Effects of intensive exercise combined with dapagliflozin on body composition in patients with type 2 diabetes: a randomized controlled trial.

This study was aimed to evaluate the effects of intensive exercise in addition to the administration of sodium-glucose cotransporter 2 inhibitor dapagliflozin (DAPA) on body composition, including fat-free mass, in type 2 diabetes. We randomly assigned 146 patients to 24 weeks of treatment with intensive exercise, including resistance training, plus 5 mg (up to 10 mg) of DAPA daily (IT group) or DAPA alone (CT group). The primary endpoint was the difference in the change in fat-free mass from baseline to 24 weeks between the groups. The skeletal muscle mass index (SMI); metabolic profile, including HbA1c; and regional fat mass were also determined. ANCOVA was used for the group comparison, with least squares mean (LSM) differences and 95% confidence interval (CI). There was no significant difference in the change in fat-free mass (LSM difference -0.1 kg (95% CI: -0.5 to 0.4) and SMI (LSM difference -0.1 kg (95% CI: -0.2 to 0.1) between the groups. In contrast, the reduction of trunk fat mass was significantly higher in the IT group than in the CT group ((LSM difference -0.5 kg [95% CI -0.9 to -0.1]). Higher adherence to the resistance training tended to be associated with changes in HbA1c and high-sensitivity CRP levels. Our study suggests that intensive exercise do not prevent the reduction of fat-free mass after administration of SGLT2 inhibitors but can increase the reduction in abdominal fat, presumably leading to further improvements of hyperglycemia and chronic inflammation than DAPA alone in type 2 diabetes patients.

Dynamic nuclear polarization magnetic resonance imaging and the oxygen-sensitive paramagnetic agent OX63 provide a noninvasive quantitative evaluation of kidney hypoxia in diabetic mice.

Renal hypoxia may play an important role in the progression of diabetic nephropathy. However, tools that noninvasively and quantitatively measure oxygen tension in the kidney are lacking. Here, we evaluated the feasibility of a noninvasive and quantitative imaging technique using dynamic nuclear polarization magnetic resonance imaging (DNP-MRI) in combination with the oxygen-sensitive paramagnetic agent OX63 for measuring oxygen tension in the kidney. Our results demonstrate that the DNP-MRI technique can yield quantitative maps of oxygen tension in the mouse renal cortex. Using this procedure, we also showed that oxygen tension was less elevated in the renal cortex of both streptozotocin-induced type 1 diabetic mice and db/db mice, a model of type 2 diabetes, than in the renal cortex of age-matched control mice of each respective model. Oxygen tension in streptozotocin-exposed mice was significantly improved by insulin treatment. Thus, the noninvasive and quantitative DNP-MRI technique appears to be useful for studying the pathophysiological role of hypoxia.

[Fulminant type 1 diabetes mellitus following acute pancreatitis and hypoglycemia with sequential imaging of the pancreas using computed tomography: a case report].

We herein report a rare case of fulminant type 1 diabetes mellitus (FT1DM) following acute pancreatitis and hypoglycemia, in which the pancreas was evaluated by serial computed tomography (CT). A 30-year-old male presented to a local hospital with a two-day history of abdominal pain and was diagnosed with acute pancreatitis based on elevated serum amylase and peripancreatic fluid collection on CT images. The patient developed sudden hypoglycemia (plasma glucose, 45mg/dL;serum C-peptide, 3.4ng/mL) the next day and hyperglycemia (plasma glucose, 250-480mg/dL) on admission day four. CT revealed a low attenuation area extending from the pancreatic head to the pancreatic tail. On admission day eight, he was referred to our hospital and diagnosed with FT1DM after he developed ketoacidosis immediately after hospitalization, with a plasma glucose level of 442mg/dL, hemoglobin A1c concentration of 5.7% and undetectable urinary C-peptide with a serum C-peptide level of 0.1ng/mL before and after intravenous glucagon loading. CT imaging revealed dramatic improvement at the time, and no pancreatic islets were detected in the pancreatic biopsy specimens.

