GDP-bound Rab27a regulates clathrin disassembly through HSPA8 after insulin secretion.

Clathrin-dependent endocytosis is a key process for secretory cells, in which molecules on the plasma membrane are both degraded and recycled in a stimulus-dependent manner. There are many reports showing that disruption of endocytosis is involved in the onset of various diseases. Recently, it has been reported that such disruption in pancreatic ß-cells causes impaired insulin secretion and might be associated with the pathology of diabetes mellitus. Compared with exocytosis, there are few reports on the molecular mechanism of endocytosis in pancreatic ß-cells. We previously reported that GDP-bound Rab27a regulates endocytosis through its GDP-dependent effectors after insulin secretion. In this study, we identified heat shock protein family A member 8 (HSPA8) as a novel interacting protein for GDP-bound Rab27a. HSPA8 directly bound GDP-bound Rab27a via the ß2 region of its substrate binding domain (SBD). The ß2 fragment was capable of inhibiting the interaction between HSPA8 and GDP-bound Rab27a, and suppressed glucose-induced clathrin-dependent endocytosis in pancreatic ß-cells. The region also affected clathrin dynamics on purified clathrin-coated vesicles (CCVs). These results suggest that the interaction between GDP-bound Rab27a and HSPA8 regulates clathrin disassembly from CCVs and subsequent vesicle transport. The regulatory stages in endocytosis by HSPA8 differ from those for other GDP-bound Rab27a effectors. This study shows that GDP-bound Rab27a dominantly regulates each stage in glucose-induced endocytosis through its specific effectors in pancreatic ß-cells.

Apigenin Alleviates Endoplasmic Reticulum Stress-Mediated Apoptosis in INS-1 ß-Cells.

The improvement of type 2 diabetes mellitus induced by naturally occurring polyphenols, known as flavonoids, has received considerable attention. However, there is a dearth of information regarding the effect of the trihydroxyflavone apigenin on pancreatic ß-cell function. In the present study, the anti-diabetic effect of apigenin on pancreatic ß-cell insulin secretion, apoptosis, and the mechanism underlying its anti-diabetic effects, were investigated in the INS-ID ß-cell line. The results showed that apigenin concentration-dependently facilitated 11.1-mM glucose-induced insulin secretion, which peaked at 30 µM. Apigenin also concentration-dependently inhibited the expression of endoplasmic reticulum (ER) stress signaling proteins, CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP) and cleaved caspase-3, which was elevated by thapsigargin in INS-1D cells, with peak suppression at 30 µM. This was strongly correlated with the results of flow cytometric analysis of annexin V/propidium iodide (PI) staining and DNA fragmentation analysis. Moreover, the increased expression of thioredoxin-interacting protein (TXNIP) induced by thapsigargin was remarkably reduced by apigenin in a concentration-dependent manner. These results suggest that apigenin is an attractive candidate with remarkable and potent anti-diabetic effects on ß-cells, which are mediated by facilitating glucose-stimulated insulin secretion and preventing ER stress-mediated ß-cell apoptosis, the latter of which may be possibly mediated by reduced expression of CHOP and TXNIP, thereby promoting ß-cell survival and function.

Dietary Problems Are Associated with Frailty Status in Older People with Fewer Teeth in Japan.

This study aimed to investigate the association between dietary problems and frailty according to tooth loss in older Japanese people. This cross-sectional study included 160 older people (mean age 82.6 years) from Japan. Frailty status was assessed using the Study of Osteoporotic Fractures (SOF) criteria, which consists of (i) weight loss > 5% in the past year, (ii) inability to perform five chair stands, and (iii) self-perceived reduced energy level. Frailty was defined as the presence of ≥2 items of SOF criteria. Multivariate logistic regression analyses were performed with frailty as the dependent variable and dietary problems as the independent variable, stratified according to having <20 teeth. Low appetite and no enjoyment of eating were associated with frailty after adjusting for covariates in participants with <20 teeth. Dietary problems, including low appetite, eating alone, and negative attitudes toward enjoyment of eating were associated with a self-perceived reduced energy level in participants with <20 teeth. However, this association was not observed in participants with ≥20 teeth. In older people with fewer teeth, dietary problems have been suggested to be associated with frailty. Therefore, it may be necessary to pay attention to dietary problems, especially in older people with tooth loss.

