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Asadi F, Dhanvantari S. Misrouting of glucagon and stathmin-2 towards lysosomal system of α-cells in glucagon hypersecretion of diabetes. Islets 2022; 14:40-57. [PMID: 34923907 PMCID: PMC8726656 DOI: 10.1080/19382014.2021.2011550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Glucagon hypersecretion from the pancreatic α-cell is a characteristic sign of diabetes, which exacerbates fasting hyperglycemia. Thus, targeting glucagon secretion from α-cells may be a promising approach for combating hyperglucagonemia. We have recently identified stathmin-2 as an α-cell protein that regulates glucagon secretion by directing glucagon toward the endolysosomal system in αTC1-6 cells. We hypothesized that disruption of Stmn2-mediated trafficking of glucagon to the endolysosomes in diabetes contributes to hyperglucagonemia. In isolated islets from male mice treated with streptozotocin (STZ), glucagon secretion and cellular content were augmented, but cellular Stmn2 levels were reduced (p < .01), as measured by both ELISA and immunofluorescence intensity. Using confocal immunofluorescence microscopy, the colocalization of glucagon and Stmn2 in Lamp2A+ lysosomes was dramatically reduced (p < .001) in islets from diabetic mice, and the colocalization of Stmn2, but not glucagon, with the late endosome marker, Rab7, significantly (p < .01) increased. Further studies were conducted in αTC1-6 cells cultured in media containing high glucose (16.7 mM) for 2 weeks to mimic glucagon hypersecretion of diabetes. Surprisingly, treatment of αTC1-6 cells with the lysosomal inhibitor bafilomycin A1 reduced K+-induced glucagon secretion, suggesting that high glucose may induce glucagon secretion from another lysosomal compartment. Both glucagon and Stmn2 co-localized with Lamp1, which marks secretory lysosomes, in cells cultured in high glucose. We propose that, in addition to enhanced trafficking and secretion through the regulated secretory pathway, the hyperglucagonemia of diabetes may also be due to re-routing of glucagon from the degradative Lamp2A+ lysosome toward the secretory Lamp1+ lysosome.
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada
- Department of Medical Biophysics, Western University, London, ON, Canada
- Metabolism & Diabetes and Imaging Programs, Lawson Health Research Institute, London, ON, Canada
- CONTACT Savita Dhanvantari Lawson Health Research Institute, PO Box 5777, Stn B, London, ONN6A 4V2, Canada
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2
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Asadi F, Fernandez Andrade JA, Gillies R, Lee K, Dhanvantari S, Hardy DB, Arany EJ. Sex-dependent Effect of In-utero Exposure to Δ 9-Tetrahydrocannabinol on Glucagon and Stathmin-2 in Adult Rat Offspring. Can J Diabetes 2022; 46:851-862. [PMID: 35985923 DOI: 10.1016/j.jcjd.2022.06.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 06/15/2022] [Accepted: 06/27/2022] [Indexed: 01/06/2023]
Abstract
OBJECTIVES Administration of Δ9-tetrahydrocannabinol (Δ9-THC) to pregnant rats results in glucose intolerance, insulin resistance and reduced islet mass in female, but not male, offspring. The effects of Δ9-THC on other islet hormones is not known. One downstream target of the cannabinoid receptor, stathmin-2 (Stmn2), has recently been shown to suppress glucagon secretion, thereby suggesting Δ9-THC may also affect alpha-cell function. The aim of the present study was to determine the effects of in-utero Δ9-THC exposure on the profile of glucagon, insulin and Stmn2 in the rat offspring islet and serum. METHODS Pregnant Wistar rat dams were injected with Δ9-THC (3 mg/kg per day, intraperitoneally) or vehicle from gestational day 6 to birth. Offspring were euthanized at postnatal day 21 (PND21) or at 5 months (adult) to collect blood and pancreata. RESULTS At PND21, control and Δ9-THC-exposed offspring showed that Stmn2 had a strong colocalization with glucagon (Pearson's correlation coefficient ≥0.6), and a weak colocalization with insulin (Pearson's correlation coefficient <0.4) in both males and females, with no changes by either treatment or sex. In adult female offspring in the Δ9-THC group, intensity analysis indicated an increased insulin-to-glucagon (I/G; p<0.05) ratio and a decreased glucagon-to-Stmn2 (G/S; p<0.01) ratio, and no changes in these ratios in adult males. Furthermore, Δ9-THC did not alter fasting blood glucose and serum insulin levels in either male or female adult offspring. However, female Δ9-THC-exposed offspring exhibited an increased I/G ratio (p<0.05) and decreased G/S ratio in serum by adulthood (p<0.05). CONCLUSION Collectively, the reduced G/S ratio in both islet and serum in association with an increased serum I/G ratio has direct correlations with early glucose intolerance and insulin resistance observed exclusively in females' offspring in this prenatal cannabinoid model.
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada
| | - Juan Andres Fernandez Andrade
- Lawson Health Research Institute, London, Ontario, Canada; Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Ryan Gillies
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada
| | - Kendrick Lee
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Department of Obstetrics and Gynecology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada; Department of Medical Biophysics, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Daniel Barry Hardy
- Lawson Health Research Institute, London, Ontario, Canada; Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Department of Obstetrics and Gynecology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Edith Juliana Arany
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada.
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3
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Asadi F, Dhanvantari S. Pathways of Glucagon Secretion and Trafficking in the Pancreatic Alpha Cell: Novel Pathways, Proteins, and Targets for Hyperglucagonemia. Front Endocrinol (Lausanne) 2021; 12:726368. [PMID: 34659118 PMCID: PMC8511682 DOI: 10.3389/fendo.2021.726368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 09/13/2021] [Indexed: 12/15/2022] Open
Abstract
Patients with diabetes mellitus exhibit hyperglucagonemia, or excess glucagon secretion, which may be the underlying cause of the hyperglycemia of diabetes. Defective alpha cell secretory responses to glucose and paracrine effectors in both Type 1 and Type 2 diabetes may drive the development of hyperglucagonemia. Therefore, uncovering the mechanisms that regulate glucagon secretion from the pancreatic alpha cell is critical for developing improved treatments for diabetes. In this review, we focus on aspects of alpha cell biology for possible mechanisms for alpha cell dysfunction in diabetes: proglucagon processing, intrinsic and paracrine control of glucagon secretion, secretory granule dynamics, and alterations in intracellular trafficking. We explore possible clues gleaned from these studies in how inhibition of glucagon secretion can be targeted as a treatment for diabetes mellitus.
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Western University, London, ON, Canada
- Program in Metabolism and Diabetes, Lawson Health Research Institute, London, ON, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Western University, London, ON, Canada
- Program in Metabolism and Diabetes, Lawson Health Research Institute, London, ON, Canada
- Imaging Research Program, Lawson Health Research Institute, London, ON, Canada
- Department of Medical Biophysics, Western University, London, ON, Canada
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Banks L, Randhawa VK, Colella TJF, Dhanvantari S, Connelly KA, Robinson L, Mak S, Ouzounian M, Mulvagh SL, Straus S, Allan K, Yin Yip CY, Graham MM. Cardiovascular Physicians, Scientists, and Trainees Balancing Work and Caregiving Responsibilities in the COVID-19 Era: Sex and Race-Based Inequities. CJC Open 2021; 3:627-630. [PMID: 34027367 PMCID: PMC8134915 DOI: 10.1016/j.cjco.2020.12.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 12/30/2020] [Indexed: 11/14/2022] Open
Abstract
Background The ongoing COVID-19 pandemic has exposed a work-life (im)balance that has been present but not openly discussed in medicine, surgery, and science for decades. The pandemic has exposed inequities in existing institutional structure and policies concerning clinical workload, research productivity, and/or teaching excellence inadvertently privileging those who do not have significant caregiving responsibilities or those who have the resources to pay for their management. Methods We sought to identify the challenges facing multidisciplinary faculty and trainees with dependents, and highlight a number of possible strategies to address challenges in work-life (im)balance. Results To date, there are no Canadian-based data to quantify the physical and mental effect of COVID-19 on health care workers, multidisciplinary faculty, and trainees. As the pandemic evolves, formal strategies should be discussed with an intersectional lens to promote equity in the workforce, including (but not limited to): (1) the inclusion of broad representation (including equal representation of women and other marginalized persons) in institutional-based pandemic response and recovery planning and decision-making; (2) an evaluation (eg, institutional-led survey) of the effect of the pandemic on work-life balance; (3) the establishment of formal dialogue (eg, workshops, training, and media campaigns) to normalize coexistence of work and caregiving responsibilities and to remove stigma of gender roles; (4) a reevaluation of workload and promotion reviews; and (5) the development of formal mentorship programs to support faculty and trainees. Conclusions We believe that a multistrategy approach needs to be considered by stakeholders (including policy-makers, institutions, and individuals) to create sustainable working conditions during and beyond this pandemic.
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Affiliation(s)
- Laura Banks
- Cardiovascular Prevention and Rehabilitation Program, University Health Network, Toronto, Ontario, Canada.,Faculty of Health Sciences, Ontario Tech University, Ontario, Canada
| | - Varinder K Randhawa
- Department of Cardiovascular Medicine, Kaufman Center for Heart Failure, Heart, Vascular and Thoracic Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - Tracey J F Colella
- Cardiovascular Prevention and Rehabilitation Program, University Health Network, Toronto, Ontario, Canada.,University of Toronto, Toronto, Ontario, Canada
| | | | - Kim A Connelly
- Department of Cardiology, St Michael's Hospital, Toronto, Ontario, Canada
| | - Lisa Robinson
- University of Toronto, Toronto, Ontario, Canada.,Department of Pediatrics, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Susanna Mak
- University of Toronto, Toronto, Ontario, Canada.,Department of Cardiology, University Health Network, Toronto, Ontario, Canada
| | - Maral Ouzounian
- University of Toronto, Toronto, Ontario, Canada.,Department of Cardiothoracic Surgery, University Health Network, Toronto, Ontario, Canada
| | - Sharon L Mulvagh
- Division of Cardiology, Dalhousie University, Halifax, Ontario, Canada
| | - Sharon Straus
- University of Toronto, Toronto, Ontario, Canada.,Department of Medicine, St Michael's Hospital, Toronto, Ontario, Canada
| | - Katherine Allan
- Department of Cardiology, St Michael's Hospital, Toronto, Ontario, Canada
| | - Cindy Ying Yin Yip
- Project Management Institute, Toronto, Ontario, Canada.,HeartLife Foundation, British Columbia, Canada
| | - Michelle M Graham
- Division of Cardiology, University of Alberta, Edmonton, Alberta, Canada
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5
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Randhawa VK, Dhanvantari S, Connelly KA. How Diabetes and Heart Failure Modulate Each Other and Condition Management. Can J Cardiol 2020; 37:595-608. [PMID: 33276047 DOI: 10.1016/j.cjca.2020.11.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 11/25/2020] [Accepted: 11/26/2020] [Indexed: 12/21/2022] Open
Abstract
Heart failure (HF) and diabetes mellitus (DM) confer considerable burden on the health care system. Although these often occur together, DM can increase risk of HF, whereas HF can accelerate complications of DM. HF is a clinical syndrome resulting from systolic or diastolic impairment caused by ischemic, nonischemic (eg, DM), or other etiologies. HF exists along a spectrum from stage A (ie, persons at risk of DM) to stage D (ie, refractory HF from end-stage DM cardiomyopathy [DMCM]). HF is further categorized by reduced, midrange, and preserved ejection fraction (EF). In type 2 DM, the most prevalent form of DM, several pathophysiological mechanisms (eg, insulin resistance and hyperglycemia) can contribute to myocardial damage, leading to DMCM. Management of HF and DM and patient outcomes are guided by EF and drug efficacy. In this review, we focus on the interplay between HF and DM on disease pathophysiology, management, and patient outcomes. Specifically, we highlight the role of novel antihyperglycemic (eg, sodium glucose cotransporter 2 inhibitors) and HF therapies (eg, renin-angiotensin-aldosterone system inhibitors) on HF outcomes in patients with DM and HF.
