Nanoscale View of Amyloid Photodynamic Damage

Abstract

A combination of time-resolved optical spectroscopy and nanoscale imaging has been used to study the complex binding to amyloids of a photocatalyst that selectively photo-oxygenates pathogenic aggregates, as well as the consequences of its irradiation. Correlative atomic force microscopy (AFM) and fluorescence microscopy reveals topography-dependent binding of the dye to model β-lactoglobulin fibers, which may also explain the observed difference in their response to photodegradation. We provide direct evidence of the photosensitization of singlet oxygen by the photocatalyst bound to amyloid fibers by direct detection of its NIR phosphorescence. The effect of singlet oxygen at the molecular level brings about nanoscale morphological changes that can be observed with AFM at the single-fiber level. We also find differential response of two α-synuclein mutants to photodamage, which can be rationalized by the presence of amino acids susceptible to photo-oxygenation. Overall, our results help to unravel some of the complexity associated with highly heterogeneous amyloid populations and contribute to the development of improved phototherapeutic strategies for amyloid-related disorders.

Versatile Near‐Infrared Super‐Resolution Imaging of Amyloid Fibrils with the Fluorogenic Probe CRANAD‐2

“…The fluorescence emission increases more than 300‐fold upon binding to ΔN, substantially higher than the 70‐fold response observed in Aβ amyloids [21] . These results are also in line with the superior fluorogenic response of other amyloid‐binding dyes observed in ΔN compared to the wild‐type α‐synuclein and other amyloid fibrils [25] . CRANAD‐2 binds to the fibrils with a relatively high binding affinity ( K d =55±6 nM, Figure 1C), although slightly lower than the values reported for Aβ amyloids ( K d =38±3 nM) [21] .…”

“…We first characterized the photophysical properties of CRANAD‐2 in the presence of an α‐synuclein mutant named ΔN, [24] which forms long and isolated amyloid fibrils that are convenient for imaging studies [14,25] . In phosphate buffered saline (PBS), CRANAD‐2 exhibits a broad and unstructured absorption band and extremely weak emission (Figure 1B).…”

How did correlative atomic force microscopy and super-resolution microscopy evolve in the quest for unravelling enigmas in biology?

“…39,40 The possibility of retrieving physical, chemical and biological information in complex systems using correlative microscopy methods set the stage for the emergence of hybrid systems. 41,42 Over the past two decades AFM has been combined with electron microscopy, 43,44 confocal Raman microspectroscopy 45 and optical [46][47][48] and fluorescence microscopy techniques. Fluorescence microscopy is a popular imaging technique † Contributed equally.…”

NIR‐II Hydrogen‐Bonded Organic Frameworks (HOFs) Used for Target‐Specific Amyloid‐β Photooxygenation in an Alzheimer's Disease Model

“…[16,17] However,p revalent photosensitizers are confined to ultraviolet or visible light which cannot penetrate thick brain tissues. [18][19][20][21][22][23][24][25][26] Although the first near-infrared light (NIR-I, 700-900 nm) shows improved tissue penetration depth and displays advantages in oxidizing Ab in vivo, [27][28][29][30][31][32][33] due to the dense skull and scalp,c urrent photooxidation therapies activated by NIR-I are suboptimal. [34] Superior to NIR-I, the second near-infrared light (NIR-II, 1000-1700 nm) has been recently revealed to possess deeper tissue penetration due to the diminished photon scattering in biological tissues and minimized tissue-background signal.…”