Role and impact of the extracellular matrix on integrin-mediated pancreatic β-cell functions

Understanding the organisation and role of the extracellular matrix (ECM) in islets of Langerhans is critical for maintaining pancreatic β-cells, and to recognise and revert the physiopathology of diabetes. Indeed, integrin-mediated adhesion signalling in response to the pancreatic ECM plays crucial roles in β-cell survival and insulin secretion, two major functions, which are affected in diabetes. Here, we would like to present an update on the major components of the pancreatic ECM, their role during integrin-mediated cell-matrix adhesions and how they are affected during diabetes. To treat diabetes, a promising approach consists in replacing β-cells by transplantation. However, efficiency is low, because β-cells suffer of anoikis, due to enzymatic digestion of the pancreatic ECM, which affects the survival of insulin-secreting β-cells. The strategy of adding ECM components during transplantation, to reproduce the pancreatic microenvironment, is a challenging task, as many of the regulatory mechanisms that control ECM deposition and turnover are not sufficiently understood. A better comprehension of the impact of the ECM on the adhesion and integrin-dependent signalling in β-cells is primordial to improve the healthy state of islets to prevent the onset of diabetes as well as for enhancing the efficiency of the islet transplantation therapy

Obésité, acides gras et cancer du foie (effets de l'oléate sur les cellules de cancer du foie)

La prévalence de l obésité ne cesse de croître dans les pays industrialisés et devient un véritable problème de santé publique. L obésité associée à l insulinorésistance sont des facteurs de risque de certain cancer. Le lien épidémiologique entre l obésité et le carcinome hépatocellulaire (CHC) qui constitue la 3ème cause de mortalité par cancer dans le monde, n est pas si évident. En effet, les mécanismes moléculaires à l origine de cette association ne sont pas déterminés. L obésité et l alimentation riche en lipides présentes dans les pays industrialisés induisent des variations physiologiques importantes à l origine entre autres, d une augmentation des taux circulants de palmitate (acide gras saturé) et de l oléate (acide gras mono-insaturé). En effet, une augmentation de 50 M d oléate chez les individus obèses est observée par rapport aux sujets de poids normal. Cette augmentation pourrait expliquer le lien épidémiologique entre obésité et augmentation de risque de développer un CHC. Le palmitate est connu pour ses effets toxiques sur les hépatocytes, à l inverse de l oléate, dont les effets sont encore très controversés. Quelques études montrent son implication dans l invasion et la progression de certains cancers. Néanmoins, son effet pro-ou anti-tumoral n est pas défini dans le CHC. Ce travail de thèse avait pour but d étudier les effets et les mécanismes moléculaires impliqués dans la prolifération de cellules de CHC induit par l oléate et indirectement par l obésité. Nous avons soumis des cellules d hépatocarcinome humain à différentes concentrations d oléate, dont une physiopathologique de 50 M. Nous avons montré que la voie mammalian Target Of Rapamycin Complex 1 (mTORC1) est responsable de la progression du cycle cellulaire et des effets prolifératifs de l oléate en concentration physiopathologique. En effet, mTORC1 est un effecteur majeur de la transduction du signal en réponse aux nutriments, impliqué dans la prolifération, la croissance cellulaire et souvent dérégulé dans les cancers, dont le CHC. Par ailleurs, nous avons observé qu en présence d oléate, nos cellules deviennent résistantes à l effet antiprolifératif de la rapamycine, un inhibiteur de la voie mTORC1 utilisé en thérapeutique. Les phospholipases D (PLD) produisent de l acide phosphatidique (PA), capable d activer mTORC1 et dans certain cas, de rendre cette kinase résistante à la rapamycine. Effectivement, l oléate induit la production de PA, responsable de l activation de la voie mTORC1/4E-BP1 et de l augmentation de la prolifération des cellules d hépatocarcinome. L inhibition de la production de PA réverse la résistance à la rapamycine induite par l oléate sur l axe mTORC1/4E-BP1. Nos travaux ont mis en évidence que l oléate constitue un lien moléculaire épidémiologique entre obésité et CHC, et aide à la compréhension moléculaire des effets de cet acide gras sur la progression du CHC. Par ailleurs, il est possible d envisager de nouvelles perspectives pour la prévention et/ou le traitement de ce cancer, réputé chimio- et radio-résistant dont seule la résection chirurgicale constitue un traitement efficace à ce jour. En effet, le traitement du CHC par des inhibiteurs de PLD pourrait être envisagé et constituerait une alternative à l utilisation de la rapamycine ou de ses dérivés, inefficaces en présence d obésité ou d insulinorésistance. De plus, nos résultats mèneront à d éventuelles recommandations nutritionnelles pour la prévention primaire ou secondaire du cancer du foie.NICE-BU Sciences (060882101) / SudocSudocFranceF

