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Remyelination in the CNS is a regenerative process carried by oligodendrocyte precursor cells (OPC), which are recruited to the demyelination site and differentiate into mature oligodendrocytes to form a new myelin sheath. Macrophages were shown to support remyelination through myelin debris clearance as well as secretion of chemokines and growth factors stimulating OPC recruitment and differentiation. Moreover, several in vivo studies demonstrated that pharmacological macrophage depletion may impair remyelination. The role of macrophages in new myelin formation is not fully understood and the involvement of these cells in remyelination process has not yet been studied in a model of inherent macrophage reduction. Osteopetrotic (op/op) mice have a mutation in CSF1 gene leading to reduction in monocytes as well as microglia number. Therefore, they make a good model for studying the role of central- and peripheral-derived macrophages in regenerative processes of the CNS. The aim of the present study was to examine the influence of reduction in macrophages in op/op mice on remyelination process in a model of focal demyelination of the spinal cord. Osteopetrotic mice were injected with myelin toxin into the ventral and dorsal funiculus of the spinal cord to induce focal demyelination. Toluidine blue staining of semi-thin resin sections at 28 days post lesion (dpl) revealed impaired remyelination in op/ op mice with the presence of extensive non-remyelinated areas in the lesion. Immunostaining of sections from op/op mice at 10 dpl showed severely reduced activity of macrophages at the lesion site as compared to control. OPC number in the lesions from op/op mice was not affected. Results of the present study provide further evidence for a crucial role of macrophages in supporting CNS remyelination. They also confirm usefulness of op/op mice as a model for remyelination studies.
Malignant glioblastomas are characterized by infi ltration of tumour tissue with brain macrophages that contribute to tumour progression through release a variety of growth factors, cytokines/ chemokines supporting tumor growth, invasion and the immune system evasion. Thus targeting of cytokine production, infi ltration and activation of macrophages may be a novel antitumor strategy. In the present study, we investigated an effectiveness and molecular mechanisms mediating antitumor effects of CsA in the murine glioma model. EGFP-GL261 glioma cells were injected into the striatum of C57BL/6 mice and tumor-bearing mice received CsA (2 or 10 mg/kg/i.p.) every 2 days from 2nd or 8th day after implantation. CsA-treated mice had signifi cantly smaller tumors than control mice. When the treatment was postponed to 8th day, only the higher dose of CsA was effective. CsA-treated mice showed a diminished number of tumor-infi ltrating, amoeboid brain macrophages. TUNEL staining revealed a DNA fragmentation mostly within infi ltrating macrophages after CsA treatment. At concentrations <10 μM CsA did not affect proliferation or viability of cultured glioma cells. Elevated IL-10 and GM-CSF levels were found in tumor-bearing hemisphere in comparison to naive controls and CsA treatment reduced signifi cantly cytokine levels. Our fi ndings demonstrate that CsA-induced decrease of cytokine production, infi ltration and activation of macrophages results in reduction of glioma growth and progression.
Malignant glioblastomas are characterized by infi ltration of tumour tissue with brain macrophages that may consist up to 30% of tumour mass and contribute to tumour progression. A relative contribution of resident microglia and peripheral monocyte/macrophages in gliomas is poorly defi ned. We generated chimeric mice with the immune system reconstituted after irradiation with hematopoietic GFP-bone marrow cells. The dsRed-GL261 glioma cells were implanted to the brains of 16-weeks old C57BL/6 chimeric mice Two weeks after implantation, tumour bearing hemispheres were isolated and the number of CD11b+ CD45low microglial cells or CD11b+ CD45high macrophages was determined by fl ow cytometry. We found that peripheral GFP+ macrophages comprise above 60% of GFP+ cells in the tumor. A co-localization of Iba-1+ cells (macrophages/microglia) with GFP+ cells has been detected by confocal microscopy. Tumor associated peripheral macrophages can facilitate glioma invasion and promote angiogenesis. We have previously demonstrated that cyclosporin A (CsA) blocks activation of microglia and its promoting effects on glioma invasion in vitro and in vivo (Sliwa et al. 2007). In chimeric mice treated CsA, a percentage of GFP+ macrophages in gliomas was reduced suggesting an inhibitory effects of CsA on immune cell migration. Our studies demonstrate that blood-borne macrophages migrate to the tumour and consist a signifi cant population of tumour-associated macrophages.
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