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Rohli KE, Stubbe NJ, Walker EM, Pearson GL, Soleimanpour SA, Stephens SB. A metabolic redox relay supports ER proinsulin export in pancreatic islet β cells. JCI Insight 2024; 9:e178725. [PMID: 38935435 PMCID: PMC11383593 DOI: 10.1172/jci.insight.178725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Accepted: 06/18/2024] [Indexed: 06/29/2024] Open
Abstract
ER stress and proinsulin misfolding are heralded as contributing factors to β cell dysfunction in type 2 diabetes, yet how ER function becomes compromised is not well understood. Recent data identify altered ER redox homeostasis as a critical mechanism that contributes to insulin granule loss in diabetes. Hyperoxidation of the ER delays proinsulin export and limits the proinsulin supply available for insulin granule formation. In this report, we identified glucose metabolism as a critical determinant in the redox homeostasis of the ER. Using multiple β cell models, we showed that loss of mitochondrial function or inhibition of cellular metabolism elicited ER hyperoxidation and delayed ER proinsulin export. Our data further demonstrated that β cell ER redox homeostasis was supported by the metabolic supply of reductive redox donors. We showed that limiting NADPH and thioredoxin flux delayed ER proinsulin export, whereas thioredoxin-interacting protein suppression restored ER redox and proinsulin trafficking. Taken together, we propose that β cell ER redox homeostasis is buffered by cellular redox donor cycles, which are maintained through active glucose metabolism.
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Affiliation(s)
- Kristen E Rohli
- Fraternal Order of Eagles Diabetes Research Center
- Interdisciplinary Graduate Program in Genetics, and
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, Iowa, USA
| | | | - Emily M Walker
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine, and
| | - Gemma L Pearson
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine, and
| | - Scott A Soleimanpour
- Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine, and
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, USA
- VA Ann Arbor Healthcare System, Ann Arbor, Michigan, USA
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center
- Interdisciplinary Graduate Program in Genetics, and
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, Iowa, USA
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Arunagiri A, Alam M, Haataja L, Draz H, Alasad B, Samy P, Sadique N, Tong Y, Cai Y, Shakeri H, Fantuzzi F, Ibrahim H, Jang I, Sidarala V, Soleimanpour SA, Satin LS, Otonkoski T, Cnop M, Itkin‐Ansari P, Kaufman RJ, Liu M, Arvan P. Proinsulin folding and trafficking defects trigger a common pathological disturbance of endoplasmic reticulum homeostasis. Protein Sci 2024; 33:e4949. [PMID: 38511500 PMCID: PMC10955614 DOI: 10.1002/pro.4949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 01/23/2024] [Accepted: 02/14/2024] [Indexed: 03/22/2024]
Abstract
Primary defects in folding of mutant proinsulin can cause dominant-negative proinsulin accumulation in the endoplasmic reticulum (ER), impaired anterograde proinsulin trafficking, perturbed ER homeostasis, diminished insulin production, and β-cell dysfunction. Conversely, if primary impairment of ER-to-Golgi trafficking (which also perturbs ER homeostasis) drives misfolding of nonmutant proinsulin-this might suggest bi-directional entry into a common pathological phenotype (proinsulin misfolding, perturbed ER homeostasis, and deficient ER export of proinsulin) that can culminate in diminished insulin storage and diabetes. Here, we've challenged β-cells with conditions that impair ER-to-Golgi trafficking, and devised an accurate means to assess the relative abundance of distinct folded/misfolded forms of proinsulin using a novel nonreducing SDS-PAGE/immunoblotting protocol. We confirm abundant proinsulin misfolding upon introduction of a diabetogenic INS mutation, or in the islets of db/db mice. Whereas blockade of proinsulin trafficking in Golgi/post-Golgi compartments results in intracellular accumulation of properly-folded proinsulin (bearing native disulfide bonds), impairment of ER-to-Golgi trafficking (regardless whether such impairment is achieved by genetic or pharmacologic means) results in decreased native proinsulin with more misfolded proinsulin. Remarkably, reversible ER-to-Golgi transport defects (such as treatment with brefeldin A or cellular energy depletion) upon reversal quickly restore the ER folding environment, resulting in the disappearance of pre-existing misfolded proinsulin while preserving proinsulin bearing native disulfide bonds. Thus, proper homeostatic balance of ER-to-Golgi trafficking is linked to a more favorable proinsulin folding (as well as trafficking) outcome.
