AMPK regulates HIF-1α to induce pupal diapause in the cotton bollworm, Helicoverpa armigera

Diapause is an adaptive strategy employed by insects to endure adverse environmental conditions and is characterized by reduced metabolic activity, primarily due to a decreased respiratory rate. AMP-activated protein kinase (AMPK) serves as an intracellular energy regulator, modulating energy metabolism in response to metabolic fluctuations. However, its role in pupal diapause of the cotton bollworm, Helicoverpa armigera, remains unclear. In this study, we found that AMPK and its active form, P-AMPK, are highly expressed in diapause-destined pupae. Furthermore, activation of AMPK delayed the development of nondiapause-destined pupae, suggesting a critical role for AMPK in the regulation of pupal diapause in H. armigera. Manipulating AMPK activity in H. armigera epidermal (HaEpi) cells and pupae significantly influenced the expression of hypoxia-inducible factor-1α (HIF-1α), which our laboratory previously reported as a key inducer of pupal diapause through the reduction of mitochondrial activity in H. armigera. Histone deacetylase 4 (HDAC4), a shuttle protein phosphorylated by AMPK which translocates between the cytoplasm and the nucleus, was found to exhibit significantly higher expression in diapause-destined pupal brains compared to their nondiapause counterparts. AMPK in both HaEpi cells and pupae positively regulated the protein levels of P-HDAC4 by binding to the HDAC4 promoter. Additionally, HDAC4 was shown to enhance HIF-1α expression in diapause-destined individuals. HDAC4 binds to and deacetylates heat shock protein 70 (HSP70), and reduced acetylation of HSP70 was found to significantly elevate HIF-1α protein levels. The AMPK-HIF-1α signaling pathway appears to play a pivotal role in reducing mitochondrial activity and facilitating diapause induction in H. armigera pupae.