Abstract
Altered cellular biomechanics have been implicated as key photogenic triggers in age-related diseases. An aberrant liquid-to-solid phase transition, observed in in vitro reconstituted droplets of FUS protein, has been recently proposed as a possible pathogenic mechanism for amyotrophic lateral sclerosis (ALS). Whether such transition occurs in cell environments is currently unknown as a consequence of the limited measuring capability of the existing techniques, which are invasive or lack of subcellular resolution. Here we developed a non-contact and label-free imaging method, named background-deflection Brillouin microscopy, to investigate the three-dimensional intracellular biomechanics at a sub-micron resolution. Our method exploits diffraction to achieve an unprecedented 10,000-fold enhancement in the spectral contrast of single-stage spectrometers, enabling, to the best of our knowledge, the first direct biomechanical analysis on intracellular stress granules containing ALS mutant FUS protein in fixed cells. Our findings provide fundamental insights on the critical aggregation step underlying the neurodegenerative ALS disease.
Highlights
Altered cellular biomechanics have been implicated as key photogenic triggers in age-related diseases
A decreased cerebral viscoelasticity has been recently observed in multiple sclerosis[3], suggesting that altered biomechanics of neurons or glial cells contribute to neuroinflammation
In Brillouin microscopy, local spontaneous acoustic waves existing at thermal equilibrium in the sample are probed by a narrow-bandwidth laser source using a scanning confocal microscope, and the Brillouin spectrum of the inelastically scattered light is analyzed by a high-resolution (
Summary
Altered cellular biomechanics have been implicated as key photogenic triggers in age-related diseases. An aberrant liquid-to-solid phase transition, observed in in vitro reconstituted droplets of FUS protein, has been recently proposed as a possible pathogenic mechanism for amyotrophic lateral sclerosis (ALS). Whether such transition occurs in cell environments is currently unknown as a consequence of the limited measuring capability of the existing techniques, which are invasive or lack of subcellular resolution. Mutations in prionlike proteins with a low-sequence complexity domain, such as FUS, have been recently associated with familial ALS5 These proteins are involved in the formation of membrane-less compartments by a liquid–liquid phase separation mechanism in the cell. Other techniques, such as destructive interference[39], cell absorption[40], etalon filtering[41], and dark-field illumination[42], have been successfully demonstrated in the attempt to suppress the elastic background light, but these leave the contrast of the spectrometer basically unvaried
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