低强度超声联合微泡通过提高ROS水平促进甲状腺癌细胞自噬性死亡

目的:探讨低强度超声联合微泡造影剂对甲状腺癌细胞自噬性死亡的作用,并分析自噬的激活机制及其对细胞活力的影响。方法:采用频率20 k Hz、功率80 m W的低强度超声联合微泡造影剂处理人甲状腺癌TPC1细胞,处理细胞60、120和240 s后,采用Live/Dead实验和CCK-8实验分析细胞死亡和活力;Western blot分析微管相关蛋白1轻链3Ⅱ(microtubule-associated protein 1 light chain 3-Ⅱ,LC3-Ⅱ)、自噬相关蛋白5(autophagy-related protein 5,ATG5)和SQSTM1/P62的蛋白水平变化;单丹磺酰戊二胺(monodansylcadaverine,MDC)染色、绿色荧光蛋白(green fluorescent protein,GFP)-LC3转染和透射电镜观察细胞内自噬体的数量;2',7'-二氯二氢荧光素二乙酸脂(DCFDA)染色分析细胞活性氧簇(reactive oxygen species,ROS)的水平,用N-乙酰半胱氨酸(N-acetyl-L-cysteine,NAC)抑制氧化应激水平,分析ROS在自噬激活中的作用;ATG5 siRNA转染抑制自噬水平并分析自噬性死亡的作用。结果:低强度超声联合微泡显著促进TPC1细胞死亡,抑制TPC1细胞活力(P0.05),并与处理时间显著相关。相对于单纯低强度超声组和微泡组,超声联合微泡显著升高LC3-Ⅱ和ATG5蛋白水平,抑制P62蛋白水平(P0.05)。MDC染色、GFP-LC3转染和透射电镜观察发现,超声联合微泡明显增加TPC1细胞中自噬体的数量。超声联合微泡与单纯低强度超声组和微泡组相比,提高了细胞的ROS水平,而NAC显著降低超声联合微泡提高的LC3-Ⅱ蛋白水平(P0.05)。ATG5 siRNA抑制自噬并显著增加细胞活力(P0.05)。结论:本研究说明低强度超声联合微泡可能通过提高甲状腺癌细胞中的ROS水平促进细胞的自噬性死亡,从而引起甲状腺癌细胞死亡。

Low-intensity ultrasound combined with microbubbles activates auto-phagic death of thyroid cancer cells by promoting ROS production

AIM: To investigate the effect of low-intensity ultrasound combined with microbubble contrast agent on autophagic death of thyroid cancer cells, and to analyze the mechanism of autophagy activation and its effect on cell viability. METHODS: Human thyroid cancer cell line TPC1 was treated with low-intensity ultrasound at 20 kHz frequency and 80 mW intensity combined with microbubbles. The cell death and viability were analyzed by Live/Dead assay and CCK-8 assay 60, 120 and 240 s after the treatment. The protein levels of microtubule-associated protein 1 light chain 3-Ⅱ (LC3-Ⅱ), autophagy-related protein 5 (ATG5) and SQSTM1/P62 were determined by Western blot. The number of intracellular autophagosomes was measured by the methods of monodansylcadaverine (MDC) staining, green fluorescent protein (GFP)-LC3 transfection and transmission electron microscopy. The level of reactive oxygen species (ROS) was mea-sured and the effect of ROS on autophagy activation was evaluated by N-acetyl-L-cysteine (NAC) treatment. The effect of ATG5 siRNA transfection on autophagy was analyzed for determining the role of autophagic death. RESULTS: Low-intensity ultrasound combined with microbubbles significantly promoted TPC1 cell death and inhibited TPC1 cell viability (P<0.05) in a time-dependent manner. Compared with low-intensity ultrasound group and microbubble group, ultrasound combined with microbubbles significantly increased the protein levels of LC3-Ⅱ and ATG5, but inhibited the protein level of P62 (P<0.05). The results of MDC staining, GFP-LC3 transfection and transmission electron microscopy showed that ultrasound combined with microbubbles significantly increased the number of autophagosomes in the TPC1 cells. Compared with low-intensity ultrasound group and microbubble group, ultrasound combined with microbubbles increased the level of ROS, while NAC significantly reduced the protein level of LC3-Ⅱ (P<0.05). Thansfection with ATG5 siRNA inhibited the autophagy, significantly decreased the percentage of cell death and increased cell viability (P<0.05). CONCLUSION: Low-intensity ultrasound combined with microbubbles promotes the autophagic cell death by increasing the level of ROS in thyroid cancer cells, leading to death of thyroid cancer cells.