Endocytic recycling prevents copper accumulation in astrocytoma cells stimulated with copper-bound neurokinin B

Spectral Phasor Analysis of Nile Red Identifies Membrane Microenvironment Changes in the Presence of Amyloid Peptides

The interaction of protein and peptide amyloid oligomers with membranes is thought to be one of the mechanisms contributing to cellular toxicity. However, techniques to study these interactions in the complex membrane environment of live cells are lacking. Spectral phasor analysis is a recently developed biophysical technique that can enable visualisation and analysis of membrane-associated fluorescent dyes. When the spectral profile of these dyes changes as a result of changes to the membrane microenvironment, spectral phasor analysis can localise those changes to discrete membrane regions. In this study, we investigated whether spectral phasor analysis could detect changes in the membrane microenvironment of live cells in the presence of fibrillar aggregates of the disease-related Aβ₄₂ peptide or the functional amyloid neurokinin B. Our results show that the fibrils cause distinct changes to the microenvironment of nile red associated with both the plasma and the nuclear membrane. We attribute these shifts in nile red spectral properties to changes in membrane fluidity. Results from this work suggest that cells have mechanisms to avoid or control membrane interactions arising from functional amyloids which have implications for how these peptides are stored in dense core vesicles. Furthermore, the work highlights the utility of spectral phasor analysis to monitor microenvironment changes to fluorescent probes in live cells.

A copper complex formed with neurokinin B: binding stoichiometry, redox properties, self-assembly and cytotoxicity

The tachykinin neuropeptide of neurokinin B (NKB) is a copper-binding amyloid peptide with important roles in the regulation of physiological functions and pathophysiological processes in the central and peripheral nervous systems. In this work, the formation of a NKB-Cu²⁺ complex in a 1 : 1 stoichiometry was confirmed by mass spectrometry. The self-assembly of NKB and its mutant species was investigated by Thioflavin T (ThT) fluorescence assay and atomic force microscopy (AFM), and at the same time, the effect of Cu²⁺ on the aggregation of NKB was studied. As evidenced by cyclic voltammetry, the redox potential of NKB-Cu²⁺ was determined to be 0.77 V (vs. Ag/AgCl). It has been demonstrated that NKB at low concentrations exerts its neuroprotective function by inhibiting Cu²⁺-mediated reactive oxygen species (ROS) production in the presence of ascorbic acid (AA). In comparison with equivalent Cu²⁺, the peptide-Cu²⁺ aggregates aggravated the viability of PC-12 cells more seriously in the absence of AA. These results should be extremely valuable for understanding the NKB/Cu²⁺ interactions and the toxicity mechanism of Cu²⁺ associated with neurodegenerative diseases.