DNA methylation of the Klf14 gene region in whole blood cells provides prediction for the chronic inflammation in the adipose tissue.

Krüppel-Like Factor 14 (KLF14) gene, which appears to be a master regulator of gene expression in the adipose tissue and have previously been associated with BMI and Type 2 diabetes (T2D) by large genome-wide association studies. In order to find predictive biomarkers for the development of T2D, it is necessary to take epigenomic changes affected by environmental factors into account. This study focuses on ageing and obesity, which are T2D risk factors, and examines epigenetic changes and inflammatory changes. We investigated DNA methylation changes in the Klf14 promoter region in different organs of mice for comparing aging and weight. We found that methylation levels of these sites were increased with aging and weight in the spleen, the adipose tissue, the kidney, the lung, the colon and the whole blood cells. In addition, in the spleen, the adipose tissue and the whole blood, these epigenetic changes were also significantly associated with inflammatory levels. Moreover, not only Klf14, but also expression levels of some downstream genes were decreased with methylation in the spleen, the adipose tissue and the whole blood cells. Taken together, our results suggest that methylation changes of Klf14 in those tissues may be associated with changes in gene expression and inflammation on the adipose tissue of obesity and T2D. In addition, the methylation changes in the whole blood cells may serve as a predictive epigenetic biomarker for the development of T2D.

Clinical significance of the laparoscopic bariatric surgeries for morbid obesity: initial 30 cases at a single institution in Japan.

BACKGROUND: Bariatric surgical procedures are becoming a standard treatment for morbid obesity in many western countries and in some Asian countries. AIM: The aim of the current study was to evaluate the efficacy and safety of the initial 30 cases of bariatric surgical procedures performed for morbid obesity at a single institution in Japan. MATERIALS AND METHODS: From March 2012 until September 2014, 30 bariatric surgical procedures were performed for morbid obesity at a single medical center (Kyushu University Hospital) in Japan. RESULTS: All of the operations procedures were planned laparoscopic procedures, and none required conversion to laparotomy. There were no perioperative or postoperative mortalities. Postoperative complications occurred in 3 patients: 1 patient developed an intra-abdominal abscess, 1 patient experienced temporary food intolerance, and 1 patient developed small bowel obstruction. The excessive body weight reduction rates after surgery at 1 month, 3 months, 6 months, and 1 year post-surgery were 26.1%, 39.2%, 41.7%, and 51.2%, respectively. The mean body mass index (BMI) at the same time points were 38.3%, 36.4%, 35.5%, and 31.4%, respectively. Eighteen patients had type II diabetes mellitus (T2DM). The mean preoperative fasting blood glucose levels were 169 ± 37 mg/dL. Following surgery, the blood glucose levels at 3, 6 and 12 months were 113 ± 12, 115 ± 22, and 110 ± 19, mg/dL, respectively. The preoperative HbA1c percentage was 7.9 ± 0.5. Following surgery, the HbA1c percentages at 3, 6, and 12 months were 6.9 ± 0.5, 6.2 ± 0.9, and 5.9 ± 0.6, respectively. CONCLUSIONS: Bariatric surgical procedures are effective and safe for the treatment of morbid obesity. Our results indicate that the mechanism of improvement of diabetes and related diseases following bariatric surgical procedures is not simply as a result of calorie restriction and weight reduction.

Maternal high-fat diet induces insulin resistance and deterioration of pancreatic ß-cell function in adult offspring with sex differences in mice.

