Protective Role of Autophagy in Palmitate-Induced INS-1 β-Cell Death

Choi, Sung Eun; Lee, Sung Mi; Lee, Youn Jung; Li, Ling Ji; Lee, Soo Jin; Lee, Ji Hyun; Kim, Youngsoo; Jun, Hee-Sook; Lee, Kwan Woo; Kang, Yup

doi:10.1210/en.2008-0483

Cited by 180 publications

(201 citation statements)

References 49 publications

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“…Primarily, we provide the first direct evidence that high-fat feeding stimulates autophagic flux in beta cells in vivo. This has been previously inferred from electron microscopy studies demonstrating increases in autophagosomes and vacuole formation [2], consistent with analyses of islets from db/db mice [2], patients with diabetes [6] and in vitro models of beta cell lipotoxicity [3][4][5]. However, interpretation of these morphological changes is problematic because an accumulation of autophagosomes could result from impaired lysosomal clearance rather than an enhancement of upstream autophagy.…”

Section: Discussionsupporting

confidence: 82%

“…Although it is commonly assumed, based on genetic models [12,13], that modulation of ER stress explains the reciprocal relationship between autophagy and beta cell apoptosis [2,4,14], we believe our CHOP data are the first to confirm this mechanistic link in the context of high-fat feeding. Our results would also tend to counter the idea, suggested by some in vitro studies [3] that lipotoxic ER stress is actually triggered by autophagy.…”

Section: Discussioncontrasting

confidence: 64%

“…Activation facilitates the conversion of LC3I to LC3II, which binds to the autophagosome membrane [1]. Morphological studies of human or rodent islets show increased numbers of autophagosomes during type 2 diabetes and chronic lipid exposure (lipotoxicity) [2][3][4][5][6]. Although usually interpreted as enhanced autophagy, this might actually reflect the opposite since disruption of lysosomal function (and thus inhibition of distal autophagy) induces similar changes.…”

Section: Introductionmentioning

confidence: 99%

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High-fat diet increases autophagic flux in pancreatic beta cells in vivo and ex vivo in mice

et al. 2015

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Aims/hypothesis Defective beta cell function during lipid oversupply and type 2 diabetes is associated with dysregulation of lysosomal function and autophagy. Whether this dysregulation represents augmentation or inhibition is unclear because of technical limitations in assaying autophagy. The current aim was to determine the effects of high-fat feeding on true autophagic flux in beta cells in vivo in mice, and to establish the relationship between autophagy, endoplasmic reticulum (ER) stress and apoptosis. Methods Green fluorescent protein-microtubule-associated protein 1 light chain 3 (GFP-LC3) mice were fed chow or high-fat diets for 8-10 weeks and injected with 100 mg kg −1 day −1 chloroquine for 5 days, prior to being killed, to block clearance of autophagic markers. Pancreases and livers were fixed and GFP-LC3 aggregates or autophagosomes were detected by fluorescence or electron microscopy, respectively. Independently, islets isolated from chow or high-fat-fed mice were treated for 2 h with chloroquine ex vivo, and immunoblotting was performed for markers of autophagy (LC3 lipidation -LC3II and p62/SQSTM1), ER stress (C/EBP homology protein [CHOP], phosphorylated eukaryotic initiation factor 2α [p-eIFα] and inositol requiring enzyme 1α ) and apoptosis (cleaved caspase-3). Results Numbers of autophagosomes and GFP puncta were increased in beta cells by combined high-fat feeding and chloroquine injection, indicative of enhanced autophagic flux. By contrast, GFP puncta were attenuated in liver under the same conditions. Relative to chow-fed controls, islets isolated from fat-fed mice exhibited higher LC3II levels when treated ex vivo with chloroquine. The combination of high-fat feeding and acute chloroquine treatment induced CHOP, p-eIF2α and caspase-3, but not either treatment alone. Conclusions/interpretation We provide the first in vivo demonstrations that high-fat feeding increases autophagic flux in pancreatic beta cells, and that this serves to protect against induction of terminal ER stress. We also highlight an approach for monitoring dietary alterations in autophagic flux using ex vivo manipulation of isolated islets.

