IU Indianapolis ScholarWorks :: Browsing by Subject "Insulin-Secreting Cells"

Browsing by Subject "Insulin-Secreting Cells"

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12-Lipoxygenase Promotes Obesity-Induced Oxidative Stress in Pancreatic Islets
(American Society for Microbiology (ASM), 2014-10) Tersey, Sarah A.; Maier, Bernhard; Nishiki, Yurika; Maganti, Aarthi V.; Nadler, Jerry L.; Mirmira, Raghavendra G.; Department of Pediatrics, IU School of Medicine
High-fat diets lead to obesity, inflammation, and dysglycemia. 12-Lipoxygenase (12-LO) is activated by high-fat diets and catalyzes the oxygenation of cellular arachidonic acid to form proinflammatory intermediates. We hypothesized that 12-LO in the pancreatic islet is sufficient to cause dysglycemia in the setting of high-fat feeding. To test this, we generated pancreas-specific 12-LO knockout mice and studied their metabolic and molecular adaptations to high-fat diets. Whereas knockout mice and control littermates displayed identical weight gain, body fat distribution, and macrophage infiltration into fat, knockout mice exhibited greater adaptive islet hyperplasia, improved insulin secretion, and complete protection from dysglycemia. At the molecular level, 12-LO deletion resulted in increases in islet antioxidant enzymes Sod1 and Gpx1 in response to high-fat feeding. The absence or inhibition of 12-LO led to increases in nuclear Nrf2, a transcription factor responsible for activation of genes encoding antioxidant enzymes. Our data reveal a novel pathway in which islet 12-LO suppresses antioxidant enzymes and prevents the adaptive islet responses in the setting of high-fat diets.
Exocytosis Protein DOC2B as a Biomarker of Type 1 Diabetes
(Oxford University Press, 2018-05-01) Aslamy, Arianne; Oh, Eunjin; Ahn, Miwon; Moin, Abu Saleh Md; Chang, Mariann; Duncan, Molly; Hacker-Stratton, Jeannette; El-Shahawy, Mohamed; Kandeel, Fouad; DiMeglio, Linda A.; Thurmond, Debbie C.; Cellular and Integrative Physiology, School of Medicine
Context: Efforts to preserve β-cell mass in the preclinical stages of type 1 diabetes (T1D) are limited by few blood-derived biomarkers of β-cell destruction. Objective: Platelets are proposed sources of blood-derived biomarkers for a variety of diseases, and they show distinct proteomic changes in T1D. Thus, we investigated changes in the exocytosis protein, double C2 domain protein-β (DOC2B) in platelets and islets from T1D humans, and prediabetic nonobese diabetic (NOD) mice. Design, Patients, and Main Outcome Measure: Protein levels of DOC2B were assessed in platelets and islets from prediabetic NOD mice and humans, with and without T1D. Seventeen new-onset T1D human subjects (10.3 ± 3.8 years) were recruited immediately following diagnosis, and platelet DOC2B levels were compared with 14 matched nondiabetic subjects (11.4 ± 2.9 years). Furthermore, DOC2B levels were assessed in T1D human pancreatic tissue samples, cytokine-stimulated human islets ex vivo, and platelets from T1D subjects before and after islet transplantation. Results: DOC2B protein abundance was substantially reduced in prediabetic NOD mouse platelets, and these changes were mirrored in the pancreatic islets from the same mice. Likewise, human DOC2B levels were reduced over twofold in platelets from new-onset T1D human subjects, and this reduction was mirrored in T1D human islets. Cytokine stimulation of normal islets reduced DOC2B expression ex vivo. Remarkably, platelet DOC2B levels increased after islet transplantation in patients with T1D. Conclusions: Reduction of DOC2B is an early feature of T1D, and DOC2B abundance may serve as a valuable in vivo indicator of β-cell mass and an early biomarker of T1D.