Intrauterine environment may influence the health of postnatal offspring. There have been many studies on the effects of maternal high-fat diet (HFD) on diabetes and glucose metabolism in offspring. Here, we investigated the effects in male and female offspring. C57/BL6J mice were bred and fed either control diet (CD) or HFD from conception to weaning, and offspring were fed CD or HFD from 6 to 20 wk. At 20 wk, maternal HFD induced glucose intolerance and insulin resistance in offspring. Additionally, liver triacylglycerol content, adipose tissue mass, and inflammation increased in maternal HFD. In contrast, extending previous observations, insulin secretion at glucose tolerance test, islet area, insulin content, and PDX-1 mRNA levels in isolated islets were lower in maternal HFD in males, whereas they were higher in females. Oxidative stress in islets increased in maternal HFD in males, whereas there were no differences in females. Plasma estradiol levels were lower in males than in females and decreased in offspring fed HFD and also decreased by maternal HFD, suggesting that females may be protected from insulin deficiency by inhibiting oxidative stress. In conclusion, maternal HFD induced insulin resistance and deterioration of pancreatic ß-cell function, with marked sex differences in adult offspring accompanied by adipose tissue inflammation and liver steatosis. Additionally, our results demonstrate that potential mechanisms underlying sex differences in pancreatic ß-cell function may be related partially to increases in oxidative stress in male islets and decreased plasma estradiol levels in males.

CTLA-4Ig immunotherapy of obesity-induced insulin resistance by manipulation of macrophage polarization in adipose tissues.

It has been established that obesity alters the metabolic and endocrine function of adipose tissue and, together with accumulation of adipose tissue macrophages, contributes to insulin resistance. Although numerous studies have reported that shifting the polarization of macrophages from M1 to M2 can alleviate adipose tissue inflammation, manipulation of macrophage polarization has not been considered as a specific therapy. Here, we determined whether cytotoxic T-lymphocyte-associated antigen-4IgG1 (CTLA-4Ig) can ameliorate insulin resistance by induction of macrophages from proinflammatory M1 to anti-inflammatory M2 polarization in the adipose tissues of high fat diet-induced insulin-resistant mice. CTLA4-Ig treatment prevented insulin resistance by changing gene expression to M2 polarization, which increased the levels of arginase 1. Furthermore, flow cytometric analysis confirmed the alteration of polarization from CD11c (M1)- to CD206 (M2)-positive cells. Concomitantly, CTLA-4Ig treatment resulted in weight reductions of epididymal and subcutaneous adipose tissues, which may be closely related to overexpression of apoptosis inhibitors in macrophages. Moreover, proinflammatory cytokine and chemokine levels decreased significantly. In contrast, CCAAT enhancer binding protein α, peroxisome proliferator-activated receptor γ, and adiponectin expression increased significantly in subcutaneous adipose tissue. This novel mechanism of CTLA-4lg immunotherapy may lead to an ideal anti-obesity/inflammation/insulin resistance agent.

Downregulation of adipose triglyceride lipase in the heart aggravates diabetic cardiomyopathy in db/db mice.

Adipose triglyceride lipase (ATGL) was recently identified as a rate-limiting triglyceride (TG) lipase and its activity is stimulated by comparative gene identification-58 (CGI-58). Mutations in the ATGL or CGI-58 genes are associated with neutral lipid storage diseases characterized by the accumulation of TG in multiple tissues. The cardiac phenotype, known as triglyceride deposit cardiomyovasculopathy, is characterized by TG accumulation in coronary atherosclerotic lesions and in the myocardium. Recent reports showed that myocardial TG accumulation is significantly higher in patients with diabetes and is associated with impaired left ventricular diastolic function. Therefore, we investigated the roles of ATGL and CGI-58 in the development of myocardial steatosis in the diabetic state. Histological examination with oil red O staining showed marked lipid deposition in the hearts of diabetic fatty db/db mice. Cardiac triglyceride and diglyceride contents were greater in db/db mice than in db/+ control mice. Next, we determined the expression of genes and proteins that affect lipid metabolism, and found that ATGL and CGI-58 expression levels were decreased in the hearts of db/db mice. We also found increased expression of genes regulating triglyceride synthesis (sterol regulatory element-binding protein 1c, monoacylglycerol acyltransferases, and diacylglycerol acyltransferases) in db/db mice. Regarding key modulators of apoptosis, PKC activity, and oxidative stress, we found that Bcl-2 levels were lower and that phosphorylated PKC and 8-hydroxy-2'-deoxyguanosine levels were higher in db/db hearts. These results suggest that reduced ATGL and CGI-58 expression and increased TG synthesis may exacerbate myocardial steatosis and oxidative stress, thereby promoting cardiac apoptosis in diabetic mice.

