Titanium nanoparticles influence the Akt/Tor signal pathway in the silkworm, Bombyx mori, silk gland

Abstract

Various nanoparticles, such as silver nanoparticles (AgNPs) and titanium nanoparticles (TiO 2 NPs) are increasingly used in industrial processes. Because they are released into the environment, research into their influence on the biosphere is necessary. Among its other effects, dietary TiO 2 NPs promotes silk protein synthesis in silkworms, which prompted our hypothesis that TiO 2 NPs influence protein kinase B (Akt)/Target of rapamycin (Tor) signaling pathway (Akt/Tor) signaling in their silk glands. The Akt/Tor signaling pathway is a principle connector integrating cellular reactions to growth factors, metabolites, nutrients, protein synthesis, and stress. We tested our hypothesis by determining the influence of dietary TiO 2 NPs (for 72 h) and, separately, of two Akt/Tor pathway inhibitors (LY294002 and rapamycin) on expression of Akt/Tor signaling pathway genes and proteins in the silk glands. TiO 2 NPs treatments led to increased accumulation of mRNAs for Akt, Tor1 and Tor2 by 1.6-, 12.1-, and 4.8-fold. Dietary inhibitors led to 2.6-to 4-fold increases in mRNAs encoding Akt and substantial decreases in mRNAs encoding Tor1 and Tor2. Western blot analysis showed that dietary TiO 2 NPs increased the phosphorylation of Akt and its downstream proteins. LY294002 treatments led to inhibition of Akt phosphorylation and its downstream proteins and rapamycin treatments similarly inhibited the phosphorylation of Tor-linked downstream proteins. These findings support our hypothesis that TiO 2 NPs influence Akt/Tor signaling in silk glands. The significance of this work is identification of specific sites of TiO 2 NPs actions.

Integrin β2 and β3: Two plasmatocyte markers deepen our understanding of the development of plasmatocytes in the silkworm Bombyx mori

“…To determine the roles of these 2 downstream pathways related to insulin signal, various inhibitors were used. LY294002 is a highly selective inhibitor of PI3K, and has been widely used in fundamental research on silkworms (Gu et al ., 2016; Xue et al ., 2018; Gu et al ., 2019). Insulin signaling enhances hemocyte proliferation and the growth of silkworm hemopoietic organs by activating the PI3K/Akt signal pathway (Nakahara et al ., 2006).…”