Identification Of Human Intestinal Akkermansia Glycaniphila And Its Role In Regulating Metabolic Disorders Induced By High-Fat Diet In Mice

Akkermansia muciniphila is one of the few gut bacteria that has been proven to improve host health.A large number of studies have shown that it has great potential in improving and preventing metabolic diseases such as type 2 diabetes.Akkermansia glycaniphila PytT,the second Akkermansia species found to have the ability to decompose mucin,was first isolated from the reticulated python feces.Reticulated pythons are very different from humans and other mammals in evolution,and the gut bacteria isolated from them may have very different role from those in the human intestine.Our research team successfully isolated 39 Akkermansia strains from human feces,and found that the strain numbered GP37 was the same species with A.glycaniphila by analyzing the complete genome sequence.In order to explore the potential function of the new Akkermansia species in the gastrointestinal tract,the physiological and biochemical characteristics of A.glycaniphila isolated from human feces were conducted,and animal experiments were performed to verify its function in vivo.All of the above studies provided a basis for further physiological function research in A.glycaniphila from human intestine.1 Objectives1.1 To explore the physiological and biochemical characteristics of human intestinal A.glycaniphila;1.2 To explore the protective role of human intestinal A.glycaniphila on the metabolic disorders induced by high-fat diet in mice;1.3 To explore the related mechanism of human intestinal A.glycaniphila affecting metabolism.2 Methods2.1 A.glycaniphila GP37 strain isolated from human intestine was selected,and A.muciniphila MucT was used as a control to observe the morphology under transmission electron microscopy,and determined the growth curve,carbon source and nitrogen source utilization spectrum,and cell fatty acid composition.2.2 Forty eight-week-old weeks of C57BL/6 mice were randomly divided into four groups according to body weight,including a high-fat diet GP3 7 gavage group,a highfat diet PBS gavage group,a normal chow diet GP37 gavage group,and a normal chow diet PBS gavage group.Each mouse in the GP37 group was given a dose of 4×109 cfu/200 μL every other day,while mice in the control group was given the same volume of PBS.The body weight and food intake of the mice were measured and recorded weekly after the start of the gavage,and the whole animal experiment lasted 20 weeks.Oral glucose tolerance test was performed before the end of animal experiments.Blood was taken to measure serum insulin levels,lipid levels and endotoxin levels.The colon and liver were collected to observe the pathological morphology,and the relative expression of inflammatory factor genes such as IL-6、IL-1β、TNF-α in mouse liver was determined.3 Results3.1 Human intestinal A.glycaniphila is a short bacillus with a size of about 0.6×1.52.0μm.It grows more slowly than A.muciniphila,but the bacterial concentration in the plateau is higher.The highest cellular fatty acid content was C15:0 anteiso.Nacetylglucosamine and rhamnose can be used as the sole carbon source,and threonine cannot be used as the sole nitrogen source by A.glycaniphila.3.2 Human intestinal A.glycaniphila can improve impaired glucose tolerance in mice induced by a high-fat diet,but didn’t affect serum insulin levels and blood lipid.It also had no effect on weight and food intake in mice.3.3 Human intestinal A.glycaniphila could not improve the endotoxemia in mice caused by high-fat diet,and had no significant effect on the number of mucus cells in the colon and transcription of Ocln gene encoding tight junction protein.3.4 Human intestinal A.glycaniphila can alleviate hepatic steatosis induced by a highfat diet,and reduce the expression of IL-1β gene in liver,and had no significant effect on expression of IL-6、TNF-α.4 ConclusionHuman intestinal A.glycaniphila is a Gram-negative Brevibacterium that grows slower than A.muciniphila but has a higher bacterial concentration in the plateau phase.It can significantly improve the impaired glucose tolerance in high-fat diet mice through oral gavage.But it had no effect on insulin secretion and hyperlipidemia.In addition,human intestinal A.glycaniphila can alleviate liver steatosis and chronic liver inflammation,but has no obvious effect in repairing the intestinal barrier and relieving endotoxemia.