The regulation mechanism of Akkermansia muciniphila on glucose metabolism of the Cyprinus carpio

Currently, the majority of studies investigating the effects of Akkermansia muciniphila primarily focus on blood glucose homeostasis, adipose tissue accumulation, intestinal permeability, and body weight regulation. However, these studies are predominantly limited to human and mammalian subjects. The specific mechanism by which A. muciniphila regulates glucose metabolism in fish remains unclear. So we investigate the molecular mechanism of pasteurized A. muciniphila regulating glucose metabolism in Cyprinus carpio. In this study, different sugar concentrations (20%, 30%, 40%, 50% glucose) were examined to investigate the temporal and spatial variations in glucagon-like peptide-1 secretion and A. muciniphila colonization at 4 and 8 weeks of C. carpio (10.5±1.0 g). Based on the different sugar concentration tests, groups with a glucose level of 40% and three varying concentrations of pasteurized A. muciniphila (10⁸, 10⁹, 10¹⁰ CFU/g) were established. The regulation of glucose metabolism and glucagon-like peptide-1 in C. carpio (16.38±0.39 g) after four weeks of pasteurized A. muciniphila supplementation was explored. Additionally, the regulatory mechanism of intestinal A. muciniphila and glucagon-like peptide-1 on carp's glucose metabolism at different glucose levels was investigated through experiments involving primary liver and intestinal cells incubated with pasteurized A. muciniphila. The results demonstrated the following findings: (1) with an increase in dietary glucose content, there was a significant decrease in serum glucagon-like peptide-1b levels (P <0.05). (2) following pasteurized A. muciniphila treatment, there was a significant reduction in serum glucose and glucagon-like peptide-1 levels (P < 0.05). Moreover, there were notable increases in villus height and muscle thickness of the midintestine along with a decrease in glucagon-like peptide-1 content and an increase in short-chain fatty acid content; additionally, muc2 mRNA expression level increased significantly (P<0.05). Furthermore, pasteurized A. muciniphila up-regulated mRNA expression levels of ampk, pi3k, akt as well as glycolytic genes gk and pfk in the liver while down-regulating mRNA expression levels of gluconeogenic gene pepck (P < 0.05). (3) incubation results from primary liver and intestinal cells revealed that after pasteurized A. muciniphila treatment, there was a significant decrease in glucagon-like peptide-1 content within intestinal cells while simultaneously increasing gpr40 mRNA expression; furthermore, hepatocytes showed significantly increased mRNA expressions of glycolysis genes gk and pfk. In conclusion, high glucose diet increases the blood glucose levels, and causes liver and intestinal damage of C. carpio. The addition of exogenous pasteurized A. muciniphila increases the content of short chain fatty acids in C. carpio intestinal contents, inhibits intestinal secretion of glucagon-like peptide-1, alleviates the increase in blood glucose caused by high glucose diet, maintains glucose homeostasis. This research can provide the practical basis for the application of A. muciniphila as a probiotic in aquatic feed.