LdAMPKα2 knockdown accelerated the growth but depressed the chitin biosynthesis in Lymantria dispar larvae

AMPK (AMP-activated protein kinase) is a crucial cellular energy sensor across all eukaryotic species. Its multiple roles in maintaining energy homeostasis, regulating cellular metabolic processes have been widely investigated in mammals. In contrast, the function of AMPK in insects has been less reported. Here, we successfully identified three AMPK subunits from Lymantria dispar (L. dispar), a Lepidoptera pest in forestry. Based on that, in particular, the role of AMPK signaling in regulating larval development, as well as chitin biosynthesis was investigated by the application of RNAi-mediated LdAMPKα2 knockdown. The results indicated that knockdown of LdAMPKα2 significantly increased the body weight of L. dispar larvae, and dramatically upregulated the expression of LdmTOR, LdS6K and LdSREBP1, the key genes in mTOR (mammalian target of rapamycin) signaling pathway. While, it significantly reduced the expression of Ld4EBP, a critical repressor of mTOR pathway. Besides, the glucose level was increased and trehalose level was decreased in L. dispar after LdAMPKα2 silencing. Furthermore, we found that the chitin content in the epidermis, as well as the expressions of four key genes in the chitin biosynthesis pathway, LdGFAT, LdPAGM, LdUAP and LdCHSA, were significantly decreased after LdAMPKα2 knockdown. Taken together, these results revealed that AMPK signaling played a pivotal role in regulating the growth and development, as well as carbohydrate metabolism and chitin biosynthesis in L. dispar larvae. The findings expand our understanding of the comprehensive regulatory role of AMPK signaling in insects.