Reduced SOD2 expression does not influence prion disease course or pathology in mice

Prion diseases are progressive, neurodegenerative diseases affecting humans and animals. Also known as the transmissible spongiform encephalopathies, for the hallmark spongiform change seen in the brain, these diseases manifest increased oxidative damage early in disease and changes in antioxidant enzymes in terminal brain tissue. Superoxide dismutase 2 (SOD2) is an antioxidant enzyme that is critical for life. SOD2 knock-out mice can only be kept alive for several weeks post-birth and only with antioxidant therapy. However, this results in the development of a spongiform encephalopathy. Consequently, we hypothesized that reduced levels of SOD2 may accelerate prion disease progression and play a critical role in the formation of spongiform change. Using SOD2 heterozygous knock-out and litter mate wild-type controls, we examined neuronal long-term potentiation, disease duration, pathology, and degree of spongiform change in mice infected with three strains of mouse adapted scrapie. No influence of the reduced SOD2 expression was observed in any parameter measured for any strain. We conclude that changes relating to SOD2 during prion disease are most likely secondary to the disease processes causing toxicity and do not influence the development of spongiform pathology.

Prion disease

Prion diseases (also known as transmissible spongiform encephalopathies (TSEs)) affect animals and humans, although only the human diseases will be discussed in this chapter. Despite TSEs having somewhat disparate causes and effects, there are unifying features: TSEs are brain diseases with neurodegenerative pathology, which is typically associated with spongiform change, and, most characteristically, there is tissue deposition of an abnormal structural form of the prion protein. Some of the TSEs are naturally acquired infections and, while others are not, they are potentially transmissible in certain circumstances.

Fatal bromethalin intoxication in 3 cats and 2 dogs with minimal or no histologic central nervous system spongiform change

Use of the neurotoxic rodenticide bromethalin has steadily increased since 2011, resulting in an increased incidence of bromethalin intoxications in pets. Presumptive diagnosis of bromethalin toxicosis relies on history of possible rodenticide exposure coupled with compatible neurologic signs or sudden death, and postmortem examination findings that eliminate other causes of death. Diagnosis is confirmed by detecting the metabolite desmethylbromethalin (DMB) in tissues. In experimental models, spongiform change in white matter of the central nervous system (CNS) is the hallmark histologic feature of bromethalin poisoning. We describe fatal bromethalin intoxication in 3 cats and 2 dogs with equivocal or no CNS white matter spongiform change, illustrating that the lesions described in models can be absent in clinical cases of bromethalin intoxication. Cases with history and clinical signs compatible with bromethalin intoxication warrant tissue analysis for DMB even when CNS lesions are not evident.

Laminar Distribution of the Pathological Changes in Sporadic and Variant Creutzfeldt-Jakob Disease

The laminar distributions of the pathological changes in the cerebral cortex were compared in the prion diseases sporadic Creutzfeldt-Jakob disease (sCJD) and variant CJD (vCJD). First, in some cortical regions, the vacuolation (“spongiform change”) was more generally distributed across the cortex in sCJD. Second, there was greater neuronal loss in the upper cortex in vCJD and in the lower cortex in sCJD. Third, the “diffuse” and “florid” prion protein () deposits were more frequently distributed in the upper cortex in vCJD and the “synaptic” deposits in the lower cortex in sCJD. Fourth, there was a significant gliosis mainly affecting the lower cortex of both disorders. The data suggest that the pattern of cortical degeneration is different in sCJD and vCJD which may reflect differences in aetiology and the subsequent spread of prion pathology within the brain.