Lycopene alleviates age-related cognitive deficit via activating liver-brain fibroblast growth factor-21 signalling

Brain function is linked with many peripheral tissues, including the liver, where hepatic fibroblast growth factor 21 (FGF21) mediates communication between the liver and brain. Lycopene (LYC), a naturally occurring carotenoid, posses multiple health-promoting properties, including neuroprotective function. Here, we investigated the effects of LYC on age-related memory impairment and the relative contribution of liver-brain FGF21 signaling in these process. The results showed that after treatment with LYC for 3 months, brain aging and age-related cognitive deficits were effectively managed. In addition, LYC ameliorated neuronal degeneration, mitochondrial dysfunction and synaptic damage, and promoted synaptic vesicle fusion in 18-month-old mice. Notably, LYC activated liver-brain FGF21 signalling in aging mice. Whereas all these central effects of LYC were negated by blocking FGF21 via i. v. injection of adeno-associated virus in aging mice. Furthermore, recombinant FGF21 elevated mitochondrial ATP levels and enhanced synaptic vesicle fusion in mouse hippocampal HT-22 cells, which promoted neurotransmitter release. Additionally, we co-cultured hepatocytes and neurons in Transwell and found that LYC enhanced hepatocytes' support for neurons. This support included improved cell senescence, enhanced mitochondrial function, and increased axon length in co-cultured neurons. In conclusion, LYC protects against age-related cognitive deficit, partly explained by activating liver-brain FGF21 signalling, hence promoting neurotransmitters release via increasing mitochondrial ATP levels and enhancing synaptic vesicle fusion. These findings revealed that FGF21 could be a potential therapeutical target in nutritional intervention strategies to improve cognitive damage caused by aging and age-related neurodegenerative diseases.