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Yang Y, Hsiao YC, Liu CW, Lu K. The Role of the Nuclear Receptor FXR in Arsenic-Induced Glucose Intolerance in Mice. TOXICS 2023; 11:833. [PMID: 37888683 PMCID: PMC10611046 DOI: 10.3390/toxics11100833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 09/26/2023] [Accepted: 09/28/2023] [Indexed: 10/28/2023]
Abstract
Inorganic arsenic in drinking water is prioritized as a top environmental contaminant by the World Health Organization, with over 230 million people potentially being exposed. Arsenic toxicity has been well documented and is associated with a plethora of human diseases, including diabetes, as established in numerous animal and epidemiological studies. Our previous study revealed that arsenic exposure leads to the inhibition of nuclear receptors, including LXR/RXR. To this end, FXR is a nuclear receptor central to glucose and lipid metabolism. However, limited studies are available for understanding arsenic exposure-FXR interactions. Herein, we report that FXR knockout mice developed more profound glucose intolerance than wild-type mice upon arsenic exposure, supporting the regulatory role of FXR in arsenic-induced glucose intolerance. We further exposed mice to arsenic and tested if GW4064, a FXR agonist, could improve glucose intolerance and dysregulation of hepatic proteins and serum metabolites. Our data showed arsenic-induced glucose intolerance was remarkably diminished by GW4064, accompanied by a significant ratio of alleviation of dysregulation in hepatic proteins (83%) and annotated serum metabolites (58%). In particular, hepatic proteins "rescued" from arsenic toxicity by GW4064 featured members of glucose and lipid utilization. For instance, the expression of PCK1, a candidate gene for diabetes and obesity that facilitates gluconeogenesis, was repressed under arsenic exposure in the liver, but revived with the GW4064 supplement. Together, our comprehensive dataset indicates FXR plays a key role and may serve as a potential therapeutic for arsenic-induced metabolic disorders.
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Affiliation(s)
| | | | | | - Kun Lu
- Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC 27599, USA
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Suresh A, Rao TC, Solanki S, Suresh MV, Menon B, Raghavendran K. The holy basil administration diminishes the NF-kB expression and protects alveolar epithelial cells from pneumonia infection through interferon gamma. Phytother Res 2022; 36:1822-1835. [PMID: 35233841 PMCID: PMC9018535 DOI: 10.1002/ptr.7428] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 01/31/2022] [Accepted: 02/01/2022] [Indexed: 11/07/2022]
Abstract
Bacterial pneumonia is one of the most important causes of mortality in the United States. The bacteria Klebsiella pneumoniae (KP) accounts for a significant proportion of community and hospital-acquired infections. Here, we determine that the holy basil (Ocimum sanctum) extract improves cell viability and dampens the proinflammatory cytokine response in an in vitro model of pneumonia. For this, A549, a human alveolar basal epithelial cell line, was subjected to a lethal KP model following a 24-hr pretreatment with basil extract. Bacteremia, cell viability, apoptosis, MTT assay, phagocytic capacity, cytokines, and Khe gene expression were assessed in these cells following pneumonia. Cell morphology analysis showed that holy basil protected A549 cells from KP infection-mediated effects by inhibiting cell death due to apoptosis. Additionally, in the presence of basil, A549 cells demonstrated significantly higher bactericidal capacity and phagocytosis. Administration of holy basil led to reduced expression of hypoxia-inducible factor-1/2a, nuclear factor kappa B, and Khe in the KP-infected cells while increasing interferon (IFN)-γ expression. Our results suggest that basil significantly reduced cell death in the setting of KP infection, likely via attenuation of cytokine and IFN-γ mediated signaling pathways. Holy basil is a promising therapeutic agent for managing and treating bacterial pneumonia based on its potency.