Asymmetric dimethylarginine accumulation under hyperglycemia facilitates ß-cell apoptosis via inhibiting nitric oxide production.

Low concentrations of nitric oxide (NO) produced by constitutive NO synthase (cNOS) has been shown to suppress apoptosis in pancreatic ß-cells. In the present study, the influence of asymmetric dimethylarginine (ADMA), the major endogenous inhibitor of NOS, on the apoptosis-suppressive effect of NO was investigated. The expression of dimethylarginine dimethylaminohydrolase 2 (DDAH2), an ADMA-metabolizing enzyme, in INS-1 ß-cells and in mouse pancreatic islets was drastically reduced by in vitro exposure to high-concentration glucose (20 mM) and by in vivo treatment of mice with the insulin receptor blocker S661, which resulted in hyperglycemia, respectively. In line with this, a higher ADMA level was observed in INS-1 cells exposed to 20 mM glucose. The treatment of INS-1 cells with ADMA, similarly to with the NOS inhibitor NG-nitro-L-arginine methyl ester, significantly facilitated 20 mM glucose-induced increase in cleaved caspase-3 protein expression. Furthermore, increased protein expression of cleaved caspase-3 and CHOP was observed in INS-1 cells with knockdown of DDAH2. These results suggest that ADMA accumulation through a decrease in DDAH2 expression in ß-cells, which is induced under hyperglycemic conditions, facilitates ß-cell apoptosis through suppression of cNOS-mediated NO production.

Harmine suppresses collagen production in hepatic stellate cells by inhibiting DYRK1B.

Liver fibrosis is a major consequence of chronic liver disease, where excess extracellular matrix is deposited, due caused by the activation of hepatic stellate cells (HSCs). The suppression of collagen production in HSCs is therefore regarded as a therapeutic target of liver fibrosis. The present study investigated effects of harmine, which is a ß-carboline alkaloid and known as an inhibitor of dual-specificity tyrosine-regulated kinases (DYRKs), on the production of collagen in HSCs. LX-2 cells, a human HSC cell line, were treated with harmine (0-10 µM) for 48 h in the presence or absence of TGF-ß1 (5 ng/ml). The expression of collagen type I α1 (COL1A1) and DYRK isoforms was investigated by Western blotting, quantitative RT-PCR, or immunofluorescence. The influence of knockdown of each DYRK isoform on the COL1A1 expression was further investigated. The expression of COL1A1 was markedly increased by treating with TGF-ß1 for 48 h in LX-2 cells. Harmine (10 µM) significantly inhibited the increased expression of COL1A1. LX-2 cells expressed mRNAs of DYRK1A, DYRK1B, DYRK2, and DYRK4, although the expression of DYRK4 was much lower than the others. Knockdown of DYRK1B, but not DYRK1A or DYRK2, with siRNA significantly suppressed TGF-ß1-induced increase in COL1A1 expression. These results suggest that harmine suppresses COL1A1 expression via inhibiting DYRK1B in HSCs and therefore might be effective for the treatment of liver fibrosis.

Association between intensive health guidance focusing on eating quickly and metabolic syndrome in Japanese middle-aged citizens.

PURPOSE: The purpose of this intervention study was to investigate whether intensive health guidance focusing on eating quickly can prevent metabolic syndrome (MetS) more effectively than standard routine guidance in Japanese citizens living in rural areas. METHODS: This controlled, non-randomized, intervention study analyzed 141 participants with MetS at baseline. Participants in the intervention group received health guidance focusing on eating quickly and standard health guidance about MetS in accordance with the guidelines of the Ministry of Health, Labour and Welfare in Japan, whereas participants in the control group received only standard health guidance about MetS. The primary study outcome was the prevalence of MetS at a 1-year follow-up. RESULTS: At 1-year follow-up, the prevalence of MetS in the intervention group was significantly lower than that in the control group (p = 0.003). The decreases in body weight, body mass index, waist circumference and triglycerides from baseline to 1 year were significantly greater in the intervention group than in the control group (p < 0.05). CONCLUSION: Intensive health guidance focusing on eating quickly is more effective for improving MetS than standard Japanese health guidance alone. LEVEL OF EVIDENCE: Level II, Evidence obtained from well-designed controlled trials without randomization. TRIAL REGISTRY NAME, REGISTRATION IDENTIFICATION NUMBER, AND URL FOR THE REGISTRY: UMIN, UMIN000030600, http://www.umin.ac.jp/ctr/index-j.htm.

