Using transgenic mouse lines and viral vectors for studying Huntingtin propagation and HD-like pathology in in vivo and in vitro models.

Huntington’s disease (HD) is a neurodegenerative disorder characterized by a triad of motor, cognitive, and psychiatric symptoms. Responsible for the pathology is the abnormal expansion of a CAG repeat (>35) in the Huntingtin gene (HTT), leading to the misfolding of the protein (mHTT) associated with the pathology. Although HTT is expressed throughout the brain, in HD the striatal medium spiny neurons and the corticostriatal pathway are the most vulnerable to degeneration. HD shares some disease-specific hallmarks with other neurodegenerative protein misfolding disorders (PMD), like Alzheimer’s-, Parkinson’s-, and Prions disease: i. The pathology is initially observed in a disease-specific brain region before progressively spreading throughout the brain following the neuronal connectivity pattern; ii. Accumulating data reveal that in PMDs, the misfolded protein can behave in a prion-like manner by spreading transneuronally and causing the misfolding of other healthy protein counterparts.
The aim of this dissertation is to set the methodological foundations for the implementation of in vitro and in vivo approaches in order to study whether the trans-neuronal spreading of mHTT is causally linked to the onset and progression of HD-related pathology in mice and to deepen the understanding of the role that neuronal connectivity plays in mHTT spreading. To this end, we use and optimize the in vitro system of mouse organotypic brain slice cultures (OTBS) and in vivo mouse models to evaluate the spatiotemporal manifestation of HD-related pathology upon mHTT spreading across the corticostriatal pathway. Το induce the expression of the mHTT we use custom-made adeno-associated viruses (AAVs) that were delivered in the primary motor cortex of OTBS and adult mice.
Two main findings emerged from our analysis: that in both the in vitro and in vivo systems, the viral vectors and HTT sequences used, could induce the expression of the mHTT variants, the aggregation of the protein and the manifestation of HD-like pathological traits; and that protein could spreading across the brain circuit. However, additional experimentation needs to be performed for the assessment of the mHTT specific spreading. Thereafter, the in vitro and in vivo systems along with the viral vectors selected, could be further used to understand whether the transneuronal protein spreading of mHTT could induce the onset of HD and unravel the underlying mechanism. Taking into consideration the common hallmarks of HD with other PMDs, the methodology and the obtained data could also be relevant for these diseases as well.