Acid β‐glucosidase mutants linked to gaucher disease, parkinson disease, and lewy body dementia alter α‐synuclein processing

Abstract

Objective: Heterozygous mutations in the GBA1 gene elevate the risk of Parkinson disease and dementia with Lewy bodies; both disorders are characterized by misprocessing of a-synuclein (SNCA). A loss in lysosomal acid-bglucosidase enzyme (GCase) activity due to biallelic GBA1 mutations underlies Gaucher disease. We explored mechanisms for the gene's association with increased synucleinopathy risk. Methods: We analyzed the effects of wild-type (WT) and several GBA mutants on SNCA in cellular and in vivo models using biochemical and immunohistochemical protocols. Results: We observed that overexpression of all GBA mutants examined (N370S, L444P, D409H, D409V, E235A, and E340A) significantly raised human SNCA levels to 121 to 248% of vector control (p < 0.029) in neural MES23.5 and PC12 cells, but without altering GCase activity. Overexpression of WT GBA in neural and HEK293-SNCA cells increased GCase activity, as expected (ie, to 167% in MES-SNCA, 128% in PC12-SNCA, and 233% in HEK293-SNCA; p < 0.002), but had mixed effects on SNCA. Nevertheless, in HEK293-SNCA cells high GCase activity was associated with SNCA reduction by 32% (p ¼ 0.009). Inhibition of cellular GCase activity (to 8-20% of WT; p < 0.0017) did not detectably alter SNCA levels. Mutant GBA-induced SNCA accumulation could be pharmacologically reversed in D409V-expressing PC12-SNCA cells by rapamycin, an autophagy-inducer ( 40%; 10lM; p < 0.02). Isofagomine, a GBA chaperone, showed a related trend. In mice expressing two D409Vgba knockin alleles without signs of Gaucher disease (residual GCase activity, !20%), we recorded an age-dependent rise of endogenous Snca in hippocampal membranes (125% vs WT at 52 weeks; p ¼ 0.019). In young Gaucher disease mice (V394Lgbaþ/þ//prosaposin[ps]-null//ps-transgene), which demonstrate neurological dysfunction after age 10 weeks (GCase activity, 10%), we recorded no significant change in endogenous Snca levels at 12 weeks of age. However, enhanced neuronal ubiquitin signals and axonal spheroid formation were already present. The latter changes were similar to those seen in three week-old cathepsin D-deficient mice.Interpretation: Our results demonstrate that GBA mutants promote SNCA accumulation in a dose-and timedependent manner, thereby identifying a biochemical link between GBA1 mutation carrier status and increased synucleinopathy risk. In cell culture models, this gain of toxic function effect can be mitigated by rapamycin. Loss in GCase activity did not immediately raise SNCA concentrations, but first led to neuronal ubiquitinopathy and axonal spheroids, a phenotype shared with other lysosomal storage disorders. ANN NEUROL 2011;69:940-953 View this article online at wileyonlinelibrary.com. DOI: 10.1002/ana.22400 Additional Supporting Information can be found in the online version of this article. 940

Specifically neuropathic Gaucher's mutations accelerate cognitive decline in Parkinson's

“…N370S appears to confer a milder reduction in GCase activity 46. In PD, however, both GBA loss‐of‐function and toxic gain‐of‐function hypotheses have been proposed 5, 47. In cultured cells, mutant GBA promoted α‐synuclein accumulation in a dose‐dependent manner without observed loss of GCase function 47.…”

“…In PD, however, both GBA loss‐of‐function and toxic gain‐of‐function hypotheses have been proposed 5, 47. In cultured cells, mutant GBA promoted α‐synuclein accumulation in a dose‐dependent manner without observed loss of GCase function 47. However, in PD patients heterozygous for a GBA mutation, GCase activity is reduced in induced pluripotent stem‐cell–derived neurons,48 brain,45 cerebrospinal fluid,48 and blood 37.…”

Ambroxol effects in glucocerebrosidase and α‐synuclein transgenic mice

“…It has been shown in SH‐SY5Y cell cultures, neuronal cultures, conduritol‐β‐epoxide (CβE)‐treated mice, and transgenic Gba1 mouse models that reduced GCase activity results in increased α‐synuclein levels 7, 8, 9, 10, 11, 12, 13, 14. Conversely, it has been demonstrated in cell models that increased α‐synuclein causes a decrease in GCase activity 15.…”

Glucocerebrosidase, a new player changing the old rules in Lewy body diseases

“…Additionally, Cullen et al (2011) showed that when wild type or mutant GBA1 is co-expressed with α -synuclein in MES23.5, PC12, and HEK293 cell lines, α -synuclein accumulation increased only in the mutant GBA1 cell lines, but not in the wild type. In another study, accumulation of α -synuclein increased in cultured cells and the SN of mice following treatment with conduritol B epoxide, a GCase inhibitor (Manning -Bog et al, 2009 ).…”

“…However, this speculation is probably an over-simplified view, because conflicting results exist. For example, treatment of the model used by Cullen et al (2011) with conduritol B epoxide does not increase α -synuclein protein levels.…”