The Ameliorative Effect Of Environmental Enrichment On Age-related Cognitive Decline Induced By Prenatal Maternal Immune Activation In Offspring Mice And Related Mechanisms

BackgroundAs the percentage of the elderly population continues to rise,aging and the associated health problems pose a tremendous burden on the socioeconomics of the society and on the quality of living of the individuals and also the caretakers.Cognitive impairment is one of the most common observations in the aging process.Unfortunately,this patient population is further expanding as effective approaches to mitigate brain aging are still lacking.Therefore,it is particularly important to understand the pathogenesis of aging-related cognitive impairment and to explore potential interventions.It has been demonstrated that prenatal maternal immune activation(MIA)accelerates brain aging and associated cognitive decline in offspring.However,to date,the exact mechanisms by which prenatal MIA stress accelerates brain aging changes remain unclear.Studies have shown that a combination of neurobiological alterations such as loss of hippocampal synaptic proteins,β-amyloid-β(Aβ)deposition,neuroinflammatory activation,increased oxidative stress and apoptosis,reduced neurogenesis,and activation of systemic inflammatory responses may be associated with learning and memory impairment.In contrast to prenatal MIA,environmental enrichment(EE)treatment may have a role in delaying aging-related cognitive deficits.Therefore,this study hypothesizes that(i)during natural aging,relevant behavioral changes are accompanied by the above-mentioned neurobiological mechanisms changes.(ii)prenatal MIA stress accelerates aging-related behavioral changes accompanied by the acceleration of the above neurobiological changes?(iii)Does EE treatment have an ameliorating effect on prenatal MIA stress-induced aging-related behavioral as well as the accelerating effect of the above neurobiological changes?Research on these questions may provide a reference for exploring brain aging mechanisms and prevention methods.ObjectiveTo investigate whether EE treatment has an ameliorative effect on aging-related behavioral changes accelerated by prenatal MIA stress;to explore the changes in hippocampal synaptic proteins,Aβdeposition,central and systemic inflammatory responses,oxidative stress,apoptosis,and neurogenesis mechanisms in mice with natural and prenatal MIA stress-accelerated(pathological)aging models,and whether EE exposure has a protective effect on damage to these mechanisms.MethodsCD-1 mice received daily intraperitoneal injections of Lipopolysaccharides(LPS;50μg/kg)or the same volume of normal saline starting from day 15-17 of gestation.The offspring mice were nursed normally by their mothers until postnatal day 21,when they were weaned and separated into cages.The male offspring were assigned to(1)control group(CON,whose mothers received saline injection during pregnancy);(2)LPS group(whose mothers received LPS injection during pregnancy);(3)CON-EE group;and(4)LPS-EE group.The the CON and LPS mice lived in standard mouse cages(31.8×20.2×13.5 cm3,4-5 mice/cage);mice in the CON-EE)and LPS-EE groups were housed in large cages(54.5×39.5×20 cm~3,8-10 mice/cage)equipped with additional toys,including running wheels,tunnels,ladders,wooden bridges,and wooden houses,and were kept regularly replacement.EE treatment(short-term EE:from weaning to 3 months of age;long-term EE:from weaning to 15 months of age)was continued until the end of the behavioral experiment.When the mice reached 3 months of age or 15 months of age,6 from each group were randomly selected to complete the following experiments.(1)Behavioral assessment:sensorimotor coordination(balance beam),anxiety and depression and spontaneous exploratory behavior(black and white alley,open-field activity and elevated plus maze),sleep monitoring,and learning and memory function(Y-maze and Morris water maze).(2)Enzyme-linked immunosorbent assays were used to measure hippocampal and serum levels of inflammatory cytokines,hippocampal Aβand 8-hydroxy-2’-deoxyguanosine(8-OHd G);chemofluorescence,thiobarbituric acid and external colorimetric assays were used to measure hippocampal reactive oxygen species(ROS),malondialdehyde(MDA)and protein carbonyl(PCO),respectively.(3)q RT-PCR and western blotting were used to detect m RNA and/or protein expression of hippocampal synaptic proteins,inflammation,neurogenesis and apoptosis-related markers,respectively.Results(1)Compared with the 3-month-old CON group,the 15-month-old CON mice showed significantly reduced motor coordination and balance function,sleep quality,and learning and memory functions,and significantly increased anxiety and depressive behavior,while no significant changes in spontaneous exploratory activity were observed.Prenatal MIA treatment significantly exacerbated the impairments in balance function,sleep quality,cognitive function,and anxiety and depressive behavior in aged LPS mice,whereas EE treatment at least partially restored the aging-related behavioral changes in aged LPS-EE group mice.(2)Compared with 3-month-old CON group mice,15-month-old CON group mice showed significantly reduced hippocampal synaptic proteins(postsynaptic density protein-95,Gephyrin,synaptophysin,and synaptosomal associated protein of molecular mass-25)and neurogenesis(doublecortin and sex determining region Y-box 2),whereas the deposition of Aβ(Aβ1-40 and Aβ1-42),activation of glial cells(glial fibrillary acidic protein and ionized calcium-binding adapter molecule 1),the production of inflammatory cytokines(interleukin-6,interleukin-1β,and tumor necrosis factor-α),and the activation of the receptor for advanced glycation end products/nuclear factor-κB and P2X7receptor/NOD-like receptor protein 3/Caspase-1 signaling pathway,the expression of neurite growth-promoting factor 2,serum inflammatory cytokine(interleukin-6,interleukin-1β,and tumor necrosis factor-α)concentrations,oxidative stress damage(ROS,MDA,PCO,and 8-OHd G),and neuronal apoptosis(Bcl-2-associated X protein,B-cell lymphoma-2,Bax/Bcl-2 ratio and Cleaved caspase-3)were significantly increased.Prenatal MIA treatment accelerated the aging-related trends in hippocampal synaptic proteins,neurogenesis and apoptosis,Aβproduction,neuroinflammation,oxidative damage,and peripheral inflammation-related markers described above in LPS mice,whereas EE intervention delayed these trends to some extent.SummaryIn summary,prenatal MIA stress could accelerate aging-related behavioral(balance function,sleep quality,especially cognitive function,and anxiety and depressive behavior)impairments as well as aging-related neurobiological changes(hippocampal synaptic protein loss,neurogenesis and apoptosis imbalance,Aβdeposition,increased neuroinflammation and oxidative stress damage,and systemic inflammation upregulation),and EE treatment could ameliorate prenatal MIA-induced aging-related behavioral impairments by reversing the aforementioned aging-related neurobiological changes in LPS mice.