Phycocyanin and phycocyanobilin from Spirulina platensis protect against diabetic nephropathy by inhibiting oxidative stress.

We and other investigators have reported that bilirubin and its precursor biliverdin may have beneficial effects on diabetic vascular complications, including nephropathy, via its antioxidant effects. Here, we investigated whether phycocyanin derived from Spirulina platensis, a blue-green algae, and its chromophore phycocyanobilin, which has a chemical structure similar to that of biliverdin, protect against oxidative stress and renal dysfunction in db/db mice, a rodent model for Type 2 diabetes. Oral administration of phycocyanin (300 mg/kg) for 10 wk protected against albuminuria and renal mesangial expansion in db/db mice, and normalized tumor growth factor-ß and fibronectin expression. Phycocyanin also normalized urinary and renal oxidative stress markers and the expression of NAD(P)H oxidase components. Similar antioxidant effects were observed following oral administration of phycocyanobilin (15 mg/kg) for 2 wk. Phycocyanobilin, bilirubin, and biliverdin also inhibited NADPH dependent superoxide production in cultured renal mesangial cells. In conclusion, oral administration of phycocyanin and phycocyanobilin may offer a novel and feasible therapeutic approach for preventing diabetic nephropathy.

Reduced expression of adipose triglyceride lipase enhances tumor necrosis factor alpha-induced intercellular adhesion molecule-1 expression in human aortic endothelial cells via protein kinase C-dependent activation of nuclear factor-kappaB.

We examined the effects of adipose triglyceride lipase (ATGL) on the initiation of atherosclerosis. ATGL was recently identified as a rate-limiting triglyceride (TG) lipase. Mutations in the human ATGL gene are associated with neutral lipid storage disease with myopathy, a rare genetic disease characterized by excessive accumulation of TG in multiple tissues. The cardiac phenotype, known as triglyceride deposit cardiomyovasculopathy, shows massive TG accumulation in both coronary atherosclerotic lesions and the myocardium. Recent reports show that myocardial triglyceride content is significantly higher in patients with prediabetes or diabetes and that ATGL expression is decreased in the obese insulin-resistant state. Therefore, we investigated the effect of decreased ATGL activity on the development of atherosclerosis using human aortic endothelial cells. We found that ATGL knockdown enhanced monocyte adhesion via increased expression of TNFα-induced intercellular adhesion molecule-1 (ICAM-1). Next, we determined the pathways (MAPK, PKC, or NFκB) involved in ICAM-1 up-regulation induced by ATGL knockdown. Both phosphorylation of PKC and degradation of IκBα were increased in ATGL knockdown human aortic endothelial cells. In addition, intracellular diacylglycerol levels and free fatty acid uptake via CD36 were significantly increased in these cells. Inhibition of the PKC pathway using calphostin C and GF109203X suppressed TNFα-induced ICAM-1 expression. In conclusion, we showed that ATGL knockdown increased monocyte adhesion to the endothelium through enhanced TNFα-induced ICAM-1 expression via activation of NFκB and PKC. These results suggest that reduced ATGL expression may influence the atherogenic process in neutral lipid storage diseases and in the insulin-resistant state.

Association of serum total bilirubin levels with progressive renal decline and end-stage kidney disease: 10-year observational cohort study in Japanese patients with diabetes.