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Affiliation(s)
- Arundhathy Suresh
- Department of Surgery, University of Michigan, Ann Arbor, Michigan, USA
| | - Tejeshwar C Rao
- Department of Cell, Developmental, and Integrative Biology, The University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Sumeet Solanki
- Department of Surgery, University of Michigan, Ann Arbor, Michigan, USA
| | | | - Bindu Menon
- Department of Medical Education and Physiology/Pharmacology, University of Toledo, Toledo, Ohio, USA
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Gut Metabolite Trimethylamine N-Oxide Protects INS-1 β-Cell and Rat Islet Function under Diabetic Glucolipotoxic Conditions. Biomolecules 2021; 11:biom11121892. [PMID: 34944536 PMCID: PMC8699500 DOI: 10.3390/biom11121892] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 12/11/2021] [Accepted: 12/14/2021] [Indexed: 12/14/2022] Open
Abstract
Serum accumulation of the gut microbial metabolite trimethylamine N-oxide (TMAO) is associated with high caloric intake and type 2 diabetes (T2D). Impaired pancreatic β-cell function is a hallmark of diet-induced T2D, which is linked to hyperglycemia and hyperlipidemia. While TMAO production via the gut microbiome-liver axis is well defined, its molecular effects on metabolic tissues are unclear, since studies in various tissues show deleterious and beneficial TMAO effects. We investigated the molecular effects of TMAO on functional β-cell mass. We hypothesized that TMAO may damage functional β-cell mass by inhibiting β-cell viability, survival, proliferation, or function to promote T2D pathogenesis. We treated INS-1 832/13 β-cells and primary rat islets with physiological TMAO concentrations and compared functional β-cell mass under healthy standard cell culture (SCC) and T2D-like glucolipotoxic (GLT) conditions. GLT significantly impeded β-cell mass and function by inducing oxidative and endoplasmic reticulum (ER) stress. TMAO normalized GLT-mediated damage in β-cells and primary islet function. Acute 40µM TMAO recovered insulin production, insulin granule formation, and insulin secretion by upregulating the IRE1α unfolded protein response to GLT-induced ER and oxidative stress. These novel results demonstrate that TMAO protects β-cell function and suggest that TMAO may play a beneficial molecular role in diet-induced T2D conditions.
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MicroRNA Sequences Modulated by Beta Cell Lipid Metabolism: Implications for Type 2 Diabetes Mellitus. BIOLOGY 2021; 10:biology10060534. [PMID: 34203703 PMCID: PMC8232095 DOI: 10.3390/biology10060534] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Revised: 06/08/2021] [Accepted: 06/09/2021] [Indexed: 12/23/2022]
Abstract
Alterations in lipid metabolism within beta cells and islets contributes to dysfunction and apoptosis of beta cells, leading to loss of insulin secretion and the onset of type 2 diabetes. Over the last decade, there has been an explosion of interest in understanding the landscape of gene expression which influences beta cell function, including the importance of small non-coding microRNA sequences in this context. This review sought to identify the microRNA sequences regulated by metabolic challenges in beta cells and islets, their targets, highlight their function and assess their possible relevance as biomarkers of disease progression in diabetic individuals. Predictive analysis was used to explore networks of genes targeted by these microRNA sequences, which may offer new therapeutic strategies to protect beta cell function and delay the onset of type 2 diabetes.
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Long-term in vivo polychlorinated biphenyl 126 exposure induces oxidative stress and alters proteomic profile on islets of Langerhans. Sci Rep 2016; 6:27882. [PMID: 27292372 PMCID: PMC4904407 DOI: 10.1038/srep27882] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 05/24/2016] [Indexed: 12/15/2022] Open
Abstract
It has been recently proposed that exposure to polychlorinated biphenyls (PCBs) is a risk factor to type 2 diabetes mellitus (DM2). We investigated this hypothesis using long-term in vivo PCB126 exposure to rats addressing metabolic, cellular and proteomic parameters. Male Wistar rats were exposed to PCB126 (0.1, 1 or 10 μg/kg of body weight/day; for 15 days) or vehicle by intranasal instillation. Systemic alterations were quantified by body weight, insulin and glucose tolerance, and blood biochemical profile. Pancreatic toxicity was measured by inflammatory parameters, cell viability and cycle, free radical generation, and proteomic profile on islets of Langerhans. In vivo PCB126 exposure enhanced the body weight gain, impaired insulin sensitivity, reduced adipose tissue deposit, and elevated serum triglycerides, cholesterol, and insulin levels. Inflammatory parameters in the pancreas and cell morphology, viability and cycle were not altered in islets of Langerhans. Nevertheless, in vivo PCB126 exposure increased free radical generation and modified the expression of proteins related to oxidative stress on islets of Langerhans, which are indicative of early β-cell failure. Data herein obtained show that long-term in vivo PCB126 exposure through intranasal route induced alterations on islets of Langerhans related to early end points of DM2.