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Affiliation(s)
- Varinder Kaur Randhawa
- Cardiovascular Medicine, Kaufman Center for Heart Failure, Heart, Vascular and Thoracic Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - Savita Dhanvantari
- Metabolism and Diabetes, Imaging Program, Lawson Health Research Institute and Medical Biophysics, Pathology and Laboratory Medicine, Western University, London, Ontario, Canada
| | - Kim A Connelly
- Division of Cardiology, Department of Medicine, St Michael's Hospital, Keenan Research Centre for Biomedical Research, Toronto, Ontario, Canada.
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6
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Banks L, Randhawa VK, Caterini J, Colella TJF, Dhanvantari S, McMurtry S, Connelly KA, Robinson L, Anand SS, Ouzounian M, Zieroth S, Mak S, Straus S, Graham MM. Sex, Gender, and Equity in Cardiovascular Medicine, Surgery, and Science in Canada : Challenges, Successes, and Opportunities for Change. CJC Open 2020; 2:522-529. [PMID: 33305212 PMCID: PMC7711008 DOI: 10.1016/j.cjco.2020.06.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 06/29/2020] [Indexed: 01/01/2023] Open
Abstract
Background A previous review of sex, gender, and equity within cardiovascular (CV) medicine, surgery, and science in Canada has revealed parity during medical and graduate school training. The purpose of this study was to explore sex and gendered experiences within the Canadian CV landscape, and their impact on career training and progression. Methods An environmental scan was conducted of the Canadian CV landscape, which included an equity survey using Qualtrics software. Results The environmental scan revealed that women remain underrepresented within CV training programs as trainees (12%–30%), program directors (33%), in leadership roles at the divisional level (21%), and in other professional or career-related activities (< 30%). Our analysis also showed improvements of career engagement at these levels of women at over time. The thematic analysis of the equity survey responses (n = 71 respondents; 83% female; 9.7% response rate among female Canadian Cardiovascular Society members) identified the following themes reported within the socio-ecological framework: desire to report inequities vs staying the course (individual level); desire for social support and mentorship and challenges of dual responsibilities (interpersonal level); concerns over exclusionary cliques and desire for respect and opportunity (organizational level); and increasing awareness and actions to overcome institutional barriers and accountability (societal level). Conclusions Although women face challenges and remain underrepresented in CV medicine, surgery, and science, this study highlights potential opportunities for improving access of female medical, surgical, and research trainees and professionals to specialized cardiovascular training, career advancement, leadership, and research.
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Affiliation(s)
- Laura Banks
- Cardiovascular Prevention and Rehabilitation Program, University Health Network, Toronto, Ontario, Canada.,Faculty of Health Sciences, Ontario Tech University, Ontario, Canada
| | - Varinder K Randhawa
- Department of Cardiovascular Medicine, Kaufman Center for Heart Failure and Recovery, Heart, Vascular and Thoracic Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | | | - Tracey J F Colella
- Cardiovascular Prevention and Rehabilitation Program, University Health Network, Toronto, Ontario, Canada.,University of Toronto, Toronto, Ontario, Canada
| | - Savita Dhanvantari
- Imaging Program, Lawson Health Research Institute, London, Ontario, Canada
| | - Sean McMurtry
- Division of Cardiology, University of Alberta, Edmonton, Alberta, Canada
| | - Kim A Connelly
- Department of Cardiology, St Michaels Hospital, Toronto, Ontario, Canada
| | - Lisa Robinson
- University of Toronto, Toronto, Ontario, Canada.,Department of Pediatrics, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Sonia S Anand
- Division of Cardiology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Maral Ouzounian
- University of Toronto, Toronto, Ontario, Canada.,Department of Cardiothoracic Surgery, University Health Network, Toronto, Ontario, Canada
| | - Shelley Zieroth
- Section of Cardiology, St Boniface Hospital, and University of Manitoba, Winnipeg, Canada
| | - Susanna Mak
- University of Toronto, Toronto, Ontario, Canada.,Department of Cardiology, University Health Network, Toronto, Ontario, Canada
| | - Sharon Straus
- Department of Medicine, St Michaels Hospital, Toronto, Ontario, Canada
| | - Michelle M Graham
- Division of Cardiology, University of Alberta, Edmonton, Alberta, Canada
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7
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Abstract
Inhibition of glucagon hypersecretion from pancreatic α-cells is an appealing strategy for the treatment of diabetes. Our hypothesis is that proteins that associate with glucagon within alpha cell secretory granules will regulate glucagon secretion, and may provide druggable targets for controlling abnormal glucagon secretion in diabetes. Recently, we identified a dynamic glucagon interactome within the secretory granules of the α cell line, αTC1-6, and showed that select proteins within the interactome could modulate glucagon secretion. In the present study, we show that one of these interactome proteins, the neuronal protein stathmin-2, is expressed in αTC1-6 cells and in mouse pancreatic alpha cells, and is a novel regulator of glucagon secretion. The secretion of both glucagon and Stmn2 was significantly enhanced in response to 55 mM K+, and immunofluorescence confocal microscopy showed co-localization of stathmin-2 with glucagon and the secretory granule markers chromogranin A and VAMP-2 in αTC1-6 cells. In mouse pancreatic islets, Stathmin-2 co-localized with glucagon, but not with insulin, and co-localized with secretory pathway markers. To show a function for stathmin-2 in regulating glucagon secretion, we showed that siRNA-mediated depletion of stathmin-2 in αTC1-6 cells caused glucagon secretion to become constitutive without any effect on proglucagon mRNA levels, while overexpression of stathmin-2 completely abolished both basal and K+-stimulated glucagon secretion. Overexpression of stathmin-2 increased the localization of glucagon into the endosomal-lysosomal compartment, while depletion of stathmin-2 reduced the endosomal localization of glucagon. Therefore, we describe stathmin-2 as having a novel role as an alpha cell secretory granule protein that modulates glucagon secretion via trafficking through the endosomal-lysosomal system. These findings describe a potential new pathway for the regulation of glucagon secretion, and may have implications for controlling glucagon hypersecretion in diabetes.
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada
- Department of Medical Biophysics, Western University, London, ON, Canada
- Lawson Health Research Institute, London, ON, Canada
- *Correspondence: Savita Dhanvantari
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8
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Lalonde T, Fowkes MM, Hou J, Thibeault PE, Milne M, Dhanvantari S, Ramachandran R, Luyt LG. Single Amino Acid Replacement in G-7039 Leads to a 70-fold Increase in Binding toward GHS-R1a. ChemMedChem 2019; 14:1762-1766. [PMID: 31469937 DOI: 10.1002/cmdc.201900466] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Revised: 08/28/2019] [Indexed: 12/29/2022]
Abstract
The growth hormone secretagogue receptor type 1a (GHS-R1a) is a class A rhodopsin-like G protein coupled receptor (GPCR) that is expressed in a variety of human tissues and is differentially expressed in benign and malignant prostate cancer. Previously, the peptidomimetic [1-Nal4 ,Lys5 (4-fluorobenzoyl)]G-7039 was designed as a molecular imaging tool for positron emission tomography (PET). However, this candidate was a poor binder (IC50 =69 nm), required a lengthy four-step radiosynthesis, and had a cLogP above 8. To address these challenges, we now report on changes targeted at the 4th position of G-7039. A 2-fluoropropionic acid (2-FPA) group was added on to Lys5 to determine the potential binding affinity of the [18 F]-2-FP radiolabeled analogue, which could be prepared by simplified radiochemistry. Lead candidate [Tyr4 ,Lys5 (2-fluoropropionyl)]G-7039 exhibited an IC50 of 0.28 nm and low picomolar activity toward GHS-R1a. Molecular docking revealed a molecular basis for this picomolar affinity.
