Effect of copper exposure on the silkworm <i>Bombyx mori</i> : Insights into the changes of metabolism, gut microbial composition and gene expression

Copper (Cu), a trace element with crucial roles in physiological processes, can exert detrimental effects when imbalanced. Despite growing research on Cu's impacts on biota, its effects on terrestrial organisms, particularly insects, at environmental concentrations remain poorly understood. This study aims to elucidate the mechanisms underlying Cu-induced damage in silkworms (Bombyx mori L., 1758 (Lepidoptera: Bombycidae)) and identify potential targets to mitigate such damage. Using an integrated approach of physiological, histopathological, biochemical and multi-omics analyses, we investigated the effects of Cu exposure throughout most of the silkworms' larval stage. Our findings reveal that Cu exposure significantly hampers the growth and development of silkworms, evidenced by reduced intestinal trehalose levels, compromised peritrophic membrane (PM) structure in the midgut (MG) and altered composition and diversity of the intestinal microbiota. Furthermore, Cu exposure leads to an increase in pathogenic bacteria and a decrease in probiotics and induces inflammation and apoptosis in the midgut and fatbody (FB) tissues. Biochemical and transcriptomic analyses indicate that Cu disrupts nutrient metabolism and energy homeostasis, resulting in decreased adenosine triphosphatase (ATP) levels. Chronic Cu exposure activates the PI3K/AKT/mTOR signalling pathway, triggering abnormal apoptosis and autophagy, altering detoxification processes, immune enzyme activities and gene expression. This study provides novel insights into the mechanisms of Cu toxicity in silkworms and establishes a foundation for identifying targets to reduce Cu's biotoxicity, offering valuable data for managing Cu pollution in insects.