Browsing by Author "Kulkarni, Rohit N."

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    Comprehensive Proteomics Analysis of Stressed Human Islets Identifies GDF15 as a Target for Type 1 Diabetes Intervention
    (Elsevier, 2020-02-04) Nakayasu, Ernesto S.; Syed, Farooq; Tersey, Sarah A.; Gritsenko, Marina A.; Mitchell, Hugh D.; Chan, Chi Yuet; Dirice, Ercument; Turatsinze, Jean-Valery; Cui, Yi; Kulkarni, Rohit N.; Eizirik, Decio L.; Qian, Wei-Jun; Webb-Robertson, Bobbie-Jo M.; Evans-Molina, Carmella; Mirmira., Raghavendra G.; Metz, Thomas O.; Pediatrics, School of Medicine
    Type 1 diabetes (T1D) results from the progressive loss of β cells, a process propagated by pro-inflammatory cytokine signaling that disrupts the balance between pro- and anti-apoptotic proteins. To identify proteins involved in this process, we performed comprehensive proteomics of human pancreatic islets treated with interleukin-1β and interferon-γ, leading to the identification of 11,324 proteins, of which 387 were significantly regulated by treatment. We then tested the function of growth/differentiation factor 15 (GDF15), which was repressed by the treatment. We found that GDF15 translation was blocked during inflammation, and it was depleted in islets from individuals with T1D. The addition of exogenous GDF15 inhibited interleukin-1β+interferon-γ-induced apoptosis of human islets. Administration of GDF15 reduced by 53% the incidence of diabetes in NOD mice. Our approach provides a unique resource for the identification of the human islet proteins regulated by cytokines and was effective in discovering a potential target for T1D therapy.
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    Insulin regulates carboxypeptidase E by modulating translation initiation scaffolding protein eIF4G1 in pancreatic β cells
    (PNAS, 2014-06-03) Liew, Chong Wee; Assmann, Anke; Templin, Andrew T.; Raum, Jeffrey C.; Lipson, Kathryn L.; Rajan, Rajan; Qiang, Guifen; Hu, Jiang; Kawamori, Dan; Lindberg, Iris; Philipson, Louis H.; Sonenberg, Nahum; Goldfine, Allison B.; Stoffers, Doris A.; Mirmira, Raghavendra G.; Urano, Fumihiko; Kulkarni, Rohit N.; Department of Cellular & Integrative Physiology, IU School of Medicine
    Insulin resistance, hyperinsulinemia, and hyperproinsulinemia occur early in the pathogenesis of type 2 diabetes (T2D). Elevated levels of proinsulin and proinsulin intermediates are markers of β-cell dysfunction and are strongly associated with development of T2D in humans. However, the mechanism(s) underlying β-cell dysfunction leading to hyperproinsulinemia is poorly understood. Here, we show that disruption of insulin receptor (IR) expression in β cells has a direct impact on the expression of the convertase enzyme carboxypeptidase E (CPE) by inhibition of the eukaryotic translation initiation factor 4 gamma 1 translation initiation complex scaffolding protein that is mediated by the key transcription factors pancreatic and duodenal homeobox 1 and sterol regulatory element-binding protein 1, together leading to poor proinsulin processing. Reexpression of IR or restoring CPE expression each independently reverses the phenotype. Our results reveal the identity of key players that establish a previously unknown link between insulin signaling, translation initiation, and proinsulin processing, and provide previously unidentified mechanistic insight into the development of hyperproinsulinemia in insulin-resistant states.
