Project Summary
ß cell dysfunction is critical for the pathogenesis of type 2 diabetes mellitus (T2DM). Studies suggested that
over-nutrition and inflammation induce profound changes in the transcriptome and the epigenome of beta cells,
resulting in impaired glucose-stimulated insulin secretion, and loss of beta cell mass. However, the molecular
mechanisms of the epigenetic regulation in beta cell function and failure remain largely unclear. Our recent
results suggest that SIRT7, a NAD+-dependent deacetylase, regulate the glucose-stimulated insulin secretion
(GSIS), and antagonize inflammation- and overnutrition-induced islet dysfunction. We found that SIRT7
activates the expression of a number of key genes in the insulin synthesis and secretion pathways, while
suppresses the inflammatory and metabolic stress-induced transcription. These results raise the possibility that
SIRT7 simultaneously activates GSIS pathway, and represses stress-induced inflammatory responses,
through diverge molecular mechanisms. SIRT7 interacts with PBRM1, a chromatin remodeler, which controls
the chromatin accessibility of regulatory cis-elements associated with the GSIS pathway genes. On the other
hand, SIRT7 deacetylates H3K18Ac, a histone marks highly enriched in stress-induced promoter/enhancers in
beta cells. In addition, the ability and specificity of SIRT7 to repress targets is regulated by the intracellular
level of NAD+, and its interacting partner, vitamin D receptor (VDR), respectively. We hypothesize that SIRT7
is an essential regulator of insulin secretion and stress responses in beta cells through integrating NAD+ and
vitamin D signaling at the chromatin level. Accordingly, Specific Aim 1 will utilize novel genetic loss-of-function
mouse models to test the hypothesis that SIRT7 promotes insulin secretion through recruiting PBRM1 and
maintaining the chromatin accessibility. Specific Aim 2 will use multiple diabetes mouse models, to determine
the molecular underpinnings of SIRT7 in antagonizing stress-induced transcription in beta cells, through
deacetylating H3K18Ac and acting as a novel co-repressor of VDR. Lastly, Aim 3 will dissect the converge of
NAD+-SIRT7 and vitamin D-VDR signaling at the chromatin level, and test the therapeutic potential of co-
activating SIRT7-VDR to antagonize both mouse and human islet dysfunction. The proposed project will reveal
novel molecular regulatory mechanisms of beta cell function in healthy and dysfunctional state and may lead to
novel strategies for the development of next generation anti-diabetic therapies directly targeting ß cell
dysfunction.