Therapeutic effects of cysteine protease inhibition in allergic lung inflammation: inhibition of allergen-specific T lymphocyte migration

Neutrophil-Derived Proteases in Lung Inflammation: Old Players and New Prospects

Neutrophil-derived proteases are critical to the pathology of many inflammatory lung diseases, both chronic and acute. These abundant enzymes play roles in key neutrophil functions, such as neutrophil extracellular trap formation and reactive oxygen species release. They may also be released, inducing tissue damage and loss of tissue function. Historically, the neutrophil serine proteases (NSPs) have been the main subject of neutrophil protease research. Despite highly promising cell-based and animal model work, clinical trials involving the inhibition of NSPs have shown mixed results in lung disease patients. As such, the cutting edge of neutrophil-derived protease research has shifted to proteases that have had little-to-no research in neutrophils to date. These include the cysteine and serine cathepsins, the metzincins and the calpains, among others. This review aims to outline the previous work carried out on NSPs, including the shortcomings of some of the inhibitor-orientated clinical trials. Our growing understanding of other proteases involved in neutrophil function and neutrophilic lung inflammation will then be discussed. Additionally, the potential of targeting these more obscure neutrophil proteases will be highlighted, as they may represent new targets for inhibitor-based treatments of neutrophil-mediated lung inflammation.

DRAM1 regulates autophagy flux through lysosomes

We have previously reported that the mitochondria inhibitor 3-nitropropionic acid (3-NP), induces the expression of DNA damage-regulated autophagy modulator1 (DRAM1) and activation of autophagy in rat striatum. Although the role of DRAM1 in autophagy has been previously characterized, the detailed mechanism by which DRAM1 regulates autophagy activity has not been fully understood. The present study investigated the role of DRAM1 in regulating autophagy flux. In A549 cells expressing wilt-type TP53, 3-NP increased the protein levels of DRAM1 and LC3-II, whereas decreased the levels of SQSTM1 (sequestosome 1). The increase in LC3-II and decrease in SQSTM1 were blocked by the autophagy inhibitor 3-methyl-adenine. Lack of TP53 or knock-down of TP53 in cells impaired the induction of DRAM1. Knock-down of DRAM1 with siRNA significantly reduced 3-NP-induced upregulation of LC3-II and downregulation of SQSTM1, indicating DRAM1 contributes to autophagy activation. Knock-down of DRAM1 robustly decreased rate of disappearance of induced autophagosomes, increased RFP-LC3 fluorescence dots and decreased the decline of LC3-II after withdraw of rapamycin, indicating DRAM1 promotes autophagy flux. DRAM1 siRNA inhibited lysosomal V-ATPase and acidification of lysosomes. As a result, DRAM1 siRNA reduced activation of lysosomal cathepsin D. Similar to DRAM1 siRNA, lysosomal inhibitors E64d and chloroquine also inhibited clearance of autophagosomes and activation of lysosomal cathapsin D after 3-NP treatment. These data suggest that DRAM1 plays important roles in autophagy activation induced by mitochondria dysfunction. DRAM1 affects autophagy through argument of lysosomal acidification, fusion of lysosomes with autophagosomes and clearance of autophagosomes.

Interleukin-10 down-regulates cathepsin B expression in fetal rat alveolar type II cells exposed to hyperoxia

PURPOSE

Hyperoxia has the chief biological effect of cell death. We have previously reported that cathepsin B (CB) is related to fetal alveolar type II cell (FATIIC) death and pretreatment of recombinant IL-10 (rIL-10) attenuates type II cell death during 65%-hyperoixa. In this study, we investigated what kinds of changes of CB expression are induced in FATIICs at different concentrations of hyperoxia (65%- and 85%-hyperoxia) and whether pretreatment with rIL-10 reduces the expression of CB in FATIICs during hyperoxia.

MATERIALS AND METHODS

Isolated embryonic day 19 fetal rat alveolar type II cells were cultured and exposed to 65%- and 85%-hyperoxia for 12 h and 24 h. Cells in room air were used as controls. Cytotoxicity was assessed by lactate dehydrogenase (LDH) released into the supernatant. Expression of CB was analyzed by fluorescence-based assay upon cell lysis and western blotting, and LDH-release was re-analyzed after preincubation of cathepsin B-inhibitor (CBI). IL-10 production was analyzed by ELISA, and LDH-release was re-assessed after preincubation with rIL-10 and CB expression was re-analyzed by western blotting and real-time PCR.

RESULTS

LDH-release and CB expression in FATIICs were enhanced significantly in an oxygen-concentration-dependent manner during hyperoxia, whereas caspase-3 was not activated. Preincubation of FATIICs with CBI significantly reduced LDH-release during hyperoxia. IL-10-release decreased in an oxygen-concentration-dependent fashion, and preincubation of the cells with rIL-10 significantly reduced cellular necrosis and expression of CB in FATIICs which were exposed to 65%- and 85%-hyperoxia.

CONCLUSION

Our study suggests that CB is enhanced in an oxygen- concentration-dependent manner, and IL-10 has an inhibitory effect on CB expression in FATIICs during hyperoxia.

