The Effects Of Enriched Environment On Age-related Cognition Impairment Induced By Early Life Stress And The Study About Akt/GSK-3? Pathway In Mice

BackgroundThe age-associated memory impairments(AACI)have become the most prevalent health risk for the elderly,which will affect the quality of life of individuals.Therefore,it is critical to investigate the exact mechanism as well as aggravating and mitigating factors of AACI.Early life stress(ELS)has a profound impact on cognitive and emotional function.Multiple studies have demonstrated that ELS might accelerate the cognitive impairment in adulthood and old age mice,the enriched environment(EE)can enhance not only the social skills and the spatial cognition of healthy old animals,but also the cognitive impairment of aging mice induced by ELS.To date,there is no clear understanding of the particular mechanism of AACI induced by ELS and whether EE can ameliorate the cognitive impairment induced by ELS in the whole life stage.The Akt/GSK-3? signal pathway is one of the most significant signal pathways involved in AACI.It can play a key role in a variety of fundamental physiological and pathological processes associated with cognitive impairment.The most important mechanism of Akt/GSK-3? regulating cognitive function are through affecting synaptic and mitochondrial function.However,it is unclear if the Akt/GSK-3? signal pathway,synaptic function and mitochondrial function are implicated in the EE postponing the AACI induced by early life stress.ObjectiveFirstly,we investigated the dynamic changes of ELS on the change of cognitive function and the protective effect of EE across the whole life cycle.Secondly,we explored the role of Akt/GSK-3? signaling pathway in the EE postponing the AACI induced by ELS.Finally,we explored if the synaptic and mitochondrial function are implicated in the EE postponing the AACI induced by ELS.MethodsBased on maternal separation(MS)model,SAMP8 mice were randomly treated with ELS or natural feeding.In the mice exposed by ELS,pups were separated from their dams on the PNDs 7-17 for 3h per day(9:00am-12:00am).At the age of 2 months,mice were given either the EE intervention or the normal environment.Mice treated with EE were fed in enlarged cages,which was regularly replaced different types and colors of toys,such as running wheels,mouse tunnels,aspen block toys,and rings.Finally,they were divided into four groups:EE group(CON+E),control group(CON),ELS+EE group(MS+E),and ELS group(MS).Mice completed the following experiments in youth(3 months old),midlife(6 months old),and old(9 months old)adulthoods,respectively.Firstly,behavioral tests were completed,including tasks consisted of beam balance,black-white alley,open field,elevated plus maze,sucrose preference,Y maze,and Morris water maze.Then,Western blotting was used to detect the protein levels of Akt/GSK-3?signal pathway-associated protein(Akt,p-Akt,GSK-3?,p-GSK-3?),Finally,the transmission electron microscope was used to observe the morphological structures of hippocampal synapses and mitochondria.Western blotting and RT-PCR were used to detect the protein and mRNA levels of synaptic-associated protein(PSD-95,Arc),and mitochondrial-associated protein(Mfn2,Drp1,Bax,Bcl-2).Results(1)Behavioral tests:In terms of age effect,the balance function and the cognitive function in the elderly mice were worse than those in the young mice,and the anxietylike and depression-like behaviors were more obvious,and some behavioral functions began to deteriorate in the middle age.In terms of treatment effect,ELS can aggravate the aging-associated behavioral impairment in middle age and elderly age,while EE can partly postpone these changes,which is more obvious in the elderly age.(2)Morphology and structure:In terms of age effect,in the young mice,the morphology and structure of neurons,synapse and mitochondria was normal,and complete nuclear membrane and nucleolus could be seen.Then in the middle-aged mice,the morphology and structure of neurons,synapse and mitochondria were basically normal,and only a few mitochondria were slightly swollen.But in the elderly group,the morphology and structure of neurons,synapse and mitochondria were significantly changed,the nuclear membrane was disrupted,the postsynaptic density was thinner,and the contents of mitochondria were disappeared.In terms of treatment effect,ELS can aggravate the above the aging-associated morphological and structural damage,but EE can partially alleviate these changes.Both treatment effects have appeared in middle age.(3)Molecular analysis:In terms of age effect,in the old mice,the protein and mRNA levels of Akt/GSK-3? signal pathway(Akt,p-Akt,GSK-3?,p-GSK-3?),mitochondrial fusion protein(Mfn2),anti-apoptotic protein(Bcl-2),synaptic-associated protein(PSD95,Arc)were higher,but the protein and mRNAlevels of dynamin-related protein(Drp1)and apoptosis-associated protein(Bax)were lower than those in the young mice,and the levels of some protein and mRNA began to change in the middle age.In terms of treatment effect,not only in elderly age but also in middle age,ELS can accelerate the above the aging-associated molecular changes,while EE can partially alleviate these changes.SummaryIn conclusion,ELS could accelerate the age-related behavioral impairments,but the EE can partly alleviate these changes induced by ELS.The changes of Akt/GSK-3? signal pathway,synaptic function and mitochondrial function may be involved in the EE postponing the AACI induced by ELS.