Glucagon is essential for alpha cell transdifferentiation and beta cell neogenesis
(The Company of Biologists, 2015-04-15) Ye, Lihua; Robertson, Morgan A.; Hesselson, Daniel; Stainier, Didier Y. R.; Anderson, Ryan M.; Department of Pediatrics, IU School of Medicine
The interconversion of cell lineages via transdifferentiation is an adaptive mode of tissue regeneration and an appealing therapeutic target. However, its clinical exploitation is contingent upon the discovery of contextual regulators of cell fate acquisition and maintenance. In murine models of diabetes, glucagon-secreting alpha cells transdifferentiate into insulin-secreting beta cells following targeted beta cell depletion, regenerating the form and function of the pancreatic islet. However, the molecular triggers of this mode of regeneration are unknown. Here, using lineage-tracing assays in a transgenic zebrafish model of beta cell ablation, we demonstrate conserved plasticity of alpha cells during islet regeneration. In addition, we show that glucagon expression is upregulated after injury. Through gene knockdown and rescue approaches, we also find that peptides derived from the glucagon gene are necessary for alpha-to-beta cell fate switching. Importantly, whereas beta cell neogenesis was stimulated by glucose, alpha-to-beta cell conversion was not, suggesting that transdifferentiation is not mediated by glucagon/GLP-1 control of hepatic glucose production. Overall, this study supports the hypothesis that alpha cells are an endogenous reservoir of potential new beta cells. It further reveals that glucagon plays an important role in maintaining endocrine cell homeostasis through feedback mechanisms that govern cell fate stability.
Hypusine biosynthesis in β cells links polyamine metabolism to facultative cellular proliferation to maintain glucose homeostasis
(American Association for the Advancement of Science, 2019-12-03) Levasseur, Esther M.; Yamada, Kentaro; Piñeros, Annie R.; Wu, Wenting; Syed, Farooq; Orr, Kara S.; Anderson-Baucum, Emily; Mastracci, Teresa L.; Maier, Bernhard; Mosley, Amber L.; Liu, Yunlong; Bernal-Mizrachi, Ernesto; Alonso, Laura C.; Scott, Donald; Garcia-Ocaña, Adolfo; Tersey, Sarah A.; Mirmira, Raghavendra G.; Pediatrics, School of Medicine
Deoxyhypusine synthase (DHPS) utilizes the polyamine spermidine to catalyze the hypusine modification of the mRNA translation factor eIF5A and promotes oncogenesis through poorly-defined mechanisms. Because germline deletion of Dhps is embryonically lethal, its role in normal postnatal cellular function in vivo remains unknown. We generated a mouse model that enabled the inducible, postnatal deletion of Dhps specifically in postnatal islet β cells, which function to maintain glucose homeostasis. Removal of Dhps did not have an effect under normal physiologic conditions. However, upon development of insulin resistance, which induces β-cell proliferation, Dhps deletion caused alterations in proteins required for mRNA translation and protein secretion, reduced production of the cell cycle molecule cyclin D2, impaired β-cell proliferation, and induced overt diabetes. We found that hypusine biosynthesis was downstream of protein kinase C-ζ and was required for c-Myc-induced proliferation. Our studies reveal a requirement for DHPS in β cells to link polyamines to mRNA translation to effect facultative cellular proliferation and glucose homeostasis.
Impaired Store-Operated Calcium Entry and STIM1 Loss Lead to Reduced Insulin Secretion and Increased Endoplasmic Reticulum Stress in the Diabetic β-Cell
(American Diabetes Association, 2018-11) Kono, Tatsuyoshi; Tong, Xin; Taleb, Solaema; Bone, Robert N.; Iida, Hitoshi; Lee, Chih-Chun; Sohn, Paul; Gilon, Patrick; Roe, Michael W.; Evans-Molina, Carmella; Medicine, School of Medicine
Store-operated Ca2+ entry (SOCE) is a dynamic process that leads to refilling of endoplasmic reticulum (ER) Ca2+ stores through reversible gating of plasma membrane Ca2+ channels by the ER Ca2+ sensor Stromal Interaction Molecule 1 (STIM1). Pathogenic reductions in β-cell ER Ca2+ have been observed in diabetes. However, a role for impaired SOCE in this phenotype has not been tested. We measured the expression of SOCE molecular components in human and rodent models of diabetes and found a specific reduction in STIM1 mRNA and protein levels in human islets from donors with type 2 diabetes (T2D), islets from hyperglycemic streptozotocin-treated mice, and INS-1 cells (rat insulinoma cells) treated with proinflammatory cytokines and palmitate. Pharmacologic SOCE inhibitors led to impaired islet Ca2+ oscillations and insulin secretion, and these effects were phenocopied by β-cell STIM1 deletion. STIM1 deletion also led to reduced ER Ca2+ storage and increased ER stress, whereas STIM1 gain of function rescued β-cell survival under proinflammatory conditions and improved insulin secretion in human islets from donors with T2D. Taken together, these data suggest that the loss of STIM1 and impaired SOCE contribute to ER Ca2+ dyshomeostasis under diabetic conditions, whereas efforts to restore SOCE-mediated Ca2+ transients may have the potential to improve β-cell health and function.
