Brillouin microscopy for contact- and label-free quantification of tissue stiffness in lung fibrosis.

Pathologically altered physical properties of the extracellular matrix are increasingly recognized as an active player in fibrosis inception and progression. Fibroblasts produce an increasingly stiff matrix, which in turn perpetuates fibroblast activation and transdifferentiation into myofibroblasts. Yet, there is still an unmet need for accessible technologies allowing detailed characterization of tissue stiffness to study this relationship. In our current study, we demonstrate the feasibility of a Brillouin microscopy-based quantitative spatial stiffness measurement for the characterization of lung tissue samples with variable degrees of fibrosis. First, we validated our Brillouin microscopy setup using hydrogels with defined levels of stiffness. We then devised a workflow to measure native murine lung tissue cryosections and successfully characterized stiffness levels of lung tissue sections with fibrosis and in non-fibrotic controls. Finally, we successfully applied our setup to fibrotic human lung tissue sections. In conclusion, our proof-of-concept study shows the feasibility of quantitative spatial lung tissue stiffness assessment by Brillouin microscopy in a setup that can easily be integrated into common research workflows. Stiffness measurements through label- and contact-free Brillouin microscopy in combination with techniques such as immunofluorescence staining, RNA-scope, spatial transcriptomics, spatial proteomics, and others have great potential to generate new insights into the mechanobiology of pulmonary fibrosis and a multitude of other diseases in the future.