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Hollmann M, Miller I, Hummel K, Sabitzer S, Metzler-Zebeli BU, Razzazi-Fazeli E, Zebeli Q. Downregulation of cellular protective factors of rumen epithelium in goats fed high energy diet. PLoS One 2013; 8:e81602. [PMID: 24349094 PMCID: PMC3857193 DOI: 10.1371/journal.pone.0081602] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 10/15/2013] [Indexed: 01/09/2023] Open
Abstract
Energy-rich diets can challenge metabolic and protective functions of the rumen epithelial cells, but the underlying factors are unclear. This study sought to evaluate proteomic changes of the rumen epithelium in goats fed a low, medium, or high energy diet. Expression of protein changes were compared by two-dimensional differential gel electrophoresis followed by protein identification with matrix assisted laser desorption ionisation tandem time-of-flight mass spectrometry. Of about 2,000 spots commonly detected in all gels, 64 spots were significantly regulated, which were traced back to 24 unique proteins. Interestingly, the expression profiles of several chaperone proteins with important cellular protective functions such as heat shock cognate 71 kDa protein, peroxiredoxin-6, serpin H1, protein disulfide-isomerase, and selenium-binding protein were collectively downregulated in response to high dietary energy supply. Similar regulation patterns were obtained for some other proteins involved in transport or metabolic functions. In contrast, metabolic enzymes like retinal dehydrogenase 1 and ATP synthase subunit beta, mitochondrial precursor were upregulated in response to high energy diet. Lower expressions of chaperone proteins in the rumen epithelial cells in response to high energy supply may suggest that these cells were less protected against the potentially harmful rumen toxic compounds, which might have consequences for rumen and systemic health. Our findings also suggest that energy-rich diets and the resulting acidotic insult may render rumen epithelial cells more vulnerable to cellular damage by attenuating their cell defense system, hence facilitating the impairment of rumen barrier function, typically observed in energy-rich fed ruminants.
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Affiliation(s)
- Manfred Hollmann
- Department for Farm Animals and Veterinary Public Health, Institute of Animal Nutrition and Functional Plant Compounds, Vetmeduni Vienna, Vienna, Austria
| | - Ingrid Miller
- Department of Biomedical Sciences, Institute of Medical Biochemistry, Vetmeduni Vienna, Vienna, Austria
| | - Karin Hummel
- VetCore Facility for Research, Vetmeduni Vienna, Vienna, Austria
| | - Sonja Sabitzer
- VetCore Facility for Research, Vetmeduni Vienna, Vienna, Austria
| | - Barbara U. Metzler-Zebeli
- Department for Farm Animals and Veterinary Public Health, Clinic for Swine, Vetmeduni Vienna, Vienna, Austria
| | | | - Qendrim Zebeli
- Department for Farm Animals and Veterinary Public Health, Institute of Animal Nutrition and Functional Plant Compounds, Vetmeduni Vienna, Vienna, Austria
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Xu Q, Chen SY, Deng LD, Feng LP, Huang LZ, Yu RR. Antioxidant effect of mogrosides against oxidative stress induced by palmitic acid in mouse insulinoma NIT-1 cells. Braz J Med Biol Res 2013; 46:949-955. [PMID: 24270904 PMCID: PMC3854338 DOI: 10.1590/1414-431x20133163] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2013] [Accepted: 07/29/2013] [Indexed: 11/23/2022] Open
Abstract