An In Vivo Zebrafish Model for Interrogating ROS-Mediated Pancreatic β-Cell Injury, Response, and Prevention
(Hindawi Publishing Corporation, 2018-03-28) Kulkarni, Abhishek A.; Conteh, Abass M.; Sorrell, Cody A.; Mirmira, Anjali; Tersey, Sarah A.; Mirmira, Raghavendra G.; Linnemann, Amelia K.; Anderson, Ryan M.; Biochemistry and Molecular Biology, School of Medicine
It is well known that a chronic state of elevated reactive oxygen species (ROS) in pancreatic β-cells impairs their ability to release insulin in response to elevated plasma glucose. Moreover, at its extreme, unmitigated ROS drives regulated cell death. This dysfunctional state of ROS buildup can result both from genetic predisposition and environmental factors such as obesity and overnutrition. Importantly, excessive ROS buildup may underlie metabolic pathologies such as type 2 diabetes mellitus. The ability to monitor ROS dynamics in β-cells in situ and to manipulate it via genetic, pharmacological, and environmental means would accelerate the development of novel therapeutics that could abate this pathology. Currently, there is a lack of models with these attributes that are available to the field. In this study, we use a zebrafish model to demonstrate that ROS can be generated in a β-cell-specific manner using a hybrid chemical genetic approach. Using a transgenic nitroreductase-expressing zebrafish line, Tg(ins:Flag-NTR)s950 , treated with the prodrug metronidazole (MTZ), we found that ROS is rapidly and explicitly generated in β-cells. Furthermore, the level of ROS generated was proportional to the dosage of prodrug added to the system. At high doses of MTZ, caspase 3 was rapidly cleaved, β-cells underwent regulated cell death, and macrophages were recruited to the islet to phagocytose the debris. Based on our findings, we propose a model for the mechanism of NTR/MTZ action in transgenic eukaryotic cells and demonstrate the robust utility of this system to model ROS-related disease pathology.
Inhibition of 12/15-Lipoxygenase Protects Against β-Cell Oxidative Stress and Glycemic Deterioration in Mouse Models of Type 1 Diabetes
(American Diabetes Association, 2017-11) Hernandez-Perez, Marimar; Chopra, Gaurav; Fine, Jonathan; Conteh, Abass M.; Anderson, Ryan M.; Linnemann, Amelia K.; Benjamin, Chanelle; Nelson, Jennifer B.; Benninger, Kara S.; Nadler, Jerry L.; Maloney, David J.; Tersey, Sarah A.; Mirmira, Raghavendra G.; Pediatrics, School of Medicine
Islet β-cell dysfunction and aggressive macrophage activity are early features in the pathogenesis of type 1 diabetes (T1D). 12/15-Lipoxygenase (12/15-LOX) is induced in β-cells and macrophages during T1D and produces proinflammatory lipids and lipid peroxides that exacerbate β-cell dysfunction and macrophage activity. Inhibition of 12/15-LOX provides a potential therapeutic approach to prevent glycemic deterioration in T1D. Two inhibitors recently identified by our groups through screening efforts, ML127 and ML351, have been shown to selectively target 12/15-LOX with high potency. Only ML351 exhibited no apparent toxicity across a range of concentrations in mouse islets, and molecular modeling has suggested reduced promiscuity of ML351 compared with ML127. In mouse islets, incubation with ML351 improved glucose-stimulated insulin secretion in the presence of proinflammatory cytokines and triggered gene expression pathways responsive to oxidative stress and cell death. Consistent with a role for 12/15-LOX in promoting oxidative stress, its chemical inhibition reduced production of reactive oxygen species in both mouse and human islets in vitro. In a streptozotocin-induced model of T1D in mice, ML351 prevented the development of diabetes, with coincident enhancement of nuclear Nrf2 in islet cells, reduced β-cell oxidative stress, and preservation of β-cell mass. In the nonobese diabetic mouse model of T1D, administration of ML351 during the prediabetic phase prevented dysglycemia, reduced β-cell oxidative stress, and increased the proportion of anti-inflammatory macrophages in insulitis. The data provide the first evidence to date that small molecules that target 12/15-LOX can prevent progression of β-cell dysfunction and glycemic deterioration in models of T1D.