Non-muscle myosin IIA is involved in focal adhesion and actin remodelling controlling glucose-stimulated insulin secretion

Actin and focal adhesion (FA) remodelling are essential for glucose-stimulated insulin secretion (GSIS). Non-muscle myosin II (NM II) isoforms have been implicated in such remodelling in other cell types, and myosin light chain kinase (MLCK) and Rho-associated coiled-coil-containing kinase (ROCK) are upstream regulators of NM II, which is known to be involved in GSIS. The aim of this work was to elucidate the implication and regulation of NM IIA and IIB in beta cell actin and FA remodelling, granule trafficking and GSIS

Short Term Exposure of Beta Cells to Low Concentrations of Interleukin-1β Improves Insulin Secretion through Focal Adhesion and Actin Remodeling and Regulation of Gene Expression

Type 2 diabetes involves defective insulin secretion with islet inflammation governed in part by IL-1β. Prolonged exposure of islets to high concentrations of IL-1β (>24 h, 20 ng/ml) impairs beta cell function and survival. Conversely, exposure to lower concentrations of IL-1β for >24 h improves these same parameters. The impact on insulin secretion of shorter exposure times to IL-1β and the underlying molecular mechanisms are poorly understood and were the focus of this study. Treatment of rat primary beta cells, as well as rat or human whole islets, with 0.1 ng/ml IL-1β for 2 h increased glucose-stimulated (but not basal) insulin secretion, whereas 20 ng/ml was without effect. Similar differential effects of IL-1β depending on concentration were observed after 15 min of KCl stimulation but were prevented by diazoxide. Studies on sorted rat beta cells indicated that the enhancement of stimulated secretion by 0.1 ng/ml IL-1β was mediated by the NF-κB pathway and c-JUN/JNK pathway acting in parallel to elicit focal adhesion remodeling and the phosphorylation of paxillin independently of upstream regulation by focal adhesion kinase. Because the beneficial effect of IL-1β was dependent in part upon transcription, gene expression was analyzed by RNAseq. There were 18 genes regulated uniquely by 0.1 but not 20 ng/ml IL-1β, which are mostly involved in transcription and apoptosis. These results indicate that 2 h of exposure of beta cells to a low but not a high concentration of IL-1β enhances glucose-stimulated insulin secretion through focal adhesion and actin remodeling, as well as modulation of gene expression

IL-13 improves beta-cell survival and protects against IL-1beta-induced beta-cell death

Objectives: IL-13 is a cytokine classically produced by anti-inflammatory T-helper-2 lymphocytes; it is decreased in the circulation of type 2 diabetic patients and impacts positively on liver and skeletal muscle. Although IL-13 can exert positive effects on beta-cell lines, its impact and mode of action on primary beta-cell function and survival remain largely unexplored. Methods: Beta-cells were cultured for 48 h in the presence of IL-13 alone or in combination with IL-1β or cytokine cocktail (IL-1β, IFNγ, TNFα). Results: IL-13 protected human and rat beta-cells against cytokine induced death. However, IL-13 was unable to protect from IL-1β impaired glucose stimulated insulin secretion and did not influence NFκB nuclear relocalization induced by IL-1β. IL-13 induced phosphorylation of Akt, increased IRS2 protein expression and counteracted the IL-1β induced regulation of several beta-cell stress response genes. Conclusions: The prosurvival effects of IL-13 thus appear to be mediated through IRS2/Akt signaling with NFκB independent regulation of gene expression. In addition to previously documented beneficial effects on insulin target tissues, these data suggest that IL-13 may be useful for treatment of type 2 diabetes by preserving beta-cell mass or slowing its rate of decline. Keywords: Beta-cells, Apoptosis, Cytokines, Gene expression, Ak

Integrin and autocrine IGF2 pathways control fasting insulin secretion in β-cells