OBJECTIVE: Previous reports have demonstrated the association of serum bilirubin levels with the progression of diabetic nephropathy. The objective of this study is to assess the association of basal bilirubin levels with progressive renal decline (PRD) and end-stage kidney disease (ESKD). METHODS: A total of 298 patients with diabetes who visited Kyushu University Hospital (Japan) were recruited and followed up for 10 years. PRD was defined as a negative change in estimated glomerular filtration ratio (eGFR) >3.7%/year, 2.5th percentile. Logistic regression analysis was performed to evaluate the association of total bilirubin levels with PRD and its cut-off point was determined by receiver operating characteristic (ROC) analysis. Kaplan-Meier method and Cox hazard regression analysis were used to evaluate the predictive ability of its cut-off point for ESKD. RESULTS: Logistic regression model showed that total bilirubin levels were significantly associated with PRD, and ROC analysis showed that its cut-off point was 0.5 mg/dL. Kaplan-Meier method showed that the percent of patients who reached two endpoints, composite endpoint (ESKD or doubling of creatinine level) or 30% eGFR decline, was significantly higher in the low bilirubin group than in the high bilirubin group (18.5% vs 11.0%, P = 0.045; 49.1% vs 42.1%, P = 0.045, respectively, log-rank test). Cox hazard regression models confirmed the independence of the predictive ability of its cut-off point. CONCLUSIONS: Serum total bilirubin levels were negatively associated with PRD in diabetic nephropathy and its cut-off point was 0.5 mg/dL. It may be clinically useful for identifying patients at high risk of ESKD.

Association between cortisol and left ventricular diastolic dysfunction in patients with diabetes mellitus.

AIMS/INTRODUCTION: Diabetes mellitus is a major risk factor for the development of cardiovascular diseases. Heart failure with preserved ejection fraction is characterized by left ventricular diastolic dysfunction (LVDD). It has been reported that excess cortisol found in patients with Cushing's syndrome was associated with the development of LVDD. However, the relationship between cortisol concentration and LVDD in patients with diabetes mellitus has not been addressed. MATERIALS AND METHODS: We enrolled 109 patients with diabetes mellitus and 104 patients without diabetes mellitus who had undergone echocardiographic examination at Kyushu University Hospital, Fukuoka, Japan, between November 2016 and March 2019. Left ventricular function was evaluated and the ratio of early diastolic velocity from transmitral inflow to early diastolic velocity (E/e') was used as an index of diastolic function. Plasma cortisol concentrations, glycemic control, lipid profiles, treatment with antidiabetic drugs and other clinical characteristics were evaluated, and their associations with E/e' were determined using univariate and multivariate analyses. RESULTS: Multivariate linear regression analysis showed that log E/e' was positively correlated with age (P = 0.017), log systolic blood pressure (P = 0.004) and cortisol (P = 0.037), and negatively correlated with estimated glomerular filtration rate (P = 0.016) and the use of sodium-glucose cotransporter 2 inhibitors (P = 0.042) in patients with diabetes mellitus. Multivariate analysis showed that cortisol was positively correlated with age (P = 0.016) and glycated hemoglobin (P = 0.011). There was no association between E/e' and cortisol in patients without diabetes mellitus. CONCLUSIONS: Increased cortisol levels might increase the risk of developing LVDD in diabetes mellitus patients.

Beta-Arrestin-1 mediates glucagon-like peptide-1 signaling to insulin secretion in cultured pancreatic beta cells.

Glucagon-like peptide-1 (GLP-1) is a polypeptide hormone secreted from enteroendocrine L cells and potentiates glucose-dependent insulin secretion in pancreatic beta cells. Recently the GLP-1 receptor (GLP-1 R) has been a focus for new anti-diabetic therapy with the introduction of GLP-1 analogues and DPP-IV inhibitors, and this has stimulated additional interest in the mechanisms of GLP-1 signaling. Here we identify a mechanism for GLP-1 action, showing that the scaffold protein beta-arrestin-1 mediates the effects of GLP-1 to stimulate cAMP production and insulin secretion in beta cells. Using a coimmunoprecipitation technique, we also found a physical association between the GLP-1 R and beta-arrestin-1 in cultured INS-1 pancreatic beta cells. beta-Arrestin-1 knockdown broadly attenuated GLP-1 signaling, causing decreased ERK and CREB activation and IRS-2 expression as well as reduced cAMP levels and impaired insulin secretion. However, beta-arrestin-1 knockdown did not affect GLP-1 R surface expression and ligand-induced GLP-1 R internalization/desensitization. Taken together, these studies indicate that beta-arrestin-1 plays a role in GLP-1 signaling leading to insulin secretion, defining a previously undescribed mechanism for GLP-1 action.

