Lysosomal lipid alterations caused by glucocerebrosidase deficiency promote lysosomal dysfunction, chaperone-mediated-autophagy deficiency, and alpha-synuclein pathology

Abstract

Mutations in the GBA gene that encodes the lysosomal enzyme β-glucocerebrosidase (GCase) are a major genetic risk factor for Parkinson’s disease (PD). In this study, we generated a set of differentiated and stable human dopaminergic cell lines that express the two most prevalent GBA mutations as well as GBA knockout cell lines as a in vitro disease modeling system to study the relationship between mutant GBA and the abnormal accumulation of α-synuclein. We performed a deep analysis of the consequences triggered by the presence of mutant GBA protein and the loss of GCase activity in different cellular compartments, focusing primarily on the lysosomal compartment, and analyzed in detail the lysosomal activity, composition, and integrity. The loss of GCase activity generates extensive lysosomal dysfunction, promoting the loss of activity of other lysosomal enzymes, affecting lysosomal membrane stability, promoting intralysosomal pH changes, and favoring the intralysosomal accumulation of sphingolipids and cholesterol. These local events, occurring only at a subcellular level, lead to an impairment of autophagy pathways, particularly chaperone-mediated autophagy, the main α-synuclein degradative pathway. The findings of this study highlighted the role of lysosomal function and lipid metabolism in PD and allowed us to describe a molecular mechanism to understand how mutations in GBA can contribute to an abnormal accumulation of different α-synuclein neurotoxic species in PD pathology.

Lysosomal storage, impaired autophagy and innate immunity in Gaucher and Parkinson's diseases: insights for drug discovery

“…In keeping with the autophagy impairments in GD, increased LC3-II/LC3-I ratios and p62 accumulation, both consistent with a defect in autophagosome-lysosome fusion, have been observed in mouse [52], patient iPSCderived neuronal models [50] and fly models of nGD [48,49]. Moreover, studies in iPSC-derived midbrain dopaminergic neurons from patients with GBA1 mutations demonstrated an increase in both LC3 and LAMP1, with a low co-localization index, suggesting a block specifically at the fusion stage of autophagy [53].…”

“…Despite this, PI3K complex components such as beclin, regulating phagophore formation, were not increased. These findings likely represent an early compensatory response to the partial loss of normal autophagic-lysosomal degradation [50]. Further upstream, mTOR phosphorylates the CLEAR (Coordinated Lysosomal Expression and Regulation) network activator TFEB to prevent its nuclear export, thus repressing transcription of autophagic-lysosomal genes.…”

“…Defects in this process lead to a failure to maintain a pool of mature and functional lysosomes crucial for the degradation of misfolded proteins such as αSyn. Moreover, it is possible that this process may reflect a common pathology in PD, especially given the fact that GCase deficiency and lysosomal dysfunction occur both with ageing and in sporadic PD [43,50,[57][58][59].…”

Autophagy‑regulating miRNAs: Novel therapeutic targets for Parkinson's disease (Review)

“…The downregulation of PINK1 decreases both starvation-induced autophagy and mitophagy (56,57). Mutation of the GBA gene that encodes β-glucocerebrosidase, which shuttles between the endoplasmic reticulum and the lysosomal lumen, promotes lysosomal dysfunction and α-synuclein pathology in Pd through blockade of chaperone-mediated autophagy (4,58). Furthermore, microglia-mediated neuroinflammation has been implicated in autophagy abnormality.…”

Glucosylceramide depletion disrupts endolysosomal function in GBA-linked Parkinson’s fibroblasts?

“…In fibroblasts from PD patients, lysosomal pH is increased (18–20). Previous studies have suggested that cytosol-facing endomembrane pools of GlcCer are linked to the regulation of lysosomal pH and vATPase activity or expression (6–9,21).…”