Control of human pancreatic beta cell kinome by glucagon-like peptide-1 receptor biased agonism

Aim

To determine the kinase activity profiles of human pancreatic beta cells downstream of glucagon-like peptide-1 receptor (GLP-1R) balanced versus biased agonist stimulations.

Materials and Methods

This study analysed the kinomic profiles of human EndoC-βh1 cells following vehicle and GLP-1R stimulation with the pharmacological agonist exendin-4, as well as exendin-4–based biased derivatives exendin-phe1 and exendin-asp3 for acute (10-minute) versus sustained (120-minute) responses, using PamChip protein tyrosine kinase and serine/threonine kinase assays. The raw data were filtered and normalized using BioNavigator. The kinase analyses were conducted with R, mainly including kinase-substrate mapping and Kyoto Encyclopedia of Genes and Genomes pathway analysis.

Results

The present analysis reveals that kinomic responses are distinct for acute versus sustained GLP-1R agonist exposure, with individual responses associated with agonists presenting specific bias profiles. According to pathway analysis, several kinases, including JNKs, PKCs, INSR and LKB1, are important GLP-1R signalling mediators, constituting potential targets for further research on biased GLP-1R downstream signalling.

Conclusion

The results from this study suggest that differentially biased exendin-phe1 and exendin-asp3 can modulate distinct kinase interaction networks. Further understanding of these mechanisms will have important implications for the selection of appropriate anti-type 2 diabetes therapies with optimized downstream kinomic profiles.     

Six-year follow-up of pancreatic β cell function in adults with latent autoimmune diabetes

AIM: To investigate the characteristics of the progression of islet β cell function in Chinese latent autoimmune diabetes in adult (LADA) patients with glutamic acid decarboxylase antibody (GAD-Ab) positivity, and to explore the prognostic factors for β cell function. METHODS: Forty-five LADA patients with GAD-Ab positivity screened from phenotypic type 2 diabetic (T2DM) patients and 45 T2DM patients without GAD-Ab matched as controls were followed-up every 6 mo. Sixteen patients in LADA1 and T2DM1 groups respectively have been followed-up for 6 years, while 29 patients in LADA2 and T2DM2 groups respectively for only 1.5 years. GAD-Ab was determined by radioligand assay, and C-peptides (CP) by radioimmune assay. RESULTS: The percentage of patients whose fasting CP(FCP) decreased more than 50% compared with the baseline reached to 25.0% at 1.5th year in LADA1 group, and FCP level decreased (395.8±713 vs 572.8±72.3 pmol/L, P<0.05) at 2.5th year and continuously went down to the end of follow-up. No significant changes of the above parameters were found in T2DM1 group. The average decreased percentages of FCP per year in LADA and T2DM patients were 15.8% (4.0-91.0%) and 5.2% (-3.5 to 35.5%, P=0.000) respectively. The index of GAD-Ab was negatively correlated with the FCP in LADA patients (rs = -0.483, P = 0.000). The decreased percentage of FCP per year in LADA patients were correlated with GAD-Ab index, body mass index (BMI) and age at onset (rs = 0.408, -0.301 and -0.523 respectively, P<0.05). Moreover, GAD-Ab was the only risk factor for predicting 13 cell failure in LADA patients (B = 1.455, EXP (B) = 4,283, P = 0.023). CONCLUSION: The decreasing rate of islet 13 cell function in LADA, being highly heterogeneous, is three times that of T2DM patients. The titer of GAD-Ab is an important predictor for the progression of islet 13 cell function, and age at onset and BMI could also act as the predictors.     