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Affiliation(s)
- Anoop Arunagiri
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Maroof Alam
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Leena Haataja
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Hassan Draz
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Bashiyer Alasad
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Praveen Samy
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Nadeed Sadique
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Yue Tong
- ULB Center for Diabetes Research, Medical Faculty; and Division of EndocrinologyErasmus Hospital, Universite Libre de BruxellesBrusselsBelgium
| | - Ying Cai
- ULB Center for Diabetes Research, Medical Faculty; and Division of EndocrinologyErasmus Hospital, Universite Libre de BruxellesBrusselsBelgium
| | - Hadis Shakeri
- ULB Center for Diabetes Research, Medical Faculty; and Division of EndocrinologyErasmus Hospital, Universite Libre de BruxellesBrusselsBelgium
| | - Federica Fantuzzi
- ULB Center for Diabetes Research, Medical Faculty; and Division of EndocrinologyErasmus Hospital, Universite Libre de BruxellesBrusselsBelgium
| | - Hazem Ibrahim
- Stem Cells and Metabolism Research Program, Faculty of MedicineUniversity of HelsinkiHelsinkiFinland
| | - Insook Jang
- Degenerative Diseases ProgramCenter for Genetic Disorders and Aging Research, Sanford Burnham Prebys Medical Discovery InstituteLa JollaCaliforniaUSA
| | - Vaibhav Sidarala
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Scott A. Soleimanpour
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
| | - Leslie S. Satin
- Department of PharmacologyUniversity of Michigan Medical SchoolAnn ArborMichiganUSA
| | - Timo Otonkoski
- Stem Cells and Metabolism Research Program, Faculty of MedicineUniversity of HelsinkiHelsinkiFinland
| | - Miriam Cnop
- ULB Center for Diabetes Research, Medical Faculty; and Division of EndocrinologyErasmus Hospital, Universite Libre de BruxellesBrusselsBelgium
| | - Pamela Itkin‐Ansari
- Development, Aging and Regeneration ProgramCenter for Genetic Disorders and Aging Research, Sanford Burnham Prebys Medical Discovery InstituteLa JollaCaliforniaUSA
| | - Randal J. Kaufman
- Degenerative Diseases ProgramCenter for Genetic Disorders and Aging Research, Sanford Burnham Prebys Medical Discovery InstituteLa JollaCaliforniaUSA
| | - Ming Liu
- Department of Endocrinology and MetabolismTianjin Medical University General HospitalTianjinChina
| | - Peter Arvan
- Division of Metabolism, Endocrinology & DiabetesUniversity of Michigan Medical CenterAnn ArborMichiganUSA
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Boyer CK, Blom SE, Machado AE, Rohli KE, Maxson ME, Stephens SB. Loss of the Golgi-localized v-ATPase subunit does not alter insulin granule formation or pancreatic islet β-cell function. Am J Physiol Endocrinol Metab 2024; 326:E245-E257. [PMID: 38265287 PMCID: PMC11193524 DOI: 10.1152/ajpendo.00342.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Revised: 01/11/2024] [Accepted: 01/11/2024] [Indexed: 01/25/2024]
Abstract
