The probable cell of origin of NF1- and PDGF-driven glioblastomas

Primary glioblastomas are subdivided into several molecular subtypes. There is an ongoing debate over the cell of origin for these tumor types where some suggest a progenitor while others argue for a stem cell origin. Even within the same molecular subgroup, and using lineage tracing in mouse models, different groups have reached different conclusions. We addressed this problem from a combined mathematical modeling and experimental standpoint. We designed a novel mathematical framework to identify the most likely cells of origin of two glioma subtypes. Our mathematical model of the unperturbed in vivo system predicts that if a genetic event contributing to tumor initiation imparts symmetric self-renewing cell division (such as PDGF overexpression), then the cell of origin is a transit amplifier. Otherwise, the initiating mutations arise in stem cells. The mathematical framework was validated with the RCAS/tv-a system of somatic gene transfer in mice. We demonstrated that PDGF-induced gliomas can be derived from GFAP-expressing cells of the subventricular zone or the cortex (reactive astrocytes), thus validating the predictions of our mathematical model. This interdisciplinary approach allowed us to determine the likelihood that individual cell types serve as the cells of origin of gliomas in an unperturbed system.     

Transcranial magnetic stimulation intensities in cognitive paradigms

Background

Transcranial magnetic stimulation (TMS) has become an important experimental tool for exploring the brain''s functional anatomy. As TMS interferes with neural activity, the hypothetical function of the stimulated area can thus be tested. One unresolved methodological issue in TMS experiments is the question of how to adequately calibrate stimulation intensities. The motor threshold (MT) is often taken as a reference for individually adapted stimulation intensities in TMS experiments, even if they do not involve the motor system. The aim of the present study was to evaluate whether it is reasonable to adjust stimulation intensities in each subject to the individual MT if prefrontal regions are stimulated prior to the performance of a cognitive paradigm.

Methods and Findings

Repetitive TMS (rTMS) was applied prior to a working memory task, either at the ‘fixed’ intensity of 40% maximum stimulator output (MSO), or individually adapted at 90% of the subject''s MT. Stimulation was applied to a target region in the left posterior middle frontal gyrus (pMFG), as indicated by a functional magnetic resonance imaging (fMRI) localizer acquired beforehand, or to a control site (vertex). Results show that MT predicted the effect size after stimulating subjects with the fixed intensity (i.e., subjects with a low MT showed a greater behavioral effect). Nevertheless, the individual adaptation of intensities did not lead to stable effects.

Conclusion

Therefore, we suggest assessing MT and account for it as a measure for general cortical TMS susceptibility, even if TMS is applied outside the motor domain.     

Immunodetection of disease-associated mutant PrP, which accelerates disease in GSS transgenic mice

The absence of infectivity-associated, protease-resistant prion protein (PrP^Sc) in the brains of spontaneously sick transgenic (Tg) mice overexpressing PrP linked to Gerstmann–Sträussler Scheinker syndrome, and the failure of gene-targeted mice expressing such PrP to develop disease spontaneously, challenged the concept that mutant PrP expression led to spontaneous prion production. Here, we demonstrate that disease in overexpressor Tg mice is associated with accumulation of protease-sensitive aggregates of mutant PrP that can be immunoprecipitated by the PrP^Sc-specific monoclonal antibody designated 15B3. Whereas Tg mice expressing multiple transgenes exhibited accelerated disease when inoculated with disease-associated mutant PrP, Tg mice expressing mutant PrP at low levels failed to develop disease either spontaneously or following inoculation. These studies indicate that inoculated mutant PrP from diseased mice promotes the aggregation and accumulation of pre-existing pathological forms of mutant PrP produced as a result of transgene overexpression. Thus, while pathological mutant PrP possesses a subset of PrP^Sc characteristics, we now show that the attribute of prion transmission suggested by previous studies is more accurately characterized as disease acceleration.     