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Affiliation(s)
- Tyler Lalonde
- Department of Chemistry, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 5B7, Canada.,Imaging Program, Lawson Health Research Institute, 750 Base Line Road East, London, ON, N6C 2R5, Canada
| | - Milan M Fowkes
- Department of Chemistry, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 5B7, Canada.,Imaging Program, Lawson Health Research Institute, 750 Base Line Road East, London, ON, N6C 2R5, Canada
| | - Jinqiang Hou
- Department of Chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, ON, P7B 5E1, Canada.,Thunder Bay Regional Health Research Institute, 980 Oliver Road, Thunder Bay, ON, P7B 6V4, Canada
| | - Pierre E Thibeault
- Department of Physiology and Pharmacology, University of Western Ontario, Medical Sciences Building, Room 216, London, ON, N6A 5C1, Canada
| | - Mark Milne
- London Regional Cancer Program, Lawson Health Research Institute, 800 Commissioners Road East, London, ON, N6A 5W9, Canada
| | - Savita Dhanvantari
- Imaging Program, Lawson Health Research Institute, 750 Base Line Road East, London, ON, N6C 2R5, Canada.,Department of Medical Biophysics, University of Western Ontario, Medical Sciences Building, Room M407, London, ON, N6A 5C1, Canada
| | - Rithwik Ramachandran
- Department of Physiology and Pharmacology, University of Western Ontario, Medical Sciences Building, Room 216, London, ON, N6A 5C1, Canada
| | - Leonard G Luyt
- Department of Chemistry, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 5B7, Canada.,Imaging Program, Lawson Health Research Institute, 750 Base Line Road East, London, ON, N6C 2R5, Canada.,London Regional Cancer Program, Lawson Health Research Institute, 800 Commissioners Road East, London, ON, N6A 5W9, Canada.,Department of Oncology, University of Western Ontario, 800 Commissioners Road East, London, ON, N6A 5W9, Canada
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9
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Sullivan R, Randhawa V, Lalonde T, Luyt L, Wisenberg G, Dhanvantari S. THE GROWTH HORMONE SECRETAGOGUE RECEPTOR, GHRELIN, AND BNP IN HUMAN HEART DISEASE WITH PRESERVED EJECTION FRACTION. Can J Cardiol 2019. [DOI: 10.1016/j.cjca.2019.07.510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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10
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Lee TK, Murthy SR, Cawley NX, Dhanvantari S, Hewitt SM, Lou H, Lau T, Ma S, Huynh T, Wesley RA, Ng IO, Pacak K, Poon RT, Loh YP. An N-terminal truncated carboxypeptidase E splice isoform induces tumor growth and is a biomarker for predicting future metastasis in human cancers. J Clin Invest 2019; 130:1804. [PMID: 30882370 DOI: 10.1172/jci128836] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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11
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Sullivan R, Randhawa VK, Stokes A, Wu D, Lalonde T, Kiaii B, Luyt L, Wisenberg G, Dhanvantari S. Dynamics of the Ghrelin/Growth Hormone Secretagogue Receptor System in the Human Heart Before and After Cardiac Transplantation. J Endocr Soc 2019; 3:748-762. [PMID: 30937420 PMCID: PMC6438351 DOI: 10.1210/js.2018-00393] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 02/11/2019] [Indexed: 12/14/2022] Open
Abstract
Currently, the early preclinical detection of left ventricular dysfunction is difficult because biomarkers are not specific for the cardiomyopathic process. The underlying molecular mechanisms leading to heart failure remain elusive, highlighting the need for identification of cardiac-specific markers. The growth hormone secretagogue receptor (GHSR) and its ligand ghrelin are present in cardiac tissue and are known to contribute to myocardial energetics. Here, we examined tissue ghrelin-GHSR levels as specific markers of cardiac dysfunction in patients who underwent cardiac transplantation. Samples of cardiac tissue were obtained from 10 patients undergoing cardiac transplant at the time of organ harvesting and during serial posttransplant biopsies. Quantitative fluorescence microscopy using a fluorescent ghrelin analog was used to measure levels of GHSR, and immunofluorescence was used to measure levels of ghrelin, B-type natriuretic peptide (BNP), and tissue markers of cardiomyocyte contractility and growth. GHSR and ghrelin expression levels were highly variable in the explanted heart, less in the grafted heart biopsies. GHSR and ghrelin were strongly positively correlated, and both markers were negatively correlated with left ventricular ejection fraction. Ghrelin had stronger positive correlations than BNP with the signaling markers for contractility and growth. These data suggest that GHSR-ghrelin have potential use as an integrated marker of cardiac dysfunction. Interestingly, tissue ghrelin appeared to be a more sensitive indicator than BNP to the biochemical processes that are characteristic of heart failure. This work allows for further use of ghrelin-GHSR to interrogate cardiac-specific biochemical mechanisms in preclinical stages of heart failure (HF).
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Affiliation(s)
- Rebecca Sullivan
- Pathology and Laboratory Medicine, Western University, London, Ontario, Canada
| | - Varinder K Randhawa
- Cardiac Imaging Research, Lawson Health Research Institute, London, Ontario, Canada
| | - Anne Stokes
- Metabolism and Diabetes, Lawson Health Research Institute, London, Ontario, Canada
| | - Derek Wu
- Pathology and Laboratory Medicine, Western University, London, Ontario, Canada
| | - Tyler Lalonde
- Chemistry, Western University, London, Ontario, Canada
| | - Bob Kiaii
- Cardiac Surgery, Western University, London, Ontario, Canada
| | - Leonard Luyt
- Chemistry, Western University, London, Ontario, Canada.,Imaging Program, Lawson Health Research Institute, London, Ontario, Canada.,Department of Oncology, London Regional Cancer Program, Western University, London, Ontario, Canada
| | - Gerald Wisenberg
- Imaging Program, Lawson Health Research Institute, London, Ontario, Canada.,Medical Biophysics, Western University, London, Ontario, Canada
| | - Savita Dhanvantari
- Pathology and Laboratory Medicine, Western University, London, Ontario, Canada.,Imaging Program, Lawson Health Research Institute, London, Ontario, Canada.,Metabolism and Diabetes, Lawson Health Research Institute, London, Ontario, Canada.,Medical Biophysics, Western University, London, Ontario, Canada
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12
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Asadi F, Dhanvantari S. Plasticity in the Glucagon Interactome Reveals Novel Proteins That Regulate Glucagon Secretion in α-TC1-6 Cells. Front Endocrinol (Lausanne) 2019; 9:792. [PMID: 30713523 PMCID: PMC6346685 DOI: 10.3389/fendo.2018.00792] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 12/17/2018] [Indexed: 12/27/2022] Open
Abstract
Glucagon is stored within the secretory granules of pancreatic alpha cells until stimuli trigger its release. The alpha cell secretory responses to the stimuli vary widely, possibly due to differences in experimental models or microenvironmental conditions. We hypothesized that the response of the alpha cell to various stimuli could be due to plasticity in the network of proteins that interact with glucagon within alpha cell secretory granules. We used tagged glucagon with Fc to pull out glucagon from the enriched preparation of secretory granules in α-TC1-6 cells. Isolation of secretory granules was validated by immunoisolation with Fc-glucagon and immunoblotting for organelle-specific proteins. Isolated enriched secretory granules were then used for affinity purification with Fc-glucagon followed by liquid chromatography/tandem mass spectrometry to identify secretory granule proteins that interact with glucagon. Proteomic analyses revealed a network of proteins containing glucose regulated protein 78 KDa (GRP78) and histone H4. The interaction between glucagon and the ER stress protein GRP78 and histone H4 was confirmed through co-immunoprecipitation of secretory granule lysates, and colocalization immunofluorescence confocal microscopy. Composition of the protein networks was altered at different glucose levels (25 vs. 5.5 mM) and in response to the paracrine inhibitors of glucagon secretion, GABA and insulin. siRNA-mediated silencing of a subset of these proteins revealed their involvement in glucagon secretion in α-TC1-6 cells. Therefore, our results show a novel and dynamic glucagon interactome within α-TC1-6 cell secretory granules. We suggest that variations in the alpha cell secretory response to stimuli may be governed by plasticity in the glucagon "interactome."
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Affiliation(s)
- Farzad Asadi
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, ON, Canada
| | - Savita Dhanvantari
- Department of Pathology and Laboratory Medicine, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, ON, Canada
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, ON, Canada
- Metabolism, Diabetes and Imaging Programs, Lawson Health Research Institute, London, ON, Canada
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13
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Abbas A, Yu L, Lalonde T, Wu D, Thiessen JD, Luyt LG, Dhanvantari S. Development and Characterization of an 18F-labeled Ghrelin Peptidomimetic for Imaging the Cardiac Growth Hormone Secretagogue Receptor. Mol Imaging 2018; 17:1536012118809587. [PMID: 30394854 PMCID: PMC6236854 DOI: 10.1177/1536012118809587] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
One-third of patients with heart disease develop heart failure, which is diagnosed
through imaging and detection of circulating biomarkers. Imaging strategies reveal
morphologic and functional changes but fall short of detecting molecular abnormalities
that can lead to heart failure, and circulating biomarkers are not cardiac specific. Thus,
there is critical need for biomarkers that are endogenous to myocardial tissues. The
cardiac growth hormone secretagogue receptor 1a (GHSR1a), which binds the hormone ghrelin,
is a potential biomarker for heart failure. We have synthesized and characterized a novel
ghrelin peptidomimetic tracer, an 18F-labeled analogue of G-7039, for positron
emission tomography (PET) imaging of cardiac GHSR1a. In vitro analysis showed enhanced
serum stability compared to natural ghrelin and significantly increased cellular uptake in
GHSR1a-expressing OVCAR cells. Biodistribution studies in mice showed that tissue uptake
of the tracer was independent of circulating ghrelin levels, and there was negligible
cardiac uptake and high uptake in the liver, intestines, and kidneys. Specificity of
tracer uptake was assessed using ghsr −/− mice; both static and dynamic PET imaging revealed no difference in cardiac
uptake, and there was no significant correlation between cardiac standardized uptake
values and GHSR1a expression. Our study lays the groundwork for further refinement of
peptidomimetic PET tracers targeting cardiac GHSR1a.
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Affiliation(s)
- Ahmed Abbas
- 1 Department of Medical Biophysics, Western University, London, Ontario, Canada
| | - Lihai Yu
- 2 Department of Chemistry, Western University, London, Ontario, Canada
| | - Tyler Lalonde
- 2 Department of Chemistry, Western University, London, Ontario, Canada
| | - Derek Wu
- 3 Department of Pathology and Laboratory Medicine, Western University, London, Ontario, Canada
| | - Jonathan D Thiessen
- 1 Department of Medical Biophysics, Western University, London, Ontario, Canada.,4 Imaging Research, Lawson Health Research Institute, London, Ontario, Canada
| | - Leonard G Luyt
- 2 Department of Chemistry, Western University, London, Ontario, Canada.,4 Imaging Research, Lawson Health Research Institute, London, Ontario, Canada.,5 Department of oncology, Western University, London, Ontario, Canada
| | - Savita Dhanvantari
- 1 Department of Medical Biophysics, Western University, London, Ontario, Canada.,3 Department of Pathology and Laboratory Medicine, Western University, London, Ontario, Canada.,4 Imaging Research, Lawson Health Research Institute, London, Ontario, Canada.,6 Metabolism/Diabetes, Lawson Health Research Institute, London, Ontario, Canada
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14
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Naghibosadat M, Lalonde T, Luyt L, Hoffman L, Dhanvantari S. GHRELIN AND DES-ACYL GHRELIN BINDING IN CARDIAC TISSUE ARE ALTERED WITH CARDIOVASCULAR INFLAMMATION IN DUCHENNE MUSCULAR DYSTROPHY. Can J Cardiol 2018. [DOI: 10.1016/j.cjca.2018.07.361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
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15
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Sullivan R, Randhawa V, Stokes A, Wu D, Lalonde T, Luyt L, Wisenberg G, Dhanvantari S. THE GROWTH HORMONE SECRETAGOGUE RECEPTOR, GHRELIN AND BIOCHEMICAL SIGNALING MOLECULES IN HUMAN HEART DISEASE. Can J Cardiol 2018. [DOI: 10.1016/j.cjca.2018.07.302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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16
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Charron CL, McFarland MS, Dhanvantari S, Luyt LG. Development of a [ 68Ga]-ghrelin analogue for PET imaging of the ghrelin receptor (GHS-R1a). Medchemcomm 2018; 9:1761-1767. [PMID: 30429981 DOI: 10.1039/c8md00210j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Accepted: 09/09/2018] [Indexed: 01/16/2023]
Abstract
The ghrelin receptor is a member of the growth hormone secretagogue receptor (GHS-R) family and is present at low concentrations in tissues such as the brain, kidney, cardiovascular system, and prostate. The ghrelin receptor plays an important role in cellular proliferation, apoptosis, invasion, and migration associated with the progression of many cancers, including prostate, breast, ovarian, testicular, and intestinal carcinomas. Ghrelin, the endogenous ligand, is a 28 amino acid peptide (IC50 = 3.1 nM) known to have poor in vivo stability. Herein, we report the synthesis and evaluation of [Dpr3(octanoyl),Lys19(Ga-DOTA)]ghrelin(1-19). This new ghrelin analogue has a binding affinity (IC50 = 5.9 nM) comparable to that of natural ghrelin. Preliminary in vivo evaluation shows higher uptake of [Dpr3(octanoyl),Lys19(68Ga-DOTA)]ghrelin(1-19) in HT1080/GHSR-1a xenografts than the non-transfected HT1080 xenografts in NOD-SCID mice, although considerable uptake is observed in the kidneys. This is the first example of ghrelin receptor PET imaging in a xenograft model using a peptide derived directly from the endogenous ligand and serves as motivation for developing more effective ghrelin-based radiopeptides.
