Regulation of Granulocyte Apoptosis by Hemopoietic Growth Factors, Cytokines and Drugs: Potential Relevance to Allergic Inflammation

Models for the Study of the Cross Talk Between Inflammation and Cell Cycle

Cyclin-dependent kinases (CDKs) have been traditionally associated with the cell cycle. However, it is now known that CDK7 and CDK9 regulate transcriptional activity via phosphorylation of RNA polymerase II and subsequent synthesis of, for example, inflammatory mediators and factors that influence the apoptotic process; including apoptosis of granulocytes such as neutrophils and eosinophils. Successful resolution of inflammation and restoration of normal tissue homeostasis requires apoptosis of these inflammatory cells and subsequent clearance of apoptotic bodies by phagocytes such as macrophages. It is believed that CDK7 and CDK9 influence resolution of inflammation since they are involved in the transcription of anti-apoptotic proteins such as Mcl-1 which is especially important in granulocyte survival.This chapter describes various in vitro and in vivo models used to investigate CDKs and their inhibitors in granulocytes and particularly the role of CDKs in the apoptosis pathway. This can be performed in vitro by isolation and use of primary granulocytes and in vivo using animal models of inflammatory disease in rodents and zebrafish. Some of the methods described here to assess the role of CDKs in inflammation and apoptosis include flow cytometry and western blotting, together with imaging and quantification of apoptosis in fixed tissue, as well as in vivo models of inflammation.

Oxidative stress and macrophage function: a failure to resolve the inflammatory response

The suppression of pro-inflammatory gene expression along with the clearance of apoptotic cells by phagocytosis can play an important role in resolving the inflammatory response. Any impairment of these processes can therefore lead to a chronic inflammatory state. Oxidative stress can have both direct and indirect effects on macrophage function. This mini-review highlights a mechanism through which oxidative stress via the production of reactive carbonyls alters the ECM (extracellular matrix) environment of macrophages, thereby altering their behaviour. Carbonyl modification of ECM proteins causes increased macrophage adhesion and activation through receptors that are also involved in phagocytosis. Moreover, interaction of macrophages with these carbonyl-modified ECM proteins leads to decreased phagocytic activity towards apoptotic cells. At a more direct level, both oxidative and carbonyl stress inhibits activity of the transcriptional co-repressor HDAC-2 (histone deacetylase 2), which under normoxic conditions helps to suppress pro-inflammatory gene expression. Consequently, macrophages activated under conditions of oxidative or carbonyl stress can lead to a more enhanced inflammatory response. Coupled with an impairment of the phagocytic response, this can lead to ineffective clearance of apoptotic cells and secondary necrosis, with the result being failure to resolve the inflammatory response and the establishment of a chronic inflammatory state.

Antieosinophilic activity of simendans

Simendans are novel agents used in the treatment of decompensated heart failure. They sensitize troponin C to calcium and open ATP-sensitive potassium channels and have been shown to reduce cardiac myocyte apoptosis. The aim of the present study was to evaluate whether simendans reduce pulmonary eosinophilia and regulate eosinophil apoptosis. Bronchoalveolar lavage (BAL) eosinophilia was evaluated in ovalbumin-sensitized mice. Effects of simendans on apoptosis in isolated human eosinophils were assessed by relative DNA fragmentation assay, annexin V-binding, and morphological analysis. Dextrosimendan [(+)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl)hydrazono]propanedinitrile] reduced ovalbumin-induced BAL-eosinophilia in sensitized mice. Levosimendan [(-)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]hydrazono]propanedinitrile] and dextrosimendan reversed interleukin (IL)-5-afforded survival of human eosinophils by inducing apoptosis in vitro. Even high concentrations of IL-5 were not able to overcome the effect of dextrosimendan. Dextrosimendan further enhanced spontaneous apoptosis as well as that induced by CD95 ligation, without inducing primary necrosis. Dextrosimendan-induced DNA fragmentation was shown to be dependent on caspase and c-Jun NH2-terminal kinase activation, whereas extracellular signal-regulated kinase, p38 mitogen-activated kinase, and ATP-sensitive potassium channels seemed to play no role in its actions. Taken together, our results show that simendans possess antieosinophilic activity and may be useful for the treatment of eosinophilic inflammation.