Relationship between serum bilirubin levels, urinary biopyrrin levels, and retinopathy in patients with diabetes.

OBJECTIVE: Previous reports have indicated that serum bilirubin levels may be associated with diabetic retinopathy. However, the detailed mechanism is not fully understood. In this study, we evaluated the relationship between the severity of diabetic retinopathy and various factors including bilirubin levels and factors influencing bilirubin metabolism. METHODS: The study participants consisted of 94 consecutive patients with diabetes mellitus admitted to Kyushu University Hospital from April 2011 to July 2012. The patients were classified into three groups: no retinopathy (NDR), simple retinopathy (SDR), and pre-proliferative or proliferative retinopathy (PDR). The relationship between the severity of retinopathy and various factors was evaluated using univariate and logistic regression analyses. In addition, multivariate regression analysis was performed to evaluate the significant determinants for bilirubin levels. RESULTS: In univariate analysis, a significant difference was found among NDR, SDR and PDR in bilirubin levels, duration of diabetes, systolic blood pressure, and macroalbuminuria. Logistic regression analysis showed that PDR was significantly associated with bilirubin levels, duration of diabetes, and systolic blood pressure (OR 0.737, 95% CI 0.570-0.952, P = 0.012; OR 1.085, 95% CI 1.024-1.149, P = 0.006; OR 1.036, 95% CI 1.011-1.062, P = 0.005, respectively). In turn, multivariate regression analysis showed that bilirubin levels were negatively associated with high-sensitivity C-reactive protein levels and PDR, but positively correlated with urinary biopyrrin levels, oxidized metabolites of bilirubin. CONCLUSION: PDR was negatively associated with bilirubin levels. This negative association may be due to a decreased production of bilirubin rather than its increased consumption considering the positive association between bilirubin and biopyrrin levels.

Bilirubin is inversely related to diabetic peripheral neuropathy assessed by sural nerve conduction study.

AIMS/INTRODUCTION: Diagnosis of diabetic peripheral neuropathy (DPN) depends on subjective findings, certain investigations for DPN risks have not been performed enough. Bilirubin protects against vascular complications by reducing oxidative stress in diabetes, but is not fully tested for DPN. This study aimed to evaluate sural nerve conduction impairments (SNCI) as an objective DPN marker and the contribution of bilirubin to SNCI. MATERIALS AND METHODS: Using DPN-Check® , SNCI was defined as a decline of amplitude potential or conduction velocity below the normal limit in 150 inpatients with diabetes. The correlations between SNCI and conventional DPN diagnosis criteria, the incidence of diabetic retinopathy/nephropathy, biomarkers for atherosclerosis, cardiac function by ultrasonic cardiogram, and bilirubin were statistically tested, followed by the comparison of logistic regression models for SNCI to find confounders with bilirubin. RESULTS: The incidence of SNCI was 72.0%. The sensitivity and specificity of SNCI for DPN prediagnosis by simplified criteria were 54.6 and 90.5%, respectively, and similarly corresponded with diabetic retinopathy and nephropathy (sensitivity 57.4 and 50.0%, respectively). SNCI significantly related to diabetes duration, declined estimated glomerular filtration rate, albuminuria and total bilirubin. SNCI incidence was attenuated in the higher bilirubin tertiles (89.8/65.3/54.8%, P < 0.001). Bilirubin was an independent inverse risk factor for SNCI, even after adjustment by known risk factors for DPN and markers for microvascular complications. CONCLUSIONS: SNCI is a comprehensive marker for diabetic complications. We first showed the independent inverse relationship between bilirubin and SNCI through the independent pathway with other complications, provably reducing oxidative stress, as previously reported.