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Affiliation(s)
- C L Charron
- Department of Chemistry , University of Western Ontario , 1151 Richmond Street , London , Ontario N6A 5B7 , Canada .
| | - M S McFarland
- Department of Chemistry , University of Western Ontario , 1151 Richmond Street , London , Ontario N6A 5B7 , Canada .
| | - S Dhanvantari
- Lawson Health Research Institute , 268 Grosvenor Street , London , Ontario N6A 4V2 , Canada.,Departments of Medical Biophysics , University of Western Ontario , 1151 Richmond Street , London , Ontario N6A 5B7 , Canada
| | - L G Luyt
- Department of Chemistry , University of Western Ontario , 1151 Richmond Street , London , Ontario N6A 5B7 , Canada . .,Department of Oncology , University of Western Ontario , 1151 Richmond Street , London , Ontario N6A 5B7 , Canada.,London Regional Cancer Program , Lawson Health Research Institute , 800 Commissioners Road East , London , Ontario N6A 5W9 , Canada
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17
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Fowkes MM, Lalonde T, Yu L, Dhanvantari S, Kovacs MS, Luyt LG. Peptidomimetic growth hormone secretagogue derivatives for positron emission tomography imaging of the ghrelin receptor. Eur J Med Chem 2018; 157:1500-1511. [PMID: 30282322 DOI: 10.1016/j.ejmech.2018.08.062] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 08/16/2018] [Accepted: 08/22/2018] [Indexed: 02/06/2023]
Abstract
The ghrelin receptor is a seven-transmembrane (7-TM) receptor known to have an increased level of expression in human carcinoma and heart failure. Recent work has focused on the synthesis of positron emission tomography (PET) probes designed to target and image this receptor for disease diagnosis and staging. However, these probes have been restricted to small-molecule quinalizonones and peptide derivatives of the endogenous ligand ghrelin. We describe the design, synthesis and biological evaluation of a series of 4-fluorobenzoylated growth hormone secretagogues (GHSs) derived from peptidic (GHRP-1, GHPR-2 and GHRP-6) and peptidomimetic (G-7039, [1-Nal4]G-7039 and ipamorelin) families in order to test locations for the insertion of fluorine-18 for PET imaging. The peptidomimetic G-7039 was found to be the most suitable for 18F-radiolabelling as its non-radioactive 4-fluorobenzoylated analogue ([1-Nal4,Lys5(4-FB)]G-7039), had both a high binding affinity (IC50 = 69 nM) and promising in vitro efficacy (EC50 = 1.1 nM). Prosthetic group radiolabelling of the precursor compound [1-Nal4]G-7039 using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) delivered the PET probe [1-Nal4,Lys5(4-[18F]-FB)]G-7039 in an average decay-corrected radiochemical yield of 48%, a radio-purity ≥ 99% and an average molar activity of >34 GBq/μmol. This compound could be investigated as a PET probe for the detection of diseases that are characterised by overexpression of the ghrelin receptor.
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Affiliation(s)
- Milan M Fowkes
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada
| | - Tyler Lalonde
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada
| | - Lihai Yu
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada
| | - Savita Dhanvantari
- Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, N6A 4V2, Canada
| | - Michael S Kovacs
- Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, N6A 4V2, Canada
| | - Leonard G Luyt
- Department of Chemistry, Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada; London Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario, N6A 4L6, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, N6A 4V2, Canada.
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18
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Affiliation(s)
- Tyler Lalonde
- Department of Chemistry; University of Western Ontario; London Ontario N6A 5B7 Canada
| | - Trevor G. Shepherd
- London Regional Cancer Program; London Ontario N6A 4L6 Canada
- Department of Obstetrics and Gynecology; University of Western Ontario; London Ontario N6A 5B7 Canada
| | - Savita Dhanvantari
- Imaging Program, Lawson Health Research Institute; London Ontario N6A 4V2 Canada
- Department of Medical Biophysics; University of Western Ontario; London Canada
- Department of Pathology; University of Western Ontario; London Canada
- Department of Laboratory Medicine; University of Western Ontario; London Canada
| | - Leonard G. Luyt
- Department of Chemistry; University of Western Ontario; London Ontario N6A 5B7 Canada
- London Regional Cancer Program; London Ontario N6A 4L6 Canada
- Department of Oncology; University of Western Ontario; London Ontario N6A 5B7 Canada
- Department of Medical Imaging; University of Western Ontario; London Ontario N6A 5B7 Canada
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19
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Hou J, Kovacs MS, Dhanvantari S, Luyt LG. Development of Candidates for Positron Emission Tomography (PET) Imaging of Ghrelin Receptor in Disease: Design, Synthesis, and Evaluation of Fluorine-Bearing Quinazolinone Derivatives. J Med Chem 2018; 61:1261-1275. [DOI: 10.1021/acs.jmedchem.7b01754] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Jinqiang Hou
- London Regional Cancer Program, London N6A 4L6, Canada
- Lawson Health Research Institute, London N6C 2R5, Canada
| | | | | | - Leonard G. Luyt
- London Regional Cancer Program, London N6A 4L6, Canada
- Lawson Health Research Institute, London N6C 2R5, Canada
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20
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Sullivan R, McGirr R, Hu S, Tan A, Wu D, Charron C, Lalonde T, Arany E, Chakrabarti S, Luyt L, Dhanvantari S. Changes in the Cardiac GHSR1a-Ghrelin System Correlate With Myocardial Dysfunction in Diabetic Cardiomyopathy in Mice. J Endocr Soc 2017; 2:178-189. [PMID: 29450407 PMCID: PMC5799831 DOI: 10.1210/js.2017-00433] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 12/19/2017] [Indexed: 01/16/2023] Open
Abstract
Ghrelin and its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), are present in cardiac tissue. Activation of GHSR1a by ghrelin promotes cardiomyocyte contractility and survival, and changes in myocardial GHSR1a and circulating ghrelin track with end-stage heart failure, leading to the hypothesis that GHSR1a is a biomarker for heart failure. We hypothesized that GHSR1a could also be a biomarker for diabetic cardiomyopathy (DCM). We used two models of streptozotocin (STZ)-induced DCM: group 1, adult mice treated with 35 mg/kg STZ for 3 days; and group 2, neonatal mice treated with 70 mg/kg STZ at days 2 and 5 after birth. In group 1, mild fasting hyperglycemia (11 mM) was first detected 8 weeks after the last injection, and in group 2, severe fasting hyperglycemia (20 mM) was first detected 1 to 3 weeks after the last injection. In group 1, left ventricular function was slightly impaired as measured by echocardiography, and Western blot analysis showed a significant decrease in myocardial GHSR1a. In group 2, GHSR1a levels were also decreased as assessed by Cy5-ghrelin(1–19) fluorescence microscopy, and there was a significant negative correlation between GHSR1a levels and glucose tolerance. There were significant positive correlations between GHSR1a and ghrelin and between GHSR1a and sarcoplasmic reticulum Ca2+-ATPase 2a (SERCA2a), a marker for contractility, but not between GHSR1a and B-type natriuretic peptide, a marker for heart failure. We conclude that the subclinical stage of DCM is accompanied by alterations in the myocardial ghrelin-GHSR1a system, suggesting the possibility of a biomarker for DCM.
