Insulin gene mutations resulting in early-onset diabetes: Marked differences in clinical presentation, metabolic status, and pathogenic effect through endoplasmic reticulum retention

Gargi Meur, Albane Simon, Nasret Harun, Marie Virally, Aurélie Dechaume, Amélie Bonnefond, Sabrina Fetita, Andrei I. Tarasov, Pierre Jean Guillausseau, Trine Welløv Boesgaard, Oluf Pedersen, Torben Hansen, Michel Polak, Jean François Gautier, Philippe Froguel, Guy A. Rutter, Martine Vaxillaire

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Abstract

OBJECTIVE - Heterozygous mutations in the human preproinsulin (INS) gene are a cause of nonsyndromic neonatal or early-infancy diabetes. Here, we sought to identify INS mutations associated with maturity-onset diabetes of the young (MODY) or nonautoimmune diabetes in mid-adult life, and to explore the molecular mechanisms involved. RESEARCH DESIGN AND METHODS - The INS gene was sequenced in 16 French probands with unexplained MODY, 95 patients with nonautoimmune early-onset diabetes (diagnosed at <35 years) and 292 normoglycemic control subjects of French origin. Three identified insulin mutants were generated by site-directed mutagenesis of cDNA encoding a preproinsulin-green fluorescent protein (GFP) (C-peptide) chimera. Intracellular targeting was assessed in clonal β-cells by immunocytochemistry and proinsulin secretion, by radioimmunoassay. Spliced XBP1 and C/EBP homologous protein were quantitated by real-time PCR. RESULTS - A novel coding mutation, L30M, potentially affecting insulin multimerization, was identified in five diabetic individuals (diabetes onset 17-36 years) in a single family. L30M preproinsulin-GFP fluorescence largely associated with the endoplasmic reticulum (ER) in MIN6 β-cells, and ER exit was inhibited by ∼50%. Two additional mutants, R55C (at the B/C junction) and R6H (in the signal peptide), were normally targeted to secretory granules, but nonetheless caused substantial ER stress. CONCLUSIONS - We describe three INS mutations cosegregating with early-onset diabetes whose clinical presentation is compatible with MODY. These led to the production of (pre)proinsulin molecules with markedly different trafficking properties and effects on ER stress, demonstrating a range of molecular defects in the β-cell.

Original languageEnglish
Pages (from-to)653-661
Number of pages9
JournalDiabetes
Volume59
Issue number3
DOIs
Publication statusPublished - 1 Mar 2010

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