PET Molecular Imaging Of Gut Microbiota Transplantation For Attenuating Cognitive Aging

Background:Aging is an inevitable process that almost all the creatures must experience.In recent years,life expectancy obtains obviously prolonged due to the improvement of living standard and medical management.World Health Organization（WTO）assessed that the proportion of people over 60 years will over 20%at the end of 2050.Aging will lead to comprehensive decrease of physiological function,including genomic instability,mitochondrial dysfunction and cognitive ability decline.Therefore,aging is one of the most important risk factors for oncology,inflammation and neurodegenerative diseases.Central nervous system（CNS）is more sensitive to the effects of aging,manifested in the shrinkage of brain tissue,increased neuroinflammation,and cognitive impairment.Herein,how to delay or even reverse this process has become a hot spot in aging research today.Gut microbiome is defined as a general term for bacteria,archaea and eukaryotesresiding in the gastrointestinal tract（GI）.In addition to participating in regulating the homeostasis of the intestinal microenvironment,gut microbiome has also been found to involve in the formation and regulation of nervous system functions by mediating the formation of the blood-brain barrier（BBB）,the maturation and function formation of microglia in the brain and synapses plasticity,which in turn affects their learning and memory extinction.Although there are many studies related to gut microbes and neurodegenerative diseases,there is no systematic research relevant to utilization of gut microbiome to interfere in cognitive aging.Positron emission tomography（PET）is a molecular imaging technology that can non-invasively reflect the activities of cells and molecules in the living body.¹⁸F-fluorodeoxyglucose(¹⁸F-FDG),as a glucose analogue,can real time reflect the uptake of glucose in cells and monitor the changes in glucose metabolism at the level of the living body.It has been used for the diagnosis in a variety of neurological diseases.In this study,we aimed to describe the changes in gut microbiome,cognition andneuroinflammation in aged mice,and selected 14 months and 18-month-old mice to receive fecal microbiota transplantation to explore whether the gut microbiome of young mice can attenuate cognitive aging and its potential mechanisms.Moreover,¹⁸F-FDG PET was used to evaluate the effect of gut microbime transplantation of young mice in cognition of aged mice in vivo,providing the evidence for the clinical tranlation of gut microbiome transplantation.Part I:The effect of aging in gut microbiome of miceWe investigated the difference of gut microbiome composition between young miceand aged mice using 16s r DNA sequencing.The results showed that the diversity of gut microbiome was lower that that of young mice.Beta diversity analysis indicated that the composition of gut microbiome in aged mice was significantly different with young mice.In aged mice,the richness of Lachnospiraceae,Prevotellaceae,Helicobacteraceae,Mucispirillum,Deferribacteraceae,Saccharimonadaceae,Rhodobacteraceae and Francisellaceae was markedly increased,while the level of Akkermansiaceae,Akkermansia,Alloprevotella,Faecallibaculum and Terrimicrobiaceae was decreased.These results suggested the potential application of gut microbiome from young mice in attenuating cognitive aging.Part II:The effect of aging in cognition and neuroinflammation of miceWe explored the effects of aging on the cognitive function,glucose metabolism in thebrain,the permeability of the blood-brain barrier and the level of inflammation in the brain.Behavioral experiments showed that the exercise and cognitive abilities of aged mice were significantly reduced.Subsequently,the ¹⁸F-FDG micro PET scan showed that the glucose uptake of the cortex,hippocampus and striatum of aged mice was significantly decreased.Western blotting showed significantly reduced expression of tight junction proteins in the blood-brain barrier（BBB）of aged mice,and real-time quantitative polymerase chain reaction（RT-q PCR）showed that the expression of inflammatory factors in the brain of aged mice was significantly increased.Besides,the count of microglia was markedly increased in the hippocampus of aged mice.In summary,aging may increase the permeability of the BBB to promote the neuroinflammation,which further leads to declined ability of neurons to utilize glucose and ultimately resultes in cognitive decline.Part III:Gut microbiome transplantation attenuates cognitive decline in aged miceWe explored whether gut microbiome transplantation could attenuate cognitive decline in aged mice and the possible mechanism underlying it.We transplanted the gut microbiome of young mice to 14-month-old and 18-month-old mice,respectively.Cognitive function evaluation was performed at three different time points when the transplantation was completed,one month after the transplantation,and 5 months after the transplantation.¹⁸F-FDG micro PET scans were performed at the completion of the transplantation and 5 months after the transplantation.The in vitro histological evaluation was performed at the end.The results showed that the glucose metabolism in the hippocampus and startium was improved in 14-month-old mice after receiving fecal microbiota transplantation,as well as the cognitive ability.The biological results showed that gut microbiome transplantationcan reduce the plasma expression level of TNF-α,restore the permeability of BBB decrease the brain expression level of TNF-αin 14-month-old mice.Besides,the number of activated microglia was reduced in the hippocampus and startium of 14-month-old mice.However,after 18-month-old aging mice received intestinal flora transplantation from young mice,glucose metabolism in the brain was improved only when the transplantation was completed,but there was no significant change in cognitive function.