GDP-Bound Rab27a Dissociates from the Endocytic Machinery in a Phosphorylation-Dependent Manner after Insulin Secretion.

Glucose-stimulated insulin secretion is controlled by both exocytosis and endocytosis in pancreatic ß-cells. Although endocytosis is a fundamental step to maintain cellular responses to the secretagogue, the molecular mechanism of endocytosis remains poorly defined. We have previously shown that in response to high concentrations of glucose, guanosine 5'-diphosphate (GDP)-bound Rab27a is recruited to the plasma membrane where IQ motif-containing guanosine 5'-triphosphatase (GTPase)-activating protein 1 (IQGAP1) is expressed, and that complex formation promotes endocytosis of secretory membranes after insulin secretion. In the present study, the regulatory mechanisms of dissociation of the complex were investigated. Phosphorylation of IQGAP1 on serine (Ser)-1443, a site recognized by protein kinase Cε (PKCε), inhibited the interaction of GDP-bound Rab27a with IQGAP1 in a Cdc42-independent manner. Glucose stimulation caused a translocation of PKCε from the cytosol to the plasma membrane. In addition, glucose-induced endocytosis was inhibited by the knockdown of IQGAP1 with small interfering RNA (siRNA). However, the expression of the non-phosphorylatable or phosphomimetic form of IQGAP1 could not rescue the inhibition, suggesting that a phosphorylation-dephosphorylation cycle of IQGAP1 is required for endocytosis. These results suggest that IQGAP1 phosphorylated by PKCε promotes the dissociation of the IQGAP1-GDP-bound Rab27a complex in pancreatic ß-cells, thereby regulating endocytosis of secretory membranes following insulin secretion.

IRR is involved in glucose-induced endocytosis after insulin secretion.

Endocytosis after insulin secretion plays a pivotal role in the regulation of insulin secretion in pancreatic ß-cells. Our recent study suggested that EPI64, a GTPase activating protein for Rab27a, contributes to the regulation of glucose-induced endocytosis, which is mediated by the GDP-bound form of Rab27a. Here, we identified insulin receptor-related receptor (IRR) as an EPI64-interacting protein. Knockdown of IRR inhibited glucose-induced uptake of transferrin, a marker of endocytosis, translocation of the guanine-nucleotide-exchange factor ARNO to the plasma membrane, and generation of phosphatidylinositol 3,4,5-trisphosphate (PIP3). These results suggest that IRR functions upstream of PIP3 generation and controls endocytosis after insulin secretion.

Pharmacokinetics of insulin disappearance after massive overdosing.

Long-term glucose supplementation is required to prevent hypoglycemia after massive insulin overdosing. We fitted the blood insulin concentration-time profile to the model: I = A·exp(-a·t) + B·exp(-b·t), where I (µU/mL) is the serum/plasma insulin concentration, A (µU/mL) and B (µU/mL) are the peak insulin concentrations of each component, a (time-1) and b (time-1) are the time constants of each component, and t (h) is the time elapsed from the peak of blood insulin level. Additional components were considered as needed. Patient 1 had auto-injected 600 U NovoRapid® 30Mix, and Patient 2 had auto-injected 300 U Novolet®R (regular) and 1,800 U NovoLet®N (NPH). We used the disappearance of therapeutic doses of the respective insulin in healthy individuals as controls, and we obtained parameters by Excel solver. In Patient 1, the parameter values were A = 1490.04 and a = 0.15 for insulin aspart and B = 60.66 and b = 0.04 for protaminated aspart. In Patient 2, the values were A = 784.45 and a = 0.38 for regular insulin and B = 395.84 and b = 0.03 for NPH. Compared with controls, the half-lives (t1/2) for insulin aspart and protaminated aspart were 4 and 2 times longer, respectively, in Patient 1. In Patient 2, the t1/2 for regular and NPH insulin were 2 and 7 times longer than those in the controls, respectively. In conclusion, the t1/2 for insulin was elongated 2 to 7 times after massive overdosing, explaining why glucose supplementation is needed for long periods in these cases.