Interleukin-6 Reduces β-Cell Oxidative Stress by Linking Autophagy With the Antioxidant Response
(American Diabetes Association, 2018-08) Marasco, Michelle R.; Conteh, Abass M.; Reissaus, Christopher A.; Cupit, John E.; Appleman, Evan M.; Mirmira, Raghavendra G.; Linnemann, Amelia K.; Pediatrics, School of Medicine
Production of reactive oxygen species (ROS) is a key instigator of β-cell dysfunction in diabetes. The pleiotropic cytokine interleukin 6 (IL-6) has previously been linked to β-cell autophagy but has not been studied in the context of β-cell antioxidant response. We used a combination of animal models of diabetes and analysis of cultured human islets and rodent β-cells to study how IL-6 influences antioxidant response. We show that IL-6 couples autophagy to antioxidant response and thereby reduces ROS in β-cells and human islets. β-Cell-specific loss of IL-6 signaling in vivo renders mice more susceptible to oxidative damage and cell death through the selective β-cell toxins streptozotocin and alloxan. IL-6-driven ROS reduction is associated with an increase in the master antioxidant factor NRF2, which rapidly translocates to the mitochondria to decrease mitochondrial activity and stimulate mitophagy. IL-6 also initiates a robust transient decrease in cellular cAMP levels, likely contributing to the stimulation of mitophagy to mitigate ROS. Our findings suggest that coupling autophagy to antioxidant response in β-cells leads to stress adaptation that can reduce cellular apoptosis. These findings have implications for β-cell survival under diabetogenic conditions and present novel targets for therapeutic intervention.
The MafA transcription factor becomes essential to islet β-cells soon after birth
(American Diabetes Association, 2014-06) Hang, Yan; Yamamoto, Tsunehiko; Benninger, Richard K. P.; Brissova, Marcela; Guo, Min; Bush, Will; Piston, David W.; Powers, Alvin C.; Magnuson, Mark; Thurmond, Debbie C.; Stein, Roland; Department of Pediatrics, IU School of Medicine
The large Maf transcription factors, MafA and MafB, are expressed with distinct spatial-temporal patterns in rodent islet cells. Analysis of Mafa(-/-) and pancreas-specific Mafa(∆panc) deletion mutant mice demonstrated a primary role for MafA in adult β-cell activity, different from the embryonic importance of MafB. Our interests here were to precisely define when MafA became functionally significant to β-cells, to determine how this was affected by the brief period of postnatal MafB production, and to identify genes regulated by MafA during this period. We found that islet cell organization, β-cell mass, and β-cell function were influenced by 3 weeks of age in Mafa(Δpanc) mice and compromised earlier in Mafa(Δpanc);Mafb(+/-) mice. A combination of genome-wide microarray profiling, electron microscopy, and metabolic assays were used to reveal mechanisms of MafA control. For example, β-cell replication was produced by actions on cyclin D2 regulation, while effects on granule docking affected first-phase insulin secretion. Moreover, notable differences in the genes regulated by embryonic MafB and postnatal MafA gene expression were found. These results not only clearly define why MafA is an essential transcriptional regulator of islet β-cells, but also why cell maturation involves coordinated actions with MafB.
Maintenance of Pdx1 mRNA translation in islet β-cells during the unfolded protein response
(The Endocrine Society, 2014-11) Templin, Andrew T.; Maier, Bernhard; Tersey, Sarah A.; Hatanaka, Masayuki; Mirmira, Raghavendra G.; Department of Pediatrics, IU School of Medicine
In type 1 diabetes, proinflammatory cytokines secreted by infiltrating immune cells activate the unfolded protein response (UPR) in islet β-cells, which leads to attenuation of global mRNA translation. Under such conditions, privileged mRNAs required for adaptation to the prevailing stress are maintained in an actively translated state. Pdx1 is a β-cell transcription factor that is required for the adaptive UPR, but it is not known how translation of its mRNA is maintained under these conditions. To study translation, we established conditions in vitro with MIN6 cells and mouse islets and a mixture of proinflammatory cytokines (IL-1β, TNF-α, and IFN-γ) that mimicked the UPR conditions seen in type 1 diabetes. Cell extracts were then subjected to polyribosome profiling to monitor changes to mRNA occupancy by ribosomes. Similar to other privileged mRNAs (Atf4 and Chop), Pdx1 mRNA remained partitioned in actively translating polyribosomes under the UPR, whereas the mRNA encoding a proinsulin-processing enzyme (Cpe) and others partitioned into inactively translating monoribosomes. Bicistronic luciferase reporter analyses revealed that the distal portion of the 5'-untranslated region of mouse Pdx1 (between bp -105 to -280) contained elements that promoted translation under both normal and UPR conditions, and this region exhibited conserved sequences and secondary structure similar to those of other known internal ribosome entry sites. Our findings suggest that Pdx1 protein levels are maintained in the setting of the UPR, in part, through elements in the 5'-untranslated region that confer privileged mRNA translation in a 5'-7-methylguanylate cap-independent manner.

Browsing by Subject "Insulin-Secreting Cells"

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