Glucagon-like peptide-1 regulates proliferation and apoptosis via activation of protein kinase B in pancreatic INS-1 beta cells

Aims/hypothesis The incretin hormone glucagon-like peptide-1 augments islet cell mass in vivo by increasing proliferation and decreasing apoptosis of the beta cells. However, the signalling pathways that mediate these effects are mostly unknown. Using a clonal rat pancreatic beta cell line (INS-1), we examined the role of protein kinase B in mediating beta-cell growth and survival stimulated by glucagon-like peptide-1.Methods Immunoblot analysis was used to detect active (phospho-) and total protein kinase B. Proliferation was assessed using ³H-thymidine incorporation, while apoptosis was quantitated using 4-6-diamidino-2-phenylindole staining and APO percentage apoptosis assay. Kinase-dead and wild-type protein kinase B was introduced into cells using adenoviral vectors.Results Glucagon-like peptide-1 rapidly activated protein kinase B in INS-1 cells (by 2.7±0.7-fold, p<0.05). This effect was completely abrogated by inhibition, with wortmannin, of the upstream activator of protein kinase B, phosphatidylinositol-3-kinase. Glucagon-like peptide-1 also stimulated INS-1 cell proliferation in a dose-dependent manner (by 1.8±0.5-fold at 10^–7 mol/l, p<0.01), and inhibited staurosporine-induced apoptosis (by 69±12%, p<0.05). Both of these effects were also prevented by wortmannin treatment. Ablation of protein kinase B by adenovirus-mediated overexpression of the kinase-dead form of protein kinase B prevented protein kinase B phosphorylation and completely abrogated both cellular proliferation (p<0.05) and protection from drug-induced cellular death (p<0.01) induced by glucagon-like peptide-1.Conclusions/interpretation These results identify protein kinase B as an essential mediator linking the glucagon-like peptide-1 signal to the intracellular machinery that modulates beta-cell growth and survival.Abbreviations AdV adenovirus - DAPI 4-6-diamidino-2-phenylindole - GFP enhanced green fluorescent protein - GIP glucose-dependent insulinotropic peptide - GLP glucagon-like peptide - GPCR G protein-coupled receptor - GSK3/ glycogen synthase kinase-3/ - KD kinase-dead - MAPK mitogen-activated protein kinase - PI3-K phosphatidylinositol-3-kinase - PKB protein kinase B - PTHrP parathyroid hormone-related peptide - WT wild-typeQ. Wang and L. Li contributed equally to this article     

Exercise-induced AMPK activity in skeletal muscle: Role in glucose uptake and insulin sensitivity

The energy/fuel sensor 5′-AMP-activated protein kinase (AMPK) is viewed as a master regulator of cellular energy balance due to its many roles in glucose, lipid, and protein metabolism. In this review we focus on the regulation of AMPK activity in skeletal muscle and its involvement in glucose metabolism, including glucose transport and glycogen synthesis. In addition, we discuss the plausible interplay between AMPK and insulin signaling regulating these processes.     

Pharmacological concentrations of irisin increase cell proliferation without influencing markers of neurite outgrowth and synaptogenesis in mouse H19-7 hippocampal cell lines

Aims/Hypothesis

Irisin is a novel, myocyte secreted, hormone that has been proposed to mediate the beneficial effects of exercise on metabolism. Irisin is expressed, at lower levels, in human brains and knock-down of the precursor of irisin, FNDC5, decreases neural differentiation of mouse embryonic stem cells. No previous studies have evaluated whether irisin may directly regulate hippocampal neurogenesis in mouse hippocampal neuronal (HN) cells.

Methods

Hippocampal neurogenesis and irisin signaling were studied in vitro using mouse H19-7 HN cell lines.

Results

We observed that cell proliferation is regulated by irisin in a dose-dependent manner in mouse H19-7 HN cells. Specifically, physiological concentrations of irisin, 5 to 10 nmol/L, had no effect on cell proliferation when compared to control. By contrast, pharmacological concentrations of irisin, 50 to 100 nmol/L, increased cell proliferation when compared to control. Similar to these results regarding irisin's effects on cell proliferation, we also observed that only pharmacological concentrations of irisin increased STAT3, but not AMPK and/or ERK, activation. Finally, we observed that irisin did not activate either microtubule-associated protein 2, a specific neurite outgrowth marker, or Synapsin, a specific synaptogenesis marker in mouse H19-7 HN cells.

Conclusions/Interpretations

Our data suggest that irisin, in pharmacological concentrations, increases cell proliferation in mouse H19-7 HN cells via STAT3, but not AMPK and/or ERK, signaling pathways. By contrast, neither physiological nor pharmacological concentrations of irisin alter markers of hippocampal neurogenesis in mouse H19-7 HN cell lines.     

