Mutations in GBA1, the gene encoding the lysosomal hydrolase glucocerebrosidase (GCase), are a risk factor for parkinsonism. Pursuing the potential mechanisms underlying this risk in aging neurons, ...we propose a new network uniting three major lysosomal proteins: (i) cathepsin D (CTSD), which plays a major role in α-synuclein (SNCA) degradation and prosaposin (PSAP) cleavage; (ii) PSAP, essential for GCase activation and progranulin (PGRN) transport; and (iii) PGRN, impacting lysosomal biogenesis, PSAP trafficking, and CTSD maturation. We hypothesize that alterations to this network and associated receptors modify lysosomal function and subsequently impact both SNCA degradation and GCase activity. By exploring the interactions between this protein trio and each of their respective transporters and receptors, we may identify secondary risk factors that provide insight into the relationship between these lysosomal proteins, GCase, and SNCA, and reveal novel therapeutic targets.
Mutations in GBA1, the gene encoding glucocerebrosidase (GCase), confer an increased risk of parkinsonism, directing attention to lysosomal pathways and proteins in Parkinson pathogenesis.Other lysosomal proteins functioning at the acidic lysosomal pH influence GCase function and/or α-synuclein clearance.Three multifunctional proteins (the PPPN): the protease procathepsin D, the pre-activator prosaposin, and the lysosomal biogenesis protein progranulin, along with their respective transporters, are all interconnected. Their interdependency creates potential feedback mechanisms to protect and support cells under stress.The interactions between the PPPN proteins directly impact GCase activity and α-synuclein degradation and lead to the identification of new risk factors and therapeutic targets for Parkinson disease.
The study of the contribution of epigenetic mechanisms, including DNA methylation, histone modifications, and microRNAs, to human disease has enhanced our understanding of different cellular ...processes and diseased states, as well as the effect of environmental factors on phenotypic outcomes. Epigenetic studies may be particularly relevant in evaluating the clinical heterogeneity observed in monogenic disorders. The lysosomal storage disorders are Mendelian disorders characterized by a wide spectrum of associated phenotypes, ranging from neonatal presentations to symptoms that develop in late adulthood. Some lack a tight genotype/phenotype correlation. While epigenetics may explain some of the discordant phenotypes encountered in patients with the same lysosomal storage disorder, especially among patients sharing the same genotype, to date, few studies have focused on these mechanisms. We review three common epigenetic mechanisms, DNA methylation, histone modifications, and microRNAs, and highlight their applications to phenotypic variation and therapeutics. Three specific lysosomal storage diseases, Gaucher disease, Fabry disease, and Niemann-Pick type C disease are presented as prototypical disorders with vast clinical heterogeneity that may be impacted by epigenetics. Our goal is to motivate researchers to consider epigenetics as a mechanism to explain the complexities of biological functions and pathologies of these rare disorders.
•Epigenetics may contribute to the clinical heterogeneity observed in monogenic disorders.•In the lysosomal storage disorders, the role of epigenetics merits increased attention.
Mutations in GBA1, the gene encoding glucocerebrosidase, are common genetic risk factors for Parkinson disease (PD). While the mechanism underlying this relationship is unclear, patients with ...GBA1-associated PD often have an earlier onset and faster progression than idiopathic PD. Previously, we modeled GBA1-associated PD by crossing gba haploinsufficient mice with mice overexpressing a human mutant α-synuclein transgene (SNCAA53T), observing an earlier demise, shorter life span and faster symptom progression, although behavioral testing was not performed. To assess whether gba+/−//SNCAA53T mice exhibit a prodromal behavioral phenotype, we studied three cardinal PD features: olfactory discrimination, memory dysfunction, and motor function. The longitudinal performance of gba+/−//SNCAA53T (n = 8), SNCAA53T (n = 9), gba+/− (n = 10) and wildtype (n = 6) mice was evaluated between ages 8 and 23 months using the buried pellet test, novel object recognition test and the beam walk. Fifteen-month-old gba+/−//SNCAA53T mice showed more olfactory and motor deficits than wildtype mice. However, differences between gba+/−//SNCAA53T and SNCAA53T mice generally did not reach statistical significance, possibly due to small sample sizes. Furthermore, while gba haploinsufficiency leads to a more rapid demise, this might not result in an earlier prodromal stage, and other factors, including aging, oxidative stress and epigenetics, may contribute to the more fulminant disease course.
