The κ-opioid receptor-induced autophagy is implicated in stress-driven synaptic alterations

Recent evidence has shown that G protein-coupled receptors (GPCRs) are direct sensors of the autophagic machinery and opioid receptors regulate neuronal plasticity and neurotransmission with an as yet unclarified mechanism. Using in vitro and in vivo experimental approaches, this study aims to clarify the potential role of autophagy and kappa-opioid receptor (kappa-OR) signaling in synaptic alterations. We hereby demonstrate that the selective kappa-OR agonist U50,488H, induces autophagy in a time-and dose-dependent manner in Neuro-2A cells stably expressing the human kappa-OR by upregulating microtubule-associated protein Light Chain 3-II (LC3-II), Beclin 1 and Autophagy Related Gene 5 (ATG5). Pretreatment of neuronal cells with pertussis toxin blocked the above kappa-OR-mediated cellular responses. Our molecular analysis also revealed a kappa-OR-driven upregulation of becn1 gene through ERK1,2-dependent activation of the transcription factor CREB in Neuro-2A cells. Moreover, our studies demonstrated that sub-chronic U50,488H administration in mice causes profound increases of specific autophagic markers in the hippocampus with a concomitant decrease of several pre-and post-synaptic proteins, such as spinophilin, postsynaptic density protein 95 (PSD-95) and synaptosomal associated protein 25 (SNAP25). Finally, using acute stress, a stimulus known to increase the levels of the endogenous kappa-OR ligand dynorphin, we are demonstrating that administration of the kappa-Omicron R selective antagonist, nor-binaltorphimine (norBNI), blocks the induction of autophagy and the stress-evoked reduction of synaptic proteins in the hippocampus. These findings provide novel insights about the essential role of autophagic machinery into the mechanisms through which kappa-OR signaling regulates brain plasticity.

Automated summary

Recent evidence suggests that G protein-coupled receptors (GPCRs) directly sense autophagy and opioid receptors regulate neuronal plasticity and neurotransmission through an unknown mechanism. In this study, the researchers demonstrate that the selective kappa-opioid receptor (kappa-OR) agonist U50,488H induces autophagy in a time- and dose-dependent manner in neuronal cells, upregulating specific autophagic markers. Molecular analysis reveals that kappa-OR activation upregulates the becn1 gene through the ERK1,2-dependent activation of the CREB transcription factor. Furthermore, sub-chronic administration of U50,488H in mice leads to increased autophagic markers and decreased synaptic proteins in the hippocampus, while administration of the kappa-OR selective antagonist nor-binaltorphimine (norBNI) blocks autophagy induction and stress-induced reduction of synaptic proteins in the hippocampus. These findings provide new insights into the role of autophagic machinery in the regulation of brain plasticity by kappa-OR signaling.