Hemolysis in the spleen drives erythrocyte turnover.

Red pulp macrophages (RPMs) of the spleen mediate turnover of billions of senescent erythrocytes per day. However, the molecular mechanisms involved in sequestration of senescent erythrocytes, their recognition, and their subsequent degradation by RPMs remain unclear. In this study, we provide evidence that the splenic environment is of substantial importance in facilitating erythrocyte turnover through induction of hemolysis. Upon isolating human spleen RPMs, we noted a substantial lack of macrophages that were in the process of phagocytosing intact erythrocytes. Detailed characterization of erythrocyte and macrophage subpopulations from human spleen tissue led to the identification of erythrocytes that are devoid of hemoglobin, so-called erythrocyte ghosts. By using in vivo imaging and transfusion experiments, we further confirmed that senescent erythrocytes that are retained in the spleen are subject to hemolysis. In addition, we showed that erythrocyte adhesion molecules, which are specifically activated on aged erythrocytes, cause senescent erythrocytes to interact with extracellular matrix proteins that are exposed within the splenic architecture. Such adhesion molecule-driven retention of senescent erythrocytes under low shear conditions was found to result in steady shrinkage of the cell and ultimately resulted in hemolysis. In contrast to intact senescent erythrocytes, the remnant erythrocyte ghost shells were prone to recognition and breakdown by RPMs. These data identify hemolysis as a key event in the turnover of senescent erythrocytes, which alters our current understanding of how erythrocyte degradation is regulated.

Developmental toxicity and endocrine disrupting potency of 4-azapyrene, benzo[b]fluorene and retene in the zebrafish Danio rerio.

This study examined the developmental toxicity of the polycyclic aromatic hydrocarbons (PAHs) 11H-benzo(b)fluorene (BBF) and 4-azapyrene (AP) in comparison to the known teratogen retene. Developmental toxicity assays were performed in zebrafish embryos exposed for 120 h. BBF and retene induced a similar dioxin-like phenotype, whereas AP showed distinct effects, particularly craniofacial malformations. Microarray analysis revealed that for BBF and retene, drug metabolism pathways were induced, which were confirmed by subsequent studies of cyp1a gene expression. For AP, microarray analysis revealed the regulation of genes involved in retinoid metabolism and hematological functions. Studies with a panel of CALUX(®) bioassays to screen for endocrine disrupting activity of the compounds also revealed novel antagonistic effects of BBF and retene on androgen and progesterone receptors. Classification analysis revealed distinct gene expression profiles for both individual and combined PAH exposure. This study highlights the potential health risk of non priority PAHs.

Gene expression microarray analysis of heat stress in the soil invertebrate Folsomia candida.

Sudden temperature changes in soil can induce stress in soil-dwelling invertebrates. Hyperthermic conditions have an impact on gene expression as one of the first steps. We use a transcriptomics approach using microarrays to identify expression changes in response to heat in the springtail Folsomia candida. An elevation of temperature (Delta 10 degrees C) altered the expression of 142 genes (116 up-, 26 down-regulated). Many up-regulated genes encoded heat shock proteins, enzymes involved in ATP synthesis, oxidative stress responsive enzymes and anion-transporting ATPases. Down-regulated were glycoside hydrolases, involved in catalysis of disaccharides. The small number of altered transcripts suggest a mild response to heat in this soil invertebrate, but further research is needed to confirm this. This study presents candidate genes for future functional studies concerning thermal stress in soil-dwelling invertebrates.

Sugar sweet springtails: on the transcriptional response of Folsomia candida (Collembola) to desiccation stress.

Several species of Collembola survive stressful desiccating conditions by absorbing water vapour from the environment. To obtain insight into the transcriptomic responses underlying this 'water vapour absorption' mechanism we subjected Folsomia candida (Collembola) to transcriptome profiling. We show that ecologically relevant desiccation stress leads to strong time-dependent transcriptomic changes. Exposure of F. candida to 98.2% relative humidity over an interval of 174 h resulted in a high number of gene transcripts being differentially expressed (up to 41%; P-value < 0.05). Additional Gene Ontology analyses suggest that carbohydrate transport, sugar catabolism and cuticle maintenance are biological processes involved in combating desiccation. However, many additional pathways seem to be affected; additional experiments are needed to elucidate which responses are primarily linked to desiccation resistance.

Profiling of apoptosis genes allows for clinical stratification of primary nodal diffuse large B-cell lymphomas.

Intrinsic resistance of lymphoma cells to apoptosis is a probable mechanism causing chemotherapy resistance and eventual fatal outcome in patients with diffuse large B cell lymphomas (DLBCL). We investigated whether microarray expression profiling of apoptosis related genes predicts clinical outcome in 46 patients with primary nodal DLBCL. Unsupervised cluster analysis using genes involved in apoptosis (n = 246) resulted in three separate DLBCL groups partly overlapping with germinal centre B-lymphocytes versus activated B-cells like phenotype. One group with poor clinical outcome was characterised by high expression levels of pro-and anti-apoptotic genes involved in the intrinsic apoptosis pathway. A second group, also with poor clinical outcome, was characterised by high levels of apoptosis inducing cytotoxic effector genes, possibly reflecting a cellular cytotoxic immune response. The third group showing a favourable outcome was characterised by low expression levels of genes characteristic for both other groups. Our results suggest that chemotherapy refractory DLBCL are characterised either by an intense cellular cytotoxic immune response or by constitutive activation of the intrinsic mediated apoptosis pathway with concomitant downstream inhibition of this apoptosis pathway. Consequently, strategies neutralising the function of apoptosis-inhibiting proteins might be effective as alternative treatment modality in part of chemotherapy refractory DLBCL.