The root extract of Scutellaria baicalensis Georgi promotes β cell function and protects from apoptosis by inducing autophagy

Abstract

Scutellaria baicalensis Georgi (SBG) is a traditional Chinese medicine with a remarkable remedial effect on diabetes mellitus. However, the precise mechanism involved has not been fully elucidated yet. Here, we aimed to explore the anti-diabetes effects of its traditional decoction in vitro and elucidate the autophagy-related mechanism. This study was designed to investigate the effects of the water extract of SBG (WSB) on the β cell viability, insulin secretion and the mechanism related to autophagy. Detection of insulin secretion using an enzyme immunoassay method, and analysis of apoptosis rate in MIN-6cells by the flow cytometry with PI and Annexin V-FITC staining. In addition, the autophagy levels and pathways were evaluated from the number of autophagosomes and the expression of autophagy-related proteins. 3-Methyladenine (3-MA) was used as the autophagy inhibitor. Autophagosomes were observed using a confocal microscopy, and autophagy-related proteins (LC3-II/I, p62, S6k, p-AMPK/AMPK, p-mTOR/mTOR) were measured by Western blot. Here we detected a significant increase in insulin release from MIN-6cells after treated with WSB. It is about 1.6 times as much as that of the control group with 2.8mM glucose and 2.2 times more than the 16.8mM glucose group. At the same time, WSB increased the number of autophagosomes and the ratio of LC3 Ⅱ/LC3 Ⅰ, indicating that autophagy were activated in MIN-6cells. When inhibiting autophagy, there was no significant difference in insulin release between the two groups. The apoptotic rate of the high glucose group was as high as 33.23%. After pretreatment with WSB, the apoptotic rate decreased to 14.95%, and increased to 22.57% when treated with 3-MA and WSB. At the same time, WSB treatment enhanced the phosphorylation of AMPK, but had no significant effect on the expression of mTOR and S6K. Our data suggested that WSB increased insulin secretion and reduced apoptosis under high glucose by inducing autophagy through the AMPK pathway, which elucidated the mechanism of WSB in the treatment of diabetes.