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Transcriptional regulation of caspases in experimental pneumococcal meningitis
M von Mering1, A Wellmer, U Michel
1Dept. of Neurology, University Hosp., Goettingen, Germany.
Abstract:
Apoptosis and necrosis in brain account for neurological sequelae in survivors of bacterial meningitis. In meningitis, several mechanisms may trigger death pathways leading to activation of transcription factors regulating caspases mRNA synthesis. Therefore, we used a multiprobe RNA protection assay (RPA) to examine the expression of 9 caspase-mRNA in the course of experimental Streptococcus pneumoniae meningitis in mouse brain. Caspase-6, -7 and -11 mRNA were elevated 6 hours after infection. 12 hours after infection caspases-1, -2, -8 and -12 mRNA rose. Caspase-14 mRNA was elevated 18 h and caspase-3 mRNA 24 h after infection. In situ hybridization detected caspases-3, -8, -11 and -12 mRNA in neurons of the hippocampal formation and neocortex. Development of sepsis was paralleled by increased transcription of caspases mRNA in the spleen. In TNFalpha-deficient mice all caspases examined were less upregulated, in TNF-receptor 1/2 knockout mice caspases-1, -2, -7, -11 and -14 mRNA were increased compared to infected control animals. In caspase-1 deficient mice, caspases-11, and -12 mRNA levels did not rise in meningitis indicating the necessity of caspase-1 activating these caspases. Hippocampal formations of newborn mice incubated with heat-inactivated S. pneumoniae R6 showed upregulation of caspase-1, -3, -11 and -12 mRNA. These observations suggest a tightly regulated caspases network at the transcriptional level in addition to the known cascade at the protein level.
Insights
Bacterial meningitis triggers brain cell death via caspases. This study reveals a complex, regulated network of caspase mRNA expression in mouse brains during Streptococcus pneumoniae infection, impacting neurological outcomes.
Area of Science:
- Neuroscience
- Molecular Biology
- Immunology
Background:
- Bacterial meningitis can cause neurological damage through apoptosis and necrosis in the brain.
- Cell death pathways involve transcription factors regulating caspase synthesis.
Purpose of the Study:
- To investigate the temporal expression of nine caspase messenger RNAs (mRNAs) in the mouse brain during experimental Streptococcus pneumoniae meningitis.
- To explore the role of tumor necrosis factor-alpha (TNFα) and caspase-1 in regulating caspase mRNA expression.
Main Methods:
- Multiprobe RNA protection assay (RPA) to quantify caspase mRNA levels.
- In situ hybridization to localize caspase mRNA expression in brain tissues.
- Experiments using TNFα-deficient and TNF-receptor knockout mice, as well as caspase-1 knockout mice.
Main Results:
- Caspase mRNA levels (e.g., -6, -7, -11, -1, -2, -8, -12, -14, -3) showed dynamic, time-dependent upregulation in the brain during infection.
- Caspase-3, -8, -11, and -12 mRNAs were detected in neurons of the hippocampus and neocortex.
- TNFα deficiency reduced caspase mRNA upregulation, while TNF-receptor knockout mice showed increased levels.
- Caspase-1 deficiency prevented the upregulation of caspase-11 and -12 mRNAs, indicating caspase-1's role in their activation.
Conclusions:
- A tightly regulated transcriptional network of caspases exists in the brain during bacterial meningitis.
- Caspase-1 is essential for the activation of specific downstream caspases (-11, -12) in this context.
- These findings provide insights into the molecular mechanisms underlying neurological sequelae in meningitis survivors.