PT  - JOURNAL ARTICLE
AU  - Zhu, Xinyu
AU  - Prakash, Sanjana Surya
AU  - McAuliffe, Geoffrey
AU  - Pan, Ping-Yue
TI  - Synaptojanin1 Modifies Endolysosomal Parameters in Cultured Ventral Midbrain Neurons
AID  - 10.1523/ENEURO.0426-22.2023
DP  - 2023 May 01
TA  - eneuro
PG  - ENEURO.0426-22.2023
VI  - 10
IP  - 5
4099  - http://www.eneuro.org/content/10/5/ENEURO.0426-22.2023.short
4100  - http://www.eneuro.org/content/10/5/ENEURO.0426-22.2023.full
SO  - eNeuro2023 May 01; 10
AB  - The accumulation of α-synuclein (α-syn)-enriched protein aggregates is thought to arise from dysfunction in degradation systems within the brain. Recently, missense mutations of SYNJ1 encoding the SAC1 and 5’-phosphatase domains have been found in families with hereditary early-onset Parkinsonism. Previous studies showed that Synj1 haploinsufficiency (Synj1+/−) leads to accumulation of the autophagy substrate p62 and pathologic α-syn proteins in the midbrain (MB) and striatum of aged mice. In this study, we aim to investigate the neuronal degradation pathway using the Synj1+/− MB culture from mouse pups of mixed sex as a model. Our data show that GFP-LC3 puncta formation and cumulative mKeima puncta formation are unaltered at baseline in Synj1+/− MB neurons. However, GFP-LAMP1 puncta is reduced with a similar decrease in endogenous proteins, including lysosomal-associated membrane protein (LAMP)1, LAMP2, and LAMP2A. The LAMP1 vesicles are hyperacidified with enhanced enzymatic activity in Synj1+/− MB neurons. Using a combination of light and electron microscopy (EM), we show that endolysosomal changes are primarily associated with a lack of SAC1 activity. Consistently, expressing the SYNJ1 R258Q mutant in N2a cells reduces the lysosome number. Interestingly, the endolysosomal defects in Synj1+/− neurons does not impact the clearance of exogenously expressed wild-type (WT) α-syn; however, the clearance of α-syn A53T was impaired in the axons of Synj1+/− MB neurons. Taken together, our results suggest axonal vulnerability to endolysosomal defects in Synj1-deficient MB neurons.