Annette Persson

Caspase signalling controls microglia activation and neurotoxicity

Activation of microglia and inflammation-mediated neurotoxicity are suggested to play a decisive role in the pathogenesis of several neurodegenerative disorders. Activated microglia release pro-inflammatory factors that may be neurotoxic. Here we show that the orderly activation of caspase-8 and caspase-3/7, known executioners of apoptotic cell death, regulate microglia activation through a protein kinase C (PKC)-δ-dependent pathway. We find that stimulation of microglia with various inflammogens activates caspase-8 and caspase-3/7 in microglia without triggering cell death in vitro and in vivo. Knockdown or chemical inhibition of each of these caspases hindered microglia activation and consequently reduced neurotoxicity. We observe that these caspases are activated in microglia in the ventral mesencephalon of Parkinson’s disease (PD) and the frontal cortex of individuals with Alzheimer’s disease (AD). Taken together, we show that caspase-8 and caspase-3/7 are involved in regulating microglia activation. We conclude that inhibition of these caspases could be neuroprotective by targeting the microglia rather than the neurons themselves.

Glial Progenitor-Like Phenotype in Low-Grade Glioma and Enhanced CD133-Expression and Neuronal Lineage Differentiation Potential in High-Grade Glioma

Background While neurosphere- as well as xenograft tumor-initiating cells have been identified in gliomas, the resemblance between glioma cells and neural stem/progenitor cells as well as the prognostic value of stem/progenitor cell marker expression in glioma are poorly clarified. Methodology/Principal Findings Viable glioma cells were characterized for surface marker expression along the glial genesis hierarchy. Six low-grade and 17 high-grade glioma specimens were flow-cytometrically analyzed for markers characteristics of stem cells (CD133); glial progenitors (PDGFRα, A2B5, O4, and CD44); and late oligodendrocyte progenitors (O1). In parallel, the expression of glial fibrillary acidic protein (GFAP), synaptophysin and neuron-specific enolase (NSE) was immunohistochemically analyzed in fixed tissue specimens. Irrespective of the grade and morphological diagnosis of gliomas, glioma cells concomitantly expressed PDGFRα, A2B5, O4, CD44 and GFAP. In contrast, O1 was weakly expressed in all low-grade and the majority of high-grade glioma specimens analyzed. Co-expression of neuronal markers was observed in all high-grade, but not low-grade, glioma specimens analyzed. The rare CD133 expressing cells in low-grade glioma specimens typically co-expressed vessel endothelial marker CD31. In contrast, distinct CD133 expression profiles in up to 90% of CD45-negative glioma cells were observed in 12 of the 17 high-grade glioma specimens and the majority of these CD133 expressing cells were CD31 negative. The CD133 expression correlates inversely with length of patient survival. Surprisingly, cytogenetic analysis showed that gliomas contained normal and abnormal cell karyotypes with hitherto indistinguishable phenotype. Conclusions/Significance This study constitutes an important step towards clarification of lineage commitment and differentiation blockage of glioma cells. Our data suggest that glioma cells may resemble expansion of glial lineage progenitor cells with compromised differentiation capacity downstream of A2B5 and O4 expression. The concurrent expression of neuronal markers demonstrates that high-grade glioma cells are endowed with multi-lineage differentiation potential in vivo. Importantly, enhanced CD133 expression marks a poor prognosis in gliomas.

Apoptosis-inducing factor mediates dopaminergic cell death in response to LPS-induced inflammatory stimulus: evidence in Parkinson's disease patients.

We show that intranigral lipopolysaccharide (LPS) injection, which provokes specific degeneration of DA neurons, induced caspase-3 activation in the rat ventral mesencephalon, which was mostly associated with glial cells. In contrast, nigral DA neurons exhibited AIF nuclear translocation in response to LPS. A significant decrease of the Bcl-2/Bax ratio in nigral tissue after LPS injection was observed. We next developed an in vitro co-culture system with the microglial BV2 and the DA neuronal MN9D murine cell lines. The silencing of caspase-3 or AIF by small interfering RNAs exclusively in the DA MN9D cells demonstrated the key role of AIF in the LPS-induced death of DA cells. In vivo chemical inhibition of caspases and poly(ADP-ribose)polymerase-1, an upstream regulator of AIF release and calpain, proved the central role of the AIF-dependent pathway in LPS-induced nigral DA cell death. We also observed nuclear translocation of AIF in the ventral mesencephalon of Parkinsons disease subjects.

