From Lysosomal Storage Disorders to Parkinson's Disease - Challenges and Opportunities

Precision Medicine in Parkinson's Disease

The continually accumulating knowledge of Parkinson's disease (PD) genetics presents potential disease modification opportunities through targeting specific genes and associated metabolic pathways. Glucosylceramidase beta 1-associated PD and leucine-rich repeat kinase 2-associated PD are attractive drug targets, since their respective mutations significantly increase PD risk and, at the same time, are relatively prevalent in the PD population. Here, we review clinical trials and preclinical efforts whose mechanisms target genetic forms of PD, focusing on these 2 genes and their metabolic pathways. Such therapies could also potentially modify sporadic (ie, without a clear genetic risk factor) PD.

Comprehensive analysis of SLC17A5 variants in large European cohorts reveals no association with Parkinson's disease risk

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder characterized by dopaminergic neuron loss and α-synuclein aggregation. Aging is the primary risk factor, with both rare and common genetic variants playing a role. Previous studies have implicated lysosomal storage disorder (LSD)-related genes, including SLC17A5, in PD susceptibility.

OBJECTIVE

This study aimed to investigate the association of SLC17A5 variants, including rare and common variants and the FSASD-associated p.Arg39Cys missense variant, with PD risk in large European ancestry cohorts.

METHODS

Rare variant burden analyses were performed at minor allele frequency (MAF) thresholds of ≤1 % and ≤0.1 % in 7,184 PD cases and 51,650 controls using whole-genome and whole-exome sequencing data. Association testing of the p.Arg39Cys variant was conducted across five cohorts, encompassing both Finnish and non-Finnish Europeans. Common variant associations were examined using summary statistics from the largest European GWAS of PD.

RESULTS

No significant association was observed between rare SLC17A5 variants and PD at either MAF threshold. The p.Arg39Cys variant, though enriched in Finnish Europeans, showed no significant association with PD across several cohorts. Similarly, common SLC17A5 variants (MAF ≥1%) were not associated with PD risk.

CONCLUSION

Our findings do not support a role for SLC17A5 variants in PD susceptibility. While lysosomal dysfunction is central to PD pathogenesis, its contribution appears pathway-specific, with SLC17A5 unlikely to influence risk. Larger, multiethnic studies and functional analyses are needed to further investigate sialic acid metabolism in PD and related disorders.

Genome-Wide Association Study of Glucocerebrosidase Activity Modifiers

One of the most common genetic risk factors for Parkinson's disease (PD) is variants in GBA1, which encodes the lysosomal enzyme glucocerebrosidase (GCase). GCase deficiency has been associated with an increased PD risk, but not all individuals with low GCase activity are carriers of GBA1 mutations, suggesting other factors may be acting as modifiers. We aimed to discover common variants associated with GCase activity, as well as replicate previously reported associations, by performing a genome-wide association study using two independent cohorts: a Columbia University cohort consisting of 697 PD cases and 347 controls and the Parkinson's Progression Markers Initiative (PPMI) cohort consisting of 357 PD cases and 163 controls. As expected, GBA1 variants have the strongest association with decreased activity, led by N370S (beta =  - 4.36, se = 0.32, p = 5.05e - 43). We also identify a novel association in the GAA locus (encoding for acid alpha-glucosidase, beta =  - 0.96, se = 0.17, p = 5.23e - 09) that may be the result of an interaction between GCase and acid alpha-glucosidase based on various interaction analyses. Lastly, we show that several PD-risk loci are potentially associated with GCase activity. Further research will be needed to replicate and validate our findings and to uncover the functional connection between acid alpha-glucosidase and GCase.

