Dual Role of Inflammatory Stimuli in Activation-induced Cell Death of Mouse Microglial Cells

Abstract

We have previously shown that mouse microglial cells undergo apoptosis upon inflammatory activation and that nitric oxide (NO) is the major autocrine mediator in this process (Lee, P., Lee, J., Kim, S., Yagita, H., Lee, M. S., Kim, S. Y., Kim, H., and Suk, K. (2001) Brain Res. 892, 380 -385). Here, we present evidence that interferon regulatory factor-1 (IRF-1) and caspase-11 are the essential molecules in activation-induced cell death of microglial cells. The apoptogenic action of inflammatory stimuli such as lipopolysaccharide (LPS) and interferon-␥ (IFN␥) was mediated through the induction of IRF-1 and caspase-11 expression in two separate events. Although IRF-1 was required for NO synthesis, caspase-11 induction was necessary for NO-independent apoptotic pathway. Microglial cells from IRF-1-deficient mice showed markedly decreased NO production, and they were partially resistant to apoptosis in response to LPS/IFN␥ but were sensitive to NO donor exposure. LPS/IFN␥ treatment resulted in the induction of caspase-11 followed by activation of caspase-11, -1, and -3. Inactivation of caspase-11 by the transfection of dominant-negative mutant or treatment with the caspase inhibitors rendered microglial cells partially resistant to LPS/IFN␥-induced apoptosis. Inhibition of both NO synthesis and caspase-11 completely blocked LPS/IFN␥-induced cytotoxicity. These results indicated that LPS/ IFN␥ not only induced the production of cytotoxic NO through IRF-1 but also initiated the NO-independent apoptotic pathway through the induction of caspase-11 expression.

Characterization of LPS and interferon-γ triggered activation-induced cell death in N9 and primary microglial cells: induction of the mitochondrial gateway by nitric oxide

“…N9 and rat primary microglial cells were treated with the NO donor S-nitroso-N-acetyl-penicillamine (SNAP). As expected from previous studies, 3,4 this treatment caused cell death in both microglial cell systems. Death was accompanied by Bax and Bak activation (NT exposure (Supplementary data, Figure S6) and activation of caspase-3 (Figure 1f)), suggesting that NO induces microglial apoptosis via the mitochondrial pathway.…”

“…Studies have shown that AICD induced by lipopolysaccharide (LPS) and interferon (IFN)g occurs via two pathways, one of them mediated via NO and the other via caspase-11. 3,4 Many aspects of this process, however, remain to be elucidated. We investigated AICD induced by LPS and IFNg in mouse N9 microglia 5 and rat primary microglia.…”

“…Collectively, these results demonstrated that NO and caspases play an important part in AICD in N9 microglia and that N9 cells exhibit the typical features of microglial AICD observed in other microglia. 3,4,6 Next, we identified the caspases that are activated in LPS/ IFNg-treated microglia. Treatment of N9 cells with LPS/IFNg induced activation of caspase -3 and caspase-7.…”

“…Mice lacking akt1 exhibit impaired growth with a reduction in body weight of 30% and a proportional decrease in the sizes of all major organs, identifying AKT1 as a key regulator of organismal growth. 3,4 Thymocytes and mouse embryonic fibroblasts (MEF) derived from these animals were reported to display an increased susceptibility to spontaneous and stress-induced apoptosis. 4 By contrast, akt2-deficient mice exhibit insulin resistance and a diabetic phenotype but are only mildly growth retarded.…”

Microglia expressing interleukin‐13 undergo cell death and contribute to neuronal survival in vivo

“…In this regard, the current study clearly demonstrates that following intracortical injection with LPS, there is a significant increase in the levels of IL-13 in the cortex in vivo and that IL-13 is expressed exclusively in activated microglia, but not in astrocytes or in neurons. In marked contrast, expression of IL-13 was not detected even in human pure microglia cultures or in human microglial cell lines in the absence or presence of treatment with LPS (Nagai et al, 2001;Lee et al, 2001). These observations raise the possibility that microglia in culture may not have interactions with other cells and/or the conditions necessary for IL-13 expression when compared to the microglia that exist in vivo.…”