Beta1 integrins regulate mammary gland proliferation and maintain the integrity of mammary alveoli

Integrin-extracellular matrix interactions play important roles in the coordinated integration of external and internal cues that are essential for proper development. To study the role of beta1 integrin in the mammary gland, Itgbeta1(flox/flox) mice were crossed with WAPiCre transgenic mice, which led to specific ablation of beta1 integrin in luminal alveolar epithelial cells. In the beta1 integrin mutant mammary gland, individual alveoli were disorganized resulting from alterations in cell-basement membrane associations. Activity of focal adhesion kinase (FAK) was also decreased in mutant mammary glands. Luminal cell proliferation was strongly inhibited in beta1 integrin mutant glands, which correlated with a specific increase of p21 Cip1 expression. In a p21 Cip1 null background, there was a partial rescue of BrdU incorporation, providing in vivo evidence linking p21 Cip1 to the proliferative defect observed in beta1 integrin mutant glands. A connection between p21 Cip1 and beta1 integrin as well as FAK was also established in primary mammary cells. These results point to the essential role of beta1 integrin signaling in mammary epithelial cell proliferation.     

Bcl-2 regulator FKBP38 is activated by Ca2+/calmodulin

FKBP-type peptidyl prolyl cis/trans isomerases (PPIases) are folding helper enzymes involved in the control of functional regrowth of damaged sciatic, cortical cholinergic, dopaminergic and 5-HT neurones. Here, we show that the constitutively inactive human FK506-binding protein 38 (FKBP38) is capable of responding directly to intracellular Ca2+ rise through formation of a heterodimeric Ca2+/calmodulin/FKBP38 complex. Only complex formation creates an enzymatically active FKBP, displaying affinity for Bcl-2 mediated through the PPIase site. Association between Bcl-2 and the active site of Ca2+/calmodulin/FKBP38 regulates Bcl-2 function and thereby participates in the promotion of apoptosis in neuronal tissues. FKBP38 proapoptotic function mediated by this interaction is abolished by either potent inhibitors of the PPIase activity of the Ca2+/calmodulin/FKBP38 complex or RNA interference-mediated depletion of FKBP38, promoting neuronal cell survival.     

Chromosomal instability and human cancer

Genetic instability is a defining feature of human cancer. The main type of genetic instability, chromosomal instability (CIN), enhances the rate of gross chromosomal changes during cell division. CIN is brought about by mutations of CIN genes, i.e. genes that are involved in maintaining the genomic integrity of the cell. A major question in cancer genetics is whether genetic instability is a cause and hence a driving force of tumorigenesis. A mathematical framework for studying the somatic evolution of cancer sheds light onto the causal relations between CIN and human cancer.     

Characterization of iron compounds in tumour tissue from temporal lobe epilepsy patients using low temperature magnetic methods

Excess iron accumulation in the brain has been shown to be related to a variety of neurodegenerative diseases. However, identification and characterization of iron compounds in human tissue is difficult because concentrations are very low. For the first time, a combination of low temperature magnetic methods was used to characterize iron compounds in tumour tissue from patients with mesial temporal lobe epilepsy (MTLE). Induced magnetization as a function of temperature was measured between 2 and 140 K after cooling in zero-field and after cooling in a 50 mT field. These curves reveal an average blocking temperature for ferritin of 10 K and an anomaly due to magnetite at 48 K. Hysteresis measurements at 5 K show a high coercivity phase that is unsaturated at 7 T, which is typical for ferritin. Magnetite concentration was determined from the saturation remanent magnetization at 77 K. Hysteresis measurements at various temperatures were used to examine the magnetic blocking of magnetite and ferritin. Our results demonstrate that low temperature magnetic measurements provide a useful and sensitive tool for the characterisation of magnetic iron compounds in human tissue.Published online: March 2005     