Brain tissue microarrays in dementia research: White matter microvascular pathology in Alzheimer's disease

Tissue microarrays (TMA) consist of up to 1000 cylindrical tissue cores from different donor paraffin blocks relocated into one recipient block, allowing for efficient histopathological studies by fluorescence in situ hybridization, RNA in situ hybridization or immunohistochemistry. On the background of the increasing interest of the TMA technique in cancer research and the suggestion of its application also in studies of non‐neoplastic intracranial disorders, the technique was applied to pathologic white matter in AD brains. Eight cases with AD and concomitant white matter pathology were neuropathologically diagnosed on whole brain coronal slides. The TMA technique was used to grade severity of white matter pathology and to quantify small vessels with traditional staining and immunohistochemical markers. These measurements were compared with the whole brain neuropathological assessment. The technique produced good results with preserved tissue structures as confirmed by the whole brain evaluation. Severity of white matter pathology evaluated on the TMA cores correlated negatively with small vessel quantities, and statistically significant differences in vessel quantities paralleled different grades of white matter pathology. It is concluded that the TMA technique could be further utilized in studies of dementing disorders, and may have its advantages in large, clinically well‐characterized materials (e.g. in quantitative mapping of white matter changes).

Glioma Cell Proliferation Controlled by ERK Activity-Dependent Surface Expression of PDGFRA

Increased PDGFRA signaling is an essential pathogenic factor in many subtypes of gliomas. In this context the cell surface expression of PDGFRA is an important determinant of ligand sensing in the glioma microenvironment. However, the regulation of spatial distribution of PDGFRA in glioma cells remains poorly characterized. Here, we report that cell surface PDGFRA expression in gliomas is negatively regulated by an ERK-dependent mechanism, resulting in reduced proliferation of glioma cells. Glioma tumor tissues and their corresponding cell lines were isolated from 14 patients and analyzed by single-cell imaging and flow cytometry. In both cell lines and their corresponding tumor samples, glioma cell proliferation correlated with the extent of surface expression of PDGFRA. High levels of surface PDGFRA also correlated to high tubulin expression in glioma tumor tissue in vivo. In glioma cell lines, surface PDGFRA declined following treatment with inhibitors of tubulin, actin and dynamin. Screening of a panel of small molecule compounds identified the MEK inhibitor U0126 as a potent inhibitor of surface PDGFRA expression. Importantly, U0126 inhibited surface expression in a reversible, dose- and time-dependent manner, without affecting general PDGFRA expression. Treatment with U0126 resulted in reduced co-localization between PDGFRA and intracellular trafficking molecules e.g. clathrin, RAB11 and early endosomal antigen-1, in parallel with enhanced co-localization between PDGFRA and the Golgi cisternae maker, Giantin, suggesting a deviation of PDGFRA from the endosomal trafficking and recycling compartment, to the Golgi network. Furthermore, U0126 treatment in glioma cells induced an initial inhibition of ERK1/2 phosphorylation, followed by up-regulated ERK1/2 phosphorylation concomitant with diminished surface expression of PDGFRA. Finally, down-regulation of surface PDGFRA expression by U0126 is concordant with reduced glioma cell proliferation. These findings suggest that manipulation of spatial expression of PDGFRA can potentially be used to combat gliomas.

Genetic intratumour heterogeneity in high-grade brain tumours is associated with telomere-dependent mitotic instability

Glioblastoma multiforme (GBM) and other high‐grade brain tumours are typically characterized by complex chromosome abnormalities and extensive intratumour cytogenetic heterogeneity. The mechanisms behind this diversity have been little explored. In this study, we analysed the pattern of chromosome segregation at mitosis in 20 brain tumours. We found an abnormal segregation of chromatids at mitosis through anaphase bridging (10–25% of anaphase cells) in all 10 GBMs. Anaphase bridging was also found in two medulloblastomas (7–15%), one anaplastic astrocytoma (17%) and one oligodendroglioma (6%). These tumours showed a relatively high degree of cytogenetic complexity and heterogeneity. In contrast, cell division abnormalities were not found in low‐grade brain tumours with less complex karyotypes, including two pilocytic astrocytomas and two ependymomas. Further analysis of two GBMs by fluorescence in situ hybridization with telomeric repeat probes revealed excessive shortening of TTAGGG repeats, indicating dysfunctional protection of chromosome ends. In xenografts established from these GBMs, there was a gradual reduction in cytogenetic heterogeneity through successive passages as the proportion of abnormally short telomeres was reduced and the frequency of anaphase bridges decreased from >25% to 0. However, bridging could be reintroduced in late‐passage xenograft cells by pharmacological induction of telomere shortening, using a small‐molecule telomerase inhibitor. Telomere‐dependent abnormal segregation of chromosomes at mitosis is thus a common phenomenon in high‐grade brain tumours and may be one important factor behind cytogenetic intratumour diversity in GBM.

Neuroblastomas and medulloblastomas exhibit more Coxsackie adenovirus receptor expression than gliomas and other brain tumors

Adenoviral vector‐mediated treatment is a potential therapy for tumors of the central nervous system. To obtain a significant therapeutic effect by adenoviral vectors, a sufficient infection is required, the power of which depends predominantly on the level of Coxsackie adenovirus receptors. We stained surgical biopsies of central nervous system tumors and neuroblastomas for Coxsackie adenovirus receptors. For gliomas, the level of the receptor was low and markedly variable among individual tumors. By contrast, neuroblastomas and medulloblastomas exhibited a higher degree of Coxsackie adenovirus receptor expression than gliomas and other brain tumors. We conclude that neuroblastomas and medulloblastomas could be suitable for adenovirus‐mediated gene therapy. Adverse effects of the treatment, however, must be considered because neurons and reactive astrocytes also express a significant amount of the receptor.

