Preliminary mechanism study on the X-linked parkinsonism caused by RAB39B gene mutation c.536dupA / 中华神经科杂志

ABSTRACT

Objective:To detect the expression level of RAB39B gene and the effect of RAB39B on autophagy and α-synuclein, and then investigate the role of RAB39B gene mutation c.536dupA in the pathogenesis of Parkinson′s disease.Methods:Based on the novel RAB39B gene c.536 dupamutation identified in the previous work, the recombinant expression plasmid (pcDNA3.1-HA-RAB39B-536) of RAB39B gene with this mutation and wild-type recombinant expression plasmid (pcDNA3.1-HA-RAB39B) of RAB39B gene were constructed, and the recombinant expression plasmid was transfected into N2a cells with liposome as experimental group. The control group was made up with N2a cells transfected with plasmid pcDNA3.1-HA-RAB39B. Real-time polymerase chain reaction, Western blotting, immunofluorescence and immunoprecipitation techniques were used to detect the expression level of mutant RAB39B gene and the effects of RAB39B on autophagy and α-synuclein.Results:In the N2a cell model, the transcription level of mutant RAB39B was about twice that of wild type RAB39B, while the protein level of mutant RAB39B (0.30±0.00) was significantly lower than that of wild type (1.50±0.25, t=8.313, P<0.05). After adding proteasome inhibitor MG132, the protein level of mutant RAB39B increased (0.70±0.10, t=6.925, P<0.05); the level of microtubule-associated protein 1 light chain 3 BⅡ/Ⅰ of mutant RAB39B (3.11±0.30) was significantly lower than that of wild type (7.03±0.20, t=18.831, P<0.05); overexpression of wild type and mutant RAB39B did not affect the level of endogenous α-synuclein; overexpression of wild-type RAB39B resulted in elevated level of exogenous wild-type (p.A53T; from 0.60±0.11 to 1.25±0.08, t=8.254, P<0.05) and mutant (from 0.55±0.08 to 1.15±0.08, t=9.293, P<0.05) α-synuclein. Conclusions:The stability of the RAB39B protein decreased with the appearance of c.536 dupA mutation, the mutant protein may be degraded through the ubiquitin-proteasome pathway, and this mutation may affect the autophagy level of cells. RAB39B protein may interact with α-synuclein in vivo and may be involved in the maintenance of the stable level of α-synuclein.