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    Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases: Workshop Proceedings
    (Wolters Kluwer, 2022) Mastracci, Teresa L.; Apte, Minoti; Amundadottir, Laufey T.; Alvarsson, Alexandra; Artandi, Steven; Bellin, Melena D.; Bernal-Mizrachi, Ernesto; Caicedo, Alejandro; Campbell-Thompson, Martha; Cruz-Monserrate, Zobeida; El Ouaamari, Abdelfattah; Gaulton, Kyle J.; Geisz, Andrea; Goodarzi, Mark O.; Hara, Manami; Hull-Meichle, Rebecca L.; Kleger, Alexander; Klein, Alison P.; Kopp, Janel L.; Kulkarni, Rohit N.; Muzumdar, Mandar D.; Naren, Anjaparavanda P.; Oakes, Scott A.; Olesen, Søren S.; Phelps, Edward A.; Powers, Alvin C.; Stabler, Cherie L.; Tirkes, Temel; Whitcomb, David C.; Yadav, Dhiraj; Yong, Jing; Zaghloul, Norann A.; Sander, Maike; Pandol, Stephen J.; Biology, School of Science
    The Integrated Physiology of the Exocrine and Endocrine Compartments in Pancreatic Diseases Workshop was a 1.5-day scientific conference at the National Institutes of Health (Bethesda, MD) that engaged clinical and basic science investigators interested in diseases of the pancreas. This report summarizes the workshop proceedings. The goal of the workshop was to forge connections and identify gaps in knowledge that could guide future research directions. Presentations were segregated into six major themes, including: (a) Pancreas Anatomy and Physiology; (b) Diabetes in the Setting of Exocrine Disease; (c) Metabolic Influences on the Exocrine Pancreas; (d) Genetic Drivers of Pancreatic Diseases; (e) Tools for Integrated Pancreatic Analysis; and (f) Implications of Exocrine-Endocrine Crosstalk. For each theme, there were multiple presentations followed by panel discussions on specific topics relevant to each area of research; these are summarized herein. Significantly, the discussions resulted in the identification of research gaps and opportunities for the field to address. In general, it was concluded that as a pancreas research community, we must more thoughtfully integrate our current knowledge of the normal physiology as well as the disease mechanisms that underlie endocrine and exocrine disorders so that there is a better understanding of the interplay between these compartments.
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    IRS1 deficiency protects β-cells against ER stress-induced apoptosis by modulating sXBP-1 stability and protein translation
    (Nature Publishing Group, 2016-07-05) Takatani, Tomozumi; Shirakawa, Jun; Roe, Michael W.; Leech, Colin A.; Maier, Bernhard F.; Mirmira, Raghavendra G.; Kulkarni, Rohit N.; Department of Medicine, IU School of Medicine
    Endoplasmic reticulum (ER) stress is among several pathological features that underlie β-cell failure in the development of type 1 and type 2 diabetes. Adaptor proteins in the insulin/insulin-like-growth factor-1 signaling pathways, such as insulin receptor substrate-1 (IRS1) and IRS2, differentially impact β-cell survival but the underlying mechanisms remain unclear. Here we report that β-cells deficient in IRS1 (IRS1KO) are resistant, while IRS2 deficiency (IRS2KO) makes them susceptible to ER stress-mediated apoptosis. IRS1KOs exhibited low nuclear accumulation of spliced XBP-1 due to its poor stability, in contrast to elevated accumulation in IRS2KO. The reduced nuclear accumulation in IRS1KO was due to protein instability of Xbp1 secondary to proteasomal degradation. IRS1KO also demonstrated an attenuation in their general translation status in response to ER stress revealed by polyribosomal profiling. Phosphorylation of eEF2 was dramatically increased in IRS1KO enabling the β-cells to adapt to ER stress by blocking translation. Furthermore, significantly high ER calcium (Ca(2+)) was detected in IRS1KO β-cells even upon induction of ER stress. These observations suggest that IRS1 could be a therapeutic target for β-cell protection against ER stress-mediated cell death by modulating XBP-1 stability, protein synthesis, and Ca(2+) storage in the ER.
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    Palmitate induces mRNA translation and increases ER protein load in islet β-cells via activation of the mammalian target of rapamycin pathway
    (American Diabetes Association, 2014-10) Hatanaka, Masayuki; Maier, Bernhard; Sims, Emily K.; Templin, Andrew T.; Kulkarni, Rohit N.; Evans-Molina, Carmella; Mirmira, Raghavendra G.; Department of Medicine, IU School of Medicine
    Saturated free fatty acids (FFAs) have complex effects on the islet β-cell, acutely promoting adaptive hyperplasia but chronically impairing insulin release. The acute effects of FFAs remain incompletely defined. To elucidate these early molecular events, we incubated mouse β-cells and islets with palmitate and then studied mRNA translation by polyribosomal profiling and analyzed signaling pathways by immunoblot analysis. We found that palmitate acutely increases polyribosome occupancy of total RNA, consistent with an increase in mRNA translation. This effect on translation was attributable to activation of mammalian target of rapamycin (mTOR) pathways via L-type Ca(2+) channels but was independent of insulin signaling. Longer incubations led to depletion of polyribosome-associated RNA, consistent with activation of the unfolded protein response (UPR). Pharmacologic inhibition of mTOR suppressed both the acute effects of palmitate on mRNA translation and the chronic effects on the UPR. Islets from mice fed a high-fat diet for 7 days showed increases in polyribosome-associated RNA and phosphorylation of S6K, both consistent with activation of mTOR. Our results suggest that palmitate acutely activates mRNA translation and that this increase in protein load contributes to the later UPR.