A neuropeptide-copper complex contributes to nuclear copper uptake via a receptor-mediated endocytosis pathway: towards understanding copper dysregulation in neurological disease
Western Sydney University, School of Science and Health, Locked bag 1797, Sydney, New South Wales, Australia, 2153.
Our central nervous system employs strict regulation of the trace element copper, and dysregulation is implicated in the neuropathology of many neurodegenerative and neurocognitive diseases. Recent interest into the contribution of copper dysregulation to neurological disease has exposed our limited understanding of neuronal copper homeostasis. For instance, known uptake mechanisms do not completely account for cellular copper concentrations, suggesting alternate mechanisms remain to be found. Past work has established that some neuropeptides can bind copper, with the tachykinin neuropeptide, Neurokinin B (NKB), able to form an unusual complex with copper. Other recent approaches focusing on NKB and its corresponding receptor NK3R, identified the endogenous ligand-induced translocation of NK3R to the nucleus. Further, the newly identified copper-NKB complex has been shown to not inhibit receptor uptake, however intracellular localisation and interactions are unknown. To identify copper-NKB complex induced changes intracellularly, we used Confocal microscopy, Spectral phasor analysis, and Inductively Coupled Plasma-Mass Spectrometry to determine receptor localisation and copper concentrations in astrocyte and neuronal cell lines. Our results indicate that receptor–mediated endocytosis (RME), particularly of the [Cu(NKB)2]/NK3R complex contributes to cellular copper levels. Additionally, nuclear trafficking of the receptor and nuclear copper concentrations increase when exposed to the [Cu(NKB)2] complex. Furthermore, results illustrate that this process is clathrin-mediated. This is indicative of a novel CNS-specific copper trafficking pathway, due to the CNS-specific expression of NKB. This study establishes a foundation for future neurobiological research into the underlying role RME plays in copper regulation within the CNS.