Autophagic lysosome reformation dysfunction in glucocerebrosidase deficient cells: relevance to Parkinson disease

Abstract

Glucocerebrosidase (GBA1) gene mutations increase the risk of Parkinson disease (PD). While the cellular mechanisms associating GBA1 mutations and PD are unknown, loss of the glucocerebrosidase enzyme (GCase) activity, inhibition of autophagy and increased α-synuclein levels have been implicated. Here we show that autophagy lysosomal reformation (ALR) is compromised in cells lacking functional GCase. ALR is a cellular process controlled by mTOR which regenerates functional lysosomes from autolysosomes formed during macroautophagy. A decrease in phopho-S6K levels, a marker of mTOR activity, was observed in models of GCase deficiency, including primary mouse neurons and the PD patient derived fibroblasts with GBA1 mutations, suggesting that ALR is compromised. Importantly Rab7, a GTPase crucial for endosome-lysosome trafficking and ALR, accumulated in GCase deficient cells, supporting the notion that lysosomal recycling is impaired. Recombinant GCase treatment reversed ALR inhibition and lysosomal dysfunction. Moreover, ALR dysfunction was accompanied by impairment of macroautophagy and chaperone-mediated autophagy, increased levels of total and phosphorylated (S129) monomeric α-synuclein, evidence of amyloid oligomers and increased α-synuclein release. Concurrently, we found increased cholesterol and altered glucosylceramide homeostasis which could compromise ALR. We propose that GCase deficiency in PD inhibits lysosomal recycling. Consequently neurons are unable to maintain the pool of mature and functional lysosomes required for the autophagic clearance of α-synuclein, leading to the accumulation and spread of pathogenic α-synuclein species in the brain. Since GCase deficiency and lysosomal dysfunction occur with ageing and sporadic PD pathology, the decrease in lysosomal reformation may be a common feature in PD.

Mitochondrial dysfunction and mitophagy defect triggered by heterozygous GBA mutations

“…Unexpectedly we found that p-MTOR and p-RPS6 protein levels were decreased in Gba L444P/WT mouse brains. While contrary to our observation of suppressed autophagy induction, these data are consistent with recent studies in GD and GBA-PD patient-derived fibroblasts [49] and Gba1 -deficient Drosophila models [50] in which the hypoactive MTOR was proposed to be responsible for impaired recycling of functional lysosomes from autolysosomes.…”

Glucocerebrosidase mutations and synucleinopathies: Toward a model of precision medicine

“…Moreover, lysosomal reformation is compromised in GCase‐deficient fibroblasts and is accompanied by an increase in total and phosphorylated α‐syn, oligomer deposition, and enhanced α‐syn release. This indicates that accumulation of defective lysosomes contributes to impaired autophagy and α‐syn buildup . It has also been suggested that protein phosphatase 2A inactivation could represent the potential mechanism through which GCase deficiency inhibits autophagy and promotes α‐syn aggregation .…”

Glucocerebrosidase Mutations in Parkinson Disease

“…Additionally they are cost-effective and free from the ethical concerns that accompany primary cell and stem cell use [21,22]. In the case of GBA-PD research, cell lines stably expressing alpha-synuclein can be transfected with siRNA to silence GBA expression and thus serve as a robust model of reduced Gcase activity in a PD setting [23].…”

“…Fibroblast lines may also be derived from GBA mutationcarrying mice. These models allow investigation of the cellular mechanisms by which altered GCase activity may affect patient susceptibility to PD and can serve as an inexpensive model for testing potential drug treatments [23,26]. These lines, however, are not neuronal, and do not express alpha-synuclein, which can limit the key research questions that can be answered using them.…”