Gaucher disease is caused by an inherited deficiency of glucocerebrosidase that manifests with storage of glycolipids in lysosomes, particularly in macrophages. Available cell lines modeling Gaucher ...disease do not demonstrate lysosomal storage of glycolipids; therefore, we set out to develop two macrophage models of Gaucher disease that exhibit appropriate substrate accumulation. We used these cellular models both to investigate altered macrophage biology in Gaucher disease and to evaluate candidate drugs for its treatment. We generated and characterized monocyte-derived macrophages from 20 patients carrying different Gaucher disease mutations. In addition, we created induced pluripotent stem cell (iPSC)-derived macrophages from five fibroblast lines taken from patients with type 1 or type 2 Gaucher disease. Macrophages derived from patient monocytes or iPSCs showed reduced glucocerebrosidase activity and increased storage of glucocerebroside and glucosylsphingosine in lysosomes. These macrophages showed efficient phagocytosis of bacteria but reduced production of intracellular reactive oxygen species and impaired chemotaxis. The disease phenotype was reversed with a noninhibitory small-molecule chaperone drug that enhanced glucocerebrosidase activity in the macrophages, reduced glycolipid storage, and normalized chemotaxis and production of reactive oxygen species. Macrophages differentiated from patient monocytes or patient-derived iPSCs provide cellular models that can be used to investigate disease pathogenesis and facilitate drug development.
Gaucher disease (GD) is a lysosomal storage disorder stemming from biallelic mutations in
, characterized by glucocerebrosidase dysfunction and glucocerebroside and glucosylsphingosine accumulation. ...Since phenotypes of murine models of GD often differ from those in patients, the careful characterization of
mutant mice is necessary to establish their ability to model GD. We performed side-by-side comparative biochemical and pathologic analyses of four murine
models with genotypes L444P/L444P (p.L483P/p.L483P), L444P/null, D409H/D409H (p.D448H/p.D448H) and D409H/null, along with matched wildtype mice, all with the same genetic background and cage conditions. All mutant mice exhibited significantly lower glucocerebrosidase activity (
< 0.0001) and higher glucosylsphingosine levels than wildtype, with the lowest glucocerebrosidase and the highest glucosylsphingosine levels in mice carrying a null allele. Although glucocerebrosidase activity in L444P and D409H mice was similar, D409H mice showed more lipid accumulation. No Gaucher or storage-like cells were detected in any of the
mutant mice. Quantification of neuroinflammation, dopaminergic neuronal loss, alpha-synuclein levels and motor behavior revealed no significant findings, even in aged animals. Thus, while the models may have utility for testing the effect of different therapies on enzymatic activity, they did not recapitulate the pathological phenotype of patients with GD, and better models are needed.
Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the acid β-glucocerebrosidase gene. To model GD, we generated human induced pluripotent stem cells (hiPSC), by ...reprogramming skin fibroblasts from patients with type 1 (N370S/N370S), type 2 (L444P/Rec NciI), and type 3 (L444P/L444P) GD. Pluripotency was demonstrated by the ability of GD hiPSC to differentiate to all three germ layers and to form teratomas in vivo. GD hiPSC differentiated efficiently to the cell types most affected in GD, i.e., macrophages and neuronal cells. GD hiPSC-macrophages expressed macrophage-specific markers, were phagocytic, and were capable of releasing inflammatory mediators in response to LPS. Moreover, GD hiPSC-macrophages recapitulated the phenotypic hallmarks of the disease. They exhibited low glucocerebrosidase (GC) enzymatic activity and accumulated sphingolipids, and their lysosomal functions were severely compromised. GD hiPSC-macrophages had a defect in their ability to clear phagocytosed RBC, a phenotype of tissue-infiltrating GD macrophages. The kinetics of RBC clearance by types 1, 2, and 3 GD hiPSC-macrophages correlated with the severity of the mutations. Incubation with recombinant GC completely reversed the delay in RBC clearance from all three types of GD hiPSC-macrophages, indicating that their functional defects were indeed caused by GC deficiency. However, treatment of induced macrophages with the chaperone isofagomine restored phagocytosed RBC clearance only partially, regardless of genotype. These findings are consistent with the known clinical efficacies of recombinant GC and isofagomine. We conclude that cell types derived from GD hiPSC can effectively recapitulate pathologic hallmarks of the disease.
