BackgroundMedulloblastoma is the most common malignant brain tumor in children. Despite recent improvements in cure rates, prediction of disease outcome remains a major challenge and survivors suffer from serious therapy-related side-effects. Recent data showed that patients with WNT-activated tumors have a favorable prognosis, suggesting that these patients could be treated less intensively, thereby reducing the side-effects. This illustrates the potential benefits of a robust classification of medulloblastoma patients and a detailed knowledge of associated biological mechanisms.Methods and FindingsTo get a better insight into the molecular biology of medulloblastoma we established mRNA expression profiles of 62 medulloblastomas and analyzed 52 of them also by comparative genomic hybridization (CGH) arrays. Five molecular subtypes were identified, characterized by WNT signaling (A; 9 cases), SHH signaling (B; 15 cases), expression of neuronal differentiation genes (C and D; 16 and 11 cases, respectively) or photoreceptor genes (D and E; both 11 cases). Mutations in β-catenin were identified in all 9 type A tumors, but not in any other tumor. PTCH1 mutations were exclusively identified in type B tumors. CGH analysis identified several fully or partly subtype-specific chromosomal aberrations. Monosomy of chromosome 6 occurred only in type A tumors, loss of 9q mostly occurred in type B tumors, whereas chromosome 17 aberrations, most common in medulloblastoma, were strongly associated with type C or D tumors. Loss of the inactivated X-chromosome was highly specific for female cases of type C, D and E tumors. Gene expression levels faithfully reflected the chromosomal copy number changes. Clinicopathological features significantly different between the 5 subtypes included metastatic disease and age at diagnosis and histology. Metastatic disease at diagnosis was significantly associated with subtypes C and D and most strongly with subtype E. Patients below 3 yrs of age had type B, D, or E tumors. Type B included most desmoplastic cases. We validated and confirmed the molecular subtypes and their associated clinicopathological features with expression data from a second independent series of 46 medulloblastomas.ConclusionsThe new medulloblastoma classification presented in this study will greatly enhance the understanding of this heterogeneous disease. It will enable a better selection and evaluation of patients in clinical trials, and it will support the development of new molecular targeted therapies. Ultimately, our results may lead to more individualized therapies with improved cure rates and a better quality of life.

Accumulation of hyperphosphorylated, ubiquitinated and N-terminally truncated TAR DNA-binding protein (TDP-43) is the pathological hallmark lesion in most familial and sporadic forms of FTLD-U and ALS, which can be subsumed as TDP-43 proteinopathies. In order to get more insight into the role of abnormal phosphorylation in the disease process, the identification of specific phosphorylation sites and the generation of phosphorylation-specific antibodies are mandatory. Here, we developed and characterized novel rat monoclonal antibodies (1D3 and 7A9) raised against phosphorylated S409/410 of TDP-43. These antibodies were used to study the presence of S409/410 phosphorylation by immunohistochemistry and biochemical analysis in a large series of 64 FTLD-U cases with or without motor neuron disease including familial cases with mutations in progranulin (n=5), valosincontaining protein (n=4) and linkage to chromosome 9p (n=4), 18 ALS cases as well as other neurodegenerative diseases with concomitant TDP-43 pathology (n=5).Our data demonstrate, that phosphorylation of S409/410 of TDP-43 is a highly consistent feature in pathologic inclusions in the whole spectrum of sporadic and familial forms of TDP-43 proteinopathies. Physiological nuclear TDP-43 was not detectable with these mAbs by immunohistochemistry and by immunoblot analyses. While the accumulation of phosphorylated Cterminal fragments was a robust finding in the cortical brain regions of FTLD-U and ALS, usually being much more abundant than the phsphorylated full-length TDP-43 band, spinal cord samples revealed a predominance of full-length TDP-43 over C-terminal fragments. This argues for a distinct TDP-43 species composition in inclusions in cortical versus spinal cord cells.Overall, these mAbs are powerful tools for the highly specific detection of disease-associated abnormal TDP-43 species and will be extremely useful for the neuropathological routine diagnostics of TDP-43 proteinopathies and for the investigation of emerging cellular and animal models for TDP-43 proteinopathies.

The frontotemporal dementias (FTDs) are a clinically, genetically, and neuropathologically heterogeneous group of diseases accounting for up to 20% of presenile dementia cases. FTD is characterized by behavioral and/or language dysfunction and may co-occur with motor neuron disease (MND).1,2 Frontotemporal lobar degeneration (FTLD) with ubiquitin-positive, tau-negative inclusions (FTLD-U) is the most common underlying pathology in FTD with and without MND.

Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease. Cytoplasmic fused in sarcoma (FUS) aggregates are pathological hallmarks of FUS-ALS. Proper shuttling between the nucleus and cytoplasm is essential for physiological cell function. However, the initial event in the pathophysiology of FUS-ALS remains enigmatic. Using human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs), we show that impairment of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling due to mutations in the FUS nuclear localization sequence (NLS) induces additional cytoplasmic FUS mislocalization which in turn results in neurodegeneration and FUS aggregate formation. Our work suggests that a key pathophysiologic event in ALS is upstream of aggregate formation. Targeting DDR signaling could lead to novel therapeutic routes for ameliorating ALS.

Hexanucleotide repeat expansion in C9ORF72 is the most common genetic cause of frontotemporal dementia and motor neuron disease. Recently, unconventional non-ATG translation of the expanded hexanucleotide repeat, resulting in the production and aggregation of dipeptide repeat (DPR) proteins (poly-GA, -GR and GP), was identified as a potential pathomechanism of C9ORF72 mutations. Besides accumulation of DPR proteins, the second neuropathological hallmark lesion in C9ORF72 mutation cases is the accumulation of TDP-43. In this study, we characterized novel monoclonal antibodies against poly-GA and performed a detailed analysis of the neuroanatomical distribution of DPR and TDP-43 pathology in a cohort of 35 cases with the C9ORF72 mutation that included a broad spectrum of clinical phenotypes. We found the pattern of DPR pathology to be highly consistent among cases regardless of the phenotype with high DPR load in the cerebellum, all neocortical regions (frontal, motor cortex and occipital) and hippocampus, moderate pathology in subcortical areas and minimal pathology in lower motor neurons. No correlation between DPR pathology and the degree of neurodegeneration was observed, while a good association between TDP-43 pathology with clinical phenotype and degeneration in key anatomical regions was present. Our data confirm that the presence of DPR pathology is intimately related to C9ORF72 mutations. The observed dissociation between DPR inclusion body load and neurodegeneration might suggest inclusion body formation as a potentially protective response to cope with soluble toxic DPR species. Moreover, our data imply that alterations due to the C9ORF72 mutation resulting in TDP-43 accumulation and dysmetabolism as secondary downstream effects likely play a central role in the neurodegenerative process in C9ORF72 pathogenesis.