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Section: Discussionsupporting

confidence: 82%

Section: Discussioncontrasting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

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High-fat diet increases autophagic flux in pancreatic beta cells in vivo and ex vivo in mice

et al. 2015

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“…8 Increased beclin 1 expression, which correlated with the onset of protection, has been previously reported in an in vivo model of myocardial stunning, 19 and a recent paper that studied the role of autophagy in palmitate-induced beta cell death concluded, according to our hypothesis, that autophagy delays beta cell loss in type 2 diabetes. 20 Thus, although still speculative, we suggest that moderate overactivation of autophagic pathways may represent a potential mechanism set in motion by different cell types to delay overlap. This greater complexity is also seen with the evidence that signals that induce apoptosis also increase autophagy, and autophagic pathways are upregulated also by necrosis-inducing stimuli.…”

mentioning

confidence: 82%

Autophagy in hypoxia-ischemia induced brain injury: Evidences and speculations

Balduini¹,

Carloni²,

Buonocore³

2009

Autophagy

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“…Whether any of the diabetogenic factors such as nutrition and obesity impair autophagy is yet unclear. In various animal models (including mice fed high fat diet) (9, 14) and cellular models of diabetes (including glucotoxicity and lipotoxicity) (9,(13)(14)(15)(16), the number of APs has been reported to increase. Whether this increase reflects an increase or a decrease in autophagic turnover is unresolved.…”

mentioning

confidence: 99%

Fatty Acids Suppress Autophagic Turnover in β-Cells

Las

Serada

Wikström

et al. 2011

Journal of Biological Chemistry

181

184

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Recent studies have shown that autophagy is essential for proper ␤-cell function and survival. However, it is yet unclear under what pathogenic conditions autophagy is inhibited in ␤-cells. Here, we report that long term exposure to fatty acids and glucose block autophagic flux in ␤-cells, contributing to their toxic effect. INS1 cells expressing GFP-LC3 (an autophagosome marker) were treated with 0.4 mM palmitate, 0.4 mM oleate, and various concentrations of glucose for 22 h. Kinetics of the effect of fatty acids on autophagy showed a biphasic response. During the second phase of autophagy, the size of autophagosomes and the content of autophagosome substrates (GFP-LC3, p62) and endogenous LC3 was increased. During the same phase, fatty acids suppressed autophagic degradation of long lived protein in both INS1 cells and islets. In INS1 cells, palmitate induced a 3-fold decrease in the number and the acidity of Acidic Vesicular Organelles. This decrease was associated with a suppression of hydrolase activity, suppression of endocytosis, and suppression of oxidative phosphorylation. The combination of fatty acids with glucose synergistically suppressed autophagic turnover, concomitantly suppressing insulin secretion. Rapamycin treatment resulted in partial reversal of the inhibition of autophagic flux, the inhibition of insulin secretion, and the increase in cell death. Our results indicate that excess nutrient could impair autophagy in the long term, hence contributing to nutrient-induced ␤-cell dysfunction. This may provide a novel mechanism that connects diet-induced obesity and diabetes.Macroautophagy (hereafter named autophagy) is the main mechanism the cell uses to degrade damaged and redundant organelles. It involves the formation of a double-membrane structure called the phagophore, which evolves into the autophagosome (AP), 2 an organelle that sequesters cytoplasmic material such as mitochondria, peroxisomes, endoplasmic reticulum, protein aggregates, and lipids. Upon acidification (1), the AP fuses with the lysosome to form the autolysosome, which degrades its content (2).The main approach to study autophagy is by tracking APs using LC3 (microtubule-associated protein 1 light chain 3), a cytosolic protein that upon stimulation of autophagy is lipidated and recruited to the AP membrane. LC3 remains bound to the AP until released to the cytosol or degraded by lysosomal enzymes (3).Stimulators of autophagy are known to increase the number of APs. However, the quantification of APs to assess autophagy can be misleading, APs being but one component in the chain constituting autophagic degradation (3). Thus, for example, in the case of various neuronal diseases, the increase in the number of APs was originally falsely interpreted as an increase in autophagic turnover, although it is now known to be the result of a decrease in autophagic turnover downstream to AP formation (4, 5).Type 2 diabetes is a disease in which glucose homeostasis is impaired due to peripheral insulin resistance accompanied by a decrease...

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Protective Role of Autophagy in Palmitate-Induced INS-1 β-Cell Death

Cited by 180 publications

References 49 publications

High-fat diet increases autophagic flux in pancreatic beta cells in vivo and ex vivo in mice

High-fat diet increases autophagic flux in pancreatic beta cells in vivo and ex vivo in mice

Autophagy in hypoxia-ischemia induced brain injury: Evidences and speculations

Fatty Acids Suppress Autophagic Turnover in β-Cells

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