PROJECT SUMMARY/ABSTRACT
In treating type 2 diabetes (T2D), there is a paucity of medications simultaneously targeting deficits in both
ß-cell function and mass. Angiotensin(1-7), a metabolite of the renin-angiotensin system, may fill this gap;
however, its underlying mechanisms of action are incompletely understood. Our data reveal that the
insulinotropic action of angiotensin(1-7) is dependent on its hydrolysis to the dipeptide, angiotensin(1-2), the
latter also conveying pro-survival and proliferative effects in ß cells. Angiotensin(1-2) activates G-protein-
coupled receptor family C group 6 member A (GPRC6A), which we show is expressed in islet a cells. Further,
angiotensin(1-2) increases a cell-derived glucagon-like peptide-1 (GLP-1) release, suggesting it acts via
GPRC6A on the a cell to promote insulin secretion in a paracrine fashion. Indeed, in GLP-1 receptor deficient
islets, we find that angiotensin(1-2) fails to potentiate insulin secretion; however, its ability to enhance ß-cell
survival and proliferation is retained. The latter suggests angiotensin(1-2)’s action is, in part, GLP-1 receptor-
independent. Based on these novel data, we hypothesize angiotensin(1-2) enhances ß-cell function via intra-
islet paracrine signaling, and promotes ß-cell survival/proliferation via a novel GLP-1-independent mechanism.
The following specific aims address this hypothesis, with the goal of improving treatment options in T2D:
Specific Aim 1. To determine the mechanism by which angiotensin(1-2) increases islet-derived GLP-1
and insulin secretion. Mice (in vivo) and islets (in vitro) with diphtheria toxin-induced a-cell destruction or a
cell-specific GPRC6A knockout will be used to determine whether angiotensin(1-2)-mediated increases in
insulin release require a cells or a-cell GPRC6A, respectively. We will probe mechanisms for increased GLP-1
release, and confirm key findings in human islets with and without GLP-1 receptor or GPRC6A blockade.
Specific Aim 2. To identify signaling pathways/proteins mediating the ß-cell survival and proliferative
effects of Ang(1-2) in human islets. The ability of angiotensin(1-2) to inhibit apoptosis, reduce
dedifferentiation and enhance proliferation of ß cells will be examined in human islets under non-diabetic and
diabetic conditions. The contribution of mechanisms independent of GLP-1 or GPRC6A will be determined.
Effectors of angiotensin(1-2) action will be identified using non-biased phosphoproteomics, then loss-/gain-of-
function studies in islets will serve as a preliminary screen for effectors that could be targeted therapeutically.
Specific Aim 3. To determine whether Ang(1-2) improves human islet function/survival in vivo, and
whether hydrolysis of Ang(1-7) is required for its anti-diabetic effects. We will utilize a human islet
transplant model to determine the ability of angiotensin(1-2) to improve ß-cell function/survival and glycemia in
diabetic mice. Further, we will test whether the insulinotropic action of angiotensin(1-7) requires its hydrolysis,
as is the case in vitro. The latter is highly significant for clinical management of T2D because it will inform on
the utility of hydrolysis-resistant angiotensin(1-7)-based medications currently in development.