The glucocorticoid RU24858 does not distinguish between transrepression and transactivation in primary human eosinophils

Background

Glucocorticoids are used to treat chronic inflammatory diseases such as asthma. Induction of eosinophil apoptosis is considered to be one of the main mechanisms behind the anti-asthmatic effect of glucocorticoids. Glucocorticoid binding to its receptor (GR) can have a dual effect on gene transcription. Activated GR can activate transcription (transactivation), or by interacting with other transcription factors such as NF-κB suppress transcription (transrepression). RU24858 has been reported to transrepress but to have little or no transactivation capability in other cell types. The dissociated properties of RU24858 have not been previously studied in non-malignant human cells. As the eosinophils have a very short lifetime and many of the modern molecular biological methods cannot be used, a "dissociated steroid" would be a valuable tool to evaluate the mechanism of action of glucocorticoids in human eosinophils. The aim of this study was to elucidate the ability of RU24858 to activate and repress gene expression in human eosinophils in order to see whether it is a dissociated steroid in human eosinophils.

Methods

Human peripheral blood eosinophils were isolated under sterile conditions and cultured in the presence and/or absence RU24858. For comparison, dexamethasone and mometasone were used. We measured chemokine receptor-4 (CXCR4) and Annexin 1 expression by flow cytometry and cytokine production by ELISA. Apoptosis was measured by DNA fragmentation and confirmed by morphological analysis.

Results

RU24858 (1 μM) increased CXCR4 and Annexin 1 expression on eosinophils to a similar extent as mometasone (1 μM) and dexamethasone (1 μM). Like dexamethasone and mometasone, RU24858 did suppress IL-8 and MCP-1 production in eosinophils. RU24858 also increased spontaneous eosinophil apoptosis to a similar degree as dexamethasone and mometasone, but unlike dexamethasone and mometasone it did not reverse IL-5- or GM-CSF-induced eosinophil survival.

Conclusion

Our results suggest that in human eosinophils RU24858 acts as transactivator and transrepressor like classical glucocorticoids. Thus, RU24858 seems not to be a "dissociated steroid" in primary human eosinophils in contrast to that reported in animal cells. In addition, functionally RU24858 seems to be a less potent glucocorticoid as it did not reverse IL-5- and GM-CSF-afforded eosinophil survival similarly to dexamethasone and mometasone.

c-Jun N-terminal kinase mediates constitutive human eosinophil apoptosis

Eosinophils are considered to play an important role in the pathogenesis of asthma. Glucocorticoids are potent anti-inflammatory agents for the treatment of chronic inflammatory diseases and they have been shown to increase the rate of eosinophil apoptosis. c-Jun N-terminal kinase (JNK) has been suggested to participate in the signaling pathways of apoptosis. The aims of the present study were to examine whether JNK is involved in the regulation of constitutive eosinophil apoptosis and whether it mediates dexamethasone-induced apoptosis of human eosinophils. Isolated human eosinophils were cultured with and without dexamethasone and the JNK inhibitor L-JNKI-1. Apoptosis was assessed by measuring the relative DNA content of propidium iodide-stained cells and confirmed by Annexin V-binding and morphological analysis with bright field microscopy. The phosphorylation of both JNK and c-Jun were measured by Western blotting. During a 40h culture, dexamethasone (1muM) enhanced human eosinophil apoptosis by 10-30%. Culture with L-JNKI1 (10muM) inhibited apoptosis in dexamethasone-treated cells by 53%. Furthermore, L-JNKI1 decreased the rate of constitutive eosinophil apoptosis by 64%. However, the enhancement of eosinophil apoptosis by dexamethasone was not reversed by L-JNKI1. Slow activation of JNK in constitutive apoptosis as well as a similar tendency in dexamethasone-induced eosinophil apoptosis could be observed by Western blot analyses. c-Jun was found to be active both in the presence and absence of dexamethasone. However, no further phosphorylation of the serine residue 63 of c-Jun could be seen. Taken together, our present results suggest that JNK is active during apoptosis of human eosinophils both in the presence and absence of glucocorticoids. JNK seems to mediate constitutive human eosinophil apoptosis. However, the activity of JNK is not enhanced by glucocorticoids and the effects of glucocorticoids cannot be reversed by JNK inhibition. JNK therefore seems not to mediate glucocorticoid-induced human eosinophil apoptosis.