Near-normoglycaemic remission in African-Americans with Type 2 diabetes mellitus is associated with recovery of beta cell function.

AIMS: To prospectively determine the frequency of remission and possible mechanism of beta cell recovery in non-Whites with Type 2 diabetes mellitus in the setting of intensive glycaemic regulation using pharmacological agents. METHODS: Twenty-six consecutive, newly diagnosed African-American, Type 2 diabetic patients presenting primarily for severe hyperglycaemia (31.0+/-12.8 mmol/l) were followed for at least 1 year. Initial hospitalization included treatment with insulin, fluids and electrolytes. Outpatient intensive glycaemic regulation included insulin or glibenclamide, diabetes education and diet that altered nutrient content. Plasma glucose and C-peptide responses to an oral glucose tolerance test and HbA1c were measured at < 14, 15-56 and 57-112 days after presentation. Remission was defined as a HbA1c < or = 6.3% and fasting plasma glucose < 6.9 mmol/l, 3 months after discontinuing all pharmacological agents. RESULTS: Eleven of 26 patients (42.3%) developed remission after a mean of 83 days of pharmacological treatment and remained in remission during follow-up for 248-479 days; one relapsed after 294 days. Fifteen patients who did not develop a remission and were followed for 168-468 days, required continuing pharmacological therapy to be well-controlled. (mean HbA1c = 7.1%). There was no significant difference in age, sex, plasma glucose at presentation, initial glycaemic regulation, final body mass index, magnitude of weight change or pharmacological agents used for treatment between the two groups. Plasma C-peptide response to oral glucose was initially (< 14 days) suppressed in all subjects and subsequently increased. The increase was significantly greater in those who underwent a remission than those who did not. Neither significant weight loss nor severe hypoglycaemia was observed in either group during intensive treatment. CONCLUSIONS: Forty-two per cent of newly diagnosed, unselected African-Americans with Type 2 diabetes, treated intensively using pharmacological agents, education and diet developed near-normoglycaemic remission. Remission was associated with a greater recovery of glucose-stimulated insulin secretion suggesting that therapies directed at promoting beta cell recovery and preservation are potentially useful approaches to the treatment of Type 2 diabetes mellitus.     

Immunometabolism of AMPK in insulin resistance and atherosclerosis

Obesity leads to insulin resistance and atherosclerosis, which precede Type 2 diabetes and cardiovascular disease. Immunometabolism addresses how metabolic and inflammatory pathways converge to maintain health and a contemporary problem is determining how obesity-induced inflammation precipitates chronic diseases such as insulin resistance and atherosclerosis. AMP-activated protein kinase (AMPK) is an important serine/threonine kinase well known for regulating metabolic processes and maintaining energy homeostasis. However, both metabolic and immunological AMPK-mediated effects play a role in disease. Pro-inflammatory mediators suppress AMPK activity and hinder lipid oxidation. In addition, AMPK activation curbs inflammation by directly inhibiting pro-inflammatory signaling pathways and limiting the build-up of specific lipid intermediates that elicit immune responses. In the context of obesity and chronic disease, these reciprocal responses involve both immune and metabolic cells. Therefore, the immunometabolism of AMPK-mediated processes and therapeutics should be considered in atherosclerosis and insulin resistance.     

Reduction of AMPK activity and altered MAPKs signalling in peripheral blood mononuclear cells in response to acute glucose ingestion following a short-term high fat diet in young healthy men

Background

Peripheral blood mononuclear cells (PBMCs) are known to respond to systematic changes in nutrient availability. The impact of a short-term high fat diet (HFD), with and without acute glucose ingestion, on the energy-sensing enzyme 5’ AMP-activated protein kinase (AMPK) as well as mitochondrial oxidative phosphorylation (OXPHOS) proteins in PBMCs is currently unknown.

Methods

Nine healthy, lean young males participated in a 7 day HFD intervention, designed to induce transient glucose intolerance. The phosphorylation status and total protein content of AMPK and inflammatory mitogen-activated protein kinases (MAPKs), and total OXPHOS protein in PBMCs, along with circulating cytokines, were assessed in the fasted state and following an oral glucose tolerance test (OGTT) before and after the HFD.

