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Published on: January 3, 2025
Fas-mediated apoptotic signaling in the mouse brain following reovirus infection
Penny Clarke1, J David Beckham, J Smith Leser
1Departments of Neurology, University of Colorado Denver Health Sciences Programs, Anschutz Medical Campus, Aurora, Colorado 80045, USA. Penny.Clarke@uchsc.edu
Abstract:
Type 3 (T3) reovirus strains induce apoptotic neuronal cell death and lethal encephalitis in infected mice. T3 strain Dearing (T3D)-induced apoptosis in primary neuronal cultures occurs by a Fas-mediated mechanism and requires the activation of caspase 8. We now show that Fas mRNA is upregulated in the brains of mice infected with encephalitic reovirus T3D and T3 strain Abney (T3A) but not following infection with nonencephalitic reovirus type 1 strain Lang. Fas is upregulated in regions of the brain that are injured during infection with T3 reovirus strains and colocalizes with virus antigen in individual neurons. In contrast, levels of FasL mRNA induced by encephalitic and nonencephalitic reovirus strains do not differ significantly. Caspase 8, the initiator caspase associated with Fas-mediated apoptosis, is activated in the cortex and hippocampal regions of both T3D- and T3A-infected mice. Furthermore, Bid cleavage and the activation of caspase 9 in the brains of T3D-infected mice suggest that the caspase 8-dependent activation of mitochondrial apoptotic signaling contributes to virus-induced apoptosis. We have previously shown that the inhibition of c-Jun N-terminal kinase (JNK) signaling blocks T3D-induced apoptosis and improves the outcome of virus-induced encephalitis. We now show that the reovirus-induced upregulation of Fas requires JNK signaling, thereby providing a link between reovirus-induced death receptor signaling and mitogen-activated protein kinase pathways and a potential mechanism for the therapeutic action of JNK inhibition.
Insights
Type 3 reovirus encephalitis upregulates Fas mRNA in injured brain regions, activating caspase 8 and mitochondrial pathways. This Fas upregulation requires c-Jun N-terminal kinase (JNK) signaling, offering a therapeutic target for reovirus-induced neuronal death.
Area of Science:
- Neurovirology
- Molecular Biology
- Immunology
Background:
- Type 3 (T3) reovirus strains cause lethal encephalitis and neuronal apoptosis in mice.
- T3-induced apoptosis involves Fas-mediated mechanisms and caspase 8 activation.
- Previous studies linked c-Jun N-terminal kinase (JNK) signaling inhibition to reduced apoptosis and improved encephalitis outcomes.
Purpose of the Study:
- To investigate the role of Fas and its signaling pathways in T3 reovirus-induced encephalitis.
- To determine if Fas upregulation occurs in infected brain tissues and its correlation with injury.
- To elucidate the connection between JNK signaling and reovirus-induced death receptor pathways.
Main Methods:
- Quantitative analysis of Fas and FasL mRNA levels in mouse brains after infection with different reovirus strains.
- Immunohistochemical co-localization of Fas and viral antigens in infected neuronal cells.
- Assessment of caspase 8 and caspase 9 activation, and Bid cleavage in infected brain regions.
- Evaluation of the necessity of JNK signaling for Fas upregulation using specific inhibitors.
Main Results:
- Fas mRNA was significantly upregulated in the brains of mice infected with encephalitic T3 reovirus strains (T3D and T3A), particularly in injured areas and co-localized with viral antigens.
- No significant difference in FasL mRNA levels was observed between encephalitic and non-encephalitic reovirus infections.
- Caspase 8 was activated in the cortex and hippocampus of T3D- and T3A-infected mice.
- Bid cleavage and caspase 9 activation indicated the involvement of mitochondrial apoptotic signaling.
- Reovirus-induced Fas upregulation was dependent on JNK signaling.
Conclusions:
- T3 reovirus encephalitis is associated with increased Fas expression in injured neurons, contributing to apoptotic neuronal cell death.
- The activation of caspase 8 and the mitochondrial pathway are critical components of T3 reovirus-induced apoptosis.
- JNK signaling is essential for the reovirus-induced upregulation of Fas, establishing a link between JNK and death receptor pathways.
- Targeting JNK signaling presents a potential therapeutic strategy for mitigating reovirus-induced encephalitis.
