Ageing-associated gut dysbiosis deteriorates mouse cognition

Ageing is an independent factor for cognitive dysfunction. Ageing-associated alterations in the gut microbiota also affect cognition. The present study is designed to investigate changes in the gut microbiota and their participation in ageing-associated cognitive impairment. Both 10-week-old and 18-month-old mice are used. Mouse cognition is examined by novel object recognition and T-maze tests. Mouse feces are collected for sequencing and transplantation. Protein expression in the mouse intestine and hippocampus is studied using immunohistochemistry and immunofluorescence staining. Senescent neurons are induced by hydrogen peroxide <i>in vitro</i>. The cell lysates are used for western blot analysis and adenosine triphosphate (ATP) measurement. Our results show that 18-month-old mice exhibit cognitive dysfunction compared with young mice. In aged mice, transplanting the microbiota of young mice increases the protein presence of synaptophysin in the hippocampus and partially restores cognition. The protein expressions of mucin-2 and E-cadherin in the intestine are reduced in aged mice but are increased by transplantation. Gut microbiota analyses reveal that the reduced abundance of the microbe <i>Bacilli-Lactobacillales-Lactobacillaceae-Lactobacillus</i> in aged mice is restored by transplantation. Fecal microbiota transplantation in young mice increases the serum level of acetic acid in aged mice. Hydrogen peroxide stimulation induces senescence and reduces the protein expression levels of synaptophysin and acetyl-coenzyme A synthetase member 2 (ACSS2) in primary neurons. Incubation with acetic acid upregulates the protein expressions of ACSS2 and synaptophysin and further increases ATP production in senescent neurons. In summary, gut microbiota transplantation increases the abundance of <i>Lactobacillales</i>, elevates serum acetic acid level, and improves cognitive function in aged mice. Gut microbiota transplantation has therapeutic importance for ageing-associated cognitive decline.