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Affiliation(s)
- Rebecca Sullivan
- Imaging Research, Lawson Health Research Institute, London, Ontario N6A 4V2, Canada.,Department of Pathology and Laboratory Medicine, Western University, London, Ontario N6A 4V2, Canada
| | - Rebecca McGirr
- Imaging Research, Lawson Health Research Institute, London, Ontario N6A 4V2, Canada
| | - Shirley Hu
- Department of Physiology and Pharmacology, Western University, London, Ontario N6A 3K7, Canada
| | - Alice Tan
- Department of Pathology and Laboratory Medicine, Western University, London, Ontario N6A 4V2, Canada
| | - Derek Wu
- Department of Pathology and Laboratory Medicine, Western University, London, Ontario N6A 4V2, Canada
| | - Carlie Charron
- Department of Chemistry, Western University, London, Ontario N6A 5B7, Canada
| | - Tyler Lalonde
- Department of Chemistry, Western University, London, Ontario N6A 5B7, Canada
| | - Edith Arany
- Department of Pathology and Laboratory Medicine, Western University, London, Ontario N6A 4V2, Canada
| | - Subrata Chakrabarti
- Department of Pathology and Laboratory Medicine, Western University, London, Ontario N6A 4V2, Canada
| | - Leonard Luyt
- Department of Chemistry, Western University, London, Ontario N6A 5B7, Canada.,Departments of Oncology and Medical Imaging, Western University, London, Ontario N6A 4L6, Canada.,London Regional Cancer Program, Lawson Health Research Institute, London, Ontario N6A 4V2, Canada
| | - Savita Dhanvantari
- Imaging Research, Lawson Health Research Institute, London, Ontario N6A 4V2, Canada.,Department of Pathology and Laboratory Medicine, Western University, London, Ontario N6A 4V2, Canada.,Department of Medical Biophysics, Western University, London, Ontario N6A 5C1, Canada
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21
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Sullivan R, Randhawa V, Stokes A, Liu S, Wu D, Charron C, Lalonde T, Luyt L, Kiaii B, Wisenberg G, Dhanvantari S. EXPRESSION OF THE GROWTH HORMONE SECRETAGOGUE RECEPTOR AND GHRELIN IN HUMAN HEART FAILURE. Can J Cardiol 2017. [DOI: 10.1016/j.cjca.2017.07.403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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22
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Charron CL, Hou J, McFarland MS, Dhanvantari S, Kovacs MS, Luyt LG. Structure–Activity Study of Ghrelin(1–8) Resulting in High Affinity Fluorine-Bearing Ligands for the Ghrelin Receptor. J Med Chem 2017; 60:7256-7266. [DOI: 10.1021/acs.jmedchem.7b00164] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Carlie L. Charron
- Department
of Chemistry, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada
| | - Jinqiang Hou
- London
Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario N6A 4L6, Canada
| | - Mark S. McFarland
- Department
of Chemistry, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada
| | - Savita Dhanvantari
- Imaging
Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
- Department
of Medical Biophysics, University of Western Ontario, 1151 Richmond
Street, London, Ontario N6A 5B7, Canada
| | - Michael S. Kovacs
- Imaging
Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
- Department
of Medical Biophysics, University of Western Ontario, 1151 Richmond
Street, London, Ontario N6A 5B7, Canada
| | - Leonard G. Luyt
- Department
of Chemistry, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada
- London
Regional Cancer Program, Lawson Health Research Institute, 790 Commissioners Road East, London, Ontario N6A 4L6, Canada
- Departments
of Oncology and Medical Imaging, University of Western Ontario, 1151
Richmond Street, London, Ontario N6A 5B7, Canada
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23
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Azad BB, Rota V, Yu L, Mcgirr R, Amant AHS, Lee TY, Dhanvantari S, Luyt LG. Synthesis and Evaluation of Optical and PET GLP-1 Peptide Analogues for GLP-1R Imaging. Mol Imaging 2017. [DOI: 10.2310/7290.2014.00057] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Babak Behnam Azad
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - Vanessa Rota
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - Lihai Yu
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - Rebecca Mcgirr
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - André H. St. Amant
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - Ting-Yim Lee
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - Savita Dhanvantari
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
| | - Leonard G. Luyt
- Departments of Chemistry, Medical Biophysics, Medicine, Pathology, Medical Imaging, Oncology, The University of Western Ontario; Lawson Health Research Institute; London Regional Cancer Program, London, ON
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24
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Dhanvantari S. Secretory Granules Tell (Almost) All in Enteroendocrine Cells. Endocrinology 2017; 158:2068-2070. [PMID: 28881871 DOI: 10.1210/en.2017-00459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 05/15/2017] [Indexed: 11/19/2022]
Affiliation(s)
- Savita Dhanvantari
- Lawson Health Research Institute and Western University, London, Ontario N6A 4V2, Canada
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25
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Abbas A, Beamish C, McGirr R, Demarco J, Cockburn N, Krokowski D, Lee TY, Kovacs M, Hatzoglou M, Dhanvantari S. Characterization of 5-(2- 18F-fluoroethoxy)-L-tryptophan for PET imaging of the pancreas. F1000Res 2016; 5:1851. [PMID: 27909574 PMCID: PMC5112576 DOI: 10.12688/f1000research.9129.2] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/04/2016] [Indexed: 12/23/2022] Open
Abstract
Purpose: In diabetes, pancreatic beta cell mass declines significantly prior to onset of fasting hyperglycemia. This decline may be due to endoplasmic reticulum (ER) stress, and the system L amino acid transporter LAT1 may be a biomarker of this process. In this study, we used 5-(2-
18F-fluoroethoxy)-L-tryptophan (
18F-L-FEHTP) to target LAT1 as a potential biomarker of beta cell function in diabetes. Procedures: Uptake of
18F-L-FEHTP was determined in wild-type C57BL/6 mice by
ex vivo biodistribution. Both dynamic and static positron emission tomography (PET) images were acquired in wild-type and Akita mice, a model of ER stress-induced diabetes, as well as in mice treated with streptozotocin (STZ). LAT1 expression in both groups of mice was evaluated by immunofluorescence microscopy. Results: Uptake of
18F-L-FEHTP was highest in the pancreas, and static PET images showed highly specific pancreatic signal. Time-activity curves showed significantly reduced
18F-L-FEHTP uptake in Akita mice, and LAT1 expression was also reduced. However, mice treated with STZ, in which beta cell mass was reduced by 62%, showed no differences in
18F-L-FEHTP uptake in the pancreas, and there was no significant correlation of
18F-L-FEHTP uptake with beta cell mass. Conclusions: 18F-L-FEHTP is highly specific for the pancreas with little background uptake in kidney or liver. We were able to detect changes in LAT1 in a mouse model of diabetes, but these changes did not correlate with beta cell function or mass. Therefore,
18F-L-FEHTP PET is not a suitable method for the noninvasive imaging of changes in beta cell function during the progression of diabetes.
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Affiliation(s)
- Ahmed Abbas
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada
| | - Christine Beamish
- Metabolism and Diabetes Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Rebecca McGirr
- Metabolism and Diabetes Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada; Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - John Demarco
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Neil Cockburn
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Dawid Krokowski
- Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Ting-Yim Lee
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada; Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Michael Kovacs
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada; Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Maria Hatzoglou
- Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Savita Dhanvantari
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada; Metabolism and Diabetes Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada; Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada; Department of Pathology and Laboratory Medicine, Western University, London, ON, N6A 5C1, Canada
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Abbas A, Beamish C, McGirr R, Demarco J, Cockburn N, Krokowski D, Lee TY, Kovacs M, Hatzoglou M, Dhanvantari S. Characterization of 5-(2- 18F-fluoroethoxy)-L-tryptophan for PET imaging of the pancreas. F1000Res 2016; 5:1851. [PMID: 27909574 PMCID: PMC5112576 DOI: 10.12688/f1000research.9129.1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/04/2016] [Indexed: 10/29/2023] Open
Abstract
Purpose: In diabetes, pancreatic beta cell mass declines significantly prior to onset of fasting hyperglycemia. This decline may be due to endoplasmic reticulum (ER) stress, and the system L amino acid transporter LAT1 may be a biomarker of this process. In this study, we used 5-(2- 18F-fluoroethoxy)-L-tryptophan ( 18F-L-FEHTP) to target LAT1 as a potential biomarker of beta cell function in diabetes. Procedures: Uptake of 18F-L-FEHTP was determined in wild-type C57BL/6 mice by ex vivo biodistribution. Both dynamic and static positron emission tomography (PET) images were acquired in wild-type and Akita mice, a model of ER stress-induced diabetes, as well as in mice treated with streptozotocin (STZ). LAT1 expression in both groups of mice was evaluated by immunofluorescence microscopy. Results: Uptake of 18F-L-FEHTP was highest in the pancreas, and static PET images showed highly specific pancreatic signal. Time-activity curves showed significantly reduced 18F-L-FEHTP uptake in Akita mice, and LAT1 expression was also reduced. However, mice treated with STZ, in which beta cell mass was reduced by 62%, showed no differences in 18F-L-FEHTP uptake in the pancreas, and there was no significant correlation of 18F-L-FEHTP uptake with beta cell mass. Conclusions:18F-L-FEHTP is highly specific for the pancreas with little background uptake in kidney or liver. We were able to detect changes in LAT1 in a mouse model of diabetes, but these changes did not correlate with beta cell function or mass. Therefore, 18F-L-FEHTP PET is not a suitable method for the noninvasive imaging of changes in beta cell function during the progression of diabetes.
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Affiliation(s)
- Ahmed Abbas
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada
| | - Christine Beamish
- Metabolism and Diabetes Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Rebecca McGirr
- Metabolism and Diabetes Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - John Demarco
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Neil Cockburn
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Dawid Krokowski
- Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Ting-Yim Lee
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Michael Kovacs
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
| | - Maria Hatzoglou
- Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Savita Dhanvantari
- Department of Medical Biophysics, Western University, London, ON, N6A 5C1, Canada
- Metabolism and Diabetes Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
- Imaging Program, Lawson Health Research Institute, London, ON, N6A 4V2, Canada
- Department of Pathology and Laboratory Medicine, Western University, London, ON, N6A 5C1, Canada
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Behnam Azad B, Rota V, Yu L, McGirr R, St Amant AH, Lee TY, Dhanvantari S, Luyt LG. Synthesis and evaluation of optical and PET GLP-1 peptide analogues for GLP-1R imaging. Mol Imaging 2016; 14. [PMID: 25762192 DOI: 0.2310/7290.2014.00057] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/29/2022] Open
Abstract
A fluorescein-GLP-1 (7-37) analog was generated to determine GLP-1R distribution in various cell types of the pancreas in both strains of mice and receptor-specific uptake was confirmed by blocking with exendin-4. Biodistribution studies were carried out using 68Ga-labeled GLP-1(7-37) peptides in CD1 and C57BL/6 mice. In addition, immunocompromised mice bearing GLP-1R-expressing insulinomas were evaluated by positron emission tomography (PET) imaging and ex vivo biodistribution studies. The optical GLP-1 probe strongly colocalized with immunofluorescence for insulin and glucagon, and more weakly with amylase (exocrine pancreas) and cytokeratin 19 (ductal cells), confirming its application for in situ GLP-1R imaging in various pancreatic cell types. Insulinomas were clearly visualized by in vivo PET. Reducing the peptide positive charge decreased renal retention as well as tumor uptake. Results demonstrate the application of the developed GLP-1 peptide analogues for in situ (optical) and in vivo (PET) imaging of GLP-1R expression.
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Charlton CL, Dhanvantari S, Luyt LG. Evaluation of [68Ga]-DOTA ghrelin (1–19) in LNCaP prostate carcinoma. Nucl Med Biol 2014. [DOI: 10.1016/j.nucmedbio.2014.05.102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Dhanvantari S. The genetics of obesity meets basic cell biology through prohormone convertase 1/3. Endocrinology 2014; 155:2343-5. [PMID: 24950989 DOI: 10.1210/en.2014-1376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Guizzetti L, McGirr R, Dhanvantari S. Two dipolar α-helices within hormone-encoding regions of proglucagon are sorting signals to the regulated secretory pathway. J Biol Chem 2014; 289:14968-80. [PMID: 24727476 DOI: 10.1074/jbc.m114.563684] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Proglucagon is expressed in pancreatic α cells, intestinal L cells, and some hypothalamic and brainstem neurons. Tissue-specific processing of proglucagon yields three major peptide hormones as follows: glucagon in the α cells and glucagon-like peptides (GLP)-1 and -2 in the L cells and neurons. Efficient sorting and packaging into the secretory granules of the regulated secretory pathway in each cell type are required for nutrient-regulated secretion of these proglucagon-derived peptides. Our previous work suggested that proglucagon is directed into granules by intrinsic sorting signals after initial processing to glicentin and major proglucagon fragment (McGirr, R., Guizzetti, L., and Dhanvantari, S. (2013) J. Endocrinol. 217, 229-240), leading to the hypothesis that sorting signals may be present in multiple domains. In the present study, we show that the α-helices within glucagon and GLP-1, but not GLP-2, act as sorting signals by efficiently directing a heterologous secretory protein to the regulated secretory pathway. Biophysical characterization of these peptides revealed that glucagon and GLP-1 each encode a nonamphipathic, dipolar α-helix, whereas the helix in GLP-2 is not dipolar. Surprisingly, glicentin and major proglucagon fragment were sorted with different efficiencies, thus providing evidence that proglucagon is first sorted to granules prior to processing. In contrast to many other prohormones in which sorting is directed by ordered prodomains, the sorting determinants of proglucagon lie within the ordered hormone domains of glucagon and GLP-1, illustrating that each prohormone has its own sorting "signature."
