The Protective Effect Of Enriched Environment On Accelerated Brain Aging Induced By Inflammatory Insult During Pregnancy And Its Possible Mechanisms

BackgroundWith the increasing number of people in the aged population,age-related disease is increasing in prevalence,such as Alzheimer disease.These bring more and more larger societal,economic and medical burden,especially age-related cognitive disorder.But the exact pathogenesis of cognitive impairment remains elusive and there is no ideal treatment.Hence,it is an urgent need to explore the underlying pathogenesis and effective treatment to reduce the adverse impact of age-related cognitive decline.Accumulating evidences indicate that mitochondrial dysfunction can contribute to the pathophysiology of age-related diseases such as Alzheimer disease.In order to sustain mitochondrial heath,several mitochondrial quality control(MQC)mechanisms exist,including mitochondrial dynamics,biogenesis,and mitophagy.Disruption of mitochondrial quality control worsens mitochondrial dysfunction.S-nitrogenization of mitochondrial related proteins directly affects the mitochondrial dynamics activity and inhibits mitophagy.Tet methylcytosine dioxygenase 1(TET1)and s-nitrosoglutathione reductase(GSNOR)are closely related to s-nitrogenization.Now there are few studies on MQC and TET1/GSNOR axis in the brain aging.Previous research has showed that gestational infection accelerates age-related memory impairment in mother mice.Enriched environment(EE)can improve age-related memory impairment,and EE has been reported to improve mitochondrial function.However,(1)Is the behavior change with aging accompanied by the decline of MQC mechanism?(2)Is the accelerated behavior change induced by inflammatory insult during pregnancy accompanied by synchronous decline of MQC mechanism?(3)Does EE mitigate the accelerated effects of age-related behavior and MQC changes caused induced by inflammatory insult?(4)Is TET1/GSNOR involved in the process of aging and accelerated aging induced exposure to LPS during pregnancy and the positive effects of EE on them? These studies can provide evidence for the mechanism and prevention of brain aging.ObjectiveIn the study,we firstly explored the protective effects of EE on accelerated agerelated behaviors induced by inflammatory insult during pregnancy.Then,we surveyed the changes of the hippocampal MQC mechanism in normal aging mice and accelerated aging mice induced by inflammatory insult during pregnancy,and the protective effect of EE on the pattern changes of hippocampal MQC mechanism.Finally,we investigated the effects of aging and inflammatory insult during pregnancy on the TET1/GSNOR levels in the hippocampus and the protective effects of EE on them.Methods(1)During gestational days 15-17,all gestational mice were received intraperitoneal injections of LPS(50 ?g/kg)or normal saline daily.After stopping normal breastfeeding,the mothers were separated from their children and bred in standard home cages(25.5�15�14 cm3,3�4 mice per cage).The half of mice received LPS were housed in enlarged cages(52�40�20 cm3,10�15 mice per cage)which hold changing toys,such as running wheels,experimental mouse tunnels,poplar block toys,rings,etc.to enrich environment until the end of the behavioral experiments and defined as LPS-E group.When the mother mice reached 6 and 18 months old,10 mice were randomly selected from each of the three groups to complete subsequent experiments,respectively.(2)Behavioral tests: balance movement coordination ability(horizontal bar task);anxious behavior and spontaneous exploration activities(black-white alley,elevated plus maze and open field activity);learning and memory ability(Y maze and Morris water maze).(3)The transmission electron microscope was utilized for the morphological observation of mitochondria.(4)RT-q PCR and western blot were employed to measure the related m RNA and protein expression of MQC and TET1/GSNOR in the hippocampus,respectively.Results(1)Compared with the 6-month old control group,the movement balance ability,spontaneous exploration activity,and spatial learning and memory ability were significantly decreased in the 18-month old control group,but the anxious behavior was significantly increased.Inflammatory insult during pregnancy can exacerbate these above behavioral impairments.However,enriched environment can significantly delay the behavioral changes in the LPS-E group.(2)Transmission electron microscopy showed that the shape of hippocampal mitochondria in all mice was mainly spherical and rod-shaped.The 6-month-old different groups had basically normal morphology and structure of hippocampal mitochondria,with the clearly visible double-layer membrane structure,and only a few mitochondria were mildly swollen.However,the morphological structure of hippocampal mitochondria significantly changed in the 18-month-old mice,with obviously swollen mitochondria,disrupted and unclear membranes,vacuolization,and sparse and dissolved cristae,especially in the LPS group.The LPS-E and CON groups had similar mitochondrial morphology.(3)Compared with the 6-month-old control group,m RNA and protein levels of hippocampal mitochondrial dynamics(Mfn2 /Mfn1,OPA1 and Drp1),biogenesis(PGC-1?)and mitophagy(PINK1/Parkin)were significantly decreased in the 18-month-old control group.Inflammatory insult during pregnancy can accelerated the decline in m RNA and protein levels associated with MQC in hippocampus of young and aged mice,but PGC-1? levels were increased in the young mice.Compared with the LPS group,the levels of m RNA or protein associated with MQC in the hippocampus were increased in the LPS-E mice,especially in the aged group.Pearson correlation analysis showed that the decline of m RNAs and proteins associated with MQC was negatively correlated with the learning and memory ability,especially in the aged mice.The increase of m RNAs and proteins associated with MQC in the LPS-E group was related to the improvement of spatial memory ability.(4)Compared with the 6-month control group,the m RNA and protein levels of hippocampal TET1/GSNOR decreased significantly in the 18-month control group.Compared with the control group at the same age,the m RNA and/or protein levels of TET1/GSNOR in the 6-month and 18-month LPS groups decreased significantly,except for TET1 m RNA in the 6-month LPS group.Compared with the LPS group at the same age,the hippocampal TET1/GSNOR m RNA and protein levels was no significant change in the 6-month LPS-E group,but they were significantly increased in the 18-month LPSE group.Pearson correlation analysis showed that the levels of hippocampus TET1/GSNOR m RNA and protein were negatively correlated with learning and memory ability in different groups at 18 months of age,and the correlation pattern was the same in the LPS-E and the control group.SummaryIn conclusion,both the hippocampal MQC mechanism and the TET1 / GSNOR axis showed age-related downregulation;inflammatory insult during pregnancy can accelerate the Age-related behavioral changes of CD-1 mothers and the changes of MQC and TET1/GSNOR axis in hippocampus;EE can delay the Age-related behavioral changes and the alterations in MQC and TET1/GSNOR axis caused by inflammatory exposure during pregnancy.