scholarly journals Enhancer of Zeste Homolog 2 (EZH2) Mediates Glucolipotoxicity-Induced Apoptosis in β-Cells

2020 ◽  
Vol 21 (21) ◽  
pp. 8016
Author(s):  
Tina Dahlby ◽  
Christian Simon ◽  
Marie Balslev Backe ◽  
Mattias Salling Dahllöf ◽  
Edward Holson ◽  
...  
Keyword(s):  
Er Stress ◽  
Molecular Mechanisms ◽  
Selective Inhibition ◽  
Human Islets ◽  
Β Cells ◽  
Β Cell ◽  
Enhancer Of Zeste ◽  
Cell Gene Expression ◽  
Nfκb Pathway ◽  
Induced Apoptosis

Selective inhibition of histone deacetylase 3 (HDAC3) prevents glucolipotoxicity-induced β-cell dysfunction and apoptosis by alleviation of proapoptotic endoplasmic reticulum (ER) stress-signaling, but the precise molecular mechanisms of alleviation are unexplored. By unbiased microarray analysis of the β-cell gene expression profile of insulin-producing cells exposed to glucolipotoxicity in the presence or absence of a selective HDAC3 inhibitor, we identified Enhancer of zeste homolog 2 (EZH2) as the sole target candidate. β-Cells were protected against glucolipotoxicity-induced ER stress and apoptosis by EZH2 attenuation. Small molecule inhibitors of EZH2 histone methyltransferase activity rescued human islets from glucolipotoxicity-induced apoptosis. Moreover, EZH2 knockdown cells were protected against glucolipotoxicity-induced downregulation of the protective non-canonical Nuclear factor of kappa light polypeptide gene enhancer in B-cells (NFκB) pathway. We conclude that EZH2 deficiency protects from glucolipotoxicity-induced ER stress, apoptosis and downregulation of the non-canonical NFκB pathway, but not from insulin secretory dysfunction. The mechanism likely involves transcriptional regulation via EZH2 functioning as a methyltransferase and/or as a methylation-dependent transcription factor.

Differential activation of ER stress and apoptosis in response to chronically elevated free fatty acids in pancreatic β-cells

2008 ◽  
Vol 294 (3) ◽  
pp. E540-E550 ◽  
Author(s):  
Elida Lai ◽  
George Bikopoulos ◽  
Michael B. Wheeler ◽  
Maria Rozakis-Adcock ◽  
Allen Volchuk
Keyword(s):  
Er Stress ◽  
Cell Lines ◽  
Cell Apoptosis ◽  
Human Islets ◽  
Pancreatic Β Cell ◽  
Β Cell ◽  
Min6 Cells ◽  
Relative Contribution ◽  
Induced Apoptosis

Chronic exposure to elevated saturated free fatty acid (FFA) levels has been shown to induce endoplasmic reticulum (ER) stress that may contribute to promoting pancreatic β-cell apoptosis. Here, we compared the effects of FFAs on apoptosis and ER stress in human islets and two pancreatic β-cell lines, rat INS-1 and mouse MIN6 cells. Isolated human islets cultured in vitro underwent apoptosis, and markers of ER stress pathways were elevated by chronic palmitate exposure. Palmitate also induced apoptosis in MIN6 and INS-1 cells, although the former were more resistant to both apoptosis and ER stress. MIN6 cells were found to express significantly higher levels of ER chaperone proteins than INS-1 cells, which likely accounts for the ER stress resistance. We attempted to determine the relative contribution that ER stress plays in palmitate-induced β-cell apoptosis. Although overexpressing GRP78 in INS-1 cells partially reduced susceptibility to thapsigargin, this failed to reduce palmitate-induced ER stress or apoptosis. In INS-1 cells, palmitate induced apoptosis at concentrations that did not result in significant ER stress. Finally, MIN6 cells depleted of GRP78 were more susceptible to tunicamycin-induced apoptosis but not to palmitate-induced apoptosis compared with control cells. These results suggest that ER stress is likely not the main mechanism involved in palmitate-induced apoptosis in β-cell lines. Human islets and MIN6 cells were found to express high levels of stearoyl-CoA desaturase-1 compared with INS-1 cells, which may account for the decreased susceptibility of these cells to the cytotoxic effects of palmitate.

scholarly journals IRS1 deficiency protects β-cells against ER stress-induced apoptosis by modulating sXBP-1 stability and protein translation