Excessive oxidative stress in pancreatic β cells, caused by glucose and fatty acids,
is associated with the pathogenesis of type 2 diabetes. Mogrosides have shown
antioxidant and antidiabetic activities in animal models of diabetes, but the
underlying mechanisms remain unclear. This study evaluated the antioxidant effect of
mogrosides on insulinoma cells under oxidative stress caused by palmitic acid, and
investigated the underlying molecular mechanisms. Mouse insulinoma NIT-1 cells were
cultured in medium containing 0.75 mM palmitic acid, mimicking oxidative stress. The
effects of 1 mM mogrosides were determined with the dichlorodihydrofluorescein
diacetate assay for intracellular reactive oxygen species (ROS) and FITC-Annexin V/PI
assay for cell apoptosis. Expression of glucose transporter-2 (GLUT2) and pyruvate
kinase was determined by semi-quantitative reverse-transcription polymerase chain
reaction. Palmitic acid significantly increased intracellular ROS concentration
2-fold (P<0.05), and decreased expression of GLUT2 (by 60%, P<0.05) and
pyruvate kinase (by 80%, P<0.05) mRNAs in NIT-1 cells. Compared with palmitic
acid, co-treatment with 1 mM mogrosides for 48 h significantly reduced intracellular
ROS concentration and restored mRNA expression levels of GLUT2 and pyruvate kinase.
However, mogrosides did not reverse palmitic acid-induced apoptosis in NIT-1 cells.
Our results indicate that mogrosides might exert their antioxidant effect by reducing
intracellular ROS and regulating expression of genes involved in glucose metabolism.
Further research is needed to achieve a better understanding of the signaling pathway
involved in the antioxidant effect of mogrosides.
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Affiliation(s)
- Q Xu
- Guilin Medical University, Department of Pharmacy, Guilin, China
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Veluthakal R, Kaetzel D, Kowluru A. Nm23-H1 regulates glucose-stimulated insulin secretion in pancreatic β-cells via Arf6-Rac1 signaling axis. Cell Physiol Biochem 2013; 32:533-41. [PMID: 24008651 DOI: 10.1159/000354457] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/12/2013] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND A growing body of evidence implicates novel roles for nm23-like proteins in the regulation of cellular functions. However, roles of these proteins in islet function and glucose-stimulated insulin secretion (GSIS) remain largely unknown. METHODS siRNA-nm23-H1 and nucleoside diphosphate kinase and histidine kinase-deficient mutants of nm23-H1 (K12Q and H118F) were used to assess roles of nm23-H1 in GSIS. RESULTS siRNA-mediated knockdown of the expression of nm23-H1 markedly inhibited GSIS in INS-1 832/13 cells. Nm23-H1 knockdown also resulted in significant inhibition of glucose-mediated activation of Arf6, a small G-protein, which has been implicated in GSIS. Expression of K12Q and H118F mutants of nm23-H1 in INS-1 832/13 cells led to inhibition of glucose-induced translocation and membrane association of Rac1, another small G-protein, which is downstream to Arf6 in the signaling events leading to GSIS. A significant inhibition of GSIS was also seen in these cells expressing K12Q and H118F. CONCLUSIONS We conclude that the nm23-H1 activation step is upstream of Arf6 activation in signaling events leading to GSIS. NDP kinase and histidine kinase functions of nm23-H1 are necessary for glucose-induced membrane association of Rac1 and ensuing insulin secretion. We present the first evidence for regulation of GSIS by nm23-H1 in pancreatic β-cells.
