Lee, Chiao-Yin; (2025) Investigating the interactions between GBA1 and LRRK2 in Parkinson disease. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Variants in the GBA1 gene, which encodes the lysosomal enzyme glucocerebrosidase (GCase), result in reduced GCase activity and increases risk of developing Parkinson disease (PD). Pathogenic mutations (e.g. G2019S) in LRRK2, which encodes leucine rich repeat kinase 2, causes late onset autosomal dominant PD. Changes in both GCase and LRRK2 kinase activities have also been reported in idiopathic PD cases. Recent literature has highlighted interplay between GBA1 and LRRK2 in dopaminergic neurons and PD mouse models, although is it unclear whether increased LRRK2 kinsae activity increases or decreases GCase activity. G2019S LRRK2 has been reported to decrease GCase activity through phosphorylation of the Rab10 GTPase. Therefore, this thesis focusses on the mechanisms in which LRRK2 kinase affects N370S GCase protein and activity levels, in particular changes in Rab10/Rab8A phosphorylation, the lysosomal pathway and the unfolded protein response. This thesis will also explore whether reduced GCase activity through the N370S GBA1 mutation or treatment of a GCase inhibitor may modulate LRRK2 expression and kinase. SH-SY5Y cells overexpressing WT or G2019S LRRK2, mouse models (primary cortical astrocytes and brain homogenates) and hiPSC-derived astrocytes heterozygous for N370S or G2019S, as well as compound mutants and healthy controls, are used. Techniques include Western blot assays to measure changes in GCase protein, autophagy and ER stress markers, qPCR for astrocyte characterisation and immunocytochemistry to measure changes in lipid droplets. Chloroquine to increase LRRK2 kinase activity are used to detect changes in phosphorylation of its substrates RAB10 and RAB8A between genotypes. Results show that G2019S LRRK2 rescues N370S GCase protein and activity in human astrocytes and GCase activity in the midbrain and forebrain of mice. Additional understanding of the mechanisms of action of LRRK2 and GCase will allow for further development of targeted drug therapies for PD.

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