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Affiliation(s)
| | - Rebecca McGirr
- the Metabolism/Diabetes and Imaging Programs, Lawson Health Research Institute, London, Ontario N6A 4V2, Canada
| | - Savita Dhanvantari
- From the Departments of Medical Biophysics, the Metabolism/Diabetes and Imaging Programs, Lawson Health Research Institute, London, Ontario N6A 4V2, Canada Pathology, and Medicine, University of Western Ontario, London, Ontario N6A 3K7 and
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Douglas GAF, McGirr R, Charlton CL, Kagan DB, Hoffman LM, Luyt LG, Dhanvantari S. Characterization of a far-red analog of ghrelin for imaging GHS-R in P19-derived cardiomyocytes. Peptides 2014; 54:81-8. [PMID: 24468548 DOI: 10.1016/j.peptides.2014.01.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 01/16/2014] [Accepted: 01/16/2014] [Indexed: 11/29/2022]
Abstract
Ghrelin and its receptor, the growth hormone secretagogue receptor (GHS-R), are expressed in the heart, and may function to promote cardiomyocyte survival, differentiation and contractility. Previously, we had generated a truncated analog of ghrelin conjugated to fluorescein isothiocyanate for the purposes of determining GHS-R expression in situ. We now report the generation and characterization of a far-red ghrelin analog, [Dpr(3)(octanoyl), Lys(19)(Cy5)]ghrelin (1-19), and show that it can be used to image changes in GHS-R in developing cardiomyocytes. We also generated the des-acyl analog, des-acyl [Lys(19)(Cy5)]ghrelin (1-19) and characterized its binding to mouse heart sections. Receptor binding affinity of Cy5-ghrelin as measured in HEK293 cells overexpressing GHS-R1a was within an order of magnitude of that of fluorescein-ghrelin and native human ghrelin, while the des-acyl Cy5-ghrelin did not bind GHS-R1a. Live cell imaging in HEK293/GHS-R1a cells showed cell surface labeling that was displaced by excess ghrelin. Interestingly, Cy5-ghrelin, but not the des-acyl analog, showed concentration-dependent binding in mouse heart tissue sections. We then used Cy5-ghrelin to track GHS-R expression in P19-derived cardiomyocytes. Live cell imaging at different time points after DMSO-induced differentiation showed that GHS-R expression preceded that of the differentiation marker aMHC and tracked with the contractility marker SERCA 2a. Our far-red analog of ghrelin adds to the tools we are developing to map GHS-R in developing and diseased cardiac tissues.
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Affiliation(s)
- Gregory A F Douglas
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
| | - Rebecca McGirr
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
| | - Carlie L Charlton
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
| | - Dov B Kagan
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
| | - Lisa M Hoffman
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
| | - Leonard G Luyt
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada
| | - Savita Dhanvantari
- Departments of Pathology, Chemistry, Medical Imaging, Medical Biophysics, and Oncology, Western University, Richmond Street, London, Ontario, Canada; Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2, Canada.
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Abstract
Proglucagon is expressed in pancreatic alpha cells, intestinal L cells and brainstem neurons. Tissue-specific processing of proglucagon yields the peptide hormones glucagon in the alpha cell and glucagon-like peptide (GLP)-1 and GLP-2 in L cells. Both glucagon and GLP-1 are secreted in response to nutritional status and are critical for regulating glycaemia. The sorting of proglucagon to the dense-core secretory granules of the regulated secretory pathway is essential for the appropriate secretion of glucagon and GLP-1. We examined the roles of carboxypeptidase E (CPE), a prohormone sorting receptor, the processing enzymes PC1/3 and PC2 and putative intrinsic sorting signals in proglucagon sorting. In Neuro 2a cells that lacked CPE, PC1/3 and PC2, proglucagon co-localised with the Golgi marker p115 as determined by quantitative immunofluorescence microscopy. Expression of CPE, but not of PC1/3 or PC2, enhanced proglucagon sorting to granules. siRNA-mediated knockdown of CPE disrupted regulated secretion of glucagon from pancreatic-derived alphaTC1-6 cells, but not of GLP-1 from intestinal cell-derived GLUTag cells. Mutation of the PC cleavage site K70R71, the dibasic R17R18 site within glucagon or the alpha-helix of glucagon, all significantly affected the sub-cellular localisation of proglucagon. Protein modelling revealed that alpha helices corresponding to glucagon, GLP-1 and GLP-2, are arranged within a disordered structure, suggesting some flexibility in the sorting mechanism. We conclude that there are multiple mechanisms for sorting proglucagon to the regulated secretory pathway, including a role for CPE in pancreatic alpha cells, initial cleavage at K70R71 and multiple sorting signals.
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Affiliation(s)
- Rebecca McGirr
- Metabolism and Diabetes and Imaging Programs, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, Canada
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McGirr R, McFarland MS, McTavish J, Luyt LG, Dhanvantari S. Design and characterization of a fluorescent ghrelin analog for imaging the growth hormone secretagogue receptor 1a. ACTA ACUST UNITED AC 2011; 172:69-76. [DOI: 10.1016/j.regpep.2011.08.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 08/17/2011] [Accepted: 08/23/2011] [Indexed: 01/11/2023]
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Ahmad N, Welch I, Grange R, Hadway J, Dhanvantari S, Hill D, Lee TY, Hoffman LM. Use of imaging biomarkers to assess perfusion and glucose metabolism in the skeletal muscle of dystrophic mice. BMC Musculoskelet Disord 2011; 12:127. [PMID: 21639930 PMCID: PMC3141608 DOI: 10.1186/1471-2474-12-127] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2011] [Accepted: 06/04/2011] [Indexed: 11/10/2022] Open
Abstract
Background Duchenne muscular dystrophy (DMD) is a severe neuromuscular disease that affects 1 in 3500 boys. The disease is characterized by progressive muscle degeneration that results from mutations in or loss of the cytoskeletal protein, dystrophin, from the glycoprotein membrane complex, thus increasing the susceptibility of contractile muscle to injury. To date, disease progression is typically assessed using invasive techniques such as muscle biopsies, and while there are recent reports of the use of magnetic resonance, ultrasound and optical imaging technologies to address the issue of disease progression and monitoring therapeutic intervention in dystrophic mice, our study aims to validate the use of imaging biomarkers (muscle perfusion and metabolism) in a longitudinal assessment of skeletal muscle degeneration/regeneration in two murine models of muscular dystrophy. Methods Wild-type (w.t.) and dystrophic mice (weakly-affected mdx mice that are characterized by a point mutation in dystrophin; severely-affected mdx:utrn-/- (udx) mice that lack functional dystrophin and are null for utrophin) were exercised three times a week for 30 minutes. To follow the progression of DMD, accumulation of 18 F-FDG, a measure of glucose metabolism, in both wild-type and affected mice was measured with a small animal PET scanner (GE eXplore Vista). To assess changes in blood flow and blood volume in the hind limb skeletal muscle, mice were injected intravenously with a CT contrast agent, and imaged with a small animal CT scanner (GE eXplore Ultra). Results In hind limb skeletal muscle of both weakly-affected mdx mice and in severely-affected udx mice, we demonstrate an early, transient increase in both 18F-FDG uptake, and in blood flow and blood volume. Histological analysis of H&E-stained tissue collected from parallel littermates demonstrates the presence of both inflammatory infiltrate and centrally-located nuclei, a classic hallmark of myofibrillar regeneration. In both groups of affected mice, the early transient response was succeeded by a progressive decline in muscle perfusion and metabolism; this was also evidenced histologically. Conclusions The present study demonstrates the utility of non-invasive imaging biomarkers in characterizing muscle degeneration/regeneration in murine models of DMD. These techniques may now provide a promising alternative for assessing both disease progression and the efficacy of new therapeutic treatments in patients.
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Affiliation(s)
- Nabeel Ahmad
- Imaging Program, Lawson Health Research Institute, 268 Grosvenor St., London N6A4V2, Canada
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Lee TK, Murthy SRK, Cawley NX, Dhanvantari S, Hewitt SM, Lou H, Lau T, Ma S, Huynh T, Wesley RA, Ng IO, Pacak K, Poon RT, Loh YP. An N-terminal truncated carboxypeptidase E splice isoform induces tumor growth and is a biomarker for predicting future metastasis in human cancers. J Clin Invest 2011; 121:880-92. [PMID: 21285511 DOI: 10.1172/jci40433] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 12/01/2010] [Indexed: 11/17/2022] Open
Abstract
Metastasis is a major cause of mortality in cancer patients. However, the mechanisms governing the metastatic process remain elusive, and few accurate biomarkers exist for predicting whether metastasis will occur, something that would be invaluable for guiding therapy. We report here that the carboxypeptidase E gene (CPE) is alternatively spliced in human tumors to yield an N-terminal truncated protein (CPE-ΔN) that drives metastasis. mRNA encoding CPE-ΔN was found to be elevated in human metastatic colon, breast, and hepatocellular carcinoma (HCC) cell lines. In HCC cells, cytosolic CPE-ΔN was translocated to the nucleus and interacted with histone deacetylase 1/2 to upregulate expression of the gene encoding neural precursor cell expressed, developmentally downregulated gene 9 (Nedd9)--which has been shown to promote melanoma metastasis. Nedd9 upregulation resulted in enhanced in vitro proliferation and invasion. Quantification of mRNA encoding CPE-ΔN in HCC patient samples predicted intrahepatic metastasis with high sensitivity and specificity, independent of cancer stage. Similarly, high CPE-ΔN mRNA copy numbers in resected pheochromocytomas/paragangliomas (PHEOs/PGLs), rare neuroendocrine tumors, accurately predicted future metastasis or recurrence. Thus, CPE-ΔN induces tumor metastasis and should be investigated as a potentially powerful biomarker for predicting future metastasis and recurrence in HCC and PHEO/PGL patients.
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Affiliation(s)
- Terence K Lee
- Department of Surgery, University of Hong Kong, Pokfulam, Hong Kong, China
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Goldhawk DE, Lemaire C, McCreary CR, McGirr R, Dhanvantari S, Thompson RT, Figueredo R, Koropatnick J, Foster P, Prato FS. Magnetic Resonance Imaging of Cells Overexpressing MagA, an Endogenous Contrast Agent for Live Cell Imaging. Mol Imaging 2009. [DOI: 10.2310/7290.2009.00006] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular imaging with magnetic resonance imaging (MRI) may benefit from the ferrimagnetic properties of magnetosomes, membrane-enclosed iron biominerals whose formation in magnetotactic bacteria is encoded by multiple genes. One such gene is MagA, a putative iron transporter. We have examined expression of MagA in mouse neuroblastoma N2A cells and characterized their response to iron loading and cellular imaging by MRI. MagA expression augmented both Prussian blue staining and the elemental iron content of N2A cells, without altering cell proliferation, in cultures grown in the presence of iron supplements. Despite evidence for iron incorporation in both MagA and a variant, MagAE137V, only MagA expression produced intracellular contrast detectable by MRI at 11 Tesla. We used this stable expression system to model a new sequence for cellular imaging with MRI, using the difference between gradient and spin echo images to distinguish cells from artifacts in the field of view. Our results show that MagA activity in mammalian cells responds to iron supplementation and functions as a contrast agent that can be deactivated by a single point mutation. We conclude that MagA is a candidate MRI reporter gene that can exploit more fully the superior resolution of MRI in noninvasive medical imaging.
