Cytoprotective response of A1, a Bcl-2 homologue expressed in mature human neutrophils and promyelocytic HL-60 cells, to oxidant stress-induced cell death

Identification of a forkhead box protein transcriptional network induced in human neutrophils in response to inflammatory stimuli

Introduction

Neutrophils represent the largest proportion of circulating leukocytes and, in response to inflammatory stimuli, are rapidly recruited to sites of infection where they neutralize pathogens.

Methods and results

We have identified a novel neutrophil transcription network induced in response to inflammatory stimuli. We performed the first RNAseq analysis of human neutrophils exposed to lipopolysaccharide (LPS), followed by a meta-analysis of our dataset and previously published studies of LPS-challenged neutrophils. This revealed a robustly enhanced transcriptional network driven by forkhead box (FOX) transcription factors. The network is enriched in genes encoding proinflammatory cytokines and transcription factors, including MAFF and ATF3, which are implicated in responses to stress, survival and inflammation. Expression of transcription factors FOXP1 and FOXP4 is induced in neutrophils exposed to inflammatory stimuli, and potential FOXP1/FOXP4 binding sites were identified in several genes in the network, all located in chromatin regions consistent with neutrophil enhancer function. Chromatin immunoprecipitation (ChIP) assays in neutrophils confirmed enhanced binding of FOXP4, but not FOXP1, to multiple sites in response to LPS. Binding to numerous motifs and transactivation of network genes were also observed when FOXP proteins were transiently expressed in HEK293 cells. In addition to LPS, the transcriptional network is induced by other inflammatory stimuli, indicating it represents a general neutrophil response to inflammation.

Discussion

Collectively, these findings reveal a role for the FOXP4 transcription network as a regulator of responses to inflammatory stimuli in neutrophils.

Phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase regulate induction of Mcl-1 and survival in glucocorticoid-treated human neutrophils

BACKGROUND

Glucocorticoids have been shown to inhibit human neutrophil apoptosis, with implications that this might help accentuate neutrophilic inflammation.

OBJECTIVE

The aim of this study was to investigate the molecular mechanisms involved in glucocorticoid-mediated inhibition of primary human neutrophil apoptosis.

METHODS

Primary human neutrophils were isolated from peripheral blood of healthy volunteers and cultured in vitro with dexamethasone.

RESULTS

Here we confirm that dexamethasone, a classical glucocorticoid, significantly inhibited apoptosis of primary human neutrophils. This inhibition was not dependent on transrepression of proapoptotic molecules but was associated with induction of antiapoptotic Mcl-1. Remarkably, glucocorticoid-mediated enhancement of Mcl-1 and survival were significantly suppressed by pharmacologic inhibition of p38 mitogen-activated protein kinase or phosphatidylinositol 3-kinase. Inhibition of the above kinases also blocked glucocorticoid-induced maintenance of mitochondrial transmembrane potential and suppression of caspases.

CONCLUSION

Phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase are protein kinases that regulate the prosurvival effect of glucocorticoids on human neutrophils.

Increased hyperoxia-induced mortality and acute lung injury in IL-13 null mice

IL-13 is a critical effector at sites of Th2 inflammation and remodeling. As a result, anti-IL-13-based therapies are being actively developed to treat a variety of diseases and disorders. However, the beneficial effects of endogenous IL-13 in the normal and diseased lung have not been adequately defined. We hypothesized that endogenous IL-13 is an important regulator of oxidant-induced lung injury and inflammation. To test this hypothesis, we compared the effects of 100% O(2) in mice with wild-type and null IL-13 loci. In this study, we demonstrate that hyperoxia significantly augments the expression of the components of the IL-13R, IL-13Ralpha1, and IL-4Ralpha. We also demonstrate that, in the absence of IL-13, hyperoxia-induced tissue inflammation is decreased. In contrast, in the IL-13 null mice, DNA injury, cell death, caspase expression, and activation and mortality are augmented. Interestingly, the levels of the cytoprotective cytokines vascular endothelial cell growth factor, IL-6, and IL-11 were decreased in the bronchoalveolar lavage fluid. These studies demonstrate that the expression of the IL-13R is augmented and that the endogenous IL-13-IL-13R pathway contributes to the induction of inflammation and the inhibition of injury in hyperoxic acute lung injury.

Increased radiosensitivity in cells of two human cell lines treated with bystander medium from irradiated repair-deficient cells

Radiation-induced bystander factors have been shown to be more toxic if they are from medium harvested from irradiated repair-deficient cells. The aim of this study was to test the hypothesis that the radiosensitivity of repair-proficient cells can be increased by exposing them to medium-borne factors harvested from sensitive cells and vice versa. Cells from a mismatch repair (MMR)-deficient cell line (Raji 10) with a sensitive response to radiation or the wild-type parent cell line were irradiated to 0.5 Gy gamma rays and then monitored for growth rate in their own medium or in the alternative conditioned medium. In other experiments, cells or conditioned medium were added to reporter cells (HPV-G, which are relatively sensitive keratinocytes, or highly radioresistant HT29 cells). The subsequent responses of the two cell lines to a 0.5-Gy dose of (60)Co gamma rays were measured. The results show that prior exposure of resistant cells to medium from irradiated sensitive cells reduced the clonogenic survival of the subsequently irradiated resistant cells. The reverse is also true. Measurement of the apoptosis index and BCL2 expression confirmed that the harvested medium was capable of modulating apoptosis after irradiation. This may have important applications in tumor therapy and also in the understanding of mechanisms involved in induction of adaptive responses.

Redox regulation of neutrophil apoptosis and the systemic inflammatory response syndrome

SIRS (systemic inflammatory response syndrome) may result from a wide variety of non-infective insults. Surgery is a recognized cause of SIRS, the onset of which can have adverse prognostic significance. Neutrophil activation is a key histopathological feature of SIRS, and neutrophil clearance through programmed cell death or apoptosis is an essential step in its resolution. Increasingly, it is recognized that ROS (reactive oxygen species), such as those generated by activated neutrophils during cardiac surgery, may have a regulatory role, influencing neutrophil lifespan and thus inflammation. In this review, we discuss the continuing importance of SIRS as a herald of inflammation and the role of neutrophil longevity in the resolution of inflammation, and we consider recent evidence for the regulation of neutrophil apoptosis by ROS.