Study on the effects of high temperature on autophagy and apoptosis in different organs of Bombyx mori based on calcium ion homeostasis

High-temperature stress differentially affects physiological functions in Bombyx mori, including growth and development, silk protein synthesis, and metabolism. To investigate the underlying mechanisms, we explored the mechanisms of autophagy and apoptosis in the midgut, posterior silk gland (PSG), and fat body of B. mori under high-temperature treatment (30 °C and 35 °C), based on calcium ion (Ca²⁺) homeostasis. The results demonstrated that high-temperature treatment significantly reduced the body weight of B. mori. Furthermore, high-temperature treatment could cause damage to the midgut and PSG of B. mori, accompanied by intracellular Ca²⁺ overload, and the transcription levels of autophagy-related genes as well as the expression of LC3-I and LC3-II proteins are both affected. The protein levels of ATG5 and NtATG5 were significantly increased, while the transcription of key apoptotic genes and the protein levels of caspase-3 and cleaved caspase-3 were elevated. Collectively, these results indicated that high temperature induced autophagy in B. mori through Ca²⁺ mediation and promoted its conversion to apoptosis. Additionally, high temperature was demonstrated to inflict minimal damage on the fat body and failed to induce upregulation of autophagy or apoptosis. This study not only unveiled the intricate interplay among Ca²⁺ homeostasis, autophagy, and apoptosis in various organs of B. mori under high-temperature stress, but also revealed differential effects of heat stress across distinct organs. These findings provide a theoretical foundation for the breeding of thermotolerant silkworm varieties.