Results

One week of HFD resulted in relative glucose intolerance. The HFD resulted in a reduction of AMPK phosphorylation under fasting basal conditions and following the OGTT (both P < 0.05), while there were no differences in OXPHOS protein expression. Although the short-term HFD had no effect on basal phosphorylation of p38, JNK or ERK1/2, the activation of MAPKs signalling in response to glucose ingestion was attenuated post-HFD as compared to pre-HFD (P < 0.05 for all). Circulating cytokines were not significantly affected by the HFD.

Conclusions

We conclude that impaired glucose tolerance in response to 7 day HFD resulted in decreased AMPK activity and impaired glucose-stimulated MAPK activation following glucose ingestion in vivo in PBMCs from young, lean subjects. Further studies are warranted to explore how dietary manipulations impact interplay between AMPK and inflammatory signalling, along with immune function, in PBMCs.     

Stimulatory effect of insulin on theca-interstitial cell proliferation and cell cycle regulatory proteins through MTORC1 dependent pathway

The present study examined the effect of insulin-mediated activation of the mammalian target of rapamycin complex 1 (MTORC1) signaling network on the proliferation of primary culture of theca-interstitial (T-I) cells. Our results show that insulin treatment increased proliferation of the T-I cells through the MTORC1-dependent signaling pathway by increasing cell cycle regulatory proteins. Inhibition of ERK1/2 signaling caused partial reduction of insulin-induced phosphorylation of RPS6KB1 and RPS6 whereas inhibition of PI3-kinase signaling completely blocked the insulin response. Pharmacological inhibition of MTORC1 with rapamycin abrogated the insulin-induced phosphorylation of EIF4EBP1, RPS6KB1 and its downstream effector, RPS6. These results were further confirmed by demonstrating that knockdown of Mtor using siRNA reduced the insulin-stimulated MTORC1 signaling. Furthermore, insulin-stimulated T-I cell proliferation and the expression of cell cycle regulatory proteins CDK4, CCND3 and PCNA were also blocked by rapamycin. Taken together, the present studies show that insulin stimulates cell proliferation and cell cycle regulatory proteins in T-I cells via activation of the MTORC1 signaling pathway.     

Anti-diabetic actions of glucagon-like peptide-1 on pancreatic beta-cells

Glucagon-like peptide-1 (GLP-1), an incretin hormone, is released from intestinal L-cells in response to nutrients. GLP-1 lowers blood glucose levels by stimulating insulin secretion from pancreatic beta-cells in a glucose-dependent manner. In addition, GLP-1 slows gastric emptying, suppresses appetite, reduces plasma glucagon, and stimulates glucose disposal, which are beneficial for glucose homeostasis. Therefore, incretin-based therapies such as GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase IV, an enzyme which inactivates GLP-1, have been developed for treatment of diabetes. This review outlines our knowledge of the actions of GLP-1 on insulin secretion and biosynthesis, beta-cell proliferation and regeneration, and protection against beta-cell damage, as well as the involvement of recently discovered signaling pathways of GLP-1 action, mainly focusing on pancreatic beta-cells.     

Rosiglitazone combined with insulin preserves islet beta cell function in adult-onset latent autoimmune diabetes (LADA)

