Molecular Mechanism By Which Proapoptotic PSAP Is Involved The Pathogenesis Of ALS And Apoptosis

Amyotrophic lateral sclerosis(ALS)is a fatal,adult-onset neurodegenerative disease characterized by a progressive degeneration of motor neuron(MN)in the brain(upper motor neurons)and spinal cord(lower motor neurons),leading to skeletal muscle atrophy and weakness,paralysis and eventually death 2-5 years after diagnosis.To date,the mechanism underlying the neurodegeneration of ALS is not fully understood.Though most cases of ALS are sporadic without family history and no specific cause has been identified,approximately 10% of cases known as familial ALS(FALS)are inherited and linked to mutations in a number of genes.In this study,PSAP gene knockout(PKO),SOD1-G93 A mutant ALS mouse model(SOD1-G93A)and knockout PSAP in the SOD1-G93 A ALS mouse model(PKO/SOD1-G93A)were compared with wild-type(WT)to determine the role of presenilin associated protein(PSAP)in the pathogenesis of ALS by immunofluorescence,H&E staining,toluidine blue staining and Nissl staining etc.First,the result led to an exciting discovery that inactivation of the proapoptotic protein PSAP gene greatly improved motor function and extended the lifespan of the ALS disease mouse(P<0.01).PSAP knockout not only protected neurons from cell death.Specifically,the finding that knockout of PSAP restored the walking ability and the control of incontinence in SOD1-G93 A mice raises the possibility that understanding the molecular mechanism by which PSAP contributes to the pathogenesis of ALS may lead to the identification of novel therapeutic target and development of methods of treatment to improve the quality of life of human patients.The novel PSAP-knockout mouse model ensures the feasibility and success of the proposed experiments.Studies have shown that PSAP induces apoptosis by releasing cytochrome C through the mitochondrial pathway.The release of cytochrome C from mitochondria is the result of mitochondrial outer membrane permeability(MOMP),which suggests that PSAP is involved in MOMP,leading to the release of cytochrome C and ultimately apoptosis.There are two basic models of MOMP: one is the Bax pore formed by Bax/Bax or Bax/Bak,the other is the opening of mitochondrial permeability transition pore(mPTP).Since PSAP induces apoptosis without the involvement of Bax and Bak,it is suggested that PSAP may represent a new pathway to regulate mitochondrial dysfunction.One possibility is that PSAP induces the release of cytochrome C by regulating the opening of mPTP.By using cultured cell model,in the course of studying the molecular mechanism by which PSAP induces apoptosis,western blots showed that overexpression of PSAP induced PARP cleavage,caspase activation and release of cytochrome C and Smac/Diablo from mitochondria into the cytoplasm.However,in the presence of Cs A,no significant PARP cleavage,Caspase activation,and release of cytochrome C and Smac/Diablo were observed even though PSAP was overexpressed.This suggests that PSAP induces apoptosis by regulating the opening of mPTP.To further determine the molecular mechanism by which PSAP regulates mPTP,it showed that PSAP colocalized and combined with VDAC1,the main component of mPTP,by immunoprecipitation and immunofluorescence.our results demonstrated that PSAP induced apoptosis was strongly inhibited by a mPTP inhibitor Cs A.This finding suggests PSAP-induced apoptosis is mediated by the opening of mPTP.In consideration of the fact that many studies support a notion that mPTP is a molecular target for ALS therapy,our finding strongly suggested that PSAP is a key molecule in understanding the pathogenesis of ALS.Further study of the role of PSAP in the development and progression of ALS may help us to find novel therapeutic targets for curing,stopping the progression or even preventing it.In conclusion,the knockout of PSAP gene can effectively alleviate the clinical symptoms of SOD1-G93 A ALS mice.PSAP interacts with VDAC1 to open mPTP and induce apoptosis.Therefore,a clear understanding of the molecular mechanism of PSAP induced apoptosis is of great guiding significance to further the study of ALS pathological mechanism and the development of new drug targets.