Lactoferrin alleviates Western diet-induced cognitive impairment through the microbiome-gut-brain axis

Abstract

Lactoferrin (Lf) is a multifunctional glycoprotein that showed demonstrated a beneficial effect on cognitive function in several mouse models; however, its mechanisms are not fully elucidated. This study investigated whether Lf improves high-energy-dense 'Western'-style diets (WD)-induced cognitive impairment and neuroinflammation through microbiome-gut-brain axis. Male C57BL/6J mice were randomly divided into the CON, WD, Lf, and Lf+AB groups. The mice in the latter three groups fed with WD. The Lf group was intragastrically administered with Lf and the Lf+AB group additionally drank a solution with antibiotics. Some of the mice in the CON, WD, and Lf groups were killed at 2 weeks. The experiments ended at 16 weeks. Behavioral tests, neuroinflammation, and gut microbiota were analyzed. WD resulted in neuroinflammation and impaired cognition. Lf improved the cognitive function as indicated by behavioral tests including nesting behavior test, novel object recognition test, and the Morris water maze test. It also increased the length and curvature of postsynaptic density as observed with a transmission electron microscope and upregulated the related protein expression, suggesting the improvement of the hippocampal neurons and synapses. Lf suppressed microglia activation and proliferation as revealed by immunofluorescence analysis. It decreased the serum levels of pro-inflammatory cytokines and downregulated their protein expressions in the hippocampus region. Lf also inhibited the activation of NF‐κB/NLRP3 inflammasomes in the hippocampus. Meanwhile, WD impaired gut permeability and induced gut dysbiosis. Lf upregulated the expression of tight junction proteins, and increased the abundance of Bacteroidetes at phylum and Roseburia at genus, bothare beneficial for anti-obesity, gut barrier, and cognitive function. The antibiotics supplemented in the Lf+AB group eliminated the effects of long-term Lf intervention on cognitive impairment, suggesting that gut microbiota participated in Lf action. The 2-week Lf intervention prevented WD-induced gut microbiota alteration without inducing behavioral changes; these findings supported the timing sequence of gut microbiota to the brain. In Conclusion, our findings demonstrated that Lf intervention alleviated cognitive impairment by inhibiting microglial activation and neuroinflammation through the microbiome-gut-brain axis.