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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 DOI: 10.1172/jci.insight.178725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [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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Gallop MR, Vieira RFL, Matsuzaki ET, Mower PD, Liou W, Smart FE, Roberts S, Evason KJ, Holland WL, Chaix A. Long-term ketogenic diet causes hyperlipidemia, liver dysfunction, and glucose intolerance from impaired insulin trafficking and secretion in mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.14.599117. [PMID: 38948738 PMCID: PMC11212871 DOI: 10.1101/2024.06.14.599117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
A ketogenic diet (KD) is a very low-carbohydrate, very high-fat diet proposed to treat obesity and type 2 diabetes. While KD grows in popularity, its effects on metabolic health are understudied. Here we show that, in male and female mice, while KD protects against weight gain and induces weight loss, over long-term, mice develop hyperlipidemia, hepatic steatosis, and severe glucose intolerance. Unlike high fat diet-fed mice, KD mice are not insulin resistant and have low levels of insulin. Hyperglycemic clamp and ex vivo GSIS revealed cell-autonomous and whole-body impairments in insulin secretion. Major ER/Golgi stress and disrupted ER-Golgi protein trafficking was indicated by transcriptomic profiling of KD islets and confirmed by electron micrographs showing a dilated Golgi network likely responsible for impaired insulin granule trafficking and secretion. Overall, our results suggest long-term KD leads to multiple aberrations of metabolic parameters that caution its systematic use as a health promoting dietary intervention.
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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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Sue N, Thai LM, Saito A, Boyer CK, Fordham AM, Yan C, Davenport A, Tao J, Bensellam M, Cantley J, Shi YC, Stephens SB, Imaizumi K, Biden TJ. Independent activation of CREB3L2 by glucose fills a regulatory gap in mouse β-cells by co-ordinating insulin biosynthesis with secretory granule formation. Mol Metab 2024; 79:101845. [PMID: 38013154 PMCID: PMC10755490 DOI: 10.1016/j.molmet.2023.101845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 11/22/2023] [Accepted: 11/23/2023] [Indexed: 11/29/2023] Open
Abstract
OBJECTIVE Although individual steps have been characterized, there is little understanding of the overall process whereby glucose co-ordinates the biosynthesis of insulin with its export out of the endoplasmic reticulum (ER) and incorporation into insulin secretory granules (ISGs). Here we investigate a role for the transcription factor CREB3L2 in this context. METHODS MIN6 cells and mouse islets were analysed by immunoblotting after treatment with glucose, fatty acids, thapsigargin and various inhibitors. Knockdown of CREB3L2 was achieved using si or sh constructs by transfection, or viral delivery. In vivo metabolic phenotyping was conducted after deletion of CREB3L2 in β-cells of adult mice using Ins1-CreER+. Islets were isolated for RNAseq and assays of glucose-stimulated insulin secretion (GSIS). Trafficking was monitored in islet monolayers using a GFP-tagged proinsulin construct that allows for synchronised release from the ER. RESULTS With a Km ≈3.5 mM, glucose rapidly (T1/2 0.9 h) increased full length (FL) CREB3L2 followed by a slower rise (T1/2 2.5 h) in its transcriptionally-active cleavage product, P60 CREB3L2. Glucose stimulation repressed the ER stress marker, CHOP, and this was partially reverted by knockdown of CREB3L2. Activation of CREB3L2 by glucose was not due to ER stress, however, but a combination of O-GlcNAcylation, which impaired proteasomal degradation of FL-CREB3L2, and mTORC1 stimulation, which enhanced its conversion to P60. cAMP generation also activated CREB3L2, but independently of glucose. Deletion of CREB3L2 inhibited GSIS ex vivo and, following a high-fat diet (HFD), impaired glucose tolerance and insulin secretion in vivo. RNAseq revealed that CREB3L2 regulated genes controlling trafficking to-and-from the Golgi, as well as a broader cohort associated with β-cell compensation during a HFD. Although post-Golgi trafficking appeared intact, knockdown of CREB3L2 impaired the generation of both nascent ISGs and proinsulin condensates in the Golgi, implying a defect in ER export of proinsulin and/or its processing in the Golgi. CONCLUSION The stimulation of CREB3L2 by glucose defines a novel, rapid and direct mechanism for co-ordinating the synthesis, packaging and storage of insulin, thereby minimizing ER overload and optimizing β-cell function under conditions of high secretory demand. Upregulation of CREB3L2 also potentially contributes to the benefits of GLP1 agonism and might in itself constitute a novel means of treating β-cell failure.
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Affiliation(s)
- Nancy Sue
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Le May Thai
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Atsushi Saito
- Department of Biochemistry, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Cierra K Boyer
- Fraternal Order of Eagles Diabetes Research Center, Department of Internal Medicine, University of Iowa, Iowa City, IA 52246, USA
| | - Ashleigh M Fordham
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Chenxu Yan
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Aimee Davenport
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Jiang Tao
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Mohammed Bensellam
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - James Cantley
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
| | - Yan-Chuan Shi
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, Faculty of Medicine, The University of New South Wales, Sydney, Australia
| | - Samuel B Stephens
- Fraternal Order of Eagles Diabetes Research Center, Department of Internal Medicine, University of Iowa, Iowa City, IA 52246, USA
| | - Kazunori Imaizumi
- Department of Biochemistry, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Trevor J Biden
- Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, Faculty of Medicine, The University of New South Wales, Sydney, Australia.
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