posted on 2021-08-23, 13:39authored bySam G. Galvin, Richard G. Kay, Rachel Foreman, Pierre Larraufie, Claire L. Meek, Emma Biggs, Peter Ravn, Lutz Jermutus, Frank Reimann, Fiona M. Gribble
To characterize the
impact of metabolic disease on the peptidome
of human and mouse pancreatic islets, LC-MS was used to analyze extracts
of human and mouse islets, purified mouse alpha, beta, and delta cells,
supernatants from mouse islet incubations, and plasma from patients
with type 2 diabetes. Islets were obtained from healthy and type 2
diabetic human donors, and mice on chow or high fat diet. All major
islet hormones were detected in lysed islets as well as numerous peptides
from vesicular proteins including granins and processing enzymes.
Glucose-dependent insulinotropic peptide (GIP) was not detectable.
High fat diet modestly increased islet content of proinsulin-derived
peptides in mice. Human diabetic islets contained increased content
of proglucagon-derived peptides at the expense of insulin, but no
evident prohormone processing defects. Diabetic plasma, however, contained
increased ratios of proinsulin and des-31,32-proinsulin to insulin.
Active GLP-1 was detectable in human and mouse islets but 100–1000-fold
less abundant than glucagon. LC-MS offers advantages over antibody-based
approaches for identifying exact peptide sequences, and revealed a
shift toward islet insulin production in high fat fed mice, and toward
proglucagon production in type 2 diabetes, with no evidence of systematic
defective prohormone processing.