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Affiliation(s)
- Donna E. Goldhawk
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Claude Lemaire
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Cheryl R. McCreary
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Rebecca McGirr
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Savita Dhanvantari
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - R. Terry Thompson
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Rene Figueredo
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Jim Koropatnick
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Paula Foster
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
| | - Frank S. Prato
- From the Imaging and Diabetes and Metabolism Programs, Lawson Health Research Institute, St. Joseph's Health Care, London, ON; Department of Physics and Astronomy, University of Waterloo, Waterloo, ON; Hotchkiss Brain Institute, University of Calgary, Calgary, AB; Departments of Medical Biophysics, Pathology and Medicine, and Medical Imaging, University of Western Ontario, London, ON; London Regional Cancer Program, London, ON; and Robarts Research Institute, University of Western Ontario, London, ON
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Goldhawk DE, Lemaire C, McCreary CR, McGirr R, Dhanvantari S, Thompson RT, Figueredo R, Koropatnick J, Foster P, Prato FS. Magnetic resonance imaging of cells overexpressing MagA, an endogenous contrast agent for live cell imaging. Mol Imaging 2009; 8:129-139. [PMID: 19723470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023] Open
Abstract
Molecular imaging with magnetic resonance imaging (MRI) may benefit from the ferrimagnetic properties of magnetosomes, membrane-enclosed iron biominerals whose formation in magnetotactic bacteria is encoded by multiple genes. One such gene is MagA, a putative iron transporter. We have examined expression of MagA in mouse neuroblastoma N2A cells and characterized their response to iron loading and cellular imaging by MRI. MagA expression augmented both Prussian blue staining and the elemental iron content of N2A cells, without altering cell proliferation, in cultures grown in the presence of iron supplements. Despite evidence for iron incorporation in both MagA and a variant, MagAE137V, only MagA expression produced intracellular contrast detectable by MRI at 11 Tesla. We used this stable expression system to model a new sequence for cellular imaging with MRI, using the difference between gradient and spin echo images to distinguish cells from artifacts in the field of view. Our results show that MagA activity in mammalian cells responds to iron supplementation and functions as a contrast agent that can be deactivated by a single point mutation. We conclude that MagA is a candidate MRI reporter gene that can exploit more fully the superior resolution of MRI in noninvasive medical imaging.
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Affiliation(s)
- Donna E Goldhawk
- Imaging Program, Lawson Health Research Institute, St. Joseph's Health Care, London, ON.
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Tai JH, Nguyen B, Wells RG, Kovacs MS, McGirr R, Prato FS, Morgan TG, Dhanvantari S. Imaging of Gene Expression in Live Pancreatic Islet Cell Lines Using Dual-Isotope SPECT. J Nucl Med 2007; 49:94-102. [DOI: 10.2967/jnumed.107.043430] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Tai JH, Foster P, Rosales A, Feng B, Hasilo C, Martinez V, Ramadan S, Snir J, Melling CWJ, Dhanvantari S, Rutt B, White DJG. Imaging islets labeled with magnetic nanoparticles at 1.5 Tesla. Diabetes 2006; 55:2931-8. [PMID: 17065328 DOI: 10.2337/db06-0393] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
We have developed a magnetic resonance imaging (MRI) technique for imaging Feridex (superparamagnetic iron oxide [SPIO])-labeled islets of Langerhans using a standard clinical 1.5-Tesla (T) scanner and employing steady-state acquisition imaging sequence (3DFIESTA). Both porcine and rat islets were labeled with SPIO by a transfection technique using a combination of poly-l-lysine and electroporation. Electron microscopy demonstrated presence of SPIO particles within the individual islet cells, including beta-cells and particles trapped between cell membranes. Our labeling method produced a transfection rate of 860 pg to 3.4 ng iron per islet, dependent on the size of the islet. The labeling procedure did not disrupt either the function or viability of the islets. In vitro 3DFIESTA magnetic resonance images of single-labeled islets corresponded with their optical images. In vivo T2*-weighted scan using 1.5 T detected as few as 200 SPIO-labeled islets transplanted under rat kidney capsule, which correlated with immunohistochemistry of the transplant for insulin and iron. Ex vivo 3DFIESTA images of kidneys containing 200, 800 or 2,000 SPIO-labeled islet isografts showed good correlation between signal loss and increasing numbers of islets. These data provide evidence that islets can be labeled with SPIO and imaged using clinically available 1.5- T MRI.
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Affiliation(s)
- Joo Ho Tai
- FRCPath, Novartis/Stiller Professor of Xenotransplantation, Robarts Research Institute, Room 200, SDRI Building, University of Western Ontario, 1400 Western Rd., London, Ontario, Canada
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41
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Abstract
We have investigated the effects of chronically elevated glucose concentrations on the pancreatic alpha-cell line alphaTC1-6. We show that basal glucagon secretion and proglucagon gene expression were increased in response to high glucose levels. The extent of acute stimulated secretion of glucagon was also increased in response to high glucose, as was the transcription of the prohormone processing enzymes PC1/3 and PC2. The secretion of GLP-1, a proglucagon-derived peptide produced by cleavage of proglucagon by PC1/3, was also increased in response to high glucose. Gene expression profiling experiments showed that a number of components of the regulated secretory pathway were up-regulated at high glucose concentrations, including processing enzymes and exocytotic proteins. Immunoblot analysis showed that the expression of the exocytotic SNARE proteins, as well as that of PC1/3, chromogranin A, and 7B2, were all increased after chronic exposure to high glucose levels. Immunocytochemistry showed no changes in the expression of the mature alpha-cell markers glucagon and brn-4 and no induction of the immature alpha-cell marker pdx-1. We conclude that chronically elevated glucose concentrations up-regulate the regulated secretory response of the alpha-cell.
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Affiliation(s)
- Rebecca McGirr
- Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, Canada N6A 4V2
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42
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Arnaoutova I, Smith AM, Coates LC, Sharpe JC, Dhanvantari S, Snell CR, Birch NP, Loh YP. The prohormone processing enzyme PC3 is a lipid raft-associated transmembrane protein. Biochemistry 2003; 42:10445-55. [PMID: 12950171 DOI: 10.1021/bi034277y] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The biosynthesis of most biologically active peptides involves the action of prohomone convertases, including PC3 (also known as PC1), that catalyze limited proteolysis of precursor proteins. Proteolysis of prohormones occurs mainly in the granules of the regulated secretory pathway. It has been proposed that the targeting of these processing enzymes to secretory granules involves their association with lipid rafts in granule membranes. We now provide evidence for the interaction of the 86 and 64 kDa forms of PC3 with secretory granule membranes. Furthermore, both forms of PC3 were resistant to extraction with TX-100, were floated to low-density fractions in sucrose gradients, and were partially extracted upon cholesterol depletion by methyl-beta-cyclodextrin, indicating that they were associated with lipid rafts in the membranes. Protease protection assays, immunolabeling, and biotinylation of proteins in intact secretory granules identified an approximately 115-residue cytoplasmic tail for 86 kDa PC3. Using two-dimensional gel electrophoresis and a specific antibody, a novel, raft-associated form of 64 kDa PC3 that contains a transmembrane domain consisting of residues 619-638 was identified. This form was designated as 64 kDa PC3-TM, and differs from the 64 kDa mature form of PC3. We present a model of the membrane topology of PC3, where it is anchored to lipid rafts in secretory granule membranes via the transmembrane domain. We demonstrate that the transmembrane domain of PC3 alone was sufficient to target the extracellular domain of the IL2 receptor alpha-subunit (Tac) to secretory granules.
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Affiliation(s)
- Irina Arnaoutova
- Section on Cellular Neurobiology, Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4480, USA
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43
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Dhanvantari S, Shen FS, Adams T, Snell CR, Zhang C, Mackin RB, Morris SJ, Loh YP. Disruption of a receptor-mediated mechanism for intracellular sorting of proinsulin in familial hyperproinsulinemia. Mol Endocrinol 2003; 17:1856-67. [PMID: 12829804 DOI: 10.1210/me.2002-0380] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In familial hyperproinsulinemia, specific mutations in the proinsulin gene are linked with a profound increase in circulating plasma proinsulin levels. However, the molecular and cellular basis for this disease remains uncharacterized. Here we investigated how these mutations may disrupt the sorting signal required to target proinsulin to the secretory granules of the regulated secretory pathway, resulting in the unregulated release of proinsulin. Using a combination of molecular modeling and site-directed mutagenesis, we have identified structural molecular motifs in proinsulin that are necessary for correct sorting into secretory granules of endocrine cells. We show that membrane carboxypeptidase E (CPE), previously identified as a prohormone-sorting receptor, is essential for proinsulin sorting. This was demonstrated through short interfering RNA-mediated depletion of CPE and transfection with a dominant negative mutant of CPE in a beta-cell line. Mutant proinsulins found in familial hyperproinsulinemia failed to bind to CPE and were not sorted efficiently. These findings provide evidence that the elevation of plasma proinsulin levels found in patients with familial hyperproinsulinemia is caused by the disruption of CPE-mediated sorting of mutant proinsulins to the regulated secretory pathway.
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Affiliation(s)
- Savita Dhanvantari
- Section on Cellular Neurobiology, National Institutes of Health, Bethesda, Maryland 20892-4480, USA
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44
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Zhang CF, Dhanvantari S, Lou H, Loh YP. Sorting of carboxypeptidase E to the regulated secretory pathway requires interaction of its transmembrane domain with lipid rafts. Biochem J 2003; 369:453-60. [PMID: 12403651 PMCID: PMC1223124 DOI: 10.1042/bj20020827] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2002] [Revised: 10/24/2002] [Accepted: 10/29/2002] [Indexed: 11/17/2022]
Abstract
Carboxypeptidase E (CPE) functions as a regulated secretory pathway sorting receptor for several prohormones, including pro-opiomelanocortin (POMC), proenkephalin and proinsulin. The association of CPE with lipid rafts in the trans -Golgi network and secretory granule membranes is necessary for its sorting receptor function. We now provide evidence that a domain within the C-terminal 25 residues of CPE functions as a signal for both raft association and the sorting of CPE to the regulated secretory pathway. A fusion protein containing the extracellular domain of the human interleukin-2 receptor Tac (N-Tac) and the C-terminal 25 amino acids of CPE was transfected into Neuro2A cells. This fusion protein floated in sucrose density gradients, indicating raft association, and co-localized with chromogranin A (CGA), a secretory granule marker. To define further a minimum sequence required for raft association and sorting, deletion mutants of CPE that lacked the C-terminal four or 15 residues (CPE-Delta4 and CPE-Delta15 respectively) were transfected into a clone of CPE-deficient Neuro2A cells. In contrast with full-length CPE, neither CPE-Delta4 nor CPE-Delta15 floated in sucrose density gradients. The sorting of both CPE-Delta4 and CPE-Delta15 to the regulated secretory pathway was impaired, as indicated by significantly increased basal secretion and a lack of response to stimulation. Additionally, there was a significant decrease in the co-localization of mutant CPE immunofluorescence with CGA when compared with full-length CPE. Finally, the sorting of the prohormone POMC to the regulated pathway was impaired in cells transfected with either CPE-Delta4 or CPE-Delta15. We conclude that the sorting of CPE to the regulated secretory pathway in endocrine cells is mediated by lipid rafts, and that the C-terminal four residues of CPE, i.e. Thr(431)-Leu-Asn-Phe(434), are required for raft association and sorting.
