induced tissue damage. However, little information is available about hypoxia and interaction of effector (neutrophils) with target cells (alveolar epithelial cells, AEC; rat pulmonary artery endothelial cells, RPAEC). The goal of this study was to elucidate hypoxia-induced changes of effector-target cell interaction. AEC and RPAEC were exposed to 5% oxygen for 2-6 h. Intercellular adhesion molecule-1 (ICAM-1) expression was determined and cell adherence as well as cytotoxicity assays were performed. Nitric oxide and heat shock protein 70 (HSP70) production was assessed in target cells. Under hypoxic conditions enhanced ICAM-1 production was found in both cell types. This resulted in an increase of adherent neutrophils to AEC and RPAEC. The death rate of hypoxia-exposed target cells decreased significantly in comparison to control cells. Nitric oxide (NO) concentration was enhanced, as was production of HSP70 in AEC. Blocking NO production in target cells resulted in increased cytotoxicity in AEC and RPAEC. This study shows for the first time that target cells are more resistant to effector cells under hypoxia, suggesting hypoxia-induced cell protection. An underlying mechanism for this phenomenon might be the protective effect of increased levels of NO in target cells.

Microarray analysis of regional cellular responses to local mechanical stress in acute lung injury

Human acute lung injury is characterized by heterogeneous tissue involvement, leading to the potential for extremes of mechanical stress and tissue injury when mechanical ventilation, required to support critically ill patients, is employed. Our goal was to establish whether regional cellular responses to these disparate local mechanical conditions could be determined as a novel approach toward understanding the mechanism of development of ventilator-associated lung injury. We utilized cross-species genomic microarrays in a unilateral model of ventilator-associated lung injury in anesthetized dogs to assess regional cellular responses to local mechanical conditions that potentially contribute pathogenic mechanisms of injury. Highly significant regional differences in gene expression were observed between lung apex/base regions as well as between gravitationally dependent/nondependent regions of the base, with 367 and 1,544 genes differentially regulated between these regions, respectively. Major functional groupings of differentially regulated genes included inflammation and immune responses, cell proliferation, adhesion, signaling, and apoptosis. Expression of genes encoding both acute lung injury-associated inflammatory cytokines and protective acute response genes were markedly different in the nondependent compared with the dependent regions of the lung base. We conclude that there are significant differences in the local responses to stress within the lung, and consequently, insights into the cellular responses that contribute to ventilator-associated lung injury development must be sought in the context of the mechanical heterogeneity that characterizes this syndrome.

Serum thymic factor, FTS, attenuates cisplatin nephrotoxicity by suppressing cisplatin-induced ERK activation

Serum thymic factor (FTS), a thymic peptide hormone, has been reported to attenuate the bleomycin-induced pulmonary injury and also experimental pancreatitis and diabetes. In the present study, we investigated the effect of FTS on cis-diamminedichloroplatinum II (cisplatin)-induced nephrotoxicity. We have already demonstrated that cephaloridine, a nephrotoxic antibiotic, leads to extracellular signal-regulated protein kinase (ERK) activation in the rat kidney, which probably contributes to cephaloridine-induced renal dysfunction. The aim of this study was to examine the effect of cisplatin on ERK activation in the rat kidney and also the effect of FTS on cisplatin-induced nephrotoxicity in rats. In vitro treatment of LLC-PK1 cells with FTS significantly ameliorated cisplatin-induced cell injury. Treatment of rats with intravenous cisplatin for 3 days markedly induced renal dysfunction and increased platinum contents in the kidney cortex. An increase in pERK was detected in the nuclear fraction prepared from the rat kidney cortex from days 1 to 3 after injection of cisplatin. FTS suppressed cisplatin-induced renal dysfunction and ERK activation in the kidney. FTS did not influence any Pt contents in the kidney after cisplatin administration. FTS has been shown to enhance the in vivo expression of heat shock protein (HSP) 70 in the kidney cortex. The beneficial role of FTS against cisplatin nephrotoxicity may be mediated in part by HSP70, as suggested by its up-regulation in the kidney cortex treated with FTS alone. Our results suggest that FTS participates in protection from cisplatin-induced nephrotoxicity by suppressing ERK activation caused by cisplatin.

Polymorphism of host response genes: Implications in the pathogenesis and treatment of acute renal failure

Acute inflammatory disorders are the result of an interaction between genetic and environmental factors, and are often characterized by an imbalance between pro- and anti-inflammatory host immune responses. Over the past decade, polymorphisms of host response genes have been explored as genetic risk and prognostic markers in the course and severity of acute inflammatory disorders. Increasing evidence supports an important role for inflammatory mechanisms in the pathogenesis of acute renal failure (ARF) following both ischemic and nephrotoxic injury. The use of genetic epidemiology may become a useful tool to identify patients with an altered susceptibility to developing hospital-acquired ARF, and stratify those who may benefit from preventive therapies that modulate host immune responses in a favorable way. This review summarizes the existing experimental and clinical studies supporting the role of inflammation in ARF and critically appraises studies that have examined polymorphism of immune response genes as potential determinants of susceptibility to and severity of acute inflammatory disorders. Conclusions are drawn on the application of genetic epidemiology to the field of ARF and the rationale for further research on the role of genetic markers in ARF.