gms | German Medical Science

Objective: The transforming growth factor-β (TGF-β)-Smad pathway plays a crucial role in the malignant phenotype of glioblastoma (GBM) and confers poor prognosis to glioma patients. Biological effects of TGF-β in GBM are linked to immunosuppression, angiogenensis, and invasion. Latent TGF-β binding protein (LTBP) binds to an inactive TGF-β complex and regulates its functions. While a role of LTBP1 in glioma has already been described, a similar role for LTBP4 was only proposed in breast cancer.

Method: The current study analysed the expression profiles of the LTBP-isoforms LTBP1 and 4 in human glioma on mRNA and protein level using immunoblot, -histochemistry (IHC) and quantitative RT-PCR. We compared glioma to control tissue, pre- and post chemotherapy, before and after radiation, different grades of malignancy and primary versus secondary glioma in more than 70 tissue samples. Moreover, we evaluated 21 patients longitudinally. Additionally, immunofluorescence, cell proliferation-, migration-, and invasion-assays were performed after adding LTBP1 in vitro.

Results: In comparison to non-malignant tissues, LTBP1 and -4 mRNA were upregulated in all tumor probes. We also found a significant increase from low-grade gliomas to high-grade gliomas (LTBP1: WHO grade II, 2.09 ± 0.4; WHO grade III, 4.03 ± 1.1; LTBP4: WHO grade II, 1.6 ± 0.4; WHO grade III, 5.7 ± 1.4; p = 0.003). No signif. difference in mRNA expression was found between high grade astrocytomas and glioblastoma. Three individual patient courses (progression from grade II to grade III to grade IV) support this finding. LTBP1 protein expression showed analog results. In the case of LTBP4, Western blot and IHC revealed significant differences between all groups in terms of an increase of LTBP4 with the grade of malignancy (control tissue: 34, diffuse astrocytoma: 48, anaplastic astrocytoma: 90, GBM: 140 arbitrary units; p = 0.002). Treatment with either chemotherapy or radiation did not influence LTBP levels. Interestingly, the LTBP4 expression was significantly lower in primary GBM compared to secondary GBM (p = 0.007). This difference was not present for LTBP1. Both LTBPs are secreted into the medium in cultured glioma cell lines and are associated with the extracellular matrix.

Conclusions: In summary, the level of LTBP1 and LTBP4 increase with the grade of malignancy in gliomas. They may play an important role during the transformation from low- to high-grade glioma because gene expression mainly changed during this process.