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Affiliation(s)
- Chun-Fa Zhang
- Section on Cellular Neurobiology, Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4480, USA
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45
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Dhanvantari S, Arnaoutova I, Snell CR, Steinbach PJ, Hammond K, Caputo GA, London E, Loh YP. Carboxypeptidase E, a prohormone sorting receptor, is anchored to secretory granules via a C-terminal transmembrane insertion. Biochemistry 2002; 41:52-60. [PMID: 11772002 DOI: 10.1021/bi015698n] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Carboxypeptidase E (CPE) is a sorting receptor that directs the prohormone pro-opiomelanocortin (POMC) to the regulated secretory pathway, and is also a prohormone processing enzyme in neuro/endocrine cells. It has been suggested that the 25 C-terminal amino acids are necessary for the binding of CPE to secretory granule membranes, but its orientation in the membrane is not known. In this study, we examined the structure and orientation of the membrane-binding domain at the C-terminus of CPE. In vitro experiments using model membranes demonstrated that the last 22 amino acids of CPE (CP peptide) insert in a shallow orientation into lipid bilayers at low pH. Circular dichroism analysis indicated that the CP peptide adopts a partial alpha-helical configuration at low pH, and helix content increases when it is bound to lipid. Protease protection experiments, immunolabeling, and immunoisolation of intact secretory granules with a C-terminal antibody revealed a cytoplasmic domain in CPE, consistent with a transmembrane orientation of this protein. We conclude that the membrane-binding domain of CPE must adopt an alpha-helical configuration to bind to lipids, and that CPE may require another integral membrane "chaperone" protein to insert through the lipid bilayer in a transmembrane fashion.
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Affiliation(s)
- Savita Dhanvantari
- Section on Cellular Neurobiology, Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4480, USA
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46
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Dhanvantari S, Izzo A, Jansen E, Brubaker PL. Coregulation of glucagon-like peptide-1 synthesis with proglucagon and prohormone convertase 1 gene expression in enteroendocrine GLUTag cells. Endocrinology 2001; 142:37-42. [PMID: 11145564 DOI: 10.1210/endo.142.1.7870] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The insulinotropic hormone glucagon-like peptide-1 (GLP-1) is synthesized in the intestinal L cell by prohormone convertase 1 (PC1)-mediated posttranslational processing of proglucagon. Previous studies have demonstrated that proglucagon gene transcription in the L cell is stimulated by the protein kinase A (PKA) pathway through a cAMP response element (CRE). Because the PC1 gene contains two functional CREs, the present studies were conducted to investigate whether the PC1 and proglucagon genes are coregulated by PKA, and to elucidate the temporal relationship(s) of PC1 and proglucagon gene expression with production of GLP-1, in the intestinal cell. The GLUTag enteroendocrine cell line, which is known to express the proglucagon gene and to synthesize and secrete GLP-1, was used as a model. Proglucagon and PC1 messenger RNA transcript levels were both increased after 12 h (but not 24 h) of treatment of GLUTag cells with forskolin/isobutylmethylxanthine (IBMX), by 2.7 +/- 0.3- and 2.4 +/- 0.3-fold, respectively, compared with controls (P < 0.01-0.001). Activation of PKA resulted in a 2.1 +/- 0.1-fold increase in PC1 reporter construct expression (P < 0.001) at 12 h, which was dependent on the presence of the CRE, and a 13- to 24-fold increment in PC1 protein levels (P < 0.01) at 12 and 24 h. Similarly, forskolin/IBMX increased secretion of GLP-1, by 1.8 +/- 0.2- and 2.2 +/- 0.6-fold at 12 and 24 h, respectively (P < 0.05-0.01). Although the cell content of GLP-1 was diminished after 12 h of treatment (P < 0.001), GLP-1 levels increased back to control values after 24 h of forskolin/IBMX treatment (P < 0.01 vs. 12-h levels). Thus, PKA-induced secretion of GLP-1 from the L cell is followed by restoration of the cellular peptide levels through a PKA-mediated, CRE-dependent up-regulation of proglucagon and PC1 gene expression.
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Affiliation(s)
- S Dhanvantari
- Section on Cellular Neurobiology Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
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47
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Dhanvantari S, Loh YP. Lipid raft association of carboxypeptidase E is necessary for its function as a regulated secretory pathway sorting receptor. J Biol Chem 2000; 275:29887-93. [PMID: 10896946 DOI: 10.1074/jbc.m005364200] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Membrane carboxypeptidase E (CPE) is a sorting receptor for targeting prohormones, such as pro-opiomelanocortin, to the regulated secretory pathway in endocrine cells. Its membrane association is necessary for it to bind a prohormone sorting signal at the trans-Golgi network (TGN) to facilitate targeting. In this study, we examined the lipid interaction of CPE in bovine pituitary secretory granule membranes, which are derived from the TGN. We show that CPE is associated with detergent-resistant lipid domains, or rafts, within secretory granule membranes. Lipid analysis revealed that these rafts are enriched in glycosphingolipids and cholesterol. Pulse-chase and subcellular fractionation experiments in AtT-20 cells show that the association of CPE with membrane rafts occurred only after it reached the Golgi. Cholesterol depletion resulted in dissociation of CPE from secretory granule membranes and decreased the binding of prohormones to membranes. In vivo cholesterol depletion using lovastatin resulted in the lack of sorting of CPE and its cargo to the regulated secretory pathway. We propose that the sorting receptor function of CPE necessitates its interaction with glycosphingolipid-cholesterol rafts at the TGN, thereby anchoring it in position to bind to its prohormone cargo.
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Affiliation(s)
- S Dhanvantari
- Section on Cellular Neurobiology, Laboratory of Developmental Neurobiology, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA
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48
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Abstract
Proglucagon (proG) is differentially processed in the A cells of the pancreas to yield glucagon, and in the L cells of the intestine to generate glicentin, oxyntomodulin, the incretin glucagon-like peptide (GLP)-1(7-36NH2) and the intestinotropin GLP-2. To establish roles for the prohormone convertases PC1 and PC2 in proG processing within the context of a physiological model, we created stable cell lines from an islet-derived cell line, InR1-G9. These cells express proG and PC2, but not PC1, messenger RNA (mRNA). InR1-G9 cells were stably transfected with PC1 or antisense PC2. Selection was carried out in G418 (InR1-G9/PC1) or Zeocin (InR1-G9/ASPC2). Both PC1 mRNA and protein were highly expressed in InR1-G9/PC1 cells (P < 0.01-0.001) compared with wild-type (WT) cells. Cells transfected with ASPC2 demonstrated significant decreases in both PC2 mRNA (P < 0.001) and protein (P < 0.05) levels. ProG-derived peptides in WT, control, InR1-G9/PC1, and InR1-G9/ASPC2 cells were identified by HPLC and RIA. Overexpression of PC1 in InR1-G9 cells resulted in increased processing to glicentin (P < 0.01), oxyntomodulin (P < 0.05), and GLP-2 (P < 0.05). Interestingly, processing to GLP-1(7-36NH2) did not increase upon transfection of PC1. Transfection of InR1-G9 cells with ASPC2 resulted in the disappearance of glicentin (P < 0.05). However, production of glucagon was not altered by antisense deletion of PC2. Surprisingly, GLP-1(7-36NH2) production appeared to be augmented (P < 0.05) in InR1-G9/ASPC2 cells, whereas GLP-2 production was not altered. In conclusion, these studies establish the role of PC1 in the processing of proG to the intestinal proG-derived peptides. This study also establishes a role for PC2 in the production of glicentin; however, the liberation of glucagon appears to be mediated by another, yet to be identified, convertase.
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Affiliation(s)
- S Dhanvantari
- Department of Physiology, University of Toronto, Ontario, Canada
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49
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Fischer KD, Dhanvantari S, Drucker DJ, Brubaker PL. Intestinal growth is associated with elevated levels of glucagon-like peptide 2 in diabetic rats. Am J Physiol 1997; 273:E815-20. [PMID: 9357813 DOI: 10.1152/ajpendo.1997.273.4.e815] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Glucagon-like peptide 2 (GLP-2) has recently been identified as a novel intestinal growth factor. Because experimental diabetes is associated with bowel growth, we examined the relationship between GLP-2 and intestinal growth in rats made diabetic by streptozotocin (STZ) injection and treated with or without insulin for 3 wk. Ileal concentrations of the intestinal proglucagon-derived peptides, i.e., glicentin + oxyntomodulin, and GLPs 1 and 2, were increased by 57 +/- 20% above those of controls in untreated STZ diabetes (P < 0.05-0.001). Similar increases in plasma concentrations of glicentin + oxyntomodulin (77 +/- 15% above controls, P < 0.01) and GLP-2 (91 +/- 32% above controls, P < 0.05) were seen in untreated STZ diabetes. Both wet and dry small intestinal weight increased by 74 +/- 20% above controls (P < 0.01) in STZ diabetes, and macromolecular analysis indicated parallel increases in both protein (P < 0.001) and lipid (P < 0.05) content. Villus height (P < 0.001) and crypt depth (P < 0.01) were also increased in untreated diabetic rat intestine. Insulin therapy prevented the changes in plasma GLP-2 and intestinal mass seen in untreated STZ diabetes. Thus STZ diabetes is associated with both increased production of GLP-2 and enhanced bowel weight, thereby suggesting a role for GLP-2 in diabetes-associated bowel growth.
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Affiliation(s)
- K D Fischer
- Department of Physiology, The Toronto Hospital, University of Toronto, Ontario, Canada
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50
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Abstract
To investigate the factors involved in the post-translational processing of proglucagon, we have examined the proglucagon-derived peptides (PGDPs) expressed in normal mouse pancreas and intestine, as well as in both islet (InR1-G9, RIN 1056A) and intestinal (STC-1) cell lines. N-terminal proglucagon processing was similar to that of normal mouse pancreas in InR1-G9 cells, but differed in RIN 1056A and STC-1 cells, which contained significant amounts of glucagon as well as the intestinal PGDPs, glicentin and oxyntomodulin. The C-terminal end of proglucagon was processed to small amounts of glucagon-like peptide-1 in InR1-G9 and RIN 1056A cells, as in normal pancreas, while processing was more extensive in both STC-1 cells and normal intestine. Northern blot analysis of mRNA transcripts for the prohormone convertases, PC1 and PC2, in the 3 cell lines demonstrated correlations between PC2 and the presence of glucagon, as well as between PC1 and production of the intestinal PGDPs. These findings provide support for the suggestion that PC1 and PC2 play roles in the tissue-specific post-translational processing of proglucagon.
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Affiliation(s)
- J D Tucker
- Department of Physiology, University of Toronto, Ontario, Canada
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