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Tomozumi Takatani ◽  
Jun Shirakawa ◽  
Michael W. Roe ◽  
Colin A. Leech ◽  
Bernhard F. Maier ◽  
...  
Keyword(s):  
Er Stress ◽  
Protein Translation ◽  
Adaptor Proteins ◽  
Nuclear Accumulation ◽  
Cell Protection ◽  
Β Cells ◽  
Β Cell ◽  
Protein Instability ◽  
Underlying Mechanisms ◽  
Induced Apoptosis

Abstract Endoplasmic reticulum (ER) stress is among several pathological features that underlie β-cell failure in the development of type 1 and type 2 diabetes. Adaptor proteins in the insulin/insulin-like-growth factor-1 signaling pathways, such as insulin receptor substrate-1 (IRS1) and IRS2, differentially impact β-cell survival but the underlying mechanisms remain unclear. Here we report that β-cells deficient in IRS1 (IRS1KO) are resistant, while IRS2 deficiency (IRS2KO) makes them susceptible to ER stress-mediated apoptosis. IRS1KOs exhibited low nuclear accumulation of spliced XBP-1 due to its poor stability, in contrast to elevated accumulation in IRS2KO. The reduced nuclear accumulation in IRS1KO was due to protein instability of Xbp1 secondary to proteasomal degradation. IRS1KO also demonstrated an attenuation in their general translation status in response to ER stress revealed by polyribosomal profiling. Phosphorylation of eEF2 was dramatically increased in IRS1KO enabling the β-cells to adapt to ER stress by blocking translation. Furthermore, significantly high ER calcium (Ca2+) was detected in IRS1KO β-cells even upon induction of ER stress. These observations suggest that IRS1 could be a therapeutic target for β-cell protection against ER stress-mediated cell death by modulating XBP-1 stability, protein synthesis, and Ca2+ storage in the ER.

scholarly journals The Hippo kinase LATS2 impairs pancreatic β-cell survival in diabetes through the mTORC1-autophagy axis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ting Yuan ◽  
Karthika Annamalai ◽  
Shruti Naik ◽  
Blaz Lupse ◽  
Shirin Geravandi ◽  
...  
Keyword(s):  
Cell Survival ◽  
Cell Apoptosis ◽  
Molecular Mechanisms ◽  
Cell Mass ◽  
Human Islets ◽  
Hippo Signaling ◽  
Pancreatic Β Cell ◽  
Β Cells ◽  
Β Cell ◽  
Large Tumor

AbstractDiabetes results from a decline in functional pancreatic β-cells, but the molecular mechanisms underlying the pathological β-cell failure are poorly understood. Here we report that large-tumor suppressor 2 (LATS2), a core component of the Hippo signaling pathway, is activated under diabetic conditions and induces β-cell apoptosis and impaired function. LATS2 deficiency in β-cells and primary isolated human islets as well as β-cell specific LATS2 ablation in mice improves β-cell viability, insulin secretion and β-cell mass and ameliorates diabetes development. LATS2 activates mechanistic target of rapamycin complex 1 (mTORC1), a physiological suppressor of autophagy, in β-cells and genetic and pharmacological inhibition of mTORC1 counteracts the pro-apoptotic action of activated LATS2. We further show a direct interplay between Hippo and autophagy, in which LATS2 is an autophagy substrate. On the other hand, LATS2 regulates β-cell apoptosis triggered by impaired autophagy suggesting an existence of a stress-sensitive multicomponent cellular loop coordinating β-cell compensation and survival. Our data reveal an important role for LATS2 in pancreatic β-cell turnover and suggest LATS2 as a potential therapeutic target to improve pancreatic β-cell survival and function in diabetes.

scholarly journals Molecular Mechanisms of Apoptosis Induction and Its Regulation by Fatty Acids in Pancreatic β-Cells

2021 ◽  
Vol 22 (8) ◽  
pp. 4285
Author(s):  
Jan Šrámek ◽  
Vlasta Němcová-Fürstová ◽  
Jan Kovář
Keyword(s):  
Fatty Acids ◽  
Er Stress ◽  
Membrane Fluidity ◽  
Molecular Mechanisms ◽  
Mitochondrial Pathway ◽  
Signalling Pathways ◽  
Apoptosis Induction ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells

