Patterns of SPARC expression and basement membrane intactness at the tumour-brain border of invasive meningiomas

The matricellular glycoprotein SPARC (secreted protein, acidic and rich in cysteine), also termed osteonectin, has been found to regulate the invasive behaviour of several tumour types by interacting with basement membrane constituents. Brain invasive meningiomas are supposed to disrupt the pial-glial basement membrane. In the present study we aimed at determining the relationship of basement membrane intactness and SPARC protein expression at the meningioma-brain border. Sections of 51 brain-invasive meningiomas (31 meningothelial meningiomas WHO grade I, 11 atypical WHO grade II, and nine anaplastic WHO grade III tumours) were immunolabelled with antibodies against SPARC, epithelial membrane antigen (EMA), collagen IV and glial fibrillary acidic protein (GFAP). Twenty-two non-invasive WHO grade I meningothelial meningiomas were included in the study for comparison. At the tumour-brain border of invasive meningiomas, spindle-shaped tumour cells expressed SPARC. The number of tumours containing SPARC+ spindle cells did not differ significantly between WHO grades. By contrast, the number of WHO grade I tumours expressing collagen IV (15/31) was highly significantly elevated when compared with WHO grade II (1/11) and WHO grade III (0/9) (both P < 0.0001). There was an inverse relationship of the presence of SPARC+ spindle cells and basement membrane material. In conclusion, the destruction of the basement membrane is correlated with meningioma malignancy grade whereas the expression of SPARC protein at the tumour-brain border is not. Destruction of the basement membrane and appearance of SPARC+ spindle cells are not coincident during the course of brain invasion by meningiomas.