BACKGROUND: LADA is thought to result from the chronic autoimmune destruction of the insulin-producing pancreatic beta cells. In addition to antidiabetic effects, the newly developed insulin sensitizer-thiazolidinediones have the potential to increase the insulin content of islet cells by downregulating local inflammation and autoimmune response. Therefore, we hypothesized that LADA patients might benefit from thiazolidinediones treatment. METHODS: LADA patients, with a fasting C-peptide (FCP) of 0.3 nmol/L or more, were enrolled and randomly assigned to receive subcutaneous insulin alone (insulin group, n = 12) or rosiglitazone plus insulin (insulin + RSG group, n = 11) to compare the impacts on islet beta cell function. Plasma glucose, HbA 1c, fasting C-peptide (FCP) and C-peptide after 2 h 75-g glucose load (PCP) were determined every 6 months. GAD-Ab and C-peptide were measured with radioimmune assays. Islet beta cell function was evaluated by PCP and DeltaCP(DeltaCP = PCP-FCP). RESULTS: All of the 23 patients have been followed up for 6 months, 17 cases for 12 months and 14 for 18 months. (1) During 6 months' follow-up, there were no significant changes for DeltaCP and PCP levels in both groups. (2) PCP and DeltaCP levels in insulin + RSG group patients stayed steady during the 12 months' observation (P = 0.161 for both PCP and DeltaCP), while in the insulin alone group, both FCP (P = 0.021) and PCP (P = 0.028) levels decreased significantly. Furthermore, PCP (P = 0.004) and DeltaCP(P = 0.015) differences between 12th month and baseline were higher in insulin + RSG group than those in the insulin group. (3) When observed up to 18 months, PCP and DeltaCP levels in insulin + RSG group patients still stayed steady, while PCP and DeltaCP levels decreased more in the insulin alone group. CONCLUSIONS: This pilot study suggests that rosiglitazone combined with insulin may preserve islet beta cell function in LADA patients.     

Honeybees and cell lines as models of DNA methylation and aging in response to diet

DNA methylation patterns change as individuals grow older, and DNA methylation appears susceptible to modification by the diet. Thus DNA methylation may be a mechanism through which diet can affect aging and longevity. We propose that effects on DNA methylation also contribute to the extension in lifespan observed in response to dietary restriction. Relationships between diet-induced changes in DNA methylation and parallel effects on aging and/or lifespan could, of course, be purely associative. Proof of these ideas requires experimental model systems in which it is possible to manipulate genome methylation status and to measure effects on aging and/or lifespan. Commonly-used short-lived and genetically-malleable metazoan species, such as Caenorhabditis elegans and Drosophila, are not suitable for such studies; the C. elegans genome is not methylated, and DNA methylation in Drosophila is dissimilar from mammalian DNA methylation, occurring at cytosines at sites other than in CpG sequences. The honeybee provides a potentially unique and tractable model for such studies. Female larval development into the long-lived queen phenotype or short-lived worker is determined purely by diet (royal jelly) through an effect on DNA methylation, and honeybee DNA methylation mirrors that of the mammalian genome. Mammalian cell lines and biochemical approaches offer complementary tools to address specific components of hypotheses relating to effects of diet on aging through DNA methylation in a more targeted manner. Our studies using mammalian cell lines are revealing effects of Sirt1 on DNA methylation, and indicate that Sirt1 and resveratrol affect the expression of different sets of genes.     

褪黑素对胰腺腺泡细胞钙超载的调节及其作用机制

目的 探讨褪黑素(MT)对急性坏死性胰腺炎(ANP)胰腺腺泡细胞钙超载的调节作用及其机制.方法 54只SD大鼠均分为假手术组(SO组)、急性坏死性胰腺炎组(ANP组,胰胆管逆行注射牛磺胆酸钠法造模)和MT组(腹腔注射MT后30 min ANP造模).术后1、4、8h分批处死大鼠并进行胰腺病理检查.用荧光控测法测定胰腺组织内游离钙离子浓度,实时荧光定量PCR及免疫印迹法分别检测胰腺细胞中钙调素依赖性蛋白激酶Ⅱ( CaMKⅡ)mRNA和蛋白表达水平.结果 ANP组随时间延长胰腺病理损伤进行性加重,MT组胰腺病理损伤较ANP组明显减轻(1、4、8h时病理评分比较的t值分别为-7.95、-9.72、-7.69,P值均=0.00).同时间点比较,ANP组胰腺组织内游离钙离子浓度均较SO组明显增高(1、4、8h时的t值分别=13.09、18.58、16.56,P值均=0.00),MT组较SO组略高,但较ANP组明显降低(1、4、8h时的τ值分别=-10.03、-11.75、-11.02,P值均=0.00).与SO组相比,ANP组CaMKⅡmRNA及蛋白表达水平均明显升高,MT对其表达有明显的抑制作用.结论 MT干预可抑制CaMKⅡ表达,从而减轻胰腺腺泡内钙超载,起到保护胰腺组织的作用.