Purifying and profiling lysosomes to expand understanding of lysosomal dysfunction-associated diseases

Lysosome storage dysfunction plays a central role in numerous human diseases, but a lack of appropriate tools has hindered lysosomal content profiling in clinical settings. In this issue of the JCI, Saarela et al. introduce a method called tagless LysoIP that enabled rapid isolation of intact lysosomes from blood and brain cells via immunoprecipitation of the endogenous protein TMEM192. Applied to the neurodegenerative lysosomal storage disorder known as Batten disease (caused by mutations in the CLN3 gene), tagless LysoIP revealed substantial accumulation of glycerophosphodiesters (GPDs) in patient lysosomes. These findings highlight the role of CLN3 in GPD clearance and present an innovative method that will enable biomarker discovery and therapeutic advancement in lysosomal diseases.

Mitochondrial DNA leakage: underlying mechanisms and therapeutic implications in neurological disorders

Mitochondrial dysfunction is a pivotal instigator of neuroinflammation, with mitochondrial DNA (mtDNA) leakage as a critical intermediary. This review delineates the intricate pathways leading to mtDNA release, which include membrane permeabilization, vesicular trafficking, disruption of homeostatic regulation, and abnormalities in mitochondrial dynamics. The escaped mtDNA activates cytosolic DNA sensors, especially cyclic gmp-amp synthase (cGAS) signalling and inflammasome, initiating neuroinflammatory cascades via pathways, exacerbating a spectrum of neurological pathologies. The therapeutic promise of targeting mtDNA leakage is discussed in detail, underscoring the necessity for a multifaceted strategy that encompasses the preservation of mtDNA homeostasis, prevention of membrane leakage, reestablishment of mitochondrial dynamics, and inhibition the activation of cytosolic DNA sensors. Advancing our understanding of the complex interplay between mtDNA leakage and neuroinflammation is imperative for developing precision therapeutic interventions for neurological disorders.

Parkinson's Disease Polygenic Risk Score and Neurological Involvement in Carriers of the FMR1 Premutation Allele: A Case for Genetic Modifier

BACKGROUND

Premutation alleles of the FMR1 X-linked gene containing CGG repeat expansions ranging from 55 to 200 are associated with diverse late-onset neurological involvements, including most severe disorder termed Fragile X-associated Tremor/Ataxia Syndrome (FXTAS). It is intriguing that at least one-third of male, and a much lower than predicted from the X-linkage proportion of female carriers are free of this syndrome. This suggests the existence of secondary genetic factors modifying the risk of neurological involvements in these carriers. Considering the occasional presence of parkinsonian features in FXTAS, we explored the possibility that the Parkinson's Disease Polygenic Risk Score (PD PRS) is related to the occurrence of FXTAS or less severe neurological involvements, in premutation carriers.

METHODS

The Genome-wide SNP genotyping and clinical data on neurological status were obtained from 250 unrelated affected and non-affected male and female adult carriers of the premutation. The medians for the Parkinson's Disease Polygenic Risk Score (PD PRS) were compared between the groups of asymptomatic and neurologically affected carriers, and the association of PD PRS with neurological involvement in context with the other known risk factors was explored by fitting univariate and multiple logistic regression models.

RESULTS

There was a significant difference between the medians from the asymptomatic versus neurologically affected (FXTAS+) groups (p = 0.009). The FXTAS+ status was significantly associated with age at testing (p < 0.001), gender (p = 0.026), and with PD PRS (p = 0.021). The contribution of PD PRS remained significant after adjusting for age and gender (p = 0.044).

CONCLUSIONS

We have obtained the first evidence for the relationship between PD PRS and the risk of FXTAS or lesser neurological involvements in the FMR1 premutation carriers. This suggests the role of Parkinson's disease polygenic variants as genetic modifiers of the risk of late onset neurological changes in these carriers.

Stage-dependent phosphoproteome remodeling of Parkinson's disease blood cells

The complexity and heterogeneity of PD necessitate advanced diagnostic and prognostic tools to elucidate its molecular mechanisms accurately. In this study, we addressed this challenge by conducting a pilot phospho-proteomic analysis of peripheral blood mononuclear cells (PBMCs) from idiopathic PD patients at varying disease stages to delineate the functional alterations occurring in these cells throughout the disease course and identify key molecules and pathways contributing to PD progression. By integrating clinical data with phospho-proteomic profiles across various PD stages, we identify potential stage-specific molecular signatures indicative of disease progression. This integrative approach allows for the discernment of distinct disease states and enhances our understanding of PD heterogeneity.