SIRT1 inhibits inflammatory pathways in macrophages and modulates insulin sensitivity.

Chronic inflammation is an important etiology underlying obesity-related disorders such as insulin resistance and type 2 diabetes, and recent findings indicate that the macrophage can be the initiating cell type responsible for this chronic inflammatory state. The mammalian silent information regulator 2 homolog SIRT1 modulates several physiological processes important for life span, and a potential role of SIRT1 in the regulation of insulin sensitivity has been shown. However, with respect to inflammation, the role of SIRT1 in regulating the proinflammatory pathway within macrophages is poorly understood. Here, we show that knockdown of SIRT1 in the mouse macrophage RAW264.7 cell line and in intraperitoneal macrophages broadly activates the JNK and IKK inflammatory pathways and increases LPS-stimulated TNFalpha secretion. Moreover, gene expression profiles reveal that SIRT1 knockdown leads to an increase in inflammatory gene expression. We also demonstrate that SIRT1 activators inhibit LPS-stimulated inflammatory pathways, as well as secretion of TNFalpha, in a SIRT1-dependent manner in RAW264.7 cells and in primary intraperitoneal macrophages. Treatment of Zucker fatty rats with a SIRT1 activator leads to greatly improved glucose tolerance, reduced hyperinsulinemia, and enhanced systemic insulin sensitivity during glucose clamp studies. These in vivo insulin-sensitizing effects were accompanied by a reduction in tissue inflammation markers and a decrease in the adipose tissue macrophage proinflammatory state, fully consistent with the in vitro effects of SIRT1 in macrophages. In conclusion, these results define a novel role for SIRT1 as an important regulator of macrophage inflammatory responses in the context of insulin resistance and raise the possibility that targeting of SIRT1 might be a useful strategy for treating the inflammatory component of metabolic diseases.

Myosin 5a is an insulin-stimulated Akt2 (protein kinase Bbeta) substrate modulating GLUT4 vesicle translocation.

Phosphatidylinositol 3-kinase activation of Akt signaling is critical to insulin-stimulated glucose transport and GLUT4 translocation. However, the downstream signaling events following Akt activation which mediate glucose transport stimulation remain relatively unknown. Here we identify an Akt consensus phosphorylation motif in the actin-based motor protein myosin 5a and show that insulin stimulation leads to phosphorylation of myosin 5a at serine 1650. This Akt-mediated phosphorylation event enhances the ability of myosin 5a to interact with the actin cytoskeleton. Small interfering RNA-induced inhibition of myosin 5a and expression of dominant-negative myosin 5a attenuate insulin-stimulated glucose transport and GLUT4 translocation. Furthermore, knockdown of Akt2 or expression of dominant-negative Akt (DN-Akt) abolished insulin-stimulated phosphorylation of myosin 5a, inhibited myosin 5a binding to actin, and blocked insulin-stimulated glucose transport. Taken together, these data indicate that myosin 5a is a newly identified direct substrate of Akt2 and, upon insulin stimulation, phosphorylated myosin 5a facilitates anterograde movement of GLUT4 vesicles along actin to the cell surface.

Aberrant activation of bone marrow Ly6C high monocytes in diabetic mice contributes to impaired glucose tolerance.

