Objective:To investigate the effect of total alkaloid of harmaline (TAH) on inducing cellular autophagy and degradating of neurotoxic proteins Tau and α-synuclein (α-Syn).Methods:(1) The in vitro cultured PC12 cells were divided into blank control group, and 1, 2.5, 5, 10, 20 and 50 μg/mL TAH groups, respectively; and they were treated with 0, 1, 2.5, 5, 10, 20 and 50 μg/mL TAH for 24 h; cell morphology and number were observed, and cell survival rate was determined by MTT assay. (2) PC12 cells were divided into blank control group, rapamycin group, and 1, 2.5, 5, 10 and 20 μg/mL TAH groups; these cells were treated with same amount of solvent, 50 nmol/L autophagy activator rapamycin, and 1, 2.5, 5, 10 and 20 μg/mL TAH for 4 h, respectively, and the number of autophagosomes was detected by immunofluorescent staining. (3) PC12 cells were divided into blank control group, rapamycin group, and 10 μg/mL TAH group; these cells were treated with same amount of solvent, 50 nmol/L rapamycin, and 10 μg/mL TAH for 4 h; the protein expression levels of p62 and microtubule-associated protein 1 light chain 3 II (LC3-II) was detected by Western blotting. (4) PC12 cells were divided into blank control group, chloroquine group, TAH group, and TAH+chloroquine group; these PC12 cells were treated with 50 nmol/L autophagy inhibitor chloroquine, 10 μg/mL TAH, and 10 μg/mL TAH+50 nmol/L chloroquine for 4 h, respectively; the LC3-II protein expression was detected by Western blotting. (5) PC12 cells were divided into TAH group and blank control group; 10 μg/mL TAH and same amount of solvent were given to each group for 4 h, and then, the phosphorylated mammalian target of rapamycin (p-mTOR) and phosphorylated 70-KD ribosomal protein S6 kinase (p-P70S6K) protein expression levels were detected by Western blotting. (6) Tet on HEK293 cells with Tau-green fluorescent protein (GFP) overexpression were divided into blank control group, TAH group, doxycycline group, doxycycline+TAH group, doxycycline+TAH+3-MA group, and doxycycline+TAH+chloroquine group. Cells in the later 4 groups were treated with 200 ng/mL Tet system inducer doxycycline for 24 h; cells in the blank control group were treated with same amount of solvent, those in the TAH group were treated with 10 μg/mL TAH, and cells in the latter 3 groups were treated with 10 μg/mL TAH, 10 μg/mL TAH+5 mmol/L 3-MA, and 10 μg/mL TAH+50 nmol/L chloroquine, respectively, for 24 h; the changes of green fluorescence intensity of these cells were observed under laser confocal microscope. The Tau-GFP and LC3-II protein expression levels were detected by Western blotting. (7) HEK293 cells with stable α-Syn expression were divided into blank control group, chloroquine group, TAH group and TAH+chloroquine group; these cells were treated with same amount of solvent, 50 nmol/L chloroquine, 10 μg/mL TAH and 10 μg/mL TAH+50 nmol/L chloroquine for 24 h, respectively; the α-Syn and LC3-II protein expression levels were detected by Western blotting. Results:(1) As compared with that in the blank control group, the cell survival rate in 20 and 50 μg/mL TAH groups was significantly lower, and that in the 50 μg/mL TAH group was statistically lower than that in 20 μg/mL TAH group ( P<0.05). (2) As compared with that in the blank control group, the number of autophagosomes in rapamycin group, and 10 and 20 μg/mL TAH groups was significantly increased, and that in 10 μg/mL TAH group was statistically higher than that in 20 μg/mL TAH group ( P<0.05); 10 μg/mL TAH group was selected for subsequent experiments. (3) As compared with the blank control group, the rapamycin group and TAH group had significantly decreased P62 protein expression and significantly increased LC3-II protein expression ( P<0.05). (4) As compared with that in the blank control group, the LC3-II protein expression in the chloroquine group, TAH group and TAH+chloroquine group was significantly increased, and LC3-II protein expression in TAH+chloroquine group was statistically higher than that in chloroquine group ( P<0.05). (5) The p-mTOR and p-p70S6K expression levels in the TAH group were significantly decreased as compared with those in the blank control group ( P<0.05). (6) The Tau-GFP protein expression in doxycycline group was significantly increased as compared with that in the blank control group ( P<0.05); that in doxycycline+TAH group was significantly decreased as compared with that in the doxycycline group ( P<0.05); that in the doxycycline+TAH+3-MA group and doxycycline+TAH+chloroquine group was statistically increased as compared with that in doxycycline+TAH group ( P<0.05). The LC3-II protein expression in the TAH group was significantly increased as compared with that in the control group, that in the doxycycline+TAH group was significantly increased as compared with that in the doxycycline group, that in the doxycycline+TAH+3-MA group was significantly decreased as compared with that in the doxycycline+TAH group, and that in doxycycline+TAH+ chloroquine group was significantly increased as compared with that in the doxycycline+TAH group ( P<0.05). Conclusion:TAH may activate autophagy by inhibiting the mTOR/p70S6K signaling pathway, which in turn promotes the degradation of neurotoxic proteins Tau and α-Syn.