ObjectiveTo investigate the effects of gypenosides (Gyp) on hippocampal neuron autophagy and pathway of mammalian target of rapamycin (mTOR)/autophagy-activated kinase 1 (ULK1)/autophagy-related protein 13 (ATG13) in depression rats.

MethodsSD rats were randomly divided into normal control group, model group, Gyp low (25 mg/kg), high (100 mg/kg) dose group, autophagy activator-rapamycin (Rap) group (1 mg/kg), and Gyp+Rap group (100 mg/kg+1 mg/kg), with 10 rats in each group.Chronic mild unpredictable stress was used to prepare rat depression models, and each group was administered for 4 weeks, once daily.Open field, sugar water preference and forced swimming tests were used to assess depression-like behavior in rats, transmission electron microscope was used to observe the changes in hippocampal neuron structure and the formation of autophagosomes and autophagolysosomes.TUNEL method was used to detect neuronal apoptosis.Immunohistochemical staining was used to detect the phosphorylation level of ULK1 (p-ULK1) and the positive expression level of p-ATG13 in the hippocampus.Western blotting was used to detect the total mTOR, p-mTOR, ribosomal S6 protein (S6), p-S6, ULK1 specific site Ser757 protein (ULK1 Ser757) and p-ULKl Ser757, autophagy-related protein Beclin1, microtubule-related protein Light chain 3 (LC3) protein, apoptosis-related protein-Caspase-3 (Caspase-3) and polyadenylic acid diphosphate ribose polymerase (PARP) protein expression levels.

ResultsCompared with the normal control group, the central exploration time in the open field experiment and the percentage of sugar water intake in the model group were reduced, the time of forced swimming immobility was prolonged, the depressive behavior was severe, the nuclear membrane of hippocampal neurons was severely damaged, and autophagosomes were formed more, the apoptosis rate, apoptosis-related protein, Beclin1 and LC3 protein expression were increased, the phosphorylation level of mTOR/ULK1/ATG13 pathway protein was decreased, and the changes of each index were significantly different (P < 0.01).Compared with the model group, with the Gyp dose increased, the depressive behavior of rats was relieved, and the hippocampal neuronal apoptosis and level of autophagy were decreased, the phosphorylation level of mTOR/ULK1/ATG13 pathway protein was increased (P < 0.01);the phosphorylation level of mTOR/ULK1/ATG13 pathway protein in the hippocampus tissue of the Rap group was further reduced, the levels of hippocampal neuron apoptosis and autophagy were further increased, and the depression-like behavior in rats was further aggravated (P < 0.01).The changes of the above indicators in the Gyp+Rap group were opposite to those in the Gyp group (P < 0.01).

ConclusionsGyp may inhibit autophagy by activating the activity level of mTOR phosphorylation and promoting the phosphorylation of ULK1 and ATG13, so as to prevent autophagic death of neurons, and exert antidepressant effect.