Antieosinophilic activity of orazipone

Orazipone is a novel sulfhydryl-reactive compound that has been previously shown to reduce lung eosinophilia in guinea pigs and rats and to inhibit degranulation in mast cells and cytokine production in monocytes and T-cells. However, the effects of orazipone on granulocyte longevity are unknown. Orazipone and its derivative 3-(4-chloro-3-nitro-benzylidene)-pentane-2,4-dione (OR-2370) reversed interleukin-5-afforded survival of human eosinophils by inducing apoptosis. In contrast, orazipone did not affect granulocyte macrophage-colony-stimulating factor-induced survival of human neutrophils. The effect of orazipone on eosinophil apoptosis is different from that of glucocorticoids in that even high con-centrations of interleukin-5 were not able to overcome the effect of orazipone. Orazipone further enhanced spontaneous apoptosis as well as that induced by CD95 ligation without inducing primary necrosis. OR-2370-induced DNA fragmentation was shown to be dependent on caspases 3 and 6 and c-jun-N-terminal kinase, whereas extracellular regulated kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol 3-kinase as well as caspases 4, 8, and 9 seem not to mediate its actions. Our results suggest that orazipone and its derivative OR-2370 possess strong antieosinophilic activity and thus may have anti-inflammatory efficacy in the treatment of asthma and/or allergic conditions.

Hematopoiesis and stem cell renewal in long-term bone marrow cultures containing catalase

Culturing mouse bone marrow in the presence of catalase dramatically alters hematopoiesis. Granulocyte output is initially increased 4- to 5-fold. This increase is transient and granulocyte production declines as immature (Sca-1+/LIN-) cells accumulate. One third of these immature cells have a phenotype (Sca-1+/c-Kit+) characteristic of hematopoietic stem cells. At 2 to 3 weeks there are greater than 200-fold more Sca-1+/c-Kit+/LIN- cells in treated cultures than in controls. This population contains functional stem cells with both short-term and long-term bone marrow repopulating activity. In addition to myeloid progenitors, this Sca-1+/LIN- population contains a large number of cells that express CD31 and CD34 and have an active Tie-2 promoter, indicating that they are in the endothelial lineage. After 3 to 4 weeks hematopoiesis in treated cultures wanes but if catalase is removed, hematopoiesis resumes. After 7 to 10 days the cultures are indistinguishable from untreated controls. Thus, protected from H2O2, hematopoietic progenitors multiply and become quiescent. This sequence resembles in vivo development in normal marrow. These results make it clear that peroxide-sensitive regulatory mechanisms play an important role in controlling hematopoiesis ex vivo and presumably in vivo as well. They also indicate that manipulation of the peroxide levels can be used to enhance the growth of hematopoietic stem cells in culture.

Macrophage phagocytosis of apoptotic neutrophils is compromised by matrix proteins modified by cigarette smoke and lipid peroxidation products

Clearance of apoptotic cells by phagocytosis plays an important role in the resolution of an inflammatory response. Macrophages interacting with extracellular matrix (ECM) proteins upregulate their phagocytic capacity. Cigarette smoke contains highly reactive carbonyls that modify proteins which directly/indirectly affects cellular function. We observed, in vitro, that human macrophages interacting with carbonyl or cigarette smoke modified ECM proteins dramatically down regulated their ability to phagocytose apoptotic neutrophils. We also show that this interaction with carbonyl-adduct modified ECM proteins led to increased macrophage adhesion in vitro. We hypothesise that changes in the ECM environment as a result of cigarette smoking affect the ability of macrophages to remove apoptotic cells. Moreover, we postulate that this decreased phagocytic activity was as a result of sequestration of receptors involved in the uptake of apoptotic cells towards that of recognition of carbonyl adducts on the modified ECM proteins leading to increased macrophage adhesion.