Delayed Golgi export of proinsulin has recently been identified as an underlying mechanism leading to insulin granule loss and β-cell secretory defects in type 2 diabetes (T2D). Because acidification of the Golgi lumen is critical for proinsulin sorting and delivery into the budding secretory granule, we reasoned that dysregulation of Golgi pH may contribute to proinsulin trafficking defects. In this report, we examined pH regulation of the Golgi and identified a partial alkalinization of the Golgi lumen in a diabetes model. To further explore this, we generated a β-cell specific knockout (KO) of the v0a2 subunit of the v-ATPase pump, which anchors the v-ATPase to the Golgi membrane. Although loss of v0a2 partially neutralized Golgi pH and was accompanied by distension of the Golgi cisternae, proinsulin export from the Golgi and insulin granule formation were not affected. Furthermore, β-cell function was well preserved. β-cell v0a2 KO mice exhibited normal glucose tolerance in both sexes, no genotypic difference to diet-induced obesity, and normal insulin secretory responses. Collectively, our data demonstrate the v0a2 subunit contributes to β-cell Golgi pH regulation but suggest that additional disturbances to Golgi structure and function contribute to proinsulin trafficking defects in diabetes.NEW & NOTEWORTHY Delayed proinsulin export from the Golgi in diabetic β-cells contributes to decreased insulin granule formation, but the underlying mechanisms are not clear. Here, we explored if dysregulation of Golgi pH can alter Golgi function using β-cell specific knockout (KO) of the Golgi-localized subunit of the v-ATPase, v0a2. We show that partial alkalinization of the Golgi dilates the cisternae, but does not affect proinsulin export, insulin granule formation, insulin secretion, or glucose homeostasis.
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Affiliation(s)
- Cierra K Boyer
- Department of Neuroscience and Pharmacology, University of Iowa, Iowa City, Iowa, United States
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States
| | - Sandra E Blom
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States
| | - Ashleigh E Machado
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States
| | - Kristen E Rohli
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, Iowa, United States
| | - Michelle E Maxson
- Program in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa, United States
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, Iowa, United States
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Na M, Yang X, Deng Y, Yin Z, Li M. Endoplasmic reticulum stress in the pathogenesis of alcoholic liver disease. PeerJ 2023; 11:e16398. [PMID: 38025713 PMCID: PMC10655704 DOI: 10.7717/peerj.16398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 10/12/2023] [Indexed: 12/01/2023] Open
Abstract
The endoplasmic reticulum (ER) plays a pivotal role in protein synthesis, folding, and modification. Under stress conditions such as oxidative stress and inflammation, the ER can become overwhelmed, leading to an accumulation of misfolded proteins and ensuing ER stress. This triggers the unfolded protein response (UPR) designed to restore ER homeostasis. Alcoholic liver disease (ALD), a spectrum disorder resulting from chronic alcohol consumption, encompasses conditions from fatty liver and alcoholic hepatitis to cirrhosis. Metabolites of alcohol can incite oxidative stress and inflammation in hepatic cells, instigating ER stress. Prolonged alcohol exposure further disrupts protein homeostasis, exacerbating ER stress which can lead to irreversible hepatocellular damage and ALD progression. Elucidating the contribution of ER stress to ALD pathogenesis may pave the way for innovative therapeutic interventions. This review delves into ER stress, its basic signaling pathways, and its role in the alcoholic liver injury.
