Effects of phoxim on nutrient metabolism and insulin signaling pathway in silkworm midgut

Silkworm (Bombyx mori) is an important economic insect. Each year, poisoning caused by phoxim pesticide leads to huge economic losses in sericulture in China. Silkworm midgut is the major organ for food digestion and nutrient absorption. In this study, we found that the activity and expression of nutrition metabolism-related enzymes were dysregulated in midgut by phoxim exposure. DGE analysis revealed that 40 nutrition metabolism-related genes were differentially expressed. qRT-PCR results indicated that the expression levels of insulin/insulin growth factor signaling (IIS) pathway genes Akt, PI3K, PI3K60, PI3K110, IRS and PDK were reduced, whereas PTEN's expression was significantly increased in the midgut at 24 h after phoxim treatment. However, the transcription levels of Akt, PI3K60, PI3K110, IRS, InR and PDK were elevated and reached the peaks at 48 h, which were 1.48-, 1.35-, 1.21-, 2.24-, 2.89-, and 1.44-fold of those of the control, respectively. At 72 h, the transcription of these genes was reduced. Akt phosphorylation level was increasing along with the growth of silkworms in the control group. However, phoxim treatment led to increased Akt phosphorylation that surged at 24 h but gradually decreased at 48 h and 72 h. The results indicated that phoxim dysregulated the expression of IIS pathway genes and induced abnormal nutrient metabolism in silkworm midgut, which may be the reason of the slow growth of silkworms.