Objective
Biallelic mutations in
GBA1
, which encodes the lysosomal enzyme glucocerebrosidase, cause the lysosomal storage disorder Gaucher disease (GD). In addition, mutations in
GBA1
are the most ...common genetic risk factor for future development of Parkinson's disease (PD). However, most mutation carriers will never develop parkinsonism. Olfactory dysfunction is often a prodromal symptom in patients with PD, appearing many years prior to motor dysfunction. The purpose of this study was to assess olfactory function longitudinally in individuals with and without parkinsonism who carry at least one
GBA1
mutation.
Methods
One hundred seventeen individuals who participated in a natural history study of GD at the National Institutes of Health were evaluated using the University of Pennsylvania Smell Identification Test (UPSIT) during a 16-year period. Seventy patients with GD (13 with PD) and 47
GBA1
carriers (9 with PD) were included. Fifty-six of the total (47.9%) were seen over multiple visits, and had UPSIT screening performed two to six times, with time intervals between testing ranging from 2 to 6 years. Comparative and control data were obtained from the Parkinson's Progression Markers Initiative (PPMI) database (519 individuals, including 340 with idiopathic PD and 179 healthy controls). Statistical analysis was performed using R.
Results
Severe hyposmia and anosmia was evident in both
GBA1
heterozygotes and homozygotes with PD. 84% without parkinsonism had UPSIT scores >30, and those who underwent repeated testing maintained olfactory function over time. No statistically significant difference in UPSIT scores was found between mutation carriers with and without a family history of parkinsonism. A small group of individuals without PD scored in the moderate-severe microsmia range. No significant differences in olfaction were found among our
GBA1
-PD cohort and idiopathic PD cohort obtained from PPMI.
Glucocerebrosidase is a lysosomal hydrolase involved in the breakdown of glucosylceramide. Gaucher disease, a recessive lysosomal storage disorder, is caused by mutations in the gene GBA1 ...Dysfunctional glucocerebrosidase leads to accumulation of glucosylceramide and glycosylsphingosine in various cell types and organs. Mutations in GBA1 are also a common genetic risk factor for Parkinson disease and related synucleinopathies. In recent years, research on the pathophysiology of Gaucher disease, the molecular link between Gaucher and Parkinson disease, and novel therapeutics, have accelerated the need for relevant cell models with GBA1 mutations. Although induced pluripotent stem cells, primary rodent neurons, and transfected neuroblastoma cell lines have been used to study the effect of glucocerebrosidase deficiency on neuronal function, these models have limitations because of challenges in culturing and propagating the cells, low yield, and the introduction of exogenous mutant GBA1 To address some of these difficulties, we established a high yield, easy-to-culture mouse neuronal cell model with nearly complete glucocerebrosidase deficiency representative of Gaucher disease. We successfully immortalized cortical neurons from embryonic null allele gba(-/-) mice and the control littermate (gba(+/+)) by infecting differentiated primary cortical neurons in culture with an EF1α-SV40T lentivirus. Immortalized gba(-/-) neurons lack glucocerebrosidase protein and enzyme activity, and exhibit a dramatic increase in glucosylceramide and glucosylsphingosine accumulation, enlarged lysosomes, and an impaired ATP-dependent calcium-influx response; these phenotypical characteristics were absent in gba(+/+) neurons. This null allele gba(-/-) mouse neuronal model provides a much-needed tool to study the pathophysiology of Gaucher disease and to evaluate new therapies.
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