Pancreatic β-cell failure and death contribute significantly to the pathogenesis of type 2 diabetes. One of the main factors responsible for β-cell dysfunction and subsequent cell death is chronic exposure to increased concentrations of FAs (fatty acids). The effect of FAs seems to depend particularly on the degree of their saturation. Saturated FAs induce apoptosis in pancreatic β-cells, whereas unsaturated FAs are well tolerated and are even capable of inhibiting the pro-apoptotic effect of saturated FAs. Molecular mechanisms of apoptosis induction by saturated FAs in β-cells are not completely elucidated. Saturated FAs induce ER stress, which in turn leads to activation of all ER stress pathways. When ER stress is severe or prolonged, apoptosis is induced. The main mediator seems to be the CHOP transcription factor. Via regulation of expression/activity of pro- and anti-apoptotic Bcl-2 family members, and potentially also through the increase in ROS production, CHOP switches on the mitochondrial pathway of apoptosis induction. ER stress signalling also possibly leads to autophagy signalling, which may activate caspase-8. Saturated FAs activate or inhibit various signalling pathways, i.e., p38 MAPK signalling, ERK signalling, ceramide signalling, Akt signalling and PKCδ signalling. This may lead to the activation of the mitochondrial pathway of apoptosis, as well. Particularly, the inhibition of the pro-survival Akt signalling seems to play an important role. This inhibition may be mediated by multiple pathways (e.g., ER stress signalling, PKCδ and ceramide) and could also consequence in autophagy signalling. Experimental evidence indicates the involvement of certain miRNAs in mechanisms of FA-induced β-cell apoptosis, as well. In the rather rare situations when unsaturated FAs are also shown to be pro-apoptotic, the mechanisms mediating this effect in β-cells seem to be the same as for saturated FAs. To conclude, FA-induced apoptosis rather appears to be preceded by complex cross talks of multiple signalling pathways. Some of these pathways may be regulated by decreased membrane fluidity due to saturated FA incorporation. Few data are available concerning molecular mechanisms mediating the protective effect of unsaturated FAs on the effect of saturated FAs. It seems that the main possible mechanism represents a rather inhibitory intervention into saturated FA-induced pro-apoptotic signalling than activation of some pro-survival signalling pathway(s) or metabolic interference in β-cells. This inhibitory intervention may be due to an increase of membrane fluidity.

scholarly journals Neuromedin U uses Gαi2 and Gαo to suppress glucose-stimulated Ca2+ signaling and insulin secretion in pancreatic β cells

PLoS ONE ◽  
2021 ◽  
Vol 16 (4) ◽  
pp. e0250232
Author(s):  
Weidong Zhang ◽  
Hideyuki Sakoda ◽  
Yuki Nakazato ◽  
Md Nurul Islam ◽  
François Pattou ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Er Stress ◽  
Cell Biology ◽  
Molecular Mechanisms ◽  
Cell Function ◽  
Mitochondrial Dynamics ◽  
Intracellular Camp ◽  
Β Cells ◽  
Β Cell ◽  
Signaling Mechanism

Neuromedin U (NMU), a highly conserved peptide in mammals, is involved in a wide variety of physiological processes, including impairment of pancreatic β-cell function via induction of mitochondrial dysfunction and endoplasmic reticulum (ER) stress, ultimately suppressing insulin secretion. NMU has two receptors, NMU receptor 1 (NMUR1) and NMUR2, both of which are G-protein–coupled receptors (GPCRs). Only NMUR1 is expressed in mouse islets and β cell–derived MIN6-K8 cells. The molecular mechanisms underlying the insulinostatic action mediated by NMUR1 in β cells have yet to be elucidated. In this study, we explored the molecular mechanism driving impairment of insulin secretion in β cells by the NMU–NMUR1 axis. Pretreatment with the Gαi/o inhibitor Bordetella pertussis toxin (PTX), but not the Gαq inhibitor YM254890, abolished NMU-induced suppression of glucose-stimulated insulin secretion and calcium response in β cells. Knockdown of Gαi2 and Gαo in β cells counteracted NMU-induced suppression of insulin secretion and gene alterations related to mitochondrial fusion (Mfn1, Mfn2), fission (Fis1, Drp1), mitophagy (Pink1, Park2), mitochondrial dynamics (Pgc-1α, Nrf1, and Tfam), ER stress (Chop, Atp2a3, Ryr2, and Itpr2), intracellular ATP level, and mitochondrial membrane potential. NMU decreased forskolin-stimulated intracellular cAMP in both mouse and human islets. We concluded that NMUR1 coupled to PTX-sensitive Gαi2 and Gαo proteins in β cells reduced intracellular Ca2+ influx and cAMP level, thereby causing β-cell dysfunction and impairment. These results highlight a novel signaling mechanism of NMU and provide valuable insights into the further investigation of NMU functions in β-cell biology.

scholarly journals Differential expression of Ormdl genes in the islets of mice and humans with obesity

