PROJECT SUMMARY
Longitudinal studies have shown that individuals at high genetic risk for type 1 diabetes (T1D) progress through
several distinct stages prior to the onset of clinical symptoms. Although the factors causally involved in the rate
of progression are poorly understood, the presence of islet autoantibodies (AAb) is currently the best biomarker
for the future onset of hyperglycemia in T1D. In particular, the single AAb+ stage (generally against glutamic
acid decarboxylase (GADA+)) represents a key window for intervention to delay or prevent progression to T1D.
Our recent study on pancreatic islets isolated from GADA+ donors revealed early a-cell dysfunction while ß-cell
mass and function are still normal. Specifically, GADA+ donor islets with normal glucose stimulated insulin
secretion have already demonstrable defects in glucose suppression of glucagon secretion (GSGS). This defect
of GADA+ donors is even more severe in T1D donor islets indicating progressive loss of GSGS. Our previous
study showed that this a-cell dysfunction could be related to elevated cAMP signaling and/or decreased glucose
metabolism. Specifically, transcriptomic analysis identified key genes as downregulated in GADA+ donors:
Protein Kinase Inhibitor Beta (PKIB, a potent PKA inhibitor), glucokinase (GCK), and genes encoding subunits
of mitochondrial complex I. Based on these data, we propose here to test the hypothesis that decreased GSGS
during the progression of T1D is causally related to altered cAMP signaling and/or dysregulated bioenergetics
in a-cells. We have devised two Aims to test this hypothesis. In Aim 1 we will position the cAMP signaling defect
by direct measurements of cAMP in human islets; modification of intracellular cAMP levels using general and
PKA- and EPAC-specific analogues; selective reduction of PKIB expression in a-cells; and assessment of
electrophysiological changes due to cAMP modulation. In Aim 2 we will explore the role of bioenergetics by
evaluation of glycolysis and oxidative phosphorylation in intact donor islets and assessment of changes in GSGS
due to drug-induced modulation of GCK and complex I activity. The proposed experiments will elucidate
mechanisms underlying the specific defects in a-cell function during the progression of T1D.