PAX6 maintains β cell identity by repressing genes of alternative islet cell types
Avital Swisa, … , Ruth Ashery-Padan, Yuval Dor
Avital Swisa, … , Ruth Ashery-Padan, Yuval Dor
Published December 12, 2016
Citation Information: J Clin Invest. 2017;127(1):230-243. https://doi.org/10.1172/JCI88015.
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PAX6 maintains β cell identity by repressing genes of alternative islet cell types

Abstract

Type 2 diabetes is thought to involve a compromised β cell differentiation state, but the mechanisms underlying this dysfunction remain unclear. Here, we report a key role for the TF PAX6 in the maintenance of adult β cell identity and function. PAX6 was downregulated in β cells of diabetic db/db mice and in WT mice treated with an insulin receptor antagonist, revealing metabolic control of expression. Deletion of Pax6 in β cells of adult mice led to lethal hyperglycemia and ketosis that were attributed to loss of β cell function and expansion of α cells. Lineage-tracing, transcriptome, and chromatin analyses showed that PAX6 is a direct activator of β cell genes, thus maintaining mature β cell function and identity. In parallel, we found that PAX6 binds promoters and enhancers to repress alternative islet cell genes including ghrelin, glucagon, and somatostatin. Chromatin analysis and shRNA-mediated gene suppression experiments indicated a similar function of PAX6 in human β cells. We conclude that reduced expression of PAX6 in metabolically stressed β cells may contribute to β cell failure and α cell dysfunction in diabetes.

Authors

Avital Swisa, Dana Avrahami, Noa Eden, Jia Zhang, Eseye Feleke, Tehila Dahan, Yamit Cohen-Tayar, Miri Stolovich-Rain, Klaus H. Kaestner, Benjamin Glaser, Ruth Ashery-Padan, Yuval Dor

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Figure 2

Hyperglycemia, hypoinsulinemia, hyperketonemia and loss of β cells in βPAX6 mice.

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Hyperglycemia, hypoinsulinemia, hyperketonemia and loss of β cells in βP...
(A) Blood glucose levels over time in Pax6fl/fl (flox/flox) and βPAX6 mice following tamoxifen (TM) injection. Tamoxifen was injected into mice at 6 weeks of age. n = 13 flox/flox and 17 βPAX6 mice. (B) Plasma insulin levels in βPAX6 and flox/flox mice at the age of 4 months and 2 months after tamoxifen injection. n = 5 mice in each group. (C) Ratio of plasma insulin to blood glucose levels in the same mice as represented in B. (D) Representative insulin staining (green) of pancreatic sections from 1 flox/flox mouse and 2 βPAX6 mice. Blood glucose of each mouse is indicated. Note that despite a loss of insulin-stained cells, islets retained typical morphology and size. Original magnification, ×400. (E) Survival of βPAX6 mice. n = 13 flox/flox and 35 βPAX6 mice. Graph shows the percentage of surviving mice up to 7 months following tamoxifen administration at 1 month of age. P < 0.05, by log-rank (Mantel-Cox) test. (F) Ketone bodies in plasma of control and βPAX6 mice (n = 6). Mice were injected with tamoxifen at 1 month of age and analyzed 3–5 months later. (G) Blood ketone bodies as a function of blood glucose levels in βPAX6 mice and other models of murine diabetes. Note that the highest levels of ketone bodies were not always detected in the most hyperglycemic mice. (H) Quantification of α cell proportion of the total pancreatic area in βPAX6 mice aged 3–6 months. Tamoxifen was injected at 1 month of age. n = 4 flox/flox and 7 βPAX6 mice. (I) Positive correlation between blood ketone bodies and the fraction of glucagon-stained area in βPAX6 mice 3–6 months after tamoxifen injection (P < 0.05, by Spearman’s correlation). Glucagon was measured and calculated from histological sections as the ratio between the area stained for glucagon and the total islet area. Each point represents 1 mouse. *P < 0.05, **P < 0.01, and ***P < 0.001, by 2-tailed Student’s t test.