Research Report
Distinctive pattern of cannabinoid receptor type II (CB2) expression in adult and pediatric brain tumors
- Aleksandra Ellert-Miklaszewskaa, c,
- Wieslawa Grajkowskab,
- Konrad Gabrusiewiczc,
- Bozena Kaminskac,
, 
, - Liliana Konarskaa
- a Department of Biochemistry and Clinical Chemistry, Medical University of Warsaw, Poland
- b Department of Neurosurgery, Children’s Memorial Health Institute, Warsaw, Poland
- c Laboratory of Transcription Regulation, Department of Cell Biology, Nencki Institute of Experimental Biology, 3 Pasteur Str., 02-093 Warsaw, Poland
Abstract
The efficacy of cannabinoids against high-grade glioma in animal models, mediated by two specific receptors, CB1 and CB2, raised promises for targeted treatment of the most frequent and malignant primary brain tumors. Unlike the abundantly expressed CB1, the CB2 receptor shows a restricted distribution in normal brain. Although brain tumors constitute the second most common malignancy in children and the prevalence of histological types of brain tumors vary significantly between the adult and pediatric populations, cannabinoid receptor expression in pediatric tumors remains unknown. In the present study, we compared the expression of the CB2 receptor in paraffin-embedded sections from primary brain tumors of adult and pediatric patients. Most glioblastomas expressed very high levels of CB2 receptors and the expression correlated with tumor grade. Interestingly, some benign pediatric astrocytic tumors, such as subependymal giant cell astrocytoma (SEGA), which may occasionally cause mortality owing to progressive growth, also displayed high CB2 immunoreactivity. The high levels of CB2 expression would predestine those tumors to be vulnerable to cannabinoid treatment. In contrast, all examined cases of embryonal tumors (medulloblastoma and S-PNET), the most frequently diagnosed malignant brain tumors in childhood, showed no or trace CB2 immunoreactivity. Our results suggest that the CB2 receptor expression depends primarily on the histopathological origin of the brain tumor cells and differentiation state, reflecting the tumor grade.
Abbreviations
- CB1/CB2, Cannabinoid receptor type 1/type 2;
- GBM, Glioblastoma multiforme;
- S-PNET, Supratentorial primitive neuroectodermal tumor;
- SEGA, Subependymal giant cell astrocytoma
Keywords
- Brain tumor;
- Cannabinoid receptor;
- Glioma;
- Immunohistochemistry;
- Pediatric brain tumor
Figures and tables from this article:
- Fig. 1. Specificity of the anti-human CB2 receptor antibody. (A) Tonsil sections were stained as described inExperimental procedures. CB2-positive cells, visualized in brown using DAB, were located to germinal centers of B-cell follicles. The immunoreactivity was completely abolished by pre-absorption of the primary antibody on the specific blocking peptide. (B) Western blotting was performed with Jurkat cell lysates. Specific CB2 signal disappeared upon pre-incubation of the anti-CB2 antibody with the blocking peptide.
- Fig. 2. Expression of cannabinoid receptor type 2 (CB2) in human brain tumors from adult and pediatric patients. Detection of the CB2 receptor in paraffin sections of brain tumors from adult (A–D) and pediatric (E–H) patients was performed as described in Experimental procedures using 3,3′-diaminobenzidine (DAB). Sections were counterstained with hematoxylin to visualize cell nuclei. Specimens incubated without primary antibody (I) or with the antibody pre-absorbed on the blocking peptide (J) were used as negative controls. Human astrocytic tumors, both benign such as pilomyxoid astrocytoma (A), juvenile pilocytic astrocytoma (E), SEGA (G) and malignant GBM (B), giant cell glioblastoma (F), exhibit significant levels of CB2 expression. Low CB2 expression was observed in other types of brain tumors: fibroblastic meningioma (C), anaplastic oligodendroglioma (D) and pediatric supratentorial PNET (H). Note a very strong reaction in areas of dense cellularity and microvascularization in GBM (B and F) in contrast to barely visible staining in S-PNET (H). Abundance of CB2 receptor in poorly differentiated cells of anaplastic oligodendroglioma (D, lower triangle) and sparse expression in cells of a less malignant appearance within distinct parts of the same section (D, upper triangle) show that CB2 expression can be related to tumor grade. Differences in immunoreactivity between the benign juvenile pilocytic astrocytoma (E) and the malignant giant cell glioblastoma (F) are also noticeable. No positive CB2 reaction was detected in necrotic areas (N) surrounded by tumor cells (T) (K).
- Fig. 3. Staining for activated microglia and the CB2 receptor within the tumor area and normal tissue margin. Immunodetection of the human HLA-DP,DQ,DR antigens (HLA), expressed on activated microglia, and of the CB2 cannabinoid receptor (CB2) in paraffin sections of brain tumors was performed as described in Experimental procedures. Cell nuclei were stained with hematoxylin. In the single staining experiments, 3,3′-diaminobenzidine (DAB) was used for detection of both antigens in the adjacent sections (A, C). Microphotographs of the corresponding regions in the two adjacent sections from SEGA–tumor area (A) and GBM–healthy margin cortex (C) are shown. In the double staining, HLA antigens were visualized using HRP/DAB and the CB2 receptors were detected using AP/FastRed. Microphotographs in two different magnifications of GBM–tumor area (B) and pilocytic astrocytoma–healthy margin cerebellar cortex (D) are shown. Although HLA co-localizes with CB2 in certain cells, the expression patterns for the microglia marker and the CB2 receptor are different. The majority of the CB2-expressing cells in the tumor area have typical tumor cell morphology.
- Fig. 4. CB2 immunoreactivity in various brain tumors from pediatric and adult patients in relation to tumor grade. Different histopathological types of tumors are represented by separate symbols. Oligodendroglial, ependymal, ganglioglial and mixed glial tumors are combined as “other glial tumors”. Despite a strong CB2 immunoreactivity among astrocytic tumors, a correlation between malignancy and CB2 expression level is still clearly visible in this group. The difference in the CB2 immunoreactivity between low- and high-grade tumors is statistically significant (*astrocytic tumors: p < 0.01, all glial tumors: p < 0.05, all glial and meningeal tumors: p < 0.05). No or hardly detected expression of the CB2 cannabinoid receptor in embryonal tumors, such as medulloblastoma and S-PNET, is observed.
- Table 1. Expression level of cannabinoid receptor type 2 (CB2) evaluated in adult and pediatric brain tumors
- All cases were classified into groups according to diagnosed WHO grade, regardless of the histopathological type of tumor. Numbers of cases refer to astrocytic tumors, which were the most abundant, and where indicated also include:aanaplastic oligodendroglioma (n = 2); bganglioglioma (n = 1); coligodendroglioma (n = 1) danaplastic ependymoma (n = 1); emedulloblastoma (n = 2) and S-PNET (n = 1); ffibroblastic meningioma (n = 1); gastrooligodendroglioma (n = 1) and ependymoma (n = 1); hanaplastic ependymoma (n = 2) and anaplastic ganglioglioma (n = 1); ianaplastic meningioma (n = 1), anaplastic ganglioglioma (n = 1) and anaplastic ependymoma (n = 1). Immunoreactivity was scored as negative, low, moderate or high, depending on the intensity of DAB staining.
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Copyright © 2006 Elsevier B.V. All rights reserved.
