A Novel Presenilin 1 M139I Mutation And Its Pathological Function In A Chinese Family With Early-onset Alzheimer's Disease

Objective:Alzheimer's disease?AD?is a progressive neurodegenerative disease.Its characteristic pathological changes are the deposition of beta-amyloid protein?A??and the formation of neurofibrillary tangles in the brain.Other changes include microglial proliferation and loss of neurons,white matter and synapses.According to the age of onset,AD is divided into early-onset AD?EOAD,onset<65 years old?and late-onset AD?LOAD,onset?65 years old?.The proportion of EOAD in all AD cases is between 2%and 10%.AD is a complex disease,which is the result of age,education,heredity,environment and other factors.The familial aggregation of AD suggests that genetic factors may play an important role in the development of AD.Early onset familial Alzheimer's disease?EOFAD?is mainly caused by presenilin 1 gene?PSEN1?mutation.We report a family of EOFAD.Through gene detection,we found that this family carries PSEN1 gene mutation?c.417 G>C,p.M 139I?.The purpose of this experiment is to confirm that this new mutation is a pathological mutation,and to explore the pathogenesis of this mutation in early-onset familial Alzheimer's disease.Materials and Methods:Clinical data was collected from members of a family with early-onset Alzheimer's disease,¹⁸F-FDG PET brain imaging was performed in 4 patients to analyze the characteristics of cerebral glucose metabolism.The genomic DNA of 53family members including proband were detected for dementia related genes?PSEN1,PSEN2,APP and APOE?,and the mutation site of the PSEN1 gene was identified and verified by gene sequencing.We constructed SH-SY5Y cell lines stably expressing human wild-type and mutant PSEN1 genes by lentivirus transfection technology.The expression of A?₄₂ and A?₄₀ was detected by Elisa.The expression of PSEN1,APP and BACE-1 were detected by Western blot.In addition,the effects of PSEN1 M139I mutation on the expression of endoplasmic reticulum stress protein BiP,CHOPand apoptosis protein Caspase-3 were investigated by hydrogen peroxide induced cell models.Results:There were 7 patients in this EOFAD family.The patients in this family are young and developed rapidly.The course of disease was only 5-7 years.¹⁸F-FDG PET/CT brain imaging showed that the metabolism of glucose in the brain was characterized by decreased metabolism in bilateral frontal lobe,temporoparietal joint cortex,lateral part of temporal lobe and subcortical structure.Gene sequencing showed that the nucleotide417 of exon 5 of the presenilin 1?PSEN1?gene in this family was mutated from G to C,resulting in the amino acid encoded by codon 139 changing from methionine to isoleucine?p.M139I?,which was a missense mutation.In the cell model,PSEN1 M139I mutation group resulted in an increase of A?₄₂/A?₄₀ ratio in the cytoplasm.Compared with the blank control group and wild-type negative control group,the expression of PSEN1,APP and BACE-1 increased significantly.In addition,in the M139I mutation group induced by H₂O₂,the expression of endoplasmic reticulum stress-related protein BiP decreased,and the expression of CHOP increased,which eventually led to the increase of Caspase-3expression.Conclusion:We first reported the p.M139I mutation of the PSEN1 gene in Chinese population,which expanded the mutation spectrum of the PSEN1 gene.The new PSEN1M139I mutation can increase the expression of APP and BACE-1,thus promote the production of A?₄₂ and A?₄₀ caused by APP hydrolysis.Under the hydrogen peroxide induction,PSEN1 M139Imutation increases the sensitivity of ER stress and apoptosis.It can be verified that PSEN1 M139I mutation is a pathological mutation.