Cathepsin B is activated as an executive protease in fetal rat alveolar type II cells exposed to hyperoxia

Alveolar type II cells are main target of hyperoxia-induced lung injury. The authors investigated whether lysosomal protease, cathepsin B (CB), is activated in fetal alveolar type II cells in the transitional period from the canalicular to saccular stages during 65%-hyperoxia and whether CB is related to fetal alveolar type II cell (FATIIC) death secondary to hyperoxia. FATIICs were isolated from embryonic day 19 rats and exposed to 65%-oxygen for 24 h and 36 h. The cells exposed to room air were used as controls. Cell cytotoxicity was assessed by lactate dehydrogenase-release and flow cytometry, and apoptosis was analyzed by TUNEL assay and flow cytometry. CB activity was assessed by colorimetric assay, qRT-PCR and western blots. 65%-hyperoxia induced FATIIC death via necrosis and apoptosis. Interestingly, caspase-3 activities were not enhanced in FATIICs during 65%-hyperoxia, whereas CB activities were greatly increased during 65%-hyperoxia in a time-dependent manner, and similar findings were observed with qRT-PCR and western blots. In addition, the preincubation of CB inhibitor prior to 65%-hyperoxia reduced FATIIC death significantly. Our studies suggest that CB activation secondary to hyperoxia might have a relevant role in executing the cell death program in FATIICs during the acute stage of 65%-hyperoxia.

Differential expression of neutrophilic granule proteins between Th1 and Th2 cells

T helper cell type 1 (Th1) and 2 (Th2) play central roles in immune regulation. To identify the novel genes differentially expressed between Th1 and Th2 cells, CD4+ T cells were isolated from DO11.10 transgenic mice and induced under Th1 or Th2 conditions. Microarray showed differential expression of neutrophilic granule proteins (NGP) between Th1 and Th2 cells. NGP was first identified as a myeloid-specific granule protein with homology to the cystatin superfamily. Here we confirmed greater expression of NGP in Th2 cells by reverse transcription-polymerase chain reaction and real-time polymerase chain reaction analysis. We also showed that the expression of NGP mRNA had a peak expression after 5 d culture under Th2- but not Th1-biasing conditions. Antibody against NGP was prepared, and in concert with the results of mRNA analysis, the level of NGP protein in Th2 cells detected by Western blot analysis was also higher than that in Th1 cells. GFP-NGP fusion proteins overexpressed in HeLa cells were localized to the cytoplasm. These results suggest NGP is a novel marker distinguishing Th2 from Th1 cells and maybe a novel cytokine secreted by Th2 cells.

Iron-binding drugs targeted to lysosomes: a potential strategy to treat inflammatory lung disorders

In many inflammatory lung disorders, an abnormal assimilation of redox-active iron will exacerbate oxidative tissue damage. It may be that the most important cellular pool of redox-active iron exists within lysosomes, making these organelles vulnerable to oxidative stress. In experiments employing respiratory epithelial cells and macrophages, the chelation of intra-lysosomal iron efficiently prevented lysosomal rupture and the ensuing cell death induced by hydrogen peroxide, ionising radiation or silica particles. Furthermore, cell-permeable iron-binding agents (weak bases) that accumulate within lysosomes due to proton trapping were much more efficient for cytoprotection than the chelator, desferrioxamine. On a molar basis, the weak base alpha-lipoic acid plus was 5000 times more effective than desferrioxamine at preventing lysosomal rupture and apoptotic cell death in cell cultures exposed to hydrogen peroxide. Thus, iron-chelating therapy that targets the lysosome might be a future treatment strategy for inflammatory pulmonary diseases.

T-kininogen, a cystatin-like molecule, inhibits ERK-dependent lymphocyte proliferation

Plasma levels of kininogens increase with age in both rats and humans. Kininogens are inhibitors of cysteine proteinases, and filarial cysteine proteinase inhibitors (cystatins) reduce the proliferation of T cells. We evaluated whether T-kininogen (T-KG) might mimic this effect, and here we present data indicating that exposure of either rat splenocytes or Jurkat cells to purified T-KG results in inhibition of both ERK activation and [(3)H]-thymidine incorporation, both basal and in response to ConA or PHA. Interestingly, T-KG did not impair [(3)H]-thymidine incorporation in response to IL-2, which requires primarily the activation of the JNK and Jak/STAT pathways. These effects were neither the consequence of increased cell death, nor required the activity of kinin receptors. Furthermore, when T cell receptor proximal events were bypassed by the use of PMA plus Calcium ionophore, T-KG no longer inhibited ERK activation, suggesting that inhibition occurs upstream of these events, possibly at the level of membrane associated signal transduction molecules. We conclude that, like filarial cystatins, T-KG inhibits ERK-dependent T cell proliferation, and these observations suggest a possible role for T-KG in immunosenescence.

Discovery of genetic difference between asthmatic children with high IgE level and normal IgE level by whole genome linkage disequilibrium mapping using 763 autosomal STR markers

The genome-wide linkage disequilibrium screen for loci associated with genetic difference between allergic and nonallergic asthma was conducted with 763 autosomal STR markers and included 190 asthmatic children. Evidence for association with differences between the two forms of asthma was observed for 36 STR markers. Marker-to-marker synergetic effect and by simulation resampling tests revealed D5S2011, D6S305, and D9S286 were important loci in allergic asthma while D6S1574, D8S1769, and D19S226 were important in nonallergic asthma. Our results show strong genetic evidence that these markers play an important role in defining allergic and nonallergic asthma and provides important candidates of susceptible genes in these two categories of asthma. This study further shows that asthma is, indeed, a heterogeneous group of underlying diseases and, although with similar clinical phenotypes, may have different clinical severities, outcomes, and need more tailor-made management.