Baicalein disturbs the morphological plasticity and motility of breast adenocarcinoma cells depending on the tumor microenvironment.

During tumor invasion, cancer cells change their morphology and mode of migration based on communication with the surrounding environment. Numerous studies have indicated that paracrine interactions from non-neoplastic cells impact the migratory and invasive properties of cancer cells. Thus, these interactions are potential targets for anticancer therapies. In this study, we showed that the flavones member baicalein suppresses the motility of breast cancer cells that is promoted by paracrine interactions. First, we identified laminin-332 (LN-332) as a principle paracrine factor in conditioned medium from mammary epithelium-derived MCF10A cells that regulates the morphology and motility of breast adenocarcinoma MDA-MB-231 cells. Then, we carried out a morphology-based screen for small compounds, which showed that baicalein suppressed the morphological changes and migratory activity of MDA-MB-231 cells that were induced by conditioned medium from MCF10A cells and LN-332. We also found that baicalein caused narrower and incomplete lamellipodia formation in conditioned medium-treated MDA-MB-231 cells, although actin dynamics downstream of Rho family small GTPases were unaffected. These results suggest the importance of mammary epithelial cells in the cancer microenvironment promoting the migratory activity of breast adenocarcinoma cells and show a novel mechanism through which baicalein inhibits cancer cell motility.

Accuracy of Estimating Step Counts and Intensity Using Accelerometers in Older People With or Without Assistive Devices.

The purpose of this study was to examine the accuracy of uni- and triaxial accelerometers in monitoring step counts and gait intensity in older people who did or did not use an assistive device. Forty-nine healthy and frail older adults wore uniaxial (Lifecorder, Suzuken Co. Ltd.) and triaxial accelerometers (Activity Monitor, Matsushita Electronic Works, Ltd., and Active Style Pro, Omron Healthcare Co., Ltd.) during three trials at different gait speeds. All accelerometers gave relatively accurate step counts for healthy older participants compared with direct observation; however, the error was greater for frail older people with assistive devices. Gait intensity detection error was unaffected by gait speed. Among frail older people with assistive devices, the gait intensity error was smaller than for step count error. To accurately assess the steps walked or the gait intensity among frail older people using assistive devices, more study is needed on these groups of participants.

PI3K regulates endocytosis after insulin secretion by mediating signaling crosstalk between Arf6 and Rab27a.

In secretory cells, endocytosis is coupled to exocytosis to enable proper secretion. Although endocytosis is crucial to maintain cellular homeostasis before and after secretion, knowledge about secretagogue-induced endocytosis in secretory cells is still limited. Here, we searched for proteins that interacted with the Rab27a GTPase-activating protein (GAP) EPI64 (also known as TBC1D10A) and identified the Arf6 guanine-nucleotide-exchange factor (GEF) ARNO (also known as CYTH2) in pancreatic ß-cells. We found that the insulin secretagogue glucose promotes phosphatidylinositol (3,4,5)-trisphosphate (PIP3) generation through phosphoinositide 3-kinase (PI3K), thereby recruiting ARNO to the intracellular side of the plasma membrane. Peripheral ARNO promotes clathrin assembly through its GEF activity for Arf6 and regulates the early stage of endocytosis. We also found that peripheral ARNO recruits EPI64 to the same area and that the interaction requires glucose-induced endocytosis in pancreatic ß-cells. Given that GTP- and GDP-bound Rab27a regulate exocytosis and the late stage of endocytosis, our results indicate that the glucose-induced activation of PI3K plays a pivotal role in exocytosis-endocytosis coupling, and that ARNO and EPI64 regulate endocytosis at distinct stages.

GTP- and GDP-Dependent Rab27a Effectors in Pancreatic Beta-Cells.

