Discovery of Novel Glucose-Regulated Proteins in Isolated Human Pancreatic Islets Using LC–MS/MS-Based Proteomics

The prevalence of diabetes mellitus is increasing dramatically
throughout the world, and the disease has become a major public health
issue. The most common form of the disease, type 2 diabetes, is characterized
by insulin resistance and insufficient insulin production from the
pancreatic beta-cell. Since glucose is the most potent regulator of
beta-cell function under physiological conditions, identification
of the insulin secretory defect underlying type 2 diabetes requires
a better understanding of glucose regulation of human beta-cell function.
To this aim, a bottom-up LC–MS/MS-based proteomics approach
was used to profile pooled islets from multiple donors under basal
(5 mM) or high (15 mM) glucose conditions. Our analysis discovered
256 differentially abundant proteins (∼p <
0.05) after 24 h of high glucose exposure from more than 4500 identified
in total. Several novel glucose-regulated proteins were elevated under
high glucose conditions, including regulators of mRNA splicing (pleiotropic
regulator 1), processing (retinoblastoma binding protein 6), and function
(nuclear RNA export factor 1), in addition to neuron navigator 1 and
plasminogen activator inhibitor 1. Proteins whose abundances markedly
decreased during incubation at 15 mM glucose included Bax inhibitor
1 and synaptotagmin-17. Up-regulation of dicer 1 and SLC27A2 and down-regulation
of phospholipase Cβ4 were confirmed by Western blots. Many proteins
found to be differentially abundant after high glucose stimulation
are annotated as uncharacterized or hypothetical. These findings expand
our knowledge of glucose regulation of the human islet proteome and
suggest many hitherto unknown responses to glucose that require additional
studies to explore novel functional roles.