Clinical, mechanistic, biomarker, and therapeutic advances in GBA1-associated Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. The development of PD is closely linked to genetic and environmental factors, with GBA1 variants being the most common genetic risk. Mutations in the GBA1 gene lead to reduced activity of the coded enzyme, glucocerebrosidase, which mediates the development of PD by affecting lipid metabolism (especially sphingolipids), lysosomal autophagy, endoplasmic reticulum, as well as mitochondrial and other cellular functions. Clinically, PD with GBA1 mutations (GBA1-PD) is characterized by particular features regarding the progression of symptom severity. On the therapeutic side, the discovery of the relationship between GBA1 variants and PD offers an opportunity for targeted therapeutic interventions. In this review, we explore the genotypic and phenotypic correlations, etiologic mechanisms, biomarkers, and therapeutic approaches of GBA1-PD and summarize the current state of research and its challenges.

Late-onset Krabbe disease presenting as spastic paraplegia - implications of GCase and CTSB/D

OBJECTIVE

Krabbe disease (KD) is a multisystem neurodegenerative disorder with severe disability and premature death, mostly with an infancy/childhood onset. In rare cases of late-onset phenotypes, symptoms are often milder and difficult to diagnose. We here present a translational approach combining diagnostic and biochemical analyses of a male patient with a progressive gait disorder starting at the age of 44 years, with a final diagnosis of late-onset KD (LOKD).

METHODS

Additionally to cerebral MRI, protein structural analyses of the β-galactocerebrosidase protein (GALC) were performed. Moreover, expression, lysosomal localization, and activities of β-glucocerebrosidase (GCase), cathepsin B (CTSB), and cathepsin D (CTSD) were analyzed in leukocytes, fibroblasts, and lysosomes of fibroblasts.

RESULTS

Exome sequencing revealed biallelic likely pathogenic variants: GALC exons 11-17: 33 kb deletion; exon 4: missense variant (c.334A>G, p.Thr112Ala). We detected a reduced GALC activity in leukocytes and fibroblasts. While histological KD phenotypes were absent in fibroblasts, they showed a significantly decreased activities of GCase, CTSB, and CTSD in lysosomal fractions, while expression levels were unaffected.

INTERPRETATION

The presented LOKD case underlines the age-dependent appearance of a mildly pathogenic GALC variant and its interplay with other lysosomal proteins. As GALC malfunction results in reduced ceramide levels, we assume this to be causative for the here described decrease in CTSB and CTSD activity, potentially leading to diminished GCase activity. Hence, we emphasize the importance of a functional interplay between the lysosomal enzymes GALC, CTSB, CTSD, and GCase, as well as between their substrates, and propose their conjoined contribution in KD pathology.

Genome-wide association study of glucocerebrosidase activity modifiers

One of the most common genetic risk factors for Parkinson's disease (PD) are variants in GBA1, which encodes the lysosomal enzyme glucocerebrosidase (GCase). GCase deficiency has been associated with an increased PD risk, but not all individuals with low GCase activity are carriers of GBA1 mutations, suggesting other factors may be acting as modifiers. We aimed to discover common variants associated with GCase activity, as well as replicate previously reported associations, by performing a genome-wide association study using two independent cohorts: a Columbia University cohort consisting of 697 PD cases and 347 controls and the Parkinson's Progression Markers Initiative (PPMI) cohort consisting of 357 PD cases and 163 controls. As expected, GBA1 variants have the strongest association with decreased activity, led by p.N370S (beta = -4.36, se = 0.32, p = 5.05e-43). We also identify a novel association in the GAA locus (encoding for acid alpha-glucosidase, beta = -0.96, se = 0.17, p = 5.23e-09) that may be the result of an interaction between GCase and acid alpha-glucosidase based on various interaction analyses. Lastly, we show that several PD-risk loci are potentially associated with GCase activity. Further research will be needed to replicate and validate our findings and to uncover the functional connection between acid alpha-glucosidase and GCase.

