In response to the microenvironment, microglia may polarize into either an M1 pro-inflammatory phenotype, exacerbating neurotoxicity, or an M2 anti-inflammatory phenotype, conferring neuroprotection. Betulinic acid (BA) is a naturally pentacyclic triterpenoid with considerable anti-inflammatory properties. Here, we aim to investigate the potential effects of BA on microglial phenotype polarization and to reveal the underlying mechanisms of action. First, we confirmed that BA promoted M2 polarization and inhibited M1 polarization in lipopolysaccharide (LPS)-stimulated BV-2 microglial cells. Then, we demonstrated that the effect of BA on microglial polarization was dependent on AMP-activated protein kinase (AMPK) activation, as evidenced by the fact that both AMPK inhibitor compound C and AMPK siRNA abolished the M2 polarization promoted by BA. Moreover, we found that calmodulin-dependent protein kinase kinase β (CaMKKβ), but not liver kinase B1, was the upstream kinase required for BA-mediated AMPK activation and microglial M2 polarization, via the use of both the CaMKKb inhibitor STO-609 and CaMKKβ siRNA. Finally, BA enhanced AMPK phosphorylation and promoted M2 microglial polarization in the cerebral cortex of LPSinjected mice brains, which was attenuated by pre-administration of the AMPK inhibitor. This study demonstrated that BA promoted M2 polarization of microglia, thus conferring anti-neuroinflammatory effects via CaMKKβ-dependent AMPK activation.
|Journal||Frontiers in Molecular Neuroscience|
|Publication status||Published - 3 Apr 2018|
Bibliographical note© 2018 Li, Zhang, Zhou, Feng, Tang, Hoi, He, Ma, Zhao and Lee. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
This study was supported by grants from The Science and Technology Development Fund (FDCT) Fundo para o Desenvolvimento das Ciências e da Tecnologia 501100006469 of Macao SAR
- AMP-activated protein kinase
- Betulinic acid
- Calmodulin-dependent protein kinase β
- Microglia polarization