Receptor-independent, direct membrane binding leads to cell-surface lipid sorting and Syk kinase activation in dendritic cells.

Binding of particulate antigens by antigen-presenting cells is a critical step in immune activation. Previously, we demonstrated that uric acid crystals are potent adjuvants, initiating a robust adaptive immune response. However, the mechanisms of activation are unknown. By using atomic force microscopy as a tool for real-time single-cell activation analysis, we report that uric acid crystals could directly engage cellular membranes, particularly the cholesterol components, with a force substantially stronger than protein-based cellular contacts. Binding of particulate substances activated Syk kinase-dependent signaling in dendritic cells. These observations suggest a mechanism whereby immune cell activation can be triggered by solid structures via membrane lipid alteration without the requirement for specific cell-surface receptors, and a testable hypothesis for crystal-associated arthropathies, inflammation, and adjuvanticity.

Disrupted organization of RFamide pathways in the hypothalamus is associated with advanced puberty in female rats neonatally exposed to bisphenol A.

Hypothalamic neurons, which produce the kisspeptin family of peptide hormones (Kp), are critical for initiating puberty and maintaining estrous cyclicity by stimulating gonadotropin-releasing hormone (GnRH) release. Conversely, RFamide-related peptide-3 (RFRP3) neurons inhibit GnRH activity. It has previously been shown that neonatal exposure to bisphenol A (BPA) can alter the timing of female pubertal onset and induce irregular estrous cycles or premature anestrus. Here we tested the hypothesis that disrupted ontogeny of RFamide signaling pathways may be a mechanism underlying advanced puberty. To test this, we used a transgenic strain of Wistar rats whose GnRH neurons express enhanced green fluorescent protein. Pups were exposed by daily subcutaneous injection to vehicle, 17beta-estradiol (E2), 50 µg/kg BPA, or 50 mg/kg BPA, from Postnatal Day (PND) 0 through PND 3, and then cohorts were euthanized on PNDs 17, 21, 24, 28, and 33 (5-8 animals per age per exposure; males were collected on PNDs 21 and 33). Vaginal opening was advanced by E2 and 50 µg/kg BPA. On PND 28, females exposed to E2 and 50 µg/kg BPA had decreased RFRP-3 fiber density and contacts on GnRH neurons. RFRP3 perikarya were also decreased in females exposed to 50 µg/kg BPA. Data suggest that BPA-induced premature puberty results from decreased inhibition of GnRH neurons.

Age and dose sensitivities in the 2-butoxyethanol F344 rat model of hemolytic anemia and disseminated thrombosis.

In hemolytic disorders, such as sickle cell disease and beta-thalassemia, the mechanisms of thrombosis are poorly understood. Appropriate animal models would increase the understanding of the pathophysiology of thrombosis. We previously reported that rats exposed to 2-butoxyethanol (2-BE) developed hemolytic anemia and disseminated thrombosis resembling sickle cell disease and beta-thalassemia. To characterize our model further, we investigated age- and dose-related differences in sensitivity to 2-BE. We exposed groups of 6- and 12-week-old F344 rats (5 animals/group) to 62.5, 125, and 250 mg/kg/day of 2-BE for up to 4 days. Blood was collected on days 2-4 for complete blood count and measurement of intracellular adhesion molecule-1 (ICAM-1). Histopathological evaluation was performed to find evidence of disseminated thrombosis. The maximum hemolytic response, resulting in decreased erythrocyte count and higher mean cell volume (MCV) occurred in the 12-week-old rats treated with the highest dose of 2-BE (250 mg/kg, p<0.0001). The highest increase in ICAM-1 levels occurred in the 12-week-old rats treated with 125 and 250 mg/kg 2-BE (p<0.0001). No intravascular thrombi were noted in the 6-week-old 2-BE-treated animals. The majority of intravascular thrombi occurred in the 12-week-old rats treated with 250 mg/kg 2-BE. Because our findings show age- and dose-related sensitivities, we suggest that 12-week-old rats and doses of 250 mg/kg be used in the 2-BE model.

Hemostatic activation in a chemically induced rat model of severe hemolysis and thrombosis.

INTRODUCTION: In hemolytic diseases such as sickle cell disease and beta-thalassemia, the mechanisms of thrombosis are poorly understood, however erythrocyte/endothelium interactions are thought to play an important role. Appropriate animal models would increase our understanding of the pathophysiology of thrombosis and aid in the development of new therapeutic strategies. We previously reported that rats exposed to 2-butoxyethanol (2-BE) develop hemolysis and enhanced adherence of erythrocytes to the extracellular matrix, possibly secondary to the recruitment of cellular adhesion molecules at the erythrocyte/endothelium interface. METHODS: We exposed rats to 250 mg/kg/day of 2-BE for 4 days, and collected blood for coagulation markers on each day. RESULTS: As previously observed, erythrocytes dropped precipitously (8.0 to 1.8x10(6)/microl in 48 h), and diffuse microvascular thrombosis developed in the heart, lungs, liver, bones and eyes. Prothrombin times, activated partial thromboplastin times, fibrinogen, and antithrombin-III were unchanged between treated and control rats, indicating that hemostasis is largely unperturbed. However the thrombin-antithrombin III levels in the 2-BE treated rats for all days were 3-7 times greater than the control rats. The plasma intercellular adhesion molecule-1 (ICAM-1) levels of 2-BE treated animals were approximately twice that of the controls on days 2 and 3 and 1.5 times the controls on day 4 (P<0.05). CONCLUSION: Our findings are consistent with the observations of increased erythrocyte aggregation, increased erythrocyte/endothelium interaction, and increased plasma ICAM-1 levels observed in sickle cell disease and beta-thalassemia patients. This model may be useful for studying therapeutic agents that disrupt erythrocyte/endothelium interactions.

