Variant‐specific effects of GBA1 mutations on dopaminergic neuron proteostasis

• Published in: Journal of neurochemistry Vol. 168; no. 9; pp. 2543 - 2560
• Main Authors: Onal, G., Yalçın‐Çakmaklı, G., Özçelik, C. E., Boussaad, I., Şeker, U. Ö. Ş., Fernandes, Hugo J. R., Demir, H., Krüger, R., Elibol, B., Dökmeci, S., Salman, M. M.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-09-2024
• Subjects: Accumulation; alpha-Synuclein - genetics; alpha-Synuclein - metabolism; Autophagy; Autophagy - genetics; Autophagy - physiology; Biodegradation; Cell fusion; Degradation; Dopamine D4 receptors; Dopaminergic Neurons - metabolism; Endoplasmic reticulum; Endoplasmic Reticulum Stress - genetics; Endoplasmic Reticulum Stress - physiology; Gaucher disease; GBA1; Glucosylceramidase; Glucosylceramidase - genetics; Glucosylceramidase - metabolism; Humans; Induced Pluripotent Stem Cells - metabolism; iPSC‐derived neurons; macroautophagy; Movement disorders; Mutation; Mutation - genetics; Neurodegeneration; Neurodegenerative diseases; Neurons; Parkinson Disease - genetics; Parkinson Disease - metabolism; Parkinson Disease - pathology; Parkinson's disease; Phagosomes; Phenotypes; Pluripotency; Proteasomes; Proteostasis - genetics; Risk factors; Stem cells; Synuclein; Ubiquitin; Ubiquitination; α‐Synuclein; GBA1; Gaucher disease; Parkinson's disease; iPSC‐derived neurons; macroautophagy; α‐Synuclein
• ISSN: 0022-3042; 1471-4159; 1471-4159
• DOI: 10.1111/jnc.16114

Glucocerebrosidase 1 (GBA1) mutations are the most important genetic risk factors for Parkinson's disease (PD). Clinically, mild (e.g., p.N370S) and severe (e.g., p.L444P and p.D409H) GBA1 mutations have different PD phenotypes, with differences in age at disease onset, progression, and the severity of motor and non‐motor symptoms. We hypothesize that GBA1 mutations cause the accumulation of α‐synuclein by affecting the cross‐talk between cellular protein degradation mechanisms, leading to neurodegeneration. Accordingly, we tested whether mild and severe GBA1 mutations differentially affect the degradation of α‐synuclein via the ubiquitin–proteasome system (UPS), chaperone‐mediated autophagy (CMA), and macroautophagy and differentially cause accumulation and/or release of α‐synuclein. Our results demonstrate that endoplasmic reticulum (ER) stress and total ubiquitination rates were significantly increased in cells with severe GBA1 mutations. CMA was found to be defective in induced pluripotent stem cell (iPSC)‐derived dopaminergic neurons with mild GBA1 mutations, but not in those with severe GBA1 mutations. When examining macroautophagy, we observed reduced formation of autophagosomes in cells with the N370S and D409H GBA1 mutations and impairments in autophagosome–lysosome fusion in cells with the L444P GBA1 mutation. Accordingly, severe GBA1 mutations were found to trigger the accumulation and release of oligomeric α‐synuclein in iPSC‐derived dopaminergic neurons, primarily as a result of increased ER stress and defective macroautophagy, while mild GBA1 mutations affected CMA, which is mainly responsible for the degradation of the monomeric form of α‐synuclein. Overall, our findings provide new insight into the molecular basis of the clinical variability in PD associated with different GBA1 mutations.
Glucocerenrosidase1 (GBA1) mutations cause disruptions in endoplasmic reticulum (ER) and lysosome‐related proteostasis pathways in induced pluripotent stem cell (iPSC)‐derived dopaminergic neurons. Severe GBA1 mutations lead to increased ER stress (increased binding immunoglobulin protein (BiP) and protein disulfide isomerase (PDI) levels), total ubiquitination rates, and unfolded protein response (UPR). Defective chaperone‐mediated autophagy (decreased heat‐shock cognate protein 70 (HSC70) levels and decreased co‐localization of lysosomal‐associated membrane protein 2A (LAMP2A) and HSC70) is observed in iPSC‐derived dopaminergic neurons with mild homozygous GBA1 mutations. Decreased autophagosome formation (decreased microtubule‐associated protein light chain 3A (LC3) levels) is observed in iPSC‐derived dopaminergic neurons with homozygous N370S and D409H GBA1 mutations, while fusion defects (decreased lysosomal‐associated membrane protein 1 (LAMP1) and LC3 co‐localization) are observed in neurons with homozygous L444P GBA1 mutation. Severe GBA1 mutations trigger the accumulation of monomeric and oligomeric forms of α‐synuclein. GBA1 mutations increase the release of α‐synuclein from iPSC‐derived dopaminergic neurons.