The glioblastoma (GB) microenvironment includes cells of the innate immune system identified as glioma-associated microglia/macrophages (GAMs) that are still poorly characterized. A potential role on the mechanisms regulating GAM activity might be played by the endoplasmic reticulum protein ERp57/PDIA3 (protein disulfide-isomerase A3), the modulation of which has been reported in a variety of cancers. Moreover, by using The Cancer Genome Atlas database, we found that overexpression of PDIA3 correlated with about 55% reduction of overall survival of glioma patients. Therefore, we analyzed the expression of ERp57/PDIA3 using specimens obtained after surgery from 18 GB patients. Immunohistochemical analysis of tumor samples revealed ERp57/PDIA3 expression in GB cells as well as in GAMs. The ERp57/PDIA3 levels were higher in GAMs than in the microglia present in the surrounding parenchyma. Therefore, we studied the role of PDIA3 modulation in microglia–glioma interaction, based on the ability of conditioned media collected from human GB cells to induce the activation of microglial cells. The results indicated that reduced PDIA3 expression/activity in GB cells significantly limited the microglia pro-tumor polarization towards the M2 phenotype and the production of pro-inflammatory factors. Our data support a role of PDIA3 expression in GB-mediated protumor activation of microglia.

The characterization of human microglia has been hampered by poor availability of human cell sources. However, microglia is involved in the physiopathology of multiple sclerosis, Alzheimer’s disease, Parkinson’s disease, HIV dementia, retinal degenerative diseases, cancer, and many other conditions. Therefore, there is an important need to have experimental paradigms of human microglia characterized and usable to study the role of microglia in the different pathologies in which it is involved. In the present work, we carried out an extensive characterization of Immortalized Human Microglia—SV40 cell line (IMhu), marketed by Applied Biological Material. The functional response of IMhu to a large variety of stimuli was studied. In particular, we investigated morphology, mortality, and changes in the production of different cytokines and chemokines, both under basal conditions and after stimulation. Moreover, western blotting analysis was conducted on phospho-mTOR (Ser 2448) and downstream parameters, p-P70S6K and 4EBP1, in order to understand if IMhu can be used for evaluations of mTOR pathway. In conclusion, IMhu cells proved to be a useful experimental model to investigate the physiopathology of inflammatory disease that involved microglia cells, including pathological conditions that involved the mTOR pathway.

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The anti-vascular endothelial growth factor-A (VEGF-A) monoclonal antibody (mAb) bevacizumab is an FDA-approved monotherapy for the treatment of recurrent glioblastoma (GB), a highly angiogenic and infiltrative tumour. However, bevacizumab does not increase overall survival and blockade of VEGF-A/VEGF receptor (VEGFR)-2 signal transduction is associated with severe adverse effects due to inhibition of physiological angiogenesis. Conversely, VEGFR-1 does not play a relevant role in physiological angiogenesis in the adult. VEGFR-1 is activated by both VEGF-A and placenta growth factor (PlGF), a protein involved in tumour growth and progression. In previous studies, it was demonstrated that inhibition of VEGFR-1 using a specific mAb developed in our laboratories reduced angiogenesis and GB cell chemotaxis and increased the survival of tumour-bearing mice. Failure of treatments directed toward the VEGF-A/VEGFR-2 axis could in part be due to inefficient targeting of the tumour microenvironment. In the present study, VEGFR-1 expression was investigated in GB-associated microglia/macrophages (GAMs) by analysing surgical specimens collected from 42 patients with GB. Data obtained from The Cancer Genome Atlas (TCGA) database revealed that upregulation of the VEGFR-1 ligands VEGF-A and PlGF was associated with a significant reduction in overall survival for patients with GB, highlighting the potential relevance of this receptor in the aggressiveness of GB. Immunohistochemical analysis indicated that VEGFR-1 is expressed not only in GB tissue but also in GAMs. Furthermore, the percentage of VEGFR-1-positive GAMs was significantly higher in the tumour region compared with that noted in the surrounding parenchyma. Thus, VEGFR-1 represents a potential therapeutic target for the treatment of GB, being present not only in GB and endothelial cells, but also in GAMs that are involved in tumour progression.

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