Differential gene expression profiling in whole blood during acute systemic inflammation in lipopolysaccharide-treated rats.

Microarrays have been used to evaluate the expression of thousands of genes in various tissues. However, few studies have investigated the change in gene expression profiles in one of the most easily accessible tissues, whole blood. We utilized an acute inflammation model to investigate the possibility of using a cDNA microarray to measure the gene expression profile in the cells of whole blood. Blood was collected from male Sprague-Dawley rats at 2 and 6 h after treatment with 5 mg/kg (ip) LPS. Hematology showed marked neutrophilia accompanied by lymphopenia at both time points. TNF-alpha and IL-6 levels were markedly elevated at 2 h, indicating acute inflammation, but by 6 h the levels had declined. Total RNA was isolated from whole blood and hybridized to the National Institute of Environmental Health Sciences Rat Chip v.3.0. LPS treatment caused 226 and 180 genes to be differentially expressed at 2 and 6 h, respectively. Many of the differentially expressed genes are involved in inflammation and the acute phase response, but differential expression was also noted in genes involved in the cytoskeleton, cell adhesion, oxidative respiration, and transcription. Real-time RT-PCR confirmed the differential regulation of a representative subset of genes. Principal component analysis of gene expression discriminated between the acute inflammatory response apparent at 2 h and the observed recovery underway at 6 h. These studies indicate that, in whole blood, changes in gene expression profiles can be detected that are reflective of inflammation, despite the adaptive shifts in leukocyte populations that accompany such inflammatory processes.

Influence of ERß selective agonism during the neonatal period on the sexual differentiation of the rat hypothalamic-pituitary-gonadal (HPG) axis.

BACKGROUND: It is well established that sexual differentiation of the rodent hypothalamic-pituitary-gonadal (HPG) axis is principally orchestrated by estrogen during the perinatal period. Here we sought to better characterize the mechanistic role the beta form of the estrogen receptor (ERß) plays in this process. METHODS: To achieve this, we exposed neonatal female rats to three doses (0.5, 1 and 2 mg/kg) of the ERß selective agonist diarylpropionitrile (DPN) using estradiol benzoate (EB) as a positive control. Measures included day of vaginal opening, estrous cycle quality, GnRH and Fos co-localization following ovariectomy and hormone priming, circulating luteinizing hormone (LH) levels and quantification of hypothalamic kisspeptin immunoreactivity. A second set of females was then neonatally exposed to DPN, the ERα agonist propyl-pyrazole-triol (PPT), DPN+PPT, or EB to compare the impact of ERα and ERß selective agonism on kisspeptin gene expression in pre- and post-pubescent females. RESULTS: All three DPN doses significantly advanced the day of vaginal opening and induced premature anestrus. GnRH and Fos co-labeling, a marker of GnRH activation, following ovariectomy and hormone priming was reduced by approximately half at all doses; the magnitude of which was not as large as with EB or what we have previously observed with the ERα agonist PPT. LH levels were also correspondingly lower, compared to control females. No impact of DPN was observed on the density of kisspeptin immunoreactive (-ir) fibers or cell bodies in the arcuate (ARC) nucleus, and kisspeptin-ir was only significantly reduced by the middle (1 mg/kg) DPN dose in the preoptic region. The second experiment revealed that EB, PPT and the combination of DPN+PPT significantly abrogated preoptic Kiss1 expression at both ages but ARC expression was only reduced by EB. CONCLUSION: Our results indicate that selective agonism of ERß is not sufficient to completely achieve male-typical HPG organization observed with EB or an ERα agonist.

Alum interaction with dendritic cell membrane lipids is essential for its adjuvanticity.

As an approved vaccine adjuvant for use in humans, alum has vast health implications, but, as it is a crystal, questions remain regarding its mechanism. Furthermore, little is known about the target cells, receptors, and signaling pathways engaged by alum. Here we report that, independent of inflammasome and membrane proteins, alum binds dendritic cell (DC) plasma membrane lipids with substantial force. Subsequent lipid sorting activates an abortive phagocytic response that leads to antigen uptake. Such activated DCs, without further association with alum, show high affinity and stable binding with CD4(+) T cells via the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1). We propose that alum triggers DC responses by altering membrane lipid structures. This study therefore suggests an unexpected mechanism for how this crystalline structure interacts with the immune system and how the DC plasma membrane may behave as a general sensor for solid structures.

Gene expression response in target organ and whole blood varies as a function of target organ injury phenotype.

This report details the standardized experimental design and the different data streams that were collected (histopathology, clinical chemistry, hematology and gene expression from the target tissue (liver) and a bio-available tissue (blood)) after treatment with eight known hepatotoxicants (at multiple time points and doses with multiple biological replicates). The results of the study demonstrate the classification of histopathological differences, likely reflecting differences in mechanisms of cell-specific toxicity, using either liver tissue or blood transcriptomic data.