Targeting the organelle for radiosensitization in cancer radiotherapy

Radiotherapy is a well-established cytotoxic therapy for local solid cancers, utilizing high-energy ionizing radiation to destroy cancer cells. However, this method has several limitations, including low radiation energy deposition, severe damage to surrounding normal cells, and high tumor resistance to radiation. Among various radiotherapy methods, boron neutron capture therapy (BNCT) has emerged as a principal approach to improve the therapeutic ratio of malignancies and reduce lethality to surrounding normal tissue, but it remains deficient in terms of insufficient boron accumulation as well as short retention time, which limits the curative effect. Recently, a series of radiosensitizers that can selectively accumulate in specific organelles of cancer cells have been developed to precisely target radiotherapy, thereby reducing side effects of normal tissue damage, overcoming radioresistance, and improving radiosensitivity. In this review, we mainly focus on the field of nanomedicine-based cancer radiotherapy and discuss the organelle-targeted radiosensitizers, specifically including nucleus, mitochondria, endoplasmic reticulum and lysosomes. Furthermore, the organelle-targeted boron carriers used in BNCT are particularly presented. Through demonstrating recent developments in organelle-targeted radiosensitization, we hope to provide insight into the design of organelle-targeted radiosensitizers for clinical cancer treatment.

Targeting GM2 Ganglioside Accumulation in Dementia: Current Therapeutic Approaches and Future Directions

Dementia in neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and dementia with Lewy bodies (DLB) is a progressive neurological condition affecting millions worldwide. The amphiphilic molecule GM2 gangliosides are abundant in the human brain and play important roles in neuronal development, intercellular recognition, myelin stabilization, and signal transduction. GM2 ganglioside's degradation requires hexosaminidase A (HexA), a heterodimer composed of an α subunit encoded by HEXA and a β subunit encoded by HEXB. The hydrolysis of GM2 also requires a non-enzymatic protein, the GM2 activator protein (GM2-AP), encoded by GM2A. Pathogenic mutations of HEXA, HEXB, and GM2A are responsible for autosomal recessive diseases known as GM2 gangliosidosis, caused by the excessive intralysosomal accumulation of GM2 gangliosides. In AD, PD and DLB, GM2 ganglioside accumulation is reported to facilitate Aβ and α-synuclein aggregation into toxic oligomers and plaques through activation of downstream signaling pathways, such as protein kinase C (PKC) and oxidative stress factors. This review explored the potential role of GM2 ganglioside alteration in toxic protein aggregations and its related signaling pathways leading to neurodegenerative diseases. Further review explored potential therapeutic approaches, which include synthetic and phytomolecules targeting GM2 ganglioside accumulation in the brain, holding a promise for providing new and effective management for dementia.

Novel Fused Pyrazole Amide Analogs as Glucosylceramide Synthase Inhibitors for Treating Lysosomal Storage Diseases, Neurodegenerative Diseases, Cystic Diseases, and Cancer

Provided herein are novel fused pyrazole amide analogs as glucosylceramide synthase inhibitors, pharmaceutical compositions, use of such compounds in treating diseases, particularly, lysosomal storage diseases, neurodegenerative diseases, cystic diseases, and cancer, and processes for preparing such compounds.

Fused Pyrazole Urea Analogs as Glucosylceramide Synthase Inhibitors for Treating Diseases

Provided herein are novel fused pyrazole urea analogs as glucosylceramide synthase inhibitors, pharmaceutical compositions, use of such compounds in treating diseases, particularly lysosomal storage diseases, neurodegenerative diseases, cystic diseases, and cancer, and processes for preparing such compounds.