Discussion

Gymnemic acid inhibits sodium-dependent glucose transporter 1(Y.Wang，Dawid，Kottra，Daniel，& Hofmann，2014).It also ameliorates oxidative stress and shows significant antidiabetic properties(Tiwari et al.，2017；Vellai，Chandiran，& Pillai，2017).But the molecular mechanism needs to be explored.Here we report that GA I ameliorates the apoptosis of MIN-6 under the high glucosestress.Our data also explores that GA I induces autophagy under normal and the high glucose stress in MIN-6 cells.GA I decreases MIN-6 cells'apoptosis level under high glucose stress，when adding 3-MA，the apoptosis level increases again.All together，we conclude that GA I-induced autophagy plays cytoprotective role in MIN-6 cellsunder high glucose stress.

Autophagy is a conserved process and possesses antidiabetic effect(Marasco &Linnemann，2018).It regulates insulin secretion and Ca2+transients(Lee，2014).βcells'autophagy is shown to protectβ-cells against apoptosis(Lee，2014).For example，It protectsβ-cells against endoplasmic reticulum stress，glucotoxicity，and inhibits human IAPP-inducedβ-cell toxicity(Bachar-Wikstrom et al.，2013；Bartolome，Guillen，&Benito，2012；Han et al.，2010；Shigihara et al.，2014).The antidiabetic drug Liraglutide protects INS-1 cells from free fatty acid(FFA)-induced apoptosis by promoting autophagy(J.Wang et al.，2015).Metformin and rosiglitazone also protect β-cells from palmic acid(PA)-induced apoptosis via the induction of autophagy(Jiang et al.，2014；Wu，Wu，Yang，Wei，& Zou，2013).In this paper，we explore that GA I-induced autophagy protects MIN-6 cells from hyperglycemia-induced apoptosis.Chronic hyperglycemia is common features of subjects with T2DM(Florez et al.，2003).It impairs pancreaticβ-cell function and decreasedβ-cell mass(Butler et al.，2003).(https://www.daowen.com)

m TOR signaling pathway regulates cell metabolism，growth，proliferation，and survival.It nucleates two distinct complexes，mTOR complex 1(mTORC1)and mTOR complex 2(m TORC2；Laplante&Sabatini，2009).Glucotoxic condition highly activates m TORC1.Sustained mTORC1 activation impairedβ-cell survival and function.mTORC1 is a nutrient-responsive kinase.It is activated by growth factors，nutrients，and the energy level.Inhibition phosphorylation activity of mTORC1 leads to the induction of autophagy(Ardestani，Lupse，Kido，Leibowitz，& Maedler，2018).Rosiglitazone or metformin induced-autophagy protected against apoptosis ofβ-cells through AMP-activated protein kinase(AMPK)activation(Jiang et al.，2014；Wu et al.，2013).We explore that GA Iinduces autophagy under normal or high glucose condition via inhibition mTOR activity in MIN-6.GA I-induced autophagy plays cytoprotective role in MIN-6 cells under high glucose stress through inhibition activity of caspase 3.It has been reported that caspases regulated the degradation of Ambra1.Ambra1 over expression and a caspase noncleavable mutant counteract cell death by inducing autophagy(Tsapras& Nezis，2017).So more investigation is required to improve our understanding of GA I and facilitate successful translation to DM.