Prion pathology in the brainstem: clinical target areas in prion disease

Prion diseases are fatal transmissible neurodegenerative disorders characterized by spongiform changes, neuronal loss, reactive astrocytosis, and deposition of disease associated prion protein (PrP). Our aim was to investigate "clinical target areas" for prion disease, responsible for disease onset, progression, and the clinical phenotype, using PrP overexpressing MloxP and PrP depleted NFH-Cre/MloxP transgenic mouse lines. Upon infection with different prion strains NFH-Cre/MloxP mice have significantly longer survival than MloxP mice (first set of experiments: Me7, ~29 weeks vs. ~17 weeks; Mouse-adapted BSE , ~33 weeks vs. ~20 weeks; second set of experiments: RML, ~35 weeks vs.12 weeks; Me7 ~29 weeks, vs. ~17 weeks; MRC2 ~31 weeks vs. ~22 week. As we found that the first pathological changes in the brains of Me7 and Mouse–adapted BSE infected mice are localized in the brainstem, and clinical signs of prion disease point to brainstem failure, we quantitatively scored spongiosis, abnormal PrP accumulation and astrogliosis at early and late stage of disease in specific brainstem nuclei of RML and Me7 infected MloxP and NFH-Cre/MloxP mice. The first target areas showing abnormal PrP accumulation and gliosis in both prion infections are the locus coeruleus (LC), the nucleus of the solitary tract (NTS) and the pre-Bötzinger complex (PBC). We then studied the pathology progression, scoring prion pathology in these and other brainstem nuclei of infected MloxP and NFH-Cre/MloxP mice in the course of the disease. We show that neural degeneration in the LC, NTS, and PBC correlate with clinical signs characteristic of terminally ill mice. We therefore propose that these areas are potential clinical target areas of prion disease. We also studied the spatial and temporal characteristics of Cre-mediated recombination. With immunohistochemistry in reporter mice, we estimated that in the LC, NTS, and PBC, Cre-mediated recombination is 60% or lower, and this can explain why mice proceed to terminal stage of the disease. In NFH-Cre/MloxP mice we found that recombination is a progressive event and in the hippocampus it is complete by 5 weeks post-natally, differently from previous data. Finally, we produced anti PrP RNAi –encoding lentivirus which could be used as focal therapy in the clinical target areas we propose