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Lang F, Ullrich S, Gulbins E. Ceramide formation as a target in beta-cell survival and function. Expert Opin Ther Targets 2011; 15:1061-71. [PMID: 21635197 DOI: 10.1517/14728222.2011.588209] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
INTRODUCTION Ceramide may be synthesized de novo or generated by sphingomyelinase-dependent hydrolysis of sphingomyelin. AREAS COVERED The role of ceramide, ceramide-sensitive signaling and ion channels in β-cell apoptosis, lipotoxicity and amyloid-induced β-cell death. EXPERT OPINION Ceramide participates in β-cell dysfunction and apoptosis after exposure to TNFα, IL-1β and IFN-γ, excessive amyloid and islet amyloid polypeptide or non-esterified fatty acids (lipotoxicity). Knockout of sphingomyelin synthase 1, which converts ceramide to sphingomyelin, leads to impairment of insulin secretion. Increased ceramidase activity or pharmacological inhibition of ceramide synthetase, inhibits β-cell apoptosis. Ceramide contributes to endoplasmatic reticulum (ER) stress, decreased mitochondrial membrane potential in insulin-secreting cells and mitochondrial release of cytochrome c into the cytosol, which are all triggers of apoptotic cell death. Ceramide-dependent signaling involves activation of extracellularly regulated kinases 1 and 2 (ERK1/2), downregulation of Period (Per)-aryl hydrocarbon receptor nuclear translocator (Arnt)-single-minded (Sim) kinase (PASK), activation of okadaic-acid-sensitive protein phosphatase 2A (PP2A) and stimulation of NADPH-oxidase with generation of superoxides and lipid peroxides. Ceramide reduces the activity of voltage gated potassium (Kv)-channels in insulin-secreting cells. The role of ceramide in β-cell survival and function may be therapeutically relevant, because ceramide formation can be suppressed by pharmacological inhibition of ceramide synthetase and/or sphingomyelinase.
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Affiliation(s)
- Florian Lang
- University of Tübingen, Institute of Physiology, Germany.
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Kowluru A, Klumpp S, Krieglstein J. Protein histidine [de]phosphorylation in insulin secretion: abnormalities in models of impaired insulin secretion. Naunyn Schmiedebergs Arch Pharmacol 2011; 384:383-90. [PMID: 21626002 DOI: 10.1007/s00210-011-0616-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Accepted: 02/18/2011] [Indexed: 12/20/2022]
Abstract
In the majority of cell types, including the islet β-cell, transduction of extracellular signals involves ligand binding to a receptor, often followed by the activation G proteins and their effector modules. The islet β-cell is unusual in that glucose lacks an extracellular receptor. Instead, events consequent to glucose metabolism promote insulin secretion via the generation of diffusible second messengers and mobilization of calcium. A selective increase in intracellular calcium has been shown to regulate the phosphorylation status key islet proteins thereby facilitating insulin secretion. In addition to classical protein kinases [e.g., protein kinases A and C], recent studies from our laboratory have focused on the expression and function of various forms of NDPK/nm23-like histidine kinases in clonal β-cells, normal rodent, and human islets. Further, we recently reported localization of a cytosolic protein histidine phosphatase [PHP] in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knock down of nm23-H1 and PHP in insulin-secreting INS 832/13 cells significantly attenuated glucose-induced insulin secretion. We also observed significant alterations in the expression and function of nm23-H1/PHP in β-cells chronically exposed to elevated levels of glucose and saturated fatty acids, such as palmitate (i.e., glucolipotoxicity). Similar changes were also noted in islets from the Goto-Kakizaki and Zucker Diabetic Fatty rats, two known models for type 2 diabetes. It is concluded that protein histidine phosphorylation-dephosphorylation cycles play novel regulatory roles in G protein-mediated physiological insulin secretion and that abnormalities in this signaling axis lead to impaired insulin secretion in glucolipotoxicity and type 2 diabetes.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, John D. Dingell VA Medical Center, Detroit, MI 48201, USA.
