XBP1 maintains beta cell identity, represses beta-to-alpha cell transdifferentiation and protects against diabetic beta cell failure during metabolic stress in mice (original) (raw)
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Aberrant islet unfolded protein response in type 2 diabetes
Scientific Reports, 2014
The endoplasmic reticulum adapts to fluctuations in demand and copes with stress through an adaptive signaling cascade called the unfolded protein response (UPR). Accumulating evidence indicates that the canonical UPR is critical to the survival and function of insulin-producing pancreatic b-cells, and alterations in the UPR may contribute to the pathogenesis of type 2 diabetes. However, the dynamic regulation of UPR molecules in the islets of animal models and humans with type 2 diabetes remains to be elucidated. Here, we analyzed the expression of activating factor 6 (ATF6a) and spliced X-box binding protein 1 (sXBP1), and phosphorylation of eukaryotic initiation factor 2 (eIF2a), to evaluate the three distinct branches of the UPR in the pancreatic islets of mice with diet-or genetic-induced obesity and insulin resistance. ATF6 and sXBP1 expression was predominantly found in the b-cells, where hyperglycemia coincided with a decline in expression in both experimental models and in humans with type 2 diabetes. These data suggest alterations in the expression of UPR mediators may contribute to the decline in islet function in type 2 diabetes in mice and humans.
Genetic predisposition for beta cell fragility underlies type 1 and type 2 diabetes
Nature genetics, 2016
Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure in T2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immune-independent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes.
Endoplasmic reticulum stress contributes to beta cell apoptosis in type 2 diabetes
Diabetologia, 2007
Aims/hypothesis Increased lipid supply causes beta cell death, which may contribute to reduced beta cell mass in type 2 diabetes. We investigated whether endoplasmic reticulum (ER) stress is necessary for lipid-induced apoptosis in beta cells and also whether ER stress is present in islets of an animal model of diabetes and of humans with type 2 diabetes. Methods Expression of genes involved in ER stress was evaluated in insulin-secreting MIN6 cells exposed to elevated lipids, in islets isolated from db/db mice and in pancreas sections of humans with type 2 diabetes. Overproduction of the ER chaperone heat shock 70 kDa protein 5 (HSPA5, previously known as immunoglobulin heavy chain binding protein [BIP]) was performed to assess whether attenuation of ER stress affected lipid-induced apoptosis.
Endoplasmic reticulum stress and the unfolded protein response in pancreatic islet inflammation
Journal of Molecular Endocrinology, 2016
Insulin-secreting pancreatic β-cells are extremely dependent on their endoplasmic reticulum (ER) to cope with the oscillatory requirement of secreted insulin to maintain normoglycemia. Insulin translation and folding rely greatly on the unfolded protein response (UPR), an array of three main signaling pathways designed to maintain ER homeostasis and limit ER stress. However, prolonged or excessive UPR activation triggers alternative molecular pathways that can lead to β-cell dysfunction and apoptosis. An increasing number of studies suggest a role of these pro-apoptotic UPR pathways in the downfall of β-cells observed in diabetic patients. Particularly, the past few years highlighted a cross talk between the UPR and inflammation in the context of both type 1 (T1D) and type 2 diabetes (T2D). In this article, we describe the recent advances in research regarding the interplay between ER stress, the UPR, and inflammation in the context of β-cell apoptosis leading to diabetes.
Diabetologia, 2012
Protein synthesis is increased by several-fold in stimulated pancreatic beta cells. Synthesis and folding of (pro)insulin takes place in the endoplasmic reticulum (ER), and beta cells trigger the unfolded protein response (UPR) to upgrade the functional capacity of the ER. Prolonged or excessive UPR activation contributes to beta cell dysfunction and death in type 2 diabetes, but there is another side of the UPR that may be of particular relevance for autoimmune type 1 diabetes, namely, the crosstalk between the UPR and innate immunity/inflammation. Recent evidence, discussed in this review, indicates that both saturated fats and inflammatory mediators such as cytokines trigger the UPR in pancreatic beta cells. The UPR potentiates activation of nuclear factor κB, a key regulator of inflammation. Two branches of the UPR, namely IRE1/XBP1s and PERK/ATF4/CHOP, mediate the UPR-induced sensitisation of pancreatic beta cells to the proinflammatory effects of cytokines. This can contribute to the upregulation of local inflammatory mechanisms and the aggravation of insulitis. The dialogue between the UPR and inflammation may provide an explanation for the parallel increase in the prevalence of childhood obesity and type 1 diabetes.
Extensive Pancreas Regeneration Following Acinar-Specific Disruption of Xbp1 in Mice
Gastroenterology, 2011
Background & Aims-Progression of diseases of the exocrine pancreas, which include pancreatitis and cancer, is associated with increased levels of cell stress. Pancreatic acinar cells are involved in development of these diseases and, because of their high level of protein output, they require an efficient, unfolded protein response (UPR), which mediates recovery from endoplasmic reticulum (ER) stress following the accumulation of misfolded proteins. Methods-To study recovery from ER stress in the exocrine organ, we generated mice with conditional disruption of Xbp1 (a principle component of the UPR) in most adult pancreatic acinar cells (Xbp1 fl/fl). We monitored the effects of constitutive ER stress in the exocrine pancreas of these mice. Results-Xbp1-null acinar cells underwent extensive apoptosis, followed by a rapid phase of recovery in the pancreas that included expansion of the centroacinar cell compartment, formation of tubular complexes that contained Hes1-and Sox9-expressing cells, and regeneration of acinar cells that expressed Mist1 from the residual, surviving Xbp1+ cell population. Conclusions-XBP1 appears to be required for homeostatisis of acinar cells in mice; ER stress induces a regenerative response in the pancreas that involves acinar and centroacinar cells and promotes organ recovery from exocrine pancreas disease.
Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature, 2016
Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure inT2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immuneindependent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes. Dooley et al.
ER stress and the decline and fall of pancreatic beta cells in type 1 diabetes
Upsala Journal of Medical Sciences, 2016
Components of the unfolded protein response (UPR) modulate beta cell inflammation and death in early type 1 diabetes (T1D). The UPR is a mechanism by which cells react to the accumulation of misfolded proteins in the endoplasmic reticulum (ER). It aims to restore cellular homeostasis, but in case of chronic or overwhelming ER stress the persistent activation of the UPR triggers apoptosis, contributing to the loss of beta cells in both T1D and type 2 diabetes. It remains to be determined how and why the transition from 'physiological' to 'pathological' UPR takes place. A key component of the UPR is the ER transmembrane protein IRE1a (inositol-requiring enzyme 1a). IRE1a activity is modulated by both intra-ER signals and by the formation of protein complexes at its cytosolic domain. The amplitude and duration of IRE1a signaling is critical for the transition between the adaptive and cell death programs, with particular relevance for the activation of the pro-apoptotic c-Jun N-terminal kinase (JNK) in beta cells. In the present review we discuss the available information on IRE1a-regulating proteins in beta cells and their downstream targets, and the important differences observed between cytokine-induced UPR in human and rodent beta cells.