Glucocorticoid-mediated regulation of granulocyte apoptosis and macrophage phagocytosis of apoptotic cells: implications for the resolution of inflammation

Glucocorticoids represent one of the most effective clinical treatments for a range of inflammatory conditions, including severe acute inflammation. Although glucocorticoids are known to affect processes involved in the initiation of inflammation, the influence of glucocorticoids on the mechanisms by which acute inflammation normally resolves have received less attention. Apoptosis of granulocytes present at inflamed sites leads to their rapid recognition and internalisation by macrophages, a process which may be important for resolution of inflammation. However, if clearance of either eosinophils or neutrophils is impaired, these cells rapidly undergo secondary necrosis leading to release of pro-inflammatory mediators from the phagocyte, potentially prolonging inflammatory responses. Physiologically relevant concentrations of glucocorticoids accelerate eosinophil apoptosis whilst delaying neutrophil apoptosis during in vitro culture. Here we discuss key pathways regulating the granulocyte apoptotic programme and summarise the effects of glucocorticoids on monocyte differentiation and the consequent changes to apoptotic cell clearance capacity. Definition of the mechanisms underlying resolution of inflammatory responses following glucocorticoid treatment may unveil new targets for modulation of inflammatory disease, allowing co-ordinated augmentation of granulocyte apoptosis together with increased macrophage capacity for clearance of apoptotic cells.

Glucocorticoid augmentation of macrophage capacity for phagocytosis of apoptotic cells is associated with reduced p130Cas expression, loss of paxillin/pyk2 phosphorylation, and high levels of active Rac

Phagocytic clearance of apoptotic granulocytes has a pivotal role in determining an inflammatory outcome, resolution or progression to a chronic state associated with development of fibrotic repair mechanisms, and/or autoimmune responses. In this study, we describe reprogramming of monocyte to macrophage differentiation by glucocorticoids, resulting in a marked augmentation of their capacity for phagocytosis of apoptotic neutrophils. This monocyte/macrophage phenotype was characterized by decreased phosphorylation, and therefore recruitment of paxillin and pyk2 to focal contacts and a down-regulation of p130Cas, a key adaptor molecule in integrin adhesion signaling. Glucocorticoid-treated cells also displayed higher levels of active Rac and cytoskeletal activity, which were mirrored by increases in phagocytic capability for apoptotic neutrophils. We propose that changes in the capacity for reorganization of cytoskeletal elements induced by glucocorticoids are essential for efficient phagocytic uptake of apoptotic cells.

Duplication and polymorphism in the MHC: Alu generated diversity and polymorphism within the PERB11 gene family

The PERB11 gene family has at least five members within the telomeric region of the MHC. The PERB11.1 and PERB11.2 genes are approximately 40 kb and 160 kb centromeric of HLA-B, respectively. Using continuous genomic sequence encompassing PERB11.1 and PERB11.2, we have found a large (approximately 25 kb) segmental duplication extending beyond the genes themselves and other potential coding sequences. The major difference between the segments are large indels which are predominantly Alu sequences. The Alu sequences within the duplicated segments have created diversity via the internal and 3' poly A-rich region. A sequence comparison of an Alu sequence between two different human ancestral haplotypes shows a high level of polymorphism, particularly in the poly A-rich regions. This study characterises the Alu sequences within the peri-PERB11.1 and peri-PERB11.2 duplicated segments in relation to diversity and polymorphism and as evolutionary markers.

Halogenated 4-(phenoxymethyl)piperidines as potential radiolabeled probes for sigma-1 receptors: in vivo evaluation of [123I]-1-(iodopropen-2-yl)-4-[(4-cyanophenoxy)methyl]pip eri dine

Several halogenated 4-(4-phenoxymethyl)piperidines were synthesized as potential sigma receptor ligands. The affinity and selectivity of these compounds were determined using in vitro receptor binding assays, and their log P values were estimated using HPLC analysis. The effect of various N-substituents on the sigma-1 and sigma-2 dissociation constants was examined. These substituents included fluoroalkyl, hydroxyalkyl, iodopropenyl, and selected ortho-, meta-, and para-substituted benzyl groups. Also determined were the effects of various moieties on the phenoxy ring; specifically 4-iodo, 4-bromo, 4-nitro, 4-cyano, 3-bromo, and pentafluoro substituents were examined. The ranges in the dissociation constants of these compounds for sigma-1 and sigma-2 receptors were 0.38-24.3 and 3.9-361 nM, respectively. The ratio of Ki (sigma-2/sigma-1) ranged from 1.19 to 121. One of the most promising of the iodinated ligands, 1-(trans-iodopropen-2-yl)-4-[(4-cyanophenoxy)methyl]piperidi ne (4), was labeled with 123I and studied in vivo in adult male rats. High uptake and good retention of radioactivity was observed in the brain and many other organs known to possess sigma receptors. Blocking studies revealed high specific binding of [123I]-4 to sigma receptors in the brain, lung, kidney, heart, muscle, and other organs known to possess these sites. These results indicate that [123I]-4 and other halogenated 4-(phenoxymethyl)piperidines of this series may provide useful probes for in vivo tomographic studies of sigma receptors.

A death-domain-containing receptor that mediates apoptosis

The cell-killing effects of the cytokines TNF-alpha and FasL are mediated by the distinct cell-surface receptors TNFR1, TNFR2 and Fas (also known as CD95/APO-1), which are all members of a receptor superfamily that is important for regulating cell survival. The cytoplasmic regions of TNFR1 and Fas contain a conserved 'death' domain which is an essential component of the signal pathway that triggers apoptosis and activation of the transcription factor NF-kappaB (refs 5,6). Here we report the isolation of a 54K receptor that is a new member of the TNFR superfamily, using the death domain of TNFR1 in a yeast two-hybrid system. This protein, WSL-1, is most similar to TNFR1 itself, particularly in the death-domain region. The gene wsl-1 is capable of inducing apoptosis when transfected into 3T3 and 293 cells, and can also activate NF-kappaB in 293 cells. Like TNFR1, WSL-1 will homodimerize in yeast. WSL-1 also interacts specifically with the TNFR1-associated molecule TRADD. The tissue distribution is very restricted and significantly different from that of Fas and TNFR1.