Restoration of energy homeostasis under oxidative stress: Duo synergistic AMPK pathways regulating arginine kinases

Rapid depletion of cellular ATP can occur by oxidative stress induced by reactive oxygen species (ROS). Maintaining energy homeostasis requires the key molecular components AMP-activated protein kinase (AMPK) and arginine kinase (AK), an invertebrate orthologue of the mammalian creatine kinase (CK). Here, we deciphered two independent and synergistic pathways of AMPK acting on AK by using the beetle Tribolium castaneum as a model system. First, AMPK acts on transcriptional factor forkhead box O (FOXO) leading to phosphorylation and nuclear translocation of the FOXO. The phospho-FOXO directly promotes the expression of AK upon oxidative stress. Concomitantly, AMPK directly phosphorylates the AK to switch the direction of enzymatic catalysis for rapid production of ATP from the phosphoarginine-arginine pool. Further in vitro assays revealed that Sf9 cells expressing phospho-deficient AK mutants displayed the lower ATP/ADP ratio and cell viability under paraquat-induced oxidative stress conditions when compared with Sf9 cells expressing wild-type AKs. Additionally, the AMPK-FOXO-CK pathway is also involved in the restoration of ATP homeostasis under oxidative stress in mammalian HEK293 cells. Overall, we provide evidence that two distinct AMPK-AK pathways, transcriptional and post-translational regulations, are coherent responders to acute oxidative stresses and distinguished from classical AMPK-mediated long-term metabolic adaptations to energy challenge. Author summaryAMP-activated protein kinase (AMPK) and phosphoarginine-arginine kinase (AK) shuttle system play essential roles in regulating the cellular and organismal energy homeostasis under various stresses in invertebrates, although the regulatory mechanisms culminating in the ATP homeostasis remain largely unknown. In this work, using the red flour beetle, Tribolium castaneum, as a model organism, we found that AMPK upregulates the expressions of AKs upon oxidative stress through direct phosphorylation of transcriptional factor forkhead box O (FOXO). The phosphorylation of FOXO followed by the nuclear translocation directly enhances the transcription levels of AK1 and AK2. At the same time, the AMPK directly phosphorylates AKs, resulting in a shift of the AK-catalyzed reversible reaction toward the direction of ATP generation. Taken together, our research presents two parallel synergistic AMPK-AK pathways that protect the cells from rapid depletion of ATP under acute oxidative stress condition, which is distinguished from classical AMPK-mediated long-term metabolic adaptations to energy challenge.