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Affiliation(s)
- Man Na
- Department of Pharmacy, The 926th Hospital of Joint Logistics Support Force of Chinese People’s Liberation Army, Kaiyuan, Yunan, China
| | - Xingbiao Yang
- Department of Pharmacy, The 926th Hospital of Joint Logistics Support Force of Chinese People’s Liberation Army, Kaiyuan, Yunan, China
| | - Yongkun Deng
- Department of Pharmacy, The 926th Hospital of Joint Logistics Support Force of Chinese People’s Liberation Army, Kaiyuan, Yunan, China
| | - Zhaoheng Yin
- Department of Pharmacy, The 926th Hospital of Joint Logistics Support Force of Chinese People’s Liberation Army, Kaiyuan, Yunan, China
| | - Mingwei Li
- Department of Pharmacy, The 926th Hospital of Joint Logistics Support Force of Chinese People’s Liberation Army, Kaiyuan, Yunan, China
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Szukiewicz D. Molecular Mechanisms for the Vicious Cycle between Insulin Resistance and the Inflammatory Response in Obesity. Int J Mol Sci 2023; 24:9818. [PMID: 37372966 DOI: 10.3390/ijms24129818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 05/31/2023] [Accepted: 06/05/2023] [Indexed: 06/29/2023] Open
Abstract
The comprehensive anabolic effects of insulin throughout the body, in addition to the control of glycemia, include ensuring lipid homeostasis and anti-inflammatory modulation, especially in adipose tissue (AT). The prevalence of obesity, defined as a body mass index (BMI) ≥ 30 kg/m2, has been increasing worldwide on a pandemic scale with accompanying syndemic health problems, including glucose intolerance, insulin resistance (IR), and diabetes. Impaired tissue sensitivity to insulin or IR paradoxically leads to diseases with an inflammatory component despite hyperinsulinemia. Therefore, an excess of visceral AT in obesity initiates chronic low-grade inflammatory conditions that interfere with insulin signaling via insulin receptors (INSRs). Moreover, in response to IR, hyperglycemia itself stimulates a primarily defensive inflammatory response associated with the subsequent release of numerous inflammatory cytokines and a real threat of organ function deterioration. In this review, all components of this vicious cycle are characterized with particular emphasis on the interplay between insulin signaling and both the innate and adaptive immune responses related to obesity. Increased visceral AT accumulation in obesity should be considered the main environmental factor responsible for the disruption in the epigenetic regulatory mechanisms in the immune system, resulting in autoimmunity and inflammation.
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Affiliation(s)
- Dariusz Szukiewicz
- Department of Biophysics, Physiology & Pathophysiology, Faculty of Health Sciences, Medical University of Warsaw, 02-004 Warsaw, Poland
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Boyer CK, Bauchle CJ, Zhang J, Wang Y, Stephens SB. Synchronized proinsulin trafficking reveals delayed Golgi export accompanies β-cell secretory dysfunction in rodent models of hyperglycemia. Sci Rep 2023; 13:5218. [PMID: 36997560 PMCID: PMC10063606 DOI: 10.1038/s41598-023-32322-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 03/25/2023] [Indexed: 04/03/2023] Open
Abstract
The pancreatic islet β-cell's preference for release of newly synthesized insulin requires careful coordination of insulin exocytosis with sufficient insulin granule production to ensure that insulin stores exceed peripheral demands for glucose homeostasis. Thus, the cellular mechanisms regulating insulin granule production are critical to maintaining β-cell function. In this report, we utilized the synchronous protein trafficking system, RUSH, in primary β-cells to evaluate proinsulin transit through the secretory pathway leading to insulin granule formation. We demonstrate that the trafficking, processing, and secretion of the proinsulin RUSH reporter, proCpepRUSH, are consistent with current models of insulin maturation and release. Using both a rodent dietary and genetic model of hyperglycemia and β-cell dysfunction, we show that proinsulin trafficking is impeded at the Golgi and coincides with the decreased appearance of nascent insulin granules at the plasma membrane. Ultrastructural analysis of β-cells from diabetic leptin receptor deficient mice revealed gross morphological changes in Golgi structure, including shortened and swollen cisternae, and partial Golgi vesiculation, which are consistent with defects in secretory protein export. Collectively, this work highlights the utility of the proCpepRUSH reporter in studying proinsulin trafficking dynamics and suggests that altered Golgi export function contributes to β-cell secretory defects in the pathogenesis of Type 2 diabetes.
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Affiliation(s)
- Cierra K Boyer
- Department of Neuroscience and Pharmacology, University of Iowa, Iowa City, IA, USA
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, 52246, USA
| | - Casey J Bauchle
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, 52246, USA
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA, 52246, USA
| | - Jianchao Zhang
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Yanzhuang Wang
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
- Department of Neurology, School of Medicine, University of Michigan, Ann Arbor, MI, USA
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, 52246, USA.
- Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Iowa, Iowa City, IA, 52246, USA.
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