J1-31 protein expression in astrocytes and astrocytomas

miRNA-204-5p acts as tumor suppressor to influence the invasion and migration of astrocytoma by targeting ezrin and is downregulated by DNA methylation

microRNAs (miRNAs), through their regulation of the expression and activity of numerous proteins, are involved in almost all cellular processes. As a consequence, dysregulation of miRNA expression is closely associated with the development and progression of cancers. Recently, DNA methylation has been shown to play a key role in miRNA expression dysregulation in tumors. miRNA-204-5p commonly acts in the suppression of oncogenes in tumors. In this study, the levels of miRNA-204-5p were found to be down-regulated in the astrocytoma samples. miRNA-204-5p expression was also down-regulated in two astrocytoma cell lines (U87MG and LN382). Examination of online databases showed that the miRNA-204-5p promoter regions exist in CpG islands, which might be subjected to differential methylation. Subsequently, we showed that the miRNA-204-5p promoter region was hypermethylated in the astrocytoma tissue samples and cell lines. Then we found that ezrin expression was down-regulated with an increase in miRNA-204-5p expression in LN382 and U87MG cells after 5-aza-2'-deoxycytidine (5'AZA) treatment compared with control DMSO treatment. In addition, LN382 and U87MG cells treated with 5'AZA exhibited significantly inhibited cell invasion and migration . In a recovery experiment, cell invasion and migration returned to normal levels as miRNA-204-5p and ezrin levels were restored. Overall, our study suggests that miRNA-204-5p acts as a tumor suppressor to influence astrocytoma invasion and migration by targeting ezrin and that miRNA-204-5p expression is downregulated by DNA methylation. This study provides a new potential strategy for astrocytoma treatment.

TERT Promoter Mutation Analysis to Distinguish Glioma From Gliosis

Among the most challenging diagnostic issues in surgical neuropathology is the distinction between scant infiltration by diffuse gliomas and reactive gliosis. The best documented ancillary marker to establish a definitive diagnosis of glioma in this setting is the identification of hotspot mutations in the isocitrate dehydrogenase 1 and 2 (IDH1/IDH2) genes, which is limited, however, by the low prevalence of these mutations in gliomas of elderly adults. Since telomerase reverse transcriptase (TERT) promoter mutations are present in the vast majority of IDH-wildtype diffuse gliomas, we hypothesized that combined analysis of IDH and TERT might overcome these limitations. For this purpose, we analyzed a series of non-neoplastic and neoplastic CNS samples for the prevalence of TERT hotspot mutations. TERT mutations were identified in none out of 58 (0%) reactive gliosis samples, and in 91 out of 117 (78%) IDH-wildtype gliomas. Based on a series of 200 consecutive diffuse gliomas, we found that IDH mutation analysis alone had a sensitivity of 28% (63% and 12%, respectively, in patients below and above age of 50) for detection of gliomas, whereas a combined analysis of IDH and TERT was 85% sensitive (87% and 84%, respectively, below and above age of 50). In sum, our findings suggest that TERT promoter mutation analysis contributes favorably to a molecular panel in cases equivocal for glioma versus gliosis on morphological grounds, especially in patients above age of 50, in which IDH analysis alone performs poorly.

Importance of GFAP isoform-specific analyses in astrocytoma

Gliomas are a heterogenous group of malignant primary brain tumors that arise from glia cells or their progenitors and rely on accurate diagnosis for prognosis and treatment strategies. Although recent developments in the molecular biology of glioma have improved diagnosis, classical histological methods and biomarkers are still being used. The glial fibrillary acidic protein (GFAP) is a classical marker of astrocytoma, both in clinical and experimental settings. GFAP is used to determine glial differentiation, which is associated with a less malignant tumor. However, since GFAP is not only expressed by mature astrocytes but also by radial glia during development and neural stem cells in the adult brain, we hypothesized that GFAP expression in astrocytoma might not be a direct indication of glial differentiation and a less malignant phenotype. Therefore, we here review all existing literature from 1972 up to 2018 on GFAP expression in astrocytoma patient material to revisit GFAP as a marker of lower grade, more differentiated astrocytoma. We conclude that GFAP is heterogeneously expressed in astrocytoma, which most likely masks a consistent correlation of GFAP expression to astrocytoma malignancy grade. The GFAP positive cell population contains cells with differences in morphology, function, and differentiation state showing that GFAP is not merely a marker of less malignant and more differentiated astrocytoma. We suggest that discriminating between the GFAP isoforms GFAPδ and GFAPα will improve the accuracy of assessing the differentiation state of astrocytoma in clinical and experimental settings and will benefit glioma classification.

