👤 Yutaka Oiso

Excess carbohydrate intake causes obesity in humans. On the other hand, acute administration of fructose, glucose or sucrose in experimental animals has been shown to increase the plasma concentration of anti-obesity hormones such as glucagon-like peptide 1 (GLP-1) and Fibroblast growth factor 21 (FGF21), which contribute to reducing body weight. However, the secretion and action of GLP-1 and FGF21 in mice chronically fed a high-sucrose diet has not been investigated. To address the role of anti-obesity hormones in response to increased sucrose intake, we analyzed mice fed a high-sucrose diet, a high-starch diet or a normal diet for 15 weeks. Mice fed a high-sucrose diet showed resistance to body weight gain, in comparison with mice fed a high-starch diet or control diet, due to increased energy expenditure. Plasma FGF21 levels were highest among the three groups in mice fed a high-sucrose diet, whereas no significant difference in GLP-1 levels was observed. Expression levels of uncoupling protein 1 (UCP-1), FGF receptor 1c (FGFR1c) and β-klotho (KLB) mRNA in brown adipose tissue were significantly increased in high sucrose-fed mice, suggesting increases in FGF21 sensitivity and energy expenditure. Expression of carbohydrate responsive element binding protein (ChREBP) mRNA in liver and brown adipose tissue was also increased in high sucrose-fed mice. These results indicate that FGF21 production in liver and brown adipose tissue is increased in high-sucrose diet and participates in resistance to weight gain. Show less

The action of incretin hormones including glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) is potentiated in animal models defective in glucagon action. It has been reported that such animal models maintain normoglycaemia under streptozotocin (STZ)-induced beta cell damage. However, the role of GIP in regulation of glucose metabolism under a combination of glucagon deficiency and STZ-induced beta cell damage has not been fully explored. In this study, we investigated glucose metabolism in mice deficient in proglucagon-derived peptides (PGDPs)-namely glucagon gene knockout (GcgKO) mice-administered with STZ. Single high-dose STZ (200 mg/kg, hSTZ) or moderate-dose STZ for five consecutive days (50 mg/kg × 5, mSTZ) was administered to GcgKO mice. The contribution of GIP to glucose metabolism in GcgKO mice was also investigated by experiments employing dipeptidyl peptidase IV (DPP4) inhibitor (DPP4i) or Gcg-Gipr double knockout (DKO) mice. GcgKO mice developed severe diabetes by hSTZ administration despite the absence of glucagon. Administration of mSTZ decreased pancreatic insulin content to 18.8 ± 3.4 (%) in GcgKO mice, but ad libitum-fed blood glucose levels did not significantly increase. Glucose-induced insulin secretion was marginally impaired in mSTZ-treated GcgKO mice but was abolished in mSTZ-treated DKO mice. Although GcgKO mice lack GLP-1, treatment with DPP4i potentiated glucose-induced insulin secretion and ameliorated glucose intolerance in mSTZ-treated GcgKO mice, but did not increase beta cell area or significantly reduce apoptotic cells in islets. These results indicate that GIP has the potential to ameliorate glucose intolerance even under STZ-induced beta cell damage by increasing insulin secretion rather than by promoting beta cell survival. Show less

Gastric inhibitory polypeptide (GIP) is an incretin secreted from the gastrointestinal tract after an ingestion of nutrients, and stimulates an insulin secretion from the pancreatic islets. Additionally, GIP has important roles in extrapancreatic tissues: fat accumulation in adipose tissue, neuroprotective effects in the central nervous system and an inhibition of bone resorption. In the current study, we investigated the effects of GIP signaling on the peripheral nervous system (PNS). First, the presence of the GIP receptor (GIPR) in mouse dorsal root ganglion (DRG) was evaluated utilizing immunohistochemical analysis, western blotting and reverse transcription polymerase chain reaction. DRG neurons of male wild-type mice (WT) were cultured with or without GIP, and their neurite lengths were quantified. Functions of the PNS were evaluated in GIPR-deficient mice (gipr-/-) and WT by using current perception thresholds (CPTs), Thermal Plantar Test (TPT), and motor (MNCV) and sensory nerve conduction velocity (SNCV, respectively). Sciatic nerve blood flow (SNBF) and plantar skin blood flow (PSBF) were also evaluated. We confirmed the expression of GIPR in DRG neurons. The neurite outgrowths of DRG neurons were promoted by the GIP administrations. The gipr-/- showed impaired perception functions in the examination of CPTs and TPT. Both MNCV and SNCV were delayed in gipr-/- compared with these in WT. There was no difference in SNBF and PSBF between WT and gipr-/-. Our findings show that the GIP signal could exert direct physiological roles in the PNS, which might be directly exerted on the PNS. Show less

Calcium plays a fundamental role as second messenger in intracellular signaling and bone serves as the body's calcium reserve to tightly maintain blood calcium levels. Calcium in ingested meal is the main supply and inadequate calcium intake causes osteoporosis and bone fracture. Here, we describe a novel mechanism of how ingested calcium is deposited on bone. Meal ingestion elicits secretion of the gut hormone gastric inhibitory polypeptide (GIP) from endocrine K cells in the duodenum. Bone histomorphometrical analyses revealed that bone formation parameters in the mice lacking GIP receptor (GIPR(-/-)) were significantly lower than those of wild-type (GIPR(+/+)) mice, and that the number of osteoclasts, especially multinuclear osteoclasts, was significantly increased in GIPR(-/-) mice, indicating that GIPR(-/-) mice have high-turnover osteoporosis. In vitro examination showed the percentage of osteoblastic cells undergoing apoptosis to be significantly decreased in the presence of GIP. Because GIPR(-/-) mice exhibited an increased plasma calcium concentration after meal ingestion, GIP directly links calcium contained in meal to calcium deposition on bone. Show less