| Now the incidence of diabetes mellitus increases with years, and gradually becomes common complaints together with cardiovascular disease and malignant tumor, with high disability rate and lethality. Moreover, more than 85% are type 2 diabetes mellitus. The leading features of type 2 diabetes mellitus are blood glucose increasing, insulin resistance and impaired islet beta cells’ function. The key for treating type 2 diabetes mellitus are reducing blood glucose, protecting pancreas islet, and promoting beta cells insulin secretion.The molecular weight of sericin is 10-300 KD, which is a kind of water-soluble protein composed of 18 kinds amino acids. The content of sericin is about 25% of cocoon silk, which is thrown away during reeling and refining. Our early study found that sericin has favorable functions of lowering blood sugar, but the mechanism is unclear. In this study, we will investigate the intervention effects of sericin on pancreatic insulin PI3K/AKT signaling pathway using type 2 diabetes mellitus rats model induced by streptozotocin plus high calorie and high sugar diet, so to open up a new way for prevention and cure diabetes mellitus. Objective:To investigate the roles and mechanisms of sericin on pancreatic insulin PI3K/AKT signaling pathway by observing effects of sericin on expression of insulin receptor(IR), insulin receptor substrate-1(IRS-1), phosphatidylinositol 3-kinase(PI3K) and protein kinase B(Akt/PKB) in pancreas of type 2 diabetes mellitus rats model. Methods:1. 60 male SD rats were randomly divided into the following 5 groups with 12 rats in each group: normal control(NC) group, diabetes model(DM) group, high-dose sericin treatment(HS) group, low-dose sericin treatment(LS) group and positive control(PC) group. The type 2 diabetes mellitus rats model was induced by high calorie and high sugar diet plus intraperitoneal injection of streptozotocin(35mg/kg), and the standard for successfully establishing type 2 diabetes model was fasting blood glucose≥11.1mmol/L. Then, the rats in HS(2.4g/kg/d) group and LS dose(1.8g/kg/d) group were lavaged with sericin in different dose for 35 days; the rats in PC group were lavaged with metformin for 35days; the rats in NC group and DM group were lavaged with normal saline in same dose and time as sericin group.2. Glucose oxidase method was used to measure the fasting blood glucose of rats in each group.3. ELISA was used to detect the insulin(INS) and adiponectin(ADP) level in serum of rats in each group.4. Western Blotting was used to detect the expression of IR, IRS-1, PI3 K and Akt/PKB protein in pancreas of rats in each group.5. Real-time FQ-PCR was used to detect the expression of IR, IRS-1, PI3 K and Akt/PKB mRNA in pancreas of rats in each group. Results:1. Blood glucose: The blood glucose of rats in DM group was(29.45±4.82)mmol/L, which was obviously higher than that of rats in NC group [(10.83±2.03)mmol/L](P<0.05). The blood glucose of rats in HS group, LS and PC group were respectively(13.20±4.09)mmol/L,(13.18±2.30)mmol/L,(10.04±2.29)mmol/L, which were all obviously lower than DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05).2. INS level: The INS level in serum of rats in DM group was(7.28±0.58)μg/L, which was significantly lower than that of rats in NC group [(11.45±1.72)μg/L](P<0.05). The INS level in serum of rats in HS group, LS group and PC group were respectively(12.65±2.17)μg/L,(13.30±1.64)μg/L,(11.13±0.99)μg/L, which were all significantly higher than DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05).3. ADP level: The ADP level in serum of rats in DM group was(49.36±12.91)μg/L, which was significantly lower than that of rats in NC group [(70.11±18.08)μg/L](P<0.05). The ADP level in serum of rats in HS group, LS group and PC group were respectively(95.20±26.80)μg/L,(76.77±10.17)μg/L,(83.50±4.63)μg/L, which were all significantly higher than DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05).4. IR: Compared with rats in NC group, the expression of IR protein and mRNA in pancreas of rats in DM group obviously decreased(P<0.05); The expression of IR protein and mRNA in pancreas of rats in HS group, LS group and PC group were obviously lower than that of rats in DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05).5. IRS-1: Compared with rats in NC group, the expression of IRS-1 protein and mRNA in pancreas of rats in DM group significantly decreased(P<0.05); The expression of IRS-1 protein and mRNA in pancreas of rats in HS group, LS group and PC group were significantly lower than that of rats in DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05).6. PI3K: Compared with rats in NC group, the expression of PI3 K protein and mRNA in pancreas of rats in DM group obviously decreased(P<0.05); The expression of PI3 K protein and mRNA in pancreas of rats in HS group, LC group and PC group were obviously lower than that of rats in DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05).7. Akt: Compared with rats in NC group, the expression of Akt protein and mRNA in pancreas of rats in DM group significantly decreased(P<0.05); The expression of Akt protein and mRNA in pancreas of rats in HS group, LS group and PC group were significantly lower than that of rats in DM group(P<0.05); Moreover, there had no statistical significance between HS group, LS group and PC group(P>0.05). Conclusions:Sericin can improve the abnormal changes of PI3K/AKT signaling pathway by up regulating IR, IRS-1, PI3 K and Akt/PKB expression in pancreas of diabetes mellitus rats; Thereby, sericin play a role in lowering blood glucose. |
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