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Kamath V, Kyathanahalli CN, Jayaram B, Syed I, Olson LK, Ludwig K, Klumpp S, Krieglstein J, Kowluru A. Regulation of glucose- and mitochondrial fuel-induced insulin secretion by a cytosolic protein histidine phosphatase in pancreatic beta-cells. Am J Physiol Endocrinol Metab 2010; 299:E276-86. [PMID: 20501872 PMCID: PMC2928511 DOI: 10.1152/ajpendo.00091.2010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We report localization of a cytosolic protein histidine phosphatase (PHP; approximately 16 kDa) in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knockdown of PHP markedly reduced glucose- or mitochondrial fuel-induced but not KCl-induced insulin secretion. siRNA-mediated knockdown of PHP also attenuated mastoparan-induced insulin secretion, suggesting its participation in G protein-sensitive signaling steps, leading to insulin secretion. Functional assays revealed that the beta-cell PHP catalyzes the dephosphorylation of ATP-citrate lyase (ACL). Silencing of PHP expression markedly reduced ACL activity, suggesting functional regulation of ACL by PHP in beta-cells. Coimmunoprecipitation studies revealed modest effects of glucose on the interaction between PHP and ACL. Confocal microscopic evidence indicated that glucose promotes association between ACL and nm23-H1, a known kinase histidine kinase, but not between PHP and ACL. Furthermore, metabolic viability of INS 832/13 cells was resistant to siRNA-PHP, suggesting no regulatory roles of PHP in cell viability. Finally, long-term exposure (24 h) of INS 832/13 cells or rat islets to high glucose (30 mM) increased the expression of PHP. Such increases in PHP expression were also seen in islets derived from the Zucker diabetic fatty rat compared with islets from the lean control animals. Together, these data implicate regulatory roles for PHP in a G protein-sensitive step involved in nutrient-induced insulin secretion. In light of the current debate on putative regulatory roles of ACL in insulin secretion, additional studies are needed to precisely identify the phosphoprotein substrate(s) for PHP in the cascade of events leading to nutrient-induced insulin secretion.
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Affiliation(s)
- Vasudeva Kamath
- Department of Pharmaceutical Sciences, Wayne State University and Veterans Affairs Medical Center, Detroit, MI 48202, USA
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Syed I, Jayaram B, Subasinghe W, Kowluru A. Tiam1/Rac1 signaling pathway mediates palmitate-induced, ceramide-sensitive generation of superoxides and lipid peroxides and the loss of mitochondrial membrane potential in pancreatic beta-cells. Biochem Pharmacol 2010; 80:874-83. [PMID: 20493824 DOI: 10.1016/j.bcp.2010.05.006] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2010] [Revised: 05/10/2010] [Accepted: 05/10/2010] [Indexed: 12/15/2022]
Abstract
The phagocytic NADPH oxidase [NOX] has been implicated in the generation of superoxides in the pancreatic beta-cell. Herein, using normal rat islets and clonal INS 832/13 cells, we tested the hypothesis that activation of the small G-protein Rac1, which is a member of the NOX holoenzyme, is necessary for palmitate [PA]-induced generation of superoxides in pancreatic beta-cells. Incubation of isolated beta-cells with PA potently increased the NOX activity culminating in a significant increase in the generation of superoxides and lipid peroxides in these cells; such effects of PA were attenuated by diphenyleneiodonium [DPI], a known inhibitor of NOX. In addition, PA caused a transient, but significant activation [i.e., GTP-bound form] of Rac1 in these cells. NSC23766, a selective inhibitor of Rac1, but not Cdc42 or Rho activation, inhibited Rac1 activation and the generation of superoxides and lipid peroxides induced by PA. Fumonisin B-1 [FB-1], which inhibits de novo synthesis of ceramide [CER] from PA, also attenuated PA-induced superoxide and lipid peroxide generation and NOX activity implicating intracellularly generated CER in the metabolic effects of PA; such effects were also demonstrable in the presence of the cell-permeable C2-CER. Further, NSC23766 prevented C2-CER-induced Rac1 activation and production of superoxides and lipid peroxides. Lastly, C2-CER, but not its inactive analogue, significantly reduced the mitochondrial membrane potential, which was prevented to a large degree by NSC23766. Together, our findings suggest that Tiam1/Rac1 signaling pathway regulates PA-induced, CER-dependent superoxide generation and mitochondrial dysfunction in pancreatic beta-cells.
