PAB39B Regulates BACE1 Transport And Participates In Alzheimer’s Disease

The progressive aggregation and deposition of β-amyloid(or Amyloid β,Aβ)in the brain plays a crucial role in the pathogenesis of Alzheimer’s disease(AD).Aβ is produced through sequential cleavages of β-amyloid precursor protein(or Amyloid-βPrecursor Protein,APP)by β-secretase and y-secretase.The human RAB39B gene is located on the X chromosome and is a member of the Rab GTPases family of proteins.However,the physiological function of RAB39B is unclear.Loss of function mutations in RAB39B have been found to be associated with mental retardation and pathologically proven early-onset Parkinson’s disease.Parkinson’s disease is the second largest neurodegenerative disease after Alzheimer’s disease.There are many similarities between them in cellular and molecular pathogenesis.However,it is unclear whether RAB39B is involved in AD.This study is intended to explore the correlation between RAB39B and AD and the underlying mechanism.ELISA detection showed that the level of A β increased in the brain tissue of Rab39b knockout(knockout,KO)mice constructed by TALEN technique,and decreased after overexpression of RAB39B in SH-SY5Y751 cells.The changes of enzymes affecting Aβ production in APP pathway in Rab39b KO mice were detected by immunoblotting.It was found that the level of β secretase(BACE1)protein in Rab39b KO mice increased.When RAB39B was overexpressed in SH-SY5Y751 cells,the total amount of BACE1 protein did not change by Western Blot,but by biotinization combined with Western Blot,it was found that BACE1 protein decreased on the surface of cell membrane.In the primary neurons of Rab39b KO mice,RNA was extracted and detected by real-time PCR.It was found that there was no difference in the level of BACE1 mRNA between Rab39b KO and WT mice,and the overexpression of RAB39B in N2a695 cells also did not affect the level of BACE1 mRNA.After overexpressing RAB39B in SH-SY5Y751 cells,cycloheximide,a protein synthesis inhibitor,combined with proteasome inhibitor MG132 or lysosome inhibitor NH4C1,RAB39B did not affect the degradation of BACE1.We also studied the localization of RAB39B in cells.Cellular immunofluorescence showed that RAB39B and endosome RAB4,RAB7 were co-located.In summary,our study found that a physiological function of RAB39B is to regulate BACE1 levels and subcellular localization,thereby affecting the production of Ap.These results suggest a correlation between RAB39B and AD,and provide new clues for the molecular pathogenesis of AD.