Inhibition of reactive astrocytosis in established experimental autoimmune encephalomyelitis favors infiltration by myeloid cells over T cells and enhances severity of disease

Abstract

Reactive astrocytosis, involving activation, hypertrophy, and proliferation of astrocytes, is a characteristic response to inflammation or injury of the central nervous system. We have investigated whether inhibition of reactive astrocytosis influences established experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. We made use of transgenic mice, which express herpes simplex virus-derived thymidine kinase under control of a glial fibrillary acidic protein promotor (GFAP HSV-TK mice). Treatment of these mice with ganciclovir leads to inhibition of reactive astrocytosis. When GFAP HSV-TK mice were treated for seven days following onset of EAE with ganciclovir, disease severity increased. Although aquaporin-4 staining on astrocyte endfeet at the glia limitans remained equally detectable, GFAP immunoreactivity and mRNA expression in CNS were reduced by this treatment. Ganciclovir-treated GFAP HSV-TK mice with EAE had a 78% increase in the total number of infiltrating myeloid cells (mainly macrophages), whereas we did not find an increase in infiltrating T cells, using quantitative flow cytometry. Per cell expression of mRNA for the macrophage-associated molecules TNFα, MMP-12 and TIMP-1 was elevated in spinal cord of GFAP HSV-TK mice treated with ganciclovir. Relative expression of CD3ε was downregulated, and expression levels of IFNγ, IL-4, IL-10, IL-17, and Foxp3 were not significantly changed. mRNA expression of CCL2 was upregulated, and CXL10 was downregulated. Thus, inhibition of reactive astrocytosis after initiation of EAE leads to increased macrophage, but not T cell, infiltration, and enhanced severity of EAE. This emphasizes the role of astrocytes in controlling leukocyte infiltration in neuroinflammation.

Upregulation of Vascular Endothelial Growth Factor Receptor-3 in the Spinal Cord of Lewis Rats with Experimental Autoimmune Encephalomyelitis

“…This is in accordance with our previous report that VEGFR-3 induction in reactive astrocytes is a generalized phenomenon following ischemic injury (Shin et al 2008(Shin et al , 2010. There are several studies demonstrating the role of astrocytes in forming scar-like barriers that serve to restrict leukocytes to perivascular clusters and limit the infiltration of leukocytes into adjacent CNS parenchyma (Liedtke et al 1998;Voskuhl et al 2009;Toft-Hansen et al 2011). In this sense, our observation that reactive astrocytes surrounding perivascular clusters of brain macrophages showed VEGFR-3 expression suggests that VEGFR-3 may be involved in the astroglial reactions associated with critical barriers to leukocytes during EAE.…”

“…Elimination of macrophages or microglia suppresses clinical and histopathological manifestations in rodent models of MS (Brosnan et al 1981;Huitinga et al 1990;Bauer et al 1995;Polfliet et al 2002;Heppner et al 2005), and infiltrating blood-borne monocytes trigger EAE progression to the severe form of the disease (Ajami et al 2011). In addition, astrocytes, CNS-resident glial cells, play an active role in the pathogenesis of EAE and MS (Voskuhl et al 2009;Toft-Hansen et al 2011), and their activation is a prominent feature in EAE and MS (Aquino et al 1988;Liedtke et al 1998).…”

Hyaluronan synthesis is necessary for autoreactive T-cell trafficking, activation, and Th1 polarization

“…We hypothesize that through this production of HA, reactive astrocytes play a role in the infiltration of pathogenic T cells into the CNS. This is in line with recent studies that illustrate a role for astrocyte activation in mediating MS and EAE progression and the recruitment of T cells to the CNS in EAE (45,46). Considering that there are currently few therapies targeting astrocyte activation in neurological disease, our finding that 4-MU treatment reduces astrogliosis in vivo is therefore particularly pertinent to its therapeutic potential.…”

Angiogenic Factors and Cytokines in Diabetic Retinopathy

“…Furthermore, in the CNS, astrocytes contribute greatly to the control of leukocyte infiltration due to both their role in the maintenance of the endothelial blood brain barrier, and by virtue of limiting leukocyte migration across the perivascular barrier formed by astrocyte end feet, the glia limitans [113]. This is evidenced by the fact that astrocyte depletion greatly amplified monocyte infiltration in experimental autoimmune encephalomyelitis and forebrain stab injury [114,115]. IL-6 can also play a direct role in leukocyte trafficking, particularly in the infiltration of monocytes and T-cells [116,117].…”