Small guanosine triphosphatases (GTPases) participate in a wide variety of cellular functions including proliferation, differentiation, adhesion, and intracellular transport. Conventionally, only the guanosine 5'-triphosphate (GTP)-bound small GTPase interacts with effector proteins, and the resulting downstream signals control specific cellular functions. Therefore, the GTP-bound form is regarded as active, and the focus has been on searching for proteins that bind the GTP form to look for their effectors. The Rab family small GTPase Rab27a is highly expressed in some secretory cells and is involved in the control of membrane traffic. The present study reviews recent progress in our understanding of the roles of Rab27a and its effectors in pancreatic beta-cells. In the basal state, GTP-bound Rab27a controls insulin secretion at pre-exocytic stages via its GTP-dependent effectors. We previously identified novel guanosine 5'-diphosphate (GDP)-bound Rab27-interacting proteins. Interestingly, GDP-bound Rab27a controls endocytosis of the secretory membrane via its interaction with these proteins. We also demonstrated that the insulin secretagogue glucose converts Rab27a from its GTP- to GDP-bound forms. Thus, GTP- and GDP-bound Rab27a regulate pre-exocytic and endocytic stages in membrane traffic, respectively. Since the physiological importance of GDP-bound GTPases has been largely overlooked, we consider that the investigation of GDP-dependent effectors for other GTPases is necessary for further understanding of cellular function.

Interplay between Rab27a effectors in pancreatic ß-cells.

The small GTPase Rab27a is a member of the Rab family that is involved in membrane trafficking in various kinds of cells. Rab27a has GTP- and GDP-bound forms, and their interconversion regulates intracellular signaling pathways. Typically, only a GTP-bound GTPase binds its specific effectors with the resulting downstream signals controlling specific cellular functions. We previously identified novel Rab27a-interacting proteins. Surprisingly, some of these proteins interacted with GDP-bound Rab27a. The present study reviews recent progress in our understanding of the roles of Rab27a and its effectors in the secretory process. In pancreatic ß-cells, GTP-bound Rab27a regulates insulin secretion at the pre-exocytotic stages via its GTP-specific effectors such as Exophilin8/Slac2-c/MyRIP and Slp4/Granuphilin. Glucose stimulation causes insulin exocytosis. Glucose stimulation also converts Rab27a from its GTP- to its GDP-bound form. GDP-bound Rab27a interacts with GDP-specific effectors and controls endocytosis of the secretory membrane. Thus, Rab27a cycling between GTP- and GDP-bound forms synchronizes with the recycling of secretory membrane to re-use the membrane and keep the ß-cell volume constant.

Protective effect of hydrogen sulfide on pancreatic beta-cells.

Hydrogen sulfide (H2S) is recognized as a third gaseous signaling molecule behind nitric oxide (NO) and carbon monoxide (CO). In pancreatic beta-cells, H2S inhibits glucose-induced insulin release. There are multiple underlying mechanisms for this inhibitory process. Apart from these inhibitory effects, H2S also protects pancreatic islets from apoptotic cell death induced by high glucose. Moreover, expression of the H2S-producing enzyme, cystathionine γ-lyase (CSE), is induced by glucose stimulation. These observations suggest that H2S is produced in an inducible manner, as are the other two gaseous signaling molecules, NO and CO. We recently reported that a lack of CSE induces apoptotic beta-cell death and promotes the development of high-fat diet (HFD)-induced diabetes. These findings tempt us to suggest that H2S produced by CSE is part of a homeostatic mechanism used by pancreatic beta-cells to inhibit insulin release and reduce cellular stress evoked by glucose, possibly via the anti-oxidant properties of H2S.

Endogenous hydrogen sulfide protects pancreatic beta-cells from a high-fat diet-induced glucotoxicity and prevents the development of type 2 diabetes.

