The most common genetic risk factors for Parkinson’s disease (PD) are a set of heterozygous mutant (MT) alleles of the GBA1 gene that encodes β-glucocerebrosidase (GCase), an enzyme normally trafficked through the ER/Golgi apparatus to the lysosomal lumen. We found that half of the GCase in lysosomes from postmortem human GBA-PD brains was present on the lysosomal surface and that this mislocalization depends on a pentapeptide motif in GCase used to target cytosolic protein for degradation by chaperone-mediated autophagy (CMA). MT GCase at the lysosomal surface inhibits CMA, causing accumulation of CMA substrates including α-synuclein. Single-cell transcriptional analysis and proteomics of brains from GBA-PD patients confirmed reduced CMA activity and proteome changes comparable to those in CMA-deficient mouse brain. Loss of the MT GCase CMA motif rescued primary substantia nigra dopaminergic neurons from MT GCase–induced neuronal death. We conclude that MT GBA1 alleles block CMA function and produce α-synuclein accumulation.

Pathologic α-synuclein (α-syn) spreads from cell-to-cell, in part, through binding to the lymphocyte-activation gene 3 (Lag3). Here we report that amyloid β precursor-like protein 1 (Aplp1) interacts with Lag3 that facilitates the binding, internalization, transmission, and toxicity of pathologic α-syn. Deletion of both Aplp1 and Lag3 eliminates the loss of dopaminergic neurons and the accompanying behavioral deficits induced by α-syn preformed fibrils (PFF). Anti-Lag3 prevents the internalization of α-syn PFF by disrupting the interaction of Aplp1 and Lag3, and blocks the neurodegeneration induced by α-syn PFF in vivo. The identification of Aplp1 and the interplay with Lag3 for α-syn PFF induced pathology deepens our insight about molecular mechanisms of cell-to-cell transmission of pathologic α-syn and provides additional targets for therapeutic strategies aimed at preventing neurodegeneration in Parkinson’s disease and related α-synucleinopathies.

Glucocerebrosidase (GCase) functions as a lysosomal enzyme and its mutations are known to be related to many neurodegenerative diseases, including Gaucher’s disease (GD), Parkinson’s disease (PD), and Dementia with Lewy Bodies (DLB). However, there is little information about the role of GCase in the pathogenesis of Alzheimer’s disease (AD). Here we demonstrate that GCase protein levels and enzyme activity are significantly decreased in sporadic AD. Moreover, Aβ_1–42 oligomer treatment results in neuronal cell death that is concomitant with decreased GCase protein levels and enzyme activity, as well as impairment in lysosomal biogenesis and acidification. Importantly, overexpression of GCase promotes the lysosomal degradation of Aβ_1–42 oligomers, restores the lysosomal impairment, and protects against the toxicity in neurons treated with Aβ_1–42 oligomers. Our findings indicate that a deficiency of GCase could be involved in progression of AD pathology and suggest that augmentation of GCase activity may be a potential therapeutic option for the treatment of AD.

Mutations in the GBA1 gene are common genetic risk factors for Parkinson's disease (PD), disrupting enzymatic activity and causing lysosomal dysfunction, leading to elevated α-synuclein (α-syn) levels. While GBA1's role in synucleinopathy is well-established, recent research underscores neuroinflammation as a significant pathogenic mechanism in GBA1 deficiency. This study investigates neuroinflammation in Gba1 E326K knock-in mice, a model associated with increased PD and dementia risk. At 9 and 24 months, we assessed GBA1 protein and activity, α-synuclein pathology, neurodegeneration, motor deficits, and gliosis in the ventral midbrain and hippocampus using immunohistochemistry (IHC), Western blot (WB), and GCase assays. Additionally, primary microglia from WT and GBA1^E326K/E326K mice were treated with α-syn preformed fibrils (PFF) to study microglia activation, pro-inflammatory cytokines, reactive astrocyte formation, and neuronal death through qPCR, WB, and immunocytochemistry analyses. We also evaluated the effects of gut inoculation of α-syn PFF in Gba1 E326K mice at 7 months and striatal inoculation at 10 months, assessing motor/non-motor symptoms, α-syn pathology, neuroinflammation, gliosis, and neurodegeneration via behavioural tests, IHC, and WB assays. At 24 months, Gba1 E326K knock-in mice showed reduced GCase enzymatic activity and glucosylceramide build-up in the ventral midbrain and hippocampus. Increased pro-inflammatory cytokines and reactive astrocytes were observed in microglia and astrocytes from Gba1 E326K mice treated with pathologic α-syn PFF. Gut inoculation of α-syn PFF increased Lewy body accumulation in the hippocampal dentate gyrus, with heightened microglia and astrocyte activation and worsened non-motor symptoms. Intrastriatal α-syn preformed fibril injection induced motor deficits, reactive glial protein accumulation, and tauopathy in the prefrontal cortex and hippocampus of Gba1 E326K mice. GBA1 deficiency due to the Gba1 E326K mutation exacerbates neuroinflammation and promotes pathogenic α-synuclein transmission, intensifying disease pathology in PD models. This study enhances our understanding of how the Gba1 E326K mutation contributes to neuroinflammation and the spread of pathogenic α-syn in the brain, suggesting new therapeutic strategies for PD and related synucleinopathies.

Huntington’s disease (HD) is a neurodegenerative disorder caused by an abnormal expansion of polyglutamine repeats in the N-terminal of huntingtin. The amount of aggregate-prone protein is controlled by various mechanisms, including molecular chaperones. Vaccinia-related kinase 2 (VRK2) is known to negatively regulate chaperonin TRiC, and VRK2-facilitated degradation of TRiC increases polyQ protein aggregation, which is involved in HD. We found that VRK2 activity was negatively controlled by glycogen synthase kinase 3β (GSK3β). GSK3β directly bound to VRK2 and inhibited the catalytic activity of VRK2 in a kinase activity-independent manner. Furthermore, GSK3β increased the stability of TRiC and decreased the formation of HttQ103-GFP aggregates by inhibiting VRK2. These results indicate that GSK3β signaling may be a regulatory mechanism of HD progression and suggest targets for further therapeutic trials for HD.