Different assessments of immunohistochemically stained Ki-67 and hTERT in glioblastoma multiforme yield variable results: a study with reference to survival prognosis.

OBJECTIVE To investigate a marker of tumor proliferation, Ki-67, and telomerase expression in glioblastoma multiforme and to compare the results of different mainly quantitative assessments, in relation to age and survival rates. METHODS Immunohistochemical stainings of Ki-67 and hTERT were evaluated in 39 formaldehyde-fixed, paraffin-embedded surgical samples of glioblastoma multiforme diagnosed during 2004, comprising all specimens with sufficient amount of vital tissue sent to the Department of Pathology during this year. Ki-67 counting and hTERT evaluation was assessed on whole tumor sections and on selected areas within each section. Age and length of survival were analyzed in relation to these parameters. RESULTS We found that different methods of evaluating the stained sections yielded different results regarding Ki-67, but less marked differences for hTERT. With Ki-67 counting on whole sections (non-selected areas), we found a statistically significant correlation with length of survival. There was no corresponding information in the hTERT assessment. We could also confirm a significant inverse correlation between age and length of survival, as previously published. CONCLUSION Our data demonstrate that different methods of Ki-67 evaluation may give markedly dissimilar results. The significant correlation found between survival and one but not with two other methods of Ki-67 assessment, implicate the value of standardized quantification methods. Our data indicate a possible prognostic use of immunohistochemical Ki-67 proliferation index in glioblastoma multiforme.

Better Prognosis of Patients with Glioma Expressing FGF2-Dependent PDGFRA Irrespective of Morphological Diagnosis.

Signaling of platelet derived growth factor receptor alpha (PDGFRA) is critically involved in the development of gliomas. However, the clinical relevance of PDGFRA expression in glioma subtypes and the mechanisms of PDGFRA expression in gliomas have been controversial. Under the supervision of morphological diagnosis, analysis of the GSE16011 and the Repository of Molecular Brain Neoplasia Data (Rembrandt) set revealed enriched PDGFRA expression in low-grade gliomas. However, gliomas with the top 25% of PDGFRA expression levels contained nearly all morphological subtypes, which was associated with frequent IDH1 mutation, 1p LOH, 19q LOH, less EGFR amplification, younger age at disease onset and better survival compared to those gliomas with lower levels of PDGFRA expression. SNP analysis in Rembrandt data set and FISH analysis in eleven low passage glioma cell lines showed infrequent amplification of PDGFRA. Using in vitro culture of these low passage glioma cells, we tested the hypothesis of gliogenic factor dependent expression of PDGFRA in glioma cells. Fibroblast growth factor 2 (FGF2) was able to maintain PDGFRA expression in glioma cells. FGF2 also induced PDGFRA expression in glioma cells with low or non-detectable PDGFRA expression. FGF2-dependent maintenance of PDGFRA expression was concordant with the maintenance of a subset of gliogenic genes and higher rates of cell proliferation. Further, concordant expression patterns of FGF2 and PDGFRA were detected in glioma samples by immunohistochemical staining. Our findings suggest a role of FGF2 in regulating PDGFRA expression in the subset of gliomas with younger age at disease onset and longer patient survival regardless of their morphological diagnosis.

Standardizing evaluation of sarcoma proliferation - higher Ki-67 expression in the tumor periphery than the center

Soft tissue sarcomas often present as large and histopathologically heterogenous tumors. Proliferation has repeatedly been identified as a prognostic factor and immunostaining for Ki‐67 represents the most commonly used proliferation marker. There is, however, a lack of consensus on how to evaluate Ki‐67 staining regarding optimal cut‐off levels, selection of tumor areas, and the number of tumor cells to evaluate. We assessed the impact of targeting peripheral versus central tumor areas using tissue microarray‐based staining for Ki‐67 throughout the tumor diameter in 25 leiomyosarcomas. In 18/25 tumors, Ki‐67 expression was higher in the tumor periphery. If 10% staining tumor nuclei was used as cut‐off and the maximal Ki‐67 staining section in the tumor periphery was considered, 21/25 tumors would have been classified as highly proliferative compared to 14/25 if the tumor center had been analyzed. Similar results were obtained also when higher cut‐off levels were used and if the mean expression rather than the maximal expression was considered and the differences were neither caused by necrosis nor by hypoxia (assessed as HIF‐1α expression). Our findings suggest that the determination of proliferation in soft tissue sarcomas should be standardized for clinical application of Ki‐67 as a prognostic marker.