Glioblastoma cells inhibit astrocytic p53-expression favoring cancer malignancy.

The tumor microenvironment has a dynamic and usually cancer-promoting function during all tumorigenic steps. Glioblastoma (GBM) is a fatal tumor of the central nervous system, in which a substantial number of non-tumoral infiltrated cells can be found. Astrocytes neighboring these tumor cells have a particular reactive phenotype and can enhance GBM malignancy by inducing aberrant cell proliferation and invasion. The tumor suppressor p53 has a potential non-cell autonomous function by modulating the expression of secreted proteins that influence neighbor cells. In this work, we investigated the role of p53 on the crosstalk between GBM cells and astrocytes. We show that extracellular matrix (ECM) from p53(+/-) astrocytes is richer in laminin and fibronectin, compared with ECM from p53(+/+) astrocytes. In addition, ECM from p53(+/-) astrocytes increases the survival and the expression of mesenchymal markers in GBM cells, which suggests haploinsufficient phenotype of the p53(+/-) microenvironment. Importantly, conditioned medium from GBM cells blocks the expression of p53 in p53(+/+) astrocytes, even when DNA was damaged. These results suggest that GBM cells create a dysfunctional microenvironment based on the impairment of p53 expression that in turns exacerbates tumor endurance.

Activated microglia mediate synapse loss and short-term memory deficits in a mouse model of transthyretin-related oculoleptomeningeal amyloidosis.

Oculoleptomeningeal amyloidosis (OA) is a fatal and untreatable hereditary disease characterized by the accumulation of transthyretin (TTR) amyloid within the central nervous system. The mechanisms underlying the pathogenesis of OA, and in particular how amyloid triggers neuronal damage, are still unknown. Here, we show that amyloid fibrils formed by a mutant form of TTR, A25T, activate microglia, leading to the secretion of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and nitric oxide. Further, we found that A25T amyloid fibrils induce the activation of Akt, culminating in the translocation of NFκB to the nucleus of microglia. While A25T fibrils were not directly toxic to neurons, the exposure of neuronal cultures to media conditioned by fibril-activated microglia caused synapse loss that culminated in extensive neuronal death via apoptosis. Finally, intracerebroventricular (i.c.v.) injection of A25T fibrils caused microgliosis, increased brain TNF-α and IL-6 levels and cognitive deficits in mice, which could be prevented by minocycline treatment. These results indicate that A25T fibrils act as pro-inflammatory agents in OA, activating microglia and causing neuronal damage.

Microglial stress inducible protein 1 promotes proliferation and migration in human glioblastoma cells.

Microglial activation is a key event in the progression and infiltration of tumors. We have previously demonstrated that the co-chaperone stress inducible protein 1 (STI1), a cellular prion protein (PrP(C)) ligand, promotes glioblastoma (GBM) proliferation. In the present study, we examined the influence of microglial STI1 in the growth and invasion of the human glioblastoma cell line GBM95. We demonstrated that soluble factors secreted by microglia into the culture medium (microglia conditioned medium; MG CM) caused a two-fold increase in the proliferation of GBM95 cells. This effect was reversed when STI1 was removed from the MG CM. In this context, we have shown that microglial cells synthesize and secrete STI1. Interestingly, no difference was observed in proliferation rates when GBM cells were maintained in MG CM or MG CM containing an anti-PrP(C) neutralizing antibody. Moreover, rec STI1 and rec STI1(Δ230-245), which lack the PrP(C) binding site, both promoted similar levels of GBM95 proliferation. In the migration assays, MG CM favored the migration of GBM95 cells, but migration failed when STI1 was removed from the MG CM. We detected metalloproteinase 9 (MMP-9) activity in the MG CM, and when cultured microglia were treated with an anti-STI1 antibody, MMP-9 activity decreased. Our results suggest that STI1 is secreted by microglia and favors tumor growth and invasion through the participation of MMP-9 in a PrP(C)-independent manner.