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Evidence for a hyperexcitability state of staggerer mutant mice macrophages
B Kopmels1, J Mariani, N Delhaye-Bouchaud
1Laboratoire d'Immunologie, URA1156, Institut Gustave Roussy, Centre National de la Recherche Scientifique, Institut de la Santé et de la Recherche Médicale, Villejuif, France.
Abstract:
We recently reported an abnormal production of interleukin-1 (IL-1) in peripheral macrophages of several neurological mutant mice that exhibit patterns of neuronal degeneration, especially in the cerebellum. After in vitro activation by lipopolysaccharide acid (LPS), these macrophages hyperexpress IL-1 beta mRNA and hyperproduce IL-1 protein in comparison with +/+ controls. In the present study, focused on the staggerer mutant mice, we investigate if this genetic dysregulation is specific for IL-1 beta or if it reflects a generalized hyperexcitability of these macrophages. The hyperexpression of IL-1 beta mRNA in sg/sg macrophages is present whatever the duration of LPS stimulation, even for periods as short as 15 min, although it reaches a maximum after 4 h of stimulation. The hyperinducibility of sg/sg macrophages is observed even when very low doses of LPS are used (0.01 microgram/ml) and reaches its maximum for 5 micrograms/ml LPS. Synthetic molecules (muramyl dipeptides), such as N-acetylmuramyl-L-alanyl-D-isoglutamine or murabutide, known as macrophage activators, are also efficient in revealing the cytokine hyperexpression in sg/sg macrophages. In addition, hyperexpression of two other cytokines, i.e., tumor necrosis factor-alpha and IL-1 alpha mRNAs, is also detected in LPS-stimulated macrophages of mutant mice. Finally, the effect of an inhibitor of protein synthesis, cycloheximide, is similar in +/+ and sg/sg macrophages. As a whole, these data lead us to conclude that the sg/sg macrophages are in a state of general hyperexcitability when compared with +/+ ones.
Insights
Peripheral macrophages from neurological mutant mice show abnormal interleukin-1 (IL-1) production. This study reveals a generalized macrophage hyperexcitability in staggerer mutant mice, affecting multiple cytokine expressions.
Area of Science:
- Neuroimmunology
- Cellular and Molecular Immunology
Background:
- Neurological mutant mice with cerebellar degeneration exhibit abnormal peripheral macrophage production of interleukin-1 (IL-1).
- In vitro activation by lipopolysaccharide (LPS) leads to overexpression of IL-1 beta mRNA and hyperproduction of IL-1 protein in these macrophages compared to controls.
Purpose of the Study:
- To investigate if the genetic dysregulation in staggerer (sg/sg) mutant mice is specific to IL-1 beta or indicative of generalized macrophage hyperexcitability.
- To characterize the response of sg/sg macrophages to varying durations and doses of LPS stimulation, as well as other macrophage activators.
Main Methods:
- In vitro stimulation of peripheral macrophages from staggerer mutant mice (sg/sg) and wild-type controls (+/+) with lipopolysaccharide (LPS).
- Analysis of cytokine mRNA expression (IL-1 beta, tumor necrosis factor-alpha, IL-1 alpha) and protein production.
- Assessment of macrophage response to varying LPS concentrations, stimulation durations, and synthetic macrophage activators (muramyl dipeptides).
- Evaluation of the effect of cycloheximide, an inhibitor of protein synthesis.
Main Results:
- sg/sg macrophages exhibit IL-1 beta mRNA hyperexpression irrespective of LPS stimulation duration, peaking at 4 hours.
- Hyperinducibility of sg/sg macrophages is observed even with low LPS doses (0.01 microgram/ml), with maximum effect at 5 micrograms/ml.
- Synthetic macrophage activators also reveal cytokine hyperexpression in sg/sg macrophages.
- Hyperexpression of tumor necrosis factor-alpha and IL-1 alpha mRNAs is detected in LPS-stimulated sg/sg macrophages.
- The effect of cycloheximide is similar in both sg/sg and +/+ macrophages, suggesting the hyperexcitability is not due to altered protein synthesis regulation.
Conclusions:
- Peripheral macrophages from staggerer mutant mice are in a state of general hyperexcitability compared to wild-type controls.
- This generalized hyperexcitability affects the production of multiple cytokines, including IL-1 beta, IL-1 alpha, and tumor necrosis factor-alpha.
- The findings suggest a broader immune dysregulation in the neurological mutant mice, potentially contributing to neuronal degeneration.