Discussion
Previous studies have shown that gut microbiota and its metabolic products are vital for many metabolic diseases, including obesity (Turnbaugh et al., 2006), insulin resistance (Cani et al., 2007), metabolic syndrome (Vijay-Kumar et al., 2010) and liver steatosis (Spencer et al., 2011). Increasing data indicate that diabetic metabolic disorders are closely related to changes in gut microbiota composition, gut microbiota affects host metabolism by altering gluconeogenesis, glycogenolysis, lipogenesis, inflammation and hormone action (Federico et al., 2017, (Muñoz-Garach et al., 2016). Hence, reverse gut dysbiosis may represent a novel strategy to treat or prevent diabetes. In this study, we demonstrated that Dios treatment remarkably ameliorated glucose metabolism in KK-Ay diabetic mice by the regulation of C. glu on IRS/PI3K/AKT signaling pathway and reshaped the unbalanced gut microbiota.
Glycogen is supposed to be the principal storage form of glucose and its metabolisms are primarily in the liver and skeletal muscle. The concerted regulation of the rate of glycogen synthesis and the rate of glycogenolysis is one of the principal methods in the maintenance of glycogen homeostasis. Defects in these two processes can be major contributors to hyperglycemia and insulin resistance (Petersen et al., 2017). Thus, glycogen homeostasis plays an important role in the development of T2DM. Insulin is the main hormone proteins produced by the β cells of pancreatic islets and regulates many important biological functions, which control the metabolism and storage of the three major nutrients (Niswender, 2011). Insulin mainly stimulates lipogenesis, glycogen and protein synthesis and inhibits lipolysis and protein breakdown, to stimulate cell growth and differentiation, and promote the storage of substrates in fat, liver and muscle (Edgerton et al., 2006). When insulin resistance or insulin deficiency occurs, it will cause a serious imbalance of these processes and metabolic disorders, which will lead to the destruction of body homeostasis (Tzeng et al., 2012). The IR and related IRS, the PI3K heterodimer, and AKT are three well-defined and essential mediators of the insulin signaling pathway. Insulin binds to the insulin receptor tyrosine kinase and activates the receptor and then phosphorylates the insulin receptor substrate (IRS), phosphorylated IRS then activates PI3K, and subsequently phosphorylates Akt, leading to Akt activation. When AKT is activated, it participates in the metabolic pathways of glucose transport and glycogen synthesis (Beale, 2013). In our study, through transcription analysis, we predicted that the potential mechanism of Dios ameliorated T2DM may be through regulating glucose metabolism and insulin resistance. As would be predicted, we found that Dios could predominantly up-regulating IRS/PI3K/AKT signaling pathway to promoting glycogen synthesis and GLUT4 translocation to regulate the balance of glucose level.
In recent years, several studies have shown that gut microbiota dysbiosis has been suggested as a prominent feature of T2DM (Ahmad et al., 2019, (Sabatino et al., 2017). In diabetic mice, an obvious shift betweenFirmicutes and Bacteroidetes when compared with non-diabetic mice, which indicates that these major phyla may play a role in T2DM, as reported previously (Qin et al., 2012). In our study, we found that Dios effectively reversed gut microbiota dysbiosis when compared to untreated diabetic mice. Moreover, Dios treatment restored the Firmicutes/Bacteroidetes ratio close to that observed in non-diabetic mice. Intriguingly, the ratio ofActinobacteria phylum was also significantly higher in the H-Dios group than in the other groups. TheActinobacteriaphylum represents one of the largest groups of bacteria. It is well known that theActinomycetes , a potentially beneficial bacteria, are a diverse phylum of Gram-positive bacteria found in the human intestinal tract and soil (Bhatti et al., 2017). Thus, we want to further explore the impact of Dios on the relative abundance of the gut microbiota at the species level. In our study, the C._glu is markedly increased by Dios (60 mg/kg) treatment compared with KK-Ay diabetic mice. Numerous studies have indicated that C. glu is a Gram-positive soil bacteria belonging to the orderCorynebacteriales within the Actinobacteria (Becker et al., 2018). Meanwhile, C. gluis an important industrial metabolite producer, and has been widely used for the industrial production of various amino acids, vitamins, and nucleotides (Lee et al., 2016). Previous studies suggested that C. glu plays a crucial role in the process of glycogen synthesis. At the same time, by encoding the glg C gene of C. glu, a key enzyme in glycogen synthesis, and studying its correlation with ADP-glucose pyrophosphorylase, it was found that the cells of C. glu grown in a medium containing glucose, sucrose or fructose as glycolytic substrates showed rapid glycogen accumulation in the early exponential growth phase (Seibold et al., 2007). Therefore, we hypothesized thatC. glu may be a potential beneficial bacteria in the development of T2DM. To test this hypothesis, KK-Ay diabetic mice were treated withC. glu , Dios or C. glu +Dios for 4 weeks. We found that the addition of C. glu alone can remarkably reduce HFD-induced body weight and blood glucose gain and significantly ameliorated lipid accumulation compared with KK-Ay diabetic mice group. However, when treatment with C. glu and Dios together, the body weight and blood glucose gain down-regulated more significantly. Besides, we found that treatment withC. glu and Dios together can markedly ameliorate glucose metabolism by up-regulating IRS/PI3K/AKT signaling pathway to promoting glycogen synthesis and GLUT4 translocation compared with KK-Ay mice.
In summary, in the present study, we demonstrated for the first time that Dios could ameliorate glucose metabolism in KK-Ay diabetic mice by the regulation of C. glu on IRS/PI3K/AKT signaling pathway and reshaped the unbalanced gut microbiota. Collectively, our results suggested that Dios may function as potential anti-diabetic agent to effectively play a positive role in the management of T2DM patients.