Emodin-induced microglial apoptosis is associated with TRB3 induction

Abstract

Emodin (1,3,8-trihydroxy-6-methylanthraquinone), a natural anthraquinone compound isolated from the rhizome of rhubarb, has been reported to treat brain injury after intracerebral hemorrhage. Treatment of neurons with emodin is able to decrease glutamate excitotoxicity, modulate calcium homeostasis, and induce Bcl-2 expression. However, the effects of emodin on the brain-resident innate immune cells are unclear. In the present study, the mouse microglial cell line, BV-2, was selected to investigate the effects of emodin on microglial activation and apoptosis. Cell viability and apoptosis were sequentially measured with the CellTiter-Glo Luminescent Cell Viability Assay, YOPRO-1 and Caspase-Glo 3/7 Assay Systems. The degree of microglial activation was evaluated using quantitative RT-PCR to measure expression of inflammatory markers. Treatment of BV-2 cells with emodin caused caspase-mediated apoptosis in a dose-dependent manner, and emodin augmented LPS-induced microglial apoptosis to repress inflammatory activation. In response to emodin treatment, reactive oxygen species (ROS) production was increased, and TRB3 was markedly activated. siRNA knockdown of TRB3 attenuated emodin-induced microglial apoptosis. Ectopic overexpression of TRB3 decreased cell viability and was associated with dysregulation of the prosurvival Akt/FOXO3 pathway. These results demonstrate that emodin induces BV-2 cell apoptosis through TRB3 and consequently eliminates inflammatory microglia. Our findings provide a novel molecular basis through which emodin exerts neuroprotective effects, treating brain injury after intracerebral hemorrhage.

Keywords::

• Emodin
• intracerebral hemorrhage
• microglia
• apoptosis
• TRB3

Acknowledgements

This work was supported by the National Basic Research Program of China (973 program) for The Special Project of TCM Basic Theory (Grant No. 2006CB504807). We thank Dr. Peixiang Zhang (Department of Human Genetics, University of California Los Angeles, Los Angeles, CA) for providing the BV-2 mouse microglial cell line, TRB3 expression vector, pCDNA control vector and technical assistance. We also thank Jenny Chen (Department of Human Genetics, University of California Los Angeles) for discussion and critical reading the manuscript.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.