The dynamics of the LPS triggered inflammatory response of murine microglia under different culture and in vivo conditions

Abstract

Overall, the inflammatory potential of lipopolysaccharide (LPS) in vitro and in vivo was investigated using different omics technologies. We investigated the hippocampal response to intracerebroventricular (i.c.v) LPS in vivo, at both the transcriptional and protein level. Here, a time course analysis of interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1) showed a sharp peak at 4 h and a return to baseline at 16 h. The expression of inflammatory mediators was not temporally correlated with expression of the microglia marker F4/80, which did not peak until 2 days after LPS injection. Of 480 inflammation-related genes present on a microarray, 29 transcripts were robustly up-regulated and 90% of them were also detected in LPS stimulated primary microglia (PM) cultures. Further in vitro to in vivo comparison showed that the counter regulation response observed in vivo was less evident in vitro, as transcript levels in PM decreased relatively little over 16 h. This apparent deficiency of homeostatic control of the innate immune response in cultures may also explain why a group of genes comprising tnf receptor associated factor-1, endothelin-1 and schlafen-1 were regulated strongly in vitro, but not in vivo. When the overall LPS-induced transcriptional response of PM was examined on a large Affymetrix chip, chemokines and cytokines constituted the most strongly regulated and largest groups. Interesting new microglia markers included interferon-induced protein with tetratricopeptide repeat (ifit), immune responsive gene-1 (irg-1) and thymidylate kinase family LPS-inducible member (tyki). The regulation of the former two was confirmed on the protein level in a proteomics study. Furthermore, conspicuous regulation of several gene clusters was identified, for instance that of genes pertaining to the extra-cellular matrix and enzymatic regulation thereof. Although most inflammatory genes induced in vitro were transferable to our in vivo model, the observed discrepancy for some genes potentially represents regulatory factors present in the central nervous system (CNS) but not in vitro.

Human UMP-CMP Kinase 2, a Novel Nucleoside Monophosphate Kinase Localized in Mitochondria

“…The number and size of mitochondria in macrophages were greatly increased after LPS induction (54). In other tissues, TYKi was also up-regulated by several inflammatory response-related cytokines (such as TNF␣, IFN␥, IL-1␤, and IFN␣) and infections of parasites (31,33,55). All these expression profiles suggest that UMP-CMPK2 is actively involved in macrophage activation and the inflammatory response.…”

Zinc Triggers Microglial Activation

“…Thus, zinc induces an attenuated and more restricted microglial activation response than that induced by LPS or TNF␣ in cell culture. The response of microglia to zinc in situ may, however, differ from that observed in culture as a result of interactions with other secreted factors (Farber and Kettenmann, 2006;Lund et al, 2006).…”

Inflammation Regulates Functional Integration of Neurons Born in Adult Brain

“…Exposure to LPS causes increased expression of interleukin-1␤ in microglia (Lund et al, 2006) and elevated levels of this cytokine in hippocampal organotypic cultures (Hellstrom et al, 2005). Similarly, intrahippocampal LPS administration gives rise to a rapid, severalfold increase of interleukin-1␤ production from microglia (Tanaka et al, 2006).…”

“…However, a major confounding factor, which would make the findings difficult to compare with the present data, is that the acute effects of LPS, which are unlikely to play a role when cells are born at 1 week after LPS injection, most probably will affect the properties of the new neurons if LPS is delivered when the neurons have already been formed. For example, LPS injection in vivo induces acute, transient increases (returning to baseline within 24 h) of several inflammatory markers such as IL-6, MCP-1, and TNF-␣ (tumor necrosis factor-␣) (Lund et al, 2006). Second, to analyze whether the alterations of excitatory and, in particular, inhibitory synaptic drive onto the new neurons are permanent.…”