Periodic Reporting for period 1 - SynECS (Combining carbon nanotubes and gold nanorods to investigate the extracellular space around synapses during neuronal communication)
Reporting period: 2019-01-01 to 2020-12-31
HiLo imaging was indeed used to correlate the position of single-walled carbon nanotubes (SWCNTs) with fluorescently-labelled synaptic regions. SWCNTs are thin and long carbon-based nanowires with excellent mechanical and photophysical properties. Indeed, these nanoprobes have attracted particular attention for deep-tissue microscopy, due to their unique brightness, photostability, and spectral imaging range in the near infrared region. SWCNTs were initially tracked in organotypic and acute brain slices up to 100 μm deep using a widefield microscopy approach at millisecond timescale. Super-localization analysis showed that the ECS is a maze of polymorphic channels with widths in the order of 50-500 nm. Importantly, tracking of individual SWCNTs could also provide simultaneous measurements of the local ECS diffusivity environment. Indeed, specific rheological properties of the space, ranging from low to high local diffusivity, were measured in brain slices. SWCNT trajectories were also correlated with the synaptic extracellular environment, showing a modulation of the diffusional NT rates depending on different conditions of neuron stimulation.
SWCNT super-localization analysis was also applied to a mouse model of α-synuclein-induced neurodegeneration. Our group firstly performed an integrative study on pathological animals, exploring the extracellular microenvironment as a whole in adult brain tissue and giving novel insights on Parkinson’s disease effects in the brain. The study revealed poor correlation between local ECS width and nanoscale diffusion, suggesting that the diffusive inhomogeneities were not only driven by geometrical factors, but also by the molecular composition of the space. Importantly, our study pointed out to hyaluronan as major actor for the local variations in ECS diffusivity properties, opening up new hypothesis for the connection between ECS and brain pathologies.
SynECS was supported by a strong international visibility throughout the 2 years of funding. The project was presented in 4 different international conferences, including Photonics West and SPIE photonics Europe, the largest biophotonics, biomedical optics, and imaging conferences in the World. Moreover, results from the project have been already published in 3 different high-impact journals (including Nature Communication). Two additional publications are on current preparation for imminent submission.
The implications of our work in understanding the brain ECS is significant. As mentioned before, the ECS environment still represent a knowledge frontier in brain research and the spatiotemporal profile of molecular mobility in relation to the nanoscopic ECS dimensions is still poorly understood. Our results paved the way for the understanding of the interplay between this unique microenvironment and neuronal signalling in both healthy and pathological conditions. This is an important step to underpin the activity of brain circuits and for a broader understanding of chemical-based neuronal communication and synaptic connectivity. Furthermore, information on the ECS network at the nanoscale will foster novel strategies for genetic manipulation and pharmacological delivery in both healthy and pathological conditions. The possibility to probe adult brain tissues opens up new opportunities on the exploration of the ECS in aging and age-related brain disorders.