Bmal1 and β-Cell Clock Are Required for Adaptation to Circadian Disruption, and Their Loss of Function Leads to Oxidative Stress-Induced β-Cell Failure in Mice

Abstract

Circadian disruption has deleterious effects on metabolism. Global deletion of Bmal1, a core clock gene, results in β-cell dysfunction and diabetes. However, it is unknown if this is due to loss of cell-autonomous function of Bmal1 in β cells. To address this, we generated mice with β-cell clock disruption by deleting Bmal1 in β cells (β-Bmal1^−/−). β-Bmal1^−/− mice develop diabetes due to loss of glucose-stimulated insulin secretion (GSIS). This loss of GSIS is due to the accumulation of reactive oxygen species (ROS) and consequent mitochondrial uncoupling, as it is fully rescued by scavenging of the ROS or by inhibition of uncoupling protein 2. The expression of the master antioxidant regulatory factor Nrf2 (nuclear factor erythroid 2-related factor 2) and its targets, Sesn2, Prdx3, Gclc, and Gclm, was decreased in β-Bmal1^−/− islets, which may contribute to the observed increase in ROS accumulation. In addition, by chromatin immunoprecipitation experiments, we show that Nrf2 is a direct transcriptional target of Bmal1. Interestingly, simulation of shift work-induced circadian misalignment in mice recapitulates many of the defects seen in Bmal1-deficient islets. Thus, the cell-autonomous function of Bmal1 is required for normal β-cell function by mitigating oxidative stress and serves to preserve β-cell function in the face of circadian misalignment.

ACKNOWLEDGMENTS

This work was supported by grant R56 DK089061-01 and a P&F grant (DRC-P30DK079638) from the NIH, American Diabetes Association grant 7-12-BS-210, the Caroline Wiess Law Fund for Molecular Medicine, and a P&F grant from BCM Huffington Center On Aging and the Alkek Foundation to V.K.Y. It was also supported by grants to K.M. from the American Diabetes Association (1-13-BS-118), to Y.X. from the NIH (R01DK093587, R00DK085330, and P30 DK079638-03), the American Diabetes Association, the Klarman Family Foundation, the Naman Family Fund for Basic Research, and the Curtis Hankamer Basic Research Fund, and to M.M. from NIH (K08HL091176).

We thank Agnes Liang and Luge Li for technical assistance. We also thank the Mouse Metabolism Core of the Diabetes Research Center at the Baylor college of Medicine (DRC-P30DK079638).

There are no potential conflicts of interest.