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Affiliation(s)
- Ismail Syed
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy, Wayne State University, Detroit, MI 48201, United States
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Abstract
Glucose-stimulated insulin secretion from the islet beta-cell involves a sequence of metabolic events and an interplay between a wide range of signaling pathways leading to the generation of second messengers (e.g., cyclic nucleotides, adenine and guanine nucleotides, soluble lipid messengers) and mobilization of calcium ions. Consequent to the generation of necessary signals, the insulin-laden secretory granules are transported from distal sites to the plasma membrane for fusion and release of their cargo into the circulation. The secretory granule transport underlies precise changes in cytoskeletal architecture involving a well-coordinated cross-talk between various signaling proteins, including small molecular mass GTP-binding proteins (G proteins) and their respective effector proteins. The purpose of this article is to provide an overview of current understanding of the identity of small G proteins (e.g., Cdc42, Rac1, and ARF-6) and their corresponding regulatory factors (e.g., GDP/GTP-exchange factors, GDP-dissociation inhibitors) in the pancreatic beta-cell. Plausible mechanisms underlying regulation of these signaling proteins by insulin secretagogues are also discussed. In addition to their positive modulatory roles, certain small G proteins also contribute to the metabolic dysfunction and demise of the islet beta-cell seen in in vitro and in vivo models of impaired insulin secretion and diabetes. Emerging evidence also suggests significant insulin secretory abnormalities in small G protein knockout animals, further emphasizing vital roles for these proteins in normal health and function of the islet beta-cell. Potential significance of these experimental observations from multiple laboratories and possible avenues for future research in this area of islet research are highlighted.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Avenue, Detroit, MI 48202-3489, USA.
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Mehta A, Orchard S. Nucleoside diphosphate kinase (NDPK, NM23, AWD): recent regulatory advances in endocytosis, metastasis, psoriasis, insulin release, fetal erythroid lineage and heart failure; translational medicine exemplified. Mol Cell Biochem 2009; 329:3-15. [PMID: 19415463 PMCID: PMC2721137 DOI: 10.1007/s11010-009-0114-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Accepted: 04/02/2009] [Indexed: 12/17/2022]
Abstract
The guest editor (AM) provides his perspective on the most recent advances on nucleoside diphosphate kinase (NDPK, otherwise known as AWD or NM23) showcasing phospho-histidine biochemistry and its impact on diverse pathology when disordered. His co-author (SO) provides state-of-the-art analyses from the European institute of Bioinformatics in an appendix to support the most recent advances made by the NDPK community. Unfortunately, to those outside the field, NDPK is often dismissed as a tiny ‘ancient housekeeper’ protein found in marine sponges, social amoebae, worms, fruit flies, rodents and humans but the state-of-the-art papers overviewed here show that NDPK does not act simply in mindless rote, inter-converting cellular ‘energy currencies’. That two NDPK isoforms regulate fetal erythroid lineage is a developmental case in point. Seminal Cancer Research UK support is gratefully acknowledged that generated additional resources to enable the NDPK community to meet in Dundee in 2007 (www.dundee.ac.uk/mchs/ndpk; next meeting is planned: 2010/Mannheim-Heidelberg). The presented papers illustrate the point that when scientists are left alone ‘shut up in the narrow cell of their laboratory’ (as the philosopher Ortega once said, a sentiment echoed by Erwin Schrödinger), then progress will ultimately occur bridging the gap between specialization and translation for human benefit. To aid translation, this overview initially introduces the NDPK family to the non-specialist, who serendipitously finds these proteins in their biology. This is immediately followed by examples of the diverse biology generated by this self-aggregating group of multi-functional proteins and finally capped by an emerging idea explaining how this diversity might arise.
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Affiliation(s)
- Anil Mehta
- Division of Medical Sciences, Tayside Institute of Child Health, Ninewells Hospital Medical School, Dundee DD19SY, Scotland, UK.
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