Gintonin stimulates autophagic flux in primary cortical astrocytes

Background: Gintonin (GT), a novel ginseng-derived exogenous ligand of lysophosphatidic acid (LPA) receptors, has been shown to induce cell proliferation and migration in the hippocampus, regulate calcium-dependent ion channels in the astrocytes, and reduce β-amyloid plaque in the brain. However, whether GT influences autophagy in cortical astrocytes is not yet investigated. Methods: We examined the effect of GT on autophagy in primary cortical astrocytes using immunoblot and immunocytochemistry assays. Suppression of specific proteins was performed via siRNA. LC3 puncta was determined using confocal microscopy. Results: GT strongly upregulated autophagy marker LC3 by a concentration- as well as time-dependent manner via G protein–coupled LPA receptors. GT-induced autophagy was further confirmed by the formation of LC3 puncta. Interestingly, on pretreatment with an mammalian target of rapamycin (mTOR) inhibitor, rapamycin, GT further enhanced LC3-II and LC3 puncta expression. However, GT-induced autophagy was significantly attenuated by inhibition of autophagy by 3-methyladenine and knockdown Beclin-1, Atg5, and Atg7 gene expression. Importantly, when pretreated with a lysosomotropic agent, E-64d/peps A or bafilomycin A1, GT significantly increased the levels of LC3-II along with the formation of LC3 puncta. In addition, GT treatment enhanced autophagic flux, which led to an increase in lysosome-associated membrane protein 1 and degradation of ubiquitinated p62/SQSTM1. Conclusion: GT induces autophagy via mTOR-mediated pathway and elevates autophagic flux. This study demonstrates that GT can be used as an autophagy-inducing agent in cortical astrocytes.