Chronic exposure to high glucose induces the expression of cystathionine gamma-lyase (CSE), a hydrogen sulfide-producing enzyme, in pancreatic beta-cells, thereby suppressing apoptosis. The aim of this study was to examine the effects of hydrogen sulfide on the onset and development of type 2 diabetes. Middle-aged (6-month-old) wild-type (WT) and CSE knockout (CSE-KO) mice were fed a high-fat diet (HFD) for 8weeks. We determined the effects of CSE knockout on beta-cell function and mass in islets from these mice. We also analyzed changes in gene expression in the islets. After 8weeks of HFD, blood glucose levels were markedly increased in middle-aged CSE-KO mice, insulin responses were significantly reduced, and DNA fragmentation of the islet cells was increased. Moreover, expression of thioredoxin binding protein-2 (TBP-2, also known as Txnip) was increased. Administration of NaHS, a hydrogen sulfide donor, reduced TBP-2 gene levels in isolated islets from CSE-KO mice. Gene levels were elevated when islets were treated with the CSE inhibitor dl-propargylglycine (PPG). These results provide evidence that CSE-produced hydrogen sulfide protects beta-cells from glucotoxicity via regulation of TBP-2 expression levels and thus prevents the onset/development of type 2 diabetes.

Activated Cdc42-bound IQGAP1 determines the cellular endocytic site.

Recruitment of specific molecules to a specific membrane site is essential for communication between specialized membranous organelles. In the present study, we identified IQGAP1 as a novel GDP-bound-Rab27a-interacting protein. We found that IQGAP1 interacts with GDP-bound Rab27a when it forms a complex with GTP-bound Cdc42. We also found that IQGAP1 regulates the endocytosis of insulin secretory membranes. Silencing of IQGAP1 inhibits both endocytosis and the glucose-induced redistribution of endocytic machinery, including Rab27a and its binding protein coronin 3. These processes can also be inhibited by disruption of the trimeric complex with dominant negative IQGAP1 and Cdc42. These results indicate that activation of Cdc42 in response to the insulin secretagogue glucose recruits endocytic machinery to IQGAP1 at the cell periphery and regulates endocytosis at this membrane site.

[Hydrogen sulfide and its effect on pancreatic beta-cells].

Hydrogen sulfide (H2S), a potentially toxic gas, is also an important signaling molecule in various mammalian cells and tissues. H2S is involved in the neuroprotection, neuromodulation, cardioprotection, vasodilatation and the regulation of inflammatory response. In pancreatic beta-cells, H2S can be produced by cystathionine beta-synthase (CBS) or cystathionine gamma-lyase (CSE). The produced H2S inhibits insulin release and regulates beta-cell survival. We demonstrated that glucose stimulation increase CSE expression in mouse pancreatic islets. We also indicated that H2S protects beta-cells that are chronically exposed to high glucose. Loss of beta-cell mass is important in the pathogenesis and/or progression of diabetes mellitus; therefore, molecular analyses of the mechanisms of H2S production and its protective effects on beta-cells may lead to new insights into diabetes mellitus.

Distribution of hydrogen sulfide (H2S)-producing enzymes and the roles of the H2S donor sodium hydrosulfide in diabetic nephropathy.

BACKGROUND: Hydrogen sulfide (H(2)S) has recently been found to play beneficial roles in ameliorating several diseases, including hypertension, atherosclerosis and cardiac/renal ischemia-reperfusion injuries. Cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CSE), the main enzymes in the transsulfuration pathway, catalyze H(2)S production in mammalian tissues. However, the distributions and precise roles of these enzymes in the kidney have not yet been identified. METHODS: The present study examined the localization of both enzymes in the normal kidney and the effect of the H(2)S donor sodium hydrosulfide (NaHS) in the renal peritubular capillary (PTC) under conditions of diabetic nephropathy, using pancreatic ß-cell-specific calmodulin-overexpressing transgenic mice as a model of diabetes. RESULTS: In the normal kidney, we detected expression of both CBS and CSE in the brush border and cytoplasm of the proximal tubules, but not in the glomeruli, distal tubules and vascular endothelial cells of renal PTCs. Administration of NaHS increased PTC diameter and blood flow. We further evaluated whether biosynthesis of H(2)S was altered in a spontaneous diabetic model that developed renal lesions similar to human diabetic nephropathy. CSE expression was markedly reduced under diabetic conditions, whereas CBS expression was unaffected. Progressive diabetic nephropathy showed vasoconstriction and a loss of blood flow in PTCs that was ameliorated by NaHS treatment. CONCLUSION: These findings suggest that CSE expression in the proximal tubules may also regulate tubulointerstitial microcirculation via H(2)S production. H(2)S may represent a target of treatment to prevent progression of ischemic injury in diabetic nephropathy.