Seven mutations in the human insulin gene linked to permanent neonatal/infancy-onset diabetes mellitus
Carlo Colombo, … , Fabrizio Barbetti, the Early Onset Diabetes Study Group of the Italian Society of Pediatric Endocrinology and Diabetes (SIEDP)
Carlo Colombo, … , Fabrizio Barbetti, the Early Onset Diabetes Study Group of the Italian Society of Pediatric Endocrinology and Diabetes (SIEDP)
Published May 1, 2008
Citation Information: J Clin Invest. 2008;118(6):2148-2156. https://doi.org/10.1172/JCI33777.
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Research Article Metabolism

Seven mutations in the human insulin gene linked to permanent neonatal/infancy-onset diabetes mellitus

Abstract

Permanent neonatal diabetes mellitus (PNDM) is a rare disorder usually presenting within 6 months of birth. Although several genes have been linked to this disorder, in almost half the cases documented in Italy, the genetic cause remains unknown. Because the Akita mouse bearing a mutation in the Ins2 gene exhibits PNDM associated with pancreatic β cell apoptosis, we sequenced the human insulin gene in PNDM subjects with unidentified mutations. We discovered 7 heterozygous mutations in 10 unrelated probands. In 8 of these patients, insulin secretion was detectable at diabetes onset, but rapidly declined over time. When these mutant proinsulins were expressed in HEK293 cells, we observed defects in insulin protein folding and secretion. In these experiments, expression of the mutant proinsulins was also associated with increased Grp78 protein expression and XBP1 mRNA splicing, 2 markers of endoplasmic reticulum stress, and with increased apoptosis. Similarly transfected INS-1E insulinoma cells had diminished viability compared with those expressing WT proinsulin. In conclusion, we find that mutations in the insulin gene that promote proinsulin misfolding may cause PNDM.

Authors

Carlo Colombo, Ottavia Porzio, Ming Liu, Ornella Massa, Mario Vasta, Silvana Salardi, Luciano Beccaria, Carla Monciotti, Sonia Toni, Oluf Pedersen, Torben Hansen, Luca Federici, Roberta Pesavento, Francesco Cadario, Giorgio Federici, Paolo Ghirri, Peter Arvan, Dario Iafusco, Fabrizio Barbetti

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Figure 7

Grp78 expression.

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Grp78 expression. Western blot with anti-Grp78 primary antibody in HEK29...
Western blot with anti-Grp78 primary antibody in HEK293 cells transfected with WT and mutated insulin. Cytoplasmic fractions were collected at 9, 16, and 24 h after transfection. Expression of β-tubulin was assessed on the same filters to normalize the amount of loaded proteins. Increased Grp78 protein expression was clearly visible at 9 and 16 h for mutations LB15YB16delinsH and CA6Y and at 24 h for mutations LB6P and LB11P.