Abnormal synaptic protein expression and cell death in murine scrapie

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.

Proteomics Analysis of Amyloid and Nonamyloid Prion Disease Phenotypes Reveals Both Common and Divergent Mechanisms of Neuropathogenesis

“…However, synaptic degeneration has been observed in multiple mouse prion disease models, 73,74 including the RML strain used for the current studies. 75 Furthermore, a decrease in SNAP25 and syntaxin has been reported in RML-infected wild-type mice. 20,75,76 Thus, contrary to the present data, synaptic transport can also be impaired in nonamyloid forms of prion disease.…”

“…75 Furthermore, a decrease in SNAP25 and syntaxin has been reported in RML-infected wild-type mice. 20,75,76 Thus, contrary to the present data, synaptic transport can also be impaired in nonamyloid forms of prion disease. The reason for this discrepancy is not clear but it is possible that decreased expression of SNARE proteins in the amyloid phenotype is the result of changes in synaptic vesicle fusion not linked to SNARE-mediated neurodegeneration, perhaps because of the lack of membrane anchored PrP C in these transgenic mice.…”

“…This hypothesis is consistent with the lack of significant gray matter spongiosis in the amyloid disease phenotype 9−11 as well as studies showing no correlation between decreased SNAP25 and apoptosis in RML infected mice. 75 …”

Activation of Pro-survival CaMK4β/CREB and Pro-death MST1 signaling at early and late times during a mouse model of prion disease

“…The levels of upstream kinases DLK, MKK7, and JNK2 were also lower in scrapie-infected mice at 130 dpi, albeit only in the brainstem-cerebellum (Figure  7). The cerebellum (in the brainstem-cerebellum) may contain ~50% of all neurons in an adult mouse brain [109] and loses the most neurons in RML-infected mice, as indicated by nuclear DNA fragmentation [96]. The changes in the total levels of proteins involved in the MST1 signaling pathway in each brain region may reflect the differences in the number of affected neurons in each brain region.…”

Unraveling the neuroprotective mechanisms of PrPCin excitotoxicity

“…70 Again parallels are found between bench experiments and CJD patients, since defective synaptic machinery in infected brains (mainly (SNAP-25), syntaxin-1 and synapsin-1) was demonstrated several years ago. 27,71 However, whether these changes affect the symptoms and the evolution of the illness requires additional study. In this regard, recent approaches analyzing gene expression changes in different rodent models lacking PrP C , 18,72 and the comparison with CJD patients and prion infected animals [73][74][75][76] main problem so far resides in our lack of knowledge of the functional relevance of these interactions.…”