Synaptojanin1 Modifies Endolysosomal Parameters in Cultured Ventral Midbrain Neurons

Area of Science:

• Neuroscience
• Cell Biology
• Genetics

Background:

• Alpha-synuclein (α-syn) aggregation is linked to brain degradation system dysfunction.
• Mutations in SYNJ1, encoding SAC1 and 5'-phosphatase domains, are associated with hereditary early-onset Parkinsonism.
• Synj1 haploinsufficiency (Synj1+/-) in mice causes p62 and α-syn accumulation in the midbrain and striatum.

Purpose of the Study:

• To investigate neuronal degradation pathways using a Synj1 haploinsufficient mouse midbrain (MB) culture model.
• To determine the impact of Synj1 deficiency on lysosomal function and α-syn clearance in neurons.

Main Methods:

• Utilized Synj1+/- mouse midbrain (MB) neuronal cultures.
• Assessed autophagy and lysosomal markers (GFP-LC3, mKeima, GFP-LAMP1).
• Employed light and electron microscopy (EM) to analyze endolysosomal structures.
• Investigated clearance of wild-type (WT) and mutant α-syn (A53T).

Main Results:

• Synj1+/- MB neurons showed reduced lysosomal-associated membrane protein (LAMP)1, LAMP2, and LAMP2A levels.
• LAMP1 vesicles were hyperacidified with enhanced enzymatic activity in Synj1+/- MB neurons.
• Endolysosomal changes were linked to reduced SAC1 activity, impacting lysosome number.
• Clearance of WT α-syn was unaffected, but clearance of α-syn A53T was impaired in Synj1+/- axons.

Conclusions:

• Synj1 deficiency leads to endolysosomal dysfunction in midbrain neurons.
• Axons exhibit vulnerability to these endolysosomal defects.
• Findings suggest a potential mechanism contributing to Parkinsonism pathogenesis in SYNJ1 mutation carriers.