Androstadienone odor thresholds in adolescents

A sex-related difference in olfactory sensitivity to androstenone has been reported to occur during adolescence. More males than females exhibited anosmia to androstenone, or an increase in androstenone threshold with age. The current study addressed the question whether similar, sexually dimorphic effects of aging over puberty can also be found for androstadienone. A total of 102 subjects participated (36 females, 66 males). Similar to previous investigations, subjects were divided into a group of 47 individuals with a mean age of 13.3 years, defined as pre/peri-pubertal, and a group of 55 subjects with a mean age of 17.1 years, defined as post-pubertal. All subjects underwent tests for verbal abilities, general olfactory function, and measurements of androstadienone thresholds. The study provided the following major results: (1) Male subjects exhibited higher androstadienone sensitivity in the pre/peri-pubertal group as compared to the post-pubertal group. This difference was not observed in female subjects. Correspondingly, a negative correlation between age and androstadienone sensitivity was found for male subjects, but not for female subjects. (2) In contrast to this sex-specific change of the androstadienone odor threshold, verbal skills and odor identification abilities increased with age in all subjects regardless of their sex. In conclusion, the present observations confirm previous research on sex-differentiated effects of aging during puberty on sensitivity towards odorous steroids. While the underlying causes are unknown, it may be hypothesized that the decreased sensitivity could result from the increased endogenous levels of androstadienone in male subjects. Future studies should include both steroid and non-steroid odorants to further explore these age-related changes.     

Exoribonuclease R interacts with endoribonuclease E and an RNA helicase in the psychrotrophic bacterium Pseudomonas syringae Lz4W

Endoribonuclease E, a key enzyme involved in RNA decay and processing in bacteria, organizes a protein complex called degradosome. In Escherichia coli, Rhodobacter capsulatus, and Streptomyces coelicolor, RNase E interacts with the phosphate-dependent exoribonuclease polynucleotide phosphorylase, DEAD-box helicase(s), and additional factors in an RNA-degrading complex. To characterize the degradosome of the psychrotrophic bacterium Pseudomonas syringae Lz4W, RNase E was enriched by cation exchange chromatography and fractionation in a glycerol density gradient. Most surprisingly, the hydrolytic exoribonuclease RNase R was found to co-purify with RNase E. Co-immunoprecipitation and Ni(2+)-affinity pull-down experiments confirmed the specific interaction between RNase R and RNase E. Additionally, the DEAD-box helicase RhlE was identified as part of this protein complex. Fractions comprising the three proteins showed RNase E and RNase R activity and efficiently degraded a synthetic stem-loop containing RNA in the presence of ATP. The unexpected association of RNase R with RNase E and RhlE in an RNA-degrading complex indicates that the cold-adapted P. syringae has a degradosome of novel structure. The identification of RNase R instead of polynucleotide phosphorylase in this complex underlines the importance of the interaction between endo- and exoribonucleases for the bacterial RNA metabolism. The physical association of RNase E with an exoribonuclease and an RNA helicase apparently is a common theme in the composition of bacterial RNA-degrading complexes.     

CCL1-CCR8 interactions: an axis mediating the recruitment of T cells and Langerhans-type dendritic cells to sites of atopic skin inflammation

Atopic dermatitis represents a chronically relapsing skin disease with a steadily increasing prevalence of 10-20% in children. Skin-infiltrating T cells, dendritic cells (DC), and mast cells are thought to play a crucial role in its pathogenesis. We report that the expression of the CC chemokine CCL1 (I-309) is significantly and selectively up-regulated in atopic dermatitis in comparison to psoriasis, cutaneous lupus erythematosus, or normal skin. CCL1 serum levels of atopic dermatitis patients are significantly higher than levels in healthy individuals. DC, mast cells, and dermal endothelial cells are abundant sources of CCL1 during atopic skin inflammation and allergen challenge, and Staphylococcus aureus-derived products induce its production. In vitro, binding and cross-linking of IgE on mast cells resulted in a significant up-regulation of this inflammatory chemokine. Its specific receptor, CCR8, is expressed on a small subset of circulating T cells and is abundantly expressed on interstitial DC, Langerhans cells generated in vitro, and their monocytic precursors. Although DC maintain their CCR8+ status during maturation, brief activation of circulating T cells recruits CCR8 from intracytoplamic stores to the cell surface. Moreover, the inflammatory and atopy-associated chemokine CCL1 synergizes with the homeostatic chemokine CXCL12 (SDF-1alpha) resulting in the recruitment of T cell and Langerhans cell-like DC. Taken together, these findings suggest that the axis CCL1-CCR8 links adaptive and innate immune functions that play a role in the initiation and amplification of atopic skin inflammation.