Deimination level and peptidyl arginine deiminase 2 expression are elevated in astrocytes with increased incubation temperature

Astrocytes respond to environmental cues, including changes in temperatures. Increased deimination, observed in many progressive neurological diseases, is thought to be contributed by astrocytes. We determined the level of deimination and expression of peptidyl arginine deiminase 2 (PAD2) in isolated primary astrocytes in response to changes on either side (31°C and 41°C) of the optimal temperature (37°C). We investigated changes in the astrocytes by using a number of established markers and accounted for cell death with the CellTiter-Blue assay. We found increased expression of glial fibrillary acidic protein, ALDH1L1, and J1-31, resulting from increased incubation temperature and increased expression of TSP1, S100β, and AQP4, resulting from decreased incubation temperature vs. optimal temperature, suggesting activation of different biochemical pathways in astrocytes associated with different incubation temperatures. Mass spectrometric analyses support such trends. The PAD2 level was increased only as a result of increased incubation temperature with a commensurate increased level of deimination. Actin cytoskeleton and iso[4]LGE, a lipid peroxidase modification, also showed an increase with higher incubation temperature. Altogether, these results suggest that temperature, as an environmental cue, activates astrocytes in a different manner on either side of the optimal temperature and that increase in deimination is associated only with the higher temperature side of the spectrum.

Co-evolution of breast-to-brain metastasis and neural progenitor cells

Brain colonization by metastatic tumor cells offers a unique opportunity to investigate microenvironmental influences on the neoplastic process. The bi-directional interplay of breast cancer cells (mesodermal origin) and brain cells (neuroectodermal origin) is poorly understood and rarely investigated. In our patients undergoing neurosurgical resection of breast-to-brain metastases, specimens from the tumor/brain interface exhibited increased active gliosis as previously described. In addition, our histological characterization revealed infiltration of neural progenitor cells (NPCs) both outside and inside the tumor margin, leading us to investigate the cellular and molecular interactions between NPCs and metastases. Since signaling by the TGF-β superfamily is involved in both developmental neurobiology and breast cancer pathogenesis, we examined the role of these proteins in the context of brain metastases. The brain-metastatic breast cancer cell line MDA-MB-231Br (231Br) expressed BMP-2 at significantly higher levels compared to its matched primary breast cancer cell line MDA-MB-231 (231). Co-culturing was used to examine bi-directional cellular effects and the relevance of BMP-2 overexpression. When co-cultured with NPCs, 231 (primary) tumor cells failed to proliferate over 15 days. However, 231Br (brain metastatic) tumor cells co-cultured with NPCs escaped growth inhibition after day 5 and proliferated, occurring in parallel with NPC differentiation into astrocytes. Using shRNA and gene knock-in, we then demonstrated BMP-2 secreted by 231Br cells mediated NPC differentiation into astrocytes and concomitant tumor cell proliferation in vitro. In xenografts, overexpression of BMP-2 in primary breast cancer cells significantly enhanced their ability to engraft and colonize the brain, thereby creating a metastatic phenotype. Conversely, BMP-2 knockdown in metastatic breast cancer cells significantly diminished engraftment and colonization. The results suggest metastatic tumor cells create a permissive neural niche by steering NPC differentiation toward astrocytes through paracrine BMP-2 signaling.