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Transl Res. 2019 Nov;213:90-99. doi: 10.1016/j.trsl.2019.08.001. Epub 2019 Aug 9.

Abnormalities in proinsulin processing in islets from individuals with longstanding T1D.

Author information

1
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana; Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine, Indianapolis, Indiana. Electronic address: eksims@iu.edu.
2
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana; Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine, Indianapolis, Indiana.
3
Departments of Microbiology and Molecular Cell Biology, Eastern Virginia Medical School, Norfolk, Virginia.
4
Diabetes Clinical Research Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington.
5
Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical Center, Ann Arbor, Michigan.
6
Department of Internal Medicine, Eastern Virginia Medical School, Norfolk, Virginia.
7
Department of Surgery, Cardiovascular Innovation Institute, University of Louisville, Louisville, Kentucky.
8
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana; Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine, Indianapolis, Indiana; The Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana; Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana.
9
Department of Internal Medicine, Eastern Virginia Medical School, Norfolk, Virginia; Departments of Medicine and Pharmacology, New York Medical College.
10
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana; Indiana Biosciences Research Institute, Indianapolis, Indiana.
11
Center for Diabetes and Metabolic Diseases, Indiana University School of Medicine, Indianapolis, Indiana; The Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana; Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana; Roudebush VA Medical Center, Indianapolis, Indiana. Electronic address: cevansmo@iu.edu.

Abstract

We recently described the persistence of detectable serum proinsulin in a large majority of individuals with longstanding type 1 diabetes (T1D), including individuals with undetectable serum C-peptide. Here, we sought to further explore the mechanistic etiologies of persistent proinsulin secretion in T1D at the level of the islet, using tissues obtained from human donors. Immunostaining for proinsulin and insulin was performed on human pancreatic sections from the Network for Pancreatic Organ Donors with Diabetes (nPOD) collection (n = 24). Differential proinsulin processing enzyme expression was analyzed using mass spectrometry analysis of human islets isolated from pancreatic sections with laser capture microdissection (n = 6). Proinsulin processing enzyme mRNA levels were assessed using quantitative real-time PCR in isolated human islets (n = 10) treated with or without inflammatory cytokines. Compared to nondiabetic controls, immunostaining among a subset (4/9) of insulin positive T1D donor islets revealed increased numbers of cells with proinsulin-enriched, insulin-poor staining. T1D donor islets also exhibited increased proinsulin fluorescence intensity relative to insulin fluorescence intensity. Laser capture microdissection followed by mass spectrometry revealed reductions in the proinsulin processing enzymes prohormone convertase 1/3 (PC1/3) and carboxypeptidase E (CPE) in T1D donors. Twenty-four hour treatment of human islets with inflammatory cytokines reduced mRNA expression of the processing enzymes PC1/3, PC2, and CPE. Taken together, these data provide new mechanistic insight into altered proinsulin processing in long-duration T1D and suggest that reduced β cell prohormone processing is associated with proinflammatory cytokine-induced reductions in proinsulin processing enzyme expression.

KEYWORDS:

CPE = carboxypeptidase E; ER = endoplasmic reticulum; IR = infrared; LCM = laser capture microdissection; LFQ = label-free quantification; PC1/3 = prohormone convertase 1/3; PC2 = prohormone convertase 2; T1D = type 1 diabetes; UV = ultraviolet; nPOD = network for pancreatic organ donors with type 1 diabetes

PMID:
31442418
PMCID:
PMC6783367
[Available on 2020-11-01]
DOI:
10.1016/j.trsl.2019.08.001

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