Accumulating evidence indicates that diabetes and obesity are associated with chronic low-grade inflammation and multiple organ failure. Tissue-infiltrated inflammatory M1 macrophages are aberrantly activated in these conditions and contribute to hyperglycemia and insulin resistance. However, it is unclear at which stage these cells become aberrantly activated: as precursor monocytes in the bone marrow or as differentiated macrophages in tissues. We examined the abundance, activation state, and function of bone marrow-derived Ly6Chigh monocytes in mice with diabetes and/or obesity. Ly6Chigh monocytes were FACS-purified from six groups of male mice consisting of type 2 diabetes model db/db mice, streptozotocin (STZ) induced insulin depletion mice, high fat diet (HFD) induced obesity mice and each control mice. Ly6Chigh monocytes were then analyzed for the expression of inflammation markers by qRT-PCR. In addition, bone marrow-derived Ly6Chigh monocytes from db/+ and db/db mice were fluorescently labeled and injected into groups of db/db recipient mice. Cell trafficking to tissues and levels of markers were examined in the recipient mice. The expression of many inflammation-related genes was significantly increased in Ly6Chigh monocytes from db/db mice, compared with the control. Bone marrow-derived Ly6Chigh monocytes isolated from db/db mice, but not from db/+ mice, displayed prominent infiltration into peripheral tissues at 1 week after transfer into db/db mice. The recipients of db/db Ly6Chigh monocytes also exhibited significantly increased serum glucose levels and worsening tolerance compared with mice receiving db/+ Ly6Chigh monocytes. These novel observations suggest that activated Ly6Chigh monocytes may contribute to the glucose intolerance observed in diabetes.

The dipeptidyl peptidase-4 inhibitor, linagliptin, improves cognitive impairment in streptozotocin-induced diabetic mice by inhibiting oxidative stress and microglial activation.

OBJECTIVE: Accumulating epidemiological studies have demonstrated that diabetes is an important risk factor for dementia. However, the underlying pathological and molecular mechanisms, and effective treatment, have not been fully elucidated. Herein, we investigated the effect of the dipeptidyl peptidase-4 (DPP-4) inhibitor, linagliptin, on diabetes-related cognitive impairment. METHOD: Streptozotocin (STZ)-induced diabetic mice were treated with linagliptin (3 mg/kg/24 h) for 17 weeks. The radial arm water maze test was performed, followed by evaluation of oxidative stress using DNP-MRI and the expression of NAD(P)H oxidase components and proinflammatory cytokines and of microglial activity. RESULTS: Administration of linagliptin did not affect the plasma glucose and body weight of diabetic mice; however, it improved cognitive impairment. Additionally, linagliptin reduced oxidative stress and the mRNA expression of NAD(P)H oxidase component and TNF-α, and the number and body area of microglia, all of which were significantly increased in diabetic mice. CONCLUSIONS: Linagliptin may have a beneficial effect on diabetes-related dementia by inhibiting oxidative stress and microglial activation, independently of glucose-lowering.

Amelioration of diabetic nephropathy by SGLT2 inhibitors independent of its glucose-lowering effect: A possible role of SGLT2 in mesangial cells.

Several clinical studies have shown the beneficial effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors on diabetic nephropathy. The underlying mechanisms are not fully understood. We found that administration of canagliflozin at a low dose (0.01 mg/kg/day) did not affect either blood glucose levels or glycosuria, but it improved albuminuria and mesangial expansion in db/db mice to a similar extent as at a high dose (3.0 mg/kg/day) that lowered blood glucose levels. This indicated the existence of a tubular SGLT2-independent reno-protective mechanism. Here we focused on the potential role of SGLT2 in mesangial cells (MCs). Western blot analysis revealed the expression of SGLT2 in cultured mouse MCs. Exposure of MCs to high glucose levels for 72 h significantly increased the expression of SGLT2. Canagliflozin or ipragliflozin (both 100 nM) treatment inhibited glucose consumption in the medium under high-glucose conditions but not under normal-glucose conditions. Furthermore, canagliflozin inhibited high-glucose-induced activation of the protein kinase C (PKC)-NAD(P)H oxidase pathway and increases in reactive oxygen species (ROS) production. Thus, the inhibition of mesangial SGLT2 may cause an inhibition of PKC activation and ROS overproduction in diabetic nephropathy, and this may at least in part account for the reno-protective effect of SGLT2 inhibitors.