2019 ◽  
Author(s):  
Rachel Fenske ◽  
Hugo Lee ◽  
Tugce Akcan ◽  
Elliot Domask ◽  
Dawn Belt Davis ◽  
...  
Keyword(s):  
Er Stress ◽  
Critical Role ◽  
Human Islets ◽  
Ceramide Synthase ◽  
Β Cells ◽  
Β Cell ◽  
Chemically Induced ◽  
The Difference ◽  
Differential Responsiveness ◽  
Obese Human

SummaryThe orosomucoid-like proteins (Ormdl1-3) are emerging as the critical regulators of sphingolipid homeostasis, inflammation and ER stress. However, their roles in β-cells and obesity remain unknown. Here, we showed that islets isolated from overweight/obese human donors displayed marginally reduced ORMDL1-2 expression while ORMDL3 expression was significantly reduced as compared to islets from lean donors. In contrast, Ormdl3 expression was significantly upregulated in the islets of leptin-deficient obese (ob/ob) mice compared to lean mice. We identified that the difference in expression of Ormdl3 between mouse and human islets was leptin-dependent, as treatment of ob/ob mice with leptin significantly reduced Ormld3 expression. Furthermore, Ormdl1-3 were significantly upregulated upon chemically-induced ER stress, but they showed differential responsiveness to cytokines in a β-cell line. Knockdown of Ormdl3 substantially increased expression of apoptotic markers, which was rescued by a pharmacological inhibitor of ceramide synthase. Taken together we demonstrate leptin-dependent regulation of Ormdl3 expression in ob/ob islets, highlight the possible importance of β-cell stress conditions in differential Ormdl expression and identify a critical role for Ormdl3 in β-cell survival.

scholarly journals Modulation of Apoptosis Pathways by Oxidative Stress and Autophagy in β Cells

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Maorong Wang ◽  
Mia Crager ◽  
Subbiah Pugazhenthi
Keyword(s):  
Oxidative Stress ◽  
Promoter Activity ◽  
Human Islets ◽  
Β Cells ◽  
Β Cell ◽  
Multiple Stresses ◽  
Apoptosis Pathway ◽  
Min6 Cells ◽  
Beta Cell Line ◽  
Induced Apoptosis

Human islets isolated for transplantation are exposed to multiple stresses including oxidative stress and hypoxia resulting in significant loss of functional β cell mass. In this study we examined the modulation of apoptosis pathway genes in islets exposed to hydrogen peroxide, peroxynitrite, hypoxia, and cytokines. We observed parallel induction of pro- and antiapoptotic pathways and identified several novel genes including BFAR, CARD8, BNIP3, and CIDE-A. As BNIP3 is an inducer of autophagy, we examined this pathway in MIN6 cells, a mouse beta cell line and in human islets. Culture of MIN6 cells under low serum conditions increased the levels of several proteins in autophagy pathway, including ATG4, Beclin 1, LAMP-2, and UVRAG. Amino acid deprivation led to induction of autophagy in human islets. Preconditioning of islets with inducers of autophagy protected them from hypoxia-induced apoptosis. However, induction of autophagy during hypoxia exacerbated apoptotic cell death. ER stress led to induction of autophagy and apoptosis in β cells. Overexpression of MnSOD, an enzyme that scavenges free radicals, resulted in protection of MIN6 cells from cytokine-induced apoptosis. Ceramide, a mediator of cytokine-induced injury, reduced the active phosphorylated form of Akt and downregulated the promoter activity of the antiapoptotic gene bcl-2. Furthermore, cytokine-stimulated JNK pathway downregulated the bcl-2 promoter activity which was reversed by preincubation with SP600125, a JNK inhibitor. Our findings suggest that β cell apoptosis by multiple stresses in islets isolated for transplantation is the result of orchestrated gene expression in apoptosis pathway.

scholarly journals Exendin-4 inhibits glucolipotoxic ER stress in pancreatic β cells via regulation of SREBP1c and C/EBPβ transcription factors

2012 ◽  
Vol 216 (3) ◽  
pp. 343-352 ◽  
Author(s):  
Yoon Sin Oh ◽  
Youn-Jung Lee ◽  
Yup Kang ◽  
Jaeseok Han ◽  
Oh-Kyung Lim ◽  
...  
Keyword(s):  
Er Stress ◽  
Cell Apoptosis ◽  
Molecular Mechanisms ◽  
Prolonged Exposure ◽  
Nuclear Translocation ◽  
Β Cells ◽  
Β Cell ◽  
Stress Markers ◽  
Glucagon Like Peptide 1

