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Abnormal synaptic protein expression and cell death in murine scrapie
1PRIOCAT Laboratory, Centre of Animal Health Research (CReSA), Department of Medicine and Animal Surgery, Autonomous University of Barcelona, Bellaterra, Spain.
Abstract:
Reduced expression of synaptophysin p38, synaptic-associated protein of molecular weight 25,000 (SNAP-25), syntaxin-1, synapsin-1, and alpha- and beta-synuclein, matching the distribution of spongiform degeneration, was found in the neurological phase of scrapie-infected mice. In addition, synaptophysin and SNAP-25 were accumulated in isolated neurons, mainly in the thalamus, midbrain and pons, and granular deposits of alpha- and beta-synuclein were present in the neuropil of the same areas. No modifications in the steady state levels of Bcl-2, Bax, Fas and Fas ligand were observed following infection. Yet antibodies against the c-Jun N-terminal peptide, which cross-react with products emerging after caspase-mediate proteolysis, recognize coarse granular deposits in the cytoplasm of reactive microglia. In situ end-labeling of nuclear DNA fragmentation showed positive nuclei with extreme chromatin condensation in the thalamus, pons, hippocampus and, in particular, the granular layer of the cerebellum. More importantly, expression of cleaved caspase-3, a major executioner of apoptosis, was seen in a few cells in the same regions, thus indicating that cell death by apoptosis in scrapie-infected mice is associated with caspase-3 activation. The present findings support the concept that synaptic pathology is a major substrate of neurological impairment and that caspase-3 activation may play a pivotal role in apoptosis in experimental scrapie. However, there is no correlation between decreased synaptic protein expression and caspase-3-associated apoptosis, which suggests that in addition to abnormal prion protein deposition, there may be other factors that distinctively influence synaptic vulnerability and cell death in murine scrapie.
Insights
Scrapie infection in mice reduces key synaptic proteins and activates caspase-3, indicating apoptosis contributes to neurological damage. However, synaptic loss and apoptosis are not directly correlated, suggesting complex mechanisms in scrapie pathogenesis.
Area of Science:
- Neuroscience
- Prion Diseases
- Cellular Biology
Background:
- Scrapie, a prion disease, causes spongiform degeneration in the brain.
- Synaptic dysfunction is implicated in the neurological impairment seen in scrapie.
- The role of apoptosis and specific protein changes in scrapie pathogenesis requires further investigation.
Purpose of the Study:
- To investigate changes in synaptic protein expression during scrapie infection.
- To determine the involvement of apoptosis and caspase-3 activation in scrapie-induced neurodegeneration.
- To explore the relationship between synaptic pathology and apoptotic cell death in experimental scrapie.
Main Methods:
- Western blotting and immunohistochemistry to assess protein levels and localization.
- Analysis of synaptic proteins including synaptophysin, SNAP-25, syntaxin-1, synapsin-1, and synucleins.
- Detection of apoptosis markers such as DNA fragmentation and cleaved caspase-3.
- Immunohistochemical analysis for microglial activation.
Main Results:
- Reduced expression of key synaptic proteins (synaptophysin, SNAP-25, syntaxin-1, synapsin-1) observed in scrapie-infected mice.
- Accumulation of synaptophysin and SNAP-25 in specific neuronal populations; granular deposits of alpha- and beta-synuclein found.
- Evidence of apoptosis, including DNA fragmentation and cleaved caspase-3 activation, in affected brain regions.
- Microglia showed reactivity to caspase-mediated proteolysis products.
Conclusions:
- Synaptic pathology is a significant contributor to neurological deficits in experimental scrapie.
- Caspase-3 activation plays a role in apoptotic cell death during scrapie infection.
- The lack of correlation between synaptic protein reduction and caspase-3-associated apoptosis suggests multifactorial mechanisms in scrapie neurodegeneration.