Gu Haoyi, Zou Hongbin, Cheng Jialu, Liu Xiaohan, Jiang Zhe, Peng Peilin, Li Fanchi, Li Bing
School of Basic Medicine and Biological Sciences, Soochow University, Suzhou, China.
Sericulture Institute of Soochow University, Soochow University, Suzhou, China.
Insect Mol Biol. 2024 Dec;33(6):551-559. doi: 10.1111/imb.12911. Epub 2024 Mar 28.
The silkworm, Bombyx mori, is a complete metamorphosed economic insect, and the silk gland is a significant organ for silk protein synthesis and secretion. The silk gland completely degenerates during pupation, but the regulatory mechanism of programmed cell death (PCD) has not yet been understood. In the present study, we investigated the non-genetic pathway of 20E-induced PCD in the posterior silk gland (PSG) based on intracellular Ca levels. Silk gland morphology and silk gland index indicated rapid degeneration of silk gland during metamorphosis from mature silkworm (MS) to pupal day 1 (P1), and Ca levels within the PSG were found to peak during the pre-pupal day 1 (PP1) stage. Moreover, the results of autophagy and apoptosis levels within the PSG showed that autophagy was significantly increased in MS-PP1 periods, and significantly decreased in PP2 and P1 periods. Apoptosis was almost absent in MS-PP1 periods and significantly increased in PP2 and P1 periods. Additionally, western blotting results showed that autophagy preceded apoptosis, and the autophagy-promoting ATG5 was cleaved by calpain to the autophagy-inhibiting and apoptosis-promoting NtATG5 since PP1 period, while decreased autophagy was accompanied by increased apoptosis. Collectively, these findings suggest that Ca is a key factor in the shift from autophagy to apoptosis.
家蚕是一种完全变态的经济昆虫，丝腺是合成和分泌丝蛋白的重要器官。丝腺在化蛹过程中会完全退化，但其程序性细胞死亡（PCD）的调控机制尚不清楚。在本研究中，我们基于细胞内钙离子水平，研究了20E诱导的后部丝腺（PSG）程序性细胞死亡的非遗传途径。丝腺形态和丝腺指数表明，从成熟蚕（MS）到化蛹第1天（P1）的变态过程中，丝腺迅速退化，且在化蛹前1天（PP1）阶段，PSG内的钙离子水平达到峰值。此外，PSG内自噬和凋亡水平的结果显示，自噬在MS-PP1阶段显著增加，在PP2和P1阶段显著降低。凋亡在MS-PP1阶段几乎不存在，在PP2和P1阶段显著增加。此外，蛋白质免疫印迹结果表明，自噬先于凋亡发生，自噬促进因子ATG5从PP1阶段开始被钙蛋白酶切割为自噬抑制和凋亡促进因子NtATG5，而自噬减少伴随着凋亡增加。总的来说，这些发现表明钙离子是自噬向凋亡转变的关键因素。