Prolonged exposure to high glucose (HG) and palmitate (PA) results in increased ER stress and subsequently induces β-cell apoptosis. Exendin-4, a glucagon-like peptide-1 agonist, is known to protect β cells from toxicity induced by cytokines, HG, or fatty acids by reducing ER stress. However, the detailed molecular mechanisms for this protective effect are still not known. In this study, we investigated the role of exendin-4 in the inhibition of glucolipotoxicity-induced ER stress and β-cell apoptosis. Exendin-4 treatment protected INS-1 β cells from apoptosis in response to HG/PA (25 mM glucose+400 μM PA). HG/PA treatment increased cleaved caspase-3 and induced ER stress maker proteins such as PERK (EIF2AK3), ATF6, and phosphorylated forms of PERK, eIF2α, IRE1α (ERN1), and JNK (MAPK8), and these increases were significantly inhibited by exendin-4 treatment. HG/PA treatment of INS-1 cells increased SREBP1 (SREBF1) protein and induced its nuclear translocation and subsequently increased C/EBPβ (CEBPB) protein and its nuclear translocation. Exendin-4 treatment attenuated this increase. Knockdown ofSREBP1creduced the activation ofC/EBPβand also blocked the expression of ER stress markers induced by HG/PA treatment. Our results indicate that exendin-4 inhibits the activation of SREBP1c and C/EBPβ, which, in turn, may reduce glucolipotoxicity-induced ER stress and β-cell apoptosis.

scholarly journals Pericytes contribute to the islet basement membranes to promote beta-cell gene expression

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Lina Sakhneny ◽  
Alona Epshtein ◽  
Limor Landsman
Keyword(s):  
Gene Expression ◽  
Cell Function ◽  
Basement Membranes ◽  
Cell Physiology ◽  
Β Cells ◽  
Β Cell ◽  
Cell Clustering ◽  
Β Cell Function ◽  
Cell Gene Expression ◽  
Glucose Stimulated Insulin Secretion

Abstractβ-Cells depend on the islet basement membrane (BM). While some islet BM components are produced by endothelial cells (ECs), the source of others remains unknown. Pancreatic pericytes directly support β-cells through mostly unidentified secreted factors. Thus, we hypothesized that pericytes regulate β-cells through the production of BM components. Here, we show that pericytes produce multiple components of the mouse pancreatic and islet interstitial and BM matrices. Several of the pericyte-produced ECM components were previously implicated in β-cell physiology, including collagen IV, laminins, proteoglycans, fibronectin, nidogen, and hyaluronan. Compared to ECs, pancreatic pericytes produce significantly higher levels of α2 and α4 laminin chains, which constitute the peri-islet and vascular BM. We further found that the pericytic laminin isoforms differentially regulate mouse β-cells. Whereas α2 laminins promoted islet cell clustering, they did not affect gene expression. In contrast, culturing on Laminin-421 induced the expression of β-cell genes, including Ins1, MafA, and Glut2, and significantly improved glucose-stimulated insulin secretion. Thus, alongside ECs, pericytes are a significant source of the islet BM, which is essential for proper β-cell function.

scholarly journals PDX1LOW MAFALOW β-cells contribute to islet function and insulin release

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Daniela Nasteska ◽  
Nicholas H. F. Fine ◽  
Fiona B. Ashford ◽  
Federica Cuozzo ◽  
Katrina Viloria ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Metabolic Stress ◽  
Human Islets ◽  
Islet Function ◽  
Β Cells ◽  
Β Cell ◽  
Ionic Fluxes ◽  
Transcriptomic Level ◽  
Adult Islet

AbstractTranscriptionally mature and immature β-cells co-exist within the adult islet. How such diversity contributes to insulin release remains poorly understood. Here we show that subtle differences in β-cell maturity, defined using PDX1 and MAFA expression, contribute to islet operation. Functional mapping of rodent and human islets containing proportionally more PDX1HIGH and MAFAHIGH β-cells reveals defects in metabolism, ionic fluxes and insulin secretion. At the transcriptomic level, the presence of increased numbers of PDX1HIGH and MAFAHIGH β-cells leads to dysregulation of gene pathways involved in metabolic processes. Using a chemogenetic disruption strategy, differences in PDX1 and MAFA expression are shown to depend on islet Ca2+ signaling patterns. During metabolic stress, islet function can be restored by redressing the balance between PDX1 and MAFA levels across the β-cell population. Thus, preserving heterogeneity in PDX1 and MAFA expression, and more widely in β-cell maturity, might be important for the maintenance of islet function.

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