LRRK2 kinase activity regulates GCase level and enzymatic activity differently depending on cell type in Parkinson’s disease

Abstract

Leucine-rich repeat kinase 2 (LRRK2) is a kinase involved in different cellular functions, including autophagy, endolysosomal pathways, and immune function. Mutations in LRRK2 cause autosomal-dominant forms of Parkinson’s disease (PD). Heterozygous mutations in GBA1, the gene encoding the lysosomal enzyme glucocerebrosidase (GCase), are the most common genetic risk factors for PD. Moreover, GCase function is altered in idiopathic PD and in other genetic forms of the disease. Recent work suggests that LRRK2 kinase activity can regulate GCase function. However, both a positive and a negative correlation have been described. To gain insights into the impact of LRRK2 on GCase, we performed a comprehensive analysis of GCase levels and activity in complementary LRRK2 models, including (i) LRRK2 G2019S knock in (GSKI) mice, (ii) peripheral blood mononuclear cell (PBMCs), plasma, and fibroblasts from PD patients carrying LRRK2 G2019S mutation, (iii) patient iPSCs-derived neurons; (iv) endogenous and overexpressed cell models. In some of these models we found a positive correlation between the activities of LRRK2 and GCase, which was further confirmed in cell lines with genetic and pharmacological manipulation of LRRK2 kinase activity. GCase protein level is reduced in GSKI brain tissues and in G2019S iPSCs-derived neurons, but increased in fibroblasts and PBMCs from patients, suggesting cell-type-specific effects. Overall, our study indicates that LRRK2 kinase activity affects both the levels and the catalytic activity of GCase in a cell-type-specific manner, with important implications in the context of therapeutic application of LRRK2 inhibitors in GBA1-linked and idiopathic PD.

LRRK2 and Lipid Pathways: Implications for Parkinson’s Disease

“…Intriguingly, recent studies [ 13 , 52 , 53 , 54 , 55 ] have pointed to a role for LRRK2 in regulating the lysosomal enzyme β-glucocerebrosidase (GCase), encoded by another common PD risk gene, GBA1 [ 56 , 57 , 58 , 59 ]. GCase catabolizes the sphingolipids glucosylceramide and glucosylsphingosine into glucose and ceramide and glucose and sphingosine, respectively [ 60 ].…”

“…Perhaps as compensation for reduced GCase protein levels, LRRK2 -/- mice brains, including striata, display significantly increased GCase activity compared to WT [ 13 , 52 ]. GCase activity from LRRK2 G2019S knock-in mice midbrain is also significantly higher compared to WT [ 55 ]. In human LRRK2 G2019S mutation carrier PBMCs [ 55 ] and fibroblasts [ 55 ], significantly increased GCase activity has been found compared to non-carriers, whereas a significant increase [ 53 ] and no change [ 63 ] in GCase activity have been reported in dried blood spots.…”

“…GCase activity from LRRK2 G2019S knock-in mice midbrain is also significantly higher compared to WT [ 55 ]. In human LRRK2 G2019S mutation carrier PBMCs [ 55 ] and fibroblasts [ 55 ], significantly increased GCase activity has been found compared to non-carriers, whereas a significant increase [ 53 ] and no change [ 63 ] in GCase activity have been reported in dried blood spots. A further study has indicated that GCase activity from dried blood spot samples decreases over time, which may explain reported inconsistencies [ 64 ].…”

“…In iPSC-derived dopaminergic neurons from LRRK2 mutation carriers ( n = 2 G2019S and R1441C, n = 1 R1441G), significantly decreased GCase activity compared to controls ( n = 2) has been reported, which could be restored upon treatment with a LRRK2 inhibitor [ 54 ]. However, another study using a different enzyme activity assay found significantly increased activity in dopaminergic neurons from LRRK2 G2019S mutation carriers ( n = 2) compared to controls ( n = 4) [ 55 ]. It has been suggested that the variability in the GCase results reported may be due to different GCase substrates utilized to measure enzyme activity, as commercial GCase substrates differ in their specificity for lysosomal and cytoplasmic GCase and sensitivity to other endogenous factors [ 55 , 65 ].…”

“…However, another study using a different enzyme activity assay found significantly increased activity in dopaminergic neurons from LRRK2 G2019S mutation carriers ( n = 2) compared to controls ( n = 4) [ 55 ]. It has been suggested that the variability in the GCase results reported may be due to different GCase substrates utilized to measure enzyme activity, as commercial GCase substrates differ in their specificity for lysosomal and cytoplasmic GCase and sensitivity to other endogenous factors [ 55 , 65 ]. In addition, GCase activity may be affected in a tissue-specific manner [ 55 ].…”