Elevated levels of fasting insulin release and insufficient glucose-stimulated insulin secretion (GSIS) are hallmarks of diabetes. Studies have established cross-talk between integrin signaling and insulin activity, but more details of how integrin-dependent signaling impacts the pathophysiology of diabetes are needed. Here, we dissected integrin-dependent signaling pathways involved in the regulation of insulin secretion in β-cells and studied their link to the still debated autocrine regulation of insulin secretion by insulin/insulin-like growth factor (IGF) 2-AKT signaling. We observed for the first time a cooperation between different AKT isoforms and focal adhesion kinase (FAK)-dependent adhesion signaling, which either controlled GSIS or prevented insulin secretion under fasting conditions. Indeed, β-cells form integrin-containing adhesions, which provide anchorage to the pancreatic extracellular matrix and are the origin of intracellular signaling via FAK and paxillin. Under low-glucose conditions, β-cells adopt a starved adhesion phenotype consisting of actin stress fibers and large peripheral focal adhesion. In contrast, glucose stimulation induces cell spreading, actin remodeling, and point-like adhesions that contain phospho-FAK and phosphopaxillin, located in small protrusions. Rat primary β-cells and mouse insulinomas showed an adhesion remodeling during GSIS resulting from autocrine insulin/IGF2 and AKT1 signaling. However, under starving conditions, the maintenance of stress fibers and the large adhesion phenotype required autocrine IGF2-IGF1 receptor signaling mediated by AKT2 and elevated FAK-kinase activity and ROCK-RhoA levels but low levels of paxillin phosphorylation. This starved adhesion phenotype prevented excessive insulin granule release to maintain low insulin secretion during fasting. Thus, deregulation of the IGF2 and adhesion-mediated signaling may explain dysfunctions observed in diabetes

Expression, phosphorylation and function of the Rab-GTPase activating protein TBC1D1 in pancreatic beta-cells

The Rab-GTPase activating protein TBC1D1 is a paralog of AS160/TBC1D4. AS160/TBC1D4, a downstream effector of Akt, has been shown to play a central role in beta-cell function and survival. The two proteins have overlapping function in insulin signalling in muscle cells. However, the expression and the potential role of TBC1D1 in beta-cells remain unknown. Therefore, the aim of this study is to investigate whether TBC1D1 is expressed in beta-cells and whether it plays, as AS160/TBC1D4, a role in beta-cell function and survival. Using human and rat beta-cells, this study shows for the first time that TBC1D1 is expressed and phosphorylated in response to glucose in these cells. Knockdown of TBC1D1 in beta-cells resulted in increased basal and glucose-stimulated insulin release, decreased proliferation but no change in apoptosis

Fractalkine (CX3CL1), a new factor protecting beta-cells against TNFalpha

We have previously shown the existence of a muscle-pancreas intercommunication axis in which CX3CL1 (fractalkine), a CX3C chemokine produced by skeletal muscle cells, could be implicated. It has recently been shown that the fractalkine system modulates murine beta-cell function. However, the impact of CX3CL1 on human islet cells especially regarding a protective role against cytokine-induced apoptosis remains to be investigated. Gene expression was determined using RNA sequencing in human islets, sorted beta- and non-beta-cells. Glucose-stimulated insulin secretion (GSIS) and glucagon secretion from human islets was measured following 24 h exposure to 1-50 ng/ml CX3CL1. GSIS and specific protein phosphorylation were measured in rat sorted beta-cells exposed to CX3CL1 for 48 h alone or in the presence of TNFalpha (20 ng/ml). Rat and human beta-cell apoptosis (TUNEL) and rat beta-cell proliferation (BrdU incorporation) were assessed after 24 h treatment with increasing concentrations of CX3CL1. Both CX3CL1 and its receptor CX3CR1 are expressed in human islets. However, CX3CL1 is more expressed in non-beta-cells than in beta-cells while its receptor is more expressed in beta-cells. CX3CL1 decreased human (but not rat) beta-cell apoptosis. CX3CL1 inhibited human islet glucagon secretion stimulated by low glucose but did not impact human islet and rat sorted beta-cell GSIS. However, CX3CL1 completely prevented the adverse effect of TNFalpha on GSIS and on molecular mechanisms involved in insulin granule trafficking by restoring the phosphorylation (Akt, AS160, paxillin) and expression (IRS2, ICAM-1, Sorcin, PCSK1) of key proteins involved in these processes. We demonstrate for the first time that human islets express and secrete CX3CL1 and CX3CL1 impacts them by decreasing glucagon secretion without affecting insulin secretion. Moreover, CX3CL1 decreases basal apoptosis of human beta-cells. We further demonstrate that CX3CL1 protects beta-cells from the adverse effects of TNFalpha on their function by restoring the expression and phosphorylation of key proteins of the insulin secretion pathway