Characterisation of a novel GBA-L444P BAC transgenic mouse model of Parkinson's disease

Thesis

Parkinson’s disease (PD) is a progressive, age-related, multifactorial disorder, primarily characterised by motor symptoms associated with the loss of dopaminergic neurons of the substantia nigra and alpha-synuclein accumulation in Lewy bodies. Despite being the second most common neurodegenerative disorder worldwide, the underlying molecular mechanisms of PD remain poorly understood. An enigmatic interplay of genetic and environmental factors is thought to form the core of PD aetiology in most patients. Of the numerous genes that are implicated in PD pathology, GBA has emerged as the strongest genetic risk factor for the disease. This gene encodes for glucocerebrosidase (GCase), a lysosomal hydrolase that converts GlcCer to glucose and ceramide. Although approximately 10% of PD patients harbour a GBA variant, the mechanisms of GCase dysfunction in PD remain elusive. Indeed, the limitations of existing strategies to model GBA-associated PD in mice pose a barrier to progress in this field. To enhance our understanding of mutant GCase-related pathology in PD, our lab created the first humanised mouse model of GBA-associated PD, using BAC transgenic technology. To achieve this, the full-length human GBA-L444P gene, along with its endogenous promoter and regulatory elements, was specifically integrated into the mouse Rosa26 locus. We chose to model the L444P mutation because it is one of the most common GBA variants found in PD patients and typically predisposes to severe clinical manifestations. The overarching aim of this thesis was to characterise pathology in our GBA-L444P mice from a molecular to a behavioural level. The experiments presented herein identified that GCase activity is impaired and immature mutant GCase accumulates in our L444P mice, thereby illustrating that this model can successfully recapitulate both loss- and gain-of-function effects related to the L444P mutation. Furthermore, evoked dopamine release is diminished in the dorsolateral striatum of the L444P mice from an early age. This marks the first demonstration of striatal dopaminergic transmission deficits in a genetic mouse model of GBA-associated PD. Notably, this phenotype was not accompanied by loss of striatal dopamine content or dopaminergic neurodegeneration in the substantia nigra. Finally, our model displays subtle gait impairments in their hindlimbs but generally does not replicate the overt motor and non-motor clinical manifestations of PD in patients. Taken together, these findings highlight the usefulness of our L444P BAC transgenic mice as a resource for future research that aims to illuminate mutant GCase dysfunction in the early stages of GBA-associated PD.

Authors: Diviney, T

• DOI: 10.5287/ora-n6pwewq1n
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: mouse model; Parkinson's disease; Neurodegeneration; GBA; BAC transgenic; glucocerebrosidase
• Subjects: Neurosciences