Toll-like receptor 3 on adult human astrocytes triggers production of neuroprotective mediators.

Toll-like receptors (TLRs) are innate immunity receptors that are expressed on a wide range of cell types, including CNS glial cells. In general, TLR engagement by specific sets of microbial ligands triggers production of pro-inflammatory factors and enhances antigen-presenting cell functions. The functional roles of TLR in the CNS, however, are still poorly understood. While adult human astrocytes in culture dominantly express TLR4, they display a strikingly strong and selective induction of TLR3 when activated by pro-inflammatory cytokines, TLR3 or TLR4 agonists, or oxidative stress. Gene profiling analysis of the astrocyte response to either TLR3 or TLR4 activation revealed that TLR3, but not TLR4, induces expression of a range of neuroprotective mediators and several other molecules that regulate cellular growth, differentiation, and migration. Also, TLR3 triggered enhanced production of anti-inflammatory cytokines including interleukin-9 (IL-9), IL-10, and IL-11 and downregulation of the p40 subunit of IL-12 and IL-23. The collective TLR3-induced products were found in functional assays to inhibit astrocyte growth, promote human endothelial cell growth, and importantly, to enhance neuronal survival in organotypic human brain slice cultures. Together, our data indicate that TLR3 is induced on human astrocytes upon inflammation and when activated, mediates a comprehensive neuroprotective response rather than a polarized pro-inflammatory reaction.

Cultured human adult microglia from different donors display stable cytokine, chemokine and growth factor gene profiles but respond differently to a pro-inflammatory stimulus.

OBJECTIVES: Brain microglia are highly responsive cells in the central nervous system that exert key functions in host defense as well as in neuroprotection and regeneration. In this study the gene expression profiles for 268 cytokines, chemokines, growth factors and their receptors were examined in cultures of purified human adult microglia, using cDNA array profiling. METHODS: Microglia from 9 different donors were compared, also following challenge of such microglia with the pro-inflammatory cytokines TNF-alpha and IFN-gamma. RESULTS: A stable pattern was observed of genes abundantly expressed in the different cultures under standard conditions. Genes abundantly expressed in all microglia cultures include CCL2 (MCP-1), thymosin beta-10, migration-inhibitory factor-related protein 8 (MRP8), MRP14, corticotropin-releasing factor receptor 1 and endothelin 2. Abundant gene products novel to microglia were neuromodulin (GAP43) and Flt3 ligand. Yet, treatment with TNF-alpha and IFN-gamma led to widely different response profiles among the different cultures. CONCLUSION: These data show a surprising level of heterogeneity among human adult microglia cultures in their response to a pro-inflammatory stimulus despite the standardized methodology to examine this response.

Modulation of the cytokine network in human adult astrocytes by human herpesvirus-6A.

Human herpesvirus-6A (HHV-6A) is a common pathogen whose role in CNS disorders including multiple sclerosis remains controversial. To understand how HHV-6A could influence inflammatory pathways in the CNS, we infected cultured human adult astrocytes and examined the expression of 268 cytokines, chemokines, growth factors and their receptors by gene profiling. HHV-6 infection alone had little effect on the astrocyte gene profile but strongly altered the astrocyte response to proinflammatory cytokines. Under those conditions astrocytes express higher levels of anti-inflammatory mediators including IL-10 and IL-11, chemotactic factors, growth factors and factors controlling type I interferon production. Our data suggest that HHV-6 itself does not evoke a pro-inflammatory response in astrocytes but rather triggers immune modulatory factors in the face of inflammation.

Cytokine, chemokine and growth factor gene profiling of cultured human astrocytes after exposure to proinflammatory stimuli.

Astrocytes play key roles in CNS development, inflammation, and repair by producing a wide variety of cytokines, chemokines, and growth factors. Understanding the regulation of this network is important for a full understanding of astrocyte functioning. In this study, expression levels of 268 genes encoding cytokines, chemokines, growth factors, and their receptors were established in cultured human adult astrocytes using cDNA arrays. Also, changes in this gene profile were determined following stimulation with TNFalpha, IL-1beta, and IFNgamma. The data obtained reveal a highly reproducible pattern of gene expression not only between different astrocyte cultures from a single source, but also between astrocytes from different donors. They also identify several gene products not previously described for human astrocytes, including a.o. IL-17, CD70, CD147, and BIGH3. When stimulated with TNFalpha astrocytes respond with increased expression of several genes, notably including those encoding the chemokines CCL2 (MCP-1), CCL5 (RANTES), and CXCL8 (IL-8), growth factors including BMP-2A, BMP-3, neuromodulin (GAP43), BDNF, and G-CSF, and receptors such as the CRF receptor, the calcitonin receptor (CTR), and TKT. The response to IL-1beta involves largely the same range of genes, but responses were blunted in comparison to the TNFalpha response. Treatment with IFNgamma had no or only marginal effects on expression of any of the 268 genes analyzed. Astrocytes treated with a mixture of all three stimuli together displayed responses that are largely similar to those found in response to TNFalpha or IL-1beta alone, with only few additional synergistic effects.