The Research Of Regulatory Roles Of Selenomethionine In Mitochondrial Function And Autophagy During Progression Of Alzheimer’s Disease

Alzheimer’s disease(AD)is an incurable neurodegenerative disease characterized by the accumulation of amyloid β(Aβ)which forms senile plaques(SP)and hyperphosphorylation of microtubule associated protein(Tau)which forms neurofibrillary tangles(NFTs)in the brain.Accumulated Aβ and hyperphosphorylated Tau exert synergistic actions on mitochondrial function.And dysfunctions of mitochondrial dynamics,biogenesis,energy metabolism and autophagy in turn promote accumulation of Aβ and hyperphosphorylation of Tau.Ultimately,this leads to accelerated pathological progression of AD.Therefore,mitochondrial damage is considered to be an early phenomenon and an important triggering factor of AD.Selenium is an essential trace element in the living organisms closely related to the maintenance of the normal function of central nervous system.It has been found that supplementation with selenium can significantly enhance mitochondrial function and thus maintain normal cell function.Selenomethionine(Se-Met)is an organic selenium compound formed by the substitution of sulfur in methionine by selenium.It has obvious anti-oxidative,anti-inflammatory and anti-tumor effects.Our previous study found that Se-Met significantly improved cognitive impairment in 3×Tg-AD mice,and reduced Aβ production and deposition,and Tau hyperphosphorylation.Moreover,Se-Met enhanced the clearance of pathological proteins Aβ and Tau through modulation the autophagic pathway.However,the effects of SeMet on mitochondrial function and mitophagy in 3×Tg-AD mice have not been reported yet.In this study,4 months and 8 months old three transgenic(Psen1,APPSwe,Tau P301 L triple transgene,3×Tg)AD mice were treated with 6 μg/m L Se-Met for 12 weeks.Western blot was used to detect expression levels of mitochondrial dynamics protein(Mfn1/2,OPA1,DRP1),autophagy related proteins(TOM20,Parkin,PINK1),synthetic proteins(PGC-1α,NRF1/2),and active proteins(Cyt c,COX IV).The primary neurons isolated from 3×Tg-AD mice and N2a-APP695-Swedish(N2a-SW)cells were treated with 10 μmol/L Se-Met for 24 h,and the morphology of mitochondrial and related autophagosomes were observed by transmission electron microscopy;The expression level of the above proteins was detected;the membrane potential of mitochondria was also detected by flow cytometry after JC-1 staining;the mitochondrial energy metabolism,oxidative stress,and apoptosis were detected by specific detection kits respectively.Findings from in vitro and in vivo studies are as followed:(1)In 8-month-old 3×Tg-AD mice,Se-Met significantly increased the expression of Mfn2(*p<0.05),decreased the expression level of DRP1(*p<0.05),and increased the expression level of Parkin,NRF1,and COX IV(*p<0.05),decreased the expression level of PINK1(*p<0.05).(2)There were no significant changes in mitochondria-related proteins after treatment with Se-Met in 4-months-old 3×Tg-AD mice.(3)In primary neurons of 3×Tg-AD mice model,Se-Met significantly decreased the expression of DRP1(*p<0.05);JC-1 aggregates exhibited significantly more red fluorescence than monomeric green Fluorescence.(4)In the N2a-SW cell,the mumber of mitochondrial in normal morphology,and autophagic vacuoles significantly increased in the Se-Met-treated group;meanwhile,the expression level of Mfn2 was significantly increased(**p<0.01);the expression level of LC3-II/LC3-I was significantly decreased(*p<0.05)and the co-localization of LC3 and COX IV was significantly increased.The intensity of red fluorescence of JC-1 was significantly greater than that of the green fluorescence monomer;the synthesis of ATP was significantly higher(*p<0.05);the level of ROS and apoptosis were significantly decreased after treated by Se-Met(*p<0.05,*p<0.05).In conclusion:(1)Se-Met maintained mitochondrial dynamics,regulated protein degradation and maintained normal mitochondrial membrane potential,enhanceed mitochondrial viability,and promoted mitochondrial function in the 8-month-old 3×Tg-AD mice.(2)In the 3×Tg-AD primary neurons and N2a-SW cells,Se-Met promoted mitochondrial fusion or fission,restored mitochondrial membrane potential,and ameliorated apoptosis.Moreover,Se-Met removed the damaged organelles by modulating autophagy,inhibited the production of ROS and reducd apoptosis in N2a-SW cells.In short,Se-Met can regulate mitochondrial dynamics,restore mitochondrial membrane potential,promote ATP synthesis,inhibit intracellular ROS generation,reduce apoptosis,improve mitochondrial dysfunction,and have the potential to be an effective drug or health supplement that slows down the progression of AD.